Ripzta

Recently I thought I blew my motor but luckily didn't and ended being a blown secondary turbo, so engine's fine. It's leaking oil onto manifold that caused that smoking isuue. So I'm thinking of rebuilding them or find a set of used 99spec twins. A single replacement is out of the question.... for now.

What parts can be upgraded/high flowed to increase power or to run more boost efficiently? If I go the other route and get a set of 99spec twins, what other mods do I need? I'm also stickng with sequential.

BTW, a custom FMIC, Microtech MT8, 3" DP, Blitz BC is going in at the same time and also removing the airpump. Would I need an E-fini Y-pipe to mate with 99 twins? This would also be a good time to replace the rats nest's hoses too.

Joseph

DaleClark

iTrader: (55)

The 99 twins just bolt right on as far as I know. You can use the old Y-pipe as well.

The '99s will give you a broader, fatter powerband, but supposedly they're not as good for high boost as the stock twins.

It's quite tricky to upgrade anything on the stock twins - BNR Supercars has it figured out pretty well. Most other shops can only do a pretty basic upgrade, like clipping the turbine. The turbo shaft is VERY thin, and many times upgraded wheels cause the shaft to snap.

Dale

Ripzta

Why would the older twins be suitable for higher boost than the 99spec twins? So you saying, upgrading wheels MAY decrease the life span of the twins?

7racer

Riptza,

since your in australia, can't you get the bathurst twins? Supposedly they are ones that you can get alot of horsepower out of. I'm not sure since we never had them in the states but from I recall reading, those are the "sought after ones" for high hp.

kuning

Not trying to dictate you Ripzta, but I did a search ages ago about how good the 99 spec is. There were quite some numbers of threads discussing the plusses and minusses of the 99 spec that explain everything throroughly(sp?).

But yeah, broadly speaking the 99 spec is prone to high boost. It does its job well under stock conditions. But if you pursue big dyno figures, it won't be suitable. I can't explain much into deatails about this because I'm no expert with rotaries. Afterall, I'm just a noob here.

Just thought i'll share my 2cents.

Yans

Ripzta

The RX7 SP twins are worth an easy $4000AU+. The SP downpipe is 3.5" SS from factory and are worth $800AU+. I'm sort of leaning towards just rebuilding them and replacing all hoses.

Is 12psi good for everyday driving or should it be kept at 10psi? Also whats the preffered high boost setting for the twins for those occasional drag races? 16 psi w/ fuel mods?

Thanks for everyones input,
Joseph

rynberg

I'm not sure where the idea came from that 99 twins are not good for high boost...Japan market maybe? There is a local guy making 380 rwhp on 99 twins....and he passed smog by just putting a stock cat back on.

ROTORhead93

Hey Rynberg, who are you talking about? And do you know what mods he has on his 7? Also, is he running them sequential or non? Anything that can make that much power at the wheels and still pass CA smog on a 7 interests me quite a bit.

Would you compare the 99's to a set of BNR's or are there alot of differences between the two?

rynberg

I don't know who it is, he is one of Rick's customers. AFAIK, the guy just has the bolt-ons, fuel system, PFC, and a Rick-built ported motor.

There is a world of difference between the 99s and the BNRs....I guess we'll see how well the BNRs do on my car in sequential, once it's finally back on the road.

BTW, my goal is to hit 350 rwhp on pump gas AND pass smog with no modifications....we'll see...

DaleClark

iTrader: (55)

I've always heard that the '99 twins aren't as reliable if routinely run at higher boost pressures than the "low power" regular turbos. Not firsthand evidence, but that's the general story.

I plan on eventually going with the '99s since I don't plan on running much boost and I'm all about maximizing the stock setup.

Dale

7racer

That was same reasoning for me to go 99. I'll post my dyno run here soon.

I just remember JT or someone from japan mentioning that the 99's ran out of steam up top and that if you were going for more horsepower in the stock setup, bathurst twins were the way to go.

jims6

I am going to have to get a set soon as well.

There are 2 types of 99-onwards twins. The 280HP top spec ones with the abraidable seal. These are the ones you guys are talking about and yes, they don't take to well to increased boost.

But the 265HP (255 auto) base model rx7's from 99 onwards still had basically the same turbos as the older models.....just that they are newer with fewer miles. I was thinking of maybe going for a set of these of an RB or RB-S model.

What do you guys think?

GoodfellaFD3S

iTrader: (213)

No comparison. The BNRs are much larger (comp, turbine, shaft, the whole nine yards) and thus will withstand 15-19 psi with less heat and less wear and tear.

FLA94FD

I have a set of 99’ spec twin and they have now problem producing 15lbs of boost all the way to red line and according to an engineering review superior in all aspect to the original twins. So I’m not sure that I’m buying that they would have high boost problems. Beside the design generates less heat because of greater efficiency. For $2500 you can’t go wrong. Now if you need more boost than that you should be going with a single setup. I normally run 12lbs of boost and other than an upgraded fuel pump you shouldn’t need other fuel system upgrades with twins unless you run it hard all the time.

Also if you don’t have a mid-pipe you should keep the smog pump with the twins. It aids in cooling the engine and cat without it your cat will die prematurely, I know. It also shuts off at 3000 RPM and WOT. Removing it would only make a 1-2HP difference from accessory drag.


“Hitachi has since come up with a new built-up construction of the compressor housing. A formed plastic inner sealing element is bolted onto the main housing, and then machined. The turbocharger is assembled, and run up to 100,000 rpm, abrading the inner surface of the plastic seal, obtaining the closest clearance between the compressor and housing. The new abradable turbocharger has an 80%-plus efficiency, whereas a typical instrument's efficiency is about 75%, according to a Mazda designer. This brings down the compressed air's temperature by 10 C, or about 10%, at the exit of the compressor. Air temperature is still in the region of 110 C (230 F), which is further cooled down by the air-to-air intercooler in the RX-7 installation.” http://robrobinette.com/sae_article.htm

ptrhahn

iTrader: (9)

Yeah, sorry kids... I don't buy the "not as good gor high boost" bit. My '99's easily make 15 psi to readline, and could probably make 18 no problem.

What I DID read once is that one of the race shops in Japan was swapping in the the non-abraidable versions into their racecars (that were late enough model years that they would have come with the abraidables)... but I would surmise that they'd do so for easy, cheap rebuildability for a frequently abused racecar.

Bryan@BNR

iTrader: (1)

Hello guys.

The reasoning behind the stockers and the 99 specs no being able to handle a lot of boost for a long period of time is the factory thrust bearings.

The factory thrust bearings are 270 degrees around the rotating assemblies. What this means is there is a 90 degree gap which drains oil from the rotating assembly while it spins. The more RPM the RA spins the more oil it needs to lubricate the bearings. About 15 psi is about the limit on reliability of the stock and the 99 spec units. After 15 or so PSI, there is not enough oil going to the RA so it causes Thrust wear and eventually ruins the CHRA (Center Housing Rotating Assembly).

The Stage 3's have 360 degree Bearings. So there is no gap for draining and oil is constant on the rotating assemblies. Up to 200K RPM is about the limit which would interpret around 25-28 psi of boost.

Next is the shaftnuts on the 93-97 versions of the FD twins. They like flying off at high boost... A left hand thread shaft nut cures that problem which comes on the 99 spec twins and the new BNR's.

The 99 turbine shaft, other than the thread change is pretty much the same as the 93-95 versions. Some of the 99 turbos come with factory clipped turbines which doesn't make a differerce.

Anyway I was bored, thought I would post...

Bryan@BNR
205 640 1193
www.bnrturbos.com