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Big Block 366

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Big Block 366

pmeffert pmeffert
I love my Chevy Chevette! | Posts: 1 | Joined: 07/13
Posted: 07/16/13
01:11 PM


I have been brutally battered on the small block forum, and was wanting an opinion from  true big block  folks.
I have an 87 V10 4x4, which the 350 has died due to hydrolock.  I really want to put a big block in this truck, but need to do so on a budget.  I have run across a 366 BBC.  This particular engine is a GM crate, with around 10k miles on it.  The engine is $500.  So after headers, and a better carb and intake, I would be in less than $1000.  My question is...
Everyone on the small block forum completely bashed the 366, pretty much claiming it was wasted iron.  I understand that this engine is not made for horsepower, which is exactly what I would want in a 4x4 pick up..?  Am I right, or is the 366 a waste?


Ravoll Ravoll
V-6 Camaros rule! | Posts: 85 | Joined: 02/12
Posted: 07/16/13
03:25 PM

I don't know anything about 366's except its a dump truck engine.A quick run through google produced this:

A 366 big block Chevy usually had between 220 - 262 hp and the torque usually ran between 450-510 they were a very low end torque engine they were built for nothing else but pulling they were put into medium duty truck usually from 2 ton to 3 ton trucks. They are a tall deck engine with a small combustion chamber and small valves for a big block but very high output at low rpms. They had a bore of 3.935 and had a stroke of 3.760 they used three compression rings. One of the major flaws of the 366 was that when you would down shift pulling heavy loads up a steep grade the heat in the combustion chamber would burn holes threw the valves because of high out put but now were for it to go.

And this:

The 366 was made for work trucks where low speed torque was needed, these engines are famous for burning a hole in the pistons due to high cylinder heat from such a small bore and a long stroke. I also don`t know of any high performance big block chevy heads that are "dirt cheap" horsepower costs money, how fast do you want to go? lastly, don`t waste your time or your money on a 366, why spend the money on a 366 when you could invest the same amount of money into a small block 350 and blow the 366`s doors off with less cubic inches?

And even something positive:

the big block 366 is a awsome motor. It is a very specialized high performance motor from the factory(it comes stock with headers).They are built for low end torque not high horse power.Anyone that knows motors,knows that high hp motors don't have low end torque.
Big cams,big carbs = less vacume pressure = less low r.p.m torque

Commercial applications
Mark IV engines saw extensive application in Chevrolet and GMC medium duty trucks, as well as in Blue Bird Corporation All American and TC/2000 transit buses (the latter up until 1995, using a purpose-built, carbureted 427). In addition to the 427, a 366-cubic inch (6.0 liter) version was produced for the commercial market. Both the 366 and 427 commercial versions were built with a raised deck, four bolt main bearing cap cylinder block to accommodate an extra oil control ring on the pistons. Unfortunately, the raised deck design complicated the use of the block in racing applications, as standard intake manifolds required spacers for proper fit. Distributors with adjustable collars that allowed adjustments to the length of the distributor shaft also had to be used with 366 and 427 truck blocks.

I am in the tree biz.I Have had them In a few of my 5 ton trucks. And they have more usable power(They take off faster with same load) and get better gas milage than my trucks with 454s(I also move a moble home time to time I have a 366 in my c60 without split rear end and can pull a 16x80 mobile home with no tires/in mud if I have enough weight on rear tires and about 2000lbs on the front it to keep it from lifting front end .
a friend of mine was looking up hp ratings on motors, and on a whem looked up the 366 it had 327 hp and over 500ft lbs of torque (It does this at less than 3200 R.P.M) verses the 454 at 290hp. and 410ft. lbs.

Why do I think it is a better motor than the 454 for a work motor

1)It has a tall deck with longer rods = longer dwell at top dead center(better fuel burn more torque more fuel effecent)

2)Smaller displacement=burns less fuel at same R.P.M

3)Smaller c.c peanut shaped Intake port runners makes the motor produce more vacume and faster rush of air in to the cyclinder.

4)Same block size as 454 but with smaller cylinders with thicker walls and larger volume of water in the block to keep it cool. Can be run at 80 to 90% of max output all day long. Do that to a 454 and you will cook it


1)All the things that make this a great high torqe/work motor make it a bad high hp race motor. Horse power is made buy burning the most air fuel/mix. Small displacement,small intake ports,small valves make it a impractical for light race car.

2)weighs more the a 454

3)I Think chevy got all the hp this motor is good for with headers,holly carb any attemps to get more power out of it other than a K&N filter would lower its performance.

4)It will max at about 3500 R.P.M I doupt it would go over 95 mph with 4:11 gears

Conclusion a 366 with a 4 speed allison in a 1 ton tow rig pulling a lot of weight would be a good option. If you don't want to go fast(you don't want to go fast pulling a heavy load anyway) It will pull as much as you can get traction.Or twist off your drive shaft/axels.

The older I get,the faster I was.

Ravoll Ravoll
V-6 Camaros rule! | Posts: 85 | Joined: 02/12
Posted: 07/16/13
03:25 PM

I'm sorry for the double post.  
The older I get,the faster I was.

68scott385 68scott385
I have an SS396 tatoo | Posts: 325 | Joined: 07/09
Posted: 07/17/13
12:47 AM

You can do what you want but IMO you'd be better off building a small cammed 383 than buying & outfitting a 366. You'd have nearly the same stroke (3.75) with a larger bore (4.03) that would allow bigger valves and better air flow. You'd also be able to use the headers, carb, and intake you already have and wouldn't be adding any weight either.  
68scott385 68scott385 68scott385