3.0, 46mm weber and 1.5 header or 40mm weber and 1.75 header

[addictionMS]

Those are the rules, you can have either

46mm webers and you are limited to a 1.5" header

or

40mm webers and unlimited headers, so 1.75"



I have both set ups and thought I would ask if anyone has any input on which will be the better set up?

I have the 9.5:1 pistons and the 39mm intake ports, both setups will have port matched tall manifolds

Plus looking for Jetting suggestions for the 46mm webers,
Jim

[Steve@Rennsport]

Jim:

First,....1.75" headers are too big for a 3.0 engine unless its a very aggressive, 8500 RPM, high HP (360+) motor.

Second,.....1 5/8's is a MUCH better choice; 1.5" ones will work depending on camshaft profiles.

Third,......Carburetor choice depends on camshaft profiles and how many RPM it will run at.


Then,.....Jetting is based on displacement, CR, cams, intake manifolds, and exhaust system. One really cannot make useful recommendations without all that information finalized.

[addictionMS]

ok,

so the motor is a Toyo Cup motor, totally stock, SC cams, CIS pistons, early heads to the 39mm intake port.

Ignition is MSD

40mm weber jetting

mains 150
idle 55
air correction 180
e Tubes F3
chokes 36mm


top rpm 7300 (ARP rod bolts, JWE race springs)

so, I drop to 1 5/8 on the headers and the 40mm webers, or should I get 1.5" headers and jet up the 46mm webers?

I am guessing it may be splitting hairs on the set up, the rules are designed to make it even, but I thought I would ask anyways since I now have a set of 46mm webers

thanks

Jim

[Steve@Rennsport]

OK,...

Use the 1.5 headers with SC cams.

There is no need to turn it even close to 7000 RPM, its well over the HP peak and anything beyond that constitutes abuse,...

Use the 40mm Webers and 36mm venturies as thats a good match for a stock SC motor. The 46mm ones will flow more air above 7K,....

Final jetting should be confirmed on a dyno but I'd start with 180 airs, 160 mains, and 55 or 60 idles; everything else is fine.