Larger Head gasket=lower compression= Safer boost?

I have a 95 vtec lewd. I want to put a turbo on it, and run it around 6-8 psi. I am planning on doing this with out upgrading the fuel system, or internals at first. But some people say that with that high of compression ratio even if tuned correctly, it can still be fatal for your engine. Would a thicker head gasket (lowering compression ration) allow me to run 8 psi. safely until I can upgrade the internals, and fuel system?

THANKS

ROB

it can help but your turbo will take longer to reach full boost and wont spool so quick 8 psi would be fine

At the bare minimum get a new fuel pump. I personaly would not take the risk of not upgrading the fuel system. :2cents:

what should be done to the fuel system?

fuel rail lager injectors and a preassure regulator, oh yea a high perf filter. they make inline fuel pumps for fuel injection. thats what i would go with. I havent seen many intank high perf fuel pumps. i know that they are out there just havent seen many. although with 8psi you could prolly get away with just a pump and a regulator. the atmospheric preassure where you live will have an effect on your compression ratio as well. the boost has to over come that preassure before it can make boost. i think in pomona its like 14.7 so if you ran 8 psi it would be like 22.7 psi of actual boost.just an example.

the atmospheric preassure where you live will have an effect on your compression ratio as well. the boost has to over come that preassure before it can make boost. i think in pomona its like 14.7 so if you ran 8 psi it would be like 22.7 psi of actual boost.just an example.PM1337?I Don't understand this last mention could you please explain itgot a turbo on othe bench at the shop waiting on fuel management

i don't use the thicker HG at my shop because in my opinion they just add more material to blow out. you are not going to blow the top of the block or the bottom of the head out but the thicker the head gasket the more risk of blowing it out. hp is a dirivitive of compresion to boost. more boost and lower comp usually equals less boost and more comp. i prefer less boost and more comp. it gives you quicker spool up time and power without being in boost.

yea klr is right. more gasket is not the way to do it. and even if you did it anywayz it would prolly nt make but a .2-.5 difference in compression ratio and on top of that you expose your self to potential risk of head gasket failure especially with the added boost. to do it right i would get new lower compression pistons. you can run high compression with boost as long as the motor can handle the preassures. alcohol cars run from 14:1 all the way up to 18:1 before boost and like 40:1 after. but the internals can handle that and that is definately not daily driven. back to the point if i was you i would leave the turbo on the bench until i got the fuel taken care of. you run the risk of a nuclear holocost if you don't. Lean=heat. Lean also =power i saw a guy with a crx and a 75 shot that put a jet that was for like a 25 shot. well need less to say he melted a whole in 2 pistons and melted those 2 spark plugs as well. we put 2 more plugs in it and the damn thing ran long enough to gat him home. weird.

1. I think you're headed on the right track. I think that you should lower your compression ratio to at least 9:1. However, I don't think that a thicker head gasket is the right way to do it. Head gaskets don't last as long on a turbo-charged car and a thicker will blow that much quicker. I feel that you should simply get lower compression pistons. Your connecting rods, sleeves, and crankshaft should be able to handle 6-8 PSI no problem.

2. The reason I feel you should lower the compression is simple, detonation. With great tuning and fuel management you can get away with 10:1 as long as you don't run across some bad fuel. However, no tuning or fuel management will save you from some bad fuel. At a 10:1 compression ratio and some bad fuel you will detonate bad enough to tear your engine apart. Go take a look at the two eclipse videos in this forum and that is what will happen to your engine. It is much better to be safe than sorry. If the car were a race setup then I could see leaving it at 10:1, but for the street, don't be stupid.

3. Adding boost does NOT raise your compression ratio. I don't know where you got that idea. The ratio stays the same there is simply more matter. I would love to see an engine that can handle a 40:1 compression ratio because I will tell you that a top fuel dragster can't. If you are running 9:1 compression ratio before boost and you add 8 PSI you're still running at a 9:1 compression ratio. There is simply more fuel and air being compressed.

Alright quite a few misconceptions here.
1. Have your heads and block milled flat and run a copper head gasket and/or have your block/heads o-ringed. Run as thick of a gasket as you want, you will not blow it out. Sure a composite gasket with a steel ring for sealing will blow if its too thick, but think about it - if you have a solid piece of .08" thick copper sandwitched at 110ft/lbs between two flat chunks of metal. Any pressure produced in the cylinder short of detonation(which I will talk about later in this post) will blow it out. HOWEVER, and I dont know if this applies but for most modern engines it does, if your heads have any quench area, you do not want an excessively thick gasket. Quench area is an area of the combustion chamber that is flat, on the same plane as the head sealing surface - So unless the chamber is the entire diameter of the cylinder bore, you have quench area. If it is the entire diameter, its called 'open chamber.' Quench is also known as 'closed chamber'. Let me show you an example:
Open chamber:
http://i20.ebayimg.com/01/i/01/61/ae/60_3.JPG
Closed chamber:
http://i1.ebayimg.com/01/i/01/62/3f/02_1_b.JPG

The idea behind quench heads is the piston extinguishes the flame front and increases turbulence in the chamber, which reduces 'hot spots' in the chamber and therefore reduces the chances of detonation. In order for this to work right, the piston has to be at maximum .060" away from the quench area. Ideally, it would be around .045". If it is over .060, it doesnt effectively create turbulence, and the sharp edges of the quench area become hot spots themselves, greatly increasing the chances of detonation. I'd use .055" as a maximum. A composite .055" gasket should be able to handle 8psi. As for a gasket not reducing compression ratio too much, in my 351c the change from a .04" gasket to .08" would drop my compression by over .7. Not too shabby. I'd much rather have a 7.9:1 compression ratio than a 8.6 in a turbo engine. Sure you'll have a little bit more lag, but the ammount of power you'll make with the lowered compression will make up for it.

2. Compression ratio vs. Boost
If compression by the piston was better than compression by boost, then no one would ever turbocharge! Compressing via boost and via piston do the same exact thing, but using a turbocharger/supercharger has a few distinct advantages. The only difference between the two is the compressor does this before the air enters the engine. This actually increases the displacement of the engine. Consider this: a naturally aspirated engine(no boost) sucks air in by creating vacuum in the cylinder by the motion of the piston down in the bore. It displaces a certain ammount of air, which means it can never fill the entire chamber. It can only take in slightly more than the volume the cylinder displaces when moving from TDC to BDC. N/A engines employ advanced pressure tuning to intake more air than the piston displaces, mainly through intake pressure wave tuning and exhaust wave tuning(also called scavenging). I will not get into the specifics of these, I don't want this post getting too long.
In a forced induction application(turbocharged or supercharged), there are two main advantages:
a) Intercooling. When you compress air, whether by piston or a supercharger/turbocharger, the temperature of the air increases by a large ammount. Cooler air resists detonation and is denser(more oxygen per given volume), allowing more compression. Even though the piston still compresses air and thereby still heats the charge, the final heat of the air from compressing to a total of 20:1 boosted compression(yes boost does affect the *dynamic* compression ratio... I'll talk about that later too) will be much less than a N/A engine with 20:1 dynamic comp ratio.
b) Increased displacement - As I said before, a N/A engine can only intake slightly more than the piston displaces. With forced induction, the boost fills the entire chamber, not just what the cylinder displaces - For example, a 393" V8 I'm building has a volume of 58.80ci in the entire chamber at BDC( (bore/2)(bore/2) x (Stroke + piston to deck clearance) + volume of head gasket + volume of chamber) - the piston itself displaces 49.125 of those cubic inches. That is a 19.7% difference in volume that a turbocharger or supercharger will get you - and this is with the same dynamic compression ratio for both the N/A and FI engines. Boost will allow you to cram more air in there than the chamber is supposed to handle, giving huge cylinder pressures, more than you're normally see with a really high compression N/A engine. Turbocharged and supercharged engines avoid detonation that would normally occur with this ammount of cylinder pressure by retarding the ignition and intercooling.
Turbo and supercharged engine's extremely dense mixtures elongate the burn time of the mixture. This means that even though maximum cylinder pressure only increases 20%, you may see a 100% increase in power.

3. Atmospheric pressure and boost
Atmospheric pressure is around 14.7psi near sea level. This means that any given time there is 14.7psi of pressure pushing on you, your table, car, everything. This pressure is from miles and miles of atmosphere being pulled on by gravity. So in order to theoretically double your power, you have to push 14.7psi. Of course, turbochargers arent 100% efficient(more around 70%) so you wont quite double your power. This brings up another advantage of turbochargers vs compression(essentially a N/A engine) - In order to make the same power as a turbo pushin 16psi, you'd need an engine of twice the displacement ... good luck finding one and fitting something like that under your hood. Turbochargers and superchargers are even more beneficial at higher altitudes where you have less atmospheric pressure. With less air density, the turbo doesnt have to work as hard to compress the air. Although it would be extra work for the turbo to compress the air to the same pressure as a place with higher atmospheric pressure, the percent increase in power will be greater at a higher altitude. If you drive your n/a car up a mountain, you will notice a large power drop, since there is less air filling the cylinders. With a turbo car, the drop will be very slight if any(your turbo might have to work a lil bit harder though, but you won't notice that..).

4. Detonation/Dynamic compression ratio
Detonation and a lean condition are the only things I fear from a turbocharged engine. Sure blowing a head gasket sucks, but it isn't gonna kill your engine. Detonation(also known as pre-ignition and pinging) is when the air/fuel mixture explodes before the spark plug fires. This uncontrolled explosion causes MASSIVE cylinder pressures and incredible heat. This will blow head gaskets like nothing, ruin bearings, bend rods, break main webs, snap cranks, put holes in cylinder walls, and burn a hole through your pistons. Detonation is not your friend, avoid it at ALL costs. Knock detectors are good insurance. They retard the ignition when ping is detected. Detonation is mainly caused by 3 things in combination: overly high compression(if you compress an air fuel mixture enough it will explode even without a spark.. hence diesel engines), hot spots(hot areas of the chamber, as in the glow plug in a diesel) and a lean condition. This is when the engine isn't getting enough gas for the ammount of air its taking in. This causes the mixture to burn very hot(hot enough to burn a hole in a piston), which increases the chances of developing a 'hot spot', which in turn increases the chances of an overly compressed mixture to explode without a spark, hence detonation and a chunk of scrap metal under your hood in place of what used to be an engine.
Static compression ratio isn't really good for much of anything. It'll give you a baseline idea of what octane fuel the engine can run on without detonation. Dynamic compression ratio is much more applicable. Dynamic compression ratio is calculated by considering many factors - the displacement of the engine and chamber size(as in static compression ratio), valve timing, and rod length and stroke, as well as airflow and pressure wave characteristics. Valve overlap and timing keeps the intake valve open after the piston starts moving up on the compression stroke, effectively lowering the compression ratio. Rod length has to do with this because a longer rod with the same stroke will make the piston 'dwell' longer at the bottom of the cylinder, meaning less reversion, and a higher dynamic compression ratio. Boost increases the dynamic compression ratio since you have more air in the cylinder than you would N/A.

As for high dynamic compression ratios, engines have been developed that push 300psi. yes 300. Indy cars in the 80s pushed near 100psi pressures, in endurance applications!!! Engines can handle extremely high cylinder pressures. If one of those indy cars has 6.5:1 dynamic compression n/a and pushed 80psi, using a little math we can figure out that that would be 35.37:1 dynamic compression w/ boost. These little 1.5L engines pushed 1500hp... 100hp/L.

One more thing:
"Lean=heat. Lean also =power" Yes lean = heat, but lean does NOT equal power!! If you run on a lean condition, you may get a few HP extra from the excessive heat for a second until your engine is toast. I suggest getting the Dawe's devices air fuel meter, and if you see that red light get the hell off the gas. even if it means losing the race. If you dont I guarentee you will lose the race and your engine. You cant win a race with a hole in a piston or two. Also, puttin a 25hp NOS shot on a fuel system designed for a 75hp shot will cause a rich condition, not a lean. Maybe his was designed for 25 and he put a 75 on? When injected, nitrous breaks down giving nitrogen and oxygen molecules. Nitrogen is inert, it doesnt do anything. It is only there to make it safer than pure oxygen(extremely dangerous! poisonous and inconcievably explosive). The extra oxygen allows more fuel to be added to react with the oxygen. going from a 75hp to 25hp will mean 50hp worth of extra fuel is in the chamber, a rich condition.
Thanks for reading, hope this helps someone.
Ben Sinclair

since when did lean = more heat?

lean conditions are when you are not getting enough fuel, meaning less of an explosion, which also equals less heat.

http://www.altimizer.com/setup.html
"Symptoms of a Lean Air/Fuel Mixture

1. Lag in acceleration of engine rpm.
2. Popping or backfiring through the intake or exhaust on deceleration.
3. Erratic idle or won't idle below 1000 rpms.
****4. High EGT reading. ****

EGT = Exhaust Gas Temperature

EGT is used by many dynos to measure determine if your engine is rich or lean. Rich = low EGT, lean = High EGT. Of course "low" and "high" depend on the engine, there is no set "correct" EGT.

since when did lean = more heat?

lean conditions are when you are not getting enough fuel, meaning less of an explosion, which also equals less heat.

Since the creation of physics and everything else in the universe. Running lean has always caused heat. In fact here is a picture of a piston from an engine that went way lean at 21 PSI. The fuel pump failed at WOT.

http://www.thedodgegarage.com/reliant/reliant_23.jpg

Great posts Duplox. Reading about dynamic CR was interesting. You went into detail with the rest when I was too lazy. Great read!

man, too much stuff to just run 8psi. I do have one auguent with what you said though, Not trying to be an ass just someing I noticed. A turbo/supercharger will not increase the ammount of air that your engine flows. Turbo/superchargers are a pressure multiplier, not a pressure adder. it's like talking all the air that is in the room your sitting in, lets say 900cfm, and stuffing it in a left over beer bottle from last nights party:icon16:, its still 900cfm its just in a smaller area That and intercooling is not really an advantage. A turbo car heats up the air so you use an intercooler to cool the charge. 99% of the intercoolers out there won't get the air back to ambieant temp. So it's more or of a necessity and not an advantage.

I would lower my compression to run more boost anyday. If you are so worried about spool up time then you need to run an atuomatic. I mean look at top fuel cars. Have you ever seen them spray that fluid in the intake before they start it up? It is 87 octane pump gas, they run 8:1 compression and put down 5000+ HP.

Since the creation of physics and everything else in the universe. Running lean has always caused heat. In fact here is a picture of a piston from an engine that went way lean at 21 PSI. The fuel pump failed at WOT.

http://www.thedodgegarage.com/reliant/reliant_23.jpg

Great posts Duplox. Reading about dynamic CR was interesting. You went into detail with the rest when I was too lazy. Great read!

oh, so the extra fuel acts as a cooling agent?

oh, so the extra fuel acts as a cooling agent?

In a way, yes.

i apoligize for not elaborating my statement. what i ment was my friend put a jet for a 25 shot on the enrichmant side of the nos sys. and a 75 shot of nitrous. and when i said that lean=power i ment to an extent. i dont know if you guys ever played with the nitro rc cars or not but when your tuning the motors you "Lean" them out. not to the extent that you creat a nuclear holocost but enough to make it clean. the same when ever i tune my holley. i would much rather have a slightly lean mixture over a slightly rich mixture any day. when it is rich it boggs and shutters when the secondary's kick in. it makes much more power and runs smoother with a slighly lean conditon. just as an example.

wow ben... you the man... i need to get to know you better!

i dont know if you guys ever played with the nitro rc cars or not but when your tuning the motors you "Lean" them out. not to the extent that you creat a nuclear holocost but enough to make it clean.
IF u want your $300 nitro engine to last about 3 tanks of gas.
If you want it to last, However like 3 gallons or more, you run rich LOTS of smoke and oil in the exhaust about 270 degrees any hotter the sleave warps and looses compression. Hense, ruined block, and motor with no compression that wont idle. and they dont idle clean like that :nono:
they pop and spit now I Know who not to listen to

"slightly rich" is not to the point where it bogs, based on that "slightly lean" would be 1500*EGTs and spark plugs that last a few hundred miles. Most of you guys have the luxury of running EFI, which have oxygen sensors to make sure you never go lean. I run carbureators, if you go lean there is nothing to stop it! If I dont notice something wrong(high engine temps or pinging) my motor is fried. Maybe that is why I am so much more agaisnt a lean condition. Whenever tuning my carb I start WAY too rich and work my way back until i think its right. It takes a lot of time and being very careful. I haven't lost a motor yet, so I must be doing something right.

Yes, fuel acts as a cooling agent, but that isnt the main reason. consider adding NOS without adding extra fuel - you arent changing the ammount of fuel added, so the cooling should be the same(in fact much cooler since NOS cools the air when it is atomized), yet if you run without fuel enrichment you'll burn your engine for sure. It has more to do with the chemistry aspect of combustion. I don't know exactly why it burns hotter with a higher oxygen to gas ratio, but believe me and everyone else it does. As for temperature drops w/ fuel - Through a carbureator air temperature drops 40*F. Atomization of a liquid into a gas causes a large drop in temperature. Many people running draw through turbocharged carbureated engines inject a water/alcohol mixture into either the turbo's inlet or somewhere after the turbo, the atomization of the water/alcohol mixture causes a huge drop in temperature(you can't intercool a draw through setup, so this is the alternative...). The atomized water also helps cool some hot spots, and as a side bonus it cleans carbon deposits off the insides of the engine. I'm planning on using water injection on my turbo'd 351c, even though its not draw through, but every bit of cooling helps!

IF u want your $300 nitro engine to last about 3 tanks of gas.
If you want it to last, However like 3 gallons or more, you run rich LOTS of smoke and oil in the exhaust about 270 degrees any hotter the sleave warps and looses compression. Hense, ruined block, and motor with no compression that wont idle. and they dont idle clean like that :nono:
they pop and spit now I Know who not to listen to

you don't have to listen to me. but ive run like 10 gallons through this motor and haven't had a single problem. not even an over heating problem. i go with what works for me. I am not insisting that anyone do what i do, but i just offer past experiences. you deduct what you want to.

you don't have to listen to me. but ive run like 10 gallons through this motor and haven't had a single problem. not even an over heating problem. i go with what works for me. I am not insisting that anyone do what i do, but i just offer past experiences. you deduct what you want to.
:screwy:In 19 years your experiences can probably be counted on one hand:lol:

:screwy:In 19 years your experiences can probably be counted on one hand:lol:
:screwy: In your 29 years you still can't do math. i don't know how many ASE test that you have taken but i am 2 away from being a master tech. and i already have eight or nine years exp working for my uncle on his prostock car. this may not make me qualified to share with you guys what has worked for me, but i couldn't care less about what some parts changer in flordia thinks about me.