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Posted by: ahdoman Jan 21 2007, 11:06 PM

Is there a way to re-gear 5th so that it acts more like an overdrive? On the freeway at 75 the RPM's are around 3500 and with the Bursch exhaust it is quite loud in the car. Anybody ever done this?

Posted by: Aaron Cox Jan 21 2007, 11:09 PM

witha 4 banger.... you dont want to go any taller.....

any fewer RPM's and it will overheat..... rpm's turn the fan... which in turn cool the motor...

3200 rpm seems to be the magic number..... wont cool well below that under load...

Posted by: Twystd1 Jan 21 2007, 11:15 PM

Put a quieter muffler on the car...

Your gearing is correct right out of the box.

C

Posted by: Aaron Cox Jan 21 2007, 11:19 PM

fifth is already pretty dang tall....

as tall as i would go with a 4... or even a 6.

factory 6's were geared SHORTER to keep em cool... and get em into the RPM they were designed to cruise at....


Attached image(s)

Posted by: nebreitling Jan 21 2007, 11:26 PM

aaron and co. are correct, but to answer your question, yes -- there are taller gears available. the v8 guys use them for cruising. ill-advised for your /4, even if you drive really really fast.

Posted by: Aaron Cox Jan 21 2007, 11:30 PM

technically NO. there are no taller ratios...

you have to FLIP or reverse the ratio of 4 speed second gears.. such as flipping an H, HA or HB....

Posted by: PRS914-6 Jan 22 2007, 12:01 AM

Yep, I took an "I" gear and flipped in for 5th

Posted by: Mueller Jan 22 2007, 12:16 AM

QUOTE(ahdoman @ Jan 21 2007, 09:06 PM)

Posted by: ClayPerrine Jan 22 2007, 08:03 AM

If you are on stock 165SR15 tires, then no, you don't want to change the 5th gear. If you are on shorter tires, like 195/50-15 or 205/50/15 tires, then you might want to think about changing 5th. The RPM you turn on the freeway is directly related to both tire size and engine gearing. If you mess with the tire size, you can get back to a lower RPM by changing 5th.


It is an involved process to change 5th, as you have to disassemble the whole gear stack. But if you do it right, it is worth it.

Posted by: Eric_Shea Jan 22 2007, 10:42 AM

Posted by: Aaron Cox Jan 22 2007, 10:44 AM

i do

thats my chart up there....
i have a shortgeared box with a big gap to ZD fifth for cruising....

Posted by: smontanaro Jan 23 2007, 07:52 PM

Can the drive ratio of the fan be increased so the fan spins at the same speed at lower RPMs (/6 or /4)?

Skip

Posted by: Aaron Cox Jan 23 2007, 08:52 PM

on a /4 its crank driven... use shorter gears or shorter tires to spin it faster....

im sure you can get overdrive pulleys for a six

Posted by: Eric_Shea Jan 23 2007, 09:10 PM

I'm in the thought process here for my GT clone.

Tranny's are Urdu to me. I have Greg Dondero's close ratio short box. I was thinking I would probably never see 5th at a track with that so 5th could actually be set for best mileage (cooling as well, but I do have a front cooler) at 75-80mph.


Would a -4 5th gear work?

From looking at that chart a ZA would be right at the edge of my powerband.

Posted by: brant Jan 23 2007, 09:51 PM

eric,

if your going to bother opening that box....
then don't make 5th into a highway gear
instead make it into a useable race gear.

you likely won't be using 1st gear very often on the track anyways
so don't cripple yourself and turn your car into a 3 speed.
at a minimum make 5th useable so that you at least have a useable 4 speed.

its really really nice... trust me.


brant (using all 5 speeds on the track F/J/O/S/V)

Posted by: McMark Jan 23 2007, 10:01 PM

I'm with Mueller, 205/50s really raise the cruising RPM. How about a set of 'cruizer' wheels and tires? Probably quite a bit cheaper than tranny work.

Posted by: SGB Jan 23 2007, 10:28 PM

I was thinking about a flipped 908 2nd gear ("I" ratio, I think), but it was too much gonna be some large $ b/c a new mainshaft is also required. Instead, I think my next tires may be mismatched. Maybe 205/55 in back and 205/50 or 195/55 in front. Hmmmmm.

Posted by: Aaron Cox Jan 23 2007, 11:18 PM

correct - you cannot change 5 speed's 2nd gear due to the gear being part of the mainshaft.... (F, GA)... you need a splined 904 shaft... OR you can CUT the second gear off and try to have one welded on (talk to brant or foley)