Hey guys,
I've done so much reading on compression, milling heads, dome pistons and getting correct swish that my eyeballs hurt.
I have a 96 FLSTN with stock evo motor that I am planning a top end build on. Bike has only 20K miles on it surprisingly.
My question is does milling the head 30 / 40 / 50 thou change the squish or quench? My thinking is that it brings the piston closer to the combustion chamber so it must? How do I achieve the ideal squish.... Is the ideal squish 30 or 35?
How much should I mill the heads, and therefore what is the ideal combustion chamber size?
Big boys compression calculator is awesome, but doesn't help me with this problem.
I'm looking at the ev27 / V thunder 3020 / S&S 510V or 502 / DME 500 cam (haven't decided). And freedom softail true duel fish tails to suit the heritage nostalgia.
Thanks heaps for anyone who can clear this up for me, first to end rebuild obviously 😁
Milling the heads doesn't change the squish it reduces the size of the combustion chamber.
Back in the Evo days a standard build was mill the heads .050 & install an EV27.
The correct is answer above -
If you look at my thread on here you will find a LOT of information (with pix).
Usually, the bottom of the cylinders need to be turned dwn to get heads closer to the piston (for standard chambers)
I am at 0.026
IMO which I believe is correct - There is no reason to mod standard HD cylinders and pistons.
It is a waste as you are still using standard aluminum cylinders and standard combustion chambers with poopy 8.5 CR.
You will never notice any difference.
I would most definitely check with "Hillside Harley" and Axtell.
Ron @ axtell makes nodular cylinders and angle top pistons.
Dont scoff at them unless you have tried them as they work!
It is the way to go as it solves several problems at once!
. With a cam, you will be at about 90 to 100 HP (depending on other mods)
I am very happy with the set up and tour with it.
It takes a healthy twink to keep up!
Quote from: wfolarry on March 25, 2020, 03:03:32 AM
Milling the heads doesn't change the squish it reduces the size of the combustion chamber.
Back in the Evo days a standard build was mill the heads .050 & install an EV27.
Thanks wfolarry, that makes sense.
So if milling the heads doesn't change squish but only combustion chamber size..... I would love to know (a) what is the ideal chamber size for evo heads? and (b) if it doesn't change the squish, how exactly do you set up the correct squish?
Thanks very much for sharing your knowledge.
Quote from: thumper 823 on March 25, 2020, 03:25:08 AM
The correct is answer above -
If you look at my thread on here you will find a LOT of information (with pix).
Usually, the bottom of the cylinders need to be turned dwn to get heads closer to the piston (for standard chambers)
I am at 0.026
IMO which I believe is correct - There is no reason to mod standard HD cylinders and pistons.
It is a waste as you are still using standard aluminum cylinders and standard combustion chambers with poopy 8.5 CR.
You will never notice any difference.
Thanks thumper, that's good to know about not needing to really change the oem cylinders and pistons. But I couldn't find your thread?
If I'm leaving the standard pistons and cylinders what other mods do you suggest for an 80" build, at what compression and all that stuff.
Thanks again. 👍
I'll be the one to say it, the exhaust you're using is not ideal. Looks cool, sounds cool, robs power.
Quote from: Hossamania on March 25, 2020, 07:15:36 AM
I'll be the one to say it, the exhaust you're using is not ideal. Looks cool, sounds cool, robs power.
I'll be the one to agree that is makes No Sense to try to improve engine performance with Top end Components, then destroy performance with a "Potty mouth" Exhaust...
I will also agree that it is So Very Common... it is almost a Given!!!
Quote from: Adam76 on March 25, 2020, 04:06:10 AM
Quote from: wfolarry on March 25, 2020, 03:03:32 AM
Milling the heads doesn't change the squish it reduces the size of the combustion chamber.
Back in the Evo days a standard build was mill the heads .050 & install an EV27.
Thanks wfolarry, that makes sense.
So if milling the heads doesn't change squish but only combustion chamber size..... I would love to know (a) what is the ideal chamber size for evo heads? and (b) if it doesn't change the squish, how exactly do you set up the correct squish?
Thanks very much for sharing your knowledge.
Squish is the distance between the top of the piston and the head surface (where it is machined for the gasket surface). Typically it is the flat machined head surface area that is not covered when you place a head gasket on it. When the piston reaches top dead center on compression the air in the squish zone (where the piston and the cylinder head machined surface meet squeezes the air into the main part of the chamber and causes the turbulence that helps the burn.
There are many tech descriptions on the internet that describe the process so you can follow it step by step. The basic procedure What is to measure the distance from the top of the cylinder when it is installed and fastened down to the top of the piston at TDC. The difference between the top of the piston and the cylinder gasket surface plus the head gasket that will be used is your quench (or squish). Many (myself included) like to set the piston at zero difference using machining or base gasket thickness. For example, if your pistons are "in the hole" at TDC you can machine that amount off the barrels making them shorter to achieve zero. The other option is to leave then there and use a head gasket that when you add that dimension to the piston in the hole measurement, you get the .030 you are looking for.
2 examples
- .003 in the hole on the piston plus .030 head gasket = .033 squish.
- .003 out of the hole on the piston plus .030 head gasket = .027 squish.
"If I'm leaving the standard pistons and cylinders what other mods do you suggest for an 80" build, at what compression"
Get with WFO Larry....
708-598-3050
wfolarry@larrysmotorcyclemachine.com
tell him your goals, cam etc. send him your heads and cylinders have him supply pistons and do machine work. And get some lifters from him too.
:agree: That may be tough as you are from Australia but FSG or one of the other members there can probably give you some leads on a local machinist. You can order the lifters from Larry too.
Bringing the piston all the way up is highly beneficial as it provides (besides more compression) a more complete burn, it's like blowing on a fire.
It increases compression MORE than milling the head does by a significant margin.
The closer the piston comes to the head (without hitting of course) the higher the velocity of the squish and the better mixing of the charge.
Not a big deal on an EVO (but still relevant) but other motors will have "dead spots" which can promote detonation as the unburned fuel in those areas will ignite in an uncontrolled fashion and at much higher pressures, when the piston comes down and exposes those areas to the burn.
It's the difference between (remember your cap gun?) scratching a cap to ignite it and hitting it with a hammer.
Under pressure it goes bang, with no pressure it burns in a woosh.
An EVO combustion chamber is superior to earlier styles because the flat piston squeezes the charge against the step in the D shaped combustion chamber.
A TC takes this a step farther with a bathtub shaped chamber that gets squeezed from all sides.
Some EVO heads have bathtub shaped chambers,
Using an Iron cylinder maintains the squish at a tighter level throughout the operating temp range as an Iron cylinder does not grow as much as an aluminum cylinder.
So the benefit of an iron cylinder is that it is more stable and rigid.
Quote from: kd on March 25, 2020, 08:10:18 AM
:agree: That may be tough as you are from Australia but FSG or one of the other members there can probably give you some leads on a local machinist. You can order the lifters from Larry too.
:up: thanks
Quote from: Hossamania on March 25, 2020, 07:15:36 AM
I'll be the one to say it, the exhaust you're using is not ideal. Looks cool, sounds cool, robs power.
Yeah, l like the looks, but I'm open to change.
The other pipe l like is the pro pipe. That's gotta be a performance winner?
Quote from: kd
Squish is the distance between the top of the piston and the head surface (where it is machined for the gasket surface). Typically it is the flat machined head surface area that is not covered when you place a head gasket on it. When the piston reaches top dead center on compression the air in the squish zone (where the piston and the cylinder head machined surface meet squeezes the air into the main part of the chamber and causes the turbulence that helps the burn.
There are many tech descriptions on the internet that describe the process so you can follow it step by step. The basic procedure What is to measure the distance from the top of the cylinder when it is installed and fastened down to the top of the piston at TDC. The difference between the top of the piston and the cylinder gasket surface plus the head gasket that will be used is your quench (or squish). Many (myself included) like to set the piston at zero difference using machining or base gasket thickness. For example, if your pistons are "in the hole" at TDC you can machine that amount off the barrels making them shorter to achieve zero. The other option is to leave then there and use a head gasket that when you add that dimension to the piston in the hole measurement, you get the .030 you are looking for.
2 examples
- .003 in the hole on the piston plus .030 head gasket = .033 squish.
- .003 out of the hole on the piston plus .030 head gasket = .027 squish.
Thanks kd, so it's as simple as zero decking and the thickness of your had gasket, no matter how much the heads has been milled??
Thanks for the explanation. Should you always aim for 30" ?
Quote from: Deye76 on March 25, 2020, 08:00:40 AM
"If I'm leaving the standard pistons and cylinders what other mods do you suggest for an 80" build, at what compression"
Get with WFO Larry....
708-598-3050
wfolarry@larrysmotorcyclemachine.com
tell him your goals, cam etc. send him your heads and cylinders have him supply pistons and do machine work. And get some lifters from him too.
Thanks deye76, l wish l could but being in Australia makes it impossible. That's why this forum is so great with people sharing their amazing knowledge that l really appreciate. Cheers
In general terms, yes, but recognize that the material you remove from the head surface reduces the volume of the cylinder head chamber. That reduction raises the compression. That's where it can get more complicated and the reason Deye suggested discussing and taking them to a good head porter. The whole package of machine work and the cams have to be fit together to give you a streetable engine that performs in the rpm range that you normally ride. Different cams have different effects on compression too.
First be honest about how you ride and where you want the power band. Search here in the dyno section and get a sense of how specific cams perform. Max numbers mean nothing if you don't use those high rpm ranges. If you're set at 0 deck it simplifies the gasket thickness for your.030 squish target. .030 is generally accepted to be the desired streetable dimension. Be prepared to purchase a good tuner and getting it tuned by an expert dyno tuner to realize the value of your new combination.
Spend some time on the Big Boyz web site calculator and enter in your components. You'll soon see how subtle changes or camshafts change your compression.
Quote from: kd on March 25, 2020, 05:01:23 PM
In general terms, yes, but recognize that the material you remove from the head surface reduces the volume of the cylinder head chamber. That reduction raises the compression. That's where it can get more complicated and the reason Deye suggested discussing and taking them to a good head porter. The whole package of machine work and the cams have to be fit together to give you a streetable engine that performs in the rpm range that you normally ride. Different cams have different effects on compression too.
First be honest about how you ride and where you want the power band. Search here in the dyno section and get a sense of how specific cams perform.
Thanks, yes I have searched through the entire dyno section but to be expected there aren't many evo dyno graphs to look at.
And yes the big boys calculator is very helpful.
One last question, what is the ideal combustion chamber size approximately? And how many thou do you need to mill of the head generally to get there?
Thanks again fort the advice. :up:
Quote from: Adam76 on March 25, 2020, 04:02:10 PM
Quote from: Hossamania on March 25, 2020, 07:15:36 AM
I'll be the one to say it, the exhaust you're using is not ideal. Looks cool, sounds cool, robs power.
Yeah, l like the looks, but I'm open to change.
The other pipe l like is the pro pipe. That's gotta be a performance winner?
A much better choice for performance. Also, Evos love ThunderHeaders, but the looks are not for everybody.
Yes a Pro Pipe is good.
I found a long primary Thunder header is slightly better than a Pro Pipe.
A little smoother and more low RPM torque.
Quote from: Adam76 on March 25, 2020, 05:25:12 PM
Quote from: kd on March 25, 2020, 05:01:23 PM
In general terms, yes, but recognize that the material you remove from the head surface reduces the volume of the cylinder head chamber. That reduction raises the compression. That's where it can get more complicated and the reason Deye suggested discussing and taking them to a good head porter. The whole package of machine work and the cams have to be fit together to give you a streetable engine that performs in the rpm range that you normally ride. Different cams have different effects on compression too.
First be honest about how you ride and where you want the power band. Search here in the dyno section and get a sense of how specific cams perform.
Thanks, yes I have searched through the entire dyno section but to be expected there aren't many evo dyno graphs to look at.
And yes the big boys calculator is very helpful.
One last question, what is the ideal combustion chamber size approximately? And how many thou do you need to mill of the head generally to get there?
Thanks again fort the advice. :up:
Adam, that's a question that I don't feel qualified to give an outright answer to. There are a few excellent head porter / builders on the site that may be able to help. I know where you are and the distance is expense relationship as where I am in Canada is similar. Of all of the great head shops as vendors here at least one that I know of is on the west coast in Edgewood Washington. Have you priced shipping to the US and return? I guess that will depend on where in Aust. you are.
I would send Don at HD Street Performance a PM from here and see if you can arrange to talk to him. Tell him about this thread so he can see where you are at before he speaks to you. The cylinder work is doable with some guidance but the head work is more exacting. Because he is on the west coast it may actually be affordable to get him to do the calcs, make some cam suggestions and do the work. You will need to settle on riding style power needs and cams before determining what cc is right for your heads. As I said, maybe one or more of the Ozzie members will see this and know someone close to you that is a trusted evo head porter / builder.
Thanks kd, I'll be sure to do that.
Thank you
Keep us informed about how you make out. Send FSG a PM too. He may know someone on your side of the pond that does the type of machine work you need once you settle on what you want.
"That may be tough as you are from Australia"
:embarrassed: I have to slow down and pay attention. KD does. :up:
Quote from: Deye76 on March 26, 2020, 07:21:43 AM
"That may be tough as you are from Australia"
:embarrassed: I have to slow down and pay attention. KD does. :up:
:hyst: I just got lucky that time. :wink:
Quote from: Burnout on March 25, 2020, 07:17:27 PM
Yes a Pro Pipe is good.
I found a long primary Thunder header is slightly better than a Pro Pipe.
A little smoother and more low RPM torque.
Thanks.
What about the Bassani RR long megaphone 2-1 pipe?
I've had the short megaphone 2-1 before and didn't mind it too much.
Thanks 👍
Linky?
This one?
https://www.bassanipipes.com/roadrage2into1b4systemwithmegaphonemuffler.aspx (https://www.bassanipipes.com/roadrage2into1b4systemwithmegaphonemuffler.aspx)
It doesn't have the length a Long Primary TH has, it's that length I attribute to the low RPM torque.
The Bassani looks like it would be better than a Pro Pipe.
Not enough better to warrant the expense if you already have a Pro Pipe.
I've never been impressed with short pipes
The ideal combustion chamber size depends on the compression you want to match the cam you're going to run. If you're trying to increase compression by just milling the heads you'll have to take a lot more off than if you went with pistons that are designed to increase compression.
I do business with a shop in Western Australia. Maybe they can help you.
:up: There you go Adam. Pm Larry for a chat.
Quote from: wfolarry on March 26, 2020, 06:50:26 PM
The ideal combustion chamber size depends on the compression you want to match the cam you're going to run. If you're trying to increase compression by just milling the heads you'll have to take a lot more off than if you went with pistons that are designed to increase compression.
I do business with a shop in Western Australia. Maybe they can help you.
Thanks Larry, that's awesome. I'll pm you. Cheers for all your help.
Quote from: Burnout on March 26, 2020, 06:47:35 PM
Linky?
This one?
https://www.bassanipipes.com/roadrage2into1b4systemwithmegaphonemuffler.aspx (https://www.bassanipipes.com/roadrage2into1b4systemwithmegaphonemuffler.aspx)
It doesn't have the length a Long Primary TH has, it's that length I attribute to the low RPM torque.
The Bassani looks like it would be better than a Pro Pipe.
Not enough better to warrant the expense if you already have a Pro Pipe.
I've never been impressed with short pipes
No, like this.
This is a long primary pipe
(https://i.postimg.cc/WbsfLwVk/IMG-2063.jpg)
This one doesn't look too bad. :up:
Cheers
That was an original shovelhead 2:1 pipe that had the fat sausage (low restriction) muffler.
Someone had beat up the muffler and there were some scuffs on it so it wasn't good for a resto.
I had to rework it to fit the trike frame and the tall motor.
I put a megaphone on it with a steep reversed cone at the outlet to tone it down.
(https://i.postimg.cc/brJTZkTQ/IMG-0039.jpg)
This is the one I favor over a ProPipe
I found a thunder header (I think) in the post above which actually looks pretty good.
Quote from: Adam76 on March 25, 2020, 04:11:08 AM
Quote from: thumper 823 on March 25, 2020, 03:25:08 AM
The correct is answer above -
If you look at my thread on here you will find a LOT of information (with pix).
Usually, the bottom of the cylinders need to be turned dwn to get heads closer to the piston (for standard chambers)
I am at 0.026
IMO which I believe is correct - There is no reason to mod standard HD cylinders and pistons.
It is a waste as you are still using standard aluminum cylinders and standard combustion chambers with poopy 8.5 CR.
You will never notice any difference.
Thanks thumper, that's good to know about not needing to really change the oem cylinders and pistons. But I couldn't find your thread?
If I'm leaving the standard pistons and cylinders what other mods do you suggest for an 80" build, at what compression and all that stuff.
Thanks again. 👍
Look here
https://harleytechtalk.com/htt/index.php/topic,110851.msg1325327.html#msg1325327