Technical SBC327 250HP vs 300HP in 1962

Since I'm on a 327 kick today, I tried to search this but couldn't find an answer - I'm hoping you guys might have 2 cents to kick in.

I always was under the impression the difference between the 250HP and the 300HP was the heads and perhaps a bigger carb. I recently acquired a Motor Trend from 1961 that explains the differences for the "new" engines. (see pic). They make it seem as the only difference is the carb (larger 4 barrel for the 300HP).

Is that it? I already have an aftermarket aluminum intake and Edelbrock 1406 carb - curious if I'm pulling closer to the 300HP power with this config? (I know - take to a dyno and prove it, right?)

 

different heads and different cast iron intake on some as well (flat on sides below carb base vs hour gl*** shape) plus carb

 

I should mention this is for the Bel Air/Impala line-up. I know the Vette had a 300HP 327 that year and they were different heads and FI too, right?

I don't have the stock intake or carb - from what I've read most of the aftermarket intakes and 1406 (600CFM) were better than the stock.

 

Camel hump heads, 1.94 intake valves, on a 300 hp.

 

Carter AFB on 300 hp

 

300HP vette is same as p*** car. FI motor is 360HP in 62-63 then upped to 375 HP at the end. 1406 should work fine but may be a little lean out of the box. 250HP had a rochester 4 bbl and 300 had a wcfb carter I think

 

The 250 hp had the 1.72 Power pac 283 heads. Some of the 300hp came with 2 and 1/2" ramhorns. Also the 300 hp has a better cam profile.

 

'62 300 horse used the Carter AFB on the stick cars only, the Powerglide used a Rochester in '62 only, then went to AFB in later years. The heads were the '461's with 1.94 intakes as compared to the power pack head with 1.72 intake valves on the 250 and I'm pretty sure the bigger ( 2 1/2") exhaust manifolds were used, even in the p***enger cars. Compression was 10.5 on both but I don't know if the 300 used a hotter cam or not.

 

Wow. Great info guys. Seems like the car rags were a little light on details even back then! I thought the heads were different so I guess I was surprised they didn't call that out.

 

X2 on the 2 1/2'' exhaust manifolds and double hump heads.

Gary

 

The 250 was pretty much the old 230 hp 283 from 61 but with 327 inches 300 had better heads intake cam and exhaust.

 

My opinion having owned 3 of the 62 cars: the short blocks were identical. The 300HP version, as stated above, had the 1.94 heads, commonly referred to as "Camel Hump". The intake was designed for the AFB carburetor and the exhaust manifolds were 2 1/2". The 250 HP had either a WCFB Carter or a 4GC Rochester with 2" exhaust manifolds and the "Power Pack" heads. They both shared the same camshaft.
Another piece of trivia: the 283's used the old cast iron Powerglide and the 327's used the new aluminum version. If your car has a cast iron transmission, it was most likely built with a 283 or you may have a 283 dressed as a 327. The heads on the 283 motors had a rectangular pad on the ends rather than the triangle (250HP) or the camel hump (300HP). I think!

 

Carter AFB OR Holley on 300 HP, depending on the CAR (p***enger, Vette, truck) I believe; Power Pack heads on the 250 HP with either a Carter WCFB or Rochester 4 jet carb (just like the 220 hp 283's). My one Chilton's (71 edition) only goes back to 64, but it "looks" like the 250 and 300 HP 327's used the same cam (a really mild hydraulic). CR the same, but larger exhaust on the 300 HP. I've got a bunch of 327 stuff sitting on the shelf I'm trying to let go of! Gman0046, a friend of mines son was GIVEN a 63 Impala SS in white with a red, bucket seat interior, by the original owner. It had LOTS of rust however, but still had the 300 HP 327 and Borg Warner T-10 4 speed that had a Hurst shifter swapped on it. It ran, just not very well, and he S****PED it out; did't save anything. Every time I see your avatar, I think of that car, and how stupid the kid was (sort of still is)! I am Butch/56sedandelivery.

 

Yeah, I think they went to Holley on the 300 horse in '66 and '67 but I'm pretty sure that engine was only available in the Corvette. There was a 275 horse engine in '66, a friend had one in a Chevelle. That 275 could be either Carter, Holley or even Rochester for some reason.
Holley got their foot in the door at Chevrolet with the Mystery 427 in '63 and then it was '65 before they used one on a production engine, the 396. I imagine it was Ralph ?, can't remember his last name, but he was one of Smokey's right hand men and I think he helped with that decision. Ralph no doubt pushed for the Holley on the Mystery Motor, he also had worked for Holley.

 

I also Had a new Chevelle in 1966 with a 275 horse 327, a iron Saginaw 4 speed and a single exhaust. I was told the single exhaust was the reason for the 275 rating. If it had dual exhaust it would have been rated at 300 HP.

 

Learn something new every day... The old 300 horse pulled that hard , I would have swore it had more cam.

 

The lift on the 250 and 300 motors was .2658 in. at the lobe. This is from the GM Heritage web site. They posted a catalog you can download published in 1962 by the Chevrolet Engineering Center. It also includes dyno reports on all motors. I have a 66 motor, 275HP that came with a Quadrajet. A friend had one with an AVS Carter. I have personally not seen a Holley application for that motor for that year.

 

The Holley is the small 540 unit. Supposedly, Chevy II's were Holley or Carter, but not the Q-jet. I've seen Holleys on Impalas too.

 

I think that power pack heads were also on earlier 283's with the power pack option. A triangle cast on the end of the head.

Sent from my VS500 using The H.A.M.B. mobile app

 

The L79 option 327/350 hp Chevelle also got a Holley in 65.

Yes, there were some of the 275 HP 327's (L30) that came with a Holley, I can't verify the cfm on those but the 350 horse 327's were 585 cfm.

 

Bingo. 1962-1965 327, 250 and 300 HP used a 0.3987/0.3987-inch intake/exhaust lift cam, PN unknown (to me). From 1966, throughout the 70s and into the 80s, most hydraulic cammed 283/307/327/350 engines used the same camshaft: 3896929 machining part number, (3896930 casting) that had a 0.390/0.410-inch intake/exhaust lift and a 310/320 degree intake/exhaust total duration.
In 1967 (I known this is an OT year, but a good example) the 283/195, 327/210, 327/275 and 350/290, all used the same 3896929 camshaft.

 

I believe the first production use of the Holley 585 cfm was on the 327/365 in 1964

 

Any time you see comparitive HP & torque ratings and one peaks at a higher rpm than the other, you can bet the farm there's a hotter cam involved in the higher HP setup.
Sure, bigger carb, better manifolds and heads, can raise HP & Torque ratings, but they'll do it at the same rpm.
It's the cam that determines when the valve events happen in relation to the position of the piston in the cylinder, and that's the only thing in our engines that will dictate rpm changes.
It's always been my understanding that the 300 hp version of the early 327's included the use of the 098 cam, on top of other things, like a larger carburetor.

 

wow, six years later....

anyways, let's see what Chevy has to say, since the answers given are all over the place. This is from the 1962 version of the Corvette Service Manual.





The carb on the 250 hp is the WCFB, while the 300 gets the AFB.

You can see the cam is the same in the 250 and 300 hp engines.

Now we'll look at the Engineering Data....



this shows that the 300 hp got the bigger valve heads, along with the larger exhaust manifolds.

So...does this clear things up?

 

Yes...at least until someone says that their ex-wife's second cousin's high school boyfriend bought one new with tripower on it.

 

poking around the GM Heritage center vehicle information kit for 62 Chevy cars and scrolling down to Powertrains page 19 (1 through 18 are 235 and 283) the 62 327 comes up. 1962-Chevrolet.pdf (gm.com)

The nitty gritty is there. As Jim's post said WCFB on the 250 HP and AFB on the 300.
The list of differences is a lot longer than I thought
Higher compression ratio on the 300HP with a 4.452 CI combustion chamber as apposed to the 4.556 of the 250 hp
300 hp had 2.5 inch outlets on the exhaust manifolds rather than the 2 inch of the 250.
A big difference in throttle bore diameters. (Now I have to go back and edit a post on a 327 intake manifold thread)

No tri power offered though.

 

Yeah, sorry about that. Didn't notice until you pointed it out....Of course, you coulda just posted your stats, but whatever.

Interesting. I think I spot a typo (it happens).
The 250 and 300 HP engines show a cam with a lobe lift of .2658". Multiply that by the rocker ratio and you get .3987" lift at the valve....rounded up, that could be expressed as .399" lift.
Now let's think about this...what cam featured .399" lift on both intake and exhaust?
It certainly wasn't the regular "stock" cam. That cam had .335" valve lift on the intake and .348" valve lift on the exhaust.
You can argue points all you want, but it still doesn't explain the difference in rpm of the peak power figures between the 250 hp engine and 300 hp engine....unless you open your mind up to the fact that your data features a typo.

 

Edelbrock 1406
Swapped one on my father's 1965 327 300 hp - continual issues with the Rochester 4GC, after 2 rebuilds.
1406 Ran great out of the box, didn't need any metering rod changes. He doesn't run high rpm. If yoire wanting to turn 6K on regular basis - choose accordingly.

1406 is listed as "mileage or economy" but aftermarket uses 350 as reference point for everything.

 

I wasn't intending to be mean, just pointing out that it's an old thread, and the guy probably was satisfied with the lack of answers he got 6 years ago. I happen to have recently got a 62 Vette with an original 250 hp engine, which I'm kind of interested in the performance of and how to improve it, so I'm glad you brought the thread back to life. It seems that it's easy to not notice the date of a thread when you post on it (maybe using a phone?) so it's not like you did anything wrong.

Think about the power curve of a 300 hp engine that you don't open the throttle on all the way. Probably pretty similar to the 250hp engine, eh? That's exactly what's going on here. You can lose the top end by just not having as much breathing ability as the cam would allow. When they put the big cam in the 300 hp, it turns into 340 hp, and has a higher red line, and more top end, even though it loses bottom end. You see the opposite with the difference between 250 and 300 hp engines, the 300 has more torque than the 250

Oh...I decided to just add a medium hydraulic cam to my 250hp, it runs pretty good, but only to about 5500 rpm. Which is fine with me, for now. It's a lot of fun to drive and I don't have to worry about over revving it accidentally (the tach is pretty hard to see when going through the gears)