The Stovebolt Site Forums The Shop Area Engine Shop manifolds

had the intake and exhaust manifolds cleaned and surfaced. just picked them up today...less than impressed with the overall quality of the job but they are better than they were.

so tonight while i have been trying to get the heat riser un-stuck and drill out the broken bolts in the exhaust manifold, i noticed the casting flashing on the interior walls of the manifolds and was wondering if there is any merit in grinding them down to improve air flow or if i should just leave them alone since the truck ran fine before the tear-down?

any and all thoughts are wecomed!

I like to clean all castings and gasket match the ports.Most here will say it doesn't do much we all have different thought.What engine are you rebuilding and will it be stock or modified ?

Air ya gonna dyno test that engine p.j.? You tint gonna see feel any difference in the performance just by light porting or deburring. All of that comes into play when you’re doing a lot of other modification and trying to milk every last pony out of an engine. Of course if you don't have anything better to do and want to spend the time it surly won't hurt anything.
You have to consider the fact that if GM could have squeezed a few more horses out of their engines buy deburring the castings that they certainly would have. But the pay back for the effort didn't justify it.
Denny Graham
Sandwich, IL

if GM could have squeezed a few more horses out of their engines buy deburring the castings that they certainly would have

I disagree. Skilled hand labor is far too expensive to justify the minor results to the accounting department, who doesn't care how fast it is even if it's a Corvette.

and the disagreement is ......

It won't hurt a thing to clean out the exhaust manifold, it will keep carbon from building up if the flashing is real nasty. Keep the intake rough, you don't want a smooth wall or the fuel droplets will stick to the smooth surface and settle on the intake floor. Roughness keeps it bouncing around down the runners. Joe

funny you should mention dyno testing denny. i was thinking as soon as the truck was up and running i was going to take to the local drag strip and go pinks all out with it! that neck snapping acceleration those 216's generate is just too much of a temptation to pass up.

seriously though, i was just curious if while it was apart would it be a good idea to clean the ports up a little to let the air flow a bit better. i will gauge my interest level and/or time availability prior to installation.

thanks for the feedback guy!

I cleaned mine just to do it. Chevy sixes are historically lacking efficiency in exhaust systems, so it would help on a modified engine more than stock.

Speaking of neck snapping acceleration, I drove me buddy's '52 last week, which he just swapped out the 216 for a '55, 235 and having driven his 216 part way from Chicago to Kansas and back in September I felt a lot of difference. I noticed quite a difference from my '50, 216 when I drove the '54, 235 home that I just bought.
Not quite neck snapping but truly a much better performing engine.

DG

Denny, about 10 years ago Mopar Muscle magazine ran an article on the subject of porting heads. In the article the benefit of each porting procedure was individually evaluated on the dyno. The low hanging fruit was in the bowls below the valves where there were sharp angles at the interface between the ground valve seats and the casting and around the valve guides where they protrude into the ports. Blending those areas created the biggest improvement per hour spent with the grinder.

I have a set of Edelbrock "Performer" heads on a SBC powered street rod. Those heads have small ports for good velocity at low RPM but the bowl and valve guide areas have no edges or bumps that would create turbulence. Those heads are probably a good example of what a street port or manifold should look like inside, small but with nothing sticking out into the air flow.

Even an ancient stovebolt engine can probably benefit from optimized airflow, distributor mechanical and centrifugal advance curves and carb. jetting and the result will be improved throttle response and economy.

The 360 CID Mopar engine in my '71 Dodge van runs better in all respects, including fuel economy, with a Comp Cams very mild camshaft, bowl ported heads, recurved distributor, small port intake manifold and optimized jetting than it did bone stock. The same result would probably be obtained with any Chevy or GMC engine.

hey if i improve the air flow in the exhaust manifold and do some jetting, i might squeeze another pony out of the old 216!

honestly i will be over the moon happy when i have my arm hanging out the window listening to that stovebolt sewing machine ticking down the road.

That is the best part isn't it? Sewing machine hit it right on the head. The head turns in traffic are also pretty sweet.

mlt,

i wish i could take credit for the sewing machine reference, but my mom was the first one i heard coin the term, and she would know. she is the betsy ross of sewing machines.

by the way. keep an eye out for any of denny's posts. he is a wealth of information and has a great collection of photos and details that should not be overlooked...sorry denny if that puts you too much on the spot.

pj - when the babytrkr was principal driver of the 57 235, I always told her if it stopped sounding like her sewing machine, speak up, it needs "some expert attention"

Bill

squeeze,

you have to love the valve "song".

nice 57 by the way. my dad's 55 is collecting dust until my brothers and i find the motivation to bring it back to its former glory.