Hey fellas! Looking at gear ratios for a road race only CRV k24 that's going in my CRX. Building to NASA st4 rules so i'll only be pushing an average hp of ~180. Still have yet to see a dyno of a k24a1 built to that power level, so i'm not exactly sure how MUCH gear spacing (or how little) would be ideal for the power band, but i'm currently debating between 2 options........ 2001-2005 CTR/ITR trans and a 02-04 RSX-S trans with M factory 2-6 gears. Things of note.... The M factory seems to have a better 3rd and 4th, with the rest being largely the same. I like Tight ratios with a longer FD (like the 02-04 4.3)... Less shifting while you're still in the meat of your power. The only problem is i'm not sure the M factory gears provide enough benefit over the ctr/itr trans to warrant another grand or two. CTR/ITR trans range from 1800 to 2000 on ebay. It'll probably be 3k+ to buy an rsx-s trans and get it rebuilt with full m factory gears.

Anyone run either of these trans for road course?? Also, are the CTR/ITR trans reliable for road course at these power levels? I'd rather not end up splurging for M factory gears 1-2 years later anyways cause the OEM trans doesn't last in enduro events.

 

this is a semi complicated subject... TrackRat/Dillion put out a "how to pick a final drive" and thats going to 100% apply here and can apply to what you are doing...

180hp is going to cap you to similar "speeds" of the Honda Challenge H2 guys in your region and at your local tracks... when you evaluate a trans setup you need to figure out what gear you will be in for the corners and the top speed you need.

These are all impacted by the wheel/tire size you are looking to run and the RPMs you intend to rev to (redline).

Assuming you dont want to rev past 7500 (because i wouldnt, especially with a 180hp cap) here are the two popular options with the popular tire diameters...

Setup 1:
Redline: 7500
Tire Size: 245/40/15
Trans: RSX Type 2 (with .78 ITR 6th gear)
Final Drive: 4.7
1st gear: 33.04 mph; 2nd gear: 50.66 mph; 3rd gear: 71.13 mph; 4th gear: 94.07 mph; 5th gear: 117.16 mph; 6th gear: 138.34 mph

Setup 2:
Redline: 7500
Tire Size: 255/40/17
Trans: RSX Type 2 (with .78 ITR 6th gear)
Final Drive: 5.1
1st gear: 33.54 mph; 2nd gear: 51.43 mph; 3rd gear: 72.21 mph; 4th gear: 95.51 mph; 5th gear: 118.95 mph; 6th gear: 140.45 mph

for the east coast... we are capping out in the low 130 mph range at most tracks... so IMHO, at your power range, the Setup 1 would be best (for me and the tracks i go to, a 4.9 FD with the setup 1 would actually be best).

Im pretty busy today but i can run better numbers at lunch if you can tell me your redline, intended tire size, max speed on your courses, and primary corner speeds.

 

really need to finish off my budget transmission series-- but shifting my focus to YouTube more so in the future. Not many people read anymore, sadly (though I think we've ascertained that given the state of the world today).

EJ2 Track Rat: Budget Transmission Part 2: How I Chose a Road Racing Final Drive

 

Same numbers with full ITR trans.

Setup 1:
Redline: 7500
Tire Size: 245/40/15
Trans: ITR
Final Drive: 4.7
1st gear: 33.04 mph; 2nd gear: 50.66 mph; 3rd gear: 71.13 mph; 4th gear: 89.03 mph; 5th gear: 111.01 mph; 6th gear: 138.34 mph

Setup 2:
Redline: 7500
Tire Size: 255/40/17
Trans: ITR
Final Drive: 5.1
1st gear: 33.54 mph; 2nd gear: 51.43 mph; 3rd gear: 72.21 mph; 4th gear: 90.39 mph; 5th gear: 112.71 mph; 6th gear: 140.45 mp

 

Thanks Kaan. I'll be running 245/40/15's. Also not sure where the engine will be redlining yet. I have to find an experienced engine builder in Norcal to see about how it could be possible to get a flat HP curve on this k24a1. Probably not possible, and 7500 is probably a realistic redline considering.

That being said, i had assumed that gear spacing should be based 100% on your power curve, while the FD should be selected to nearly top out at your fastest tracks. This makes me feel like a CTR/ITR trans would be the bare minimum. But thinking critically about the FD...... as long as my gear spacing is putting me at/near peak power 100% of the time, why not have a tall FD? Less shifting means more time spent going forward...... and a lower chance to be caught inbetween gears in some corners.

I just moved to Norcal so i have no idea what the tracks are like here yet, i've only run laguna so far in an accord. This CRX should be cornering much faster than the accord so its still not an apples comparison.

 

I just realized your article answered a bunch of the questions in my last post lol. Is anyone here familiar with the norcal tracks? Eventually i'd like to run the 25hr thunderhill course

 

IMHO gearing should never be based on the power curve... because you should have the best power curve possible at all times. period. you want the power and torque to come in ASAP... you want to flatten it out as early as you can... you want it to maintain power as long as the motor will rev to whatever RPM you have in mind. shorter gears and "higher" FD require you to have "less" power, but will be much better with more power.

for the sake of being simple... the FD will ensure you never fall out of Vtec if you redline each shift and will always make sure you are closer to vtec when you have to short shift. you need to graph it out and run your lines to check (i use zealworks and a custom spreadsheet... but the spreadsheet is a mechanical advantage math thing).

a FD will likely gain you (depending on which one you go with) 10% mechanical advantage in every gear... i did the math for Dublo and its 12.9% mechanical advantage going from a 4.7 to to a 5.4... less if you have to go to a 4.9... so the goal is to the "highest" FD that will allow you to reach the top speed needed with the shortest gearbox you are allowed by the rules.

I wheel to wheel... so "sometimes" i get caught in 2nd gear... but generally, racer, like TT folks... only need to worry about 3rd gear and above. I've found that if you get your gearing and FD to a point where you need to "float" the older (lower) gear you used to use, its better to "short shift" and try to carry speed in the next higher gear... this technique helps save me a shift and forces me to carry much more speed than i was used to.

 

for a time i was actually sitting on my 5th gear rev limiter for 500ish yards twice at our largest track. we bumped my rev limit a little and thats not a big deal anymore... BUT that alone didnt have a major impact on my lap times... accelerating down the straights take a lot more time than the 500 feet at the end of a straight and the FD and short gearing work that whole time.

the FDs limitation is your top speed, but the bonus is more acceleration through all the gears. its a balance... i also might be crazy because i'm the only one with a 5.1, everyone else is on a 4.9

 

Did you honestly notice a big difference drag racing the other h2 cars down the straights with the 5.1?

 

VIR has an up hill on the back straight... 100% yes.

VIR also has the uphill esses and I close the gap going up the esses like woah... it pulls like a freight train.

on flat ground it’s hard to tell a difference... but any slight elevation change and it’s easy to tell

 

Thanks again btw for crunching the numbers =-). To echo getting caught between gears.. I noticed at VIR with the 4.7 two places that I was in that position coming into oak tree its a 5-3 shift and entering rollercoaster its a 6-4 shift. Hopefully with a 5.4, that will allow for a 5-4 and 6-5 respectively. It should help save time with a single shift. Summit is similar with the chute, and T5, it would be a 5-4 and ride 4 it all the way through carousel, 3 is to much through there but 4th leaves me waiting a little.
I think the mechanical advantage for any car would be beneficial as long as you are not over your rpm/mph limit of gearing on the fastest point on the track.

 

Why would you leave texas and come here?????
Where are you in the nor cal? Dirty will be out tracking again soon, im closer to Laguna than other tracks but I do make those three hour trips to hit up buttonwillow and thunderhill.

 

So i guess i'll start with the ITR/CTR transmission and go from there... eventually selecting the FD based off the tracks i'll be running?

 

Hah, career changes brought me to SF! So far i've only run laguna out here. Was gonna try to swing buttonwillow this weekend but can't do it

 

you have pm.

 

I used the MFactory 3-6 in the Eibach ITR trans. Someone mentioned FD keeping you in VTEC when redlining. That is solely from the higher shift point, the FD ratio doesn't affect RPM drop. Unless you're going to have multiple transmissions for different tracks, select gear ratios based on your dyno graph and FD will be a compromise based on the tracks you'll be running. If you don't see a ratio that will work well for all of them, MTM can do a custom ratio for you. 1/2 don't really matter aside from standing starts. The main benefit of running the MFactory 1/2 along with the 3-6 is getting rid of the weak and wear-prone stock gears.

 

that FD/Vtec thing was me... now that i have charted it out you are right. but in charting it out, the FD will effect your mechanical advantage greater than a gear change (i used a GSR vs. a ITR/B16). Combining them is exponential. I think the butt dyno of the mechanical advantage might be fooling me.

when i use zealworks or the Mfactory gear mapping, the overlay will show the mechanical advantage of a gear set (gears and FD). both items in the gearset can impact top speed... you need to balance it all together. Id post pictures but i'm at work and dont have access to hosting.

Racing Honda Challenge i'm limited by rules... racing in general i'm limited by money also. Here is the example i use because i live it every race weekend... my competitors use the B16/ITR trans with a 4.9 and a .875 5th gear (b series kids... /sigh) to hit the speeds we need at the tracks we go to... thats a $500ish FD and a $350 5th gear. Charted out i can get the SAME mechanical advantage (and top speed) in 5th gear with a stock 5th gear and a 5.1... and i gain the extra mechanical advantage in gears 1-4. this is the balance... i got more performance for less money while breaking tradition.

also with breaking tradition... i dont believe you need to pick your gear ratios based on dyno chart. achieve the gears/FD balance with the best/steepest line on the charts... and fix your motor/dyno curve. EVERYONE should be shooting for early power/tq and flattens to the max as early as it can (within any rules). I'm fortunate that i have a very nice dyno curve (so good i'm afraid to go to a 3 inch exhaust from my 2.5). We dyno with each other around... one of my competitors saw my curve and decided he needed a refresh on his motor (it smoked like andrew dice clay anyway).

 

Can we get a bay area honda fan boy Lemons team going?

 

Im game, i know of other former honda challenge nor cal guys who might be interested.

 

Once I get the CRX build finished, I'll need some drivers for champ car

 

If you wish to use OEM gears, use EP3 or TSX mainshaft with TSX 3rd gear. Then 2012ish TSX 4th gear, along with an Accord 4th gear as fifth, and then an RSX-S sixth.

1st: 3.0625
2nd: 1.769
3rd: 1.355
4th: 1.073
5th: 0.872
6th: 0.738
Final: your preference.

If EP3 mainshaft (1st and 2nd) cannot be found, use something with a 1.88 second gear.

If an even tighter 5-6 is desired, you can use a 0.921 fifth along with the 0.78 type R sixth.