rpm

347 · #1 (**permalink**) 10-14-2002, 06:30 AM

i have quad 44 mm idf webers on my 347,does anybody have an opinion about where/what rpm the engine would slow/stop reving and makeing power??

Excaliber · #2 (**permalink**) 10-14-2002, 10:59 AM

If the Webers are set up correctly they will not be the limiting factor as to HP\Torque at any rpm. Your cam will be done or your pistons will "leave" the block long before the Webers get tired.

Ernie

Sizzler · #3 (**permalink**) 10-14-2002, 12:19 PM

actually IR manifolds CAN limit performance at higher RPM's if the carbs are too small for the engine. 44's may very well be too small to supply air to a 347 at higher RPM's. Unlike other manifold designs, all the air for a cylinder must flow through just one venturi in an IR manifold, it cannot 'share' air between cylinders.

Bob Putnam · #4 (**permalink**) 10-15-2002, 05:19 AM

Sizzler's right. My "guestimate" is that the 44s with stock venturi will be great from 2000-5500 rpm. After that, the horsepower will flatten out quickly.

Jeff Frigo · #5 (**permalink**) 10-15-2002, 06:09 AM

Please do not post the same question in multiple posts. Makes it hard to keep track of.

750hp · #6 (**permalink**) 10-15-2002, 06:16 AM

Jeff - yeah, I was wondering where my previous reply went....

Excaliber · #7 (**permalink**) 10-15-2002, 10:17 AM

I stand corrected on the 44's! What about 48's? Surely THEY will be big enough?

Ernie

Sizzler · #8 (**permalink**) 10-15-2002, 11:43 AM

I thought the original 289's used 48's.

If so, then the 347 engine displaces 20% more volume, and is pulling through an opening that is 9% SMALLER than the 289's weber setup.

Some 427's use 48's, so they're probably the size you want (19% more area to draw through than the 44's), though racing 427's used 58's which have 74% larger openings than the 44's.