What Head Gasket ???

[stevepudney]

If you have replaced your Head Gasket for a steal one, what thickness have you used. 1,2mm is standard thickness.

I have the option of using a 1mm or 1.4mm, I have no intension of running huge boost, probally maxed out at 1.5 bar, and only lookig for 380 - 400 bhp with Power FC, AVCR, GTRS Turbo, Forged Pistons and bigger injectors.

I was thinking of using the 1mm to get better off boost responce which would make it a better street car but I would loose out top end as the timing will be knocked back a few degrees after 5500 - 6000rpm to compensate for the extra compression.

Not sure what to do, any advice guys

 

[Mr GTiR]

Steve, i'm not an expert on CR but i've just slung a 1.2mm steel H/G in to keep the CR pretty stock. I'm also aiming for 400bhp and have been advsed that this set up is fine for a road car. Don't know if this helps.....

 

[Anonymous]

I was thinking of using the 1mm to get better off boost responce which would make it a better street car but I would loose out top end as the timing will be knocked back a few degrees after 5500 - 6000rpm to compensate for the extra compression.

if you go for the 1mm gasket,why would you lose out at the top end :?:

you'll not need to retard the timing if your larger injectors can supply the required fuel for the boost level you intend to run.

another reason to possibly go for the 1.4mm gasket instead of the 1mm gasket is greater inherent strength and longevity as well as the option for greater boost :twisted:

 

[stevepudney]

I've been told (by the reinstated God) that for a street car I'd be better off with a 1mm gasket as I'd get a car that was much more responsive off boost, thus spooling would be quicker e.t.c. e.t.c. BUT because of the higher comp ratio I might have to edit the ignition map on top end rpm to retard a bit, but only a couple of degrees.

 

[GINGA]

iirc the standard gasket is 1.4mm thick :?:
1mm would indeed give slightly better response etc but doubt you'd loose top end power it would probably be more likely you'd have to slightly retard it in the midrange as this is where peak boost and torque normally happen and hence peak load on the engine :?:

 

[Nad]

iirc the standard gasket is 1.4mm thick :?:

Thats what I thought as well. I originally went for a 2mm one, then down to a 1.2 as I thought this was standard, but found out that it isnt but will increse the comp ratio which I now want to do anyway.

Its not specifically the top end, its where ever ur using WOT and the car is making the max compression ratio, normally as GINGA said where ur curves are peaking.

Are u retarding it due to lack of fuel supply or detonation occurance??

Nad

P.S. Typed this bit for reference (Detonation will happen due to the heat unless u can either keep the block cool or use a higher octane rated fuel to stop it burning too soon. Injecting more fuel may cool the chamber slightly but will not stop it setting the fuel off otherwise detontation wouldnt be an issue on any car, u would just put more fuel in.)

 

[skiddusmarkus]

I've gone for a 1mm HG which should raise the CR from approx 8.3:1 to 8.7:1 and help spool up by a few hundred rpms.I've got a fmic,WI,mappable ECU and better cooling though to compensate.

 

[MarkTurbo]

iirc the standard gasket is 1.4mm thick :?:

Thats what I thought as well. I originally went for a 2mm one, then down to a 1.2 as I thought this was standard, but found out that it isnt but will increse the comp ratio which I now want to do anyway.

I've got the 1.2 mm hks gasket on my car cos i thought that was the standard thickness. How much does does it raise the compression ratio by? Surely .2mm wont make that much differance anyway :?: And what are the advantages/disadvantages of having a slightly higher comp ratio?

 

[Nad]

High comp ratio = more power over the whole rev range, better off throttle response but more likely event of detonation.

Nad

 

[skiddusmarkus]

I think 0.1mm is roughly 0.1 point of CR.Higher CR will make a more powerful burn in the cylinder as the fuel/air is squashed more.
Advantages are better off boost driveability as you're getting closer to NA CR's and potentially better fuel economy.
Disadvantages are you need better control of the mixture/ignition to stop det. and may not be able to run as much boost.

 

[MarkTurbo]

Cheers for the info guys 8)

I'm not worried about not being able to run high boost I'm only gonna be running about 1 or 1.1 bar when its back on the road.

That'll be enough after being on standard boost for the last 2 years :lol:

 

[stevepudney]

Well, I got all the info I said earlier from Ian (Hiteq) and as I said before I was told 1.2mm was standard and going down to 1mm was fine and perfectly acceptable but you MIGHT (not definately but might) have to retard the ignition map slightly in places.

I'm not concerned in the slightest about the cooling or fuel supply side of things as Power FC Pro and 700cc injectors, 24 row thermostated oil cooler and R33 front mount will take care of that and once I get a 3" elbow and front pipe that will ease the exhaust side of things and let even more heat out.

The whole point of this exercise for me is to concentrate on the off boost pre spool up breathing of the engine, then as long as your not going to run huge amounts of boost (1.4 - 1.5 max) the rest will follow and make reasonable power for a street car.

I was just after an opinion from the masses about the off boost diferences between say 1mm and 2mm and all in between.

(I think) My mind is made up now anyway and I'm going for a 1mm (or mybe 1.2 :? ).