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I'll provide some first hand, known measurements.

Both the GE and GTE motors have almost identical squish albeit from completely different geometry. Squish is approximately 0.060" for both. The difference is that the NA squish band is shared between the head and the piston. The NA head has about a 0.023" recessed squish surface that's cast into the combustion dome; the remaining ~0.040" is due to the piston-to-deck clearance at TDC. For the GTE head, however, the TT piston is completely responsible for the squish gap because the combustion dome squish band is flush with the bottom of the head.

EDIT... the following statement is incorrect. See my follow-up post below.
Consequently, that leads me to believe the wrist pin to piston crown distance is different between the two pistons because we all know the rods are identical.

-scott

 

so running TT pistons with an NA head is probably not a good idea. Same with running a thicker head gasket as that will cause less of a squish area.

I currently am running both. TT pistons with an NA head AND a TT head gasket. ALthough I have got great results on the dyno pushing E70 to 30psi and 24 degrees of timing. That does however bring my compression down to LESS than 8.5:1 which decreases my need for octane and allows for more boost. The downfall is less off boost power and quicker spool, not to mention my exhaust note went from really sharp and powerful, to really lazy and mellow.


I wonder if the squish is accounted for when ordering aftermarket NA pistons?

How strong is the NA head gasket? As strong as the TT?

 

Doh!... I'll have to retract an earlier statement regarding wrist pin to piston crown distance.

The TT head gasket may account for most of the squish gap between the piston crown and head on the GTE motor. Sorry... silly oversight. Consequently, the piston crown to deck clearance at TDC might be identical between the GE and GTE motors.

As far as the NA headgasket goes, I wouldn't count on using it for an substantial boost; however, that's just an opinion.

SuperRunner, you and I have nearly identical setups (TT aftermarket pistons, NA head, TT hg). I never took measurements of squish after assembling the motor, but now you have me motivated to do so. ;-)

-scott

 

Yeah, I wrote that just before I left for work. While driving I was like DUH! HG. That would account for the difference. I still would like to know what my C/R is, as I am sure it is lower than 8.5.

I got other motors I can take some measurments on, and I would assume the JE pistons are same as stock. But I can make sure that the piston deck height is the same.

 

Sorry dumb question here but I want to ask...SuperRunner when you say the intake ports are higher in the head, what exactly does that mean and how is that relevant?

 

The intake ports are physically higher in the head. This allows for a better angle on the valve. One of the biggest factors on how well a head flows is the SSR(short side radius). This radius must allow for air to pass over and change direction easily. Too small of a SSR and the air will overshoot and go across the valve and conflict with other incoming air.

Because the ports are higher in the NA head, the SSR isn't as drastic as it is on the TT head, allowing for a better distribution of air over the valve.

I have recently flow tested a VVTI 1UZ head which used this design. The stock 1uz valves are 1mm smaller than 2JZ valves, but due to the angle on the valve, a BONE STOCK vvti 1uz head flows around 235cfm @28" VERY IMPRESSIVE. Also recently I was examining a 2UR head, I couldn't believe how steep the angle to the head was. Impressive to say the least. I wonder what it would flow.

 

So hear is a question.

Which is stronger?

A thicker multilayer HG
A thinner single layer HG

 

Subscribed.

 

Thanks for answering SuperRunner, I had a hunch that it had something to do with angle of entry but wasn't quite sure how it worked. Definately in for more discussion.

 

In my opinion the GE head is better in unmodified form and my theory is based in the fact that the GE engine need to produce its power in N/A form so Toyota give a better design on the head to make it up for the lack of boost on the GE engine, Thats my opinion and i say thanks God for Toyota and such awesome engine with 4 diferent head designs, 1jz,GTE,GE,VVTI

 

Guys go back and search. Big name shops have said over and over that the GTE head at the end of day is superior when porting and going all out. In any case I'm sure the GE head would make big power too

 

Oh really? I would like you to find such a claim as I don't believe it exists.

 

Here are pix of each head. There is a big difference in design on each head in the valve area. I dont know if that makes a difference. Maybe the way the TT head is, its better designed for boost? The TT has a small deeper area whereas the NA has a wider shorter area.

TT Supra Head

My IS300 head

And heres my intake side which has been ported.

 

hey guys, ill chime in here because i have talked extensivly with kean at bl, chris johnson, and justin nenni about this.

what i belive, and have seen from my builds, is that with using the NA head a thicker headgasket and NA(GE) pistons makes a significant difference in the detonation threashold. basically the squish factor between the head and piston gets screwed by the thicker headgasket and make it more prone to detonation with certain octains, like pump 93. what we have seen though is that once you do get enough octain into the motor that it doesnt make a difference as far as tuning but it makes it harder to ignite the fuel at higher boost levels.

the general consensus from kean and chris, is that the GTE head is better designed for pressurized air flow and the GE head is designed for NA air flow. Funny things happen to air when its pressurized as far as flow goes. the GE might flow slightly better but the GTE head has physical size to the ports which makes a difference under boosted applications. you can see an example of this from when changing an intake manifold on a GTE makes little difference, need only look at darin and his success with the stock style intake manifold. also my own success with the stock na intake manifold and throttle body (722 rwhp at 29psi on a 71mm with some 264 cams).

its not about how much boost you run that makes more power its about how much air your motor can move to make more power. this includes the intake flow, dynamic compression, and exhaust flow. im sure im forgetting something in there so i hope that helps you guys.

 

Hmmmm, I have never had any issues making power safely using a GE head.

IMO, not one is better than the other. When the heads are properly ported and the combustion chamber is properly ported then you will make power with either head.

Ex. GE Head with a GT47-88R at 36.5PSI boost we have made 1050RWHP through an auto with a high stall converter running about 11:1 AFR and very conservative timing.

 

... When the heads are properly ported and the combustion chamber is properly ported then you will make power with either head...

I think we must draw the line somewhere and state that comparisons can only be made on unmodified heads. After all, going hog wild porting a head and modifiying the combustion chamber doesn't establish any level of common ground between the GE and GTE heads. The workmanship alone could make all the difference in the world.

Gamimnon, I concur on your assessment. Squish is the single biggest contributor to defeating knock on pump gas alone. I'll take your word that the mixture is harder to ignite at high boost; although, I don't recall having that issue when I use to run a stock GE longblock with a thick hg. However, I did use a CDI back then.

-scott

 

Fallguy made 905whp thru a powerglide on a stock GE head w/ cams.

http://www.youtube.com/watch?v=aTSHzGvN0vU&feature=channel_page

 

Gamimnon, there are too many variables that happen when you start forcing air.

STOCK/STOCK, and there is really no way you can make that call. Because the intake manifolds are soo completely different, you can't really get a true HEAD ONLY difference.

NA have much smaller ports than the TT, now take the intake manifolds. Stock TT intake manifolds flow like 260's CFM stock, and the NA's only flow about 235. That is a HUGE difference in the manifold, and not the head.

I gasket matched my intake manifold and head. I have a custom NA intake manifold with velocity stacks and it flowed around 265cfm per runner. AFTER I gasket matched the intake manifold increased to 280cfm per runner.

Too many variables. That is why I posted the question about the squish. Flow cam be made on either head, but if one had a better combustion design, that could make a difference.

 

The quench area on the TT head is a much better design for detonation threshold. It is similar to the GSR head in the Honda world. The NA Supra head is similar to the B16/Integra Type R head.

While this means little to the Supra guys, the concept is the same. When the quench area is smaller (closer to the valves), it promotes better flame travel and better detonation threshold and keeps the flame in the middle of the piston where it is the strongest.

Some of the honda builders use to think it was better to open up the combustion champer similar to the NA Supra head but in reality it just lowered the compression and spread the flame out. In my opinion it is best to have largest piston possible and smallest diameter quench area for flame travel (within reason of course and not factoring in depth).

Some of the old Corky Bell readers would do a clover leaf design in the quench area on a Supra TT head to open up the area a LITTLE around the valves to help them breath and go oversize valves but still not a complete circle design like the NA head. In the end they both work good and don't think it's worth selling your kidney if you have one or another....I don't port heads so I'm no expert and would listen to any professional head builder taking my own advice.

 

earlier in this thread it was said the quench area was identical. Just recessed in the head for the GE head because of the thinner head gasket.

 

Now that I'm looking at them again, I don't think the NA head has an open chamber, it looks like the headgasket just produced a CIRCLE around the chambers that gave it that opened chamber look. There probably both similar in detonation threshold.

 

Hmm, this looks like a future head modification.

I have already welded a couple heads with GREAT success. My current engine has had some combustion welding done on it from some previous damage.


This is a nissan head

 

Wow thats some serious work there. How would you benefit from this?

 

That is a nissan head.

You benefit from having more squish(quench) area. Could, not will, but could benefit for better combustion reducing the need for octane.

 

Looks very similar to the 2j head