Are these " dyno numbers" or theoretical dyno numbers?

why do you do it in 2nd gear?

These are virtual dyno numbers only . I've found that if I use the exact same procedure everytime, the uncorrected numbers closely match what I see on a real dyno. I normally show it without correction but the above one is shown with dynojet correction ............just cuz it makes it look good and because it just happened to sqeeze it out to 500 :) .
I can edit any number I want into the gearing part . The 1.391 is actually for 3rd gear on a 5 speed gearbox , which is what I have. The other numbers match different ratios in my gearbox and other rx8 US and JDM 6 speed boxes . I just need to tick whichever one is correct for the log.

How do you like the 5 speed box compared to the 6 speed box? There have been discussions on the forum before between the two, however i want to say nearly all of them have been comparisons on N/A applications.

To me the 5 speed ratios feel better . Plus the 6 speed always felt like too many gears to me . They might make an NA car a bit quicker but it does nothing for a turbo.

The biggest difference is the 6 speed breaks.... and the 5 speed doesn't at that power level..

The 5 speed is much better suited for higher horsepower levels due to the longer gears. With 26" tires I shift at 40, 70, 100, 140 with the 5 speed. With the 6 speed the ratios were way too close.....Was one of the best changes I made...

I wish I could make the gearing even longer so I could make 1st and 2nd gear more usable on the street as the turbo doesn't have time spool up....

Follow up question! At what power level would you say it is worth upgrading?

Lets be honest the 5 speed is an upgrade. Overall more durable and also better suited for F/I.

I think it's worth it for just about any turbo ...just for the ratios.

I broke 2 6 speed right around 400hp. They were both on hard uphill pulls and weren't shock loading the transmission at all. Gear teeth just gave out from the torque

Out of curiosity, were they S1 or S2 6-speeds?

Both S1...

Yep, they give out under shock loading at NA power levels :tear: :tear: :tear: :tear: :tear:


it would be better to say the 5 spd is better suited to increased, broad torque output. In addition to the 5 speed you’d also be better served swapping in an FD 3.9 rear gear too. Lots of gears with short gaps and a short rear gear are to help NA engines with no torque that need to rev high. With a strong turbo setup you rely on torque to pull against taller gearing. Those are the differences between the RX8 and FD3 in design and intent.


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I really don't find any issues with the 4.44 . Not for a street car , and even on track I don't see the need for taller gearing.

Updated front page with my latest(and final?) design for the manifold as shown below.
NOTE : this design will spool the turbo really well but ONLY if the engine port timing favors the outer ports.

https://cimg5.ibsrv.net/gimg/www.rx8...4dd8f90dd7.png

How did you convince the fabricator to have another crack at it after the swear words he spent fitting the last manifold?

Good opportunity for you to try out a bigger WG and downpipe diameter.

Your design will be a neater version of what you suggested for me, pictured below. I obviously didn't see the benefits as I haven't done any internal exhaust porting for timing changes.
https://cimg2.ibsrv.net/gimg/www.rx8...c25f95a8c0.jpg

This is same design I've had since before you made yours ... only changes I've made were to make the balance pipes curve as shown to favor flow to the WG. But I doubt I'll go back to original fabricator as he.......... "never wants to see my manifold again" . Guys at HPR are really helpful so that's where I'll go from now on.

WG doesn't need to be any bigger than 38mm as it has such good priority. The Siamese was always more limiting than the WG . The balance tubes are there for two reasons.
1/To give Siamese gases somewhere to go when WG is closed
2/To supplement flow to WG when Siamese is overwhelmed.


Yep, my original design had poor spoolup as well....till I ported the outer ports . Gained over 1000rpm of spoolup from a relatively minor port timing mod.

I guess you love filling the tank up as often as possible then. And spinning the tires excessively in low gears. Plus you’re too chicken to rev it out in 5th gear :p:

That’s what torque is for. When I had a Z06 Corvette the only gears I used on the street were 2nd, 4th, and 6th. And it was a quick change from a dead stop to 6th and let it do all the work. 30+mpg on the highway too. Not sure what I was thinking going back to rotary :rofl:

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You are 100% on the money about reving it out in 5th - on public roads anyway ;) ....... Mileage ...do you really think a few hundred rpm is going to make much difference ? 1st gear is a little bit of a waste off the line ...... but I hardly ever go into boost in first anyway.

Yes, not just mileage but that droning sound drilling into the deepest core of your brain too.

But thanks for confirming and agreeing with me at the end. :)

the 5 spd RX8 had a 4.3 gear, but that’s for a pukey NA “little factory engine that can almost do it” to rev quickly. Which you don’t really need on a strongly boosted engine like yours unless racing on high grip tires. Even a 3.9 ratio is considered sort of a racing gear on V8 engines.

If it sounded that way It was an accident ! :lol:

Pic of the 1.06 turbine housing in place ...just to show that it does indeed fit nicely . I had to fit the spacer plus grind some of the housing to clear the manifold . Note the heat shield around the outside of the housing ...works really well!

https://cimg4.ibsrv.net/gimg/www.rx8...2c60b0f1ac.jpg

Compressor outlet is really squeezed in there ...but it all works !Blue hose in background is actually a sleeve for heat sheilding over top of the 76mm aluminium intake tube. That plus the heat shield over the manifold itself help (along with efficient IC) keep intake temps to within 1 degree of ambient when cruising.
https://cimg5.ibsrv.net/gimg/www.rx8...46d0520ee7.jpg

No wonder your manifold fabricator hates your car :lol:

you must have small hands :suspect:

This from the guy that thought he could make the mani. out of 2" ID pipe ! :suspect:

With an undersized IWG turbo though :p: and it was 2” OD T321 tube, not pipe. So not much bigger than 1.5” pipe on the outside, but more open on the inside.

also 4-port, so no APV assembly etc., I was going to check fitment on my 6-port car soon, maybe this weekend.

I did find a source for Sch 5 T321 pipe elbows though and might have gone with 1.5” (1.9” OD) instead.

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Enjoying this thread ...thanks all.
I am trying to get back into the rx8, but the lack of power ( for me) mandates a plan to accomplish that before I jump.
325 rwhp with a great torque curve and ability to survive a road course is my goal. This thread helps in understanding how to acceive this. Appreciate it.