Exhaust Backpressure- 3" vs. 2 1/2"

[Hog]

Excellent comparison, boy are we spoiled nowadays. Engine dynos with data graphs and overlays that can be pulled up in seconds. A lot different than it was done back when these Mark 4 BBC's were being developed.
It would have been interesting to see the difference between open headers with the 18" collector extensions compared with the same open headers without the extensions.
Dropping the exhaust on any header equipped vehicle I have owned has always been greeted by a massive drop in low rpm torque, but sure screams up top. But my examples were usually low duration hydraulic roller cams set up for low-mid rpm torque.


It would have been nice to see a set of Corvette style BBC manifolds tried as well. The manifolds/Camaro exhaust on the 1969 ZL-1 Camaro with the all aluminum ZL1 427 BBC brought the 500-535hp output of the ZL1 427 down to about 275hp as per testing done at the Tonawanda plant. Chev knew that the buyers of these cars were going drag racing and would be ripping the stock Camaro manifolds and exhaust off of them anyways, so why design a complete new exhaust for only 69 cars.

I'm sure the 2 or 3(depending who you're talking to) ZL=1 Corvettes stock exhaust would cut into the power a bunch as well, although there would be more incentive to do a better exhaust for the Vettes, as there was the ZL-1 cars, and the 20 L88's for 67, 80 for 68 and 116 for 1969.

Good thread on the more rare BBC Chev cars with famous RPO's(now-back when new, very few even knew what RPO ZL1 or L88 entailed)
http://www.zr1.net/forum/showthread....hlight=ZL1+L88