I have a 1978 GMC C15 with a .030 over 292 and a 700R4 in it. The engine has a stage 1 Lowe roller cam in it. The head is big valve, lump ported, 59cc chambers with 30cc dished pistons. Clifford intake with a Holley 390. 700R4 trans is a heavy duty build with a B&M shift controller and a 2200 converter. Yukon 3.73 posi rear. Pertronix ignition. 255/65/16 wheels. Electric fans and Vintage Air AC. On a wheel dyno it hit 196HP and 248FT at the rear wheels at 4200RPM. Peak torque was 260 at 3800 RPM. It runs very well, very strong. It is my daily driver and is driven to work and used every day in a regular truck fashion. However, I am doubting my choice in converter. The gas mileage is abysmal, 10.5MPG at best. And as I spend the large majority of my drive time at low RPM, generally below 2000RPM, it always feels like I am just spinning the converter uselessly. When I floor it off the line or when passing and the cam comes on at about 2500 it pulls seriously hard but I rarely do that. 99% of my time is just slow driving with traffic to work or around town. I'm thinking of dropping to an 1800 converter. Anyone have any suggestions or thoughts on this? On what you think might be the best converter considering my use?

Stock convertors are around 1600 RPM. That cam should be able to idle down nicely. What does it idle at?
I see no reason to use a 2200 convertor. That cam makes plenty of TQ. I'd go with the 1800 in a heartbeat. Maybe even consider a 1600-1650 convertor. Your vehicle is hevy and will also cause a convertor to slip more as the rpm's are less than it's rated 2200. Sounds slippery to me.

Your converter isn't locking up.

No lock-up in OD and to much stall from the sounds of things.
Your driving RPM is low Not good for the convertor and can Put to much heat into the tranny And That is the last thing a 700r needs They don't like being over heated Per say

That's kind of what I am thinking also. Thanks for your input.

Yes, it is, I can get it to lock up fine when I want it to at highway speeds. Just don't spend too much time at those speeds.

It locks up fine in OD at highway speeds. I just don't spend too much time at those speeds. Thanks for your input.

Also, it idles fine at 750.
Steve

You should explore the heavy duty, (think towing package) pickup truck converter for your application. The 700 shuts it's cooling circuit down in lockup.The torque converter clutch stops the turbine action of the converter and the nigh gear and overdrive functions have next to no slippage, so cooling in high and overdrive with the TCC engaged isn't necessary.

You should also make CERTAIN that the throttle cable to the transmission is adjusted properly. It's a great tuning tool for adjusting the shift and lockup points to the way you drive. The 700 offers some latitude if you are careful with the adjustments.

A tighter converter may cost you a little on all out acceleration, but your overall driving experience will be enhanced greatly.

Yes, the general consensus I am getting is what you are saying, go low on stall. I'm going to change it. What's in there is a C48HDT. I think I'm going to drop to a C40HDT. Any recommendation would be much appreciated.
Also, I have played with the cable some. It does affect shift points. I found it worked best when it had a small bit of slack, like a 1/16", before it pulled on the pump.
Thanks for your suggestions and I'll welcome any others you have.

the tv cable is NOT a kick down cable like a th350! buy the correct bracket for your carb and set correctly (push release button on cable and open carb to full throttle) this insures you have correct line pressure at idle. raising shift points can be done with a lighter governor and easy to swap on the 700r4.

Setting up 700R4 linkage: http://tinyurl.com/yhzqbu3

What intake manifold are you using? Somehow you need to increase your intake velocity to help with mileage. Smaller intake port volume needed.



MBHD

The Clifford intake is not as good for mileage as compared to the Offy intake
The Clifford intake has huge runners, too much volume.
I would look for a smaller intake manifold.
Do you have an air/fuel ratio gauge?
I would not use such a tight converter as 1600 RPM stall.
What does the 2200 stall converter actually stall to?
Having a lock-up torque converter let’s you have the best of both worlds, acceleration, then will lock up when you want it to for mileage.
A lot of newer cars with V-6’s will have 2200- 2600 stall and still get 28 MPG example 2010 Chevy Malibu 3.6 V-6 6 speed trans.

Hank is correct.The late model vehicles can use a loose converter. The lockup feature takes up for the stall in the higher gears. It must be noted that these vehicles are "computer" controlled, with the ECM controlling shift points and torque converter clutch lockup. Makes 'em a little more versatile.

If you can control the shift points and the lockup point, a looser converter WILL work. Perhaps modifying the governor could change the shift points further, allowing the converter clutch to engage in the lower gears or at lower RPM. That and some fiddling with the TV cab;e could make a higher stall converter more usable. There isn't any electronic control on the 700R4.

In my application, a completely stock 700R4 behind a 153" Chevy four cylinder, also stock, the pickup converter is plenty loose for idle and low speeds and tight enough to deliver excellent traffic manners and good fuel mileage. Idle speed is around 750 RPM and it drives well. I should add that my induction is a hand fabricated tubular intake with a Holley NASCAR 400 cfm double pumper carburetor with mechanical secondaries. The ONLY modification to the transmission was careful, gradual adjustment of the TV cable.

My Willys and Anglia coupes have 2500 rpm stall converters. I think they are a good match in a light car. 300 and 240 ci respectively.

I like a looser converter for light cars too. Particularly with a higher horsepower engine! It doesn't work as well for heavier vehicles that don't move as easily at low rev.

Something that gets overlooked when selecting a torque converter is the "flash" point in the torque curve of the converter. Many loose converters have a higher flash point, the RPM that the converter will spin to under heavy acceleration before it approaches hydraulic lockup. While two converters may have the same stall rating, they may flash at entirely different RPM. Talk to a knowledgeable converter specialist when making this kind of investment. That guy at the sales counter may not have the knowledge or the information that you need to optimize your combination!!