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Old 03-10-2012, 04:17 PM
revspan revspan is offline
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Tuning a 700R4

I would like some help tuning my 700R4. Hopefully, someone out there has some ideas to help me.

First, here are the basics of my setup.

350 SBC making 360hp, and 380 ft/lb torque. Max rpm of this engine should be 5800, as the power falls off after that. These are dyno proven numbers.
Engine has a Holley carb, with proper linkage for the trans pressure cable(TV made easy)
700R4 with a 2300rpm stall converter.
Ford 9" with a 4.30 gear, 255-55R16 tires
Vehicle is a 1937 Chevy truck that most likely weighs about 3000-3200lbs.

I have very few miles on this as I have just got it on the road, but for the 30-40 miles that I have driven, I definitely need to work on the transmission shifting.

Currently, I am not happy with the responsiveness that the transmission has in relationship to the throttle. In short, when I add throttle input, I would like to have a linear response to downshifts and later(higher RPM) shifts, which I currently don't have.

As an example,

Mild acceleration: the transmission shifts at maybe 2500rpm, which is fine.
Medium acceleration: The transmission may shift at 3500rpm, which is borderline.
Medium acceleration from a rolling start. Seems that the transmission just does not want to downshift enough, and stays in a higher gear and kind of lugs the engine.
Hard acceleration from a rolling start. Seems that if you REALLY stand on the throttle, that you can get the RPMs up, but then the transmission will "hang" at a high rmp(5500-6000), before it shifts.

So, there is something that I don't have tuned correctly. In an effort to make the medium power upshifts happen sooner, I changed the weights in the governor. The weights that were in there apeared to be stock and weighed 0.45 oz each. I replaced them with weights that were 0.30 and 0.25oz, thinking that that would make all of the shifts happen later. I also put in springs that were the middle two of the kit that I got(Shift technology). The springs that I put in seemed to be a little lighter than what was in there, but I can't be sure as I had no way of measuring them.

Also, I believe that I do have the TV cable set correctly, although I have taken the PSI gauge off the transmission due to the fact that I dropped the truck off today to have the interior installed.

So, any ideas?.... I have the governor kit that I can lighten the weights and springs more if that may help, I also have some fine tuning that could be done on the cable connection on the carb that changes the amount of "pull" in relation to the throttle position.

But......before I do any more testing, could someone give me some theory as to why the trans would behave in this manner? Is it the combination of really light vehicle and really low rear end gear that is making this a challenge?

Any thoughts or discussion would be appreciated.

Thanks



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