RotorMotor

iTrader: (5)

ok i wanted to know a few things about the 280hp twins. if i remember correctly the only difference between the older turbos and the 280hp ones is the abraidable seal on the compressor side. does anyone know if there is anything else that they changed?? such as blade pitch, or anything else like that?

its my understanding that there is some sort of coating sprayed on to the compressor side and the wheel is ground into that seal to make a perfect fit. if this is true what happens when you get some shaft play? woundnt that shave some of that seal off and shoot it into the intake tract? im wondering if there is a way for us to do something similar to the intake side to increase efficiancy (spray something on there and slowly spin the wheel into it.

basically i had a spare set of twins which took a crap (from a project car), and ive torn them apart to learn more about them. im polishing the compressor housings, and when its time to rebuild my twins ill swap the polished ones on (just for fun)... but i was wondering if there was anything else i could do to them to increase efficiancy (such as smoothing out the sand castings inside of the exhaustm and intake side, or smoothing out some of the bends (for better flow)...

-heath

areXseven

iTrader: (1)

Physical appearance: The Jspec 99s should have bolts (four I think) and retainers securing the Compressor Housing onto the Bearing Housing. Unlike the pre-99 255HP Hitachi's, which are secured by a big Snap-Ring. Otherwise they are built on the same mechanical principal and function, but for the abraidable seal as you already stated.

RotorMotor

iTrader: (5)

am i correct that there is only an abraidable seal on the compressor side? has anyone (besides BNR) messed with a set of twins and had improved results? im talking about something that doesnt require a lathe....

RX7SpiritR

iTrader: (1)

yes, only difference is the abradable seal, and it flows more. I don't think anyone has messed with the stock twins. The BNR turbos are the stock 93-98 turbos, not 99 specs because it doesn't matter since they are rebuilding them all over. But other than BNR messin with the stockers I don't think any other company has yet, M2 might have I don't remember though. But 99' specs are an upgrade by itself but for the price you pay for them you might as well get the BNR's.

RotorMotor

iTrader: (5)

so theres nothing i can do on my own to make them flow any beter? polishing the sand casting wont help much? i wonder if i can make my own abraidable seal...... hmmm

r0t0r-rooter

The primary is slightly smaller in diameter (from what I remember reading).
Part of the whole "better flow" is from the efini y-pipe.

RotorMotor

iTrader: (5)

the primary is not slightly smaller.... they are both ht-12 turbos.

RotorMotor

iTrader: (5)

ok well here is a picture of the 99 spec abradable seals.... im assuming this is some sort of soft plastic, rubber, or teflon material that is sprayed on.


now i have a few questions that hopefully someone can answer.

1. what is stopping me from doing something similar? all that would be needed is to find something that will stick to the housings easily, and then grind in the wheels to make a better seal.

2. what happens when 99 spec turbos develop shaft play?? doesnt this seal get chewed up and shot through the intake tract?

3. how can you make more HP with just the 99 turbos? either way your restriction is the ecu and the maximum boost it can handle... and our stock turbos dont have a problem pumping out that pressure. maybe you can reduce lag a little, but i cant see how you can get more HP with just those turbos and the stock ecu... as the ecu is the restriction... the turbos we currently have can be pushed further than the ECU can handle. with an aftermarket ecu, maybe we have a slightly different story? is the efficiancy range higher for the abradable seal turbos?

Hamza734

Heath,

There's info on RX7.com about the 99-spec twins. You can also read the SAE paper written by Jack Yamaguchi on Rob Robbinnette's site.

http://robrobinette.com/sae_article.htm

Hamza734

For those to lazy to click:

"The turbocharger, two of which are used in the sequential setup, is a new Hitachi instrument with an abradable compressor sealing and an "ultra-high-flow" turbine design. The abradable compressor housing sealing has been in U.S. markets, Toyota being the first to use it in the MR-2 sports car, some years ago. It was one of the more promising items in the menu the Mazda's rotary engine designers had prepared a few years ago to get more power out of the 13B-REW, but, according to Yamamoto, the company was in a dire financial state, and the design team could not dare ask for the expensive turbocharger. The Toyota unit had plastic layer hot-sprayed onto the housing's surface, a methodology hardly suitable for large scale production, therefore costly.

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.

The latest trend in high-performance turbo technology is a "diagonal flow" turbine. Mazda asked Hitachi to come up with several candidates of this design, hoping it would boost the engine's output. They did not quite match the rotating piston engine's unique characteristics. Back to the tube, as it were, to research basic flow dynamics. The fruit of the toil is the "ultra-high-flow" turbine, with its blade length extended and its shapeless acutely curved, enlarging gas passage and reducing flow resistance. Turbo response in the low speed zone has been greatly improved. The turbocharger adopts a smaller diameter turbine, 50 mm (1.9 in.) now versus the previous unit's 51 mm (2.0 in.), again reducing inertia mass. The new "ultra-high-flow" turbine realizes about a 10% gain in efficiency, according to Mazda's turbo engineer. The twin ultra-high-flow turbochargers supply a maximum boost of 74.7 kPa (10.8 psi) at 6500 rpm to the previous high-flow instruments' 62.7 kPa (9.1 psi) at the same rpm."

RotorMotor

iTrader: (5)

so what im hearing is that the increase in efficiancy is only slightly due to the abradable seal... the rest is due to the new wheels. sounds like its not going to be worth it to screw with trying to add seals, so i will just plan on a rebuild, and possibly some ceramic coating if im sending a bunch of other parts out at the same time for ceramic.