Thicker HG theory Please Read

[eta]

So a euro eta engine with 10.2:1 compression ratio running 99 octane fuel can be mildly boosted relaibly and safley for the engine. I was under the impression that was a non starter.

[Pinepig]

wow might be alittle late with this but my experience with thicker head gaskets have been nothing but good. I havnt seen with honda or anyone actually have trouble engine wise while running a thicker gasket. Me coming from VW, when youd turbo a vr6 it seemed like the limit for tuning was smaller with the stock gasket and you could make alot more power with the 8.5:1 head gasket. 20 + lbs of boost would = boom on the stock compression but would usuallly make 350-400whp with the 8.5:1. And I know cardcounter on bimmerforums made 600-640whp something in that range with a stock m52 with studs and .140 gasket. I dunnooo. :-?

The VR6 is a wierd animal as the cumbustion chamber is in the piston, the head is completely flat. I always love the posts over on the vortex with VR folks asking how much the compression went up on their VR after shaving 50 thousandths off the head.

[ForceBangBlow]

wow might be alittle late with this but my experience with thicker head gaskets have been nothing but good. I havnt seen with honda or anyone actually have trouble engine wise while running a thicker gasket. Me coming from VW, when youd turbo a vr6 it seemed like the limit for tuning was smaller with the stock gasket and you could make alot more power with the 8.5:1 head gasket. 20 + lbs of boost would = boom on the stock compression but would usuallly make 350-400whp with the 8.5:1. And I know cardcounter on bimmerforums made 600-640whp something in that range with a stock m52 with studs and .140 gasket. I dunnooo. :-?

[AjRose]

I said this in my last post, but you got so flustered by someone mentioning OMG, a HONDA, that you didn't even bother reading it. Typical.

I have no problem with honda I love em I think they are very capable cars.

I guess I missed that last part of your post sorry.

[lateapex31]

stop right there.

Why, because my knowledge on the subject of tuning engines producing ~150HP per cylinder isn't relevant to your conversation? Try 300 HP per liter, then you can tell me to stop right there.

I am pretty sure no one specifically mentioned this so... You will obviously not make as much HP with a lowered compression ratio engine as one with stock compression.

All else being equal, more compression will make more HP per lb of boost, but with a much smaller window between MBT and knock.

I said this in my last post, but you got so flustered by someone mentioning OMG, a HONDA, that you didn't even bother reading it. Typical.

[AjRose]

Using thicker HG will lower the compresssion of the engine, but if you lower your stock compression, your motor will obviously be underpowered until you can reach boost. So your underpowered from say idle-4K rpm.

I am pretty sure no one specifically mentioned this so... You will obviously not make as much HP with a lowered compression ratio engine as one with stock compression.

However you will not be underpowered compared to stock power (as I interpreted it) before boost 1k-3k,3.5k rpm. You are slowly building boost before you reach full boost.

Also lowering the compression ratio makes it much safer to run more boost and essentially make tuning easier.

With Honda engines.

stop right there.

A thick headgasket is a cheap fix imo. Most people who a building a diy turbo setup dont have or want to spend the money on proper tuning.

Also alot of people have had success with MLS or other thicker headgaskets. And why someone would use a thicker HG that wasn't a metal HG I dont know But m20's dont have the problem of blowing out MLS headgaskets.

[lateapex31]

With Honda engines, I've definitely seen on my dyno that a stock engine with a thick headgasket is much more prone to detonation than a stock engine is. People like to put thick HGs in to lower the compression ratio from 10.5:1 to about 9.5:1. Even with reduced compression, these engines don't like the geometry change of the combustion chamber (remember, the piston makes the floor, so moving the head up changes the whole thing). These head gaskets are more prone to blowing out too due to increased surface area inside the chamber for combustion pressure to push against. All in all, I've never seen any good results from thicker HGs. The money is better spent on proper engine management IMHO.

All else being equal, more compression will make more HP per lb of boost, but with a much smaller window between MBT and knock.

[mops]

lower compression will allow you to run more boost (without detonation, given all other factors remain the same) therefore making more top end power. it's hard to say whether it will get you from 0 to 100 mph faster, depends on alot of factors. with lower compression you are loosing low end power and off boost power, economy and throttle response... but gaining on high end... it's hard to say exactly how much but every point down in compression will get another about 50-150 hp of top end power on moderately sized engine 2-3L (achieved with increase of boost, so all other systems must be capable of operating in that range). this is very rough estimate i know, and should not be used as a direct rule.

all in all a race motor, which spends alot of time on top end will benefit greatly from lower compression... i.e. 80's forumla 1 engines ran between 6:1 to 7:1 static compression, and m12/13 bmw engine (1500cc) of the time made about 1500hp at 60+psi of boost...

too low compression is not as good for street due to bad fuel economy. modern oem turbo engines run 8-8.5:1, sometimes built engines are dropped to 7:1, but that's only for extreme boosting.

generally speaking decide on your goals and how much $$$ you want to spend and then we can advice on possibly configurations...

[ForcedFirebird]

I thought I did say effective. It's still a misconception that CR needs to be lowered to run boost, and it's simply not true.

Either way, thicker gaskets makes the combustion less efficient by increasing quench.

I'll be finishing up the new motor in the Firebird soon, and I will have to let you know how much better the extra point is. I might go a bit higher than 9.7:1 to help quench. With a deck height of .0095, I'm thinking of using .040 gaskets instead of .060, so I can get closer to the magical .040 ideal quench.

EDIT: Although, Tchao, you are correct about flow being more important than PSI. PSI is just a number to referance by. You can have two turbos that are set to the same PSI, and one can make significant gains over the other (also requiring more fuel).

[matt]

It doesn't change the static compression ratio, it does change the effective compression ratio.

[Tchao]

Thicker Headgasket is no good, thicker= more gasket surface exposed.

When under boost you are effectively raising the compression ratio, so with higher compression comes lower boost.

When under boost you are effectively adding more air, not adding more compression. The point is to to add air, lowering the compression will sometimes allow the motor to add even more air safely then not lowering it.
The more air the more power. Whatever it takes to do it.
Boosting your car doesnt change the compresion ratio, as its a RATIO.

[ForcedFirebird]

you will gain roughly 7% for every pound of boost above atmospheric

OK, let's use 100hp to make it easy...
100+((.07*14.7*100))=202.9hp

As I said if you double the atmosphere, you essentially double the power output because you are fitting twice as much air in the same volume (just make sure you have at least twice as much fuel as well ;))

[Primo]

you will gain roughly 7% for every pound of boost above atmospheric

[ForcedFirebird]

Well im going to boost my m50 non vanos engine for street use.
I read that the motor is stock 10.1 compression, and that most people will boost 10psi at the most on 93 octane at this compression ratio.

I figure the tuner will be the one to decide how much boost i can saftely run when the car is in front of him and on the dyno, but how much compression can these motors take for daily driven street use, 10.6-11.1 ???

I know there are more variables involved to get a more accurate estimates in power but what kind of numbers would 10psi put me around, 290-320 whp??

Thanks

Well 14.7 PSI should double your HP...

Cick here for calculations :)

[nholm325e]

Well im going to boost my m50 non vanos engine for street use.
I read that the motor is stock 10.1 compression, and that most people will boost 10psi at the most on 93 octane at this compression ratio.

I figure the tuner will be the one to decide how much boost i can saftely run when the car is in front of him and on the dyno, but how much compression can these motors take for daily driven street use, 10.6-11.1 ???

I know there are more variables involved to get a more accurate estimates in power but what kind of numbers would 10psi put me around, 290-320 whp??

Thanks