Throttle bodies

[PnOyGhost]

i am doing a 7mgte project. i have 2 turbos to choose from i have a gt35 style and a gt45 style turbos. i will be going 0.40 overbore with forged pistons and balanced rods. ported head, arp bolts, will buy bigger injectors and lexus afm. just need to know what size of throttle body i shud go with. 80mm, 90mm or 100mm? also i would like to know what size of wastegate i shud go with.

[annoyingrob]

Go with whatever is easier for throttle bodies. The size difference isn't THAT important with a forced induction system.

As for wastegates, if you're going to be running the GT35 style, I would suggest a 44-50mm wastegate. If you're going with the GT45 style, 50-60mm style. If you're going to be running low boost, get a bigger wastegate. It's always better to err on the large side with wastegates.

[Funkycheeze]

step 1 should be to pick the turbo size, boost and horsepower goals, not the other way around. Unless you intend on running BIG power (600+ RWHP) then I wouldnt bother with anything other than a bored out stock TB, usually to 62mm. Larger than that and you will need to make a whole custom intake. Go too big and your throttle response is going to be pretty crappy.

[azrael]

100mm with an FFIM.

It will do you absolutely no good, and cost a lot of money, but no one will question what a badass you are.

[Dan_Gyoba]

LOL @ Keegan. Nice.

@PnOyGhost: Fromt he comment about the Lexus AFM and the larger injectors, would that mean that you plan to keep the stock ECU and rung the Lexus/550cc injectors on that? If so, then there are limits to the amount of power that you're going to make.

IMO, the GT35 turbo should be a better match to the 550cc injectors and stock ECU. If you're going for BIG power, then you're looking at standalone management, at which point, I would be ditching the AFM entirely for a MAP system, which can then be callibrated for whatever injectors you need for your power goals.

If you haven't bought the internals yet, I'd also reconsider the .040 overbore. That's at the generally accepted limit for the 7M block for overbore, and I like overdesign. The .020 overbore leaves a thicker cylinder wall leaving the block stronger. It's not like the difference in displacement is all that huge.

When buying your pistons, you'll want to consider your final power goals as well. Lower compression pistons will allow more ultimate boost, but will make less off boost power. The result is more lag, and a bigger "turbo bite." Not so bad on the dragstrip, but it can make road course racing and even regular street driving more challenging. :)

[Keros]

Are you doing an FFIM?

[PnOyGhost]

dont know wat a ffim is but yes ill be running the stock ecu until i can get a standalone ecu. for size of injectors i was going to get some 750cc injectors. i already have the gt45 on a shelf in my garage and a gt35 in my other garage. im thinking that, that the gt45 turbo mite be to big lol but i am willing to go a little smaller. wat i want BIG power. but i want the power to be there more quickly dont really want to much leg. i will be buying some 0.40 pistons.i also have some balanced rods and
ported head coming aswell. i want a badass street machine, i basically want to roll up to a viper or a vet and just wax them. i want to take it to the strip whenever i can. dont like to STREETRACE unless theres a hot girl in the car im racing haha

mods on the car as of right now:
- 2mm MHG
- turbonetics manual boost controller set at 11 psi
- greddy turbo timer (didnt work when i bought the car)
- 3 pod pillar pod
- boost, volt, and water temp gauges
- custom down pipe and 3" exhaust to an apexi fart cannon
- lowering springs
- performance shocks
- greddy intercooler and piping
- HKS Super sequential BOV

parts sitting on a shelf in my garage:
- GT45 turbo
- GT35 turbo
- NGK Spark plug wires
- New Radiator hoses
- HKS electronic boost controller (this thursday)
- stage 3 clutch kit
- stainless steel turbo manifold
- clutch slave cylinder (coming from driftmotion)
- Clutch master cylinder (coming from driftmotion)
- Manual tranmission to be rebuilt (blew up auto tranny)
- standard sized forged pistons
- Manual ecu
- 2 shifters
- all belts from toyota
- all new tranny bolts from toyota
- a bunch of other stuff
- also going to be buying more internals

cud i go with an 80mm Throttle body? or shud i just bore out my stock one?

[Keros]

Judging by what you want, you should do some research on a Front Facing Intake Manifold [FFIM], on SM. It's worth numerous ponies due to the change in restriction from the IC system.

IMHO, it's not worth doing spit to the stock throttle body unless you're changing to an FFIM or something is wrong with yours. If you're going to spend the money on a TB, may as well get the full benifit and get the best intake system possible on the car. IIRC, our 70mm throttle body that comes stock will do quite well for most applications.

Do some research on the FFIM, it's worth it.

[Dan_Gyoba]

FFIM = Front (or Forward) Facing Intake Manifold. Like the JZ engines, so that the intercooled air does not have to be run back over top of the hot exhaust manifold.

As has been stated, the throttle body size isn't that big an issue under boost. If you really want larger, start with boring the stock unit. If you're unhappy with that, you can probably recoup your costs reselling it anyway, or at least a reasonable portion of your costs.

[adampecush]

I think you should worry about engine and fuel control before worrying about what throttle body you need.

At the bare minimum:
- fuel pump (genuine walbro as we discussed at a minimum...this won't flow 500+ HP reliably though)
- fuel pressure regulator
- fuel computer (S-AFC or equivalent)
- wideband O2 sensor/gauge

Above this, i'd recommend a programmable piggyback (MAFT-Pro) or a full blown standalone (megasquirt ($), AEM ($$), Motec ($$$$), etc)

And remember, most larger throttle bodies make no provision for our throttle position sensor, so some tinkering is required.

[Keros]

I'm fairly certain that the stocker throttle body has flowed some serious power on other cars before. Probably more than 500hp.

I'd put the TB at the bottom of the list of things to deal with.

EDIT: Clarity

[adampecush]

edit: stupidity. carry on :)

[Dan_Gyoba]

I think Keros was referring to the stock throttle body. In which case, yeah. I don't think that's something that really needs to be upgraded until you've got a LOT of other mods to support/require it.

Fuel pump? Yeah, a Mk4 pump would be good. I'm happy with my Walbro.

[Keros]

I think Keros was referring to the stock throttle body.

Yeah, I was referring to the throttle body.

Upgrading the fuel system is alot more important than the throttle body, in agreeance with what Adam said.

[10secdream]

Well I am sorry to tell you this but BIG power and very little lag are not possible. You have to choose one or the other.

[suprago]

Big power and zero lag no problem, just install a bigger motor.