C/R with TT pistons/hg on NA motor
 

First, some may wonder why you'd go with the NA motor and TT pistons/hg. Here are some good reasons:

1) Squish effect is what directs the charge in the chamber toward its center as the piston reaches TDC. This is the biggest deterent to detonation.*

2) Removing squish can cause a low compression motor to ping worse than a high compression motor with proper squish. *

3) Having a "dished" piston helps maintain squish while minimally upsetting the squish effect.*

4) TT pistons/hg are reasonably priced and reliable to very high boost levels.

*(Maximum Boost p 157)

I finally got reliable sources for the volume of the TT piston "dish". Accordng to Lance W. (to4r.com) and Carchitect, the dish volume on a TT piston is approximately 4 cubic cm. I averaged the value each gave me. Both were very close. Additionally, I have numbers from Lance that show the TT hg compressed is 1.35mm (almost dead on with my estimate).

Using those numbers, I recalculated the compression ratio and determined that an NA motor with TT pistons and hg has a final compression ratio of **EDIT** ~8.62:1.

-scott

Appreciate the info. This will likely be the route I'm going. ;)

Wow.

Someone out here is actually making decent, informative posts besides lexluthor !?!?!?!

Thanks MHD. I plan to blow my motor soon and go with this setup.

meaning less post #1164 served with pride.:golf:


edit: Is that Tiger Woods?

I believe the Supra manual states that the GE and GTE block, crank and rods are identical.. not sure about the head. If the head is the same, then with a set of GTE pistons, I believe you just built a 2JZGTE?

Wtihout the squirters, yep. Oh, no the head is different dog.

O.k., just for grins, I'm posting the same kind of information for the TT head.

Lance Wolrab is very well respected in the Supra community, and we had a discussion on the mkiv mailing list that I thought was worth posting. Here's some *very* good info: :D

-----Original Message-----
From: mkiv-bounces@mkiv.com [mailto:mkiv-bounces@mkiv.com]On Behalf Of
lance
Sent: Tuesday, October 21, 2003 3:03 AM
To: 'The MKIV.com National Mailing List'
Subject: RE: [mkiv] cylinder head answers

OK, let's get some numbers working here. First we have a fixed number
for the head volume, 44.9cc, and a fixed number for the total combustion
chamber volume, at 66.5cc. The headgasket is 1.35mm thick when crushed.
Bore is known to be a nominal 86mm, but Motorola cup is allowing for a
very slight oversize of about a half a thousandth of an inch. So, we know a
few really important things, first,

For every millimeter of squish, we get 5.81cc of volume. (I really
screwed this up the first time, my head was not clear, no coffee yet)

Motorola Cup engines must be zero decked, which means squish MUST be
1.35mm or 7.84cc.

If the total combustion chamber volume is no less than 66.5cc, then
let's figure out what the dome MUST be:

Vt = Vhead + Vsquish + Vdish (unless you are also including the volume
above the top ring, some do, some don't, I usually don't)

So:

(66.5 - 44.9) - 7.8 = 13.8cc

So the dish volume needs to be nominally 13.8cc.

The 66.5 number is immutable. If you have an 86mm bore and stroke, your
combustion chamber total volume must be 66.5cc or your compression ratio
will not be the factory claimed 8.5:1. Motorola Cup uses dimensions
supplied by the manufacturers, so it's pretty safe to say, these are the
design numbers from Toyco.

If an enterprising person were to set up squish tighter than factory, at
1mm, what would be the result?

44.9 + 5.8 + 13.8 = 64.5cc and compression ratio (after a little
algebra) is (Vswept/Vcombustion chamber)+1. An 8.6cm bore and stroke
gives us:

(499.6/64.5)+1 = 8.75:1 compression.

For you guys who measured your squish at 1.5mm (0.060"):

(499.6/67.4)+1 = 8.41:1

If you were unfortunate enough to make it all the way to 2mm (0.080"):

(499.6/70.3)+1 = 8.1:1 compression.

And how about a flat top piston with no dish and 1mm squish?

(499.6/50.7)+1 = 10.85:1

So there you have it, corrected. Can somebody check my work???

Lance
'93 TT 6 speed Coupe
--------------------------------------------------------------------------------------

-scott

Scott, great info, does the GE head also have a 66cc chamber?

Hmm.... I don't know. Nobody has really done that much research on the NA head.

-scott

I'll try to get some measurements on the head this winter if no one else has them by then. But I think its a tad larger than the tt head just by guesstimating from all the other numbers.

BTW Scott... Theres a rumor that toyota sells .20 over gte pistons...I haven't had the chance to ask Curt A. about it but it would definetly be somehting nice to go with if you're rebuilding.

Lance (the guy that wrote that) has one of my GE heads. I'll see if he can cc it.

DaveH

Great.

I'm interested, too b/c I think I will be building/rebuilding soon. Also, am I to understand that you would opt for the 2JZ block w/TT pistons RATHER than the 1JZ? Isn't the only difference between the actual blocks the oil squirters? Correct me if I'm wrong; I'm still learning. ;)

edit - nevermind, I'm asking dumb questions... sorry!

RST, the 1JZ has half a litre less displacement and problems with parts availability here, stick with the 2JZ, and yes the TT pistons fit into the GE block without oil squirters.