Picked up a 1970 GMC C3500 dump truck that needs some TLC

[pclausen]

I know the 305 is not the dream motor for this truck, but unless there are major mechanical issues, I think I'll keep it. I might throw some long tube headers on it when the current exhaust is gone, which I don't think will be that much longer.

I had a LS1 350 that I put long tube headers on, no cats, head job, different cam profile, ls6 intake, and it woke it up to the tune of 418 at the rear wheels, or about 500hp at the crank! I also put in a 3.77 rear. It would run 11s all day long on street tires (325's out back). This was the stock motor in a 2000 vette convertible. Here's the dyno run sheet:

I got pretty good at launching it from my garage.

 

[murphy1244]

Wifey must of loved the burnouts. I have a buddy that put his GTO thru the back of his garage trying to set his rev limiter.
I had a 70 SS 454 LS-6 450HP that did 12.9s on stock tires. Could not keep its rear end from hopping. Those factory tires were hopeless.

 

[pclausen]

There was no wifey back then 10 years ago. Now the vette and bike are both gone and there are 2 little girls in the house and I'm all exited about a 42 year old dump truck. Things sure have changed... :laughing:

I hear you about stock tires. When running stock rims/tires (Goodyear runflats) after the engine mods, it was like driving on ice. I could get sideways in 1st, 2nd and 3rd pretty much at will. Winter time too with the 325's. They like a hot pavement to hook. They were Michelins.

 

[deerefan]

I know the 305 is not the dream motor for this truck, but unless there are major mechanical issues, I think I'll keep it. I might throw some long tube headers on it when the current exhaust is gone, which I don't think will be that much longer.

I had a LS1 350 that I put long tube headers on, no cats, head job, different cam profile, ls6 intake, and it woke it up to the tune of 418 at the rear wheels, or about 500hp at the crank! I also put in a 3.77 rear. It would run 11s all day long on street tires (325's out back). This was the stock motor in a 2000 vette convertible. Here's the dyno run sheet:

I got pretty good at launching it from my garage.

You will be surprised at how much a good set of headers and nice 2 1/2" dual exhaust will wake up the 305. Restrictive exhaust and small cams held these motors back along with low compression ratios. The ls1 is the motor of choice for racers in my area. There is a vette making over 800hp on a stock bottom end ls1 with a single turbo, tame cam, headwork and other bolt ons. With a mild tune he runs low 10s. Turn the wick up and he plays in the 9s all day. He drives the car to the track. Like the small block did 50 years ago, the ls1 is doing now.

 

[Mace Canute]

pclausen, I wouldn't swap out the 2V intake and carb for a 4V. Your money and time will be better spent tuning the 305 and making sure it has a decent exhaust on it. Small tube headers would work well but the old rams horn cast iron exhaust manifolds are a good choice too. The old Corvette ones (harder to find) had a nice 2 1/2" outlet but the regular car and truck ones came with two different size outlets but are still harder to find due to age of vehicles they came in.

Many trucks around the 25,000 GVW weight limit used to come factory stock with 2V carbs and intakes and at the RPMs they were expected to work at, typically around 3,600 to 4,000 governed RPMs @ 60 to 65 MPH or so (going from several decade old memory here), they had adequate breathing.

I used to do oval track racing in two classes that required 2V carbs & intakes and cast iron exhaust manifolds, so I have quite a bit of experience with them. ([brag]We won the track championship in our class 8 years in a row.[/brag] )

hawkeye08's suggestion of making sure the HEI has full 12 V power to it isn't just a good suggestion, it's almost mandatory! Depending on what application the 305 in it now was designed for, the advance curve might be woefully inadequate. An engine that was in a light(er) weight car with lots of gear (as compared to a 305 in a half ton with more gear) will probably have quite a different advance curve that will be too fast for the truck it's in now and if it is, it will likely be into detonation much of the time it under load (whether you can hear it or not). A little detonation that you can't hear probably won't hurt things but it is robbing you of power and if you can hear it, it definitely is robbing you of power an d is damaging the engine. Worth checking out, eh?

It's too bad the 292 wasn't still in it; they were good motors. They all came with a forged crank and seven main bearings with a 4.125 in stroke and the 1967-'74 292 exhaust manifold had a 2.5" outlet if it was in a heavy duty application (large truck/bus). They could also put out up to a gross torque of 280 pound-feet at 1,600 rpm and a net of 262 pound-feet of torque at 2,000 rpm.

 

[boxygen]

Correct me wrong (I probably am) but I thought that dual headlight style is for the older of that generation truck like 67 or 68. I had a buddy who had a 67 gmc 1 ton which was red with white trim and a flatbed. His dad had owned it since new and he had redone the truck. I had hoped to buy it since he didnt really use it but I dont think he thought I was serious because he sold it without me knowing it. I was a little annoyed that it got away from me because I think I could have bought it for around 3k. I like the dual headlight style the most. Good score. Please keep us informed on its transformation.

 

[pclausen]

Appreciate the insight Bubbles, I mean Mace. I did pick up a relay today and plan to do the HEI mod this weekend. I got the tach all connected today. I was able to fish the wires through a vent hole and slide the mounting base under the old crackled dash cover. So no holes drilled in the dash!

What should I consider the max safe rpm for this engine? Is it likely to be self-governing, meaning that the valves will begin to float at some point, and that's the safe (bottom end) max rpm? I ran it up a little past 4k once I got the tach working, it I don't think I would want to take it much past that.

I'll trow a timing light on it once I do the HEI mod and see that the curve looks like, as best I can without going down the road with a load on it.

Boxy, I was wondering about the year myself, but then I looked at this:

My V.I.N. is CS303-BZ54764, so that would be:

C = 2 Wheel Drive
S = Inline 6 Cylinder
3 = 6,600 - 14,000 1 Ton
03 = ? This is not on the chart (I guess I have what have been called "custom camper")
- = Not for Pennsylvania, Maryland or New York
B = Baltimore Assembly Plant
Z = 1970
54764 = 4,764th unit built

Here's the truck history for those years:

 

[Grumpy Old Man]

Appreciate the insight Bubbles, I mean Mace. I did pick up a relay today and plan to do the HEI mod this weekend. I got the tach all connected today. I was able to fish the wires through a vent hole and slide the mounting base under the old crackled dash cover. So no holes drilled in the dash!

What should I consider the max safe rpm for this engine? Is it likely to be self-governing, meaning that the valves will begin to float at some point, and that's the safe (bottom end) max rpm? I ran it up a little past 4k once I got the tach working, it I don't think I would want to take it much past that.

I'll trow a timing light on it once I do the HEI mod and see that the curve looks like, as best I can without going down the road with a load on it.

Boxy, I was wondering about the year myself, but then I looked at this:

My V.I.N. is CS303-BZ54764, so that would be:

C = 2 Wheel Drive
S = Inline 6 Cylinder
3 = 6,600 - 14,000 1 Ton
03 = ? This is not on the chart (I guess I have what have been called "custom camper")
- = Not for Pennsylvania, Maryland or New York
B = Baltimore Assembly Plant
Z = 1970
54764 = 4,764th unit built

Here's the truck history for those years:

Really ? Really? what are you doing to my truck , It's a farm truck and your trying to take it to Nascar status ! leave it alone and drive it ! Everything you change and rework takes away from the fact it has basically made it for what 42 years with its soul still intact leave it alone it will work just fine the way it is , You kids don't always have to change what made it a legend before you were born . It's not a Camaro !

 

[Grumpy Old Man]

Really ? Really? what are you doing to my truck , It's a farm truck and your trying to take it to Nascar status ! leave it alone and drive it ! Everything you change and rework takes away from the fact it has basically made it for what 42 years with its soul still intact leave it alone it will work just fine the way it is , You kids don't always have to change what made it a legend before you were born . It's not a Camaro !

It made it to your driveway with nobody taking it's soul ! hands off ~!

 

[npalen]

It's interesting how a 42 year old dump truck can generate as much or more interest than a brand new truck! It's always fun to buy something old and put it in good running condition and much cheaper than a new one.