is it possible or feasable to keep the stock primary turbo and exchange the secondary with a larger one?

whatcha think?

 

this will keep quick spoolup time plus give more upper end power if you have a tunable ECU , go for it for street use.

 

so people have actually done it with success...i was actually planning on getting flamed for my stupidity..
thanks

 

i don't believe that it would be feasible since the larger turbo can over pressurize/out flow the smaller turbo and slow it down and depending on the amount of force behind both(stock, uneven manifold design does not help this), and the characteristics of the larger turbo, may even cause it to stop or spin backwards. i think that this is the reason that it is necessary two turbos running in tandem be of the same size. if proper valving were in place to isolate the smaller turbo when the second larger turbo begins to go beyond the capabilities of the smaller unit, it would be worth it but complicated. a little bit different than the supercharged turbo configuration though. i may be wrong. anyone care to comment??

 

the air from the larger turbo should draw air out from the smaller one (ventura pump effect) if the manifold is configgured correctly.

 

i don't think that this would be the case. You will have pressure instead of the needed vacuum for this to work properly. Hope that made sense.


Didn't one of the cosmo's come with different sized turbos?

 

i have been in for a ride in one with both turbos hi-flowed to the same size and i didnt notice much difference over standard, it still had the standard ecu with the turbos staged in the original sequence.
the australian spec rx7s had different sized turbos, it apparently gives it a larger kick on the second turbo.

 

The 20B twin sequential Cosmo engine has two different turbos. One is a Hitachi HT12 like the RX-7 and the other one is a bigger HT15.

Is this worth doing on the RX-7? I don't think so. It would probably be hard to make it work very well, and you would be better off with bigger turbos in both spots. On heavily modded sequentail FDs, the primary runs out of steam before the transition anyway.

-Max