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BBC exhaust manifold performance

General engine tech -- Drag Racing to Circle Track

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psychomonte
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Re: BBC exhaust manifold performance

Post by psychomonte »

There are smog bosses inside the ports of some manifolds. A friend of mine spent two hours grinding these out and swears that he noticed the difference. I have a 1972 monte carlo with a numbers matching 402 that I rebuilt. Here's the engine: 8.8 to one,cast iron intake, 292 casting heads, stainless valves 2.06 int/1.88 exh ( i installed the larger exh valves) pocket ported and short side cleaned, crane powermax flat tappet (216/228 .515/.510 112) Jet performance quadrajet. 2500 converter, 3:31 gear. K and n filter in a stock snorkle
Flowmaster 2.5 inch x pipe american thunder exhaust.

with headman headers: best pass 14.38

with exhaust manifolds: 14.81

This is just my cruiser and I never intended on racing it. I changed to manifolds because i got tired of pulling driver side header to remove the oil filter.
cjperformance
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Re: BBC exhaust manifold performance

Post by cjperformance »

psychomonte wrote:There are smog bosses inside the ports of some manifolds. A friend of mine spent two hours grinding these out and swears that he noticed the difference. I have a 1972 monte carlo with a numbers matching 402 that I rebuilt. Here's the engine: 8.8 to one,cast iron intake, 292 casting heads, stainless valves 2.06 int/1.88 exh ( i installed the larger exh valves) pocket ported and short side cleaned, crane powermax flat tappet (216/228 .515/.510 112) Jet performance quadrajet. 2500 converter, 3:31 gear. K and n filter in a stock snorkle
Flowmaster 2.5 inch x pipe american thunder exhaust.

with headman headers: best pass 14.38

with exhaust manifolds: 14.81

This is just my cruiser and I never intended on racing it. I changed to manifolds because i got tired of pulling driver side header to remove the oil filter.
On the 460 Ford and 302 windsor you can notice the difference by just removing the smog lumps in the exhaust.

How heavy is that Monte Carlo? With a very basic 302windsor, 204/214@050, factory 4bl intake, 735 holley, 9.8:1, No head porting, try y pipes and dual 2.25" into 2" tail pipes , c4 auto 2200stall, 3.5 diff. In an Aussie Falcon @ 3300lb will run 14.62 using 5300shift points. So im thinking the Carlo is heavy! Forgive me, im more Ford orientated, dont know a lot about USA chev vehicles.

Also i must ask, why not run the extractors and run a remote oil filter?
Did you notice much low end difference with the manifold's?
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Re: BBC exhaust manifold performance

Post by MadBill »

cjperformance wrote:MrBo or MadBill, which one of the cams listed were also used with manifolds?
The later 178 cam produced more power with cast manifolds and stock exhaust. The 346 was substantially better with open headers.
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psychomonte
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Re: BBC exhaust manifold performance

Post by psychomonte »

my monte is 3850 # with me (170lbs) or 13 stone for you cj. that sounds like good numbers for your ford. BTW I have been to south australia and it was wonderful. Sydney, melbourne, torquay, lorne, jeelong...nice places
cjperformance
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Re: BBC exhaust manifold performance

Post by cjperformance »

psychomonte wrote:my monte is 3850 # with me (170lbs) or 13 stone for you cj. that sounds like good numbers for your ford. BTW I have been to south australia and it was wonderful. Sydney, melbourne, torquay, lorne, jeelong...nice places
For a while i had an aussie 68 fairlane with 460 and c6 auto, that was 3940 lb with me -175lb- in it. Motor was only mild, but an awesome tq'y cruiser that would shock the hell out of much hotter sounding small block cars! Lol . Never got it on the 1/4 though. Our strip closed! Would of had to drive 500 miles at the time to run 1/4 mile in melbourne! Stuff that!

Yes it is nice here, great balance of weather but can get bloody hot in summer! Just not enough hot cars and drag strips!
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Re: BBC exhaust manifold performance

Post by GOSFAST »

To answer this directly, on most N/A BB pump-gas builds, there's actually very little noticeable difference from the cast exhaust manifolds and "headers".

Recent test on 496" BB (9.5:1) retro-hydraulic roller with the factory exhaust manifolds ("smoggers") produced
some 463 HP @ 5700 RPM and 541 Ft.Lbs. Torque @ 3600 RPM. These were factory 1972 Chevelle "LS-5" manifolds!

Changed to 1.750" headers and produced 471 HP @ 5500 RPM and 523 Ft.Lbs Torque @ 4200 RPM.

Thanks, Gary in N.Y.

P.S. On higher end builds the headers would "widen" the gap!
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Greg Gessler
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Re: BBC exhaust manifold performance

Post by Greg Gessler »

I modify BBC exhaust manifolds for cars that race in the F.A.S.T. series (Factory Appearing Stock Tire) Corvette manifolds work better in stock form. Camaro manifolds can be improved on especiallly if internal welding is done to the weak runners. Give me a call if your interested.
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lucas bremer
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Re: BBC exhaust manifold performance

Post by lucas bremer »

GOSFAST wrote:To answer this directly, on most N/A BB pump-gas builds, there's actually very little noticeable difference from the cast exhaust manifolds and "headers".

Recent test on 496" BB (9.5:1) retro-hydraulic roller with the factory exhaust manifolds ("smoggers") produced
some 463 HP @ 5700 RPM and 541 Ft.Lbs. Torque @ 3600 RPM. These were factory 1972 Chevelle "LS-5" manifolds!

Changed to 1.750" headers and produced 471 HP @ 5500 RPM and 523 Ft.Lbs Torque @ 4200 RPM.

Thanks, Gary in N.Y.

P.S. On higher end builds the headers would "widen" the gap!
thanks GOSFAST
that is some real world info im looking for
lucas bremer
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Re: BBC exhaust manifold performance

Post by lucas bremer »

Greg Gessler wrote:I modify BBC exhaust manifolds for cars that race in the F.A.S.T. series (Factory Appearing Stock Tire) Corvette manifolds work better in stock form. Camaro manifolds can be improved on especiallly if internal welding is done to the weak runners. Give me a call if your interested.
thanks greg i spoke to you last weak some time
(via email) im looking into it
lucas bremer
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Re: BBC exhaust manifold performance

Post by lucas bremer »

anybody have any more info they woul like to share .
cjperformance
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Re: BBC exhaust manifold performance

Post by cjperformance »

lucas bremer wrote:anybody have any more info they woul like to share .
Custom made tapered log type manifolds can work surprisingly well if you dont have room for extractors and are not bound by rules to use stock manifolds, i know thats a bit off the origional topic.
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Re: BBC exhaust manifold performance

Post by StockerChevy »

Only lost 25 horsepower between headers and manifolds. 560 vs 535. We did not run the heat bypass valve that normally sits on the right exhaust manifold.
novadude
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Re: BBC exhaust manifold performance

Post by novadude »

psychomonte wrote: Fri Aug 20, 2010 7:03 am There are smog bosses inside the ports of some manifolds. A friend of mine spent two hours grinding these out and swears that he noticed the difference.
Bumping this post as I might have a 396 project using Chevelle manifolds. Can anyone confirm / deny that it's worth grinding out those smog bosses? They look like they would be a restriction, but sometimes air doesn't always behave the way you would think. I'd hate to spend time grinding if it wouldn't help (or even hurt) performance.
Machtuck
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Re: BBC exhaust manifold performance

Post by Machtuck »

Refer to top post of this 4th page. I still have that 72’ monte however, I switched back to headers. A friend of mine spent a couple hours grinding the air fitting bosses and like i said previously, believed he noticed a seat of the pants difference. He’s a very experienced racer and trustworthy. He’s recently restored his 69’ chevelle 396/325 and placed a 496 with the 396 badges. Factory appearing with stock manifolds Hyd roller, bathtub heads and also spent a bunch of time on factory intake. I’m waiting to hear how it runs at the track. Internally balanced with the 396 balancer.😎
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