4.11s but no power

[Mertz]

I finally got around to checking my gear ratio on my 72 C20 and found the tag that told me it is a 4.11 Dana 60 non posi. I don't think the cover has ever been pulled to I have to believe it is correct. With my t350 w/ shift kit and tuned 350 getting probably 290hp I still have problems getting off the line and I can not burn the tires. I am running 265/75/R16 in the rear. Where is all my power going? I should be able to break them loose at any time. Could it be the torque converter? It was new when the trans was rebuilt a couple of years ago.

[71tahoe]

How big a cam and what stall TC?

Too big a cam with a stock TC has no low end power.

[Mertz]

Stock cam and stock TC

[hugger6933]

a good place to start would be the basic tune of the motor. Do the plugs look good check the wires ,cap, rotor, timing, carb adjustment. any one of those thing if out of place could cause a loss of power. If that happens over time you may not notice untill it is [the power] is all gone. Jim

[Mertz]

Its got a fresh tune with timing (initial and mech) at 36 all in at 2800. MSD ready to run ignition, new spiral core wires and new plugs. Cliff's Perfromance dialed in Quadrajet. Ceramic headers with dual exhaust and cross pipe. Carb adjusted with an LC-1. Plugs are tan in color. Mileage is at 14 plus mpg.

[raycow]

What happens when you brake torque it? How many rpm do you get?

Ray

[Mertz]

Power braking doesn't really work. It revs up to a point and then drops off and acts real sluggish. I let go of the brake and it plods along with not much pickup. Punching it from the line is about the same. I bogs and then when the speed is right it takes off. I am sure it is not a carb issue. I think with 4.11s even with a little pedal it should launch. The truck is really not that heavy.

[raycow]

Originally Posted by Mertz

Power braking doesn't really work. It revs up to a point and then drops off and acts real sluggish.

Oh you really do have a problem then. There is no way you should get a bog. What kind of carb do you have?

Ray

[Mertz]

The first one was an Edelbrock then I put on a quadrajet that I rebuilt and tuned with an LC-1 air/fuel meter and the one on it now is one built and tuned by Cliff Ruggles the guy that wrote the book on Quadrajets. The last one has worked the best although mine wasn't to shabby.

[t&tkennels]

im running 4.10s in my 71, 350 with about 300hp, th350 with stock convertor. never touching the brake it will spin all the way thru first & half thru second, with 255/60/15 tires.it should easily spin with your setup.

[Mertz]

That is exactly what I think it should be doing. Now I have to find out why it isn't. I guess I will double check the gear ratio by spinning the tires. Your tires are a lot small than my 32" diameters I have on so that helps a bunch.

[68gmsee]

Can you explain the part where you mention tuned 350 with app 290 h.p.?

Does this mean the the engine has been sent to a shop and tuned for performance and tested? Your truck should definitely spin those tires if this is the case.

If not and it's a stock engine, be aware that cams didn't last very long in these 350's. Usually at 60K on up they would start to go flat and would start to lose power. By 100K most of them were in dire need of replacement.

The other possibility is the transmission/torque converter.

[71 super]

If it is a crate motor the 290 hp is at flywheel not rear wheel, the power is cut considerably by converter and auto trans, 350 not as bad as 400 but still eats up some. If you are getting a bog, you need a bigger fuel shot initially not less. The bog comes from not enough not too much most of the time. If it were bogging the black smoke should roll. Try changing the pump rod position a little bigger front jet and check the secondary flaps on the q jet , the flaps should have some resistence there is a small allen head set screw that can be adjusted to loosen of tighten this flap, again this is one of those things that has to be tested and played with to get the prime, not just bench set, that will get close but not exact for your motors particular needs, and you might try to pull a little time out of the motor. The last motor that I had that was pretty hot hated alot of timing, it actually made more power at 34 than on up. Try one thing at a time and take numbers and write down what you do do not go by the seat of the pants, your butt will lie to you.

[Mertz]

The engine is stock. I checked the lifter travel when I installed the roller tip rockers and new push rods. I rotated the crank to adjust the valves. The carb was tested on Cliff's 350 test engine and he said it test out fine. The shot is fine and would only help from a standing launch not when power braking. The secondaries are adjusted correctly. I can hear them open when I get on when I am cruising. They are set correctly because you are not supposed to feel them come in and that is just what it is doing. Again I don't think the secondaries come into play when doing a hole shot. There is no black smoke. I tried a lot of timing settings and where I am now seems to be the best. I assume I have 290hp since in stock form I believe the output was 275. I would hope that with the intake, iginition and headers I would have bumped that up a few hp.

After the current blizzard subsides I will go out a do a tire rotation check on the rear gear but I am pretty sure it has never been messed with but you never know.

[ERASER5]

Just because I'm nosy, do you have 6 lugs or 8?

[Mertz]

It's a 3/4 ton with 8 lugs and a Dana 60

[Notrodder]

From what you say about your motor, it should be able to light tires with even the higher gear ratios. I'd bet your problem is somewhere between the flex plate and the brake drums.

[Mertz]

I am thinking its the torque converter. Is there a way to test it? I know the brakes aren't hanging up from when I raised the truck to check for the tag on the diff. The trans shift hard as it should with the shift kit. It is just not getting the power to the wheels.

[raycow]

I know you are going to beat this torque converter thing into the ground until you find out that it isn't the problem. If the TC really tossed its cookies you would have metal bits in the fluid. Do you see any?

Ray

[Mertz]

I just talked to my transmission builder and he convinced me it is not the TC. I need to figure this out. I think I will brave the subzero temps we are having and do the spin test on the diff.

[capev86]

did you put dielectric grease on the plugs wires/terminals? my dad found out the expensive way (all new distributor)s that the easy fix for sluggish performance on his stock 87 suburban 350 tbi was to repack the plug wires with dielectric grease. had to do it once a year or so for the 10 years he had the truck. GM products really like dielectric grease!

[oldblue1968chevy]

Hmm never put dielectric grease in my automobile connectors...both ends of the plug wires?

[Mertz]

As a little thanksgiving day fun I went out in the middle of a snow storm and 13 degrees and checked the rear end ratio with the tire spin test. 2 turns of the wheel netted a little over 4 turns on the drive shaft confirming the 4.10 gears. Now what? I did a few other checks and found my PCV hose was loose at the carb so I put a clamp on it and it seemed to run a little stronger. It ran even stronger when I pinched the hose. I checked voltage at the coil and got 12.43v with ignition on and 14.21v with the engine running. The truck is running well because it started after a few cranks with no choke and with yesterdays high of 12 and a low of -14. I also separated some of the coil wires on the cap so they all radiated out from the cap instead of some over the cap.

With a strong motor like mine and 4.10 gears I should be having trouble keeping the tires from spinning. To bad I can't do any test drives with the 12 inches of snow on the ground. No problem breaking them loose now.

Happy Thanksgiving

[mtdave2]

Man, I feel your frustration. I have the same dam problem. Still have not figured it out.. here is a link the one of the threads
http://67-72chevytrucks.com/vboard/s...d.php?t=365777

perhaps something in there will solve your issue.

[Shyguy]

I sure wish I had some help for you, problems like yours sure are frustrating. Please keep us posted.