Hey all. I was wondering what the consensus is on which transmission is a better fit for a K24 build used in track day / road racing application. The planned setup for the K24 are as follows:

Lightwieght rods
13.1:1 pistons
Buddy club or Blueprint MFG stage 2 camshafts
Street "stage 1" ported RBC IM
Street "stage 1" ported head
Hytech header and exhaust

Expected power output 280+whp

It will be pretty much like this setup, http://www.k20a.org/forum/showthread.php?t=52700, only with stage 2 camshafts instead of stage 3 and tuned on 93 octane instead of e85. However, the graph should be similiar, only with lower numbers. On the dyno graph with the RBC intake manifold, it seems like the "sweet spot" is ~5200 to 8000 RPM.

I started checking out gear ratios through a few calculators and these are my RPM drops using an 8000 RPM shift point:

Base RSX:
2nd 4605
3rd 5157
4th 6079
5th 6410
Top Speed 172.23

EP3:
2nd 4622
3rd 5481
4th 6079
5th 6410
Top Speed 158.67

US Type-S:
2nd 5217
3rd 5698
4th 6049
5th 6424
6th 6410
Top Speed 172.23

Seeing this, the base RSX and EP3 transmissions don't too bad considering they run around $500 used compared to the $1000 of a RSX Type-S transmission. The problem I see with both the 5sp transmissions is the potential for bog after the 1-2 shift, however I wonder if the torque output will be able to compensate and pull it forward. Obviously the EP3 transmisison with the higher FD will have a bit quicker acceleration. The advantage I see with the Type-S 6sp transmission is that it'll drop the engine to 5200 rpm at the 1-2 shift putting the motor at the start of the sweet spot.

So, thoughts, comments, experiences?

 

First: the 1-2 shift will be completely inconsequential for track use. You'll do that exactly once, when leaving pit lane.

Second: I don't have a ton of experience on track in a K-car, but what I do involved never using 2nd gear. That makes the 2-3 shift between the RSX base and EP3 inconsequential as well. With ~280whp, you'll just be lighting up the tires in 2nd, almost surely in 3rd, and maybe in 4th.

Third: Again with my limited experience, I think I'd save a little money on gearing and put the money towards a killer diff. Even with less power than what you're describing, the car will need it, and the stock ITR one is just sort of ok.

In general, your top speed on track will most likely never exceed 160, and that is even a bit high. You'll be limited by the length of the straights more than your top gear.

 

Thanks for the insight Stinkycheezmonky. I was thinking along the same lines based on my experiences on tracks as well. I think I'll stick with the base RSX tranny and use the money towards an MFactory clutch type LSD.

 

If your N/A or even spray I'd get the 6 speed tranny or pretty much anything under 350whp, and anything above that your really just gonna be spinnin through your gears and would want the longer 5 speed. I think your gonna have a nice setup and with a 6 speed you should be pretty happy!

 

6 speed the only way to go!

 

5sp 1
6sp 2
....interesting.....

 

6 speed. KAAZ LSD. Seat Time.

 

5 speed, Mfactory LSD = more seat time?

5sp = 1
6sp = 3

I should turn this into a poll, LOL.

 

you should be able to find 6speed transmissions for around $600-$700.

$500 is about max for a 5speed and $1000 is about max for a 6speed. But i have seen plenty of 6speeds go for $600 to $700.

My gut says go 6speed but it is something i have been trying to figure out which is "faster".

For me 6speed trans means i have to add 50lbs to my car, and would be shifting a BUNCH more (7500rpm rev limit). Add to that, every shift takes ~.2 seconds and i am not sure the better acceleration would out weigh the 50lbs and increased time lost spent shifting...

 

There is not a 50lb difference between a k-series 5-speed and 6-speed tranny.

OP, go with the 6-speed

 

I'm guessing Jimmy is (maybe) referring to a 50-lb penalty for the class he's racing in.

 

please read what i wrote.

For me 6speed trans means i have to add 50lbs to my car

That in no way shape or FORM says anything about there being a 50lbs difference between 5spd and 6spd.

What it does say is that if i go with the 6spd i have to add 50lbs to the car.

correct

 

That's the way I read it as well...

I don't know. I'm still a few months away from coming back from Afghanistan and lots of time away from completing my build so I have enough time to research and see other people's setups. I'm sure my friend is probably running out of garage space since I keep ordering parts and having them shipped to his place.

Maybe I can travel and go for a drive in someone's K24 6sp car to see what it feels like.

 

It'll feel awesome. But will it be best for track use, on a budget if you require one?

 

hi.

it def depends on the power (and especially tq) that you are making, plus your weight and tires. my car is a k20 EG hatch; it has a greddy turbo kit at 14psi, and i am running a USDM RSX 6 speed with 5.0 fd and type R lsd. my weight, with me in it is 2200 lbs. with 225 Hoosiers.

on the track, i never ever run it in any gear lower than 4th. when i leave the grid, i shift up to 4th (5th, 6th) and never use any gear lower than 4th. this would be on every track in the NE (summit, VIR, WGI, NJMP). it makes so much power and tq that even lugging it down to 3k rpm in 4th is more than any of the corners can take; 3rd gear just creates mad wheelspin.

i originally ran this car in H1, with the K20 (na of course) and the USDM 6 speed/5.0. it was perfect there. i really wish i had the 4.7 in it now; it would give me more top end (most every track i can hit the rev limiter in 6th at 8500 rpm).

i am pretty sure that my car would be just as fast with a 5 sp as it is with the 6 sp (maybe even quicker; less shifts?). it all depends on just how much tq and power you can actually make at the wheels with your super built na k24.......

good luck
todd
ReidSpeed

 

Todd Reid,
Thanks for the information and personal experience. What kind of power numbers are you putting down?

 

OP, To be honest, You will have a violent wake up call when you realize what it takes part wise to handle that amount of power in even a 2400-2500 lb car.

Provided the engine idea you have works for an extended period of time, the engine is going to be easiest part of that car. You should think of the car as a whole.
If you have the steel nuts to have a maximum speed of 160-165 at VIR, in a HPDE / Track Day situation, two things to think about.

1) If you don't have a proper brake, tire, suspension, and aero combination you are going to go flying off the top of the rollercoaster.
2) You should be amazed that your instructor is letting you do this.

What would be smarter here is instead of worrying about what transmission you are going to use, you should think about what else will you need on the car to even handle that speed (Again, brakes, tires, aero, suspension)

Transmission choice wont matter really, You can go with a 5spd or a 6spd, some tracks gearing choices will work out with one trans and not the other, and vice versa.

My own car is a 2.0L K integra, and I like my 6spd ITR trans alot, although it works in some places well (VIR) for my driving style, and some places (summit main) I think there are too many shift points for my driving style. Don't go off other peoples opinions, develop your own ideas on what works for YOU.

On another note: I've tuned a number of motors in the exact setup that you are describing. All of them were drag engines, K24's have insane piston speed. I would seriously rethink that engine set up from a piston speed standpoint and a compression standpoint in a road racing situation. 13.7:1 is too high for 93 octane on a race engine. Remember track day / race engines get major MAJOR abuse compared to 10-14 seconds at full load at a time like you would see in a drag race.

cliffs notes:
Don't think about just the motor, think about the car, and you.

 

sander,
Thank you for the concern but I've already thought about all of that. For my current setup, I'm running Wilwood 4 pots over 10.2" rotors, Toyo RA1's and TEIN FLEX coilovers, Mugen 26mm stabilizer bars front and rear. I'll probably continue to run R compound tires, but I'll probably change to S2000 calipers over 11" rotors and get a custom coilover setup. I also may install a roll cage, but it being primarily a street car, I may forgo that option and just go with a roll bar. Again, thanks for the concern, and for the assumption I'm a complete idiot. <what happened to the smileys?>

 

Yeah sounds like you have it totally covered.

 

Don't be. I really do appreciate the concern and that last comment was just sarcasm.

As for the engine configuration, I'm being told by two VERY competent and experienced builders that this is possible, and not only possible but street reliable. I was skeptical at first but from my understanding the key is the ability to tune VTC.

 

Not so much on the VTC, its overrated. Depending on the blueprint cams, you will only really get around 20 degrees max advance. Before P to V. They are very "street" reliable, but extended use on a track you may find that you have accelerated engine wear in a track situation at the rpm point that you are planning to shift at.

 

First, I'd like to identify a mistake on my behalf. The static compression ratio should be 13.1, NOT 13.7. I'll change the original post.

Only one of the setups is using these brand components, although the other setup from the other builder is near identical.

And if the concern is piston to valve contact, why couldn't valve reliefs get enlarged?

 

This is a design aspect of the cam, not so much the valve relief. If I recall correctly they make max around 15 degrees.

Piston to Valve is not the concern really interms of the longevity of the engine, it is the piston speed at 8000 rpm for 20-30 minutes at a time.

Independent of all of that, interms of your transmission choice question, If i had to pick one I would choose as Todd said a US 6spd, with a 4.7. But you may find that the 5spd is faster as Jimmy noted in regards to number of shifts.

 

Sander brings up a good point, one most people don't usally like to hear....

What you building is a pretty big monster... And can really destract you from learning the basics on the track.

The 8000 red line is pretty high for a 24... I don't know many 24s that rev that high for too long on a RR car.

If the is a once in a while HPDE toy I think you'd be fine with just limiting your rpms (7200 or so) and picking a gear and staying in it.

 

Thanks for the tips guys. I think for budget reasons I'm going to stick with an 5 speed tranny for now and use the money saved towards a LSD. I didn't think I'd be running NASCAR, so I don't think I'd be stuck at 8000 RPM for 20-30 minutes at a time. LOL. There is shifting involved after all. And besides, I could always decide to shift at a lower RPM and only use the extra range when needed, say to outrun on the straight.

You're right, people don't usually like to hear things like that, but I take criticism very well. However I also believe in keeping things in context. Yes the 8000 RPM redline may seem high, but are we talking about RR cars with K24s that are limited to OEM internals due to the series/class restrictions? That has ALOT to do with it IMHO.

I'm not a proffesional racer by any means, but I think I have a pretty good handle on the basics. I've got over 250 hours of track seat time. There is always room for improvement and somthing new to learn, but please don't consider me a noob due to my low forum post count. Yes I am trying to build a pretty big monster. Will it distract me, possibly. I know I was distracted the first few times after I went from a D15 replacement engine to my B16A from the sheer accelleration difference, but I quickly got back in the groove and improved my previous lap times by substantial amounts. I belive the same thing will happen here.

I was originally planning on building the engine myself, but being my first engine build and the cost of K series in general, I'm not confident in my abilities in that department. So I decided to outsource the engine build and tuning and focus on chassis setup. I don't want to mention the 2 builders I'm currently corresponding with because I don't want that to detract from the post, but rest assured they are well known to be excellent builders that can make things work that the common home builder can't.