Thicker HG theory Please Read

[nholm325e]

The whole concept of a "thicker" HG doesent make much sense to me. It seems like your taking 3 steps back just to take 5 steps forward. i know what your thinkin please read on.

**Please dont get caught up in the actual numbers im making up(their just examples), im refering more to the concept or "theory" of things...

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.

So say you have a 2 engines, one with stock compression boosting 10psi, then you have another engine with a thicker HG boosting 15psi,(they have equal compression when their at their full boost levels) wouldnt it take the engines the same amount of "time" to get from say 0-100mph(thats all i care about).
**HP and Torque numbers dont mean a thing, the actual amount of time it takes you to get your car from one speed to another speed is the only thing that matters.

I see people use the thicker HG and boost say 15psi, if they just kept the stock HG size and boosted say 10psi, wouldnt it be the same??

--I understand a thicker HG adds displacement, thus more room for compressed air, but come on it cant be adding that much room to create a HUGE difference.

Please i would like to see your point of view on this "concept" becuase so far it seems like you should just put your $$ somewhere else for power gains...

[backtrail69]

The only reason I see that people run a thicker HG is if the compression ratio is already extremely high and they are trying to drop it down in favor or less detonation and easier tuning.

[Borat]

The way I understand it...

--I understand a thicker HG adds displacement, thus more room for compressed air, but come on it cant be adding that much room to create a HUGE difference.

Displacement is a function of bore, stroke, an cylinders. Combustion chamber volume has nothing to do with it.

Even if compression was the same the engine at 15psi still has an extra 20% (approx) of oxygen in the cylinders, so there can be a bigger bang.

While lowering the c/r allows you to run more boost, the aim is to make power, not boost so a compromise has to be found.

Also, (This is where I get lost) a thicker HG can muck up the combustion chamber shape, or quench, which could result in detonation if its extreme enough. Camshaft timing is also affected with changes in HG thickness.

[ForcedFirebird]

Not to mention when using thicker gaskets, quench is compromised.

People are under the notion that you NEED lower compression to boost a motor, which isn't entirely true. When under boost you are effectively raising the compression ratio, so with higher compression comes lower boost.

I know people who (mildly) boosted a 9.6:1 motor, only to go with thinner head gaskets to get as close to 10:1 as possible with good results (actually I see 13second 3l engines with 400+ hp).

My Firebird (3.1l) has 8.9:1 now and with my new engine combination, I will be at 9.7:1 ;). With 6psig I'm seeing 275hp and went from low 17's (stock) to low 14's in the quarter. And this engine is consevative until I get some larger injectors (currently 24# Denso), but when the higher compression engine is finished, I can let you know the results.

[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

[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 :)

[Primo]

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

[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 ;))

[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.

[matt]

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

[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).

[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...

[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.

[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]

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.