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Old 04-01-2009, 01:47 AM   #1
HamFist
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Default No BS. 4.60 final drive mod--tiny tires! Predictions?

This is going to be fun. I picked up some 15x7 aluminum rims that clear my RS brakes. The idea is to put about a small diameter tire on it to give it close to a 4.70:1 final drive. 4500-6k is my torquey sweet spot on the top end. In trying to get my gears "strung" just right, I need to plan my shifts near the distance marks. I'll be in 5th well before the 1,000 foot mark, hopefully.

Car:
4.11 gear, .78 5th gear, 22in tall tire (soon.), about 200hp/tq in 3000lbs.

(Edited) Situation:
4th gear will travel from 60-80mph right across the 8th mile. Entry rpm to 5th will be about 5300rpm @ 86mph from 4th. That's right in the "meat" of my powerband on the top end. The shift point is likely between the 1/8th mile (660) and 770ft.

That's some serious torque to pull 23mph in 500rpm. It sounds too ambitious at this power level, to be honest.

22in tires should still make 5th gear fly by pretty quickly. I'm going to drop right into the meat of my powerband at the 1/8th mile into 5th. Top speed drops to 120 on these tires. It doesn't have enough power to trap at 120mph. From the 8th mile, scrabbling into 5th, that's 40mph to cover in 1 gear. No, I'm not that optimistic . However, what's going to happen for that last 660ft with a cracked out 4.60 final drive?

How does 4th-5th feel in a 4.44 geared STi on the top end? That is the closest thing comparable. An Sti with 16s or something is going to be kinda close. Where do you guys hit 4th and 5th with and without mods? I should be in the end of 4th by the 1/8th mile and will have a long pull ahead of me in 5th gear with about 5-700rpm to use. An 80ish mph head start is going to be important.
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Last edited by HamFist; 04-01-2009 at 09:57 PM.
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Old 04-01-2009, 01:53 AM   #2
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Your going to need to shift real real real fast...

Usually more power + less shifts = faster

Less power + more shifts = slower

MOST of the time - taking advantage of your gearing would mean being ridiculously fast at shifting..

For perspective - my 01 gsxr 1000 - with clutch consistent 7.0 1/8 mile - yea I suck at launching (you try launching 178whp and 560lbs!!)

same bike same track NO clutch consistent 6.85-6.9.. nearly same 60ft time between runs (yea 1.90 60ft time - vs decent rider on stock 600 running 1.5 60ft times - I suck!)

GL love to see the results

-Jerod
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Old 04-01-2009, 01:58 AM   #3
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I dig ya. I still think 1st gear is going to be absolutely useless. It won't even hit 20mph with this steep of a gear. 2nd gear looks like the ideal launch and should hit about 35mph out of the hole. 1-2-3 are 1000rpm drops in rpm per shift. Its 500rpm drop in each gear from 3-4-5.

This is going to be a hell of a highly strung ride, but what do you think it'll do? 13s look doable now with no boost...
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Old 04-01-2009, 02:03 AM   #4
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With perfect traction on a cool day.... 200 whp or fhp?

To be honest I don't know - your gear ratio's will help but my 185whp H22 civic could only click off 9.2 1/8 mile runs.. Given I had no traction till the end of 2nd - but my car also weighs in at an astonishing 2420lbs with me in it and full tank of gas....

My gear ratio's aren't that good but better than most...

Just as a wild guess somewhere around 13.9-14.4 with a perfect run


-Jerod
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Old 04-01-2009, 02:34 AM   #5
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200chp. It will have a crappy 60ft launching in 2nd. I'm easy on launches to not break it. Hondas use tiny tires to get around those looooong gears at the cost of traction. This should grab and go much like an STi 6spd. Even a 16in rim and 24in tall tire seem too big and heavy for this lower power level. I'm dropping almost 20lbs of rotating mass and allowing the car to spin up much faster. It doesn't need a big wide tire to hook up. It needs a smaller tire and wheel to reduce drag at higher speeds.

How long is an STi in 5th before needing 6th? Do they shift 4-5 at the 1/8th mile, too? Maybe that's a better question to ask.
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Old 04-01-2009, 03:15 AM   #6
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Oh, beautiful! You guys will like this spreadsheet calculator for gear rpm and mph.

http://www.car-videos.net/tools/spee...B1=Recalculate

Basically, I'll see 60-80 in 4th like I do in 3rd right now. @ 5500 in 4th, it's doing 80. Dropping 500rpm to 5000rpm in 5th gear means another 30mph with that 500rpm. That just sounds really difficult . I'll definitely be in 5th by the end of the 1/8th. What a smoking 1/8th mile that's going to be .

5500rpm shift points play out like this:

1_____60ft___2__220ft__3__330ft___4___660ft___5___ _
24.6 41.3 60.2 80.1 111.7

It's literally going to be:
*Launch*
20mph
SHIFT 2
40mph
SHIFT 3
60mph
SHIFT 4
80mph
SHIFT 5
ride it until the end of 5th.

I AM going to be shifting like hell .

Last edited by HamFist; 04-01-2009 at 03:32 AM.
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Old 04-01-2009, 04:04 AM   #7
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sounds like run, might try skipping a gear to see if that helps. Something 1st to 3rd you can always play around
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Old 04-01-2009, 05:14 AM   #8
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April fools joke?

Where do you plan on finding a 205/40/15 tire?

Hoosier makes a 225/45/15 which is 23 in diameter and so does hankook in the ventus... http://www.tirerack.com/tires/Compar...=1&RunFlat=All

I think that is really as narrow as you'll want to go otherwise you're going to downgrade your 60 ft times with wheelspin.

Last edited by FunkRider; 04-01-2009 at 05:24 AM.
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Old 04-01-2009, 05:29 AM   #9
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Subscribed i want to see how this works out...
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Old 04-01-2009, 06:26 AM   #10
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I have something similar in my civic 205/45/15 with 4.71 gears... but unlike you I could rev to 9,500 rpm so... there's the difference.

This would be like launching a 4 X 4 truck on 4 LO... it feels fast (because all the torque multiplication done by the gearing) but since the gears are so short and they don't last at all (lack of rpms) it ends up being slower.
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Old 04-01-2009, 06:38 AM   #11
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5th is still going to be a dog
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Old 04-01-2009, 08:45 AM   #12
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Drive a Forester XT with 225/45-17's on it, that will put you pretty close.

Basically boils down to shift, shift, shift,shift It's really nice gearing/powerband for auto-x/rally-x
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Old 04-01-2009, 11:47 AM   #13
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[quote=FunkRider;26174133]April fools joke?QUOTE]

Really...

I appreciate your enthusiasm, and understand the gearing angle a bit but I HIGHLY doubt that you will hit anyhwere near 80mph in the 1/8 with your NA 2.5 (You haven't moved to death valley have you?).

And again, I doubt that you will get close to the 13's here at ~6000ft ASL.

What is your best time in the car before tinkering with the gearing? (IBhigh16s) - some gears aren't going to magically drop 3+ seconds off your ET. If fact they may hurt you (as stated above).

Not trying to rain on your parade, but it just seems unlikely. Go try it and post the results
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Old 04-01-2009, 12:53 PM   #14
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Hai gaiz. Wheel sea how it goes wif teh upgradez lulz. Glad 2C t3h inturest in mah creatives. U can plai 2!

Fif geer will surely be a "dog" but not like stock. The idea is to pick up acceleration by cropping the top speed. I think the gears might drop me into the 14's up here. Wheel sea!
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Old 04-01-2009, 02:34 PM   #15
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on 215/50-16 (diameter = I'm too lazy right now ) with 4.44 on about 300whp/280tq I broke the tires free snatching 4th...

I was spending all day shifting when getting on it but it was always pulling hard.
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Old 04-01-2009, 02:48 PM   #16
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That short shifting will be very interesting. My friend had a mustang with 4.10s then went to 4.30s and actually was slower in the 1320. Had the same 60' and drove the hell out of it but was slower. Dont you think you'll have traction problems in 1st?
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Old 04-01-2009, 06:21 PM   #17
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Shaved 195/50-15s it is . The effective size becomes a 195/45-15 as far as some of the calculators are concerned. That plugs in a 22in tire height. Effective FD for me now becomes about 4.60:1.

Notes:

-Cutting about 25mph off of the top end to gain more acceleration.
-Each gear is going to lose about 10mph.
-2nd gear launching looks very doable.
-60-80 is going to be insane in 4th. 5-6k in 4th gear is already a killer and I'm getting to a faster 4th gear sooner.

It should be "a faster 4th with a less slow 5th.


Last edited by HamFist; 04-01-2009 at 08:49 PM.
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Old 04-01-2009, 07:46 PM   #18
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Quote:
Originally Posted by Homemade WRX View Post
on 215/50-16 (diameter = I'm too lazy right now ) with 4.44 on about 300whp/280tq I broke the tires free snatching 4th...

I was spending all day shifting when getting on it but it was always pulling hard.
iirc those are pretty close to 225/45/17s

edit: nvm they are about a half inch smaller diameter, I was thinking of the 205/55/16s.

Last edited by Trevor723; 04-01-2009 at 07:52 PM.
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