Hi All,

My current setup is a 96ci fxstb that has a 103ci kit with 255 cams in it. k n n filter and v n h short shots and SEPST. It rides well but has a slight ping under load.

I've had people recommend swapping the cams as the SE255 is the issue ever after dyno tuning.

The bike is pulling 88HP and 113ft/lbs of torque.

As I'm not a 100% sure about what's in this bike as it was built in the US before getting imported to Aus I'm having to make assumptions. the bike had a heap of torque down low and runs out of puff up top, exactly as a SE255 would.

I've used the big boys head porting calculator to try and look at different options. Plugging my existing setup into the calculator with stock heads gives me a corrected compression ratio of 9.84:1 and 201.6 psi. A compression test done at 1000ft above sea level produced 210 psi F and 205 psi R. This leads me to think the heads have been shaved, if i drop the head cc. from 85 to 83cc I get a corrected compression ratio of 10.03:1 with 206.7psi so I think it may have had beadwork.

A highly recommended shop has suggested s&s570 easy starts as a replacement to the SE255.

I ride this bike daily through the city so I need it to not be a pig at low rpm but I would prefer to more the torque curve a little to the right so it still responds well down low but keeps pulling up high.

Before seeing this shop I was looking into Andrews 54 cams but know I'm not really sure how I want to go through it.

The s&s570 change ​​​​​​the setup to 9.54:1 with 193.8psi and the Andrews 54 gets 9.45:1 with 191.6psi.

From my limited knowledge and what the shop shop was saying, aiming for a Corrected compression ratio of 9.3:1 is the go.

Anyone care to suggest a cam or if my build would suit a s&s570 or Andrews 54.

Also, I have a 2 into 1 thunderheader to go on after the cam install

Any help is appreciated.

Chee​​​​​​t's

Ryan

 

The 255 (bright green/red) really does better down low by a bunch, and the S&S570s (dark colors) move the power band to the right a bunch. The S&S cams are better mid range and up, but unless you spend a lot of time in the upper RPM ranges, you may be better off pulling a little timing. Simulation shows why:

 

As stated, much easier to fix the tune first. If you don’t mind giving up substantial low end torque, then you can change to one of the cams you mentioned if desired. Be aware that the Thunderheader will also kill some of the available low end torque as well.
You might consider the Andrews 48 if you’re wanting to retain the bottom end but that pipe still won’t help.

 

I would caution against making decisions based on the variance in CCP between calculated and actual; rarely to they matchup. The OP is flying blind on data used to calculate CCP like chamber volume, head gasket thickness and deck height. Additionally, the dyno numbers are very typical of the SE255 in a 103" Stage I motor. Pulling timing out will very likely turn the motor into the "pig" the OP is trying to avoid. Based on what the OP has posted, swapping the SE255s for the Andrews 57 and a trip back to the dyno should solve the problem; decent low end torque with more "puff" above 4000rpms. The Sideshots are not the greatest but swapping cams and re-tuning would come first for me before making a decision to swap exhausts.

 

More than likely there is not head work done. Your raised compression is more than likely due to carbon build up plus the larger pistons. The Cyclerama 575 would supply everything you’re looking for IMO. You’re probably at or near 10:1 static which is perfect

 

Thanks for getting back to me everyone.

The bloke who initially tuned it is a great tuner and he took the bike from being a pig down low in the rev range that pinged to a bike that Is smooth down low but still pings, just nowhere near as bad.

New tuner is highly regarded aswell, I just don't know if the 570 is too much cam for my bike and if i would be better off with a milder cam.

Choices are always hard to me make when it comes to bike haha

Another thing, I just got the thunderheader second because I have seen raving reviews about it. Why in particular would it not help.my setup? I thought any pipe would.be an improvement over the short shots.

 

The 570, CR575 and Andrews 57 are all "bolt in" cams for the later models.

Like Dave, I think your static CR is somewhere between 10.1 and 10.2. So all three of the afore mentioned cams would work but I would pass on the 570 in favor of one of the other two and never look back.

 

TH is an improvement. But the softail version has the shorter rear head pipe compared to the dyna which wraps around cam cover. So it might not perform as well.

 

Why don't you start with small reductions of the spark advance in the area's where you notice the ping with your SEPST and put high octane fuel in (oct 98). Do some tests and take it from there.

 

Do the cams like Dave and djl said. Or you can take the motor down and measure everything (peace of mind).