Mid-year 327/300 vs. 327/350??

[Dwight P.]

It is easy to understand how higher horsepower is achieved with more cubes. In the case of the 327/350, it has a .5 higher compression ratio, a different intake manifold, and a different carb. Are these the only differences between the 327/300 and 327/350 that give it the extra 50 horses?

Thanks,

DP

[Gerard F.]

Re: Mid-year 327/300 vs. 327/350??

On a 67, the same carb, but I think a little different cam.

Jerry Fuccillo
#42179

[John H.]

Re: Mid-year 327/300 vs. 327/350??

Dwight -

The 327/350 has:

0.75 higher compression domed pistons (11:1 vs. 10.25:1)
Bigger valves
Performance camshaft
High-rise intake manifold
Same carb
Different distributor advance curve and initial timing

[Dwight P.]

Re: Mid-year 327/300 vs. 327/350??

John:
I was not aware of the valve difference. "The 1953-1967 corvette Spec Guide" indicates that the 327/350 came epuiped with a Holley 4150 vs a Carter AFB for the 327/300.

Thanks for the info.

DP

[Joe L.]

Re: Mid-year 327/300 vs. 327/350??

Dwight-----

The last year for the use of a Carter carburetor on a Corvette was 1965 (although Carter did build some Q-Jets for Rochester in the early 70's). For that year, the 250 and 300 hp engines used Carter carburetors, The 1965 L-79 as well as L-76 used Holley carburetors and these were model 4150.

For 1966 and 1967 all Corvettes used Holley carburetors. The 300 hp base engines and L-79 Holley carbs were model 4160, though.

[Kent K.]

Re: Mid-year 327/300 vs. 327/350??

Dwight, John & Joe,

Holley carburetor 3610 was used on 1967 327/300 Corvettes. I believe a diffetent Holley was used on the 1967 350HP engine, the number I don't have access to at the moment.

Kent

[Peter L.]

Re: Mid-year 327/300 vs. 327/350??

Kent - Same carb, LIST 3810, on both 1967 engines. Pete

[Kent K.]

Having a senior moment

and can't even remember which carb is on my car. Thanks Pete for the wake up note.
Kent

[Joe R.]

Re: Mid-year 327/300 vs. 327/350??

Hi Dwight:

The difference in valve size is small, and probably accounts for very little of the power difference between the two configurations. IIRC, the 300 HP valves are 1.5/1.94 inches, and the 350 HP valves are 1.6/2.02 inches. Both heads use the same raw castings but are machined for different size valves. Most of the flow data I have seen shows very little difference between the two configurations.

In my view, the three main reasons for the power difference, in rank order, are probably:

1) Cam
2) Intake
3) Compression

Note that the 350 HP cam is optimized for higher RPM, which helps when comparing peak horsepower. The 300 HP cam generates considerably more torque than the 350 HP cam at low RPMs, but the 300 HP cam is pretty much out of gas at about 4500 RPM, while the 350 HP will pull nicely up to 6000 RPM.

[Joe C.]

Re: Mid-year 327/300 vs. 327/350??

The '64-'65 327/300 was equipped with 2 1/2" exhaust manifold outlets when mated to the M20 trans; 2" manifolds were used with Powerglide. This made no difference in the L75 power rating though, because its peak torque occurs early (360 ft-lbs.@ 3200).

The engine's peak torque comes on sooner than the higher horsepower versions, and trails off earlier. Since horsepower equals torque X RPM / 5250, you can see that horsepower will peak in relation to the torque peak. The high horsepower engines produced about the same peak torque, but at a higher RPM, thus, higher horsepower. Stroke length will always produce a torque increase, all other things being equal.

Look at the Chevrolet SBC camshaft specs below, and compare those of the 3896929 to those of the 3863151:

Joe

[Dwight P.]

Re: Mid-year 327/300 vs. 327/350??

Joe:
Thanks for all of the info...a lot to digest.

Dwight