Max HP through stock exhaust manifolds SBC [Archive] - Team Camaro Tech

: Max HP through stock exhaust manifolds SBC


67FamilyFun
Sep 9th, 07, 07:16 PM
I know I've seen this posted before, but I couldn't find it with a search (even the google search on the front page)...

Say you stroked to 383...and had good flowing heads...the stock exhaust manifolds would be the restriction.
If you wanted to keep them for the stock look, what could you do? and how much horsepower could you expect?

cornbread
Sep 10th, 07, 10:42 AM
Read on another web site up to 70 HP loss using stock manifolds. Said headers much better. BB use long headers , sb use the shorter headers. good luck

XLexusTech
Sep 10th, 07, 10:56 AM
well I can testify to 410 hp through stock "Rams Horn" manifolds.
this was a well built 355

gschuld
Sep 10th, 07, 11:01 AM
Well I don't think it would be reasonable to expect a HP guess without giving a lot more details as to your engine combination(cam, head flow #'s, etc) but to give you an idea as to how much power can be "forced" past a set of cast iron manifolds look up the "factory appearing stock tire" series. Big block corvettes are running in the mid 10's on skinny bias ply tires and small block cars are deep into the 11's. Granted, these engines are poked/stroked/and every trick in the book has been trown at them (including very extensive exhaust manifold porting and extrude honing) but the performance of these cars are downright impressive for LOOKING as stock as they do. But for a basic idea, if you take a sbc with heads that flow well with a good head/cam/intake combo with a free flowing exhaust after the manifolds(ram horn style mid 60's corvette manifolds are generally considered the best flowing iron sbc manifolds, especially when ported well) I see no reason why a 1hp/cubic inch would be difficult to achieve without getting too radical and unstreetable.

George

DjD
Sep 10th, 07, 11:06 AM
If you want stock exhaust for the apearance and don't have anything to prove at the track etc don't sweat it. If you build a stout 383 it will run better with headers just like a stock 327 2bbl will run better with headers. There is no set hp limit you can push through stock exhaust, there is no set HP gain from headers. If you build your engine with the exhaust you want to run in mind when selecting heads, cam and carb, you will loose less through stock exhaust. Of course if you use large valve high flow heads and a high lift cam the stock exhaust will really choke things down.

Look into extrude honing if you want to open up stock manifoldes a bit but my understanding is the return is not worth the expense.

I can't resist, a 383 is a stroked 350 (400 crank) what is a stroked 383? :D and stock rams horns are not stock on a Camaro... ;)

pdq67
Sep 10th, 07, 03:38 PM
And fwiw, the aforementioned ramshorns that are 2.5" in dia., are the best cast-iron exhaust manifolds we have, but they won't fit our A/F/X cars b/c the suckers dump right into the S/F or Frame.

And I don't think they are made bent back like some of the smaller ramshorns are..

pdq67

67FamilyFun
Sep 10th, 07, 04:41 PM
Thanks! Those are some great answers!:thumbsup: So if the goal is a Peppy street only motor that looks stock on the exterior, including manifolds, how do you get there? The 454 car is pretty peppy...I'd like a similar snappiness in the vert, but want it to remain very stock appearing (NOM, 4spd, 3:55, stock tires)...Oh, and of course cost is a factor.
ps. Don't say put a BBC in it...:D


Look into extrude honing if you want to open up stock manifoldes a bit but my understanding is the return is not worth the expense.

I can't resist, a 383 is a stroked 350 (400 crank) what is a stroked 383? :D and stock rams horns are not stock on a Camaro... ;)

Hey! Are you making fun of me :D I said stroked to 383...(unless someone edited it for me:o)...now it's my turn...what's 'manifoldes', manifolds made in Spain? :p

cornbread
Sep 10th, 07, 05:01 PM
Thanks! Those are some great answers!:thumbsup: So if the goal is a Peppy street only motor that looks stock on the exterior, including manifolds, how do you get there? The 454 car is pretty peppy...I'd like a similar snappiness in the vert, but want it to remain very stock appearing (NOM, 4spd, 3:55, stock tires)...Oh, and of course cost is a factor.
ps. Don't say put a BBC in it...:D



Hey! Are you making fun of me :D I said stroked to 383...(unless someone edited it for me:o)...now it's my turn...what's 'manifoldes', manifolds made in Spain? :p
The High dollar SORRY ones are probably manufactured in Spain.lol:yes:

DjD
Sep 10th, 07, 06:05 PM
I guess manifoldes would be needed on a strokeed 383... ;) Where did that "to" come from, I know there was an "a" there before... :clonk: really :yes: lol... and my lens perscreption isn't due for another year! :eek:

gschuld
Sep 10th, 07, 06:30 PM
As to a recommendation....hmmm. I would think that the manifolds would prefer a lower rpm torquer than a high rpm big breather type of motor. Say a Lunati flat tappet hydraulic cam(230/230 @0.050, 0.455/0.455-inch, 144 degree lobe seperation) with a fresh set of iron vortec heads(with the adapters so you can use earlier style valve covers). Factory Z-28 intake manifold, holley 750 vacuum secondary with dogleg or annular boosters, 9.5:1 d-dish forged or hyper pistons on 5.7 factory rods. It may seem to be a bit tame, but in a 406 based motor the combo was good for 427 hp at 5100 and 525ft/lbs at 3500 and was putting out over 450ft/lbs from 2200-5000rpm(according to BIG-INCH CHEVY SMALL BLOCKS by Graham Hansen's "406ci Torque Monster" example). Granted the 406 was using an air-gap intake instead of the z-28 manifold and 1 5/8 headers rather than cast iron manifolds and 23 extra cubes, but you should be able to reach say within 20% of those numbers. Thats not bad at all. It wouldn't be a very expensive build either. Just an idea.

George