----- Original Message -----
Sent: Friday, May 27, 2005 12:05 PM
Subject: Re: [Chevelle-list] 396 Rebuild
- Piston Question
Are those pistons flat topped or do they have any
dome,Larry? Most standard 396 pistons of the 1966-1970 era were at least
10.25:1 compression and weren't flat topped. The 375hp L78 units were 11.0:1
compression. Anything over 10.0:1 with cast iron heads is pushing it with
regards to detonation. Aluminum heads allow you to run a half to full point
higher. Anyway,getting back to your L78 heads,,those are rectangular port
units that aren't very efficient below 5,000 rpm. If I were building a pure
street motor,I would sell or trade them for a good pair of 781 or 049 oval
port castings. These would really improve the engine's street manners by
flattening the torque curve,work well with the lower compression needed for
pump gas,and will improve the fuel mileage over the rectangular
units,too.
Something else to consider is the rpm limits of
those rectangular port heads will tax the limits of that two bolt 396 block,if
you decided to build a screamer BBC to take advantage of the superior high-rpm
power of the heads.
However,it all boils down to what you want to do
with that 396.
----- Original Message -----
Digging through my "basket case" 396 parts,
I've discovered I have a set of "hi perf" rectangular port heads used on the
375HP 1968 Chevelles - casting number 3919840. The block I got is just
a 2 bolt main block. The block is still
standard bore, and the stock GM pistons look to be in good
shape.
Based on your experience, would you reuse the
used pistons? If so, do you think the compression will be low enough to
avoid detonation issues?
If you recommend I replace the pistons, what
would you suggest I install? I'm looking for a setup where I can maximize
power/torque, normally asperated, running on pump gas.
Thanks for your help!
Larry Shouse