Let's say you have a TII engine with S4 rotors. It's tuned to 11.5:1 across the board. You're running 17psi off a PT61. Advance is 13* and split is 10* at said boost level. Haltech E6X is controlling it. Plugs are the stock 7 and 9. You make a hard pull to 8000rpm. You lose the apex seals on the rear rotor. Intake temps at the time of demise at 135*. You happened to actually log the pull that did you in. Did the hot leading plugs do the engine in?

 

When the hot plug on the rear rotor was pulled, was the elctrode still intact? or was it gone?

CJG

 

i dont think that would do it unless like said above the electrode came off.. i ran sotck plugs on a modded engine as well and above 6.5K - 7K at full boost it would break up. i just backed off and its all good.. just make sure you run decent plugs next time.

 

yes the hot plug would seen it done a few times before.

 

are S4 rotors 9.7:1? if that's the case...that seems like a lot of advance and boost for pump gas

 

11.5 AFR at 17psi boost is too lean for street gas unless running WI, and 7 plugs are also too hot for over 300whp.

 

I've been running 20lbs @ 11.5 afr for 1 year no problem

 

Street 92-93 octane without water injection?

 

Thanks for the comments guys. Keep them coming. The rotors are S4 TII rotors to clarify. We'd ran up to 19psi earlier without issues. But on 9s. The car is kind of a partnership effort and I didn't realize the plugs had been swapped for 7s until I tore the engine down. Just want to get a handle on why it detonated.

 

93-94 octane, no water injection

 

S4 T2 rotors are 8.5 compression

 

yes too hot of plugs can cause preignition.

 

did you bouce of the rev limit?

 

Sure did. Pulled strong to the rev limiter. Large backfire at the limiter. Coasted down then when we eased back on the power to cruise it was on one rotor. The Haltech is set to ignition cut though. Think the limiter caused it? How?

 

I wouldn't necessarily point the finger at the plugs yet. I ran 18 psi on a half-bridge FC, S5 9:1 rotors, 60-1 turbo, on 91 octane @ approx 10.8 AFR, with around the same intake temps. I was running 7s and 9s, stock ignition, and no breakup all the way to 8500. This was over a year ago, I sold the car and its still running fine @ 15 psi.

 

100% YES.

Hot plugs will detonate a motor maybe not on the first pull but once she is loaded up you can kiss it good bye !

9's all round a bare minimum
10's if your serious
11's or higher if you make allot of grunt and are on it all the time.

7's and 8's or stock plugs and you or your tuner will learn the hard way about automotive spark plugs becoming diesle glow plugs in rotary engines.