I know kinda a n00b question....But what causes it and what can be done to prevent it?

I know....I did do a search for it and would have had to spend a half an hour reading through **** cuz nothing was directly on this subject

 

Too much cylinder pressure. You can buy some head studs and take care of the problem until you get into HUGE power numbers.

 

I bought my car new in Dec of 99 and after 3k miles I installed a nitrous kit on it. Ever since I have never had a head lift on me, but I had a window switch, and I never got greedy.

 

This is true. It's not really the nitrous that lifts the heads, but the effect the nitrous has. When the N2O breaks down, every 2 molecules of N2O = one molecule of O2 (otherwise known as oxygen). When you put more oxygen into the chamber (and likewise more fuel via through the wet kit fuel lines or adjusted by the maf through the injectors on a dry kit) you get more air/fuel mixture in the same volume of combustion chamber. This is essentially how all power adders work. Nitrous just works chemically (i.e. there is a chemical reaction that takes place to shove more air into the cylinder) while FI does it mechanically by forcing air into the cylinders.

A good way to think of it is like a coke bottle. Take a 2 litre coke bottle and fill it half way with coke. Shake it up and put your thumb over the bottle opening to create pressure. You can probably hold it pretty easy. While there is some pressure built up, you are able to control it using your thumb muscle. Now fill it all the way with coke. In this instance there will be a greater amount of pressure built up and it will likely be more difficult for you to hold your thumb over the bottle. Cylinder heads are similar to the bottle cap on a can of coke. The more pressure you plan to build the stronger cap you will need to hold it.

This can be done by using head studs instead of head bolts, adding girdles, or going with a 6 bolt head/block combo (like the lSX/ETP). Good luck, and I hope this was helpful.

 

You can also go with larger head studs for the huge shots, but then your heads are also going to require some special machining.

 

if only we had 6 bolt mains...

 

are you serious?

 

we do have 6 bolt mains. one of the only blocks made with 6 bolt mains.

you meen 6 bolt heads? the lsx has 6 bolt holes. im still running 4 bolt heads without an issue. alot of its in the tune, and gasket as well. and with a good thick head deck helps as well.

 

whoopsies....

 

As Noyzee said...its the tune.

Not many of us that have ever blown a head gasket has ever done so by having too much cylinder pressure on a PROPERLY TUNED setup. I would be there are only a handful of people on this board that have actually exceeded the limits of a properly sealing heads gasket and good bolt set due to too much cylinder pressure (with no detonation or preignition).

The analogy of the 2 liter coke bottle is incomplete and over simplified (not picking on your BTW, your analogy is helpful).
The reason that analogy is incomplete is because combustion in a cylinder is a variable process. its all about energy release. Here is the real story......

On every complete cycle in each piston a specific amount of fuel is released via the injector (we are talking NA right now) into the cylinder. The volume of that cylinder is changing as the piston comes up to increase compression and conversly the volume increases as the piston travels back down. This change takes place over time. The combustion process also takes place over time. When the fuel ignites it just doesnt explode instantly and slam the piston down...atleast thats not what you want. You want the fuel to ignite and continue to burn that specific amount of fuel injected over a very specific lenght of time. That lenght of time for burn should correlate to the travel of the piston from TDC to BDC. It should be a nice even controlled burn...and all energy contained in the fuel that was injected in that single stroke should be burned during this piston travel. Thats the simplified version.

So we are assuming our NA motor is consuming...or burning...the energy contained in the single squirt of fuel from the injector over a period of time that corresponds to piston travel during the compression stroke. This makes for a smooth running engine that makes alot of power since there is force applied to the piston tops in the form of cylinder pressure during the entire downward travel of the piston applying force to the crank.
Cylinder pressure is fairly consistant and even due to the time release of energy from the fuel.

Now add nitrous...it should basically be doing the same thing...the SAME EXACT THING...just in a larger quantities over roughly the same period of time.

The difference in cylinder pressure...actual measured cylinder pressure between an NA engine that is 300 rwtq (tq is a direct measure of avg cylinder pressure not HP) and a motor that makes 450 rwtq on juice is not that much really. Say for arguement sake the NA engine has 500 psi of avg cylinder pressure through out that stroke. The nitrous motor might have 575 or 600 psi. Not really that big of a difference.

But what happens during detonation is something altogether different. The energy from the single squirt of fuel and the nitrous kit that should release its energy over that entire single compression stroke evenly....is completely and rapidly released in a FRACTION of the time. See.. time is the key factor here. Same amount of energy to release...but in one instance its released in say .05 seconds for normal combustion and with detonation that same amount of energy is released in .00005 seconds. Obviously the peak pressure for the second scenario is going to be HUGE. But the large peak pressure over the very short time will still roughly equate to the same energy as the much lower peak pressure over a longer time period. But the second scenario is devastaing to parts.

Keep in mind these are generalizations...the specifics of cylinder pressure during combustion are much more detailed.

So the point of this example is to say what I alwasy say. with a PROPERLY tuned engine, rnning the correct octane fuel, with the correct Af ratio and the correct timing and plugs....you will get away with more HP than most think possible. Even with stock parts.

I bet there are maybe 5-10 people here who have exceeded the limits of good head gaskets and studs with a good tune in place. The rest have just run bad tunes or had a mishap or bad gas or some other failure causing detonation/preignition.


So unless you are running around 900+ crank HP IMO...and probably more for large cube motors....dont blame the hard parts...its the tune and setup that is causing failures.

 

Sure u didnt mean head bolts

 

To much timing = detonation which = head gasket issues.

 

I bet on the timing also.

383LQ4SS.....What he said is a real good understanding of how it works. These are the things you can buy to make it easier on you and the tuner. I spray 500 dry on one car (Going to 700 this season) and spray 350 on a plate on another LS1. Both cars have the same things to keep them alive.

Wideband (BS3)
EGT data logging system for all 8 cylinders
1/2 head studs with Cometic gaskets
Special blend Sonoco 116 for nitrous applications
On the 500 shot I am running a total of 11 degrees of timing while the hose is on. DO NOT be scared to pull more timing. It is better to be safe then sorry. On both of these cars we have tested all kinds of systems. We can see the EGT on 1 cylinder as high as 200 degrees over another cylinders. (Chances of detination are higher now) We can go into the tuning on the BS3 and add fuel or timing to cylinders in need to lower temps. We have thus gotten both cars to reading within 25 degrees of each cylinder. With timing pulled across the board we have yet to blow a head gasket. Before we invested in all this logging stuff we replaced head gaskets on a regular basis. The forced induction guys don't have to worry about this problem from cylinder to cylinder near as much. That is why the boosted guys can make alot of power without lifting heads. Invest in new things to keep the detination away or you will blow another head gasket. I understand that I have alittle different setup then your usual nitrous LS1 guys but they are big hp cars with respectable ETs to go with it.

Check your plugs alot. If you want to do the cheaper way you can change your plugs to colder ones on the cylinders that are getting to hot. I also run a NGK10 in both cars. The car with the plate has ported 317 casting heads that have been angle cut to hell and it still doesn't lift the heads. The 500 shot has Dart heads.

 

I agree with what's been said, and some guys that really understand things. Timing is key to lifting imo, of course there are other variables as Al stated. I have had some pretty big shots and no studs, and never lifted a head, knock on... Here's a little bit on the timing thing from my web, that expands on why timing along with increased cylinder pressure can lift em, and why we need to retard:

Robert

 

This is what happened to me.

 

Good stuff !

Someone should sticky this, it will save more motors than any other N20 thread.

The only other advise I have is dont think that richer is better or safer.
You will hurt the motor just as fast being to rich as you will being lean if not faster!

Now Pill it til you kill it.

 

happend to my buddys stang last year. to fat, lifted the ringlands. also happend to my buddy this winter with his sled. he was scared to jet (fuel) it down and it ran to fat and washed the motor down and junked the rings and jugs.

 

THANK YOU 383LQ4SS and GueSS Who......

Wow that was much more of a response than I ever thought i woudl get.....
HOLY **** SOMEONE SHOULD STICKY THIS!!!!!!
Might save a motor or two!

So....is there a way to reduce timing without taking to a tuner?
There arent any tuners here in South tx near Corpus CHristi.....
Doesnt Msd make a thing that u can retard ur timing with?

 

MSD timing twister, Timing Tuner or the HSW interface...but without tuning in conjunction with the interface you can only 3 degrees of retard for the F bodies.

Since you dont want to go to a tuner I would suggest the MSD or the timing tuner.

 

Well...With that New nx dry shot do u still suggest having a tune???

I would figure it would be nessesary......

I would think that at the most I would progress to a 150 or a 175 shot over time