Hot Rod Forum banner
1 - 12 of 12 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter · #1 ·
I love low-end torque. Blame it on youth spent on 2-cylinder "Poppin' Johnnies", B&S 6.00x6.375 inches, 60 hp @ 1125 rpm

The 401 is a GMC "Big Block" 60-degree V-6 truck engine made from 1960-66.
210 [email protected] rpm, 348 lb.ft @1600 rpm. 4.87"bore, 3.58" stroke, 7.5:1 CR, "Pass everything but a gas pump." Engine is the "Magnum" version with bigger head passages.

What can I do to improve gas mileage?
With the low CR and massive 4-ring pistons is this a candidate for a turbo?

Would I be better off grinding crank to use modern rods and pistons to raise CR? This would also involve lightening the crank (which is not a bad thing!)

There's also a crank with 3.86" stroke that could be offset ground for even more stroke.

Would any of this improve the gas mileage? I'm wanting to make some trips in it but cost of improvements could pay for a lot of gas.

But more torque is always a good thing:p
 

·
Hates: Liver. Loves: Diesel
Joined
·
6,313 Posts
So, yes... you're crazy, but I like it.

The big V6 is insanely heavy, low-revving, low compression slug. The name of the game is reliability in HD applications. It's an odd choice, which is kind of why I like it. Just don't expect to get any of the MPG you're hoping for. I tend to prefer a turbo over a supercharger. SCs are RPM-based. They make boost proportional to the RPMs. Turbos make boost proportional to your right foot, which means they tend to be more efficient (in terms of how much power they require to operate) than a supercharger.
 

·
Old(s) Fart
Joined
·
6,016 Posts
A big block Olds or 500 CI Caddy is a much better choice for "low end torque". 800 lb lump with 348 ft-lbs and near-zero parts availability vs a 650 lb engine with 500 ft-lbs for a fraction of the cost. I'm a big fan of "dare to be different", but sometimes different is just different. I guess this would only make sense if the "extended cab pickup" were a customized 60-66 GMC.
 

·
Registered
Joined
·
4,269 Posts
That info along with much more is here cerial.


Yes, I know what could be there.

But there are seversl ratios etc available in the transmissions. Or he could have no transmission at all.
Like if he has a rare new process (or clark) gearset with no overdrive or damaged gears that would be a nail in the coffin for me despite getting the engine for next to nothing. If he had no transmission to start with that would also be a deal killer because nothing chevy bolts up to that gmc without some work.

I have ran a few cad 500 engines in pickups, a few 4bt engines, one 455 buick, one 400 pontiac, all mated to sm465 or th400. All cheap under $500 running carb to pan engines dropped into a engine bay then ran offroad floating valves at fun angles till something had enough. Have some biscuit motor mounts(bolt through) and its easy to swap junk engines.

When I say nail in the coffin im not talking about scrapping it. Lots of guys want parts off these engines and a 401 you get for (free to ) $300 can be sold for $500 complete or parted out for even more if you want to mess with the additional labor/organization involved. The gmc v6 engines do " run forever" if you keep them maintained.

I like diffrent. One of my failed builds was going to use a 2 stroke 8-71 engine just because I like the sound. It was cheap and already had a "good" transmission/clutch mated to it . It was going to be mounted mid engine(behind me) and have the transmission next to me me then a reverser case sending torque back to a 5 ton rear. The cheap engine I got for a steal ended up being stolen:rolleyes:. So that killed the build as the .25 wall monoque was designed around it.



Personally if I wanted to be diffrent with a model A.
I would run a(dirt track) 2.3 mated to a 5 speed.
"Light weight", tons of parts availablity, tons of support, give you good handling, would not look horrible(especially with sidedrafts) , fit in the engine bay, and would give you decent mileage. Oh and those engines can rev. At 6500 to 7000rpm a 2.3 just sounds right.

Your not making axle breaking torque. But thats a good thing. Less power(and torque) means you can run lighter weight parts. Lighter weight parts means a lighter car. With less torque bracing etc. Lighter car needs less power to have a good power to weight ratio.

You could run a lightweight IRS diff(with aluminum/ magnesium arms) in the rear or a lightened 8.8. Have a pinto/M2 front end or transverse leaf with the 2.3. Even run the stock fuel tank (gravity feeding a fuel pump) with the 2.3 avoiding cutting things up and potentially hiding the 2.3 under the stock hood.
 

·
Hates: Liver. Loves: Diesel
Joined
·
6,313 Posts
A big block Olds or 500 CI Caddy is a much better choice for "low end torque". 800 lb lump with 348 ft-lbs and near-zero parts availability vs a 650 lb engine with 500 ft-lbs for a fraction of the cost. I'm a big fan of "dare to be different", but sometimes different is just different. I guess this would only make sense if the "extended cab pickup" were a customized 60-66 GMC.
A big block anything will make more torque than the GMC V6 for far less money.

Keep in mind that stroke doesn't affect torque. That myth died 30 years ago. You need displacement. Doesn't matter if it's a Pontiac 455, a Chevy 454, a Buick 455, or an Olds 455, if you feed them the same air and fuel with the same cam duration, they'll make pretty much identical numbers in a sub-5500 rpm application.

A later Caddy 500 is cheap. People pay more money for the early high-compression engines but it's just kind of dumb if you ask me. They're built to be low-rpm engines, and the only real reason why Caddy dropped compression was for emissions and the lack of leaded/higher octane fuel. A stock cam with some mild porting on the intake side and a bit more porting on the exhaust side is all you need for well over 500 ft-lbs just off idle, well over 300 hp, and a redline of 4500. Plus, it only weighs about 50-75 lbs more than a SBC. Swap for headers and an aluminum intake and you're within a few pounds of an all-iron SBC.

I agree with Joe. Sometimes different is just different, and that's OK if you want to spend more for less to be different. I applaud it, actually... just know what you're getting into.
 

·
More for Less Racer
Joined
·
20,945 Posts
Just wanted to mention, as it seems to have been overlooked in the discussion....

You will also have to completely build a new frame and front suspension....the stock frame and suspension for a Model A is definitely not strong enough for the job of holding 800 lbs of iron on the front axle, nor dealing with the intended torque.
Nothing in the aftermarket either, everything made for a common street rod chassis will also not be strong enough.

Either you are going to be the custom chassis builder....or your going to pay someone big $$$ to do it for you.
 

·
Member - AMC/Rambler "guru"
Joined
·
1,848 Posts
So it seems that the engine was designed to pull a heavy load efficiently with a relatively low rpm, flat torque curve -- at least from the GMC hype from the sales brochure -- reproduced here: http://6066gmcguy.com/gmcv6a.html.

That might even be so -- though it states "light weight", but the data page (http://6066gmcguy.com/EngineData.html) has dry weight from 738# for the 305 to 1485# for the 702... then add the weight of coolant and oil! So "light weight" compared to what -- some other GMC HD truck engines?? Maybe some of the big old IHC V-8s???

That said, this might indeed be an economical engine... for a 5-10 ton dump truck. In a car it's just a very overweight engine with the weight adding nothing. The extra mass helps traction and durability in a big truck, but I wouldn't even use one in a pickup -- unless it's going to be pulling a big trailer most of the time, then it might make sense.

But say you want to use it anyway. Peak torque is 351 ft/lbs (NET) at a measley 1400 rpm. So gear the rear axle so your high cruise speed is about 1400-1500 rpm. Most modern engines I-6, V-6, V-8) want to cruise at around 1900-2000 rpm (for comparison, a 1972-78 Jeep 258 I-6 put out peak torque at 2000 rpm -- 195 ft/lbs), with very few exceptions. So gear it to run about 1400-1500 rpm at say 70 mph, even with an OD trans, in high gear. It should have enough low speed torque to be fine in first gear with a high rear axle ratio. But that's the only way I'd do it. As far as speed parts... who needs them? Build it back stock and run it. It's not going to be a speed demon, but will still melt tires in that light Model A even with a very high rear axle ratio!! Might make a good highway cruiser, but would be more at home in a motorhome...
 
1 - 12 of 12 Posts
Top