BBC exhaust manifold performance

[Keith Morganstein]

This one used in the Camaro and Nova is very poor.

[bigjoe1]

That looks like the ones that would LOOSE 100 horsepower== Remember, that was without any mufflers too


JOE SHERMAN RACING

[427Impaler]

This thread is interesting and perfectly timed for me. I am just about to start a build up on a 1968 L72 427 that needs to look stock, but of course i want to make as much power as possible and the stock manifolds are the going to be the biggest problem. Has anyone had any positive experience with stock manifolds using extrude honing? Any suggestions would help.

[MadBill]

ExtrudeHoned manifolds were used on the (GM-sold, SLP-built) SS Camaros, I recall the gain being ~ 10-15 HP on ~320(?) HP base...

[SchmidtMotorWorks]

I'm curious what would people be willing to pay for a really nice ex manifold?
Maybe stainless?

My guess is that people think of ex manifolds as junk yard items (how many 1960's ex manifolds did we all throw in dumptsers in the 70s?) and can't imagine paying a few hundred for them even though that is what they would cost to make in low production.

I wonder is there one design of outlet position that would fit most cars? Talking BBC and SBC.

[jamie]

Doesn't Sanderson make a header/manifold for big blocks.Anyone ever dyno a set of these?

[SchmidtMotorWorks]

I just checked thier web site and didn't find them.

I looked at some articles on them, they look kind of crude, I was thinking of making something really nice if there was a market for them.

[MadBill]

I suspect unfortunately that the main market would be for manifolds with much of the power potential of good headers but in exact-appearing replicas of the dozens of different OEM parts. The only practical approach I can see is for Brezinski-style subtle re-works http://www.castheads.com/log_systems.php with possibly Extrudhone http://www.extrudehone.com/auto/auto-performance.php as a final touch.

There might be a market for headers compromised a little re ultimate performance in exchange for appearance*/fit and with really thick tubing to quell the exhaust 'ping' that drives some people mad... *(Is anyone familiar with the CNC port stubs that are starting to appear? Done up in polished Stainless they would be a nice touch...)

[jamie]

These are the ones I was thinking about. http://www.sandersonheaders.com/Sanders ... r-Set.html

[pdq67]

Just thinking out loud here is all.

SB's have several different exhaust manifolds to pick from, some are SS piped, header-like off of heavy-duty trucks. Them and the '94 to '96 LT-1 jobbers(??)...

So do BB's have any free-flowing big truck SS pipe manifolds that we don't see only because they are in a bread truck or a school bus?

pdq67

[gnicholson]

there are the corvette manifolds but they are hard to find ,expensive, probably wont fit and heavy. unless you have a completely original car then headers are allmost required. there are good ones available with thick flanges and heavy guage tubing

[af2]

Dorman makes the right side one for 1/2 the price of these guys. I don't think Dorman offers a left side though.

http://www.cranescorvette.com/new_page_15.htm

[lucas bremer]

To run manifolds you need to run way different cam timing than typical performance stuff thats generally avaliable. You will loose some power, but if its done right it will still make decent numbers and look stock, if thats what your after.

yes this is what im looking for do you have any more knowledge that you would like to share

[lucas bremer]

http://www.gesslerheadporting.com/gessl ... enDocument
i talked to greg via email:
cost about $400 to port them
(and that was what he recommends)
$1000 with extrude hone to get every single hp after that( out of my budget)
he didnt want to share any info other than that which i do understand
any body have any nknowledge that they would like to share on porting?

[MadBill]

Re camming for manifolds, just my top of the head opinion and hopefully CamKing, dfree or someone will chime in, but I'd expect the engine would need less overlap via later IVO and earlier EVC to prevent backflow due to lack of scavenging, and earlier EVO to make up for the presumed flow restriction. Using standard cam nomenclature, this might translate to going from say a 230°/230° on a 108°LCA advanced 4° to a 226°/236° on a 112° LCA, advanced 6°.

FWIW if someone has the specs., the early Z-28 cam made more power on open headers than the late one ('70½ on), but less through the stock exhaust.