I'm wondering if anyone has an educated answer as to what is deemed reliable (for the turbo's) on the 99 spec twins. I use the general rule to keep the stock 93's at no more then 14 PSi but maybe the 99's can take more reliably? This is probably a long shot asking but figured I would try hehe.

thewird

 

Having pulled both a set of 92/93 turbos apart and a set of 99 spec turbos, I can offer you the following information which may be of use to you.

The turbine shaft diameter is marginally thicker, which may resist shearing the turbine wheels off under higher boost.

The iron manifold on the hot side was recast in a higher nickel-content cast iron to resist the heat/stress cracking that the earlier turbos were prone to get.

I ran a set of these on a friend's relatively stock car. It ran a PFC, full exhaust, sequential, manual, rebuilt engine with a slight port polish and some sort of Apexi power intake kit thing.

It was a daily driver and at 10psi sequential gave no problems for many years. Make of it what you will, but I would still stick around 14psi or less.

The compressor fin design is much better also, so there is a good chance they will make higher boost than the 93' turbos before they begin chopping and heating the boost air and efficiency drops.

The abradable yellowish resin seal in the compressor housings would also help raise efficiency to a higher peak along with the revised compressor wheels. (Someone would have to have compressor maps 93' vs 99'.) As far as reliability goes, turbine wheel design and abradable seal would not help much. Reliability would be helped more by the nickel-iron casting and the slightly thicker turbine shaft.

 

I wouldn't run more than 15-16 psi on any twins on pump gas probably—and that's what I've run on these for YEARS on the street.

On the track, any more than 12-13, and you'll have heat issues, but I think the 12-16 psi range is the sweet spot with these anyway.

 

I've always heard that the '99+ N3G1 twins can't reliably run as much boost as the earlier twins. I've even heard that in Japan people reguarly swap the earlier twins in because they can run more boost.

That said, I've been running 12-13 PSI for years now on my '99s with good luck (knock on wood).

There are 3 versions of the twins - N3A1, the originals, N3C1, updated originals that are less prone to cracking but design-wise the same, and N3G1 which are the '99 twins with the revised compressor/turbine wheels, abradeable seal, etc.

Dale

 

I can't imagine the '99's are actually any less tolerant of boost than the others, since you're talking about minor differences. If you track the car, you'll go through turbos (especially TT's at higher boost), so it could be that the originals are cheaper/easier to replace as a wear item.

It's probably not unlike many Porsche owners "downgrading" their wheels/brakes to steel 6-lug from Ceramic/centerlock.

 

99s are genuine upgrades

I've heard the exact opposite about the 99s vs what Dale has heard

If anyone in japan wants to trade their low mileage 99s for some US 93s let me know

 

Some years ago, some forum member started espousing that the 93-95 USDM turbos were capable of running higher boost. Of course he had no facts. Just his opinion - probably stated emphatically b/c he was selling a set of twins.

Since there was nothing else to talk about on the forum since these cars are 20 years old, people started parroting that statement on every other thread on twins. "I've heard...." "I've read...."

Gotta love the internet.


99 twins are awesome.

 

I can't imagine the 99's being any less reliable. They came 12 PSI from the factory. I'll just tune it to 14-15 I guess. Thanks guys.

thewird

 

You got a way to bolt them up to your 20B? :-)

 

Its for a tuning customer. I normally just tune to 14 PSi on twins unless asked for otherwise but this customer asked for 16 so I wasn't sure hehe.

thewird

 

I have been running mine for more than 6 years at 13-15 psi with no issues. Not a huge amount of miles on them, but no problems.

 

Ray at PFS tuned mine for 16 psi, per my sig. I believe he put some 100 octane in it for that run though.

 

additionally the N3G1 engine was optional, so the "93" turbo was used from 93-2003, in the 265hp models. only the 280hp cars got the "99" twins