Was 327/350 Cam, Now Varoom Intake Manifold Questi

[Christopher R.]

Can you expand some more on cast iron versus aluminum intake manifolds? Why is cast iron better for low end torque? Wouldn't the design count more than the material?

[Joe L.]

Re: Was 327/350 Cam, Now Varoom Intake Manifold Qu

Chris----

Design does count more than material---way more. The deal is that, generally, GM manifolds which are of cast iron material are the lower performance manifolds, principally used for passenger car applications where low end torque is more important than top end horsepower. Consequently, they have smaller intake port runner volumes than do many GM aluminum manifolds which are typically designed for higher performance applications.

In general, the lower performance Corvette engines are the same as passenger car engines and receive the cast iron manifolds designed for such applications. This doesn't make them "bad", though. The lower performance engines are, OVERALL, some of the sweetest running engines ever installed in a Corvette and have more than adequate power for most street applications.

[Dale Pearman]

Re: Was 327/350 Cam, Now Varoom Intake Manifold Qu

BEWARE of the psychology behind the phrase, "High Performance". The phrase means "High RPM" which through a given mathematical formula with fixed torque results in higher horsepower. High horsepower lets you go fast. High bottom end torque lets you go fast a lot quicker! That's acceleration! What you want to build is acceleration for the street. FORGET horsepower. all you need to go 120 mph is about 250 hp. But you don't want to take all day to get up to 120 mph.

Small intake runners cause the incoming air/fuel charge to have higher velocity which means mote inertia. This tends to more completely fill the cylinders at lower RPM resulting in greater volumetric efficiency which translates into torque. Sorta like a supercharger. The John Dolza Corvette Fuel injection systems have runner lengths tuned for maximum inertia at a particular rpm. The old Chrysler 300 series had cross ram runners that did the same thing. They made torque UP THE KAZOO at low rpms with two AFB carburetors. A ride in one of those 300 series cars was like a rocket sled!

That's what I call high performance! Low RPM torque! I agree with Joe's above post 100%. The "manly" thing of course is aluminum. The SMART thing is iron. Appearance is everything until ya get to thinking about it!

Dale.

[Dale Pearman]

P.S.

It's hard to beat a 1962 300 hp iron intake with an AFB 3269S sitting on it. 901 & 902 ram's head exhaust manifolds into a 2 1/2 inch exhaust using International Harvester turbo mufflers is also hard to beat!

Dale.

[Joe Pennington]

Re: Was 327/350 Cam, Now Varoom Intake Manifold Qu

Also, one of the primary reasons, for an engine that is designed for low RPM applications, is that the intake manifold runners are of a small cross section, in that increased velocity is needed to keep the fuel atomized. Large runners, at low velocity, tend to have the fuel seperate from the air thus collecting along the walls of the runner. On low RPM applications it is better that no polishing be done on the intake runners as the roughness aids is keeping the fuel from collecting on the walls of the runner. Also, if you do any porting of the intake ports in the heads and "port match" the intake manifold runners, leave the intake manifold runner sightly smaller the the head port. This will result in a small lip which will cause the fuel that is now in a fully liquid stage, and adhearing to the walls, to be pulled loose and partially atomized as the mixture enters the combustion chamber. A incoming fuel/air mixture that does not have good atomization makes for poor combustion which results in poor torque. Hope my explanation is clear.

[Joe Pennington]

Re: Was 327/350 Cam, Now Varoom Intake Manifold Qu

Joe L., I meant for my response to go to Chris, not you, sorry.

[Lawrence Berte]

Re: Was 327/350 Cam, Now Varoom Intake Manifold Qu

Chris,

You may want to try the GM Performance cast iron version of the old LT1 intake. It features, both square-bore and spread bore carburetor mount pad, OEM divorced choke, and large raised runners. After trying both an original 300HP cast iron, and Weiand Action Plus aluminum intake manifold on my '70 300HP with the GM 151 cam, the iron LT1 intake demolished the contenders, in low end torque, as well as mid to upper end ( 151 over @ 5400 ) power. I also ran an original Quadrajet vs a Holley replacement carb test, only to find the quadrajet overpowering. Keep in mind these are my (non-dyno), but real world test results, yours may differ.

Keep The Faith!

Lawrence Berte