Thinking of a cam swap

[Jim Bronson]

I'm currently running an S&S585 in a 2013 Dyna with an S&S110 top end. I'm not liking having to keep the RPMs up and shifting above 4500. I knew about this behavior before I had the work done, but I'm having a hard time getting used to such high RPMs. I'm more of a low-mid kind of rider.

I'm thinking of swapping the S&S585 with a SE255 for a more sedate ride, yet plenty of low-mid torque. I'm pretty sure the dealer will swap the cams, since the 255 is an EPA street cam. I'm just wondering about the tuning. I'm sure they can install a download, but it may take more than a simple download, since the bike has V&H 2-into-1 exhaust.

I have a PV, so I could use autotune for any tweaks, but I'm wondering if I can load the PV from the ECM, perform the autotune tweaks and then reload the ECM.

There is also a Dyno shop nearby that would do the work and could dyno vs download. I may have some credit with them on the dyno. They did the dyno for the 585. I'll need to check.

Suggestions appreciated.
 Many thanks.

[scott7d]

I'm currently running an S&S585 in a 2013 Dyna with an S&S110 top end. I'm not liking having to keep the RPMs up and shifting above 4500. I knew about this behavior before I had the work done, but I'm having a hard time getting used to such high RPMs. I'm more of a low-mid kind of rider.

Good Lord. If you are realistically having to shift that high, I would think there is an underlying problem aside from the cam. Especially on a lighter bike like a Dyna. What exhaust are you running?

Are you dead set on the 255? With a good tune and exhaust there may be a better middle ground option like the CR575. You can still keep "some" top end if you want it while still being able to pull stumps.

But yeah, 4500 seems way over the top for it just to be a cam issue.

[Ohio HD]

I'd take a compression reading before doing anything. I bet the compression ratio is way too low for those cams. They need to be at a "true" 10.5 to 10.8 and not an advertised 10.5.

If the compression ratio is truly 10.5 the compression should read about 190 to 200.

[rigidthumper]

Couple questions- is it 110 cylinders with factory 103 heads, or S&S heads?
I've found the SE255 to be too short of a cam for >10:1.

[harpwrench]

If you want to use SE parts, they used the SE585 in 110 kits for stock 103 heads. That would pump up the low end torque. It seems possible to me from looking at old posts that your tune might be the problem rather than the SS585. I've used it a couple times, it might have been a little soft but it had good drivability. 

[Jim Bronson]

First, thanks a lot to everyone who replied. I'll answer the questions in order.

1. I can shift well below 4500, but the cams are advertised as making the most power at 4500+. After using other cams, the engine sounds like it will fly apart above 4500. I'm just not used to hearing the engine reving that high, even though it does sound sweet. If I nail it at 4500, I can feel lots of power until redline. It is a good feeling, but I'm still scared something nasty will happen.

2. I'll take a compression reading and post it.

3. The heads are untampered stockers with ACRs installed.

4. I'll check out the SE585. A friend is using SE255s on his stock 103, and he's happy with them. The tune seems to be fine. It starts and runs OK.

[Hossamania]

How does it run between 2500 and 4000 rpm?
In what conditions are you running it to 4500 rpm and beyond? You have a cam that turns on late, so it should be no surprise that 4500 is the sweet spot of the start of the powerband. It's just a matter of if you can work with it or not. (I run a cam with a similar powerband, it is what I was looking for and use it that way, often using a shorter gear for certain cruising situations)
If the motor is sound, running to redline, especially if still the stock limit of 5850(?), should not harm the motor. That doesn't mean you have to, it just means you should be able to without much fear. If it seems to vibrate excessively, make sure your exhaust and other parts are not rubbing or binding.
Take a look in the Dyno section for a more acceptable cam for your needs. The 255 would be the opposite of your current cam, running out of power by about 4500 or sooner.
For me, any cam change with that much difference from what you now have would warrant a proper Dyno tune.

[Jim Bronson]

I haven't noticed any problems with the way the engine runs. I seldom shift later than 4500, but on those few times that I did, I didn't notice any problems.

I pulled the dyno sheet today, and I noticed a puzzling issue. I'm aware that the curves should cross at 5250 RPM, but mine cross at about 4450. I'm wondering why. I would post it, but the board requires SAE smoothing and mine is STD smoothing. Are the two related? The H/P equation calculates a H/P of 84, not 102 as the graph shows. Is this a graphing error, Dyno calculating error or ?

[Hossamania]

Double check to make sure the scales are the same. Sometimes the numbers on each side don't match, putting HP and TQ on different scales of the same graph. Not a common thing, but I've seen it happen. Not sure why.

[speedzter]

Post the sheet so we can see where your at .
This isn't the dyno section, so the sheet should be ok ?  (correct me if wrong )

[Jim Bronson]

Double check to make sure the scales are the same. Sometimes the numbers on each side don't match, putting HP and TQ on different scales of the same graph. Not a common thing, but I've seen it happen. Not sure why.

Thanks Hoss. The scales are not the same. I'll try to post. If you don't see it, you'll know it went to the shed. 

[rigidthumper]

If you happen by the shop, ask them if they can reprint your sheet, in SAE, with Axis locked. The sheet will then be in compliance with board norms

[Jim Bronson]

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[Hossamania]

That graph makes it difficult to get a decent read on HP/TQ relationship.  Certainly gives a perception that the horsepower is higher than it actually is.

[Jim Bronson]

I agree. Numbers don't lie:

HP=(TQ X RPM)/5252
  =(118 X 3740)/5252
  = 84

The question is why this differs from the actual dyno-measured value (101.56).

[Ohio HD]

Left side column of values is HP right side column of values is torque.


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[Jim Bronson]

I understand. That still does not explain why the calculated HP value is so different from the graphed value and why the torque/HP crossover point (TQ=HP) violates the 5252 constant.

Sorry to get sidetracked with the dyno sheet. I'll look into this further, but it seems to me like there's a graphing or calculation error.

[Hossamania]

The sheet is correct, just need to look at each line relative to each side of the listed values. The crossing line at 4500 rpm is incorrect. That's one reason there are rules here about how Dyno graphs need to look to be posted, it takes confusion out of the mix.

[Ohio HD]

The reason the values don't cross at 5252 is because there are two varied columns of data. See rigidthumper's post, asking the shop to do that will display the sheet as most are normally. There are more than one way to display the data. Example below.


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[Ohio HD]

They are crossing at 5,252 rpm, just not being displayed in the format you want to see it.


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[Hossamania]

Now, the question is, which cam to choose for replacement?

[Ohio HD]

Not yet, the questions are, how much cylinder pressure do we have with this setup, and can the tune be improved to make the motor run more like he wants it.

[harpwrench]

Either way it's graphed, rpm is correct. Your torque line is crashing before 4000rpm and hp is far from begging for 4500+ rpm shifts. The bottom of the tq dip is still almost 100 ft lbs. If you want it to come up sooner then you might want to change cams, but not because you believe this is a higher rpm combo.

[speedzter]

It's making good torque, ~ 100 ft.lb at 2500 rpm and ~ 115 at 3300 rpm ,
You really don't need to be shifting at 4500 .

This is not a top end Cam in this build, more a low-mid .
It should still ride fairly strong even short shifting at 3000 .

[Hossamania]

Not yet, the questions are, how much cylinder pressure do we have with this setup, and can the tune be improved to make the motor run more like he wants it.

Good point.