Engine and Transmission Tech

Or, not so much, So your ported TA heads are with impressive flow #'s, but how about velocity for street use ? Some flow gurus like to fill the bottom of the intake port. Long term durability ? What if you were to install a skilled shaped, vertical port divider ? Would need flow bench refinement, Because velocity is up, perhaps no need for filling bottom of port ?
Art.

Then why get them ported in the first place Art? Wouldn't that be an unnecessary added expense? Better yet, don't port the TA heads and stack a blower on top of them for when you want max power. That's what I did.

Jim

Well Jim, not everyone wants to run a blower. Why change heads, just add nitrous. Why do any of this.? Just leave stock motor in there. Wait a minute, then it wouldn't be British V8...

I know but you were talking about porting the heads and then de-porting them? Why would you do that?

Jim

Is filling the bottom of intake port, de-porting ? Is adding a thin vertical port divider, de-porting? Flow #'s are only part of the picture,
especially in a street use motor. Port velocity equals driveability. Why did Offy bother with a dual-port intake ? Sales gimmic only ?
Onward, Art.

My Offy dual port was a sales gimmick. It was dead above 4K.
All I'm saying is if that's what you want don't port the TA heads to begin with. I didn't, but then I also added a blower. Best of both worlds.

Jim

> It was dead above 4K.

That's odd. Ted Schumacher tested a rebuilt Rover 3.5L (standard bore and stroke but with 10.5:1 compression pistons and an Isky 264 hydraulic flat tappet camshaft) with both an Offenhauser Dual Port and an Edelbrock Performer Rover and they both peaked in the 5500 to 5700 RPM range but the Performer was up 20 HP by then. I've tested a bunch of intake manifolds on a Ford 351C and they generally peaked within +/-100 RPM of each other, whether they were single or dual planes. Ted mentioned the long tube (TR8 tri-y) headers were a fair bit better than the MGBV8 block huggers. Mufflers can also make a big difference. I had a Dual Port on my low compression (8:1) TR8 3.5L then switched to a Performer. The biggest difference was the Dual Port was really smooth whereas you could feel the Performer when the dual plane plenum effect kicked in. I've seen a similar thing on the dyno with the 351C. Not apples-to-apples (different camshafts and compression with the Dual Port having a point less compression but higher lift on the cam) but the Dual Port made better power at low and high RPM while the Performer had a stronger mid range.

> My Offy dual port was a sales gimmick.

With the small ports, a Buick 215 or Rover V8 is the last place a dual port would be needed. On the other hand, something like a 351C-4V Ford with huge ports and valves the dual port has its place, especially with a spread bore carb where the port cross-sectional area can match the flow rate of the carb's primary and secondary circuits. Here are a couple of pictures comparing the Rover and Ford dual ports.

I haven't heard a compelling reason for horizontal port divider vs vertical ?

It was about 30 years ago, Chet Herbert of "Cams" fame, had built a new hemi head for Top Alcohol/Nitro drag racing. He told me it it flowed 550 cfm @ 28" ? Supercharging not withstanding, I asked, " How do you get port velocity" ? " In the intake manifold", he replied. We see this today in current engines. . 348" hemi has quite large intake ports but well designed, high-velocity intake manifold. Onward, Art.