verskel

After more research on my engine, I've discovered that I'm running a '71 454 (425hp) intake which I believe is square port.......on 3993820 heads which are 113cc with Oval ports.

How does this affect performance ?
I've heard about guys mixing square & oval ports to increase torque but does anyone have any experience with this ? .....(maybe an article link) :confused:

GDaina

How does the car perform with that combo? I've never heard anyone mixing and matching

Wrencher

My 3x2 is a square port (435 hp) intake on a 400hp 427 with stock oval port heads. It won't work the other way around. The ports obviously do not match, but with the future alloy heads it'll work fine! :D

Hans

verskel

Seems to have more than enough torque but at higher RPM's it doesn't seem to pull as hard......I'm still doing carb. adjustments so I'm sure there's about 15-20hp left to pick up through tuning. Other than that, the car runs pretty strong.

Here's a quote off another message board :
"When we tore down our BBC with 781 OVAL ports we were surprised to find that the intake was a factory RECTANGLE port version. A little bit of questioning around from some local guys led to one who said it was an old truck pullers trick to create more torque from the "lazy" air in the plenum...just what I was told... can't prove a thing by me. I would think DART would be able to test & explain their reasoning with a fair degree of accuracy though. "

http://www.prestage.com/Message+Boar...st&PostID=2290 :chevy

zwede

I've heard of putting oval port intakes on rect port heads. This builds torque without hurting top end much. The other way around is probably not a good idea. Air likes to go the shortest way which is along the top of the port. With your combo the air will hit a vertical wall creating quite a bit of turbulence.

verskel

:eek: ....Sounds like I'll need to take off my manifold to see what's going on. :crazy:

This could explain why the car seems to loose power at higher RPMs..... :(

Simmo

If thats a low rise square port intake, they were never good at higher rpm. Some of those runners drop right down near the bottom of the valley than come up and pull a right angle bend to get into the head port. But those manifold do fit under the hood.

verskel

Hmmm.........so I'd stand little to gain from the ports matching up to bigger inlets on the heads (i.e. - square ports) ? :confused:

I've had this setup on my car since I bought it 5 1/2 yrs. ago. Also, I've racked up about 15k on it with a mis-matched intake / heads.........but now I'm trying to 'squeeze' more power out of it. ;)

Wrencher

Hood clearance was an issue for me, and believe me, it BARELY fits! I had the wrong wing nut on it and it just touched the hood!

Hans