Blown head gasket????

[mx671]

I'm trying to find the cause, we went from a 150 shot to a 200 shot & got a head gasket # 2 & 3 cyln. As soon as it shifted to second a major back fire. Fuel was set at 9.5 psi with nx flow gauge timing pulled back to 30. It is a gemini twin 4150. 2 plug tips were burned off, but I dont see how it could have been lean @ 9.5psi. With the the old efi set up we 2 major back fires from puddling in the intake, could that have caused a weak link & just give up on the 200 shot? Looking for some reason & how to avoid it again. The head needs to be welded & reserfaced, left a pretty good hole. Oh ya it's a 331 vic. jr. heads. Thanks for the help!

[Tim mcmann]

I got alot of experience with this kind of stuff. Its definetly still puddling! You must take some fuel out. It seems risky i know but its the only way. Good luck .

[mx671]

Thanks for the reply I was about to give up. On my 466 i was runnig 9.5psi & never had an issue. The head on the 331 had a hole the size of pencil between the cyln. Are you runnig a high pressure system? What do you set the fuel at?

[FX331]

On my 331 (with a NOS Cheater Plate) I set the fuel pressure flowing through the plate at 7.5psi. Seems to be working great. This is with the 175hp jets.
I pull 10 deg for a total of 28deg & run NGK -8 plugs.


9.5psi seems like alot of fuel.

[mx671]

Your kit is probably jetted square, NX uses a smaller fuel jet & more pressure.

[smallblock]

timing timing fords don't like alot at all if you burned a few tips and lift a gasket pull out alittle more. make sure you pointer is indexed those factory ones ain't worth a dam. fat fuel won't lift a gasket usually. those 10 bolts don't like alot of pressure. also what kind of gas were you running that plays a major role in timing as well i like vp116 for basic stuff i use vp n2o for my car now. but the 116 is fine for most

[mx671]

we are useing 110, it's a pump gas motor. I agree with you on the timing, it does have stock pointer, it's not a bad idea to index it. I'm going to bring #1 up & check it. We will be using to c16 next time.

[smallblock]

c-16 is a more stable fuel for nitrous. i'll tell you i rarely get a stock pointer that is on the money.some are off as much as 3 degrees pm me if you have any questions

[speer13]

I think you have way to much timing in there for 110.... 30 degrees with a 200 shot.... the fuel pressure is fine when people compare NX to nos dont listen they have different ways of jetting and pressures to go with them as stated above... when I ran dragradial with my nx plate it loved to be around 9-9.5 up to a 350 shot when I tried to play with the pressure is when I lifted ring lands... as the nitrous jets go up you need to figure the timing accordingly 2 degrees for every 50 is a recomendation and it can go up or down depending on the amount of nitrous.... even with that you say you were running 38 degrees on motor to much in my eyes... with that fuel and depending on the plug I would have been more around 26 and worked from there maybe even 24 depending on what timing the engine liked best... my other question is is this on an efi engine or carbed engine? I'm not a big fan of running carbed plates on efi converted intakes...

[mx671]

speer13 I agree about the timming, on my 466 with a 250 shot I was@ 30 with 9.5psi. My buddy had his 514 with 300 shot @ 32 with 10.5psi I'm sure with better fuel. His car was tuned on his chassis dyno, he claims the motor was happy @ those settings. I'm learnig that a small block is a differrent animal. It's a carb plate, with 850 q- fuel carb. I think c16, less timeing will be the cure.

[speer13]

Are those timing numbers before pulling some out for the nitrous? I cant speak for big blocks I know they can take a lot more in reguards to nitrous tuning, but 32 degrees total with a 300 hit? with my experience if you tune nitrous on a dyno I always lean towards the rich side before the car comes off and fine tune it at the track...

[mx671]

I hate to speak for him, but he pulls 1 degree for every 50hp. Total of 38 on motor. NX says it will work per their instruction book. I' m too chicken sh*% for that kind of tune. My car made it's best motor pass @ 36 degrees. I just bought a 2 stage pro flow for my soon to be 521. Thanks for your help.

[chevyeater]

Not sure if this is what happened to you're engine. The previous backfire may have been the culprit. But thought i would throw this at you. First we ran a 351 stock crank rods with hyper pistons to mid nines using 300 shot. not suppose to do that on hypers. anyway never hurt a thing. I believe we could have gotten deep nines except for hook up problems.stock susspension. anti rollbars were illegal to run at that time. this all was done over 8-9 years ago. anyway read an article some years ago in the old superford mag on 408 dyno build up. engine was pulling strong then, boom. same symptoms you have. melted plugs blown gasket and a nice hole in the head. the conclusion was severe detonation on paired cylinders caused from cross firing off the plug wires. this may have been your'e cause in previous backfire and the later too. all i'm saying is to check the wires and dist for any problems. too lean or too much timing would show up in the other cylinders as well.

dave