Transmission Choice

Al G · #1 (**permalink**) 03-09-2010, 05:49 PM

I'm working on the build sheet for the Cobra I hope to have built this year and need some help with the transmission selection. So far I have talked with several dealers and builders. Some say get a 4-speed toploader for authenticity and others say get a 5-speed Tremec for drivability. Others say with proper rear gear ratio the 4-speed can be just as drivable. I'm looking for opinions of owners who have experience with either choice.

The engine will be a 427 in the 550 hp range.

Thanks for your comments.

SMOKNAC · #2 (**permalink**) 03-09-2010, 06:03 PM

I run a 428 in the 510 hp range and run a 5-speed Tremec. (Superformance)
Works good for me. In 5th, going 60 I'm turning 2000 rpm.

bobcowan · #3 (**permalink**) 03-09-2010, 06:50 PM

When's the last time you saw a new car with a 4 speed in it? Why do you think that is? Heck, even a Harley doesn't have a 4 speed any more. And you know how far behind they are.

Unless you're building an exact replica of an original car, use a 5 speed.

patrickt · #4 (**permalink**) 03-09-2010, 07:21 PM

Go with the TKO600, spend a couple of hours reviewing the many, many threads that discuss the .64 versus the .82 fifth gear, and then spend another couple of hours learning about the need for a spacer with the long input shaft, or switching out to the short input shaft, the dangers of jamming your shaft in to the crank, correctly angling your drive shaft, what bellhousing you want, your clutch and flywheel set up, u-joints....

FUNFER2 · #5 (**permalink**) 03-09-2010, 07:25 PM

You have a pm.

ratsnst1 · #6 (**permalink**) 03-09-2010, 09:39 PM

Quote:

Originally Posted by Al G

I'm working on the build sheet for the Cobra I hope to have built this year and need some help with the transmission selection. So far I have talked with several dealers and builders. Some say get a 4-speed toploader for authenticity and others say get a 5-speed Tremec for drivability. Others say with proper rear gear ratio the 4-speed can be just as drivable. I'm looking for opinions of owners who have experience with either choice.

The engine will be a 427 in the 550 hp range.

Thanks for your comments.

The guys that told you to run the 4 speed will be the ones that drive by you on the free way at 75 mph at 2300 rpm laffing at you, while your doing the same but at 3000 rpm.The 5 speed is the way you want to go, but if you want to be original then what ever floats your boat, but either way have fun in your new build.

undy · #7 (**permalink**) 03-10-2010, 03:55 AM

Stay away from the Tremec TR3550 5 speed as it's a little "weak" for your application.

vector1 · #8 (**permalink**) 03-10-2010, 04:55 AM

good advice from patrick. find somebody's to ride in and have them not use 5th, see how you like it.

joyridin' · #9 (**permalink**) 03-10-2010, 05:09 AM

I used to have a 4 speed in my car. It sounded awesome cruising down the highway at 3200 RPM. Motor singing away...for about 45 minutes. When I stopped, my head was pounding and I was half deaf.

I put in a 6 speed. Now it cruises at 2100 RPM. I can drive it for hours and although it doesn't sound as "cool", I don't need to wear earplugs. Wanna look stupid? Drive a Cobra with earplugs. EVERYBODY laughs at you!!!

olddog · #10 (**permalink**) 03-10-2010, 06:41 AM

For a mostly raced car 4 speed - why because every now and then when going for 3rd gear I hit half way between 3rd and 5th. I haven't done it in a long while. Maybe I got better, but it still is in my mind.

For a mostly street car 5 speed - an hour of 3000 rpm and loud pipes is just no fun.

Get a TKO - 600 with the .82 5th gear. If you want a .64 then get a 6 speed. The step from 1.0 4th to .64 5th sucks. I know. I have one. 5th gear is useless unless I'm on a interstate, as the cam does not like 1500 rpm.

patrickt · #11 (**permalink**) 03-10-2010, 08:16 AM

Al G. -- The fifth gear issue on a TKO is a perfect example of why you can not take a blanket statement on any aspect of your Cobra build and rely on it as the gospel truth. You have to research the issue until you are at the point where you can tell yourself "I understand this issue, I understand how the variables that are involved will comparatively impact the outcome, and I can now figure out the answer that best suits me all by myself." To help you along (even though we all know that one-time posters 99.999% of the time will never get a Cobra), here is the decision tree for deciding between a .64 and .82 TKO.

If you are going to be doing any serious racing at speeds above the redline speed of your fourth gear then you must choose the .82 transmission. For most of the folks around here, that's roughly 125-135 mph. Otherwise, you must ask your engine builder "What is the lowest RPM that my cam will comfortably drive on the highway without hiccupping?" Take that RPM value, along with your rear end ratio, and your tire size, and using an RPM calculator available on the web, calculate the resulting speed with the .64 ratio fifth gear. If that value is equal to or less than the customary highway cruising speed that you expect to be driving, then the .64 gear is a viable option for you. Otherwise, you must go with the .82 gear.

As an example, I have 15" wheels, a 3.54 rear, and my cam is comfortable on the highway at 2000RPM. Using the .64 fifth gear, that calculates out to 68MPH. In my neck of the woods, the far right lane on the major highways moves along at 70MPH and state troopers will be passing you on the left. Thus, for me and my build, the .64 gear was the right choice (and my first four gears will still take me to 140MPH). The .82 fifth gear would be the wrong choice for me.

Al, I'm not going to rag on you, but you really have to strap on your thinking cap when your spec'ing your Cobra. Don't rely on what we tell you other than to use it to understand the issue itself -- then you have to figure out the answer. After all, we're not going to be driving your car.

(But Mr. Mustang will buy it from you for a song after you spec it wrong and put it up for sale on Cobra Country.)

Wbulk · #12 (**permalink**) 03-10-2010, 08:50 AM

That's really good accurate advise. Understand the issue to the point you can debate it.

patrickt · #13 (**permalink**) 03-10-2010, 09:03 AM

Quote:

Originally Posted by Wbulk

That's really good accurate advise.

Yep, I keep telling RodKnock and ERAChas how great I am, but they just don't seem to listen.

Al G · #14 (**permalink**) 03-10-2010, 09:45 AM

Thanks for all the great comments and advice. That's what I'm looking for. I realize I have a lot of thinking and research to do. Ultimately the decision will be mine and I'll to live with it. Your comments are helping to identify what's important and causing me to think about some things that didn't originally come to mind. I know the answers I got from dealers and builders were somewhat biased toward their typical package and what they're comfortable with.

blykins · #15 (**permalink**) 03-10-2010, 09:52 AM

I'm comfortable with about all of it.

I'm also an engine builder, so I know what parts jive together and which parts won't get along well.

If you want to talk, just give me a yell. I'll give you some input. I sell this stuff everyday.

Have your head, intake, and cam specs, along with your rear gear ratio and tire size that you plan to run. We'll get her nailed down.

Austin_Snake · #16 (**permalink**) 03-10-2010, 10:07 AM

Quote:

Originally Posted by joyridin'

Wanna look stupid? Drive a Cobra with earplugs. EVERYBODY laughs at you!!!

At least you will be able to hear them laugh.
Richard

RodKnock · #17 (**permalink**) 03-10-2010, 10:28 AM

Quote:

Originally Posted by patrickt

Yep, I keep telling RodKnock and ERAChas how great I am, but they just don't seem to listen.

I can only think of one person greater than Patrick and by shear coincidence he made the local sports news this morning too...

http://abclocal.go.com/kgo/story?sec...all&id=7322005

RodKnock · #18 (**permalink**) 03-10-2010, 10:31 AM

In today's world, I have no idea why you would not want a 5-speed. The authenticity argument is amusing to me. Consider the newest Richmond 5-speed tranny too.

Z-linkCobra · #19 (**permalink**) 03-10-2010, 11:34 AM

I think a good question is, do yo live in area with alot of interstates. Where I live there are 2 major highways...one going north and south and the other obviously east and west. I live about 20 miles away from work and to be honest with you its faster to take the city streets then the highway. I am going with a 4 spd simply because I dont plan on driving on the highway all that much and I like the light weight 4 spd (aluminum muncie). With 17" wheels and a 3.00 gear...I think it will be fine when I do put it up on the highway.

Sharroll Celby · #20 (**permalink**) 03-10-2010, 12:01 PM

I put about 8,000-9,000 miles a year on my Cobra with a 351W/5 Speed w/.64 and a 3.23 gear, and a lot of that is freeway miles. I cruise about 80 MPH at 1900 RPM, and the Cobra still accelerates from that RPM, admittedly at a not-so-fast rate. If I needed to REALLY accellerate, I can pop it back into 4th for a bit.
I might change the gears to a 3.54 this summer, just to see what the lower gears do to my overall driving experience.