From Single Turbo Forum:

My friend just purchased an 88 10thAE (basically an S4 TII). The previous owner installed a 3 inch exhaust from the turbo back, with no cat. MBC is set at 10 psi. For fuel the car has an FD fuel pump (BTW..weren't these supposed to be unreliable...killing many FDs back in the day??) and some sort of fuel cut defensor. HKS filter at the front leading to a stock turbo I believe, then to the stock TMIC.
First off..the MBC was set at 10 psi but the damn thing creeped to 16~17 psi at the top of almost every gear. Not surprisingly, the car smokes as if the turbo is blown but I haven't gone down and checked for end play.

The part that really surprised me, though, is that the turbo FC had little boost before 3.5K...car was almost as much of a dog to drive as an NA. Since the turbo is shot, we're looking to replace it with something that will spool earlier.


So:
Current setup-- builds boost from 3.2K all the way to redline...satisfied with the power (Butt dyno says around 220 hp?).

Looking for-- a whole lot less lag. Looking for boost as early as 2.2K and would like a broad power band, but I understand that it will probably trail off at higher rpm. (Rather have low down torque than peak power...looking for 230 hp...reasonable with the afforementioned mods I think)

What would you guys recommend we look for? Is a ball bearing turbo worth the expense? We are on some sort of budget, so there is a price cap. I read that a T25 on ball bearings will spool really fast. I don't know what kind of A/R or trim I should look for. What do you guys recommend?

Thanks in advance,
Grant

 

only way to get any turbo to spool even remotely that quick would be to up the rotor compression ratio.

 

Hmm..bummer. Well any advice on how to get it as early as possible? Anybody have experience with a T25?

 

isnt a t25 a turbo from a 2nd gen DSM/eclipse?
If so that thing would spin like crazy and You'll kill it soon!....Plus You will not have any top end power

 

My goal is torque. T25 at 10 psi won't fry it will it? But yeah, it could very well be for DSM only, the book i'm reading is relating to piston engines.

 

What is torque?

 

lol ..sigh.. i'm starting to notice there's so little of it that noone cares about torque anymore in the rotary forums! But yeah, anyone?

 

N/A rotors + careful tuning, and limited boost, or

supercharger.

 

supercharger is the only real way to get torque.

turbos are more for top end power.

 

he could get closer if he fixes his twin scroll
and floor it in 5th gear!



but really.. the twin scroll should help...

 

nitrous MUUHUHAHAHAHAAA

 

rotary + torque=goodluck

 

So how do you know if the twin scroll doesn't work? It's a flapper valve on the S4 model right? Howcome an S5 is better down low w/o the flapper system?

My 04' SAAB 9-3T get's plenty of power below 2300 rpm...I don't think turbos are for high end performance exclusively. But for rotaries, I just don't know anymore.

It isn't worth taking apart the engine and bumping up the compression for this. And I fully intend to stay turbocharged...kinda on a time and money budget here.

So should I be going for a hybrid turbo or an S5 turbo and manifold? What gives me the best response per dollar spent?

If boost is kept below 10 psi, can I get away with the TMIC? I can always add an aquamist system.

Any other suggestions or advice?

 

heat! advanced timing, more stoich afr....

 

K not really the answer I'm searching for...and even then, wouldn't advanced timing be dangerous on a car running more boost?

 

I've got the s4 N/A rotors in my TII, and the boost response isn't phenominal or anything...

 

wrong
it would be retarded timing and rich...
advanced timing lowers the exhaust heat

 

Try the TB mod or just wire open those out board butterflies. Thats what I did and holy crap does my BNR stage III spool quickly. I am through 1st gear in the blink of an eye almost, and 2nd is just as quick. It damn near makes the car feel as responsive as a well built N/A V8. I am not and would not support the V8 in a RX7, but I have owned a few nice V8 powered cars and this really brought back the punch in the stomach feeling those gave me on take off.

 

first of all you should port the wastegate or you will end up blowing it up from boost creep also your injectors might be maxing out since it's going up to 16 psi the stock turbo only is good up to around 15psi then it is useless bc its just creating hot air maybe give the turbo to BNR to upgrade your turbo that will make it have more power and you dont have to worry about custom dp or manifold

 

What do you mean wire open the out board butterflies? Do you mean as part of the TB mod? I'm still not sure how the TB will improve responsiveness.

What can BNR do for me?

 

You can run 10 psi with no problems.

But you will always benefit with an aftermarket intercooler.

Personally i feel aquamist or other cooling "spray" systems with the top mount is more as a bandaid.

But again, with limited funding comes limitied performance.

-Justin

 

I thinkmy 10th ae has stock internals..just a mild port. Anyways, on my stock turbo it would start building power at 2.2k and be fully boosted at 10psi (or more...boost creep sucks..) by 3k

 

By testing it as per the instructions on page 4B-54 of the FSM.

Correct. The flap in the exhaust manifold blocks off one of the turbine housing's scrolls at low revs, which increases the velocity of the exhaust gases hitting the turbine, spooling it up faster.

Because Mazda added a fully divided exhaust manifold and electronic boost control. Both of these reduce lag considerbly.

 

3.5" exhaust!

 

my car hits boost pretty damn quick ...
check my sig for mods

i swear i hit 5 psi before i hit 1, and by 4k or so im maxing out my boost .. which is usually around 10psi