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  #1  
Old January 7th, 2019, 09:49 PM
azcbass azcbass is offline
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Default 351 Identification M or no?

Hey All

I have been moving through upgrades on my 305E that's in the 66 GMC Open Road camper. New GM HEI setup, duel exhaust, Holley 500. Had to go to a 4.11 rear end because i couldn't find any other gear locally in AZ. It had the 4.57 or 4.56? The former was burned up on a long haul trip across death valley in July quite a few years back. I have the SM 420 trans. I still run 16.5 wheels (not splits) and the only tire i can find for those are Firestone 9.5R x 16.5.

The reason for my post today is to ask some questions on how to get some better performance on the highways. The main thing i'm trying to solve for are those slight inclines that go on for 5-15 miles at a time. I'm reduced to running in 3rd gear at 3000 to 3200 rpm which as i'm geared now i'm maxed at about 40 Mph. These hills are barely noticeable just steep enough to keep me from gaining any momentum in 4th at 2100 rpm which i drop into from a 3750-4000 RPM rev out of 3rd. I'm more than fine with running in 3rd or 2nd if need be for shorter steeper climbs. The reality of my situation is im driving a wind sail with a under powered engine and a gap to big to fill with current setup between 3rd and 4th gear.

So what do i do without a endless supply of cash and the strong desire to stay with these v-6's?

1. gear vendor? ($4000)
2. find magnum intake, heads and headers for the 305? (can i make a
305M?)
3. find a 351 or 401M? do a complete engine swap?
4. Brownie AUX trans?

I did find a 351 just down the street and went to take a look at it last night partially in the dark. here is the CL link to pictures and description:

https://tucson.craigslist.org/pts/d/...786164181.html

The number on the block was 351059999, i was really hoping that there was going to be an M after the 351 but it was a 0? No plaid head cover. the intake manifold and headers did look different from mine. Its was in a 72 GMC 4500 40' long school bus. it looks in good condition and was retired with 40k miles on the clock. I would be very surprised if 140K+ were put on a 40' long school bus? Or is that not as unlikely as i think?

If i could id just stay on state routes and live with it the way it is but being based in Tucson AZ its difficult to get out of town with any efficiency with out hitting the highways for a while.

Let me know what other information i can provide to help find a solution or a way to identify that 351.

Thanks!

azcbass
Sebastian Lauber

1966 GMC Open Road Camper
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  #2  
Old January 8th, 2019, 04:34 PM
azcbass azcbass is offline
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Default Re: 351 Identification M or no?

Sorry update on the number on the block of the 351 i forgot the 7:
3510759999

Thanks

SL
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  #3  
Old January 8th, 2019, 08:29 PM
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Funky61 Funky61 is offline
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Default Re: 351 Identification M or no?

Welcome AZCBASS!

Take a look at the 351 intake manifold. I was trying to determine by looking at the carb mounting flange in those photos. The magnums had the trapezoidal mounting.
I’d vote for the 351 even if it’s not the magnum; do the swap and go from there.
Henry

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  #4  
Old January 9th, 2019, 02:02 AM
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LEWISMATKIN LEWISMATKIN is offline
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Default Re: 351 Identification M or no?

Viewing the top side view of the intake tells me this is either a magnum or a 351E engine. the 351C takes the same intake as the 305.
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  #5  
Old January 9th, 2019, 02:16 AM
bigblockv6 bigblockv6 is offline
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Default Re: 351 Identification M or no?

Quote:
Originally Posted by azcbass View Post
Hey All

I have been moving through upgrades on my 305E that's in the 66 GMC Open Road camper. New GM HEI setup, duel exhaust, Holley 500. Had to go to a 4.11 rear end because i couldn't find any other gear locally in AZ. It had the 4.57 or 4.56? The former was burned up on a long haul trip across death valley in July quite a few years back. I have the SM 420 trans. I still run 16.5 wheels (not splits) and the only tire i can find for those are Firestone 9.5R x 16.5.

The reason for my post today is to ask some questions on how to get some better performance on the highways. The main thing i'm trying to solve for are those slight inclines that go on for 5-15 miles at a time. I'm reduced to running in 3rd gear at 3000 to 3200 rpm which as i'm geared now i'm maxed at about 40 Mph. These hills are barely noticeable just steep enough to keep me from gaining any momentum in 4th at 2100 rpm which i drop into from a 3750-4000 RPM rev out of 3rd. I'm more than fine with running in 3rd or 2nd if need be for shorter steeper climbs. The reality of my situation is im driving a wind sail with a under powered engine and a gap to big to fill with current setup between 3rd and 4th gear.

So what do i do without a endless supply of cash and the strong desire to stay with these v-6's?

1. gear vendor? ($4000)
2. find magnum intake, heads and headers for the 305? (can i make a
305M?)
3. find a 351 or 401M? do a complete engine swap?
4. Brownie AUX trans?

I did find a 351 just down the street and went to take a look at it last night partially in the dark. here is the CL link to pictures and description:

https://tucson.craigslist.org/pts/d/...786164181.html

The intake manifold and headers did look different from mine. Its was in a 72 GMC 4500 40' long school bus. it looks in good condition and was retired with 40k miles on the clock. I would be very surprised if 140K+ were put on a 40' long school bus? Or is that not as unlikely as i think?



Let me know what other information i can provide to help find a solution or a way to identify that 351.

Thanks!

azcbass
Sebastian Lauber

1966 GMC Open Road Camper
The 351M V6 was actually discontinued after the 1970 model year and usually found in 7500 to 8500 series trucks, it's most likely a 351C.
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  #6  
Old January 9th, 2019, 03:08 AM
bigblockv6 bigblockv6 is offline
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Default Re: 351 Identification M or no?

Looking at the pics of the 351 it has the 1972 valve covers with the "V6" logo stamped in, 1971 and earlier had "GMC" stamped on the covers. It has been upgraded to the Holley 500 and looking at the runners of the intake manifold it's definitely a 351C.
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  #7  
Old January 9th, 2019, 07:39 AM
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Default Re: 351 Identification M or no?

Quote:
Originally Posted by bigblockv6 View Post
Looking at the pics of the 351 it has the 1972 valve covers with the "V6" logo stamped in, 1971 and earlier had "GMC" stamped on the covers. It has been upgraded to the Holley 500 and looking at the runners of the intake manifold it's definitely a 351C.
I agree with Pete -- looks like a 351C to me too. That's what's in my 1965 one ton Suburban. I also agree with Funky -- that it would be a definite upgrade to your 305. Even though it's not a magnum engine, it's a step in the right direction. You could upgrade it to a magnum at a later date if you can find the magnum heads and manifolds. It probably is a low mileage engine, and the price is right.
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  #8  
Old January 9th, 2019, 05:00 PM
jrmunn jrmunn is offline
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Default Re: 351 Identification M or no?

You might get an extra ring on the piston with a big truck 351C engine. So there could be some benefit beyond more power. This doesn't look like a straight swap because the pump bolted on at the front of the engine might not fit under the hood of a pickup. There might also be problems fitting this engine behind the radiator with the extra pulley. These are probably not hard to deal with unless your camper special needs power steering and something on the 351 setup is in the way of what is on your 305.

Good luck with your decision and, if you go ahead, making the switch.

JRMunn
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  #9  
Old January 9th, 2019, 11:06 PM
azcbass azcbass is offline
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Default Re: 351 Identification M or no?

Thanks all for the replies! I had the seller pull the carb and as you guys had mentioned it didn't have the correct intake for a magnum. So if i can get this now for $300 and a few hours labor helping the seller pull this out of the bus. What have people been getting for magnum heads, intake and headers? am i looking at another $500-1000 to acquire these parts as they come available? Does anyone in the group have these in good condition that they want to sell me?

Again thanks for all the help.

AZCbass
Tucson
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  #10  
Old January 10th, 2019, 11:10 PM
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Default Re: 351 Identification M or no?

Rather than a gear vendor have you considered a road ranger splitter? It mounts between the engine and trans and actually adds another shifter. Half the cost of a gear vendor. Heck I'd do the 351 and a splitter for the fun of it. Either way, the extra cubic inches will make an improvement no matter what.
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