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chuck0960 05-05-2011 12:45 AM

so im new to this, first supra (91 mk3 auto), i was wanting to get some recommendations on what to do to be able to turn my boost up to 15psi?? i know i will need fuel system upgrade and turbo upgrade. Anything else needed/recommended?

ochowdero 05-07-2011 11:39 AM


Originally Posted by chuck0960 (Post 95010)
so im new to this, first supra (91 mk3 auto), i was wanting to get some recommendations on what to do to be able to turn my boost up to 15psi?? i know i will need fuel system upgrade and turbo upgrade. Anything else needed/recommended?

You need to do a engine rebuild to with stand that much boost. Mhg, 550cc or higher fuel injectors, lexus afm or bigger? a bigger turbo, ct26(??) can't hang lol... Even all that youll blow the 7m trying to tune it that high.. Maybe,
I don't know much I'm just giving you an idea..

But I do know this...

You gotta remember basic science, normal atmosphere pressure is 14.2 psi on everything(maybe 14.7?) so take that and add it to the 15 psi you want to force inside your already pressured engine...that's why it's a common mistake to over do your turbo.. Besides fuel cut is 14 psi( unless you upgrade) with that your beasting already.. Haha
again idk much about this but I do know a engine rebuild is in store for that much boost....


Bump bump...

Krem 05-07-2011 10:44 PM

wow, with that amount of adjustments, I'd prob guess a higher capacity fuel pump and a larger fuel rail may help? Also, you'd prob want to replace the head bolts w/ head studs and torque them down 72~76 ft·lbf.

One thing to also keep in mind about the 7m is there are two separate compression ratios... the 7mgte has compression ratio 8.4:1, whereas the 7mge has compression ratio of 9.1:1. This leads me to believe the NA is not made to be boosted, or should not be boosted very much if at all. Only the 7mgte can support a turbo; and at that point, you still have to concern yourself with the upgrades previously mentioned to increase the reliability of the engine...

Finally, for those guys boosting excessively during these times of nearly $5/gal of gas... since you're throwing it away... can I get some cash?

87hilux7mge 05-08-2011 12:51 AM

GE is 9.2:1, and true it isnt made for boosting, but it can be and has been done. running high boost on a GE is not recommended, as detonation will insue, as well as the cast pistons turning to glass. the stock GTE pistons were high silica content pistons, so they dealt with the higher heat and abuse better.

15 psi is only really gonna be achieved well with a standalone or FCD (fuel cut defender) and the latter is not recommended. the KVAFM and stock fuel system have a hard time properly metering fuel when you reach higher boost levels.

cre 05-11-2011 07:35 PM

The stock fuel rail is plenty big and unless you're putting down over 600RWHP it fine. Yes, a GTE fuel pump or larger is a must.

A GTE oil pump and a full flow oil cooler are requirements in my book... Don't waste your time with the stock GTE oil cooler though, it's a crap setup. The GE has no oil cooling.

Atmospheric air pressure varied wildly with weather trends and altitude. It doesn't matter much unless you're tuning an aftermarket system or have (for some bizarre reason) deleted the stock ECU's HAC circuit (not an issue if you're running GE electronics).

Fuel cut is not actually determined by boost pressure. The ECU has NO idea what your boost pressure is. It's all calculated by RPM, measured air flow, air temp, engine temp and the programmed acceptable limits. Varying weather conditions and engine health can cause you to see boost cut starting earlier than 12psi (in severe weather conditions where you hopefully won't be driving anyway).

I'd like to know where you heard the difference in the piston alloys. It's never been proven to be more than guess (wishful thinking really) and they both get holes blown in them just as easily. What the GTE does have that helps reduce temps is oil squirters which spray oil at the bottoms of the pistons (and no, there's no practical way to add them to the GE block).

I blew a hole through a piston and fried the HG in a very well tuned GE at 10psi... and it's not uncommon. Some folks get lucky and run 12psi for years without issue, but don't count on it being you.

The KVAFM is reliable well past 15psi... the limitation is the ECU's programmed "acceptable" range. The GE's ECU has no fuel cut (if you're thinking about running that) but has a much more aggressive timing map and will require a piggy-back fuel controller for tuning.

87hilux7mge 05-12-2011 03:42 AM

apologies, i should have used the term hypereutectic. high silica (meant to be silicon) content was a bad choice of words. anyway, supra forums has an article concerning toyotas piston manufacturing processes from the late 80s to the early 90s.

they transfered from standard cast/hypoeutectic pistons to a hypereutectic, which had a higher silicon amount in it (albeit, only about 4-8% more: 8-10% vs 12-18%)

so in theory the piston can "absorb" more abuse from the inherent forces of a boosted application.

and the KVAFM, i stand corrected. i made assumptions about it and the fuel cut situations based on my prior experiences with other applications. anyway, im not well versed with them, so thanks for the correction! :bigthumb:

i learned something today lol

cre 05-12-2011 04:28 AM

AFAIK, the JZ series was the first to see production use of hypereutectic alloy... the JZ pistons aren't an uncommon upgrade for a number of earlier Toyota blocks (including the 7M) for this very reason.

Here's a thread where they recommend just that (from SF ;) ):

For those who want to know more though:


So, do you have a link to the aforementioned article?

The KVAFM is actually a very good and accurate system.

Back to the original discussion though, over 12psi on a stock CT-26 isn't advisable. Beyond 13 or 14psi (ambient conditions always a consideration) the CT-26 isn't efficient and tends to blow hot to the point that you may actually lose power and you significantly increase the risk of damage from detonation; The compressor isn't large enough to provide a cool charge at that volume.


I'm still looking.. Looks to me like the JZ series and UZ series were the first blessed with this hardware from what I can find. I suspect that if Toyota were using it earlier it would have been in their race engines; This includes limited "not for market" 7Ms: see: 1988 Group A Supra (not to be confused with the Turbo A model which was sold to the JDM in a quantity of only 500).

This has taught me more about the process and it's effects than I had ever planned on knowing. I think I'm done looking now... if you find that article or anything else I'd like to see it.

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