metal head gasket thickness.

ronniek

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Hi guys,
What sort of compression pressure would I get if I used 1.5mm head gasket instead of stock thickness gasket.

Thanks,
Ronnie.
 

ronniek

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the deck hasn't been touched and cylinder head has just been skimmed.
I put in titan metal head gasket coated with copper cement ,but i still put low compression.Average 120 psi.
I have heard that cometic head gasket might be better.Is this a metal head gasket and what makes it a better gasket.
Ronnie.
 

mrnickleye

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Did you have a valve job done while head was off???
How many miles on the bottom end??? That's low compression you've got there. :icon_conf
 

p5150

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what is the bore diameter of your HG? When selecting a HG you should measure all parameters of your engine. You cant really go by what somebody else used...
 

cjsupra90

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like p5150 said, there are a number of factors that can make a differance. I have a titan on mine and have no problem. on thing though, did you remove the one side rivet form the gasket? the rivet could be your problem. I dont know if Titan had the design changed to move the rivet out further so that it is not inbetween the head and block. but either which way, there could be a number of other things that can contribute to the problem. You should really do a leak down test and not a compression test to determine what or where the problem is.
 

ronniek

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head gasket is 86mm bore,which is correct.Also I had a 1.2mm hks gasket for 5 years and it started leaking a month ago.The coolant grooves on cylinder head had corroded to thr combustion ring area.The hks gasket was still intact.
That was with no. 6 cylinder and I had good compression on all other cylinders.So I am thinking that the bottom end should be ok.it has done just over 100,000 kms.
I did get the valve job done.
thanks for info on rivet,I will have a look.
Ronnie.
 

p5150

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why is 86mm bore correct? did you have the engine bored out? I think stock bore is around 83mm.
 

ronniek

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Finally I sorted out why My car had low compression.I bought a compressor and did a leakdown test and found air leaked from all intake ports and 3 of exhaust ports.I also removed a rivet from one of the titan head-gasket.
Hopefully by next week,the supra will be back on the road.
Ronnie.
 

7M-GTE

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ronniek said:
Finally I sorted out why My car had low compression.I bought a compressor and did a leakdown test and found air leaked from all intake ports and 3 of exhaust ports.I also removed a rivet from one of the titan head-gasket.
Hopefully by next week,the supra will be back on the road.
Ronnie.

how exactly do you perform a leak down test... I've been told to do this with my car but don't know how to do it...
 

cjsupra90

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You need a leakdown tester and a air compressor. The leakdown tester can be picked up at any Napa or Snap-on dealer. They are not to badly priced. If I recall, mine was around $60 at Napa....

They are fairly simple to use. They are a unit that is a block with 2 gauges on it. One is the in or test pressure. the other is a precentage gauge representing the lose of pressure within the tested cylinder. The unit has 2 hook-ups on it. one is the compressor hook up and the other is just like a compression tester hook-up and threads into the spark plug hole just as the compression tester. To use, you turn the motor over to TDC compression stroke for the cylinder that you are testing. hook the unit up to that cylinder and hook up your shop air. Most units have an adjuster knob to set the test pressure. I usually use 100 to 120 PSI as the test pressure. If it seams like the motor is turning over, make sure that the motor is perfectly at TDC, and or lower the pressure slightly. Once hooked-up and pressurized, look at the percentage gauge and see what it is at. O to 5% is typicaly a good cylinder, 5 to 10% could use attension. Anything over 10% needs attension. If you find a cylinder that has a high % of leakdown, listen in the intake, exhaust, oil cap opening and remove the radiator cap.

Air heard from intake = leaking intake valve
Air heard from exhaust = Leaking exhaust valve
Air heard from oil cap oplening = bad rings and or problem with cylinder wall also possibly a crack in the block.
bubbles seen in radiator = leaking headgasket and or possibly a crack in the head or block
 

7M-GTE

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cjsupra90 said:
You need a leakdown tester and a air compressor. The leakdown tester can be picked up at any Napa or Snap-on dealer. They are not to badly priced. If I recall, mine was around $60 at Napa....

They are fairly simple to use. They are a unit that is a block with 2 gauges on it. One is the in or test pressure. the other is a precentage gauge representing the lose of pressure within the tested cylinder. The unit has 2 hook-ups on it. one is the compressor hook up and the other is just like a compression tester hook-up and threads into the spark plug hole just as the compression tester. To use, you turn the motor over to TDC compression stroke for the cylinder that you are testing. hook the unit up to that cylinder and hook up your shop air. Most units have an adjuster knob to set the test pressure. I usually use 100 to 120 PSI as the test pressure. If it seams like the motor is turning over, make sure that the motor is perfectly at TDC, and or lower the pressure slightly. Once hooked-up and pressurized, look at the percentage gauge and see what it is at. O to 5% is typicaly a good cylinder, 5 to 10% could use attension. Anything over 10% needs attension. If you find a cylinder that has a high % of leakdown, listen in the intake, exhaust, oil cap opening and remove the radiator cap.

Air heard from intake = leaking intake valve
Air heard from exhaust = Leaking exhaust valve
Air heard from oil cap oplening = bad rings and or problem with cylinder wall also possibly a crack in the block.
bubbles seen in radiator = leaking headgasket and or possibly a crack in the head or block
thank you very much man... I'm going to have to do that when I change my timing belt b\c I get a little bit of blow by that comes out my exhaust and it's starting to dull my freshly painted white car...
 

Joel W.

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ok just to clearify for my own info. with turbos, lower compression is better because we can run higher boost with less ping? so a 2mm gasket will lower the compression more than a 1mm gasket? is this correct?
 

IJ.

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Joel: Correct.

It all depends on the octane of the fuel you'll run.

Best combination is as much cylinder pressure as you can run without detonation.

X:1 static + XX psi boost + XXX octane you just need to juggle the numbers to get the safest result allowing a margin in case you get a dud load of Gas.
 

Joel W.

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so for example on my car with stock block for now and with my mods and run with the best pump gas, what would be the prefered thickness of gasket? any idea?
 

IJ.

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Stock!

I think it compresses to 1.27mm or maybe 1.4mm someone will jump in shortly.

Again this all depends on if the block and head have ever been surfaced and by how much as this will bump the comp ratio up.

Main thing is to keep out of detonation as nothing kills these motors faster.
 

Joel W.

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i took .006 off the head when it was surfaced to remove warp and the gravel imbedded in the head and i think thats the only time the head was off.
 

IJ.

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Not enough to make a difference Joel!
that's only 0.15mm.

As an example I'll be running a stock deck height block a 5 thou clean up cut on a new head 104 octane LPG and 30 pst boost.

I haven't run the numbers yet but going by past experience I bought a 3mm Cometic as this "should" put me in the high 7's for comp ratio.

When I get my head back I'll CC it then do the calculations properly to double check.
 

Joel W.

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been reading your build, sounds like its gonna be a monster... gj.. thanks for the info btw.
 

Joel W.

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i hear 1 or 2 ping sometimes. is this normal under boost? then the ecu should retard the timing back a bit as needed? i only hear it about 14 psi rarely? i dont like it but have been told its normal... sorry im hijacking the thread...
 

IJ.

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Doh! sorry I misread one of your earlier posts and didn't realise you were running 14 psi.....

Either run some better gas or back the boost down a touch, you're correct the ECU should hear the detonation and back it down but under certain conditions this all may happen to late to save the HG :( (Boosting up a hill on a hot day)(good excuse for a bigger more efficient IC)
 

Joel W.

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with this new 3" dp and exh installed, i have backed the boost back to about 12psi, i retarted the timing to 8 deg. this seems to help. i plan on a metal hg when and if this new stock one blows.. start ordeing parts and put em on the shelf. low budget here...
 

Joel W.

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yeah, ty, the boost creeps up on me now with this setup. like in my (boost creeping ) post so i have to watch it carefully.. should i go back to the 10 deg timing? my hood sticker is unreadable so i dont know if its 10 deg stock or where i should set the timing at with my mods? again im a hi-jacker...:3d_frown: hehe.. thanks
 

IJ.

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Correct 10 degrees.

I'd even back the boost down to maybe 10 psi in case it spikes on a hard pull.

As I said detonation will kill it so better safe than sorry!
 

Joel W.

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auzie, auzie, auzie,,,
ahhaha watchin the wsop tourniment finals
 

Joel W.

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but i secretly in the back of my mind want to blow it, so i can justify the rebuild... :icon_evil
 

IJ.

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LOL thought you said funds were tight?

Even a basic rebuild on a 7M is expensive Joel :(

Better NOT to hurt parts before the rebuild.
 

Joel W.

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ya im not in any hurry. bhg is not bad as long as stop drop and roll.. dont drive it.. happend 26 miles after i bought it lol..
 

Joel W.

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ohh, ya...when mine went, it was like the smoke screen on james bond movie under boost. the car (i had just passed) behind me disapeared instantly... i stopped right there and towed it home.. it never overheated that i know of..

have a good one, gotta go eat turkey....
 

ronniek

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Finally my supra is back on the road with pwr radiator and cylinder head ported and polished.
Only 1 problem left to fix.The temperature gauge does not work.
I did a compression test when I put the engine together and average cylinder pressure was 150 psi.
Ronnie.