Re: 1961 GMC 5500 Tilt Cab Project
 

I would do a 4 barrel for that engine. :thumbsup:

Re: 1961 GMC 5500 Tilt Cab Project
 

Swapping out for the HEI and the carb won't improve your mileage by more than 1-2 mpg. You'll see 12-15mpg on average, which was pretty decent for the time.

The HEI and carb will make cold starts easier and will make the engine run smoother though, provided it's running not-so-smooth now. If that ain't broke, you can keep it as a rotor/points system and drive it like you stole it. These engines are very tough.

Re: 1961 GMC 5500 Tilt Cab Project
 

He'd be lucky to see 10 in a truck that size. The bigger carb and HEI swap with dual exhaust on my 305 was quite an improvement. More power over anything.

Re: 1961 GMC 5500 Tilt Cab Project
 

He's got a two speed rear end and a 401.

As for your truck, you had issues with yours before you dropped the HEI in, remember? I won't argue that exhaust though. GMC choked the trucks with a single tiny exhaust.
:thumbsup:

Re: 1961 GMC 5500 Tilt Cab Project
 

Still...that is a heavy truck. lol Nope, never had fuel issues with mine even with the 4 barrel and points setup. The old dizzy on mine had a sticky advance.

Re: 1961 GMC 5500 Tilt Cab Project
 

A 4bbl would definitely be even better as long as Dan doesn't mind the extra fabrication which really is no big deal as long as a Magnum manifold is used:thumbsup:

Re: 1961 GMC 5500 Tilt Cab Project
 

And with a Mill you can get the perfect job. :upyes:

Re: 1961 GMC 5500 Tilt Cab Project
 

will the 4bbl be much different than a 2 bbl on that motor?
Also, it runs a little rough, but the plugs and wires look way old.
gonna do a normal tune up and then plan on an HEI, and holly.
I don't believe a have a Magnum manifold...
Are those hard to find?
Also, if i would see big gains in the 4bbl, which one would be the "best"?
Thanks again for the advice, i truly appreciate it.

Re: 1961 GMC 5500 Tilt Cab Project
 

I have done a 4bbl but have not tested it yet. I've heard from others it is a noticeable difference the bigger cubic inch V6 engines. GMC actually did offer a dealer installed option 4bbl conversion. The Magnum 2bbl manifold is based on that 4bbl manifold design it's just cast with a different top base and that's why it's so easy to convert it to a 4bbl. 600-650 cfm would be a good choice for the 401. TJ is the one to talk to about his 4bbl experience though it's on a 305 V6:upyes:

Re: 1961 GMC 5500 Tilt Cab Project
 

Your 401 should be a Magnum, if it's not I will be a little surprised. There are numbers stamped on the block just forward of the right head. If yours is a Magnum it will say 401M.

As for my 305, much better over the 2 barrel. :upyes:

Mileage is decent if I can keep my foot out of it and it has no problems lighting the tires in 2nd. I went with an HEI and dual exhaust(recommend, especially for a larger engines).

Ed Snyder would be the one to talk with as he has a 401 with a 4 barrel. :thumbsup: