85% Nitro...Why is this causing problems? (1 Viewer)

[Marchboom]

Having built a few race engines (gas) and raced bracket dragsters in my time, I know a little about how engines work. BUT, what I'm not up on is why the reduction to 85% nitro is causing engine damage. Are the crew chiefs trying to spin the motor too fast using other tuning approaches?

I'm sure there are some folks here that know what's going on.

Thanks

 

[Keith Burgan]

John,
with 85% you have less latent energy to start with so the first thing that the tuner does is try to stuff more fuel/air into the engine. That entails more blower OD, higher lift/longer duration cam etc. Then to light the mix you need to add more timing and/or use a longer rod to keep the piston at TDC longer in an effort to be able to adequately fire the mix.
So now you have this thing all hopped up and the retard comes in to play and pulls away a bunch of timing on the top end. Is it surprising that these things are blowing up all the time.
I had a discussion with a leading crew chief on this exact subject yesterday and the hope is that Dan Olson will bring some sanity back to the regulations. Most tuners evidently feel that a fuel pump volume restriction or a spec pump would be the best solution as restricting the % just means that the tuner will continue to try to stuff more fuel into the motor to regain the prior energy level.

Roo Man

 

[Toejam]

Because they are running so much static Compression, the Rods are just getting Hammered! One co-crewchief told me they're are running a half-point higher Compression at 85% than at 90%, Not to mention bearing and Crankshaft life.