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Hello CL,
so, I overheated my 1st gen on my way to San Bernardino from L.A.
I got the top end tore apart and had the head machined. The shop said they removed around 0.015 of material. My question is what size head gasket should i use to bring my 1993 lexus gs300 back to spec.
I have ordered a gte HG. Will this bring it back to 10:1 ratio?
No mods, factory motor. Don't plan on boosting, not yet.
Thanks in advance
The GE combustion chamber is virtually a GTE chamber with a .030” recess machined at bore diameter. When you add the GE head gasket, .010” compressed, you get about .045” (1.14mm) piston to cylinder head clearance. With the GTE (no recess) the head gasket is .050”compressed and you get about .055” (1.4mm) piston to cylinder head clearance.
It is generally accepted that .032”(.8mm) is the minimum safe piston to cyl head clearance.
It is also generally accepted that when the piston to cyl head clearance exceeds .060”(1.5mm) the squish effect is severely diminished.
So, if you use a GE head gasket and a GTE head, .015”(.37mm) clearance, THE PISTON WILL HIT THE HEAD.
If you use a GTE head gasket and a GE head (NA/T) you end up with .085”(2.15mm) clearance and a less than effective squish.
The GE HG volume is 1.51cc & the GTE HG volume is 7.55cc a difference of 6.04cc
GE combustion chamber (head, gasket, piston) 55.5cc
+ GTE head gasket extra 6.04cc Gives .085”(2.15mm) squish
= 61.54cc = 9.12: 1
So it looks like with the GE head and GE head gasket, with removing .015 will leave you at about .03 when the minimum reccomended is .032, so two thousands under reccomended. Whereas if you go with the GE head/GTE head gasket you'll be looking at .085 - .015, which leaves you .07, which exceeds the recommended clearance and will provide less squish but sounds safer than having valve to piston contact.
So it looks like with the GE head and GE head gasket, with removing .015 will leave you at about .03 when the minimum reccomended is .032, so two thousands under reccomended. Whereas if you go with the GE head/GTE head gasket you'll be looking at .085 - .015, which leaves you .07, which exceeds the recommended clearance and will provide less squish but sounds safer than having valve to piston contact.
hey thanks for the reply joewitafro,
So, if GE combustion chamber (head, gasket, piston) 55.5cc
+ GTE head gasket extra 6.04cc Gives .085”(2.15mm) squish
= 61.54cc = 9.12: 1
then 0.070 will raise my compression ratio from 9.12:1 to something closer to 10:1 ?
So looking at someone elses calculations the NA head/NA head gasket results in a 10.14:1 ratio, and with the TT head gasket on the GE motor is a 9.30:1, So I don't know the exact calculation but it seems like removing .015mm from the .085 crunch of the TT head gasket (1.35mm un squished), that .085 to .07 reduction would raise the compression but I don't think to 10:1, probably closer to 9.5-9.7:1, so I think you'll be fine doing that. Still much above the 8:5:1 for turbo cars.
So looking at someone elses calculations the NA head/NA head gasket results in a 10.14:1 ratio, and with the TT head gasket on the GE motor is a 9.30:1, So I don't know the exact calculation but it seems like removing .015mm from the .085 crunch of the TT head gasket (1.35mm un squished), that .085 to .07 reduction would raise the compression but I don't think to 10:1, probably closer to 9.5-9.7:1, so I think you'll be fine doing that. Still much above the 8:5:1 for turbo cars.
Much thanks bro
I feel confident in what I'm doing now..
Was a little unsure but i think 9.5-9.7 should be good.
I also ordered some BC stage 2 cams, will this run smoothly with the tt head gasket. I'm kinda of worried about reliability.
also, ARP studs ordered also
07-02-20, 01:05 PM
What is my compression after 0.015 inch milling.
