Triumphrat

wogs

have been advised to drop the compression from 9.5 to 8.5,i agree,if i used a head-gasket with sealant instead of regular base gasket,would anyone know how much the decress would be,what effect the change in this area would have,in cress in the stroke and combustion chamber due to the increase in the height of the lungs,are there any tolerances that should beconsidered here or is this a possitive at all,received suggestion to loweraftewr buying the 750 kit to put on my 650tr6 bottom end,wide open on this one,informed there is access to wider head gaskets,which thichness would bring in this compression range,any scientist out there,enjoy your ride,paul

Slinky

I have never heard of using a head gasket instead of a base gasket to lower compression- it is more usual to fit two base gaskets instead of one.

Either way would have no effect on the stroke, that is fixed by the crank throw.

Post this in the Classics forum, you should get a better response.

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98 Thunderbird, 03 Speed Master

wogs

i,m playing withthe idea of two metal gaskets,my thoughts are based on the compession under torque effect,when the engine has been assembled,if my budget would allow,and not throwing two good pistons out,i,d order proper one,s.if someone has the science on doing this,possibly it could make an easytake down,i thank you for the reply,thinking of the stroke effect was based on the change in the height of the barrels due to the increase in the metal gasket,would not the stroke in-effect be decressed in respect to the new reach to top end becoming less,this a ratio that is kept constant on the crank but has a change in effect to the reach it normally had,slow down my brain here,i,m wide open and interested as to the effect on engine responce this way,maybe the race guys could lend a hand with some of their secreds,have a nice day,paul

tridentt150v

What was your compression?????

Are you pinging????

My original head gasket was very 2nd hand and quite thin, plus the head had been skimmed for run out making my compression way high. I lowered compression from 220 to 175 just by using a 80 thou head gasket.

If you want to lower it more than that you woul probably have to also install a base gasket or change pistons. You can skim your piston crowns as well, but it is a decision best left to the experts [it depends on the type and brand of piston and the amount of meat in the piston crown].

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tridentt150v,
Great Southern Land.
(Where women blow and men chunder).

Timtiger

Why lower the compression? What s the problem?
A few comments.
I think you are suggesting using silicone on the headgasket. This will have NO effect on the compression as the silicone will simply fill any gap as the head is torqued down. It will not increase the hap between head and barrel, not raise the height of the head and not alter the compression.
You could use 2 haed gaskets but you are asking for trouble. I have heard of this on old, low compression BMWs as a way to cope with very very bad fuel - like in Russia, but it was temporary and there will be a very high chance of blowing a head gasket.
It is common to use 2 base gaskets and select their composition to give a specific compression.

You can calculate the compression change that can be acheived by raining the barrell, but you need to measure a few things - and it is not easy. I won't go into the maths, but the compression ratio is the ratio of cylinder at Bottom dead centre vs the cylinder volume at Top Dead Centre. Measuring these volumes can be done by filling the cylinder with oil, but you beed the motor our to tip out the oil each time. Think it of being like having a 10mL syringe, block the end and puch the plunger in from 10mL to 1mL. The compression ratio is 10:1.

Mostly people just measure the compression pressure with a gauge, add a gasket and retest.