stall speeds, vehicle weights, transmissions, rear gears...revisited

[allcarfan]

I had a thread about this a few months back. It was decided that with my 2600# 66 coupe, a C4 transmission with a 3000-3500 stall speed, that a rear gear of at least 3.89 was needed in order to keep the cruising rpms above the stall speed.

The converter is rated at 3000-3500 stall. I am assuming that it will stall just above 3000 because of the low vehicle weight.

This is my new concern: I am really leaning towards a Gear Vendors Gear Splitter transmission addition for my C4. I have been in contact with a guy at Gear Vendors and he says everything that I have (reverse manual valve body, ratchet shifter) will work with the gear vendors gear splitter. Now, this gear splitter will give me 6 fwd gears. It makes the first few gears much shorter because of the addition of two other gears. Which translates to, a lot more shifting. Now, the final gear ratio is .78:1. Which means my 3.90 gears will perform like 3.05s. This means, much less RPMs when the overdrive is on. The overdrive kicks in with a preset Eprom from GearVendors. This Eprom can be programmed to have the overdrive kick in at what vehicle speed one chooses.

So, now my vehicle will act like it has 3.05s when in over drive, but suppose to accelerate faster. Does this mean that I should get a stall converter that has a little less stall?? Since the RPMs will be lower they would more than likely be below or right at what the stall speed is.

Ideas? opinions?

FYI: a different transmission(AOD, AODE, T5, T56, etc ) is out of the question

 

[mustangdave]

Just guessing, but I would think you would need less stall speed or your tanny will be slipping in o.d. and using huge amounts of fuel. I would think the Gear Vendor unit would rev your engine up pretty quick and keep it in the optimum torque range during normal accelleration. 3000 seems a bit much anyway. What is your cam and engine combo?

 

[302 coupe]

it sounds like you have a decent budget for this project, why limit yourself to a C4 for highway driving? The C4 is a fine piece no doubt, but if you plan to run 3.89 gears and a 3000+ stall, and do a good bit of highway driving.....that just doesn't work out right. My choice would be an AODE with the Baumann controller and a lockup converter. You could run your gears, have your stall, then lock the converter in overdrive and cruise in comfort, for probably the same price as yur C4, converter, and splitter.

 

[Fostang]

it sounds like you have a decent budget for this project, why limit yourself to a C4 for highway driving? The C4 is a fine piece no doubt, but if you plan to run 3.89 gears and a 3000+ stall, and do a good bit of highway driving.....that just doesn't work out right. My choice would be an AODE with the Baumann controller and a lockup converter. You could run your gears, have your stall, then lock the converter in overdrive and cruise in comfort, for probably the same price as yur C4, converter, and splitter.

........and with less parts to break.

 

[allcarfan]

I dont want to run a different transmission...as stated in my original post. I would have to change the flexplate on my engine and the engine has been balanced and blue printed. I would also have a larger bell housing from the AOD/e and my custom 1 3/4" long tubes will not clear it. Plus, my c4 has been built ...and built well. It has plenty of goodies in it.
I wont be doing a lot of highway driving, but id like to be able to do some.

The engine is a 331. Twisted Wedge 185cc heads from Total engine airflow. The cam is an XE282HR (232/240 duration @ .50 .565/.574 lift). Victor Jr intake and a speed demon 650 carb.

The flash stall speed ont he converter that I have now is 3000 rpms. Which means, my car SHOULD stall a little before that because of the light weight. Id like to find something with a stall speed of 2700-2800, but it seems like all the name brand converters are either 2000-2400-3000-3500+

More ideas and opinions are welcome. The gear vendors option is something I am considering down the road a bit, but I would like to have all of my ducks in a row right now.

 

[Edbert]

The only problem I have with the GV overdrive is that they split your gears. I was wishing it could just add an OD ratio to the end but thats not how it works. You get a 6-speed alright, as well as overdrive, but two of those gears are pretty much wasted, one sits between your current 1st and 2nd, how much can you see needing a ratio in between those two? The other sits between your current 2nd and 3rd, not as useless as the other one but still pretty much a waste.

The bellhousing of the AOD bolts right up to the SBF, and you can get a flywheel balanced to fit your engine (I assume you have the 28oz right?). An AODE would require a computer, but the older AOD does not. I'm not trying so much to change your mind, it seems made up already. I just wanted to throw that out there for anyone else reading this who might be considering a similar idea. I was about to buy the GV unit myself and opted for a built AOD for about the same price.

• Less weight than a C4 with the GV box
• Fewer moving parts
• 33% fewer shifts means less heat/slip/loss of acceleration

 

[allcarfan]

Thanks for the input.

I know what you mean about splitting gears. I thought of that myself - a lot of hassle and having to constantly push a button on and off between shifts. I would be doing it more for the overdrive option to lower RPMs on the highway a bit. I may just opt for a smaller torque converter and a little less gear in the back. Maybe a 2500 stall and 3.50 gears (have 3.50 in there now.)

I know I could get a flexplate rebalanced or just buy a new one. However, my entire rotating assembly was balanced together witht he flexplate that I have now. It was also blue printed.

And, another big concern...those headers...$775 made specifically for a 289-302 with a small c4 bellhousing.