too much compression for andrews TW26a cams

[harleyd]

mike, i've got a 2004 Heritage Softtail most of riding is done two up and loaded. just did 95" flat tops w/ andrews tw26a cams and ported and polished heads. running thunderheader and stock carb w/ 48 pilot, 195 main, and sportster needle. heads were supposed to be 82 cc @ 9.5-9.6 compression. with .030 gasket. bike ran good with me on it but when loaded down it started slight detonation. not real bad but just a slight clattering sound coming from the exhaust. checked compression on each cylinder with two different testers and got 197 and 203 psi. and second test was 190 and 196 psi. talked to dude that did my heads and he said i could get detonation out with SE race tuner. local dealer also said he could fix w/ SE race tuner on the dyno. my question is this too much static compression to try to tune. my first thought was to put more cam, but got to be concerned about valve to piston clearance issues. if tuner does not work , what cam could i use with out clearance issues and keep my low end grunt. appears that the se 211 will bring pressure down but concerned about the .208 tdc. your opinion will be greatly appreciated. Thanx

[Mike]

Any cam that brings your pressure down will also do the same to your low end grunt. Tq is all about cylinder pressure. Your pressures are really about right and tuning should be able solve your issues. Your compression ratio also calculates correctly for the info given and you've got the correct cam for your performance goals (though it may not be taking full advantage of your ported heads).

If your head porter used stock valve diameters, the TDC numbers for the 211 will not be an issue (even with the .030 gaskets). If oversized valves were installed, then it would be close. The 211 really likes closer to 10.2 compression to work well.

You have not stated whether you have an ignition module installed so I'll assume your using the stock module. I'll also assume your dealer is talking about SE Ignition Race Tuner. This would be the correct move to allow ignition tuning to optimize your combo and reduce detonation. Another option is a plug in, tunable module like the Dyna or Daytona Twin Tec. These would allow you to make changes as needed, by simple trim pot adjustments, until the detonation is reduced.

Another theing to do is fold two of the baffle fins over in the T-header. This really helps tq from 2-3k rpm.
Mike

[oscar]

Mike, I failed to tell you yesterday that I am running stock valves & springs and a screamin eagle pro ignition module that retards timing 5 degrees at wide open throttle. What module do I use with the SE ignition race tuner system, NO. 32124-04b. I still have my stock module if I need to use it. You mentioned the DTT and DYNA modules,can they be used with the race tuner ? Thanks for your reply,all of your help is greatly appreciated.

[Mike]

The SE Ignition Race Tune is used with the stock module. The Dyna and DTT do not require Race Tuner as they are adjustable on their own (basically replaces Race Tuner). With these, no need to hook up to a computer to make changes.
Mike

[JLOCKHART29]

Mike, We did Oscars build in March and the run to Ennis was the 1st time on the open road loaded down with any kind of outside temp. We trailered his bike to the dealer and had the Race tunner installed and dynoed the same day I did mine. This was only the 2nd time the tech had ever used a Race Tuner and baisically what he did was do an innitial run and plug it canned maps till he fouund one with the most retardation but keept original preformance . Ended up with 10 degrees I believe. It took care of 85% of detonation. He asked me to ride it last week and listen to it. I can make it detonate by running 1 up level round in 5th gear running 50 mph if I instantly pin the throtal. It is a Heratage with windshield and if I hold my head down to the tank I can hear 2 or 3 light rings before it clears. Like fingernail on a cylinder fin. I realize this is baisically lugging the motor but we have all done it and will again in our day to day ridding. He is afraid this light, ocassional detonation will cause him problems still. What do you think? Should he ride it and not worry just get out of it if it starts "pinging" or do something else? This was the only place I could make it detonate in "real world" situations. I did make it do it by pinning throtal in 4th gear at 30 mph but I realize thats abuse.I was just trying to make it detonate as I had not been able to hear any at that point. This is the original run w/o Race Tuner and ofter Tuner with a 220 main added. Thanks

[Mike]

It sounds like Knock Control is working and able to subdue the detonation. So long as you do not have continuous pinging you should be OK. Knock control has to hear a certain amount before if can actively kick in to control. So a few pings would be normal.
Mike

[JLOCKHART29]

Mike, Excuse my ignorance in computer ignition adjustment but what exactly is "knock control"? The wrench did not mention any thing like that. Does it activate automaticly with the race tuner or did he have to enable it threw the race tuner program. My partner hears a clattering sound on occasion coming from his Thunderheader. He is afraid this is some detonation. It is a completely different sound that the detonation I hear in the heads. Can detonation of any form (ie very light) be heard in exhaust and not heard in the head area? Both HD wrenches that fooled with the Race Tuner rode bike and thought it was the Thunderheader pipe itself making the noise. Seams to be worse w/ passenger. Right now he is seriously considering the 211 cam to bring down his cylinder pressure. In your oppinion would this be a good move or would you leave it as is? Thanks mike.

[Mike]

Knock control can be activated or deactivated using the SERT software. Some tuners will deactivate during the tuning process to allow more consistant data sampling but it should be reactivated when done. This is done in the "tuning constants" table. Going to the 211's seems a little dramatic for a tuning issue. Your combo's are not that radical that tuning should not be able to solve. I've not known pinging to manifest in the exh as sound other than maybe a kind of crackling noise. What you will see is a lot of white smoke out the pipe when detonation is occuring (bad). Detonation is around the top ring lands and cylinder walls and will be heard there. Your freind may have a loose baffle or similar in the muffler.
Mike