How much RWHP can a 6 speed tranny handle?
 

I am completing my build for a road race only miata. I purchased a 6 speed (non MSM) tranny and rebuilt it. I am planning on my car having 350 to 400 RWHP and after searching around it seems like the 6 speed tranny is questionable at those power levels. Should I sell my 6 speed (while it is still good) and get a 5 speed with Quaife gears? or is that a waist of money and run the speed? Thanks

Run the speed. Honestly, as far as the 6 speed, no one has a definitive number on them. 350-400 is the general consensus. I have seen one crap out as low as 280 (whp) btw. That being said, My car at 18psi handled a 5 speed. When you are at that power level, you should expect breakage. Although, I finally gave up on my saab 900 when I changed my 4th transmission in about a year an a half. God that was the worst trans set up.

Where are you and how much for the 6-speed if local?

run the six speed and pray to jebus

If you can be mechanically empathetic it can handle 400rwhpfor a while. Its really the ftlbs you need to worry about. I have 398/357. I finally blew 4th gear after 4 events :) My other lasted 4 also, but I didnt shred a gear,the syncros are just fugged to shit.

I am personally interested in the queef 5 speed sets myself.

Unless you have $3k for a Quaife box for $3500-4000 for a TKO600 setup the 6-speed is your only option.

I think the real question is how do you plan on making 400whp? Better have a good plan with good parts.

Fully built 1.9 liter with 3071 GTX turbo on E85 should be close to 400 whp. The problem is I cannot find any Quaife gear sets. Does any one know where I can find one as I have had no luck. What is the TKO600 set up and where can I find it? Thanks for your help with this!

AFAIK nobody's done the TKO swap yet. The basic breakdown:

Lakewood bellhousing: $650
TKO600R: $2100
resplined clutch disc & altered pilot bearing: $???
V8R framerails and crossmember: $~600
custom front diff mount: $??
custom driveshaft: ~$300-350

$4k into the car. The rest of the drivetrain will cost you $10-14k depending on your intended usage, so in the long run it isn't all that expensive - just hurts to shell it all out at once.

Are you just going to run the 6 speed and break it if it is a sure thing. Are you going with the six speed again or are you going to take on this project? I would be interested in doing this with you if you are going to engineer some of the parts. Thanks again!

What about a t5z? Should be able to handle the 400rwhp. Our local brake and clutch can make a clutch combo with whatever hub you like, so I'm sure you have the same locally.

http://www.jegs.com/i/G-Force-Transm...ductId=1343711

this with an adapter plate, maybe 3k total if someone stepped up to the plate. Could handle just as much as a TKO but for about the same without then need for a pricey bell housing or the rest of the drive line to be tampered with

T5z is just a WCT5 - only rated for 300wtq. And the gearing is crap - .63 5th is way, way, way too tall. The TKO600R's 2nd is too short (1.89) but 3-5 are the same as the 4-6 split in the OEM 6-speed.

I will have new clutch discs done for my 949 twindisc, or I'll have the current discs resplined (if that's even possible). I haven't gotten that far down the road.

I have absolutely no idea how you came to those conclusions. The G-Force box is $400 more expensive, still doesn't come with a bellhousing, and you still have to have a trans/diff mount made, respline the clutch disc(s), and have a custom driveshaft made. You cannot just have an adapter plate made, because neither Miata box came with a removable bellhousing. Unless you own a machine shop, get free materials, and value your time at $0/hr, there is absolutely no way you are putting a $2600 T5-based gearbox into a Miata for under $3k.

The easy way to do this is exactly what I said above - Lakewood bellhousing, TKO600, and everything else will be custom. The TKO600R box has a crap 2nd gear (1.89) so if I actually moved forward with this I would seriously look into having a custom 2nd gear made to drop that ratio down into the 1.59-1.65 range. I want the same 3-4-5-6 split as I have now, and the TKO600R box has the right 3-4-5 ratios to make that work.

Who's manifold and downpipe are you using? Who is building the motor? What ECU are you running? What manifold are you using?

I think it's 300 engine torque, not wheel, but I may be wrong. But the factor of safety has to be high...I know of a few of these that survive drag slick clutch dumps on 3600lb mustangs that make waaayyyy more than 300ftlbs. They don't last forever in that application but they don't grenade instantly either. I'm hoping in a lighter car and more forgiving torque curve, my T5z will survive. We'll see...but then the TKO's will swap in with a clutch disk swap and new driveshaft yolk...and maybe some hammering to the tunnel.

As far as gearing, I'm looking forward to the lower rpms of 5th. I'm even leaning towards the 3.42 GM rear, which will cut off 1000rpm at 75mph in 5th compared to what I have now. For the track guys who actually use/need 5th on the track, I can see that being a big issue.

T5 is 1.94, TKO is 1.9, and 5speed is 1.89? This is too short? I like my second with the 3.90 torsen. First is useless.

New T5z retails for 1370 but you can get them cheaper. Plus you need a bellhousing and all that other stuff. I see no way to do it under $3k.

I decided to use the mustang bellhousing, flywheel, starter, clutch, etc because I have none of the OEM equivalents anyway on my V6 build, but that route should also work on the BP. Would it be the cheapest or best idea? Probably not. Most of us already have fancy flywheels & pressure plates that work with the miata starter. There should be a way to adapt some bellhousing to the BP pattern and having a T5 (or TKO) splined clutch disk made. Then it's a matter of correctly spacing the flywheel if it's in the wrong place with respect to the trans input shaft. I have both the miata 5 speed and T5z/mustang bellhousing in solidworks, but don't have the miata flywheel modeled. I think I gave away my old flywheels so I can't model that. The T5's pilot bearing is in the crank, not the flywheel.

Why a lakewood bellhousing? For safety reasons?