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.
1. TV cable should be 100% pulled out at max throttle, controls operating pressure as well as shift patttern. Very important to have it right.
2. With the 4.30 gear the governor is turning alot faster at a lower speed than it was designed for with a low to mid 3's ratios. You'll want the lightest weights you can find and springs that will keep the valve from being pushed in too soon.
Take the Garage tour: http://www.youtube.com/watch?v=cZIhuocG2ig
Any other ideas out there?......
Above Info is correct.
As for the hanging shifts & rpm, the TV plunger may be binding/sticking or Governor problems.
What TV setup are you using on the Carb, BTO?
the carb is a holley 4150 with a kit from Bow Tie Overdrives.
I just ordered a "Corvette" Governor and will take it apart and weigh the parts, reassemble and see if I can get the shift RPMs up.
As for the hanging RPM, you may be right, because I really have to mash the throttle for it to rev up, and I may be pulling the cable too far.
Here is a question for someone...... If the governor is not calibrated properly(engine speed too low), can the TV force the tranmission to generate a higher RPM? In other words, if the governor isn't properly tuned, does this limit the transmission speed in all conditions?
Thanks for the comments so far.....
Simplified: The governor dumps presssure, when then centrifical force swings the weights out the valve is pushed in blocking off fluid exhaust passages. This causes fluid pressure to "back up" and puts pressure against the shift valves in the valve body and they shuttle against their respective spring pressures thus opening passages for fluid to apply the various clutches and band. You can makes some changes with the governor but with limitations.
Once the gov. valve is 100% in the control action shifts to the valve body.
Thanks for that explaination....it helps in understanding what is going on in the transmission.
Anyone replace a governor that is forcing shifts at 2500rpm and direct replace for a "corvette" governor? Wondering what could be expected.
I have seen a few pictures of them, and it looks like they are simply lightened up somewhat to reduce centrifical force.
Correct, the weights are lighter. You will probably see a 1/2" hole in the outer heavy weights and perhaps lighter springs betweem the Lg / Small weights. This might give you some small change but probably nothing major.
A photo of a corvette style governor. Please keep in mind that a matching valve body on a vette is calibrated a bit different for this design of governor.
wow. Compared to the weights that changed in the tuning kit I have, the changes to the outer weights is HUGE. I weighed the inner weights in my stock governor, and they were 0.45oz. The kit I have as weights that are 0.50, 0.45(stock), 0.35, 0.25, and 0.20oz. It will be interesting to compare the mass of the outer weights.....I bet it will be a lot compared to the small changes in the inner weights.
With this, I am hopefull that I can get the shift points up where they need to be. Unfortunately, I have the truck at the interior shop now and can't make any adjustments.
Thanks again for all of the information! This site rocks!
Well, I installed the medium weights and the lightest springs and definitely had an impact in mid throttle response. Actually, under light throttle, the shift points may be a little high, as the trans will now rev to roughly 2800rpm at very light throttle. With a little tuning, I am sure that I will be able to get the mid-throttle shift point where I want with the adjustment kit that I have.
During the one full throttle blast that I did, the transmission downshifted and then proceeded to run right up to thye 5500 RPM rev limiter and hang there until I let off the throttle, at which time it shifted fine.
I do have an aftermarked good quality dipstick, but was wondering if fluid level could impact this.
Not sure where to go as this really needs to be worked out.
let us know the final springs and weights alone with the results.
if there still advabile get a tpi 350 governer from a f body camaro or trans am they shift about 200 rpm lower than the vette governer the tpi 305 wot shifts around 4800 the 5.7 shifts about 5200
This might not help. Made a chart after calibrating my 85 c10 with a 3.73 rear and th350c. 1st 3.08 number/ 2nd 3.73 both 28" tire.
B&M governor calibration kit for WOT.....AN APPROXIMATION!!
GM#24202127 = 4400 rpm
Blue&Yellow 2 & 3 = 4900 rpm C10 tried good torque jump to 2nd at 4300
GM#24202117 = 5000 rpm
Blue & Yellow 4 & 3 = 5100 rpm 4500 chirp 2nd
GM#24202122 = 5200 rpm
Blue & Yellow 2 & 5 = 5300 rpm C10 tried revs out till done at 4700
Blue & Yellow 5 & 3 = 5500 rpm
Blue & Green 4 & 5 = 5600 rpm c10 revs 5000 full pull, hard kickdown
Blue & Green 3 & 5 = 5600 to 5700 rpm with 3.08 and 4700 with 4.10 s10 v6 +500rpm from stock
is the 700r4 governor the same as a 350 ?????
just thought they were different ?
|All times are GMT -6. The time now is 06:07 PM.|
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.