Krazy the Face

I'm circle track racing my DX, which has a JDM D15B VTEC under the hood. I'm using the DX tranny from the old motor, and the gearing of it is perfectly wrong. I'm exiting the corner at about 55, which is a tick too fast to gain anything by downshifting into 2nd. And I'm entering the following corner at about 73, which is just getting into the meat of the power in 3rd (approx 5,100 rpm).

Since everything need remain stock (so no posts of MOAR BOOST! ;p), I thought a good pickup would be switching to the HF tranny. One of the front runners in a Civic I'm almost sure runs an HF trans. I never hear him shift on the on-board footage, and he pings the rev limiter just before he begins to brake for corner entry. That, to me, says HF. It would keep the revs up in the corner, keeping me from bogging down like I do, and would give the meat of the powerband all down the straights. Sounds good, yes?

But I can't find one. A few cursory checks all send me to Ebay, the cheapest of which was like $450 for a used, or well over a grand for new/refurbished. That's laughable. So short of looking in a junkyard and hoping (not easy when you live in the middle of nowhere), I'm feeling kind of pinched. So, some questions...

Does this sound like an option worth pursuing? Without the option to add go fast parts (stock only), would the HF gearing be the best bang for the buck?

If so, what should I reasonably expect the cost to be?

Also if so, would it make sense / be possible to get my hands on just the HF second gear from a parts store, and plop that in my DX tranny? It's a track only car, so not worried about gas mileage or drivability.

And just a random pose to the masses, are there any other upgrades you could think of to get a little more bang out of my 1.5L? Like I said, it must remain "stock", so changing heads, headers, air intake, all that is easily noticed by the scrutineers and would result in a DQ. If you have an ideas, it would need to be some old school backyard trickery.

jlicrx

probably not

with a stock HF transmission with 1.65 2nd gear and 2.954 final drive, running in second gear would result in ratio of 4.874:1 (1.65 x 2.954) - the stock DX transmission with 1.259 3rd gear and 3.888 final drive, running in third gear would result in ratio of 4.895:1 (1.259 x 3.888), which is basically the same as the HF running in second (about 1/2 if 1% difference) - the only way the HF transmission would make any sense would be with the DX final drive in it which would result in ratio of 6.415, running in second gear - about 30% lower gearing which would increase the rpm up to near the rev limiter

the problem with that solution is that in order to swap the HF 2nd gear into your DX transmission, you would also need to swap in the HF mainshaft since 2nd gear is a fixed part of the mainshaft, not a separate piece - the countershaft gear is separate, but not the mainshaft portion

another option would be to use the Si transmission running in 3rd with a ratio of 5.35:1

Krazy the Face

Thanks for the in-depth tech advice. So swapping "just the gear" is definitely out.

Also interesting on why the swap to HF won't work. You saved me tons of work and cash with that one.

So SI is the way to go? I remember seeing a chart somewhere where it showed max speeds in each of the gears for DX, HF, and SI. Can't find it for the life of me. I just need something that will red line at about 73-75mph, gear doesn't matter.

I guess back to the Googles...

alex14

thought about taller tires?

Krazy the Face

I have 13's on it now with 60 series rubber. 50 series is the limit on the low end, so I'd get very little gearing down by switching.

14's are the upper limit in rim size, and while there isn't an upper limit to the series, I don't know how much bigger I could go. I don't want some huge, floppy side wall that's gonna roll over in the corners, ya know? Even if I could possibly find a super stiff side wall, could I ever go up enough in series to get to 75mph in a DX in second gear?

ej1995

http://www.zealautowerks.com/transcalc.php


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