Building a nice drivable C6...need advice
 

Ok. No automatic tranny bashing, please.

In a nut shell. When I started out on my CRII build. I had the motor and rearend built to take a 5 speed manual. Well... once we got the body on and the seats in. It was plain as day that there was not enough room in the foot well for my size 12s %/ and a clutch, break and gas pedal. At least not enough to make me feel safe on the road.

The engine dyno'ed at 470hp and 520FPT. I had a C6 built with heavier clutches , bands and all that other stuff. Not knowing what I was doing. I put a 3400 stall TCI converter in the C6 and the rearend still has the original 3.73 gears. With the current setup the car seems to just want to sit there and then as the RMPs get north of 3400, it launches like a bat out of hell. This setup makes it virtually impossible to get on or off a trailer or easily pull in or out of a garage/parking spot.

What I want is a car that drive like a normal everyday automatic, but if I want to jump on it.... well she'll get up and go.

Right now myself and others are thinking we need to take the stall down to around 2000-2200 and gear the rear back towards 3.08 or 3.20

Anyone have some thoughts or experience with something similar?

Thanks in advance!!!!

Where does your engine idle? 2000 seems kind of high for a stall.

C6 or not to C6
 

Before you commit to a C6 tranny consider your options. I have a built up C6 behind my BB Ford and a 2.75 rear gear. I don't like the highway cruising RPM's. The stall converter recommended by the engine builder which I have is a 2600. With the huge amount of torque my engine delivers I'm still running at 3K+ on the freeway, leaving me short on cruising pleasure as well as MPG's. Also the high rear end causes the car to behave in a less spirited manner than I expect at low speeds. I have been considering switching to a 2200 convertor as well.

I'm giving serious thought to converting over to an AOD with lockup torque converter which would drop my cruising RPM to 2200 +/-. If I then change to 3.55's I can have a more spirited launch along with still allow for cruising at the original RPM's. Right now I have the best of neither world. Tom Wells drives a C6 and doesn't mind the RPM's at all, so maybe you wouldn't, I don't know. With an AOD I could at least choose much more relaxed cruising or fun quick launches.

BTW I too have difficulty using a clutch (size 14-15's plus many ankle surgeries) so a manual setup which would sort out all these difficulties isn't in the offing for me either.

Regards!

Dirk

P.S. I just revisited the Gear Calculator page and sure enough my VDO speedo is STILL way off. (I've set it many a time and after failing to get it to run at more than 1/2 my actual speed had a shop adjust and set it on the DYNO...I'll check it with my GPS soon to be sure)...my gears calculate to 2700 at 75MPH and would just drop to 2400 with an AOD at 75MPH BUT that would be with 3.73's, making QUITE a change in my low speed responsiveness!:)

Dirk,

Thanks so much for your input and insight to my C6 issues. I was on my way back home from the airport reading your post and one of the guys I've had running this problem down called me. Long story short, his tranny guy had pretty much the same response as you. If I went with an AOD, I could keep the 3.73 gearing in the rear end and maybe get a great balance.

Going to start checking out some options for an AOD....

PS> I'm getting ready to start a new build of a 34 Ford 3 window. That will be a lot milder than the cobra, so I can always use the C6 in that car :3DSMILE:

Thanks again!!!

While not quite apples to apples, I have a 351w with around 390 hp. I went with a Lentech AOD. I have 3.50 gears. I gave them my engine and car specs. etc. and they matched me up with a 2400 stall converter that they build. They were quite helpful and have done several Cobras.

I can't remember why now, but they recomended a non lockup converter for my application. The bottom line is I couldn't be happier with the combination. The drivability, cruise rpms, and acceleration is perfect for me. I hope that helps you some.

Sydney

Gear Calculator - incalculably helpful
 

Ed, thanks for your note - I forgot to include the web address for the most wonderful gear calculator I've found - all the most common trannies calculated in one table for any tire size, gear ratio or speed, plus you can design your own gear ratios and check out the RPM for every gear in your section of the table for any gear ratio or check out the speed at any given RPM....free too!

http://www.5speedtransmissions.com/gear_calculator.html

Sydney, I guess they recommended the 2600 stall converter so the engine wouldn't be pushing to move the car at idle, perhaps even a smoother takeoff? I've read lots about torque converters and remain somewhat confused....I'm looking into the lockup converter though my feedback from professionals has been mixed - the lockup on the OD would allow me to cruise at an RPM below full torque converter engagement, improving the power to the tranny and the mileage I get in OD.

Ed, please let me know how it works out with the AOD - fitment, source, cost, etc.

Regards!

Dirk

Keep the C6 but go to 2000 stall (assuming you dont have too wild of cam in it) and replace rear gears with 3.27. What you have now is good for a pure drag racer that rarely sees the highway.

I have a 2500 stall TCI converter in my C6 with 3.40 gears and 255/60-15s and mine launches like a drag car and cruises just fine........

Here's my set-up...Power is in the 750 horse range, th350 auto with manual valve body, this tranny is built to the max to take this much power. 4000 stall converter that flashes to 5500. 3:54 rear In gear I am at 1000 rpm's. If I take my foot off the brake, my car starts moving, just like any other automatic. I have no driving on the street issues what so ever. I guess what I'm saying, is that I'd be looking for a problem with what you have. My last converter was 3000 stall, and it didn't have any issues either.
I'm going to be changing the converter back after driving season because the tranny fluid temps get to high on the street.

Thanks for all the feedback/suggestions!!!! This is why this forum is so great!!! You can easily find others with some of the same experiences or ideas, thanks again! :3DSMILE:

After one of my guys talked to a friend of his that owns a tranny shop. Its sounding like I have an issue with the transmission it self. You guys seem to have torque converters with stalls all over the range and are not experiencing the problem I'm having currently.

I think I'm going to look into buying an AOD from someone like TCI or Jasper, knowing that I'll get it already tested and dyno'ed and with the AOD I can keep my 3.73 gears in the rear. I'll then ship the C6 off to get checked out to see what's wrong with it and then maybe use it in my 34 coupe project.

Thanks everybody! I keep the posts coming to let you know how everything turns out.

Capt. The torque convertor you have now is probably well matched to your camshaft and power range in a normal streetcar. You can get away with the tighter convertor in a Cobra because of the light weight. I went the overdrive automatic route and think it makes a good combination with a 2000 stall. The overdrive is only put to use on the open road. I have 3.55 gears and 70 mph is only about 2200 rpm. Makes for easy cruising. Everyone has their own idea of what is streetable though. I had a blown '62 Nova with a loose convertor at one time and loved it but it was supposed to be a street/strip car.
-Greg

Well. I just bit the bullet and ordered a new AOD package from TCI. Its about a week out for delivery, so as soon as it get installed. I'll post my observations and opinions.

Thanks for all the advice and suggestions!!!