6066 (1960-1966) GMC Truck Club Bitcoin now accepted here! 
Pay Dues
Pay Dues or become a Site Supporter
 



Go Back   6066 (1960-1966) GMC Truck Club > 6066 GMC Truck Club Forum > GMC V6 and V12 Engines


GMC V6 and V12 Engines Engine repair and rebuilding

Reply
 
Thread Tools
  #11  
Old November 15th, 2014, 02:02 AM
bigblockv6 bigblockv6 is online now
-= Dues Paid =-
 
Join Date: Jan 2013
Location: Rohnert Park, ca.
Truck: 1968 KM2500
Posts: 983
Rep Power: 272
bigblockv6 is on a distinguished road
Default Re: Forced Induction

I'm aware the 305E is not a magnum, however there are different 305s. There is an A, B, C, D etc. Difference in intakes and heads is my understanding. Still not a "magnum" though.

Of course we still have no clue as to how many RPMs we can squeeze out of one of these engines because nobody has done this before. We'll have to see how much weight we can remove, judge the strength of everything, do some calculations, and guestimate a max .

The difference from A through is A and B engines produced from 1960-61 were equipped with 1 bbl carbs. The A engine used in light duty trucks had the Holley 1 bbl and 3 rings per piston, the B engine used in medium duty trucks used a Zenith 1bbl carb and had 4 rings per piston. The 305C used in medium duty trucks from 1960-74 had the Stromberg ww carb and 4 rings per piston. The 305D basically a Stromberg 2bbl version of the A was introduced in 1961 and replaced with the 305E. At some point after these years mentioned the 305E and C engines did get larger diameter exhaust valves. As far as nobody doing what you're attempting, it has been done before, Babe Erson brother of Sig Erson(Cams) built a 478M with lighter Chrysler 426 Hemi rods, turned down the journal diameter of the rod journal, ran higher compression custom pistons with 3 rings, custom cam and 4bbl carb to achieve a 5500 rpm screamer out of a GMC 478M V6 that could take on a mildly built 454. There's no substitute for cubic inches, I would not waste the time on the 305 as heavy as it is for that little bit of displacement, you can take the same engine block that house 400 plus cubic inches of displacement. We had a member a couple years back take a 478 and basically apply Babe Ersons formula but he also stroked the crank and had Manly custom stainless steel valves made to replace the hollow stem sodium filled exhaust valves that snap from over revving, by the time he was done this engine has a displacement of 523 ci. I also dumped the 305 in my 68 KM2500 for a mildly built 478M V6.
Reply With Quote
  #12  
Old November 15th, 2014, 02:12 AM
bigblockv6 bigblockv6 is online now
-= Dues Paid =-
 
Join Date: Jan 2013
Location: Rohnert Park, ca.
Truck: 1968 KM2500
Posts: 983
Rep Power: 272
bigblockv6 is on a distinguished road
Default Re: Forced Induction

Quote:
Originally Posted by hjennings View Post
Net vs Gross horsepower. They used to measure the HP without the accessories, now they measure them with (that started that in '71 or '72 I believe).

Some of the specs are hard to find on these old engines. I've found some data on the heads that says the flow about the same as a 350 from that era. That sounds OK, except those flow numbers are total, and the V8 is split between 8 cylinders while our engines are only feeding 6 (so less flow per cylinder).

I said above I'd probably go with a 305E engine. My thinking there is it probably has the most flow per cubic inch of any of the GMC V6 engines. If somebody can confirm or deny this please let me know. I'm sure it'd be between a 305E and a 351E (Magnum heads). The 351 may be the one to use. Not sure until I find the flow numbers.

500hp is a complete wild *** guess. I hate evening saying that, as we have built several engines and can usually tell a customer what a certain combo will make and the dyno is always really close. With a buildup of a turbo GMC V6, it's never been done. So who knows. A big part of it is how much boost and how many RPMs the block/crank/rods can take. I'm guessing that these engines are very strong (as far as how much HP they can take.... they've never been tested at any sort of limits). So who knows, might be able to handle some insane boost levels.
The highest horsepower ratings on all GMC V6 engines were from 1966-71. They dropped in 1972 due to emissions and also gross ratings were no longer used that year.
Reply With Quote
  #13  
Old November 15th, 2014, 03:35 AM
FetchMeAPepsi's Avatar
FetchMeAPepsi FetchMeAPepsi is offline
-= Dues Paid =-
 
Join Date: Jan 2013
Location: Edmond, Ks
Truck: 1962 4x4 GMC CECILIA
Posts: 1,334
Rep Power: 360
FetchMeAPepsi is on a distinguished road
Default Re: Forced Induction

If they used to measure the HP with the engine bare then today our engines would measure as LESS hp, instead of more. Isnt that right? I thought I read that they would measure more under the new system. Guess I was wrong there. We might be at 100hp at this rate.



Quote:
Originally Posted by hjennings View Post


Fun stuff, right?
__________________
Step by steps:

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Some people are like slinkys. Not worth much but funny as heck when pushed down stairs.
__________________
If the women don't find you handsome, they should at least find you handy.
Reply With Quote
  #14  
Old November 15th, 2014, 04:31 AM
hjennings hjennings is offline
Banned
 
Join Date: Jan 2013
Location: Jacksonville, IL
Truck: 1965 1/2 ton
Age: 42
Posts: 10
Rep Power: 0
hjennings is on a distinguished road
Default Re: Forced Induction

Yes with today's net system they'd be rated at less horsepower.

I'm not concerned with the stock horsepower ratings. Really just need to know two things. First, can the heads be interchanged? Second, what are the flow ratings of each of the different heads for all the different GMC V6 engines?

Once I get this engine I'll begin my twin turbo fuel injected GMC V6 project. Lets just hope it doesn't blow up on it's first run down the track.

Evil Monkey Kustoms
Jacksonville, IL
Reply With Quote
  #15  
Old November 18th, 2014, 03:41 AM
duallyjams's Avatar
duallyjams duallyjams is offline
Junior Member
 
Join Date: Jan 2013
Location: Deale
Truck: 64 GMC
Posts: 13
Rep Power: 30
duallyjams is on a distinguished road
Default Re: Forced Induction

305 351 401 heads can be inter changed 432 have a extra bolt not sure about the 478, so for a turbo you could use the magnum head on a 305. There is a lot of info on the old forum and on Jolly's site.
Reply With Quote
  #16  
Old November 18th, 2014, 05:29 AM
bigblockv6 bigblockv6 is online now
-= Dues Paid =-
 
Join Date: Jan 2013
Location: Rohnert Park, ca.
Truck: 1968 KM2500
Posts: 983
Rep Power: 272
bigblockv6 is on a distinguished road
Default Re: Forced Induction

All Magnum heads are the same and interchangeable regardless of displacement. The biggest difference was in 1973-74 when larger diameter 12 point head bolts were used, bushings can be fitted on the heads to allow the use of smaller diameter bolts on earlier engine blocks. All gas GMC V6 engines use 14 bolts per head and that includes the 432 engine also.
Reply With Quote
  #17  
Old January 12th, 2015, 02:30 AM
duallyjams's Avatar
duallyjams duallyjams is offline
Junior Member
 
Join Date: Jan 2013
Location: Deale
Truck: 64 GMC
Posts: 13
Rep Power: 30
duallyjams is on a distinguished road
Default Re: Forced Induction

got a 2015 update
Reply With Quote
  #18  
Old January 12th, 2015, 06:39 AM
BobBray BobBray is online now
-= Dues Paid =-
 
Join Date: Feb 2013
Location: Los Angeles, CA.
Truck: 1967 CM 2500
Posts: 75
Rep Power: 45
BobBray is on a distinguished road
Default Re: Forced Induction

I wonder if GMC ever thought about a turbo gas V-6. They did turbo the Toro-Flo.
Reply With Quote
  #19  
Old January 12th, 2015, 07:11 AM
hjennings hjennings is offline
Banned
 
Join Date: Jan 2013
Location: Jacksonville, IL
Truck: 1965 1/2 ton
Age: 42
Posts: 10
Rep Power: 0
hjennings is on a distinguished road
Default Re: Forced Induction

Quote:
Originally Posted by duallyjams View Post
got a 2015 update
Nope, not even close at this point. I took the winter off as I had knee surgery in Nov and have another one coming up in another month or so. So sort of out of commission right now.

Should be back at it by spring, but I have three vehicles I have to finish before the pet project V6 build.
Reply With Quote
  #20  
Old January 13th, 2015, 03:50 PM
George Bongert George Bongert is offline
Senior Member
 
Join Date: Jan 2013
Location: Oshkosh Wisconsin
Truck: Former owner Repowered by GMC 305 V-6 1963 Chevy 30 Series SM420 Long Bed (9') Step/Fenderside
Posts: 105
Rep Power: 53
George Bongert is on a distinguished road
Default Re: Forced Induction

Greetings to all!

The subject of putting a Turbo on the GMC Big Block V-6 has reminded me of the fellow who posted on the site some time back (in the Yahoo Group days) about seriously modifying a 305ci Big Block V-6 (boring/stroking, and other serious modifications to the same) and turning it into and 808ci engine. With what he was talking about doing, I wondered where he would ever find a starter with enough torque to crank up such a beast. Whatever happened to him and his extreme modification project?
Reply With Quote
Reply

Bookmarks

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Forced Induction Archiver Previous Forum Posts 11 January 30th, 2011 12:49 AM


All times are GMT +1. The time now is 11:35 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2013, Jelsoft Enterprises Ltd 116|0