Diff. between Mk3 and MK4 engine?

[Wayne G.]

This to all the real Supra techs. What was changed about the Mk4 engine
by Toyota to gain HP and relyability. On the outset they both seem to be
close in specs?? 3.0 liter 24 valve head both turbo (although the Mk4 is
twin turbo that should only improve throttle response maybe no). Is the
head that much better? There are Mk4s with 1000+ Hp w/o self destructing.
The Mk3 seems to max out around 700 HP or so. Give me some tech stuff
here if you would I am curious. Thanks in advance.

PS I love my 87 Turbo targa anyway

 

[IJ.]

Head design

Mk4 Valves have wider spacing/better angle so you can fit bigger valves in.

And being a square layout 86x86 they have a lower piston speed and more room for valves.(7M is 83x91)

 

[Reign_Maker]

IJ rules!

 

[Reign_Maker]

BTW: Wayne, I love your 87 targa too...

Welcome to the best MKIII site around... You'll learn alot! Just read, ask questions... Anything you wanna know, someone will tell you...

 

[CTsupra]

while were on this subject.

somebody please explain to me how the 2jz-gte is 86x86 3.0ltre and the 7m-gte is 83x91 3.0ltre, yet if you were to destroke the 7m-gte to 83x83 you would lose a crap load of displacement. is there a way to destroke the 7m-gte and keep the 3.0 litres of displacement without designing a new block?

reason why i ask, is i want to build a destroked 7m-gte in the near future. probably somwhere around 2.7 litres with a 8k red-line.

 

[IJ.]

CT: 7M is 83x91

 

[CTsupra]

whoops.

bah! i was close


edit: fixed :icon_razz

 

[CTsupra]

you get were i'm coming from, right? what about making the 7m 86x88? or anything else lol. somebody explain boring, stroking and destroking to me in detail please! i want to build me a high-reving 7m one of these days.

 

[IJ.]

CT: It would be risky trying to punch a 7m out to 86 as these engines are thin wall castings and with the bore spacing so close together there's not a lot of meat there.

One of the guys had one sonic tested awhile back and I think "safe" was 85mm.

The only real "benefit" from destroking is RPM potential and as not many people want to drop the $$$ for a really good valve train this potential would be wasted.

I sat and had a think about it and used to run my old BBChev into the mid 7000's with a longer stroke with a monster Piston compared to our little featherweight ones so I can't see any problem running 8000 on a built 7m with good valvetrain.

Hope this helps.

 

[CTsupra]

Thanks IJ, you rock!

If my memory serves me correctly, I believe Mello built a 7m motor that was either .60 or .80 over, and said there was enough wall left for it not to be a problem. Since sf is down, I can't go search for the thread. Maybe he'll chime in here.

I plan on building a insane 7m in the future with a BIG ass, like Ron - jt2ma71 big, turbo, so it must be able to rev to 8k, and i'm going to go all out on the head, get custom cams made, de-stroke, et cetera.

I hear people are worrying about piston travel at such high rpms i.e over 7k with the 7m. I don't know much about piston travel and all, but I'm assuming the piston might hit the valves or something? :dunno:

What is sonic testing, btw?

Anybody else have any input?

 

[Furball]

CT: It would be risky trying to punch a 7m out to 86 as these engines are thin wall castings and with the bore spacing so close together there's not a lot of meat there.

One of the guys had one sonic tested awhile back and I think "safe" was 85mm.

I believe that Defiant7M treated his block with Hard Blok and after sonic testing determined that he could go to 86mm, though he chose 85mm because the extra mm wouldn't make that much of a difference and because they were having trouble finding the right size rings.

 

[SuprAng]

i rev to 7k + regularly. Anyone who says a 7m cant rev, only relays false information, get the power up there and she will take it. i have logs of 7300. totally stock. While the stroke is longer on the 7m, piston velocities are relatively close to the 2jz. No one has gone past rev limit long enough to find out though.

STock for stock, the main difference is that 2jz turbos flow more cfm at 10 (or whatever they run stock) psi than one ct26 at 6psi.

 

[figgie]

i rev to 7k + regularly. Anyone who says a 7m cant rev, only relays false information, get the power up there and she will take it. i have logs of 7300. totally stock. While the stroke is longer on the 7m, piston velocities are relatively close to the 2jz. No one has gone past rev limit long enough to find out though.

STock for stock, the main difference is that 2jz turbos flow more cfm at 10 (or whatever they run stock) psi than one ct26 at 6psi.

agreed!!

I know Melloyello was reving his to 8k rpm all the time bvefore he sold it off.

I even looked at what BMW was doing int there S54 engine.

same stroke as the STOCK 7m and they have a factory redline of 8000 rpm. Mind you that they have a bigger piston as the bore is bigger and have no problems doing that. If they can do it why the hell can't we? (not taking into consideration the stock valve train.

 

[Slow66]

I'll be spinning my 7m to 8500 or so. Its not so much the bottom end as it is the valvetrain. They take a hell of a beating at high rpms, and with not enough spring pressure and heavy valvetrain components, floating the valves is inevitable. Kevins block was .080 over and routinely revved it to 7500. IMO destroking a 7m would not show any gains unless you plan on spinning 9000rpm+. Besides a better head and a square bore/stroke, theres nothing more special about a 2j than the 7m....

 

[88turboma71]

another difference is that the 2j/1j heads were designed by yamaha instead of toyota

 

[SuprAng]

another difference is that the 2j/1j heads were designed by yamaha instead of toyota

so was the 7m

 

[ToyoHabu]

Yeah, I believe all twin cam performance heads have been designed for Toyota by Yamaha

 

[CTsupra]

good replies here!

 

[Wayne G.]

CT: It would be risky trying to punch a 7m out to 86 as these engines are thin wall castings and with the bore spacing so close together there's not a lot of meat there.

One of the guys had one sonic tested awhile back and I think "safe" was 85mm.

The only real "benefit" from destroking is RPM potential and as not many people want to drop the $$$ for a really good valve train this potential would be wasted.

I sat and had a think about it and used to run my old BBChev into the mid 7000's with a longer stroke with a monster Piston compared to our little featherweight ones so I can't see any problem running 8000 on a built 7m with good valvetrain.

Hope this helps.

Now that you mention it back in the 70s I had a 69 Camaro with a Big
block Chevy engine 4 bolt main that I built (cams valve springs balance job
everything) and it would go 7200 to 7400 rpm and remember this ingine has
4 1/4" (106mm) bore size. So maybe there is something in the MK4 valve
train that (stiffer springs lighter parts etc.) that allows more rpm. What is
the redline on a MK4 turbo? The Mk3 is 6500 rpm.

 

[silver88turbo]

Rev LIMITER is 6800 (pre 89).