1966 GMC 305 V6 Service

[TommyDuncan]

Originally Posted by awbrown

rufton , what port do you have the vacuum on now ?? From what you are telling us it looks like it is on the ported vacuum , it should be on manifold vacuum .. all the vehicles I have had got much better milage on manifold vacuum than ported...

Anyone else have an opinion on this?
The Holley PDF says to connect it to ported. I tried both but I made so many changes at once that I haven't figured it out yet.

[monolith]

Gorgeous write up!

Makes me want to drag my 64 out of the back 40 and see what the racket was all about and maybe try to do something about it.

[Rufton]

Thanks for the compliments.

I took the GMC 305E on an I-75 trip 3-4-14 and got 13.4 mpg and 14.1 mpg driving approx 70mph. Need to get her out more but I've been tied up.

[starrman30]

wow what tranny do you have? my 69 feels like its revving up to 5000 rpm when I hit 60MPH. I'm pretty sure they al came with the 4 speed granny low tranny, except the automatic version. I have never tried to hit 70 MPH

[gmcbrandon]

Great thread with tons of information and detailed pics. I myself am rebuilding one of these and was wondering did you use as far as the rear main seal? I order felpro set from summit, seal bs40048 and its just a rope seal, curious if you were able to find a two piece rubber or you settled with the rope seal? Thanks alot

[BigDan3131]

I know this is an old thread but now that you seem to be a master rebuilder of these engines have you thought about adding some performance upgrades to them? From the look of the heads they could handle much larger valves and do they really need 4 rings on the pistons? Knife edging the crank to make it lighter and blueprint the rods too. Not in the sense to make it rev higher but to increase performance at its regular rpm range. Has anyone stuck the massive 472 with its 5" bores in one of our trucks yet?

My 65 had the 305E behind the Powergilde, was there an adapter plate needed to mount the glide to the 305E? I know where one is...can it be used to bolt other autos to it?

[TJ's Chevy]

Originally Posted by BigDan3131

I know this is an old thread but now that you seem to be a master rebuilder of these engines have you thought about adding some performance upgrades to them? From the look of the heads they could handle much larger valves and do they really need 4 rings on the pistons? Knife edging the crank to make it lighter and blueprint the rods too. Not in the sense to make it rev higher but to increase performance at its regular rpm range. Has anyone stuck the massive 472 with its 5" bores in one of our trucks yet?

My 65 had the 305E behind the Powergilde, was there an adapter plate needed to mount the glide to the 305E? I know where one is...can it be used to bolt other autos to it?

Guy stuck a 478 in a 68 Chevy so I know its possible. Also a guy took a 478 and put hemi pistons and rods in it. Had a custom cam ground. Catapiller diesel valves were installed in the head. Needless to say it KILLED anything near its cubic inch. Had a WAY better cool factor than a BBC. lol Guy who owned it said it would do 6K. I installed a 4 barrel on my 305. Did a 4 down to 2 adapter. Worked out really nice. Plan to install flat top pistons, shaved 351M heads and have the intake machined to directly fit a 4 barrel. Might have a little more duration added to the cam.
https://www.youtube.com/watch?v=mdZlZlWRRMI

[Matt's k5]

Originally Posted by Rufton

Converted clutch to diaphragm a few years ago and like it.

question for you, did this kit work great? no modifications of the disc? I'm looking for a clutch for my 62 with the 305 I found for sale on ebay nu551 and wanted to verify before purchasing thanks

[factorystock]

Originally Posted by Rufton

Thanks for the compliments.

I took the GMC 305E on an I-75 trip 3-4-14 and got 13.4 mpg and 14.1 mpg driving approx 70mph. Need to get her out more but I've been tied up.

Old post yes, but, there are plenty of V6 owners out there that might find this old post and this article I found recently interesting. Mileage reported by Rufton is almost indentical to the owner of the GMC in this 1967 letter to the editor. The "cold" plug and the "hotter" plug confusion may be the culprit of some V6 owners reporting lower gas mileage than they should be getting.