Transmission gearing questions

[Slither]

OK guys and gals, so after the cruise on Saturday I was picking Butch's brain on rear-end gear ratios and transmission options. He suggested the close ratio toploader with either 3.31 or 3.54 rear gears. I had been thinking that the wide ratio box with a 3.08 gear would be a better option, and here's why.

If you run the numbers with a gearing calculator (I used the SecondStrike version), it appears that first and second gear with the wide box and 3.08 rear would perform almost exactly the same as the close box with the 3.54 rear, i.e. the overall ratio (end to end) for first/second gears is 8.56/5.94 and 8.24/6.00 for the wide/3.08 and close/3.54 respectively (interestingly, first gear in the wide/3.08 combo, 8.56, is lower than first in the close/3.54 combo, 8.24!).

Next, if you look at third and forth, third in the wide/3.08 setup is identical to a close ratio box with the 3.31 gear set, while fourth is equivalent to the rear end ratio in each of the setups, since it is a one-to-one ratio in the tranny. This gives a little lower cruise rpm for the 3.08 over the 3.31, and even more difference in rpm over the 3.54 gear set.

The engines you all are running are more than capable of pulling in any of these combinations, as I witnessed (quite impressively) over this last weekend. I plan to run either the 408 Windsor or the 427FE engine, so no problem here with torque/power. The only issue I could see is that the split between second and third or third and fourth might be a bit tall for the wide box, but it doesn't seem that large from the numbers at 1.42 and 1,36 for the wide box versus 1.36 and 1.29 for the close box.

So is there any flaw in this logic? I realize that this is more of a clinical approach rather than the seat of the pants feel needed to really make a good choice. However, you can't just go and drive a bunch of Cobras of all different combinations to help you make a choice. Besides, it's the engineer in me that wants to see the numbers:rolleyes:.

Additionally, I found a potential replacement for my lost toploader, and I suspect it is for a small block application... price is right and right now I can't be choosey;). Let me know what you think. Is this too much of a compromise?

[Brent]

Quote:
"However, you can't just go and drive a bunch of Cobras of all different combinations to help you make a choice. Besides, it's the engineer in me that wants to see the numbers."

If you can't drive every Cobra with every combination then you should listen to someone that has driven every Cobra with every combination.

It would be even better if that person had not only driven every Cobra with every combination but also built transmissions and rear ends every day for a living.

Butch Capps!

As far as cars go, in the battle of clinical vs. experience I would always lean toward experience.

[chris knueven]

paul,

i will second the comment brent made.....listen to mr. capps.....

chris

brent...if you see this i am sending you a p.m.........gots a question for ya...

[brfutbrian]

paul, butch`s advise is right on ( it always is). imo, if youre going to run posi go with the 3.54, if youre going with an open rear the 3.31 would give you a little better traction with only half the rubber having power put to it. any higher ratio than that, youll never see anything near the top end of that combo cause the front end will have too much high speed lift before you get there (unless you have a death wish). i went with the 3.31/ posi / cr trans and wish i had gone with the 3.54 instead. later, freakin`brian

[Slither]

Right, great answers, but to the wrong question;). Butch has a world of experience... thats why I was discussing it with him. I just could not tap into all of that experience in such a short period of time. In our discussion, we did not have time to cover all of the subtleties and nuances of different combinations. He did not say this was a bad combo (maybe he was just being polite). As you know, he is a busy man and I don't want to keep bothering him (maybe every once in a while;)). And collectively, you all have good experience, as well.

I asked David Kee about it and he said it is a great combo, and that there is a 428FE/wide ratio topoader car there in San Antonio that is delightful to drive:D.

Rick mentioned trying a 3.54, so I wonder why, and if a 3.54 with effectively a taller 3rd and 4th would be advantageous or not... pros and cons.

Chris, I thought you said you have a 5-speed??? - which I understand is a wide ratio box. What rear gearing, and would you rather have something different, and why?

Brent, you mentioned doing a taller rear gear if you were to do it ever again... so...?

Thanks!

[juanone]

Paul:

When are you getting your car? Have you ordered it already? I know you wrote me some e-mail middle of last year during my build and I got the impression you already had ordered yours.

What did you finally decide to order from Unique? When will you be driving it?

Juan

[Justin Upchurch]

Paul,

My car has a TKO 600 w/ .64 OD and 3.54 axle ratio. If you go with the small block I do not think I would go taller than a 3:54. A BB car, maybe the 3:31. Both Chris and I have a 5 speed trans, and if you are going to be on the highway that may be the best way to go.

Justin

[eliminator]

David Kee as far as I know has never owned a Cobra in his life time.....

He is a Drag Racer and not a Road Race Man..........

He gave me the same advice about the wide ratio TL 5 years ago.

For the 427 with the torque and cubes the close ratio in my opinion is the ticket, on the road the 3:31 with the Auburn Unit works well, I would like to have a 3:54 in it for one day for comparision. I may still do that one day, cant advise because I havnt been there.

In Juan's car, 302. 355 HP, open rear end, 3:54 with close ratio top loader, I love it. Don't know how it could be better!

Many variables here, and a lot of opinions, just like clothes and pick-up trucks, personal preference rules.

[chris knueven]

paul....

you are making this waayyyyyy more complicated than it needs to be....
only 2 questions need answered...
1- how much freeway running will you honestly do ??
2- what rpm can you live with going down the freeway ??
not much freeway..go with a toploader...
are you honestly going to climb in the cobra and do 700 plus miles like i
did on wed and sunday ?? if so then go for the overdrive(.64).

as for gear spreads....who cares ??? you are talking about a 2400lb car
with most guys running 400+ ftlbs of torque. the drop off between gears
is not a issue. ask brent how much mine drops off from the first(3.27)
to second (2.20?) shift..not enough to even notice.

as for diff ratios,
3.54+bfg 295/50/15 is identical to
3.73+quick time 295/50/15
the hoosiers are roughly 2" taller.

i have driven a unique with a 408/tremec/3.31 posi,does it pull hard ??
yep...does it pull as hard as mine...nope. is it a great driving car ??
yes. all the combos will work great...just be honest about what you
intend to do with it....

chris

[Brent]

I had a chance to ride with Chris and the only problem with his car is it misses ALL THE TIME.

OOOHHHHHH wait, that was the rev limiter. (-:

Way too much fun!!!!!!!!!!!!!!!!!!!!

[Naumoff]

Paul,
I am running 427FE with CLose ratio Toploader 295/50/15 3.31 posi.
Right now with 4000 miles I wish I had a shorter gear. An all around gear of 3.54 but I am leaning toward a 3.77.
I am driving to Carlise tomorrow and will know if I like the combo I have on a 200 mile oneway Highway trip.
Around my back road area I wind up leaving it in 3rd at 50mph. It could be me I just would like more gear.

Maybe a 3.31 with a TKO600/.81

[Master]

Paul, I run a 3:54/1 toploader 428 and love the combination. Intense acceleration and good topend. I picked this combination with the help of Butch Capps. This setup will run 140mph est. (I have only had it to 120) and it scares the crap out of you, I don't want more topend just the ride up to that. My two cents:D

[Slither]

Juan: I have a car on order and had planned to get it this summer... before the storm put a wrench in my gears:o. I really don't know when it will come to fruition. However, I remain hopeful against the odds:rolleyes:.

[juanone]

Hope you get it soon, you will not regret it.

Juan

[scott h]

don't forget to determine your motors rpm needs. my small block needs to run around 3500 rpm any less and it loads up and starts running like sh**.i didn't consider this when i chose the tremec 5-speed ,now i can't use 5th gear unless i'm going in the mid eighties or faster. now my only choice is a rear end gear change or a cam change

[Slither]

Justin:

While it is not the exact same thing, I was considering the stroked Windsor to be effectively a big block, since it has similar displacement and performance characteristics... so it seems it would be a wash between the two (fire-breathing big blocks not withstanding;)).

[Slither]

Thanks for the clarification Rick. Let me ask you this. Just for discussion sake, what if you could have your close/3.31 setup with fourth gear a shade taller... say .93... how would that change your opinion of drivability or would it not make a difference?

Anyone else that has this combination could comment, too.

[Justin Upchurch]

Scott h

What are the specs on your motor?

Chris,

At what RPM do you shift your car into 5th gear?

Justin

[scott h]

i have a dutton perf. 351 W. comp cam part #35-250-4, edelbrock perf headsvictor jr intake with holley hp 650 CFM. engine dyno'd at 410 HP at 5800 rpm and 371 torque, at 3800 rpm's its 243 hp and 335 torque. when shifting into 5th rpms drop to around 2500 at about 75mph. these are ball park figures since i have not used 5th since last fall. its raining right now so i cant go driving but i think i need to make a couple of runs to get some accurate numbers. i was not aware of all the different factors involved when i picked my set-up

[chris knueven]

justin,

most of the time it is around 3200-3500,about 70-80 on the interstate.
i put about 100 miles on it last nite terrorizing:) the local populace
and never used 5th. 1st thru 4th are great gears for around town and
fifth is for the interstate.

scott...

by chance do you have 3.31 gears ???? a change to 3.54/3.73 makes a pretty
good difference. going from 3.54 to 3.73 with a 88" circumfrence tire brought
my rpms up just enough to get me out of the lumpiness of my cam. i actually
wish i had put 3.91's in the diff,but i had already bought my auburn pro(you
change carriers from 3.73 to 3.91). one other thing to try is to bring the
front jets down a size or two. you can then increase the secondary jets to
compensate to keep your a/f good. since low throttle/low rpm generally
is the primary side of the carb you might be able to keep it from loading up...

also i see you are running a hp series carb. i have a 950hp and i found that
the idle air bleeds were to small in mine. what this causes is when you adjust
your idle mixture screws you will have a very limited adjustment range. i
would go from really lean to blubbering rich on my carb in less than a 1/8
of a turn. really hard to set it with that amount of travel........

but i beg of you...please read the tech articles on holleys site about air
bleeds and how they function before changing anything......you can get in
trouble really quick....

chris
p.s.-i pulled your cam card up,it is a fairly hot cam but you should be able to
clean up the running problem with some carb tuning....

[Naumoff]

I just made a nice trip to Carlisle. 160 miles one way. Lots of Highway driving. I kept it under 70 on the way up. On the way back I was running 80 at 3500rpm with the toplaoder close ratio and 3:31.

She was just cruising at that RPM. And I don't need to risk getting another ticket.
I still think I would prefer 3.54 or 3.77 for all around street use. I don't do much highway and my engine likes 2800rpm or better.
I wore earplugs for the long trip. I have Tendenitice(sp?) in my right ear and the cold wind slapping on my ear will make it sore after a while.
Not being able to hear the exhaust so much I was able to pay attention to the pull of the engine as I hit the gas as compared to the lumpyness of the cam with no earplugs. The engine pulled smooth and steady under light acceleration.
On another note when I was leaving Carlisle through the fairground and on my drive today. If I am trying to creep real slow I have to constantly push my clutch in and out so I can keep the speed down. The engine idle is set at 900rpm as the engine builder recommends.This is really annoying and a shorter gear would be nicer for that.

[scott h]

"tinnitis", ringing of the ears

[Slither]

paul....

you are making this waayyyyyy more complicated than it needs to be....
only 2 questions need to be answered...
1- how much freeway running will you honestly do ??
2- what rpm can you live with going down the freeway ??
not much freeway..go with a toploader...
are you honestly going to climb in the cobra and do 700 plus miles like i
did on wed and sunday ?? if so then go for the overdrive(.64).

as for gear spreads....who cares ??? you are talking about a 2400lb car
with most guys running 400+ ftlbs of torque. the drop off between gears
is not a issue. ask brent how much mine drops off from the first(3.27)
to second (2.20?) shift..not enough to even notice.

chris

This is the kind of info I was hoping to get from the gang. I suspected that gear split did not make much of a diference in these cars. I imagine that most guys could literally melt the tires off of them in the first three gears... pretty much at will.

I drive a whole lot... that said, I don't think I would be intimidated by a 350 mile (one-way) trip in a Cobra, but 700 miles might be a different story:rolleyes:, yet...?





as for diff ratios,
3.54+bfg 295/50/15 is identical to
3.73+quick time 295/50/15
the hoosiers are roughly 2" taller.

i have driven a unique with a 408/tremec/3.31 posi,does it pull hard ??
yep...does it pull as hard as mine...nope. is it a great driving car ??
yes. all the combos will work great...just be honest about what you
intend to do with it....

chris


Yep, but all 408's are not created equal... don't know about the one you drove, but I doubt it was anything near what you are runnin' in yours:D, so I believe in your observation.

I can see that it is a compromise regardless of choice. If a close ratio toploader with a .68 overdrive were available then it would be a no-brainer... that and a 3.54 or 3.77 gear set would be the ticket. (And yes guys, I know that there are 5-speed racing trannies available for gobs of cash:(.)

You did not mention what gear set you have...

[Slither]

Chris, Brent, and anyone else that might know:

For the Windsor project, I got the Comp Cams #35-426-8 cam, which has a 2200-6200 rpm operating range for use with the stock displacement.

I am under the impression that stroking the engine out to 408 will move that power band down in the rpm range. I am curious as to how much you would expect that shift to be based on greater than 16% increase in displacement?

Thanks!

[Brent]

I do not think it will lower the powerband in direct relation to the percentage of displacement increased.
I figure it will lower the powerband 7.3285636352%
Or about 491.235858236 rpm

If you run a SW tach you will never know it anyway.

[chris knueven]

brent,

you'll just have to get very good at tapping the glass on the tach
like i do.....:)

chris

shifting at the miss :)

[Slither]

:p!!!!!!!!!!!!!

[Justin Upchurch]

Paul,

When in doubt always go with a larger cam............. :) If the tac isn't accurate just set your MSD limiter as your shift point.

Justin

[chris knueven]

justin,

see,one weekend around me and i have already corrupted ya.......

i have been reading up on some combos,i think your motor ought to
be in the 400's somewhere,maybe even around 450 rwhp. just dont be
afraid to rpm it......

chris