Looking for ideal 5spd for my cobra

[robbiecanuck]

I'm pretty new to the forum, so please forgive me if I'm repeating a past thread. I'm in the research stage of purchasing a Cobra kit or turn key minus. I've narrowed the engine builders down to a reasonable list. Most recommend a Tremec 3550 or TKO product, but some have also suggested a Richmond Gear or g-force product as well.

I plan to build an IRS equipped car with likely a bored/stroked 351w. Likely displacement will be in the 392-427 ci range, and HP probably with be in the 430-530 range. I realize torque is the real question here, but I don't have figures off the top of my head. I might go for an FE as well, but with price being an unfortunate reality, I've more likely to look at something based on the Windsor.

Most of my driving will be cruising, but I may spend a bit of time at the strip or the track (small component mileage wise though)

I am price sensitive, but I will spend an extra grand or so if it will save myself money down the road. Any thougts will be appreciated

[iwantacobra427]

You want to play around with this site

http://www.368s.com/tools_rpm.phtml

to get an idea how rear tire size, differential ratio, gear ratio etc... effect engine speed. What rpm range does your cam "work in"? You probably want to ask your engine builder what cruising rpm your engine will like. You don't want to be lugging the engine...

It took me a long time to decide on a TKO 600 with 0.64 OD.. Still not sure I made the right choice

[Tommy T]

Don't know where you are located, I've got a Tremec 3550 and 351 crate ready to come out of my car in a month or two. Works fine on the road, but has a big hole between 4th and 5th. On a long straight (with a 3.73 rear) I'm either close to redline in 4th, or a breadtruck in 5th. Replacing with a 600 RR version when I change the motor. Probably change the rear end gear too.

[jwd]

Here's another site for figuring rear end and transmission ratios. It talks about the split between gears and what to shoot for and what to avoid. The 600TKO with the .82 5th gear seems to be the one to go with. There was a previous thread about the TKO with the .64 and those with it were complaining that it was too high and bogged the motor under 70-80 mph. Some have changed from that one to the .82 and were very happy with the results.

www.secondstrike.com/Technical/GearCalc.asp

[newBDR]

I'm playing in the lower end of the ci/hp scale (302/<300hp), but I just want to attest to the gaping whole between 4th and 5th thing. I have a t-5 with the tall 5th gear and have to get around to swapping it for a .82 or changing the rear. If I go with a taller rear it'll make 1st, 2nd more usable, but I'll pretty much be making a 4-sp out of my t-5. 5th'll be more usless than it is now.

[eschaider]

Use the .82 fifth gear unit and you won't be writing any of those posts about draggin' the motor down in fifth. I have a TKO 600 with a .82 fifth gear and it is real nice to drive.

[PDUB]

Originally Posted by eschaider

Use the .82 fifth gear unit and you won't be writing any of those posts about draggin' the motor down in fifth. I have a TKO 600 with a .82 fifth gear and it is real nice to drive.

What rear gearing are you using?

[427SnakeSC]

http://www.368s.com/tools_rpm.phtml
That is a great site! Thanks! With the CR toploader and a 3.54 final drive, and a .82 4th gear, I get a top end of 163 mph and 2,200 rpm at 60 mph. Works for me!

[Anthony]

Originally Posted by robbiecanuck

Looking for ideal 5spd for my cobra

It's like saying you're looking for the ideal woman. Different for different people, and some may not even want a woman at all.

All tremecs are wide ratio trannies ( some wider than others) with overdrives, and are likely not as durable as the Richmond, and then the G-Force, in that order, which both are close ratio trannies (or are probably most often ordered that way).

They all will be fine for the street. For racing purposes, the close ratio trannies will probably have an edge for performance and durability.

[Jack Zupan]

I have a TKOII with a 0.82 final drive and the 5th gear is great on the highway. There is no big hole as discussed with the 0.64 5th. If I have a gripe it's that first is geared too low to be very useful with the 3.73:1 rear I have in my car.

Jack Z.

[Streetwize]

With a big torque 400+ inch stroker small block, there's no reason you shouldn't use a wider ratio trans like a Tremec, close ratio trannies do best behind high-winding (relatively peaky and narrow powerband) smallblocks. A tight ratio behind a big torque motor is IMO, a waste and really dimishes the fun. In a car as light as a Cobra, big torque and moderate gearing is the best recipie for a true '427' experience.

A well set-up 500lb/ft, 500hp 410-427 stroker with 3.50 gears will easily pull a .68 ratio 5th gear (2.38 final) at ~2100rpm at 70mph and your roll-on power in any gear will be nothing short of phenominal, mine twists up (to 6500) from any gear and any speed effortlessly. The trick to setting up the motor for a broad powerband is to put a lot of stroke, ~10:1, very good flowing heads and induction with only a moderately (mid 230's to low 240's @.050) hot cam. Perfect streetability, nice lope with decent 12-13" vaccuum 900rpm idle, and wall-to-wall torque at any rpm.

[PatBuckley]

IMO - a TKO600 with the .82 5th gear and a 3.31 or 3.54 rear gear....first and 5th become useable.....