Twins: Building a better Manifold
 

I remember seeing this idea bumped around some time ago, and it's been bouncing around in my head since then.

Has anybody with the know-how and equipment ever contemplated making a "better" exhaust manifold for the twins? I know that this is a major chokepoint wrt exhaust flow, and I, for one, would happily pick up a newer/better version that gave less restriction/better flow. Heck, I might even think about a street port if I thought that it wouldn't go (largely) to waste considering I'm sticking with my twins...

There are a few reasons why no one will try to make a new manifold for the stock twins.

#1: The amount of R & D needed to design a new manifold would out weight the profit margin by 100:1 --- this is due to the fact that the Rx-7 is no longer even in production.

#2: On top of the fact that designing a manifold on a commercial scale would be extremely expensive, it would be a waste. These turbos have a historically short lifespan and always have issues somewhere along the line ( not that other turbos dont ) but these are not a "standard" type of turbo and very few people will even bother trying to rebuild these and warranty them due to their unreliability.

#3: Building off of point #2, why would a company build a custom manifold for such an unreliable turbo setup? They wouldn't, they would go for a more reliable, easier to rebuild, and more popular turbo setup than a setup that is 15 years old.

#4:These turbos in good working order kick ass, I love the sequential setup. The power in the low rpm's gives me a hard on. Mine were rebuilt 28,000 miles ago and already failed, so I am going single. <--- historically, probably over 75% of 7 owners have gone this route as well. Not because they dislike the sequential setup, but because they can get a single setup that is almost the same price (as a rebuilt pair or 99 spec pair) that makes more horsepower, is far less prone vacuum line related failure, oil seal failure etc, and it is much cheaper to rebuild / replace in the future.

#5: The internal waste gate setup on these cars would be a PITA to replicate

My point is... unless you are going to do a custom fabrication for your self --- there is not a large enough market for the stock twins ( or 7's in general ) for someone to make such a large investment.

going along with all his points:

by the time you do the research on WHERE the changes for efficiency sake would be at, you would find that you'd be better off not changing a damn thing or go single.

supposedly David Garfinkle is working on one (to be used with the BNRs) for low volume production, I don't think making a huge profit is really his goal :)

Trust me, a street port on stock twins with the stock manifold is entirely worth it. I made 340HP at 9psi on a dynapac. Fuel issues kept me from getting any more but the car is a completely different animal since going from stock ports to a large street port

I always wanted to design a system with a set of identical GT28r's, with a custom manifold and dual maybe 2.5" downpipes, in the stock configuration with the cold sides facing away from each other, and the turbo's staggered by a few inches to just make room for the downpipes.

Screw that! GO SINGLE!

You would have to think that mazda put more then enough R&D into designing the twin manifold & turbo setup before they came up with what they did. I think the biggest downfall in making a better setup would be room. its pretty tight in the engine bay so options are limited.
I agree with the above posts and just go single, port your motor and with a small to medium size turbo you wont notice much lag, you'll make more power and have way less stress on your cooling systems due to getting rid of the heavy heat retaining, flow restricting stock twins

there is interest. but, i don't think anyone's interested in doing the work.
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/ss-oe-replacement-exhaust-manifold-663329/

I think the old M2 GT28R-based stock replacement turbos made 385 rwhp sequentially on artguy's car. With a proper manifold, I'd bet they'd make 400 @ 15 psi, and have torque and spool-up for days. Run them with the upgrade solonoid system, and it would be HOT.

^ I'm currently running the BNR's (sequentially) and when I had them installed/tuned I made (US equivilant) 383 rwhp on stock ports at 16psi.

I know for a fact that a good pair of twins can crank out some solid power! It's just a matter of having one weak point in the system, the stock Manifold.

That's why I asked if anybody has ever pursued the idea of engineering an upgraded piece. I, for one, would happily pay for a Manifold that was new, and would flow significantly better than the stock one.

There are so many little things that need to/can be tweaked to run big power/high psi on twins that it's just a shame one of the major weak spots has never been addressed =(

yeah all this talk of a new manifold and twins and stuff make me want to stay rotary lol.. but i agree im suprised a aftermarket manifold was never made..

it cannot be that hard to fabricate a stainless steel or wondermetal manifold inside the dimensions of the old stopped up cast unit. i refuse to believe that the expertise and will to design and fabricate such a manifold does not exist inside the rotary community.

i'm currently looking for a set of <100k mi twins to convert to full nonsequential. I'd be more than happy to talk to the machine shops around here when i finally get them to see if something like that can't be built for a reasonable price. i think there are more enthusiast turbo cars on the road now than ever for us to snag turbos from. it's just a matter of finding some with specs that we can use.