Technical 327 250 or 300 Hp

The 250 and 300 engines use the same exact same pistons? Thanks

 

yeah, 10:50 -1: CR. Even the cam is the same.

 

250 horse engines use power pack heads with Rochester 4bbl carbs and 300 horse engines use double hump heads and AFB 4bbl carbs. The short blocks are the same.

 

The 300 uses the 2-1/2 inch outlet ram horn ?

 

On passenger cars, no. Possibly on Vette's.

 

I think when they first came out, the 340 hp. and up used the 2 1/2, anything lower was the smaller. FYI, U can still get these aftermarket and i feel are def. worth the money-my opinion as good as short headers. I use 'em and never worry about leaks or heat.

 

I think the 275 hp uses the 1.94 heads and a quadrajet. The 300 uses 1.94's and an AFB. Lippy

 

A few of the 250 motors came from the factory with WCFB carb. I used to own one. My next car had a 250 with the 4GC, then last was a 300 with an AFB. As Lippy said, the 66 and 67 275 small blocks used the Q-Jet, mostly. But some had the AVS carb; though not many have I seen.

 

i'm certainly no expert on these, just old age and remembering. The 250 came with a single rochester 4 bbl, small rams horns, and single "point" heads (old power pack). The 300 came with double humps (1.94's), single carter afb that flowed around 600 cfm, and the small rams horns also (might be wrong here). Each motor had a different suffix for the hp rating, it can be looked up elsewhere. Everything else was the same. Real easy to take a 250hp and make 300+ out of one today.

 

I do know that ‘62 passenger car 300 horse engines had 2 1/2” rams horns and exhaust all the way to the rear bumper, but the PowerGlide cars used the 2”. I think the exhaust manifolds later went to 2” on the 300 horse stick cars but I don’t know what year.
@Oilguy is right on the money with the carb info, I have a Carter 4028S AVS from a 327/275 on a 283.

 

Running changes??? My 65 327/300 had 2" ram horn manifolds with head pipes that opened up to 2 1/2" after the flange. Who knows what the General was thinking about back then...

 

A lot of 66 275/327's (passenger) came with a Holley 600 #3230 carb.

 

My '68 275hp had a Quadrajet. Don't know what heads.

 

The GM Heritage site has original specifications for many model years..Looking at 1964 full size it does appear to say 2-1/2 outlet manifolds for the 300 hp….

 

Had a new '66 Chevelle out of high school with a 327 and Saginaw iron 4 speed.
Was rated 275hp because of single exhaust.
If it had dual exhaust, would have been rated at 300hp.
Had a lot of fun with that car.

 

Had a '66 300hp 327 in a Triumph Spitfire. Originally came with a Carter AFB. It was my "Cobra killer"...

 

I could be out-to-lunch here but I have never heard of a 300HP 327 for 1966. The 250 and 300 motors were dumped after 1965. The 1966 stuff was 275HP.

 

Also 327/350 h.p. in 66 Novas, but they are OT, right.
And I can't count the number of times I've had to tell people no, you never owned an original 66 Chevelle with a 350 h.p. 327.

 

I need to clarify that I was told that if you put dual exhaust on a single exhaust 275hp 327 you would have a 300hp 327. Not that a 300hp 327 came in a '66 Chevelle.
Sorry for the confusion

 

Father has a 65 impala SS 327 PG A/C, had a WCFB on it. Block numbers are right. Who knows how that carb ended up on there, original or changed along the way. Had the WCFB rebuilt by long time local carb guy and fought it over and over. It's in a box on the shelf. Edelbrock 1406 - not an issue since.

 

The truly mystifying thing is, you could take a 275 hp 327 from a 66 Impala and put it between the fenders of a 66 Vette and it was instantly 300 hp...

 

It's a transformative thing... new surroundings, new environment... you know?

 

Scroll down the page to the 327 Section it pretty well gives the differences.
The main difference is carb and intake. AFB as apposed to WCFB https://www.gmheritagecenter.com/do...information-kits/Chevrolet/1963-Chevrolet.pdf