motorheaddown

O.K... more food for thought.

Grant (mkiv mailing list) and I measured piston squish a few months ago, and the measurements yielded similar results.for the GTE motor (~0.062") and GE motor (~0.058"). Based on those measurements, I have a question. With the TT hg compressed to 1.35mm, it's clear that the TT hg accounts for most if not all of the squish clearance. The NA hg, however, is only 0.3mm, but the GE squish band is approximately the same as the GTE motor. So where does the GE motor make up the difference? Are the NA pistons shorter than the TT pistons at the squish band? Or does the NA head have a machined squish band that's receded into the dome?

Hmm... kinda makes ya wonder.

-scott

awj

The difference is in the dome of the combustion chamber yea? So how about TT pistons on a stock GE head gasket thickness. What is the cr there? Since we are crunching #'s.

motorheaddown

Just for giggles, why don't you give it a shot? You have all the information you need to figure it out in this thread. I'll let you know if you're correct.

My point is that a very thin hg on the GE motor yields the same squish as the GTE motor. That's important for two reasons:

1) It's clear that a 0.060" squish is the Toyco design spec independent of compression ratio
2) It says something about the geometry differences of either the dome or pistons for the NA and TT motors.

I severly doubt that the squish difference is made up by machining it into the NA dome. It's just too expensive to produce. Consquently, the only other option is that the NA piston is shorter from the rod wrist pin to the top of the squish band. (You following me here?) If *that's* true, then using a TT hg with TT pistons on an NA motor should get the right CR *and* proper squish.

Think about it...

-scott

awj

Sure ting. Eh, the ge heads are cast different. Who said anything about machining? Also, machining is a normal end operation in all heads, from the factory or on a rebuild. The stroke is the same in both motors is it not? It came out around 9.5:1 way back if I recall correctly. I don't have the volume of the ge head handy though.

motorheaddown

I think you're confusing squish with clearance volume. The GTE and GE blocks are identical; the rods are identical; the domes and pistons (i.e. clearance volumes) are *different*; but the squish is identical. The dome and piston account for differences in CR but do *not* explain the identical squish measurement. Consequently, either the squish is machined into the NA dome, or the NA pistons are shorter from the wrist pin to the squish band.

-scott

P.S. I get 9.44:1 with TT pistons and an NA hg. However, if my theory above is correct, using TT pistons with an NA hg would make the squish *very* small.

awj

Oh. Thanks man.

Lex Luthor

Careful Scott...

motorheaddown

Oh... I'm very careful. You should know that by now.

This discussion isn't about engine internal strength; it's about geometry. I'll bet a paycheck that the rod bearing to wrist pin *geometry* of the VVT-i rods are identical to the original 2jz rods, but that's not my main point. The issue is one that centers around equal squish with different hg thickness' on the NA and TT motors.

If someone can help explain how the NA motor makes up for squish with a thin hg, then I'm all ears.

-scott

awj

I thought it was clear...

you answered it yourself, yes?

RSTSpeed

iTrader: (4)

Not to go backwards, but...
Yea sorry... I was *butt*-backwards - had the 1JZ and GTE confused. Thanks.
So if you swap the TT pistons, head, and hg into the GE, THEN you have built the GTE but w/o squirters - right or wrong? Either way, does that setup creat the correct (same) CR and squish as the GTE?

*EDIT* Also, should you even consider getting doing the actual GTE swap unless you're shooting for HP > 500? What HP point should oil squirters become and issue?

Lex Luthor

If I were you I would spend like a week using the search engine with the contents GE, GTE, and turbo, there is much to learn grasshopper. There is no advantage really to swapping the GTE head onto the GE block (other than more cam and turbo manifold options)...matter of fact the GE head can be made to flow better. So you would swap the pistons and head gasket into the GE long block, and use a turbo manifold designed for a GE head (GTE manifolds won't work incase you were going to ask ), clear?

Scott, I should have assumed you were referring to the geometry of the rods and not the strength. Would really like to know what size chambers the GE head has, and if the GE VVT-i head is any different chamber-wise. Should've cc'd that bad boy when I had it apart...
- Jon

RSTSpeed

iTrader: (4)

lol, ok thanks... sorry if I'm getting on anyones nerves.

motorheaddown

O.k., time to wrap this thread up.

Lance Wolrab has one of DaveH's NA heads, and he inspected the dome geometry. Turns out I was half right. The NA head has a squish band machined into the dome that's about 0.023". That means the NA piston also contributes 0.025" to the 0.060" squish.

Bottom line: An NA-T motor with TT pistons/hg gets you a 8.62:1 CR and a squish of about 0.090". That's about half the squish I'm currently running, but it's still 0.030" over spec.

Case closed.
-scott

DaveH

Looks to me like it's time to machine that 0.023" squish band off of the NA head.

DaveH

motorheaddown

Hmm... interesting thought, but taking out the squish that's receded into the head means that you also reduce the clearance volume by ~3.3cc. That basically negates the contribution of the TT piston dish (4cc) bringing the CR back up near 9:1. Nothing a little meth/water injection couldn't handle.

-scott