Power versus Gears

bajajoaquin

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Poking around here and other places, there seems to be a lot of disagreement and talk about how much power or raciness is appropriate for C bodies. It occurs to me that one of the issues is the three-speed transmission. What these cars really need is a four-speed. I did some math, and with an OD fourth, you could run 3.23 gears and have a 10% lower first gear, with a 1000 RPM drop at 70mph. 3.55s would still see a drop in revs.

I think parts are out there for A518 swaps, and as a Torqueflite with an overdrive in the tailshaft, they should be appropriate transmissions for the big blocks in our cars. There seem to be some clearance issues that are resolved with very small mods (at least in B, E bodies and trucks) and bellhousings are available.

So it seems that if you were rebuilding a drivetrain, it might make sense to rebuild stock, or at least not spend any money on anything that cost more than stock, and spend extra dollars instead on a trans swap. It seems like you would get better acceleration, lower wear, and easier cruising.

Comments? Thoughts? Criticism?
 
Definatly doable on a bigblock now with the bolt on ultra bells. Should be easier with c body with more room in tunnel go for it.
 
Three speeds are definitely old hat and the 727/A518 conversion would be a great update to take advantage of fuel cost savings and having a car that is more responsive on the street, i wouldn't expect big gains though in some circumstances so it really comes down to making sure you don't pay a lot for the transmission you put in, you will also have to factor in the cost of a new driveshaft and wiring placement for the electric overdrive engage button.
 
My friend put a Gear Vendors overdrive in a 78 NYB...no cutting of the floor required.
 
Was that Kip? He did a nice job .

Yup. Honestly, after all the modifications to put in an A 518 (bellhousing, rear mount, electrical hook-up etc). not to mention the outlay for a new (rebuilt) A 518 (I wouldn't do the swap unless the trans was essentially new); I bet you'd be close to $2500 anyway.
 
Since there was no real result when I searched for 518, I decided to go back to the oldest page (it's only 9 pages) and read through. There seem to be 3-4 threads about 518 swaps, and one member who did one (and described it as the best thing he's ever done).

Rather than go back and forth about cost and relative value of Gear Vendors versus 518 (or TH700), I think the comments about price are a good way to frame it. For $2000-$3000, what gets you better driveability and day-do-day performance, a modded engine or a 4-speed OD transmission?
 
Just for grins, I put together a matrix based on what I've read about the different OD options. Because while that's not what I was getting at with my original post, it is kind of a key consideration.

Gear VendorsA518TH700
Gear RatiosGood, uses stock ratiosGood, uses 727 RatiosGood 1st gear, big gap to 2nd
OD22%31%30%
Lockup TCNoYes, depending on source transmissionYes
Powerfull power ok in all gears/od gearsFull power probably ok in gears 1-3, not rated for full power on OD or lockupProbably ok on 4L65
Cost$3,000$1500-$2500??
DurabilityVery durableProbably ok as long as you don't hammer itDepends on build?
Ease of installationStraight forward, lots of documentationLittle documentation, takes substantial, but straight-forward, fabrication??
 
Regular 727 with a 3.23 rear.
You're in the sweet spot 85% of the time for the lowest cost.
I can't see spending 2-3 grand trying to achieve the last 15%

Cost no object? New ChryCo 9 speed auto. and have Hennesy figure out how to wire it.
 
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I cant imagine that spending over 2000 dollars can be made back too soon on a car that most people would drive say maybe a few thousand miles a year if you are lucky. The fuel cost savings per mile would be around say 3 or four mile per gallon provided you did a lot of highway driving, no real savings around town. So if you do say 5000 miles a year on the highway in your C-body it would save you about 80 gallons or 250 to 300 bucks a year in gas.
 
It would be a cool thing to do.Who cares if it pays itself off. You will only see C body and ROI ever together in this sentence.
 
In most cases if you have original rear in car your going to have to change it to a lower ratio >3.55 otherwise your converter is getting down below its stall at anything under 70 mph then anything you are saving is gone in the converter. So in the matrix include swapping rear gears.
 
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