Samoht's 1996 Mazda RX-7 Type RS

[Random]

20B swap!

[thesameguy]

I feel that something like a GT3071R would be a great option on an FD with no or very modest HP goals. That unit delivers very good response even on relatively small (eg, 2.0l) motors while being capable of big HP - up to 500 - and still being suitable for ~300 or so. Again, I know nothing about turbos on 13Bs, but I've driven Saabs with this turbo and it's very good - little to no lag and a big punch. The weight loss of a single turbo is worthwhile, but it sure seems like a single exhaust path through a properly sized single turbo would inherently yield more power. These types of turbos didn't exist in the '90s hence the sequential approach, but I believe if Mazda did it again today, it'd be a single turbo all the way.

[samoht]

Here's a dyno graph for a standard sequential twin FD. The blue line is torque:

see how it's virtually the same at all revs? That, I think, is what makes it easy to measure out the torque at corner exit, and easy to feather the throttle when the tail starts to rotate, because the relation between your right foot and torque at the rear wheels doesn't change as you increase speed away from the apex.

I honestly don't know how a good modern single would compare, except I don't think it would manage to hit peak torque quite so low down, so would be a bit worse in that regard.

[thesameguy]

You'd be surprised what a modern turbo can do. Modern turbo technology is light years beyond what they in the '90s - which is why they are suddenly so in vogue. Lag and responsiveness aren't really huge considerations for folks with modern power goals. My Solstice made 1bar at 1800rpm out of 2.0 - less flow and less RPM than a 13b for sure. That dyno shows peak boost at about 2800rpm - I don't know what peak boost is, but probably around 1bar. I don't think that is even somewhat ambitious for your engine.

[Godson]

I know the Turbo'd E36 guys are running 20+ PSI and making strong NA like boost with a GT35R...and 600whp.

[neanderthal]

The MotoIQ RX7 is a sexy sexy LS3 powered beast. So much want.

[KillerB]

Peak boost on a factory Series 6 (93-95) FD is 10psi.

V8 swapped RX-7s can die in a fire.

[Kchrpm]

No LS7 should ever die in a fire.

[thesameguy]

Peak boost on a factory Series 6 (93-95) FD is 10psi.

V8 swapped RX-7s can die in a fire.

Seriously??? They did sequential turbos for 10psi? Nutso. With that info, I wouldn't even consider rebuilding that setup - there is definitely performance up for grabs here.

[KillerB]

FWIW it can't be compared 1:1 with piston engines. You can't run as close to stoich on rotaries.

I think the later non-US cars ran more like 12psi.