Gear issue or too tall tires?

[rico7769]

Team,

I am running a 350/400 setup in our truck. I am not sure about the gear ratio but it is whatever is stock for a 67 GMC short bed with the CST pkg with the original motor being the 292.
When we drive the truck, it feels like our gear setup is approx to the following numbers...
1st- 0-10
2nd - 10-25
3rd-25-65 (around 3500rpm @ 65mph)

We are running 255/70/15's all around and cannot get over the lack of power it seems to provide with the motor we run on. 350(decked), aftermarket cam, performance heads, Holley 600, Accel ignition/wires, headers, etc. Feels like we are pulling about 5000lbs behind the truck at all times but will still get sideways if you get on it. Seems overall like we're missing out with the gear combination or do you guys suggest a change in tire size to accomodate?

[ERASER5]

Running some quick calculation with the numbers you gave, makes wonder what is going on. Your tire size is 29". Using your rpm/speed numbers,I get a 4.65 or so gear. That should give you stump pulling power! Some of those 6 cyl. trucks had deep gears like 4.10 and 4.56. A small error in the rpm will throw off the calculation. A 4.56 gear would give you 65mph@3434rpm.

If you are experiencing low power, then check your timing and tuning. Find out exactly what cam you have. I once put in a "recommended" cam that was big for a 383 let alone a 350. Absolutely no power until 3500 rpm, and I never got above 2500 with my 3.08 gears! So, I say, check your cam specs.

[highperf4x4]

Yeah it doesn't sound to me like you have a gear problem. I'd say the cam is probably too big. Need more info on the motor though. Is it bored? What pistons? What intake? What crank? Stall converter? What's the timing?

[pmpski_1]

Determine what your rear ratio is. Until you have all the numbers you're just guessing.

[aboveall]

hello just testing trying to figure out how to post here ty

[tjsblazer]

Don't know if this will help you or not but it is an awesome calculator. Try the link.

http://www.grimmjeeper.com/gears.html

[69GMCLonghorn]

Something else that I constantly bring up in threads like this is to calibrate your gauges! Make sure that your tach and speedo are reading true numbers. My factory tach was showing 3600 at 60 MPH. It was actually at about 2800!! Also, at 60 by the speedo, I was actually doing 64 MPH. So get all the facts as accurate as possible.

Now, in terms of no power: Sounds like you need to re-arch your distributor for that cam. I had a no power issue in the low end on a built 350. After I re-arched it, I had som much low end, that I if I stood on it under 2000 RPM in 4th, the tranny gears would whine from the torque!

[rico7769]

Thanks for all the input everybody!