In case anyone is curious, I asked Bryan of BNR Supercars about the measurements of the wheels on the stock HT18 turbo.

He told me these measurements:

Turbine major: 2.51" 63.75 mm
Turbine exducer: 2.15" 54.61 mm

Compressor inducer: 1.72" 43.68 mm
Compressor exducer: 2.48" 63 mm (48 trim)

After looking through some catelogs and other sites like FC3Spro http://fc3spro.com/TECH/TURBO/tmodels.html , I figure that puts the turbine wheel somewhere near the Turbonetics/Garrett T3 stage 2. The compressor wheel is right around the size of a TD04-14B on a manual tranny 1G DSM. The closest Garrett compressor wheels are the T3 50 trim and GT22.

Because it's a rotary the turbine wheel and housing are actually really big compared to most other turbos out there with that size of compressor wheel, which is probably why hybrids (BNR or Knightsports) work pretty well. Interestingly enough, both the compressor and turbine wheels are a little smaller than the ones on the Mark III Supra CT-26.

 

here is the compressor map of the Garrett T3 50 trim:



and here is the compressor map of the Garrett GT22:



Just looking at it, it's no surprise that these cars make 220-250rwhp at the wheels with the boost around 12-13psi. The compressor wheel can't flow much more than that and the backpressure builds up in the turbine housing as well, making boost fall off.

 

side question: how would the compressor map change if you made the turbine inducer larger, decreasing the trim (it appears the stock turbine trim is around 71), but keeping everything else the same. what affects woudl that have on spool and torque curve?

 

The compressor map is not dependent on the turbine wheel. They are two different things.

 

let me rephrase, how would increasing the stock turbine inducer (major diameter) affect spool time and torque curve? like from going from stock 71 trim turbine to 60 trim, keeping everything else the same size

 

There's nowhere near as much knowledge out there about the turbine side of a turbo. Most of the time people just clip the stock wheel, which hurts spool slightly but gives you more topend.



clipped wheel on left

 

thread revive.

Question. Is there an exhaust housing that can be a direct swap for the stock turbo exhaust housing to make it match a T4 manifold flange?
In other words HT18 turbo to T4 manifold.

 

no

 

^lol, why would you want to do that?

 

T4 turbos need external wastegates and the FC manifold is not for an external wastegate. The only turbo car I can think of that has external wastegates from the factory is the Porsche 944 and I think some random Saabs.

Now, you could get an adapter flange from the factory s5 manifold to a divided T3. That would make sense. But you'd still probably need an external wastegate. There are very few turbos with divided T3 inlets that are internally wastegated, and the ones that are usually for diesels. And diesels don't have high flowing wastegates (BorgWarner turbos on Caterpiller engines and Holset turbos on Cummins engines).

even if you mated an undivided s4 manifold or a divided s5 manifold to an undivided T3 turbo, you still have the wastegate issue. Few T3 turbos have internal wastegates. Your main choice would be the internally wastegated GT3071R which is used on Rx-8's. But then you might as well save money and get a hybrid.

 

we did a stock s5 manifold to gt35 "kit" its got a little adaptor for the turbo, dp, all the lines etc etc and still fits with the air pump and smog equipment, and stock air box/afm

so it can be done, although it wasn't cheap.

gt35 is nice cause its internal wg, that was supposed to keep it simple

 

that's my secrete. its not what you guys think.