883 to 1200/1250 conversion questions

[Adam76]

Hey guys,
Tried searching but couldn't find the info I was after.

I'm looking for some advice on the  conversion of a 1996 883 to either a 1200 or one of the "bolt on"  specially designed 1250cc kits like from hammer performance and the like, plus a set of cams of course.

I want to do the work myself as well and then just get it tuned. A/c and thunder header pipe or bassani RR III  pipe also in the mix...

My question is, do I

(A) get my 883 cylinders bored and honed locally to fit a set of 1200 weisco reverse dome pistons, drop the cylinders straight in, add some andrews cams, set at around 10:1 and get it tuned?

(B) buy the compete 1250 kit that comes with nice jugs, pistons and rings all pre installed if you want, bolt it together with the addition of cams and get a tune. These performance 1250cc kits like the NRHS kit can be had from US $650!!!! And others like hammer performance and S&S kits seem to be around the US$1100 mark, which is not too bad for a built on kit with all gaskets included.

Thanks for any advice.
Oh, and my aim is not a high HP build chasing numbers... All I want is some more grunt and a lumpy sounding sporty. Cheers

[hdbikedoc]

bore cylinders reverse dome pistons  top end Harley gasket kit ,no cams , 45 pilot 175 main in carb  don't modify slide,  gear final drive to 1200 spec have fun   best bang for your buck

[To The Max]

Hi ,I have just done that conversion and I used the hammer crusher kit . first of all a very professional outfit and they back themselves all the way and good reliable advice . I used the patriot pipe because it gave the best power by far and I tuned it myself. when I put it on the dyno to check the fuel and the horse power I got 106 hp and I think ? it was about 84 ft pound of torque and the dyno guy only took it to 7000 rpm and the grafe was still climing and it was still a little lean . I am very happy with the whole deal and its awesome to ride. if you want to know more PM Me Max

[72fl]

106 HP on a 1250 kit, I,I, would take it to another Dyno and see what it does elsewhere, I am not doubting you but I question your Dyno guy 106 hp out of 1200/1250 kit sounds to me unbelievable 80-90 yes but 106 that is really really impressive if they were being straight up with you.

[To The Max]

106 HP on a 1250 kit, I,I, would take it to another Dyno and see what it does elsewhere, I am not doubting you but I question your Dyno guy 106 hp out of 1200/1250 kit sounds to me unbelievable 80-90 yes but 106 that is really really impressive if they were being straight up with you.

We have backed to back this dyno with others in our area and we found it very honest. The guy doing the run said he was only expecting around the 90's and was very surprised. when I get a chance to finish tuning it I will take it back for another run . be assured this is avery quick sportster. Max

[Adam76]

Not looking for outright speed our biggest HP numbers... Just more grunt and a lumpier/better sounding motor.

So the cruiser kit is definitely not what I'm looking for. Thanks for the info though. Cheers

[Adam76]

bore cylinders reverse dome pistons  top end Harley gasket kit ,no cams , 45 pilot 175 main in carb  don't modify slide,  gear final drive to 1200 spec have fun   best bang for your buck

Ok thanks. So boring the 883 cylinders is totally safe? There's enough thickness in the walls? If so that may be the best way to go.  But why no cams?

Isn't that a key part of the combination? Like baking a cake and not putting the eggs in, right?

[borno]

I was told when I did my '95 the wall thickness is the same if you bore the 883 jugs as the factory 1200cc. I got a deal on some reverse dome 10:1 ross pistons and got mine bored out and it ran great. I think the needle I found to work best with mine was an NOKH. I was looking for some buell heads and so I put n-8 cams in it but they made it hard to start when it was cold out(should have waited) I never did the heads before I sold it. I probably should have went with the n-4 cams.

[PC_Hater]

bore cylinders reverse dome pistons  top end Harley gasket kit ,no cams , 45 pilot 175 main in carb  don't modify slide,  gear final drive to 1200 spec have fun   best bang for your buck

Ok thanks. So boring the 883 cylinders is totally safe? There's enough thickness in the walls? If so that may be the best way to go.  But why no cams?

Isn't that a key part of the combination? Like baking a cake and not putting the eggs in, right?

Boring the 883 cylinders is safe.
The 883 and the 1200 use the same cams.
You miss out on a bit of horsepower at the top end because your 883 has smaller valves, but you should pickup a bit more midrange power because of the smaller valves.
A lot of people did the simple conversion from 883 to 1200 and were very happy with the results.
Have a look at the gearing and pulley options available from Baker Transmissions. You can keep 883 gearing and have great acceleration or fit the 1200 pulley for less vibration at speed, or do something in-between and/or fit the 6 speed gearbox.

[guppymech]

These are my thoughts on a 883/1200 conversion after 30yrs and 4 EVO sportsters.  I've never converted a 883 but one of my bikes was a '96 1200S that I bought new and hot-rodded with a pipe and Andrews N4 cams.

A 883/1200 with 883 heads runs strong up to 5500 rpm or so then the small ports/valves start to choke it off.  Fitting high perf cams (N4) that work best above 6K are no good with this conversion as they take away low rpm power and you can't get the high rpm power with 883 heads.  I found this somewhat true with my 1200S also and went back to the stock cams. 
With a 1250 or larger conversion the cylinder liner is so thin at the spigot end that fits into the crankcase that there is no possibility of going with oversize pistons to renew the engine later on.  With a 883/1200 conversion Wiseco offers many overbore pistons to refresh the engine.   To some people this my not matter but to me it would.
One other thing to watch for is piston speed (RPM) with the long stroke XL engine.  For max engine life you should limit rpm to 6500 or so.  At 7K the piston speed is more than a XR750 at 9K.  Higher speed equals sooner engine overhauls IMO.

Good luck with your choice and have fun!
Tom

[aswracing]

And others like hammer performance and S&S kits seem to be around the US$1100 mark, which is not too bad for a built on kit with all gaskets included.

Not that I want to give a sales pitch here, but I'll issue a correction. Our 1250 kits cost precisely half of that number, $550.

Also, just an FYI, we introduced 1275 kits in February, and they run $650.

[72fl]

106 HP on a 1250 kit, I,I, would take it to another Dyno and see what it does elsewhere, I am not doubting you but I question your Dyno guy 106 hp out of 1200/1250 kit sounds to me unbelievable 80-90 yes but 106 that is really really impressive if they were being straight up with you.

We have backed to back this dyno with others in our area and we found it very honest. The guy doing the run said he was only expecting around the 90's and was very surprised. when I get a chance to finish tuning it I will take it back for another run . be assured this is avery quick sportster. Max

very very impressed.

[harley_cruiser]

(A) get my 883 cylinders bored and honed locally to

Uñless you live close to a reliable shop that does this all the time, I would look in the vendor section. We have some of the best HD machine shops in the country in this forum.
They can machine your cyinders to fit a set of rings and pistons, answer any questions you have, and save you money.
Please don't make the mistake of taking them to a local machine shop that does not specialize in HDs just because it is handy.

[Adam76]

And others like hammer performance and S&S kits seem to be around the US$1100 mark, which is not too bad for a built on kit with all gaskets included.

Not that I want to give a sales pitch here, but I'll issue a correction. Our 1250 kits cost precisely half of that number, $550.

Also, just an FYI, we introduced 1275 kits in February, and they run $650.

Apologies.
Thanks for the correction!

Would you say that the cams are a vital part of the equation? And which cams would you suggest for my needs in the OP?
Cheers

[aswracing]

And others like hammer performance and S&S kits seem to be around the US$1100 mark, which is not too bad for a built on kit with all gaskets included.

Not that I want to give a sales pitch here, but I'll issue a correction. Our 1250 kits cost precisely half of that number, $550.

Also, just an FYI, we introduced 1275 kits in February, and they run $650.

Apologies.
Thanks for the correction!

Would you say that the cams are a vital part of the equation? And which cams would you suggest for my needs in the OP?
Cheers

OK, well, HTT has rules about not making a sales pitch in the general forums, rules that I agree with and try really hard to follow. So I have to be really careful how I answer here. I'm going to answer generically and not about our offerings specifically. If you want to know more about our offerings, please contact me directly.

The vast majority of conversions are done with stock heads and cams. Converting a bike from an 883 to a 1200/1250/1275 makes such a massive difference in the torque and power of the bike that even doing nothing else, it's all that many people ever want or need.

It's a bit problematic to put much cam into stock 883 heads as well. Let me see if I can explain. 883 heads have the same valvetrain geometry as the 1200, but the bore is a half inch smaller. The chambers are therefore smaller diameter, and to get the CR right with the smaller displacement, they make the chamber shallower as well. Then to get the valves to fit inside and reach the small diameter, shallow chamber they make the valve heads smaller and the valve stems longer.

Well, longer valve stems means the valves start out much closer to the pistons than they do with 1200 heads. As a result, piston-to-valve clearance is in short supply. You really can't run much overlap in the cams at all before you get into the danger zone. The operative cam spec is the "TDC Lift", you'll find that the more overlap the cams have (overlap is the intake open point plus the exhaust close point), the higher the TDC lifts, generally speaking. TDC lift is how far the valves are open when the piston is passing through TDC, completing the exhaust stroke and beginning the intake stroke. That's where you get into trouble. Max lift has nothing to do with piston to valve clearance because max lift always occurs with the piston well down the bore.

With stock 883 heads, anytime you're running TDC lifts of more than about .200 on either valve, you're pushing piston to valve clearance. Ideally you'd like .080" or so of clearance on the exhaust and .060" or so on the intake - you need more on the exhaust because the piston chases the exhaust valve closed, but the intake chases the piston down. So the intake only has to have enough clearance for piston swelling and rock, but the exhaust also has to deal with float.

Now that said, a lot of guys run more overlap, and the vast majority never check it and they get away with it. If they ever clayed it, I guarantee it would be too tight, but ignorance is bliss. A reputable shop, especially one that does any volume and can't afford to have problems, won't put people into combinations that push valve to piston clearance.

Now you might be wondering why the valve pockets on the pistons aren't bigger and deeper. Well, it has limits. If you make the pocket too deep, you make it thin in the area between the bottom of the pocket and the top ring groove, and it's prone to breakage. With pistons that you know will only go under 883 heads with stock valve diameters, you can move the pocket inboard and that allows you to make it deeper, but still, you can only gain so much. You can also lower the ring pack a little to make the floor of the pocket thicker. A good 1200/1250/1275 conversion piston has all these features . But it's still dicey to run much overlap with stock 883 heads.

Really the right way to fix the problem is to sink the valves in their seats and unshroud around them to restore the low lift flow you'd otherwise lose with the sinking. Now you've got clearance, and you've probably improved your valvetrain geometry as well (depending on the cams you're running), but now the chamber is too big for the common reverse dome conversion piston. So you need a piston with more dome to reach your target CR.

And this kind of gets back to something I preach: pistons, cams, and head work should be a matched set. And this is just one example of how they're matched, there are several others. Bottom line is that trying to hop up a motor incrementally over time is a bad, bad way to go about it. You just can't move any of those three things very far without bringing the other two along. If you for example do a basic conversion with reverse dome conversion pistons, and then later try to run more cam and/or head work, you're either going to need new pistons or you're going to end up with a compromised result. It just doesn't work.

Sorry to get so carried away, it's just hard to give simple answers to complex questions. Bottom line is that if your heads are stock, run cams that have low TDC lifts, and of course intake close timing that's appropriate for your compression ratio. Like I said, most conversions are done with the stock cams. If you want to change them, a good choice given your comments and this being a '96 model would be the Andrews N2. They have similar IVC timing to the stock cams but more overlap, about as much overlap as will safely work with stock 883 heads. Overlap is a key, key thing for making power, but it relies on an exhaust system that works well in the rpm range you care about. And that's a whole 'nother long digression, I'll spare you. The intake close timing of the N2's will work with a common 10:1 conversion piston.

Another popular cam swap for a basic conversion is the factory "W" grind. These have a really early 25 degree intake close point. Making them work at 10:1 requires careful tuning. But they make a lot of bottom end and mid range. If you go this route, be SURE to get an ignition that implements a soft curve (the Dyna 2000 8-pin on curve 4 would be a good choice and plug and play on your bike). Also be sure the "W" cams you find have the end of the #2 cam machined for the timing cup. They went to crank trigger in 2004 and they stopped machining for the timing cup in late 2005 or early 2006.

But there's nothing at all wrong with doing a conversion with your stock cams, and most are done that way. Even with the stock cams, the extra power is going to amaze you.

[ptbjork]

I had done the conversion on my 2002 883/1200 back in 2003 using new HD cylinders Wiseco 10-1 dished pistons, SE A/C, SE ignition and SE Mufflers.  Ran great made decent power.  Last year decided to mess with it again.  Had Hammer Performance do some work to the stock 883 heads and added W Cams.  Now this little bike pulls hard!

[DrSpencer]

OK, well, HTT has rules about not making a sales pitch in the general forums, rules that I agree with and try really hard to follow. So I have to be really careful how I answer here. I'm going to answer generically and not about our offerings specifically. If you want to know more about our offerings, please contact me directly.

The vast majority of conversions are done with stock heads and cams. Converting a bike from an 883 to a 1200/1250/1275 makes such a massive difference in the torque and power of the bike that even doing nothing else, it's all that many people ever want or need.

It's a bit problematic to put much cam into stock 883 heads as well. Let me see if I can explain. 883 heads have the same valvetrain geometry as the 1200, but the bore is a half inch smaller. The chambers are therefore smaller diameter, and to get the CR right with the smaller displacement, they make the chamber shallower as well. Then to get the valves to fit inside and reach the small diameter, shallow chamber they make the valve heads smaller and the valve stems longer.

Well, longer valve stems means the valves start out much closer to the pistons than they do with 1200 heads. As a result, piston-to-valve clearance is in short supply. You really can't run much overlap in the cams at all before you get into the danger zone. The operative cam spec is the "TDC Lift", you'll find that the more overlap the cams have (overlap is the intake open point plus the exhaust close point), the higher the TDC lifts, generally speaking. TDC lift is how far the valves are open when the piston is passing through TDC, completing the exhaust stroke and beginning the intake stroke. That's where you get into trouble. Max lift has nothing to do with piston to valve clearance because max lift always occurs with the piston well down the bore.

With stock 883 heads, anytime you're running TDC lifts of more than about .200 on either valve, you're pushing piston to valve clearance. Ideally you'd like .080" or so of clearance on the exhaust and .060" or so on the intake - you need more on the exhaust because the piston chases the exhaust valve closed, but the intake chases the piston down. So the intake only has to have enough clearance for piston swelling and rock, but the exhaust also has to deal with float.

Now that said, a lot of guys run more overlap, and the vast majority never check it and they get away with it. If they ever clayed it, I guarantee it would be too tight, but ignorance is bliss. A reputable shop, especially one that does any volume and can't afford to have problems, won't put people into combinations that push valve to piston clearance.

Now you might be wondering why the valve pockets on the pistons aren't bigger and deeper. Well, it has limits. If you make the pocket too deep, you make it thin in the area between the bottom of the pocket and the top ring groove, and it's prone to breakage. With pistons that you know will only go under 883 heads with stock valve diameters, you can move the pocket inboard and that allows you to make it deeper, but still, you can only gain so much. You can also lower the ring pack a little to make the floor of the pocket thicker. A good 1200/1250/1275 conversion piston has all these features . But it's still dicey to run much overlap with stock 883 heads.

Really the right way to fix the problem is to sink the valves in their seats and unshroud around them to restore the low lift flow you'd otherwise lose with the sinking. Now you've got clearance, and you've probably improved your valvetrain geometry as well (depending on the cams you're running), but now the chamber is too big for the common reverse dome conversion piston. So you need a piston with more dome to reach your target CR.

And this kind of gets back to something I preach: pistons, cams, and head work should be a matched set. And this is just one example of how they're matched, there are several others. Bottom line is that trying to hop up a motor incrementally over time is a bad, bad way to go about it. You just can't move any of those three things very far without bringing the other two along. If you for example do a basic conversion with reverse dome conversion pistons, and then later try to run more cam and/or head work, you're either going to need new pistons or you're going to end up with a compromised result. It just doesn't work.

Sorry to get so carried away, it's just hard to give simple answers to complex questions. Bottom line is that if your heads are stock, run cams that have low TDC lifts, and of course intake close timing that's appropriate for your compression ratio. Like I said, most conversions are done with the stock cams. If you want to change them, a good choice given your comments and this being a '96 model would be the Andrews N2. They have similar IVC timing to the stock cams but more overlap, about as much overlap as will safely work with stock 883 heads. Overlap is a key, key thing for making power, but it relies on an exhaust system that works well in the rpm range you care about. And that's a whole 'nother long digression, I'll spare you. The intake close timing of the N2's will work with a common 10:1 conversion piston.

Another popular cam swap for a basic conversion is the factory "W" grind. These have a really early 25 degree intake close point. Making them work at 10:1 requires careful tuning. But they make a lot of bottom end and mid range. If you go this route, be SURE to get an ignition that implements a soft curve (the Dyna 2000 8-pin on curve 4 would be a good choice and plug and play on your bike). Also be sure the "W" cams you find have the end of the #2 cam machined for the timing cup. They went to crank trigger in 2004 and they stopped machining for the timing cup in late 2005 or early 2006.

But there's nothing at all wrong with doing a conversion with your stock cams, and most are done that way. Even with the stock cams, the extra power is going to amaze you.
[/quote]


Thanks for the detailed response.

I just picked up a 2017 883 Iron. Nice little bike to putt around on, but it is a bit underwhelming compared to my other bikes.

Do I sacrifice any 'street manners' when doing a 1250/1275 conversion? What about when doing this conversion with the head & cam upgrade?

For comparison, my 2011 103" FLHX has SE255's and my 2007 FXSTC 96" has SE204's. While these cams are more lumpy than a smooth-as-glass stock cam, I don't find them to be the slightest bit uncomfortable.

Thanks

[aswracing]

Thanks for the detailed response.

I just picked up a 2017 883 Iron. Nice little bike to putt around on, but it is a bit underwhelming compared to my other bikes.

Do I sacrifice any 'street manners' when doing a 1250/1275 conversion?

Absolutely not! A basic conversion, i.e. stock cams, runs just like the stock bike, except it has a ton more power. Here, let me show a chart:



This is an EFI 883, before and after a 1250 conversion - a 1275 makes an additional 2-3% more power. This one is a 2007, but they've made no changes that affect performance between 2007 and 2017, it's all the same. The bike is also equipped with a Patriot exhaust and Air Hammer air cleaner and Powervision, for both pulls, and was tuned in both configurations.

There's nothing else you can do for the money that delivers anywhere near this much bang for the buck. And it comes in over the whole rpm range, too, as you can see.

Low speed manners don't change at all, not with the stock cams.

What about when doing this conversion with the head & cam upgrade?

I often see people talk about performance and powerband and manners in terms of cams and head work. But put any overlap into the cams and the pipe has a profound effect on the motor. So it's a huge part of the answer to your question. In fact, let me show you another chart that really drives the point home.



Busy chart, huh? That's because the results are so radically different. Well, what if I told you that both pulls are the same bike, tested on the same day, with absolutely no changes to the motor between these two pulls? Literally all I did was change the pipe and tune the motor for each.

Why such a big difference? Because the cams in this motor have 60 degrees of overlap, which is a really healthy amount. That means that for every two revolutions of the crank (720 degrees), there's a window of 60 degrees where both valves are open at the same time, connecting the intake and exhaust together. This window happens at an incredibly critical moment, as the exhaust cycle is finishing and the intake cycle is beginning. It gives the exhaust an opportunity to affect intake flow on the upcoming intake stroke, and that influence can be good or bad depending on what the pipe does. The more overlap in the cams, the bigger that opportunity.

Overlap in the cams is a big deal for making power, especially when you're talking about undervalved engines, and these engines are more or less the definition of undervalved.

But besides the lumpy idle, more overlap makes the engine more sensitive to the exhaust. You can think of it as basically abdicating control of the powerband over to the exhaust.

The best running motors have an exhaust that pulls well over the rpm range you care about, enough overlap in the cams to make it work, and intake close timing appropriate for that rpm range. We call that a "happy marriage" between the pipe and the cams.

Without getting into too much boring detail, just be aware that the shape of the torque curve is basically a map of the cylinder fill, and therefore when the cams have overlap, the torque curve shape tells you a lot about how the pipe is behaving. Ideally what you'd like to see is a flat or broad parabolic shaped curve, indicating good cylinder fill over a wide rpm range. But more typically you see valleys (the pipe pushing back) and peaks (the pipe pulling). There's a whole long explanation behind why a pipe wants to pull at some rpm's and push back at others, but at it's core, it's about pressure wave travel in the pipe and how those waves travel at a constant speed regardless of the rpm of the engine, where the interval between overlap windows changes with rpm.

Power is just torque times rpm, so it follows what the torque curve is doing. They're not independent of each other as many people mistakenly assume. A table flat torque curve generates a straight diagonal power curve, up and to the right. The two curves are mathematically tied together.

So anyway, my point here is that the answer to your question has a lot to do with your pipe. For example, the red curve above, that pipe is not well mannered below 2800rpm. The pipe is pushing back. The blue is better there.

There are plenty of pipes that have bad push backs at various rpm's, and with high overlap cams, you're going to know about every one of them.

Unfortunately, misbehaving pipes seem to be more common than well-behaved pipes. I think a lot of pipe sales are more about looks and sound, and as a result, that's what the pipe makers focus on. Some of the pipes I've tested, I just can't hardly believe the company would ship such a crappy performing pipe. It's like they never even tested it for performance. Don't these guys even own a dyno? Price doesn't seem to have any relationship to performance, either.

Bottom line, when doing a performance build choose your pipe carefully, it's an enormously important component. If your pipe pulls well over a wide rpm range, you're going to be happy with your high overlap cams and it's going to have good manners everywhere and tons of power. If you have a pipe that pulls and pushes back at different rpm's, not so much. So a hot rod build may or may not have good "street manners", much depends on your pipe choice.

For comparison, my 2011 103" FLHX has SE255's and my 2007 FXSTC 96" has SE204's. While these cams are more lumpy than a smooth-as-glass stock cam, I don't find them to be the slightest bit uncomfortable.

Personally, I like a lumpy idle. I like to feel like the bike is alive and kicking, not just some appliance I'm sitting on.

[DrSpencer]

Thanks for the detailed response.

I just picked up a 2017 883 Iron. Nice little bike to putt around on, but it is a bit underwhelming compared to my other bikes.

Do I sacrifice any 'street manners' when doing a 1250/1275 conversion?

Absolutely not! A basic conversion, i.e. stock cams, runs just like the stock bike, except it has a ton more power. Here, let me show a chart:



This is an EFI 883, before and after a 1250 conversion - a 1275 makes an additional 2-3% more power. This one is a 2007, but they've made no changes that affect performance between 2007 and 2017, it's all the same. The bike is also equipped with a Patriot exhaust and Air Hammer air cleaner and Powervision, for both pulls, and was tuned in both configurations.

There's nothing else you can do for the money that delivers anywhere near this much bang for the buck. And it comes in over the whole rpm range, too, as you can see.

Low speed manners don't change at all, not with the stock cams.

What about when doing this conversion with the head & cam upgrade?

I often see people talk about performance and powerband and manners in terms of cams and head work. But put any overlap into the cams and the pipe has a profound effect on the motor. So it's a huge part of the answer to your question. In fact, let me show you another chart that really drives the point home.



Busy chart, huh? That's because the results are so radically different. Well, what if I told you that both pulls are the same bike, tested on the same day, with absolutely no changes to the motor between these two pulls? Literally all I did was change the pipe and tune the motor for each.

Why such a big difference? Because the cams in this motor have 60 degrees of overlap, which is a really healthy amount. That means that for every two revolutions of the crank (720 degrees), there's a window of 60 degrees where both valves are open at the same time, connecting the intake and exhaust together. This window happens at an incredibly critical moment, as the exhaust cycle is finishing and the intake cycle is beginning. It gives the exhaust an opportunity to affect intake flow on the upcoming intake stroke, and that influence can be good or bad depending on what the pipe does. The more overlap in the cams, the bigger that opportunity.

Overlap in the cams is a big deal for making power, especially when you're talking about undervalved engines, and these engines are more or less the definition of undervalved.

But besides the lumpy idle, more overlap makes the engine more sensitive to the exhaust. You can think of it as basically abdicating control of the powerband over to the exhaust.

The best running motors have an exhaust that pulls well over the rpm range you care about, enough overlap in the cams to make it work, and intake close timing appropriate for that rpm range. We call that a "happy marriage" between the pipe and the cams.

Without getting into too much boring detail, just be aware that the shape of the torque curve is basically a map of the cylinder fill, and therefore when the cams have overlap, the torque curve shape tells you a lot about how the pipe is behaving. Ideally what you'd like to see is a flat or broad parabolic shaped curve, indicating good cylinder fill over a wide rpm range. But more typically you see valleys (the pipe pushing back) and peaks (the pipe pulling). There's a whole long explanation behind why a pipe wants to pull at some rpm's and push back at others, but at it's core, it's about pressure wave travel in the pipe and how those waves travel at a constant speed regardless of the rpm of the engine, where the interval between overlap windows changes with rpm.

Power is just torque times rpm, so it follows what the torque curve is doing. They're not independent of each other as many people mistakenly assume. A table flat torque curve generates a straight diagonal power curve, up and to the right. The two curves are mathematically tied together.

So anyway, my point here is that the answer to your question has a lot to do with your pipe. For example, the red curve above, that pipe is not well mannered below 2800rpm. The pipe is pushing back. The blue is better there.

There are plenty of pipes that have bad push backs at various rpm's, and with high overlap cams, you're going to know about every one of them.

Unfortunately, misbehaving pipes seem to be more common than well-behaved pipes. I think a lot of pipe sales are more about looks and sound, and as a result, that's what the pipe makers focus on. Some of the pipes I've tested, I just can't hardly believe the company would ship such a crappy performing pipe. It's like they never even tested it for performance. Don't these guys even own a dyno? Price doesn't seem to have any relationship to performance, either.

Bottom line, when doing a performance build choose your pipe carefully, it's an enormously important component. If your pipe pulls well over a wide rpm range, you're going to be happy with your high overlap cams and it's going to have good manners everywhere and tons of power. If you have a pipe that pulls and pushes back at different rpm's, not so much. So a hot rod build may or may not have good "street manners", much depends on your pipe choice.

For comparison, my 2011 103" FLHX has SE255's and my 2007 FXSTC 96" has SE204's. While these cams are more lumpy than a smooth-as-glass stock cam, I don't find them to be the slightest bit uncomfortable.

Personally, I like a lumpy idle. I like to feel like the bike is alive and kicking, not just some appliance I'm sitting on.

Another outstanding explanation.

In addition to a 1250/1275 conversion, my 2017 Iron will get nothing more than a Stage 1 intake, some type of slip-ons (keeping the stock head pipe), and a DIY TTS tune.

My preference is to not have to wind the motor to high RPM in order to enjoy any additional power gains.

Given the above, what would you suggest?

Thanks

[aswracing]

Here, let me show you another chart (I got tons of'em), to show what to expect from a cam change ...



Andrews N2's are shown in blue. These have a 38 degree intake close point and 40 degrees of overlap.

Your stock cams are W's, shown in red. These have a 25 degree intake close point and 22 degrees of overlap.

"D" cams (stock in 91-06 883s) are shown in green. These have a 40 degree intake close point and 4 degrees of overlap.

The pipe is a bit soft down low, and you really see it in the N2's due to the extra overlap. The W's are much better in this situation, and their early intake close point is helping build cylinder pressure. So they win handily way down low.

But then through the rpm range where the pipe pulls hard, the N2's take over.

Up top the pipe isn't really pulling hard but the later intake close of the N2's keeps it on top.

The D's have very little overlap, which would help down low where the pipe is misbehaving, but the intake close point is too late to work well there.

Bottom line is that even using an extremely mild grind like the N2's, we're shifting the power from left to right and making it sensitive to the exhaust. More mainstream street performance type grinds will make this shift much more pronounced. I have those charts too . But as I mentioned in my first post, I generally discourage those grinds with stock 883 heads just because I know that piston to valve clearance is not what it should be, not while the heads are stock anyway.

You should make your own decision of course, but my personal opinion is that the stock W's are a pretty decent choice as an all-around cam grind on a near stock motor, i.e. stock heads. There's no cam miracle that will give you more everywhere, at least not in this situation. Now with prepared heads and a good combination, that changes of course. But so long as your heads are stock, the stock W cams are a pretty good choice.

The best slip-ons I've ever tested were 3" Rush units, for whatever that's worth. I'd sure like to test the S&S pieces though.

For do-it-yourselfers, I much prefer the Powervision over other tuners. It's just much, much easier to DIY tune with. They simplify the whole process and boil it down to just a few taps of the screen. Plus you get a ton of other cool features by virtue of having a small screen you can mount on the bike. You can basically monitor everything going on in your motor, plus do things like read and clear codes, you've got trip computers, etc. It natively supports wideband tuning and even closed-loop wideband operation, too, with add-on products. It's really a remarkable little device. But everyone has their opinion of course.

[sfmichael]

great info as always from AWS 

hope to build a hopped up Sporty one of these days 

[DrSpencer]

Here, let me show you another chart (I got tons of'em), to show what to expect from a cam change ...



Andrews N2's are shown in blue. These have a 38 degree intake close point and 40 degrees of overlap.

Your stock cams are W's, shown in red. These have a 25 degree intake close point and 22 degrees of overlap.

"D" cams (stock in 91-06 883s) are shown in green. These have a 40 degree intake close point and 4 degrees of overlap.

The pipe is a bit soft down low, and you really see it in the N2's due to the extra overlap. The W's are much better in this situation, and their early intake close point is helping build cylinder pressure. So they win handily way down low.

But then through the rpm range where the pipe pulls hard, the N2's take over.

Up top the pipe isn't really pulling hard but the later intake close of the N2's keeps it on top.

The D's have very little overlap, which would help down low where the pipe is misbehaving, but the intake close point is too late to work well there.

Bottom line is that even using an extremely mild grind like the N2's, we're shifting the power from left to right and making it sensitive to the exhaust. More mainstream street performance type grinds will make this shift much more pronounced. I have those charts too . But as I mentioned in my first post, I generally discourage those grinds with stock 883 heads just because I know that piston to valve clearance is not what it should be, not while the heads are stock anyway.

You should make your own decision of course, but my personal opinion is that the stock W's are a pretty decent choice as an all-around cam grind on a near stock motor, i.e. stock heads. There's no cam miracle that will give you more everywhere, at least not in this situation. Now with prepared heads and a good combination, that changes of course. But so long as your heads are stock, the stock W cams are a pretty good choice.

The best slip-ons I've ever tested were 3" Rush units, for whatever that's worth. I'd sure like to test the S&S pieces though.

For do-it-yourselfers, I much prefer the Powervision over other tuners. It's just much, much easier to DIY tune with. They simplify the whole process and boil it down to just a few taps of the screen. Plus you get a ton of other cool features by virtue of having a small screen you can mount on the bike. You can basically monitor everything going on in your motor, plus do things like read and clear codes, you've got trip computers, etc. It natively supports wideband tuning and even closed-loop wideband operation, too, with add-on products. It's really a remarkable little device. But everyone has their opinion of course.

With respect to aftermarket cams, it sounds like there isn't a tremendous power gain when using anything different than the stock 'W' cams (as found in my 2017 883 Iron) when doing a 1200/1250 conversion. It seems like the pistons & jugs make up the bulk of the power increase.

What would be the difference in power, if any, between a 1200/1250 conversion and a stock 2017 1200 Sportster, such as a Roadster or a 48?

BTW, per your recommendation, I just ordered some Rush slip-ons (w/1.75" baffle).

Thanks, once more.

[Pete_Vit]

And others like hammer performance and S&S kits seem to be around the US$1100 mark, which is not too bad for a built on kit with all gaskets included.

Not that I want to give a sales pitch here, but I'll issue a correction. Our 1250 kits cost precisely half of that number, $550.

Also, just an FYI, we introduced 1275 kits in February, and they run $650.

NICE! 

[cyclobutch]

There's some real good info in this thread - thanks.

[Carl 1969]

When I did my '94, I used factory 1200 pistons & the heads had the chambers opened up to "9.5 to 1", 1200 valves, 5-angle valve job & pocket port.

Stock cams, jetted CV40 & Supertrapp 2-1 w/18 disks. Dyno'd 73 hp/79 tq. Not "big" numbers, but good enough for to run 12.90 at 105mph in the 1/4. Pulled hard & a lot of fun.