thundering347

So Im building a newer, more violent version of my 347 this winter....the fattest part of the powerbad is going to be between 5000-7000 rpm. The old motor used a 650 speed demon, which was more than adequate. But,Im thinking with this rpm range and the breathing capabilities of the top end, a 750 would be a solid investment. Any recommendations?

Old motor:
347, 10.5 comp ratio, torker II intake, twisted wedge track heat heads, trick flow stage 3 cam (.574"/.595" 236/248 dur. at .050" hyd roller)
1 5/8" long tube headers, 3" 40 series cans with dumps, topped with that 650.

New motor:
Same bottom end, cam, exhaust, but switching to a set of vic jr heads, putting it up to 10.7 comp ratio, and a port matched vic jr intake manifold.

Think this thing is begging for a 750?

67mustang302

Around725cfm would give the best average power between 5k and 7k with 100% VE, so a 750 would be a better bet than a 650

BlessedHellride

A 750 would work great on your engine combo. Did you ever run that car at the track? If so, what was your numbers?

thundering347

Well, with the old combo backed by a 3550 tremec and 4.11 auburn diff on 10.5 mt cheaters, it ran a 13.6 at 99mph, sputtering after 1000 ft because of some unrelated timing issues. Timing's fixed now. This new combo I want to create dyno's out at around 520hp on desktop dyno, but we all know how much trust to give those gizmos.

Lord help us all if I click 'checkout' on my current summitracing shopping cart.....theres a pro shot NOS fogger setup on there......

tinman

My thinking is that the 750 wouldn't be a bad idea at all........

thundering347

I like the 650's throttle response a lot though. Its got all forged internals and an aluminum flywheel, so with the midrange tw heads and that 650, it bangs the rev limiter instantaneously almost. Im just afraid it'll get that classic over-carbed bog-down the second I slam the butterflies open.

thundering347

Holley 750 HP mech secondaries........solid choice?

67mustang302

A bigger engine needs a bigger carb and launches at bigger rpm. A 7,000rpm 347 needs at least 700cfm