AutoXdriver

OK I know this is a bit off the wall but just wondering if anyone's ever attempted it. I like the RX-7 TT philosophy of sequential turbos: one small quick spooling turbo for the low end and a big one for huge horsepower at the upper ranges. Would be a great way to get rid of turbo lag. I guess I could always rip out the turbo & bolt on a SC ;-)

Don't take this too seriously I don't have the ***** or wallet to actually undertake such a project, just curious if anyone else has.

SamGrant951

Ive heard Porsche may have attempted it, but quickly realized the project wasnt worth it. Protomotive Engineering (build 700+ hp 911 turbo's) once claimed they were going to build one and sell a installed kit. Never happened. Im sure they quickly realized too much $$$$ for a twin turboed 4 cyl.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

P-NUT

I do remember seeing a listing on Autotrader about a year ago for a red "twin turbo" 944, I believe the price was something outrageous like 40,000 and I didn't look into it any further. Does anyone else recall this add?

superjet.1

im shure AMAF would sell you his twin turbo 924s for 40000

Olli Snellman

Sam is right.Factory planned first to make a twin turbo 944.They tried it and found out it too expensive to build.It was also too complicated and difference to single turbo was not so impressive.

Olli
'88 951

kasturbo

Mikef, I do remember that add. I tried to contact that guy for a week just to find out if it really was a twin turbo and to see how it came about. No one would ever return my calls.

Twinspool

The RX-7 has a pretty wide rev-range and the sequential twin turbos do help expand useable power. With a car like ours that is running out of breath around 6000-6500 rpm, the benefits of a TT setup are dubious. Look at the MkIV Supra guys, those cars come with sequential turbos and many of them switch to single turbos or run the stock turbos in parallel instead of sequential.

Has anyone figured out why the torque curve on the 951 dives so hard? The head flows well for an 8 valve but undoubtedly would flow better if it were a 16... opinions?

Twinspool

Oh yeah, just to clarify...

Many people think the turbos in the Supra and RX-7 are different sizes.
[quote] one small quick spooling turbo for the low end and a big one for huge horsepower at the upper ranges. <hr></blockquote>

They are the same size. By using a really slick but somewhat complex wastegate system, all the exhaust is pushed through one turbo until a specific rpm and then the exhaust is gradually used to push both turbos up to speed.

rage2

[quote]Originally posted by Twinspool:
<strong>Look at the MkIV Supra guys, those cars come with sequential turbos and many of them switch to single turbos</strong><hr></blockquote>

As far as I know, the reason for the switch to a single turbo is because it's simpler so there's less energy loss for driving the turbos. The powerband for those cars are so narrow that any lag assosiated with a sequential twin turbo setup would affect top end power because the turbo just doesn't have the energy to completely spool up. I thought my lag was bad (4000rpm full boost), my friend's single turbo Supra (800rwhp) doesn't even begin to make boost until 3500rpm, full boost at a bit past 4500rpm.

[quote]Originally posted by Twinspool:
<strong>Has anyone figured out why the torque curve on the 951 dives so hard? The head flows well for an 8 valve but undoubtedly would flow better if it were a 16... opinions?</strong><hr></blockquote>

It's because the stock K26 runs out of steam a bit past 4800rpm. Boost starts to drop, along with torque.

Mledbetter

[quote]Originally posted by AutoXdriver:
<strong>OK I know this is a bit off the wall but just wondering if anyone's ever attempted it. I like the RX-7 TT philosophy of sequential turbos: one small quick spooling turbo for the low end and a big one for huge horsepower at the upper ranges. Would be a great way to get rid of turbo lag. I guess I could always rip out the turbo & bolt on a SC ;-)

Don't take this too seriously I don't have the ***** or wallet to actually undertake such a project, just curious if anyone else has.</strong><hr></blockquote>

I'll throw my 2 cents in on this subject.

I love cars that are different. I had a twincharged Mr2 for a few years. Supercharged and Turbocharged. Stock supercharger to scoot across the intersection and a built hi-flow turbo for top-end. It was a complete money-pit project, but was a lot of fun.

I currently have a 93 rx-7 with all the normal bolt-on mods. Its a mid 12 second street-tire car and, knock on wood, pretty reliable. Zero lag and a strong top-end as well. Not as fast as a single turbo supra (or rx-7) in the 1/4.

I just picked up the 951 about 3 months ago and I've managed to increase the performance a bit. Replaced the bad factory wastegate with the unit from Lindsey, replaced the bypass valve (leaking), and installed a manual boost controller to up the boost a bit. It already had a set of chips and it seems to be a good daily-driver. On the highway, it pulls rather well... off the line it is REALLY depressing. Considering most of my driving is in the city, the power curve below 4500 is my biggest concern.

I think you could put together a twin turbo kit for less than 5 or 6k *if* you can do some of the work yourself and tune the engine management system youself. Probably tune it for a reliable 300hp with very little lag. The potential for 400+ hp is there with a lot more money building the motor.

I doubt its something I'll try, but its fun to talk about.

-Matt

toddk911

Turbo lag???? NO2 will get rid of it. Just a small shot in low rpms. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

guardsred951S

I think the add for the 944 Twin Turbo had something to do with twin INTAKES on the turbo. Don't know how but it would have been neat to see. I heard this from someone who actually talked to the guy selling the care for $40K

SamGrant951

[quote] Don't know how but it would have been neat to see. <hr></blockquote>
At 40 grand..Im sure he still has it
Look him up...

Nico

Somebody allready came up with this idea, but if you can't live with the lag, then buy the REGULAR 924 and supercharge it with the nitrous! Some 200hp nozzles or so... :-)
Just a little over 300hp woudn't even be much out of that old VW engine. Didn't the factory take 375hp out of it in some racing model???

alengyel

from what I understand is, most of the RX-7 owners who modified them started by changing the compressor setup to be in parallel. By doing this they could remove the very complex waste gates and vacuum spaghetti that made if function. Everything I read suggested that there was a very little increase in lag. It makes sense that two half size turbos will spool faster than one large one by the reduction in the moment of inertia. I have thought if trying this but completely lack the funds. One thing I do intend to try is a pre turbo cat, keep the exhaust expanded until after spoolup. <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />