Flat32: 2/10/00 - 10:44:48 PM
Manifold heat risers
How is performance affected by blocking off the manifold heat risers??

Rolf: 2/10/00 - 11:00:27 PM
RE: Manifold heat risers
The old myth in the '50's was that by driving pennies in the heat riser holes in the block, you will get a colder charge of fuel to the carburetors, which made you go faster, never saw any difference at all myself.

Flat32: 2/10/00 - 11:15:50 PM
RE: Manifold heat risers
What got me thinking about it is how much better my engine ran in cooler weather. It seemed to especially like cool damp air. Another thing I've noticed is there are performance manifolds for overheads made with space between the lifter valley and the runners to keep the runners cooler. Then there are the wood carb spacers that are supposed to keep carbs cooler. Is it possible the risers only boost gas mileage??

Lars Brandow: 2/11/00 - 2:13:16 AM
RE: Manifold heat risers
During normal driving conditions the typical manifold gets ICE cold. And this means that the atomization of the fuel air mixture is not optimal. that the reasson all cars have some provison for heating of the intake charge. On the other hand a cold mixture is denser. The thing with the flathead is that you get a 'harder' exhaust sound with the block of. On th eother hand the gas milage get worse. All this is marginal of course so i guess you have to try and see whats best for you ..

JWL: 2/11/00 - 7:09:18 AM
RE: Manifold heat risers
The potential boost is quite small and even with mixture optimization would hardly be noticed. Eventually, the intake absorbs heat from the block and from the oil, so the temperature differential nearly disappears on a long drive. It may have been an overly rich fuel/air combination which gave the symtoms you describe. Maybe the overall performance could have been improved with an adjustment?

32tom: 2/11/00 - 6:52:27 AM
RE: Manifold heat risers
my early Edelbrock 2x2 doesn't have them. runs fine. I plan to plumb the water heated plenum on the Eddie Meyer just to make people ask 'whathehellisat' ;-)

Lars Brandow: 2/11/00 - 7:55:27 AM
RE: Manifold heat risers
Here in sweden we need the manifold heat. You will lose up to one Dl per 10 Km when disconnecting it. And we pay 1,20$ per Liter Not gallon !!

John 2/11/00 - 11:16:03 AM
RE: Manifold heat risers
My expierence of blocking the heat risers resulted in a different exhaust sound but didn't notice any performance change. The sound was a lot harsher.

GasHouse: 2/11/00 - 12:02:09 PM
RE: Manifold heat risers
Whew, are we disspelling a myth? Someone posted the other day that Henry lived in Michigan. As I understand it the, need guidance here, the lake racers used the blocking trick. Now when was the last time it ever freezing temps at these lake runs? My point is that I believe blocking off the heat risers was a racer trick to squeeze out that extra half of a moment. I guess that says those in cooler climes should leave the heat risers alone.

philbill: 2/11/00 - 3:06:13 PM
RE: Manifold heat risers
got pennies in mine.good/bad,???in there?Truly believe exaust tone is different but would really like to see a fast quick trick for more horse power.

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