Head gasket advice please

[TrickyBlue]

Hi all,

So I shall be getting my na-t engine rebuilt soon as was wondering which headgasket to use.

I'll be installing CP 9.0:1 pistons but I don't really understand the compression ratios and 'squish'

Any advice on which HG to use?

 

Thanks

[Noz]

9.0 CR pistons on a GTE engine? Or a GE engine.

They may fit the same. But they won't automatically give you 9.0 on both, as the starting ratios are different.

I expect it'll be GTE pistons. Which means you are increasing compression slightly from the stock 8.5.

I believe the combo of an NA engine with GTE gasket gives you around 9.2. Which means 9.0 GTE pistons will increase you to around 9.7 roughly. Which isn't far off stock NA ratio.

From memory the stock gasket is 1.3mm.

What are your power goals. Why did you choose 9.0 pistons out of interest.

500hp. I'd use a 1.3 gasket and you should be okay if you've a good stand alone ecu. But 1.5mm would be nicer. Anything more power wise. Up the gasket thickness. Closing in on a ratio of 10 on pump gas is less than ideal.

I think you can get a 2mm gasket. 

This of course depends if they were intended for the TT or NA.

[TrickyBlue]

It's a GE engine but GTE pistons. The reason for 9.0CR is due to recommendations really from a few people. 

Power wise I'm hoping for around 600bhp. Its currently 490 at the wheels with Whifbitz na turbo kit, r35 coils, 775cc injectors and a link ecu.

[Noz]

The problem is you arent going to get a ratio of 9.0 using 9.0 CR pistons in a GE engine.

Whoever recommended that compression ratio, did they forget it was an NAt or something.

I've not heard anyone recommending 9.0 pistons in an NA before.

600 is 525whp. You arent far away anyhow. I've got 525 at the wheels on my NA and I'm using oem pistons.

You're going to have to lower your ratio with a 1.5mm or above gasket. Using high compression TT pistons on an already high compression NA setup puts the setup at risk. 

Edited May 14, 2021 by Noz (see edit history)

[TrickyBlue]

I have no idea tbh, what setup would you suggest?

Sorry i meant 600bhp at the wheels.

[Mike2JZ]

Put an oem TT head gasket. Will be fine

[Noz]

7 hours ago, Mike2JZ said:

Put an oem TT head gasket. Will be fine

Surely 9.7 estimated is going to be fairly high for 600whp?

I'd go 1.5mm surely. To at least lower it slightly.

[Mike2JZ]

1 hour ago, Noz said:

Surely 9.7 estimated is going to be fairly high for 600whp?

I'd go 1.5mm surely. To at least lower it slightly.

Not sure how you are arriving at 9.7CR

Let's talk about the blocks contribution to static compression first.

GE and GTE are the same thing in terms of stroke/bore/crank/piston to deck clearance etc etc. The only difference when it comes to the factory bottom end is the pistons. GTE piston is domed and GE piston has raised section in middle to bump up compression. 

So if you stick an aftermarket piston which is rated for 9:1 and you dont have any additional piston/deck clearance, then your bottom end will contribute around 9:1 compression to the equation. 

Now let's talk about heads & gaskets. 

The only way you are going to get accurate numbers on the following is to get your head's combustion chamber volume measured whilst it's off as it will change depending on combinations of hardware used. 

However for this example, let's use some common values for 2J head chamber CC that the internet dishes out on a quick google search. 

2JZGTE head combustion chamber CC typically around 44-45CC

2JZGE head combustion chamber CC ranges from 42-44CC. 

So if we use these head CC values, paired with a 9:1 bottom end, with a TT headgasket you get the following:

2JZGTE Head with 9:1 bottom end + TT Headgasket CR = ~8.96 CR [45cc] to 9.1 CR [44cc]

2JZGE Head with 9:1 bottom end + TT headgasket CR = ~9.0 CR [44cc] to 9.36 CR [42cc]

I know this is a broad example and real world results will vary slightly, but with these combo's of parts you will be closer to 9.0 CR then you would 10.0 CR. 

9.0C CR is perfectly boostable on pump fuel and will do 600whp with ease. So with this in mind, in most cases the OEM headgasket is going to be ideal. Larger headgaskets work, but I'd usually avoid unless absolutely necissary. Far better to control CR via headwork and piston choice imo. 

Plus we are only debating static compression, which is relevant. But once the engine is spinning and depending on the cams, overlap, cam settings and other headwork done, the dynamic compression of the engine may make the engine act like it has less compression then it has statically. But that's a whole different discussion. 

Back to the OP. 

If you want 600whp, then you may struggle on whifbits NA-T kit and your current fuel system. I'd recomend FIC1000 injectors, 264 or larger camshafts, a Borg warner S366/S369 or Precision 6870 and possibly a different exhaust manifold, something tubular. 

 

[Style]

I went for 9:1 Manley pistons and fitted a TT gasket after working out I should be at around 9:1

Car does feel a little more sluggish off boost which backs up that theory.

[TrickyBlue]

Great post @Mike2JZ that's alot of useful information. 

Regarding upgrades that is something that will all come in time. Right now I'm just looking to build the engine suitable to reach that power later on. The only thing i put off buying was the pistons for the above confusion. 

 

@Style are you happy with it? Or would you change if were to do it again? 

[Style]

With the same budget and goals id do it again, yeah. What’s your end goal?

Obviously the higher the better, but you’d be talking 625+ head studs and all that jazz to keep the head in place once you start going for high boost. 

[TrickyBlue]

I'd like to hit 600whp but I'm not too bothered if it's just under. I'd like to keep as much driveability as possible, I've been told some of these high power Supra's are a bit laggy to drive. 

 

What's your setup?

Edited May 15, 2021 by TrickyBlue (see edit history)

[Swampy442]

600whp is over 700 actual hp, that needs a big turbo which will be laggy. Why not aim for 550/600 actual hp, minimise the lag but still have a very fast car

[AC93]

I made 616whp at 1.6bar thanks to Mike ..Manley 9.5:1 pistons and rods, 264 cams, Borg S364, FIC1000's and tubular manifold

My VVTi helps with spool and torque, 0.88 AR and full boost at 4k, I don't feel like my NA-T is laggy at all.

 

[Noz]

@Mike2JZ got to 9.7 as an estimate based off the TT HG arriving at around 9.2 with GE pistons. Therefore higher compression pistons adding more compression that this. Perhaps my estimation of 9.2 is outdated and incorrect.

[Noz]

6 hours ago, TrickyBlue said:

I'd like to hit 600whp but I'm not too bothered if it's just under. I'd like to keep as much driveability as possible, I've been told some of these high power Supra's are a bit laggy to drive. 

 

What's your setup?

Laggy supras are because people incorrectly size their turbo and go for numbers not response or area under the curve.

Personally I'd stick to a 62mm turbo, as many can reach 750hp so you shouldn't be pushing it so hard it reduces the life of the turbo.

Mike's advice for 264 cams is spot on. Some people have done amazing numbers with those. No need to over size that.

Vvti as mentioned definitely helps. Heads fairly well prices if you can get one.