Hey all, hoping to get a gut check from everyone here. Today for track days, I run a 200TW tire, in the southeast heat. I run 7psi on a 6258 (roughly 200whp) on a built motor (can post specs if matters). Have upgrade breaks etc. The car came with a 6 speed. I really dislike the 6 speed for track driving. Don't get me wrong, I have a lot of fun on track, but as a former sim racer, I miss the days of paddle shifting through a track and really being able to focus on my throttle control, braking/trail braking, and steering inputs. With shifting, there's an entirely new element, sometimes fun, sometimes not so fun. Specifically, my issue with the 6 speed is they put ******* reverse on the right side. What tends to happen is most of the day goes fine, then I will have a miss shift into 5th, then suddenly I'm constant misshifting into 5th for the rest of the day. This is because I can't take the smooth brain approach of jamming the stick all the way to the right and going up because of reverse on a 6 speed. I've gotten a better shifter, miata roadsters, and the issue is significantly better, but still happens. Worse yet, I live with the fear of a 4th to 3rd money shift b/c I'm trying to avoid pushing to far right for 5th. That being said, the only fixes I've come up with for this are:

• 3.6 Differential
• 5 speed trans
• 3.6 Diff + 5 speed

Here's the original, and other options from a gear ratio to speed standpoint. The fastest track I've driven at is Road Atlanta and I generally get up around 120 to 125 on the back straight. I just picked up the 3.6 rear end from Prestige and I'm really considering "downgrading" to a 5 speed. I'd like to get thoughts/feedback on why that should work or not. As I understand it 5 speeds, in particular NA 5 speeds are not nearly as robust, but at my current hp/tq level, I don't think that will be an issue but again wanted to get feedback. I have driven my friend's stock 5 speed+4.3 and there's half the shifts to be done and as a result, imo, more focus on the driving and fun is had.

For some reaosn imagines aren't uploading, so here's the raw dog text of the different setups. 3.6+5speed would save me a lot of shifts.

3.9 + 6 Speed @ 7200 (Stock Setup)
1st - 34.25 MPH
2nd - 55.8 MPH
3rd - 77.03 MPH
4th - 100.8 MPH
5th - 126.71 MPH
6th - 149.95 MPH

3.6+6speed @ 7200 RPM
1st - 37.1MPH
2nd - 60.5MPH
3rd - 83.44MPH
4th - 109.2 MPH
5th - 137.3 MPH

3.9 + 5 Speed @ 7200 RPM
1st - 40.4 MPH
2nd - 67.11 MPH
3rd - 95.05 MPH
4th - 126.71 MPH
5th - 155.66

3.6 + 5 Speed @ 7200 RPM
1st - 43.77 MPH
2nd - 72.7 MPH
3rd - 102.98 MPH
4th - 137.27 MPH
5th - 168.63 MPH

 

Imo there is two reasons people run 6 speeds in their track cars. One is they are supposedly stronger, which if you aren’t pumping 400ftlbs through it shouldn’t be an issue. The other and the reason my car runs a 6 speed is they are quicker on track, because you have more ability to keep the car in its peak rpm range.

having an extra gear within almost the same spread of speed gives you the advantage of more likely to have the ‘right’ gear to maximise your drive out of the corner.
Eg using a ridiculous hypothetical example to highlight the advantage, if you had two cars both with 200hp with a peak power between 5000 and 7000 rpm. One has a two speed gearbox and the other has an 8 speed gearbox. Almost every corner in the 2 speed you would be lugging the car out with it way out of its preferred 5000-7000 window, whereas the 8 speed car would almost always be in the window so would be significantly faster even though they have the same power.

Also having extra gears means the car doesn’t drop so far down in the rev range with each gear change so the car pulls harder in the next gear gaining time on a 5 speed car.
Ideally you run the shortest (numerically highest) diff ratio you can to reach your max speed (ie 125 in your case) and then you get to use 4-5-6 rather than 3-4-5.
the ratio spread between 4-5-6 is much less than 3-4-5 so the car stays within a better rpm range for acceleration.

if you are missing shifts then I would check your engine & diff mounts for slack. Fwiw my 240hp rotrex’d NB1 runs a (NB2) 6 speed with hybrid poly engine mounts and once I got a miataroadster shifter I don’t miss any shifts and don’t have any 5/6 change anxiety. And I spend 90% of laps in 4-5-6 (4.1 diff)

if however you just prefer the lesser number of shifts, then just do it. It’s your car and what makes it enjoyable for you is more important than what anyone else says. Just be aware you will probably be slower on track with a 5 speed vs a 6 speed. This may or not matter to you..

 

A NB 5spd in good shape will live well with the power you are making. If you have the money to spend, Walter Motorsports can build you a strengthened version.

Pairing a 5spd with a 3.9 or 3.6 at your power level is probably going to lead to a less-than-ideal gearing for most tracks. I would suggest looking into 4.1, 4.3, or 4.4 final drives to go with a 5spd. They are going to more similar to the 6spd/3.9, but slightly longer. They would be better suited for the tracks you're likely to be running in the SE. If you start adding significantly more power, then swapping to the 3.9 or 3.6 would make more sense.

 

It seems the commonly said things that a 5 speed is only good for about 250hp on the street, is there any concert that it wouldn't hold up at the 200hp I'm running in the track? Luckily they seem a heck of a lot cheaper than the 6 speed

 

The S1 Supermiatas ran 6spd x 3.9 @ 7200 rpm, 2300# / 220whp. Perfect gearing. The weakness was the aluminum shift forks expanding and binding when the box got hot. 75w140 Motul and/or a cooler took care of that.

 

Transmissions care more about torque than horsepower. 400 ft-lbs at 2850 RPM is only 200 hp, but it's way more likely to blow up the transmission than 200 ft-lbs at 5700 RPM making the same 200 hp. You can run a 5-speed on track for a long time in the 220-240 ft-lb range if you show "mechanical empathy" (don't shift it hard, don't do drag race launches, etc).

As for the shifting thing, the key is doing it right is to slow down your shifts and make it three deliberate motions instead of just trying to slam it across diagonally. Up <fraction of a second pause>, right, <fraction of a second pause>, up. IMHO this is a skill worth mastering, sequential/flappy paddle transmissions are likely to take a while to work their way down to the budget end of the club racing world.

My Miata doesn't go to the track any more, but I liked the 6-speed + 3.6 combo a lot. In terms of shift mph points it's actually very similar to the 5-speed + 4.3, except with an extra gear up top. 6-speed + 3.3 would have been even better except those were mythical.

--Ian

 

I saw an old video of yours about the S1s and putting an trans and oil cooler on them. Either I forgot or missed it, but I noticed you used the fill and drain plugs on both, but how did the system actually pump the fluid to the cooler?

 

Just to play devil's advocate, perfect for the track y'all ran? I run 6spd/3.9 in my GLTC car with a similar power (195-220whp depending on the dyno) and I find that it was not ideal at a few tracks I visited. Mostly because 5th @ 7500rpm wasn't quite enough and going to 6th was problematic because the following turns were 3rd gear turns.

A note to OP, I feel you on the 4-5 shift. I run a MR angled shifter as well. I've basically just learned that I have to "slow" that shift to get it right all the time. Because it is a race car only, I've been debating a 5spd with a shorter final. I've always enjoyed the feel of a 5spd as well. 4.3 final drives are common and still top out between 135-145mph depend on tire sizes and rev limit.

 

Sweet! It's not just me! Maybe some 6 speeds have some defects and or wear/tear that simply make them harder which is why it seems some people seem to be just fine with the nasty 5th gear shift and others are like you and I. I mean, I get through it, but sometimes it's a struggle and for an HPDE car, I want fun and safety. Feeling like I can't get into 5th easily b/c I can't go hard right to force it that way and then the correct for that is a possible built engine ending money shift into 3rd, just suhucks. I'm with all of your race bois on your time trial cars and S1s wanting perfection ratios for top speed! I did post to the Race Prep forum afterall!

 

I have been through my 6spd. I replaced all the syncro's and replaced some warn gears. So even in good shape, the 4-5 shift just has to be deliberate. Right now I'm having a debate between adding a cooler to keep the shift forks happy, or just rebuilding one of the 5spds I have sitting in the corner and swapping in a shorter final drive. I can always swap back to a 6spd down the road if I decide to turn up the power and run outside of GLTC.

 

Pump and tiny Setrab in the trunk. Can also be mounted under car.

 

Found a link to a pump for sale referred to in the video from @emilio700 :Ebay link

 

As has been said in other threads, though I’ll probably murder the exact wording with my lack of memory and my faux-folksy writing style, ya gotta know if heat is the problem before you try and solve your heat problem.

I’ve semi-solved my 4-5 shift issues on my six speed with my modified IRP shifter, but the exhaust for my K24 passes tightly under the trans and I wonder what that does for trans temps.

I’ve got some spare inputs on my ECU and dash, a spare GM coolant temp sensor, maybe even a spare Honda or Mazda one, and the ability to drill/tap a trans/diff drain bolt for a temp sensor.

Doing some simple math, a 3/8 NPT GM sensor needs a 0.578” tap drill, 18mm is 0.708, leaving 0.065” on either side, not accounting for thread depth… I think this is a bad idea, so maybe one of the 1/8” NPT sensors? This doesn’t even take into account the math of getting the sensor tip to clear the plug end so it can get valid measurements…

Looks like I need to place another order at Ballenger for a 1/8” sensor…

 

those particular pumps are really heavy. There are probably something lighter that will work. In our case, we never had to run the tiny fans. The air flowing across the cooler was enough just circulating the oil through. It was crazy, I would forget to turn the fans on, see 220° temps, turn the pump on and immediately would drop to like 160. We needed to put some tables into the MS3 so it ran automatically but we never got a roundtuit.

 

Before adding a cooler, ensure your transmission is completely shielded from the exhaust. Radiant heat is line-of-sight so if the transmission can "see" the exhaust pipe it is a problem. Stock exhausts are shielded from the transmission.

Before I went to the BMW transmission, I contemplated a pump and cooler. I had the idea of making a bracket to mount a power steering pump I already had near the tailshaft of the transmission. It would be serpentine belt driven off the driveshaft and spring tensioned. There's room for a small cooler between the trans and the passenger side of the tunnel. IDK how well it would work but it was an idea.

 

My turbo setup as an external wastegate. The piping for said wastegate was originally out the top of the hood for fun fire effects according to the guy I bought it from. I've since had a local (bad) exhaust shop custom make me a wastegate pipe in a bit of a rush and it was like you said, dumping right at the side of the transmission. It didn't occur to me until my most recent track day that I could be super heating my trans. Since I run very low boost for track days, and you stay on throttle for long periods of time, there's a ton of exhaust coming out of it and heating up the trans. Because I can't weld (taking classes starting in 2 weeks), I found one of the exhaust fix it kits at Autozone that had a 'flexible' metal tube. As a temporarily solution now the output of the wastegate points as left and down (away from the trans) as I can get the tube to be flexible. As a fun side effect, having it dump farther rearward makes the open pipe sounds way louder for the driver (also sometimes not so fun) when you are hammering on it.

 

Sounds horrendous to hear

 

Eh, not as bad as i made it sound. The pipe is only a 3/4 inch. Its loud, but not earth shattering.