Gearing questions??????

[Haus]

I took my truck to town for the first time yesterday. On the way I was at 2850rpm at 55mph. Here is my setup.

1970 351 Cleveland with 4V quench heads
C4 trans with shift kit
TCI 2500 stall converter
4.11 posi rear end

If money was no object I should probably add an overdrive unit. I would have to sell my motorcycle to do that though. So heres my question. The cheapest option at this point is to switch out the rear gear ratio. Would this work with my converter? At the stop light you can hear the converter slip until you get to about 2200-2400 RPM, then she kicks in and away you go. Once I'm kicked in it seems to stay locked it until I stop again. Then its time to race again, lol. Also after running the numbers I think a 3.5 would drop my RPMs enough. Any suggestions. Would a 3.5 ruin my get up and go?

[1961 slickwilly]

you could run 3:50 ratio for lower rpm wise i had them in my 65 with 390 4v but you could stomp it and spin tires but it really ddidnt come alive till you were around 65 or 70 you can run 3:73 ratio it will give you for pep in your step from a stop than the 3:50 but not like the 4:10s your running now. the 3:73 will be a better all around for power in bottom in and top end unlike your 4:10 you will be able to do more than 55 lol and it all depends on your tire size to smaller tires and low profile tires with lower your gear ratio and taller will raise your gear ratio you can run your 4:10s now and put 265/60 or 275 and it will lower your rpm

[BarnieTrk]

Remember that if you drop the cruising rpms to 2600 or less, your converter will be slipping some all the time and it'll make lots of heat (and won't last long) and your mileage will suffer due to the converter slippage. With that converter, you have to keep the rpms up so that it locks up fully.

What is it you want - drag racing prowess or highway cruising mileage?
Unless you plan on drag racing your truck, then you're NOT going to worry about fuel mileage. If your plans are more cruising and mileage oriented, then I'd suggest you consider changing the converter to a lower lockup rpm unit.

If you just change the rearend gears to a lower numerically ratio and/or install taller tires, your stop light launches will not 'snap' like it does now and you'll STILL have to rev it up to ~2500 rpms before the converter stops slipping, bites and grabs in......

BarnieTrk

[Haus]

Well I don't plan on drag racing (much). I do have a trip to my old town planned. My best friend thought it was funny to smoke me when I had my 91 ford and straight 6 300. Little rematch is called for.

The donar truck I started with had a 351 2v cleveland with 2.75 rear end. It was a turd from a dead stop, so thats what got me to get the 4.11. I hear you on the slipping clutch and heat. Making an overdrive unit sound like my best option.

[BarnieTrk]

Well I don't plan on drag racing (much). I do have a trip to my old town planned. My best friend thought it was funny to smoke me when I had my 91 ford and straight 6 300. Little rematch is called for.

The donar truck I started with had a 351 2v cleveland with 2.75 rear end. It was a turd from a dead stop, so thats what got me to get the 4.11. I hear you on the slipping clutch and heat. Making an overdrive unit sound like my best option.

So....... maybe wait to make the changes until AFTER the "little rematch" has been "handled".

As you probably already know, an OD unit will be VERY pricey ($2500+).... so in the meantime, I'd suggest you shop around and find a good RV converter that locks up sooner and put it on the shelf. Then once you've performed the "little rematch", then once back home, you can pull the converter off the shelf and replace the converter that will reduce the heat (which your trans will thank you for) and you'll improve your drivability & fuel mileage. After driving a week or two with the RV torque converter, if you find yourself doing a lot of high rpm driving (highway) and want to reduce the rpms, then I'd consider going to either the taller rear tires or changing the rear end gears.

One issue I see is that you've got a hot rod engine/converter/trans/rear gears combination. Those combos are NOT designed to be run at low rpms nor provide good mileage.

Good Luck!
BarnieTrk

[modeleh]

Even if you had an overdrive, once you engaged it, the rpms of the engine would fall off below 2600 rpms, then the converter would be slipping again. Am I correct on this? I've known a few guys that had high stall converters in street cars but they never drove worth a damn. BarnieTrk is right, get rid of that converter, they are for purpose built drag cars only, IMO.

[Truckfarmer2]

If you are running 4 barrel heads on a Cleveland, the overdrive will do you no good as you have to keep the RPM's above 2500 so your engine does not load up. That engine has to keep the R's up to be able to use all the breathing capacity in those awesome heads.

[BarnieTrk]

Even if you had an overdrive, once you engaged it, the rpms of the engine would fall off below 2600 rpms, then the converter would be slipping again. Am I correct on this? I've known a few guys that had high stall converters in street cars but they never drove worth a darn. BarnieTrk is right, get rid of that converter, they are for purpose built drag cars only, IMO.

I believe it depends.
I'm not an automatic guru, but from what I understand is that it is generally the case, especially with a C4.

Now if you had a AOD transmission, the OD kicks in AFTER the converter, so the high stall converter would still work as designed at launch time and then lock up once your truck was up to highway speed and OD kicked in.....

What you may want to do, Haus, is call the manufacturer of your stall converter and discuss your converter model with your transmission type combination to confirm its performance properties.

Good Luck!
BarnieTrk