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Hey all...I've got a pretty chewed up LT1 race motor that I wanted some feedback on.:-damnit

Overview - Built/forged LT1 396ci race motor. N/A, pump gas, LS1 PCM and coil on plug ignition. Compression was high at 12.3:1, but was tuned accordingly and had no knock. Tuned by a reputable local tuner and made 500 RWHP through a TH400, 9" and a loose converter. Spins to 7,200 RPM. Ran strong - 10.6s at 127 MPH.

The motor had only been together for about 25 total runs before it fell off to a mid-11 pass and I shut it down. Oil pressure was not happy on the return road. Leak down tests showed a few hurt cylinders. Pulled the motor and found some serious carnage - spun main bearing, 4 (front 4 only) chewed pistons and subsequent head damage.

I have a couple of theories as to what happened:

--- I just filled up with a new 6 gallons of Sunoco 93 on my way to the track. I either got a bad batch or a lower than expected octane. That doesn't explain the below...
--- The front 4 pistons are clean but destroyed, the rear 4 are black as can be. Same goes for the intake ports. Fuel rail or injector problem? I'll be sending the injectors out for flow testing regardless. They are Racetronix flow-matched 63 lb. injectors.

The way I see it, the 4 cylinders leaned out, pistons went and then the main bearing went. Am I missing something? I'm trying to figure this out before I put it back together so I can avoid this happening again in the future. I will say this - Pump gas is off the table...I'm going to race gas moving forward.

Thanks for the help.

-Rick
 

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I would venture to say you're still detonating with that much compression regardless if the sensors pick it up or not. We've had to repair a 12.5:1 "pump gas" LS in the past that broke the top ring land.
 

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It's an Advanced Induction spec'd setup - ported stock heads and intake manifold. Mid 25X/low 26X on a 106 with .61X lift. Switched to solid roller from HR a few months back, but kept the HR cam.
 

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Thats not a big cam and being a mech roller the advertised is proballly in the 290-300 range.... Not enough duration IMO to run 12.3 to one on 93 octane... espc pulled down on 106...

A chassis dyno is not even close to replicating the load an engine has on the race track, running up thru the gears and then bucking 130MPH worth of drag in high gear on the big end....

Your not the first person I've seen push a pump gas LTX like this, have it be fine on the dyno and then melt it down after a few trips to the track.

IMO what you are seeing in the aftermath is the first 4 cyls which are the leanest because of the LTX intake, detonated to death killing the mains and the rear cyls look pig rich because they ran a little while with a bunch of extra fuel and oil comming back in the intake from the reversion of the 4 dead front cyls.

Once you go back together and run a good race gas like C-12 you will be fine.
Will
 

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What causes the reversion?
 

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What causes the reversion?
Overlap is the main cause of reversion in the intake... but you also get it to a smaller degree when the intake valve closes and that harmonic wave forces itself back along the intake tract into the plenum to get canceled out.

Reversion happens when any engine is running normally but it's not a problem, when all 8 cyls are strong, the fuel is not overly contaminated and the engine is capable of burning that fuel. Unburned fuel from one cyl just hangs out in suspened in the air (hopefullly) in the plenum until another valve opens and it's intake signal carries some of that reverted fuel/air to that cyl.....

If you have ever seen an IR set up with the wrong cam in it you could visualize better... but I have seen what appears to be a fog of suspended fuel hanging over the entry of the injector tubes at WOT.... and that's close to what reversion looks like inside the plenum of a short runner intake manifold.

So in your case - When you have 4 pistons self destructed and the other 4 pulling the them along - You end up with a lot of contaminated fuel and oil from the dead cyls that during reversion gets pulled out of those dead cyls, into the plenum and then into the 4 still good cyls....

IMO This probally happened during the last bit of your 11 sec pass and on the return road until you shut the engine down, making the 4 rear (still good) cyls apear overly rich upon teardown.
Will
 

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pics of everything, particularly plugs and chambers etc
 

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12.3 on pump gas? Isn't that something that would need a very precise tune up and strict control of things like coolant temperature and fuel quality? I really don't know anything but it seems to me that isn't going to work very well. Am I wrong?
 

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I dunno what happened but the compression is crazy high for 93 octane.
 

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Discussion Starter #11
pics of everything, particularly plugs and chambers etc
I'll load up pics tonight.

12.3 on pump gas? Isn't that something that would need a very precise tune up and strict control of things like coolant temperature and fuel quality? I really don't know anything but it seems to me that isn't going to work very well. Am I wrong?
All involved understood the risk. I'm not denying that we were walking a tightrope, rather I'm trying to ensure we learn from our mistakes. With the LT1's reverse flow cooling, 12.5:1 isn't unheard of with pump gas. Coolant temps never breached 180*, even during runs. Obviously, we pushed this setup too far and/or ran into an octane issue with the pump gas. It's certainly an expensive lesson that I only want to learn once.
 

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Here's ur feedback , next time keep a 5 gallon jug of 110 to mix in with pump gas, 12 to 1 is to much for 93,u need to be mixing 93 and 110 for safe measures.keep a timing light to back down timing when u are going to use questionable fuel. I run 11 to 1 and mix 110 with 93 always atleast 30-40% vp or sunoco 110 leaded, Not worth the risk IMO
 

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Just curious why you were on pump gas? Were you going for a pump gas record or class?
 

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Just curious why you were on pump gas? Were you going for a pump gas record or class?
We were running a stock head/intake pump gas LT1 in a full weight convertible to see how fast it could go. It's a registered street car as well so pump gas was the plan.
 

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A little too much compression for that gas. Stick with Shell 93 if you can, but 12:3 is too much even for Shell with your combo.
You have a couple of good options. One, Renegade offers a street legal 102 octane gas. Two, you could move up to Renegade 110 leaded, but sensors are going to be a problem if you're running them.
Mixing pump gas with leaded race gas is the least desirable option. They don't work well together unless the pump gas is ethanol free. Running 110 will give you a lot more room for error before damage occurs.
 

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A little too much compression for that gas. Stick with Shell 93 if you can, but 12:3 is too much even for Shell with your combo.
You have a couple of good options. One, Renegade offers a street legal 102 octane gas. Two, you could move up to Renegade 110 leaded, but sensors are going to be a problem if you're running them.
Mixing pump gas with leaded race gas is the least desirable option. They don't work well together unless the pump gas is ethanol free. Running 110 will give you a lot more room for error before damage occurs.
What does that Renegade 102 run for a 55 gallon drum?
 

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with that camshaft, compression and pump fuel of today even the best tuning in the world would of been a should i snip the blue wire or red wire kinda deal. U were just askin a bit much from what u had and it gave up the ghost.
 
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