I've been reading the 99 Efini's have smaller compressor wheels and actually make less power at higher boost levels (14 plus lbs) versus the original stock twins. Well I started looking at the 99's and I do know the compressor housing is slightly larger as the water line will hit the housing on the 99' Efinis but not the stock twins. I called Ari over at RX7.com and asked if he knew if there was a size difference and his response was "let's find out". He actually took apart a set of both, 99 Efini's and 93 stock twins. Ari measured the wheels (inducer and exducer) and they are absolutely identical, zero difference.

I think the belief that the 99' Efini flow less than the originals is just a myth. Has anybody else actually done this with different results?

 

Good to see you are still kicking around Mr rx-7 tt! I've never seen 99 spec turbos up close, but the thing that strikes me most from what I've heard is they have a abradeable compressor wheel.

 

It's not the wheel that's abradable; It's the small section of the turbo inlet that's in immediately contact with the wheel.

There is a minor housing difference between the two, but Mazda certainly would not *upgrade* the Efini turbos to such a shape that they wouldn't fit on the engine or have different bolt-ups to the stock lines. (That just looks ridiculous after having typed it.) Furthermore Mazda would not have made the 1999 Efini turbos produce LESS flow than the 1992-designed units. (Again, ridiculous.)

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[ I recently replaced my stock turbos with Efini turbos with nothing but a floor jack and a couple jack stands at my disposal - which was a pain-in-the-butt to install, as well as legs, back, arms and neck. I had to take off the air pump and Efini y-pipe, and there's about 7 bolts holding the manifold/turbos on that you can't see that need to be removed and then replaced. The turbos have to be brought in from under the car. (Lying on my back in a puddle of oil and coolant with the car only a foot-and-a-half off the ground, holding and balancing 45 lbs of turbos with one arm while finding and tightening bolts you can't see was not exactly fun.) Also be sure not to over-tighten the banjo bolts; I broke one and just happened to have an extra one from an S13 that fit perfectly. ]

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Visually there weren't any huge differences between the two turbos (actually "turboses").

At 2am when I finished (Did I mention it was freezing outside - yea, I don't have a garage....), I immediately noticed a huge difference in spooling, turbo "sounds" and power, but this is comparing my new Efinis to the original 16-year old turbos. And since there are no new "1993" turbos to compare to new 1999 Efinis, there's no way to actually compare the two side-by-side. We just have to take Mazda's word that the 1999 units push a little more air.

I've also spoken with Ari a few times myself, and he is a cool dude. Chris and Mary are too. Well, Mary's a female, but ya know...

 

I didn't mean the compressor wheel it's self. I meant inside the compressor housing.

We are comparing apples to oranges here. Series 6 USDM vehicles vs Series 8 JDM vehicles. There are plenty of differences between the two, even if some of the variations are minor. I don't think we can say for sure what Mazda intended unless we get concrete proof to back it up, be it engineering papers or turbo flow maps.

 

Not going off internet hearsay, I had both and installed my Efinis, so I'm sharing what I know, and what I observed visually firsthand. I think that carries a little weight to my original post.

"Plenty of differences" that total up to a "minor" difference = a minor difference, so the bottom line is ...

*Who really cares?*

Simply put: In 2010, there's no "1993" unit that will spool faster or push more air than a new 1999 unit.

Disagree if you will.

 

Hey Glassman,
Glad to see you are still kicking around as well!

 

Agreed. I think it got started by some loud mouth on here. There is no logical reason the newer turbos would perform worse.

 

I replaced my 60K 94 turbos when I rebuilt the engine. The 60K turbos had some cracks but were functioning properly. Since they were on the way out, I decided to replace them with the 99's. The new 99's definitely pull harder at low rpm. I can't comment on high rpm, because my engine was ported during the rebuild. As was mentioned above, there is no way Mazda would put in lower performing turbos at high rpm. Didn't the later model RX7's put out 280 hp at high rpm (as compared to 255 for early models)? A lower powered turbo doesn't add up in the later cars.

 

i always thought of upgrading my stock twins to something better .. more powerful.. with less heat .. i did a lot of research and i found that anything better than oem or 99 specs is bnr stage 3.... however .. even the bnr takes in ur oem turbos and do somthing to it...
the only twin turbos i found that are a bolt on replacement to stock twins are the revolution ball bearing twins... in japan tho
before .. ever going to a single turbo .. i will give them a try.. on the website it said on 1.0 bar it makes 398whp and 1.5 bar around 425hp .....
any1 esle heard about revolution twins?

 

Yes you can pull them out from the top, done it twice, its also quite a bit easier if you have a friend hold them in place while you put in those STUPID inconel bolts and nuts.

 

doesnt the series 7 and 8 turbos output slightly more psi to justify the increase in power? (with the addition to the better tuned 16bit ecu of course)

 

S8 got about 1lb more. Also, you'll find the front intake elbow at least, is different taper and larger, so the standard S6 rubber connector wont fit....probably won't see that just buying new turbos.

The smaller thing was regarding the compressor housing intake, which was 1/2mm!!! smaller from memory. Factory model release briefing notes appear to back that up, somewhere on a NZ site???

 

I noticed the compressor housings themselves are actually slightly larger.
As far as dyno numbers I have seen numbers from 360 to 370 rwhp and I saw one post where one forum member stated he made 400 rwhp on them but now I can't find post.

 

Good to know. Except that I will never do THAT again. The bolts aren't even visible; It was all about *finding* the bolts with my finger, then *re-finding* them with the socket. And man it was cold that night

 

Honestly, there's no really dramatic difference between the original and the '99 units. There are hardly even small differences. So unless Mazda had them extrude-honed, they really - I mean REALLY - look the same. The fact that they're freshly new is the difference. If your motor's in good condition, you can get 360 out of them, but hp numbers don't always make a fast car. It's torque that pushes you into the seat.

Unless you're concerned about smog testing, for what you want to accomplish, you might consider a T35. I'd dyno tuned with twomucboost4u when he had one in his FD, and below 3000 it spooled almost as fast as the twins, and above 4000, it was no competition. The car got up to 380 whp and 320 (330?) torque with room to go when we found a hole in one of his oil metering lines and had to stop.

400 rwhp on stock twins is questionable, and understand that different dynos produce different numbers.

 

According to BNR, the housing has higher nickel content to resist the cracking of the earlier turbos.

 

Pettit Racing will get about as much output from the stock 93 vintage turbos as anyone. They will either rebuild yours- if it does not have significant heat cracks- or use a new one to upgrade. They blueprint all the clearances and then radius the curves in the air chambers. Two hot spots are ceramic coated. I upgraded from stock (working perfectly) to the Pettit and noticed improved spool-up and increased maximum boost attainable. I did not think that 17 psi was possible with stock twins, but the Pettit holds 17 up to 7000 rpm. I run at 15 for engine longevity, but it is nice to know the turbos have more capacity if needed. I spent about $4500 a couple years ago- do not know what their current price is, but if you do not want to go single turbo, this is a good alternative.

We just had one of the first cold days in northern VA and I forgot what it was like to have that cold, dense air give you another 10% power!

 

I have run 17 plus psi on the stockers for years, they hold the boost fine. The issue with the twins including the Efini's is the exhaust housing, it's very restrictive.
I just rebuilt the motor and since the car is in Ca. we stick just with the twins. If the car wasn't in Cali. it would be either a big single or triple rotor, we were evening thinking of going LS7 with cams etc but we like the rotary.