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Discussion Starter #1
Is 20 psi about the absolute "sorta safe occasionally" limit for a OEM head gasket?

I'm looking to get a concensus from those of you more experienced with tuning (and blowing up) 3S-GTEs.

This is my set-up. Understand that my question is ONLY about the limits of the Toyota head gasket, not whether or not my fuel system or tuning is adequate to prevent detonation.

Greddy TD06-20g and IC
.020" over JE pistons, 8.5:1 C/R, Swain coated
HKS 264 cams
1 mm oversize Ferrea valvetrain
mild "street port" headwork
ARP fasteners throughout
Apex'i S-AFC and AVC-R
Supra 550 injectors and pump
SMC water injection (onset at 14.5 psi)
Apex'i GT spec exhaust
OEM Toyota head gasket

I typically run about 17-18 psi on the street. I'm referencing this boost level to what I see on the Autometer mechanical gauge (referenced to the line going to the intake manifold) and the peak readings on my AVC-R (converted from kg/cm2). I was planning on upping it to right around 19.5-20 psi on the dyno and maybe for a few runs at the dragstrip (assuming it appears my fuel system is up to it after checking the AFR at the dyno).

It would seem to me that dropping the static C/R from 8.8 to 8.5 would give me a little extra "safety cushion," no?

I live and drive at over 5,000 feet of elevation, if that matters.

Thanks in advance for your input.
 

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not so sure about your situation but i have gone to 20 psi a number of times without any issues. Alot of it depends on how well the engine was put back together. You have water injection and 550cc injectors so i think you are pretty safe.
 

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Hsun Chen said:
I'm looking to get a concensus from those of you more experienced with tuning (and blowing up) 3S-GTEs.

This is my set-up. Understand that my question is ONLY about the limits of the Toyota head gasket, not whether or not my fuel system or tuning is adequate to prevent detonation.

Thanks in advance for your input.
Not sure about the Gen II, but the Gen III can definitely handle more:

http://www.mr2board.com/forums/general-mr2-discussion/3721-stock-internals-24-psi.html

-- DavidV :D
 

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Discussion Starter #4
DavidV said:
Not sure about the Gen II, but the Gen III can definitely handle more:

http://www.mr2board.com/forums/general-mr2-discussion/3721-stock-internals-24-psi.html

-- DavidV :D
Thanks DavidV. How many pulls have you done on the dyno (or at the track) at 24 psi? And did you actually stand there and watch during these pulls, or did you go and hide in the corner of the shop? :p

I don't know about you guys, but I get very afraid watching/hearing my car winding up on the dyno . . .

Anyone know if the Gen III OEM HG is the same as for the Gen II 3S-GTE engine?
 

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Well I just blew a (we think) stock HG on saturday. I've been pushing her hard to see what she could take since we are just about done with my stroker. I was running 20-23 psi daily with a SB46. The motor was rebuilt with Ross Forged Pistons by the previous owner, and when we pulled the valve cover off we were suprised to see ARP Headstuds, which should have helped with the HG holding.

I have pushed stock HGs up to 20 no problem (on TD06) but never been on it all the tiem like I have on this one.

Based on these experiences I would not be comfortable running much more than 20 psi on a stock HG.

Reading thru your list of mods I think that as long as your AFR is holding strong and you are running higher octane fuel, you should have no problem upping it to about 20 psi for the track and dyno. I wouldn't go much above that. BTW I have had a few autometer mechanical gauges. They were all OFF by a large margin.

EDIT: IT WASN'T MY HG THAT WENT, IT WAS A PISTON. PLEASE SEE POST BELOW RETRACTING WHAT I JUST SAID ABOUT 20 PSI MAX ;)
 

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Justin311 said:
How do those strengthen a HG? :confused:
sorry i wasnt exactly clear in what i was saying. I meant that with water injection and larger injectors there is a much less chance of detonation and all the goodies that come with running a td06 at 20psi on stock injectors which would create a hostile "enviroment" for the head gasket. I guess the pistons might go before the head gasket in that situation though :p
 

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Discussion Starter #8
Justin311 said:
Reading thru your list of mods I think that as long as your AFR is holding strong and you are running higher octane fuel, you should have no problem upping it to about 20 psi for the track and dyno. I wouldn't go much above that. BTW I have had a few autometer mechanical gauges. They were all OFF by a large margin.
Thanks for the info Justin.

AFR of 11.5 to 12 is OK, right?

So how far off were the Autometer boost gauges you've seen, and what was your reference? Mine seems to dovetail with the peak readings the Apex'i AVC-R records pretty closely . . . it's hard to see exactly what the needle hits when you're driving, watching out for cops, etc., anyway . . .
 

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I think the stock HG is pretty reliable until about 400RWHP. Jeff Fazio was on his third one in like one season once he got up and above the 400RWHP level.
 

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Hsun Chen said:
Thanks for the info Justin.

AFR of 11.5 to 12 is OK, right?

So how far off were the Autometer boost gauges you've seen, and what was your reference? Mine seems to dovetail with the peak readings the Apex'i AVC-R records pretty closely . . . it's hard to see exactly what the needle hits when you're driving, watching out for cops, etc., anyway . . .
Ha, ha. Well first off scratch what I just said. I new revert back to my original conclusion that the stock HG is good to over 20 psi. I just pulled my head off and the HG survived all the BS...it was the hole straight thru piston #3 that put a damper on things :eek:

AFR all depends on your fuel, but 11.5 is pretty good for pump gas. I beleive most guys tune to right around 12.5 on race. So that should be your range. Please double check the values tho I'm kinda tired and greasy ;)

The autometer boost gauge I had was compared against a number of gauges including Zeitronix MAP sensor boost gauge, Blitz peak and hold, etc. The autometer always read higher and was sporadic. I would say +/-2 psi max tho. I just wouldn't trust it for super accurate readigns...but IMO boost gauges are like dynos. They're only useful for comparison. FWIW my DEFI and my GM Map sensor read ~2.5 psi different form each other. Both are considered high end map sensors. :dontknow:
 

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Hsun Chen said:
Anyone know if the Gen III OEM HG is the same as for the Gen II 3S-GTE engine?
nope, the Gen 3 is a metal gasket, infact if you buy a TRD gasket you're actually getting the standard gen 3 one :)
 

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Po' Kid said:
I think the stock HG is pretty reliable until about 400RWHP. Jeff Fazio was on his third one in like one season once he got up and above the 400RWHP level.
I think my original stock headgasket was failing for a very long time (maybe as much as 2 years). It went through hell and back and at the beginning of the season the occasional overheaeting just started happening more frequentyl so we replaced it.

It held 440 rwhp just fine, the reason it blew the second time was DRIVER ERROR. Like a fool, I kept my foot planted to the floor in a drag race when I there was serious, audible mis-firing going on.

After we replaced the OEM ignition with an MSD box and coil, the mis-firing went away and the car was pretty good (still occasionally overheated).

That being said, if I would have had a proper ignition and/or got off throttle when it started mis-firing, that OEM gasket could have very well just been fine.

I'm not sure what I would say the OEM gasket is good for, but I would venture a guess that it is a lot more than most people will ever see.
 

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Justin311 said:
Ha, ha. Well first off scratch what I just said. I new revert back to my original conclusion that the stock HG is good to over 20 psi. I just pulled my head off and the HG survived all the BS...it was the hole straight thru piston #3 that put a damper on things :eek:
I always thought the initial limiting factor in pushing around 20 psi or more was the stretching of the OEM head studs which allowed the head to lift enough to blow out the gasket.

What did you learn from the hole in piston #3? Bad tuning...faulty piston?

Bruce
 

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Justin311 said:
The autometer boost gauge I had was compared against a number of gauges including Zeitronix MAP sensor boost gauge, Blitz peak and hold, etc. The autometer always read higher and was sporadic. I would say +/-2 psi max tho. I just wouldn't trust it for super accurate readigns...but IMO boost gauges are like dynos. They're only useful for comparison.

I feel the same way. I think my autometer boost may be off by 1 psi or so. I just use it as a reference though and always use a wideband while at the dyno.
 

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Bruce H. said:
I always thought the initial limiting factor in pushing around 20 psi or more was the stretching of the OEM head studs which allowed the head to lift enough to blow out the gasket.
Bruce, I think that is an IUL (Internet urban legend) :)

I raced Hyde at 20+ psi for 4 years.
The first 3 years were all on the same original stock headgasket.
 

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I'de say until you get proper diagnotstics olike Wideband, and standalone you shouldn't be running 20 psi anyway :) 17-18 psi is a pretty fast street car as is....You should save for EMS, then run closed wastegates on teh 20g :)
 

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I ran my car for 3 years with everything 100% original stock in the engine ... HG, studs, everything. :)
 
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