tow vehicle

To be honest I really don't want to change the gears I'm looking into a top end rebuild. First I have to do the compression test and see how the rings are maybe a valve job. What I have found out so far is the gears are not going to really make the differance I'm after

I’ll give ya 5 grand for the C20. Use it as a down payment for something that tows better

What are you expecting? If you change gears there is a possibility that some hills that you are now hitting the top at 30 wound out in first youll be able to crest in second doing 38 mph. But, on the other hand, there will be steeper hills that you now crest at 30 in first that after the gear swap you'll end up cresting at 24 mph still in first. Gears don't make power .... so don't expect a gear swap to make you hit the hill tops at 45 mph.

If it still has the Rochester spread bore, 4 barrel carb.....keep it and find a good...great rebuilder

Most common issue will be worn butterfly rod bores in the body. Drill it out and press in a sintered, journal bearing of the right size

There used to be a "power" tune kit

If too much and/or can't find a great renulder...any of the performance carbs work well.

Consider the cam as mentioned, but if you wish to stay outside the engine...a dual plane, high raise intake make another big diff

Not much help to OP, but love reading the replies from folks with knowledge of older engines and trans AND trucks in general from the 70's, 80's. Having a '72 GMC, 4x4, 4 Spd, manual steering, 350 cu in 4bbl, as my 1st truck then adding dual exhaust w/ Cherry Bombs she sounded GOOOOOD. When plowing snow w/ 8' Fisher plow, steering was a B****, but she'd plow! Anyways, love learning things about the older stuff.

It’s a Mark IV engine. Steel crank and good, not great, oval port heads.
Mods are plentiful and you can easily get another 100hp out of a stock short block.
But again, why?
I mean, great classic truck, but if you’re towing far enough or often enough that going slow pulling a hill is an issue, your options are much better with a different truck. Period.

If it’s for nostalgias sake, then build a motor, tighten up the trans to handle it and burn some rubber!

Gears will likely make a good difference but there might be a few other easy-ish things to make more power too.
Hopefully the spark plugs, wires, filters are good and fairly new.
Chances are pretty good with the age and miles on the truck that the timing chain is worn out. As it stretches the cam timing r etards and that hurts low end power.
GM engines of that era were also known to wear out cams quickly. If the engine ticks at all that could be the problem. If you replace the cam you could check with a company like Comp Cams for a recommendation.
If you can find an old school hot rod shop they might be able to get you some more power with some tuning. Recurving the advance in the distributor and playing with the ignition timing can make a decent difference.
If the air cleaner housing has the big oval inlet without a cool air hose going to the rad support you might try adding one of those. If the housing has the small round inlet you can add a second one to the other side for some extra air.
Dual exhaust might be worthwhile too.

Charles F Fisher wrote:
it is 2 wheel drive 400 trans. I may be leaning towards the cam. the engine has 102,000 it turned 100k while we had it. I really would like keeping it as stock as possible but I still need it to pull.

With 100K that engine might be getting tired. Motors from the 70s typically didn't last like they do today. If you're changing the cam it might be smart to rebuild the heads. Does it have good compression in all 8?

rjstractor wrote:


You could do both, but changing gear ratios would likely help a lot. If you are down to 30 mph it sounds like you are in first gear at the top of the hill. Lower gears might allow you to pull the hill in second to give you another 10-15 mph. But like was pointed out, you only have around 200 hp or so. If you change the gear ratio to 4.11 a GearVendors unit would give you about the same final drive ratio in overdrive as what you have now. It's a little spendy and like was mentioned previously doesn't work in 4WD.

Lower gears might would help on the up hill. My first question is are you overheating? That is the first sign the engine is overloaded. Any change to bump the power will make that problem worse.
I know many feel it is a assault on manhood to have somebody pass. But what percentage of the miles you run in a day are you on a hill that will pull you down to 30? 6 miles at 60 takes 6 min. If the hill drops you to 30 as soon as you start up, that same 6 miles will take 12 min. Spend money build things up to where the truck is more likely to damage itself, but it can now climb at 45, you save 3 min.
Spend your time keeping the old girl cleaned and polished up. You might go by slow, but you will be looking good as you go. Your truck will last longer.

it is 2 wheel drive 400 trans. I may be leaning towards the cam. the engine has 102,000 it turned 100k while we had it. I really would like keeping it as stock as possible but I still need it to pull.