heres a rather interesting post , a guy on a different web site made about upgrading a street driven 496 BBC
ShouldntBeHere posted this interesting bit of info
I recently had Mark refreshen my tried and true 496 that he built for me over 9 years ago. It had 25k miles, almost 100 passes, and countless street races and highway pulls, not to mention 2 cross country road trips. I was restoring the car so it was a good time to go through the motor. Mark has wanted to update it for a few years now, both with changes in port design and windage control. Originally, 9 years ago, it made 661.8 hp @ 5900 / 674 tq @ 4400..
After a refreshen, updated heads, new cam and valve train, here is what he have now:
We spent the better part of a day testing different things I always wanted to know about...different carbs, distributors, air cleaners etc... We made 14 pulls, as the day went on, we started loosing a little baro pressure so we decided to call it a day.
Here is a vid that Mark made of the engine the day before it was final tuned..
GM Iron Oval Port Headed 496" Big Block Chevy Dyno Test - YouTube
The new combo is:
496" (reused the same pistons)
9.8-1 compression
GM 049 oval port heads with 2.19"/1.88" Ferrea valves and a lot of work in the ports/bowls/chambers. Flowed in the 320s @ .600"
Isky 248/258* @ .050", .608" / .617" lift, 109 lsa HYD roller cam, Morel SOLID roller lifters, tight lashed.
RPM Air gap intake (stock)
#4781 Holley 850 DP (also tested an AED1000). Peak numbers were with the 850.
Windage tray and oil pan mods
A lot of attention to every detail in the engine, especially valve train weight.
Roughly a 37hp gain, 5# avg tq gain, better oil pressure through out...And extended my usable rev range by 400-500 rpms...
I'd call this one a win.
I can't wait to get it in the car, dial it in and see how it does..... I'm hoping to bust 130 mph traps with the rest of my car combo identical as before. We'll see.