Jamie what exactly is dynanic compression. is it measured with the spark plug wires pulled off and using a compression gauge to get a reading. why does the 255 seems to be a higher value then the woods. does the 255 swallow more air on the down stroke due to different valve timing.
I have a set of 255 in my 103 kit and I am getting 197lbs in rear cyl and 195 in front cyl.
another question some one asked if you needed decompression releases and you said no if recall the post info. I know that if I try to start mine without the manul ones pushed on it usually wont start and I get one heck of a kick out of the starter. my rear one sticks until i pull it up after it starts, which is kind of a pain. now I am holding the front one down with my finger since I find on occasion that it pops up before the bike starts then kicks out the starter. I will be switching out the heads at some point and getting heads with the decomp release hole in the center of the head so I can get the electric ones that will stay open until I release the start button.

 

Static compression is determined as the ratio between the cylinder volume compared to combustion chamber volume on a full crank stroke. Dynamic compression however uses the point the intake valve closes rather than BDC. Unlike static compression, dynamic compression will allow you to accurately calculate cylinder pressure. The earlier intake valve close of the 255 cams will create more cylinder pressure than the Wood TW-555. As a general rule you will need compression releases if your CCP is over 195.

 

Guys

This is a good deal for the bucks. Sure you can go crazy and hit 130 square and have a dyno queen.

This 107 hits hard with good torque down low just what a bagger needs. The CCP is good and won't wear out your starter. Much better than the SE 255's all around most likely easier to tune and you don't need high octane fuel either. If you have Jamies PC and get a good map included it save 300 to 400 on a dyno tune.

Beats the PS harley stage 3-4 and costs less too.

 

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Once again, great work Jamie and thanks for keeping us in the loop as this develops. I know if you are putting your stamp on this, it's gonna be top notch stuff. All for less than 2k installed? One of the best deals I have seen. Two thumbs up.

I have a couple questions about this build.

Does boring the 96 to 107 reduce reliability or structural strength?

Will you be offering other pistons that have a lower compression? I would like to be at about 10:1. Will the current build run well on standard 91 octane without pinging or detonation?

Once again, thanks Jamie. Great work.

 

If you run a stock thickness head gasket instead of the .030, you'll knock your static compression down by about a quarter point. If your heads are CC'd at the same 87cc as Jamies, you'll bring it in pretty close to 10:1 static.

 

Quick follow-up question about head work: remember we were talking about stock 96" heads ideally having 85cc displacement if I was thinking about using stock heads for a 107" build? Is that where Jaime wound up with each head, at 87cc? I remember you saying the most important thing is getting the heads cc'd so they'd have exactly the same displacement, so one piston won't work harder than the other as a function of compression. I thought Jaime said his static compression wound up at 10.25:1, where you said it be at 85cc. I'm guessing 2cc's makes a difference (duh.)

I want to stick with stock heads and not get exotic with the build. If we're talking street port and polish, does that necessarily imply removing some head material, thereby increasing head capacity, or is it possible to have the "ideal" 85cc heads, get a mild port and polish, and still end up at 85cc's?

John

 

Boring the cylinders to 107" has been well proven by many top engine builders and piston manufacturers over that past several years, Fuel Moto is not a pioneer there. However there are a few companies that are using speculation and scare tactics instead of any kind of real information or support data for their claims.

Our combination at 10.25:1 runs excellent on 91 fuel with zero detonation and it has been well tested at extreme engine temps, I dont see a real reason to change from that. With a .040 gasket that would put the compression right at 10.0:1 (9.20:1 dynamic), however with .010 more squish area there would be greater chance of detonation.

 

Our stock heads actually tested at 86 and change, and production variances will likely put most heads between 85 and 87 CC's. The difference in static compression between a 85 and 87 CC head would be approx .18 of a point. There are also differences in deck height from variations in crankshaft and connecting rods as well as pistons and cylinders. For the purist each component could be blueprinted and corrected, however we designed this kit to be a little more forgiving as we did not push any limits and feel users will have no problems hitting the numbers we are posting. We will be testing what we wil be calling our Fuel Moto Stage 1 heads which will feature new guides, bigger valves, springs, along with some minor porting work mainly to blend the transition area at the guide. We should be posting results next month.

 

Thanks for the reply Jamie. Time to start saving some cash! It's great to have such a renowned tuner/builder within 5 hours of home!