7m headgasket mileage with high horsepower

[toniz]

What kind of mileage have you made with your high horsepower 7m-gte without blowing your headgasket? I have built my supra quite far now (530rwhp dynoed with 24psi) and the headgasket went again, this time I had the HKS Stopper gasket torqued to 90 ft-lbs with ARP head studs. There's definetly no knock and the surfaces (head and block) are flattened, altought I'm not sure about the RA value what the local machining shop can achieve (they just told me their machinery should be good with mhg).

Last year I had Titan motorsport mhg and it lasted 10000km (~6000 miles) but back then the supra had only around 300rwhp. This time it took 6500km (~4000 miles) for the headgasket to blow with 530rwhp. So if it should hold for more miles, I guess I'll look for another machining shop and get the surfaces lapped or if there's no way to get the gasket hold I'll just throw in a new one or use sealer spray on the current gasket.

Thanks in advance.

-Toni

 

[Nick M]

You can't blow a good MHG unless you really try.

 

[Mr. Y]

24psi? What fuel are you using and how much timing running?

 

[figgie]

What kind of mileage have you made with your high horsepower 7m-gte without blowing your headgasket? I have built my supra quite far now (530rwhp dynoed with 24psi) and the headgasket went again, this time I had the HKS Stopper gasket torqued to 90 ft-lbs with ARP head studs. There's definetly no knock and the surfaces (head and block) are flattened, altought I'm not sure about the RA value what the local machining shop can achieve (they just told me their machinery should be good with mhg).

Last year I had Titan motorsport mhg and it lasted 10000km (~6000 miles) but back then the supra had only around 300rwhp. This time it took 6500km (~4000 miles) for the headgasket to blow with 530rwhp. So if it should hold for more miles, I guess I'll look for another machining shop and get the surfaces lapped or if there's no way to get the gasket hold I'll just throw in a new one or use sealer spray on the current gasket.

Thanks in advance.

-Toni

24 psi?

Please tell me that you are not trying that much power on a "piggy back" based system? Some form of standalone?

MHG. Detonation kills pistons. A MHG will not stand to detonation anymore more than the AL pistons or head

 

[toniz]

24 psi?

Please tell me that you are not trying that much power on a "piggy back" based system? Some form of standalone?

MHG. Detonation kills pistons. A MHG will not stand to detonation anymore more than the AL pistons or head

I'm running AEM EMS, tuned to 11.5 afr at full boost, dual walbros, larger fuel lines, 750cc rc injectors. ~8cr, at 24psi advance is about 10 degrees. Using Shell v-power which is rated 99 RON. Also the combustion chambers are smoothened to avoid detonation.

Anyway I just wanted to know if you have made your headgasket hold even higher horsepower for long periods.

Also have you retightened your head studs after warming up the engine a few times? (I didn't retighten the head studs).

 

[Keros]

Also have you retightened your head studs after warming up the engine a few times? (I didn't retighten the head studs).

Potential problem right there... the headstud's expansion and contraction during the first 1000-2000 miles of driving, thus, heatcycling, can cause headgasket failure if they're not retorqued.

A commonly overlooked detail.

 

[figgie]

Also the combustion chambers are smoothened to avoid detonation.

That is not a function of the CC or how smooth it is. Smoothing the cc addressed pre-ignition but not detonation

For a given octane, it will detonate if it has the right "formula" ( Too much ignition advanced, not enough octane for the given compression ratio)

Anyway I just wanted to know if you have made your headgasket hold even higher horsepower for long periods.

yes. It is all in the tune!

One question I forgot to ask. What turbo? Is the timing spot on or is it flucuating?

Also have you retightened your head studs after warming up the engine a few times? (I didn't retighten the head studs).

Yes. After a couple of heat cycles. The head studs/bolts need to be re-torqued

 

[toniz]

Potential problem right there... the headstud's expansion and contraction during the first 1000-2000 miles of driving, thus, heatcycling, can cause headgasket failure if they're not retorqued.

A commonly overlooked detail.

How to properly retorque the head studs? One by one? Or loosen everyone of them at once and then retorque?

I guess it wont help at this point as I already hear burbling behind the dashboard, but I'll give it a try

 

[toniz]

One question I forgot to ask. What turbo? Is the timing spot on or is it flucuating?

I checked my logs from the dyno, actually running around 13 degrees of advance at full boost, but there's minor flactuation present (probably because the map sensor reading flactuates also), but at idle the timing is very stable and the ems is most likely reading the cps correctly.

We also made these "headphones" to listen for the engine while driving hard. A hose goes next to the engine and you can hear the engine running quite clearly and haven't heard anything weird noises from the engine at full boost.

And the turbo is T04R.

 

[92nsx]

Do a re-torque like you said, just don't go any higher than what your at now. To do a re-torque properly, you "crack" the nuts counter clockwise ~ 1/8 - 1/4 turn, then torque back to spec. In this case, go to 85 ft/lbs to keep the same force on the HG.

One stud at a time.

Actually IJ wrote it, Jdub just posted it.

 

[figgie]

I checked my logs from the dyno, actually running around 13 degrees of advance at full boost, but there's minor flactuation present (probably because the map sensor reading flactuates also), but at idle the timing is very stable and the ems is most likely reading the cps correctly.

We also made these "headphones" to listen for the engine while driving hard. A hose goes next to the engine and you can hear the engine running quite clearly and haven't heard anything weird noises from the engine at full boost.

And the turbo is T04R.

with the amount of noise the 7m has stock, (forget if internal have been "upgraded' to forged where you need them loose.) very doubtful you will hear detonation above mechanical noise.

Again. Things do not break out of the blue because.

 

[IJ.]

One of the high HP 2J guys lost 4 motors running an AEM since changing to MoTeC not a one.

"could" be a bug.

 

[Mr. Y]

IJ, wasn't that guy using AEM P&H driver box?
toniz, have you checked timing mark with gun at high RPMs? May be your "pickup delay comp" parameter set wrong and actual timing at high RPMs is more aggressive than it should.

 

[IJ.]

Yuri: Dunno just heard about it second hand so it might be applicable in this case.

Engines don't "just die"

 

[toniz]

toniz, have you checked timing mark with gun at high RPMs? May be your "pickup delay comp" parameter set wrong and actual timing at high RPMs is more aggressive than it should.

Haven't done that. I'll check that before tearing it all down. I started wondering about the flactuation of the map sensor, maybe adding the filter available in the ems (I guess it averages N samples of map reading) or placing the map sensor differently would result also in more stable map reading. Do you think 13 degrees advance is too much advance for 24psi? I guess the v-power fuel I'm using here is about the same as your 91 pump gas.

 

[toniz]

I guess the v-power fuel I'm using here is about the same as your 91 pump gas.

Had to look more into this, the v-power is rated minimum of RON 99 and MON 87. I guess in USA you use RON + MON, so the v-power would be the average between RON and MON (87 + 99)/2 = 93. So it would be 93 pump gas.

 

[Mr. Y]

to IJ, "Y" in my nickname isn't "Yuri" Actually my name is Denis.

toniz, I'm in Russia and we use same octane rating here. I run 19 psi at 15* on 98 octane. Resurfaced head and 2mm headgasket (CR is lower than stock).

As for map sensor readings, mine does the same. More load - more fluctuation. Setting MAP filter option to 12 helps a lot but doesn't completely fix it. BTW, I use GM 3 bar map, and a friend of mine use it with MAFT-Pro. His readings are a lot noisier.

 

[IJ.]

DOH I'm thinking of someone else then

 

[figgie]

Had to look more into this, the v-power is rated minimum of RON 99 and MON 87. I guess in USA you use RON + MON, so the v-power would be the average between RON and MON (87 + 99)/2 = 93. So it would be 93 pump gas.

well then.

We usually never go above 18 psi for a given turbo on that low an octane. Asking for trouble!

The real number that is important is the MON. A higher MON usually is pretty good indication of how much power to run. At 87 MON. Yikes!

 

[Keros]

How to properly retorque the head studs? One by one? Or loosen everyone of them at once and then retorque?

I guess it wont help at this point as I already hear burbling behind the dashboard, but I'll give it a try

Yeah, one by one, so that pressure across the whole head stays approximately the same. Follow the same pattern as what's in the TSRM, break each stud loose by backing it off until you hear it 'crack', and then retorque to spec.