I have A tandem axle L900 with A 477 in it.The truck was upfitted with a 60 foot crane when it was new in '72 or '73 (I can't remember right now)Anyway I recently bought the truck from the company who bought it new.The problem I have is that the truck is very slow and underpowered.I do understand that this is an old truck and I do not expect it to run 10's in the qtr. mile,but I really can't believe that this truck could have been this gut less when it was new.The truck seems to have been very well taken care of and does not burn oil and runs very well.Can anyone tell me what can realisticly be expected from this engine?
Well, these engines as well as some rather large International gas engines were designed to have the maximum torque to move the load. They are not fast, but steady. It takes horsepower to go fast and these engines don't have it.
Torque to move the load --- horsepower to make it go fast. (simplified)
Yes, they really made trucks this slow. I have driven them and still drive a 12t crane (crane capacity, not truck weight) truck with a mere 130hp. Makes you find hills where you thought there were none!
Either upgrade the running gear-- engine, trans and rear axle(s) or stay in the right lane and just drive the thing as best as possible. One possible low budget choice may be a 3208 turbo Cat, it is a 10 litre engine with about 160 to 300 hp (higher and lower (non turbo) ratings are available) with a fairly high rpm band, which means that you might be able to use your existing transmission(s) and rear axle(s)
New class 7 trucks are packin' (or can be) around 500hp and 1400 ft lbs of torque at 1600 rpm, along with a close ratio many speed transmission. That is why they move along as well as they do.
Check your carb for proper operation, if it is a Holley 4bbl they had vacuum secondaries and if things aren't right they won't open. Also look down the the primaries with the engine off and open the throttle wide open. The governor set up on these carbs spring loads the throttle to the open position, if the tension spring behind the cover with four screw on the choke side of the carb isn't set tight enough they won't open much. It has a little stud that can be moved to 5 positions to select different spring rates and set the top rpm's. If the primaries don't open all the way the secondaries will never open.