Re: SO who came up with the GMC V6's???
 

I'm glad to hear that Don Meyer is still alive, Dave. I corresponded with him a few times several years ago. I sent him color copies of all my 60-66 GMC sales brochures that he didn't have. He seemed really appreciative. I don't remember exactly where I first got his contact info, but do remember him being identified as the official GMC historian. I'm guessing he might be in his 80s by now.

Re: SO who came up with the GMC V6's???
 

I talked with Don Meyer a few times over the years, he is is very knowledgeable about GMC in the old days.

As for the low compression, there are a couple of factors. First, large bore engines can be more prone to knocking, all other things being equal. Also, gasoline truck engines of the era were designed to use low octane (cheap!) fuel. None of the GMC V-6's contemporaries had very high compression, most were in the 7:1 to 8:1 range. These engines were designed to be abused!

Re: SO who came up with the GMC V6's???
 

You got that right. lol I've ran 87 in this thing no problem at all. Though I prefer 91, it's nice to know the engine will run happily on low octane. :thumbsup:

Re: SO who came up with the GMC V6's???
 

Wish I could meet this guy!

Re: SO who came up with the GMC V6's???
 

That makes sense, but man....imagine what a compression boost would do. lol

Re: SO who came up with the GMC V6's???
 

GMC did have what the called the HC(High Compression) series of V6 engines, never installed in trucks. They were sold for industrial purposes, though they called them high compression the ratio did not exceed 9 to 1.

Re: SO who came up with the GMC V6's???
 

Yes they did. I think the idea was that those engines were primarily for use with propane/LNG/CNG fuels.

I wonder if any of the high compression engines ended up in forklifts.

Re: SO who came up with the GMC V6's???
 

I'll bet the extra compression boost helped alot though. Would be neat to find one.

Re: SO who came up with the GMC V6's???
 

Don Meyer, GMC Historian can be reached at 248-693-1227, he is in Michigan. My 1966 Owners manual specifies 92 octane gasoline, back when these trucks were new this was considered regular gas, today this is considered high octane. Anyone over 65 will remember being able to purchase 110 to 120 octane gas without any problem at most all gasoline retailers.

Re: SO who came up with the GMC V6's???
 

Great thread. Enjoy reading it.

All the the V12s, I've ever been around came factory equipt with hi-compression pistons since all of them was used as irrigation power plants, and used natural gas or propane.
I was never around V6s, except a few 478s on pumps, too.

Re: SO who came up with the GMC V6's???
 

Cool! Thanks for his number! Yeah, the good ol days when fuel was really fuel. lol

Re: SO who came up with the GMC V6's???
 

The Pontiac Oakland International Chapter #93 (POCI) was established in 2007. The GMC Times is published 6 times a year by the GMC Truck Chapter of the POCI. The dues are $20 per year, I feel it is well worth joining as they are dedicated to our beloved GMC's. Anyone interested in joining can contact: Paul Bergstrom, 1165 County Road 83, Maple Plain, MN 55359 (763) 479-2248 pontiacpaul@gmail.com. You can also check them out at gtcpoci.info.

Re: SO who came up with the GMC V6's???
 

Thanks for the info Clyde. :thumbsup:

Re: SO who came up with the GMC V6's???
 

Well I did a test for the heck of it today....sorry...no pictures or video. Anyhow, I towed my 1947 Case VAI and that was loaded on a double axle trailer....so the load wasn't light....Bout 6000+ pounds. Well...I really hate the SM420 for towing applications because when you go from 3rd to 4th shifting at 3000 RPM things drop to 1500 rpm and pulling a slight grade things pretty much Stay there. lol I was at half throttle and slooooooooooooooooooooooooooooooooowly picking up speed. Good thing the highway leveled out. haha But on flat ground getting up to 55 no problem at all. GOOD torque in the low range....motor had NO problem at ALL pulling from 8 MPH in 3rd gear...bout 900 rpm lug if I remember right. Starting on Flat ground...rev it quick in granny then shift to 2nd and shift at 2700 rpm into 3rd then at 2700 rpm into 4th and sitting at around 2500 going down the highway...which was around 50-55. On a slight incline I would shift from 2nd to 3rd at 2700 then 3rd to 4th at 3000 and keep it half throttle the rest of the way. There was a hill I pulled in 4th no problem....bout 40 mph and hill ended before I needed to downshift. Motor has some guts for its smallish size as far as cubes go. But a gear vendors OD I think is needed now. Mainly to have something between 3rd and 4th for towing cause the engine hates that drop. I'll say one thing...I'm sure the 4 barrel and split exhaust helped a ton. lol If I ever run across a 478 I think I won't be able to resist a swap. LOL! Love my 305 v6 though! Good running engine...did what it needed to do with no problem and pulled hard with no complaints. She's a runner. :)

Re: SO who came up with the GMC V6's???
 

I do have a question though....anyone have an NP435 tranny behind their v6? Looking at the closer split between gears I may lean towards a swap. Looked into a gear vendors OD and said "**** No!!!" when I saw the price. lol

Re: SO who came up with the GMC V6's???
 

In later years like 1967-69 there was a NP435GA that was a close ratio version, didn't have the granny 6.68 to 1 ist gear.:thumbsup:

Re: SO who came up with the GMC V6's???
 

My 2WD '67 has the NP435. Per the '67 sales brochure, it was the "heavy duty" optional 4 speed compared to the SM420. Starting from a stop in normal driving, you still start in synchro second, just like in the SM420. Non-synchro first is definitely a taller gear in the NP435, though, compared to the SM420. The shift pattern is different too -- reverse is to the right and down. The "bar" in the H between second and third is pretty narrow too. If you're used to shifting from second to third in an SM420, you'll overshoot third every time in the NP435 and go too far to the right and end up above reverse.

Re: SO who came up with the GMC V6's???
 

My '67 has the NP435GA. The ratios are 4.56:1 1st., 2.28:1 2nd., 1.31:1 3rd., 1:1 4th.. Quite a bit closer than an SM420 as Peter and Ed pointed out! Be advised that Dodge and Ford also used a lot of NP435's, and most are wide ratio like the SM420's. Also, the NP435 was common in GMC medium duty trucks, but again these were wide ratio versions. The NP435GA was very well suited for the 351E, that engine's low r.p.m. torque didn't need the lower 1st./2nd./3rd. ratios.

Re: SO who came up with the GMC V6's???
 

Thanks guys! Yeah, according to the specs I've seen my SM420 has a 7.06 1st gear. I never did get what it was with GM and these crazily wide ratio trannys. They are horrible for towing heavy stuff. I mean 1st, 2nd, and 3rd aren't to bad....but 3rd is so low that you can't rev it high enough to shift to 4th. lol Unless on perfectly flat ground or downhill. Or you shift at 5000 rpm. haha For the occasional heavy towing I'm doing I think it'll work OK. Hoping to search so local yards though.

Re: SO who came up with the GMC V6's???
 

we had 292's in c/50 ten wheelers back in the 70's and they pulled and ran better than 350's and we were young then, alway kept to the floor(4000 rpm) and never had one come apart. they did a good job.

Re: SO who came up with the GMC V6's???
 

also had a 65 4000 ten wheeler with a 351 v6 in it paid 500. for it. and it would out pull a 350 too. and couldn't blow it up. it just kept on running no matter how hard you pushed it.

Re: SO who came up with the GMC V6's???
 

Same experience for me. lol Reved my stock 292 to 5000 RPM a few times doing burnouts. Thing ran like a champ...even when the valve train went south while I was driving it...still made it home. My V6 has been the same way, I am much more conservative with it....Highest I have reved it is 3400 RPM and I Don't do it often. 2700 is what I shift at.

Re: SO who came up with the GMC V6's???
 

http://youtube.com/watch?v=75UFbtNlmYgPrevious owner of our bus told me over the Christmas Holiday he cranked it up to 80mph driving east from CA back in the early 70s. 55 mph is 2900rpm(direct drive Spicer 4 spd) on the 401M. I don't even want to know what rpm 80mph was. He had to shut it down and let it cool after he sucked the radiator hoses shut. 55 mph with the new Allison 1000 is 2200rpm in overdrive. Theres north of 450k on this engine and it still has 145-150psi in all cylinders. First rotation goes right to 95psi. Spark plugs and exhaust pipe are medium ashy gray. No smoke and uses about 1/2 qt per 1000 miles. No equal to this engine. One tough *****. Youtube link not working for some reason. just type 1947 Allison into the Youtube search window.

Re: SO who came up with the GMC V6's???
 

That's a cool bus! Yes, The ol V6 was GM's best motor they ever made. Interesting design, but a really neat engine proven reliable and durable.

Re: SO who came up with the GMC V6's???
 

Greetings to all!

I've been following this topic with great interest, and all I have to add to it is that it's a crying shame that GM ever discontinued production of these extremely reliable and durable engines! Just imagine what could have been if these engines were still produced with the technology that we have available today. Just plain a doggone shame that these engines have gone the way of the Dinosaurs! For those of you out there that have any of these engines lying around that can be restored--for God's sake--please don't scrap them!! And shame on anyone that pulls a Big Block V-6 out of a 60-66 GMC Truck in favor of replacing it with a Chevy 350 V-8!! To me, that's a Sin of the worst kind!

Re: SO who came up with the GMC V6's???
 

The GMC V6 family of engines was prematurely phased out,:pullinghairout: I would have to say it was all a matter of dollars and cents with GM. You could see the trend from the late 60's of incorporating Chevrolet engines and more interchangeability lead to the final demise of the GMC V6 after 1974:ahhhh:

Re: SO who came up with the GMC V6's???
 

AMEN to THAT!

Re: SO who came up with the GMC V6's???
 

Anyone know the intake and exhaust valve size on the 305 v6?

Re: SO who came up with the GMC V6's???
 

TOMMR - 80 mph as geared was at 4218 rpm. Just a little outside the recommended operating range!

Re: SO who came up with the GMC V6's???
 

And I'm scared to get mine past 3500! LOL!

Re: SO who came up with the GMC V6's???
 

If the valves don't float, keep your foot in it!

Re: SO who came up with the GMC V6's???
 

I'm good. lol My V6 is running like a top and I wanna keep it that way for a long time. haha Have no doubt in the motor, but never hurts to be easy on them....occasional burnout or two works for me. lol!

Re: SO who came up with the GMC V6's???
 

I found this thread from some time back this morning. I followed with interest when discussing driving in heavy haulers with the V6s, as I have a 1960 GMC 35' motor home conversion All-American bluebird Coach with a Clark 5-speed trans behind the original 401 V6 engine.

I drove it quite a bit after I purchased it in 1987, going to British Columbia, Canada. I got 6 mpg consistently, which I thought it was all it would get, but the previous owner told me he got 10 mpg on long trips. After several trips I did something I should have done after purchase--I pulled the plugs and saw that they were close to being gas fouled. The 2-bbl carb was spilling fuel into the air stream while running. After corrected, I was getting close to 10 mpg @ 60-65 mph.

My rig weighs 23000 pounds, which is a lot of mass to climb hills. The trans has a bad gap in the 3-4 shift, which becomes quite annoying when climbing long grades, which are numerous here in the West. I learned to simply be patient and stay in the lower gear at a slower speed.

I have plans to return this to the road after replacing the wheels and tires to eliminate the old rag 20" tires on split rims. I also have a new, old stock (2001) Holley pro-jection throttle body retrofit EFI system which I intend to install. It is 2-bbl sized which should ease the adaptation to the pre-magnum 2-bbl intake manifold.

Though slow on grades, the coach performs very well on the flats, and steers and rides quite comfortably. I recently had the opportunity to acquire a low-mileage 478-M with the idea I could swap it into the Bluebird, but I think I am going to stay with the workhorse 401.
Regards, Andy Carlson, Ojai CA

Re: SO who came up with the GMC V6's???
 

Back around '74, I was talking to the parts manager at a GMC Dealership and he told me that the V-6 did better and was more liked on the East Coast with all the hills we have, but not that favorable on the flat areas in the Central and Western US. He said because of that, the demand was dropping off and they decided to phased it out, to my dis-appointment.

I had both a 6-292 and V-6's. I like them both, but really liked the V-6 in Heavier trucks. My '62 6500 with the 478 was a powerhouse. It would pull a full load of 20,000 lbs like nothing. Hills would not phase it either, lol.

Re: SO who came up with the GMC V6's???
 

The economics of replacing a well regarded engine design with something cheaper has not been only with the GMC V6 family.

In the 1950s Chrysler produced many trucks under the Dodge brand which were fitted with the Chrysler double rockershaft engine, a highly regarded design which became popular for drag racing where they were known as "Hemis". These strong, well built engines were long-lived and very durable. But the complexity of the valve layout and the machined combustion chamber made this an expensive engine to produce--more than the other competitors in the luxury car market.

The replacement was a big block engine which shared a lot of design elements of the small block Chevy V8 and was used from 1958 until 1978. Though nice engines, they weren't anywhere nearly well regarded as what was replaced.

I look at the GMC V6 and I am impressed with the 100% great design incorporated into the engines. I guess 14 years was a good run, though. And here we are, all singing the praise!

-Andy Carlson
Ojai CA

Re: SO who came up with the GMC V6's???
 

What I would like to add to BillT's response is yes the GMC V6's were great for pulling uphills and I've mentioned this before on Jolly's site which is my Uncle drove prototype GMC Tow Trucks that wr given to the California State Automobile Association(AAA) in the mid 50's which were the 55-59 design trucks with the V6 engines. San Francisco was an excellent test bed as it has a lot of hills as well as real steep hills. As far the west coast and central parts of the country being flat I would say that's is really doubtful that let to the demise of the V6, it was all about dollars and cents from the corporate big wigs, It was just cheaper to use a Chevrolet engine:pullinghairout:, the GMC V6 was known for it's longevity so it was less prone to break down. GMC historian Don Meyer has even said that. Myself growing up in San Francisco in the late 60's and early 70's and being in a family that owned a grocery market I can say the GMC Trucks powered medium and heavy duty trucks by the V6 were very dominant compared to other trucks:thumbsup:

Re: SO who came up with the GMC V6's???
 

I look at the GMC V6 and I am impressed with the 100% great design incorporated into the engines. I guess 14 years was a good run, though. And here we are, all singing the praise!

-Andy Carlson
Ojai CA[/QUOTE]

14 years not long enough, the V6's could have lasted longer if GM wasn' so cheap, anytime GM has something that's real good they tend to get rid of it. What was apparent though after the demise of the V6 was more Diesel engines were added to the larger Heavy duty series trucks, evidently the 366 & 427 engines couldn't quite muster the duties of the 432 and 478 V6 engines.

Re: SO who came up with the GMC V6's???
 

14 years not long enough, the V6's could have lasted longer if GM wasn't so cheap, anytime GM has something that's real good they tend to get rid of it. [/QUOTE]

The GMC dealer where my Dad bought the one ton Suburban new in 1965 once told him that one reason General Motors dropped the V6 was because so many of the GMC dealers were complaining that their repair shops weren't making enough money because the V6s were too reliable and long-lived. Switching to Chevy engines solved that complaint!

Re: SO who came up with the GMC V6's???
 

This reminds me of a great 305 V6 vs 350 v8 story a buddy of mine told me. He used to own a 65 GMC LWB C10 with a 305E/sm420 and 3.54 rear gear. He Loved that v6 and wouldn't have traded it for any v8.

Now here's the story:

He and a friend of his were ripping this deck down with their trucks.....his buddy had an early 70's or 80's Chevy 4x4 with a 350/th350. Well he backed up to the deck, and from what I remember hearing....in 1st gear that truck either couldn't spin the tires for it's life.....or they spun and the truck did nothing to that deck. Needless to say.....my buddy pulled up to the deck....hooked up...and in granny low, that v6 tore that deck apart without a thought. :thumbsup:

And don't get me going on 305 v6 vs 305 v8 stories! :teehee: Never will Any chevy engine beat the durability and performance of the v6. Best engine GM ever made, not many can claim an easy 300,000 miles!