Engine comparison question (307 & 327)

[VinnyT]

Okay, I can't say why I need your opinion, but I just do. I know the differences, but need third-party input. Here it is:
Please give me the value and desirability of these two motors:

1967 rebuilt Chevy 327 with double-hump heads.
1973 rebuilt Chevy 307 with stock heads.

Thanks all.

[MrPbody]

Vinny,

The value of either is a subjective opinion. A 327 would certainly be worth more money. How much more? Can't say unless we know EXACTLY what was used in the rebuild, and how qualified the machine shop is to do a rebuild on a classic.

327 has a 4" bore and 3.25" stroke. With a rod length of 5.7', it has an excellent rod/stroke ratio, and the bore/stroke ratio makes for very good RPM capability. The larger bore diameter also aids in cylinder head flow by "unshrouding" the intake valve. "Double hump" heads are strictly 327 heads. There are claims that 302 got them the first year, but I've never seen a FACTORY "DZ" engine (Z/28 302) with them.

307 has a 3.875" bore and 3.25" stroke. This means it has the same rod/stroke ratio as 327, but the bore/stroke ratio is not near as desirable. Chevy knew this, as no 307s ever got the "good" heads (all "small valve"). 307's primary mission was an economical and efficient, yet "snappy" engine for mid- and full-sized cars.

Generally, if performance is your goal, go with 327. You can always move "up" to 350 or 383 later. If economy and many miles of driving pleasure, without tire-smokin' power, 307 wouldn't be a BAD choice... The 307 heads respond to performance mods, but with all the good stuff available, it would be a waste of time and money (IMO).

Jim

[66 chevelle]

Vinny, Jim is right take the 327 even if you don't want the extra power just don't put your foot on the floor.
They are very good motors. I have one in my garage from a '68 vette.
Anyway the camel hump heads are some good high perf stuff. The valves are 2.02" int. and 1.60" exh. Plus if you find a cheap short block 350 or 383 down the road you can use the same heads.
The heads on the 307 are basically junk as far as performance goes. I believe the valves are 1.72" int. and 1.5" exh.
Let us know what you do? What car are you putting the motor in?
Jim

[MrPbody]

66,

Just for clarification... The ONLY "double hump" or "camel hump" heads that were factory-equipped with 2.02 intake valves were the '64-'66 365 and 375 HP versions of 327. The casting number ends in "461X". It is essentially the same casting as 461, and very similar to 462, with the exception of the intake valve size. ALL 327 heads had 1.5" exhausts.

Not to worry. This is a common misconception.

Lastly, we're of the opinion, all the "double hump" heads were rendered obsolete in '69 when "041" was released in production cars. The intake runners in the 041 and 441 (large chamber version) are about 8 CCs larger than previous SBC heads. The 292 and 492 (street version) are FAR superior. Those are the "over the counter race" heads sold by Chevy in the early '70s. The 292 is also refered to as the "turbo" head. Any of the 350 performance heads will outperform the 327 stuff on engines larger than 331 or so.

FWIW

Jim

[66 chevelle]

MrPbody with all due respect I have a '68 327 out of a wrecked vette.
It's a numbers matching engine. I checked myself. Camel hump heads.
67,500 original miles. When I first bought the motor I did a top half re-build on it and I actually measured the valves because I was not that knowledgeable about motors 20yrs ago. Anyway it has 2.02 int. and 1.60 exh. valves that are the original valves for those heads.
Just thought I'd let ya know.
Jim

[66 chevelle]

MrPbody, Here's a couple links though not by GM but I think you'll find most/all 2.02" int. valve heads have 1.6"exh. valves and a few 1.94"int. valve heads have 1.6"exh. valve too.
http://www.73-87.com/chevy_ids/sbheads.htm
http://www.auto-ware.com/techref/castnum.htm

[MrPbody]

I went out and looked at that list. The vast majority of numbers that had 2.02s and 1.6s "stock" are over-the-counter RACE heads, not production car heads (examples are the "292" and 494"). Only one number shows for 327, and it lists it as '64-'70. Take what you read there with a grain of salt.

The 186 is VERY rare, and the only ones I ever saw were on 302s, not 327s, even though it lists them as such. Except the "High Torque" and some 2-bbl. engines, the three comomon numbers were 461, 462 and 291 for 327. The 2-bbl. and High Torque (C-20 and bigger) had small valve heads.

It wasn't my intent to point the finger. I live in "the real world" of engines. I hear stories and see heads and blocks. Some of them are true, some not. It IS possible, some of these numbers got out on production cars, but they're so rare, it isn't relevant. It's like guys claiming they have "Ram Air" heads on their Pontiac because they're "12s". If the heads came from the factory on a "Ram Air" car, then, yes, they could be called Ram Air heads. But what knowledgeable guys are refering to when THEY say "Ram Air heads", they mean Ram Air IV "round port" (exhaust) heads. BIG difference. Same holds true for the Chevys.

I've been building engines for over 30 years. Many of those Chevy numbers you pointed to, I've never seen anywhere except in magazine pictures. My only point is to be realistic in your search. Truth be known, a pair of Dart Iron Eagles out-perform ANY factory iron head, including the Bowtie stuff. The "new" "Vortec" (a misnomer) head is better than most of the old stuff, too. We recently finshed a 406 bracket engine with Pro-Topline heads (I always though them to be "junk"). They WORK! No porting, just milling for compression. 3,100 lb. '87 T/A, 10.51 @ 129! They couldn't be TOO bad... (:-

PAX

Jim

[66 chevelle]

I've been building engines for over 30 years. Many of those Chevy numbers you pointed to, I've never seen anywhere except in magazine pictures. My only point is to be realistic in your search. Truth be known, a pair of Dart Iron Eagles out-perform ANY factory iron head, including the Bowtie stuff. The "new" "Vortec" (a misnomer) head is better than most of the old stuff, too. We recently finshed a 406 bracket engine with Pro-Topline heads (I always though them to be "junk"). They WORK! No porting, just milling for compression. 3,100 lb. '87 T/A, 10.51 @ 129! They couldn't be TOO bad... (:-

MrPbody, yes I've heard the vortec heads are some good heads oh and I agree with you on the casting numbers. Most were in production for a very short time. Doesn't make sense to me but oh well.
Hey I have a '71 454 in my chevelle with the "990" heads and over sized 2.25"int. and 1.88"exh. valves. Cam specks are .553 int. & .571exh. with a duration of .236/.246 @ .050 lift. She runs really good but I can't seem to get a pic up here of it though??
Take care, Jim

[MrPbody]

990s are about the best production head Chevy made for the BBC, for high rev use. Interesting that whoever built them chose to upsize the intake, but not exhaust. Must have done some real research! BBC heads are notorious for the aforementioned valve train issues, but they are less known for, but DO have, TOO good an exhaust port. That is, the balance isn't there. The exhaust ports aren't "defficient", as 1/2 of the intake ports are. My compliments! We usually see 1.94" exhaust valves with the 2.250s... I'll bet it runs nice!

Jim

[66 chevelle]

MrPbody, yea it runs really good. It's all over the road till about 50-60mph(lack of traction)after that it just keeps you pinned to the seat till about 100-110. 4.11 posi 12 bolt rear end. 3 speed reverse linkage auto trans. Also have the edelbrock air gap intake matched to the heads. S.S. hooker comp headers 2" primaries with 3" flowmaster super 40 exhaust. Too bad gas is $3.40+/gallon.

[MrPbody]

66,

You might consider a Victor or Super Victor to soften up the bottom-end "grunt" that's blowing the tires off. We've had some success doing that with the higher-torque engines. RPM is a good intake, but may make TOO MUCH low-end. Some of those big Pontiacs will just SHRED the tires. Going to Torker II or Victor has helped many of them get their 60' down where it needs to be.

I know, I know. Less torque? The guy must be daft... Nope. Experienced. Any engine with a 4" or greater stroke, will make a ton of low-end. The heads help or hurt, but in this case, it's the sheer size of the engine, and the long stroke. It will actually be faster with less torque under 4,000 RPM.

Jim

[victimizati0n]

i have fullie heads on a 355

[66 chevelle]

Originally Posted by MrPbody

66,

You might consider a Victor or Super Victor to soften up the bottom-end "grunt" that's blowing the tires off. We've had some success doing that with the higher-torque engines. RPM is a good intake, but may make TOO MUCH low-end. Some of those big Pontiacs will just SHRED the tires. Going to Torker II or Victor has helped many of them get their 60' down where it needs to be.

I know, I know. Less torque? The guy must be daft... Nope. Experienced. Any engine with a 4" or greater stroke, will make a ton of low-end. The heads help or hurt, but in this case, it's the sheer size of the engine, and the long stroke. It will actually be faster with less torque under 4,000 RPM.

Jim

Jim I agree. But(there's always a but LOL)I just drive my car to the local cruise nights and out in the country for some fun and actually prefer it this way. That's why I like the automatic for longer burnouts because I don't take it to the strip and don't have a desire to. I do like going to the strip watching the NHRA guys though. Isn't this fun?
Jim

[jveik]

i have seen some people refer to 307's as "boat anchors." however, i bet with a little modification, they can easily pump out 350 horsepower, and thats by todays standards for horsepower. however, the 327 is a better motor. in many stock vs. stock applications, a 327 will blow the doors off a 350, which i would hazard to guess is because of the difference in stroke. they have the same 4 inch bore, but the 350 has a 3.48 inch stroke, though you can still rev them well over 6000 rpm with the right valvetrain components.

[C2Z06]

Originally Posted by MrPbody

66,

You might consider a Victor or Super Victor to soften up the bottom-end "grunt" that's blowing the tires off. We've had some success doing that with the higher-torque engines. RPM is a good intake, but may make TOO MUCH low-end. Some of those big Pontiacs will just SHRED the tires. Going to Torker II or Victor has helped many of them get their 60' down where it needs to be.

I know, I know. Less torque? The guy must be daft... Nope. Experienced. Any engine with a 4" or greater stroke, will make a ton of low-end. The heads help or hurt, but in this case, it's the sheer size of the engine, and the long stroke. It will actually be faster with less torque under 4,000 RPM.

Jim

Why is this? Just a guess but I'm thinking a possible broader power band? Flatter and on average, higher torque curve? Because of the less torque onver 4,000 RPM, you hook up the tires better and therefore a quicker launch?