On the first engine dad and i built he had me block the "heat risers" (dont know if that is the right term but that is what he called them) on each side of the intake manifold. (manual choke carb) He said it had to do with letting the left exhaust stay left, and the right likewise. (there was also no "H" in the exhaust so it was true duals) The cam was big enough that you could stand behind the truck and think you were hearing every cylinder fire thru each pipe. (esp with open headers) Anyhoo, does anybody else do this or even heard of it? As a side note, I am thinking of painting an intake and thought doing this might keep the paint from burning off on each side of the carb.
Felpro gasket sets come with heat riser "restrictors"..... Many guys block off the risers to help keep the intake charge cooler.....most race intakes have no provisions for the crossover too.....
Makes a street car cold blooded as hell even in warm country, nearly undriveable when cold in cold country. Works good for race cars, pack the heat risers full of tin foil then cut a plate for over the hole or blocked heat riser gaskets
i thought it would help keep the intake cooler but i didnt know how much it would help... i believe i have seen intakes without heat risers as well.... but i have never been looking for that. thanks.
It also makes a difference if your automatic choke uses the crossover. Some 60's cars had the bi-metalic spring on the intake manifold. If you block the crossover, the heat will not get to the choke
Mr. Gasket and FelPro both make performance style intake gaskets with the heat passage blocked from the factory.
Plenty of applications had the heat riser blocked... it's not really a negative. Im not sure what you mean by cold blooded...
you can find a "freeze Plug" type plug at Napa that will press fit into the heat riser hole on the intake. I did this on the 350 in my '55 and it worked with no problems. the heat generated from the risers will definitely discolor the paint on the intake. I blocked off the heat risers the same way on one of my Flatheads, with no problems.
FelPro 1204 H/P Intake Gasket SBC 262-400 V8 Engines Stock Port w/ Blocked Heat Crossover Port Size: 1.23" x 1.99" Thickness: .060"
The paint is cracking & peeling on the heat crossover of my Y-block Ford. I wonder if I could've blocked it off and still had the engine warm up at a reasonable rate.
I used to block them off on a small block chev. in the warm months. Made a blockoff out of thin Aluminum with a tab on the top ,so I could loosen the adjacent manifold bolts and remove it in the winter, worked great.
use good heat /chemical paint and you shouldn't have prolems. as for the blockoffs, they are used in performance applications to help keep the intake charge cool. which in turn aids in better combustion and more power. on the street,especially in cooler regions, the heat risers allow exhuast heat to aid in the opening of heat activated chokes thus leaning out the fuel mixture and letting the engine run more efficiently. if you have a manual choke or dont run a choke, go ahead and block em.
In my younger years back in the 50s those of us with flatheads used "pennies in the manifold" to make the seperation from one bank's exhaust to the other complete, thus producing a more pulsing or "flutter" sound in the Smithys or straight pipes we ran. The cooler intake charge helped power a little also, but you damn sure needed the choke hooked up on cold mornings on the way to school! You took copper pennies, hammered and filed as needed to make an interference fit in the manifold's heat riser passage on both side, then wedged them in. Dave
I would like to think that if you block off the heat risers you won't get the proper atomization of the air fuel mixture from the increased heat and won't get better gas mileage due to the same reason. Not enough atomization. No I didn't go to U.T.I., no I'm not Mr. Goodwrench. Just my thought. Think about it, why does NASCAR run their cars at 210 dgrees? Atomization.
R. Seghi, when I was 16 gas was about $.30 per gallon, and we didn't give a rat's ass about fuel mileage! The NASCAR boys use high temp because the engine does get more horsepower per gallon of fuel, and they need all the mileage they can get because you don't win races while making more pit stops than everybody else. More horsepower per gallon doesn't necessarily mean the maximum horsepower the engine can produce is at the same temp level. Dave
I believe it came about simply as a quick and dirty method in the late 50s and 60s to keep the air/fuel charge cool for drag racing through stock exhast manifolds. Where I lived we rolled up tinfoil balls and crammed them into the heat riser passages. But as stated above it was miserable to get the car warmed up in winter. Another trick was wiring the spring loaded manifold heat risers open since after a while the springs on them tended to freeze in position restricting good flow.
even if you're drag racing 210 is a good temp to start your pass. espacially with a smallblock chevy. the major factors in atomization is intake runner shape, lenght and texture. heat causes evaporization. evaporation is bad. it can lead to vapor lock. atomization does help increase efficency, power and milage, but engine temp effects it very little. on the other hand a cooler intake charge is a denser charge. this translates to more oxygen in the combustion chamber,which in turn produces a more complete fuel burn. this means more usable power. heat shields,cool cans aluminun fuel lines , carb spacers,and blocked heat risers can all be used to help achieve the desired results,together or seperately. these are all rudimentary methods to gain power but everything helps when you're on a budget. one more thought,nitrous injection works on the same principles of a cooler ,denser intake charge. the nitrogen cools the gasses in the intake runners, and the extra oxygen promotes a bigger combustion event ,thus increasing power.
Ok so like I said. I'm not Mr. Goodwrench, more like Mr. Pipewrench. So what the hell are the heat risers for anyway? Are they JUST for cold weather starting? Now I want to know too!
to the best of my knowledge yes they are primarily designed to aid in cold weather operation and were a convenient way to control the choke when heat activated springs were added to the choke mechinism. the warmer the riser gets the more heat is transfered to the spring. the tighter the spring contracts the more the choke opens. thus allowing the operator to not have to worry about the choke. one of the first automated engine control systems if you think about it. once the spring was added the driver no longer had to pay attention to how the engine was performing to adjust the choke to a proper setting. i'm sure there is more to it but thats my understanding of the situation.
Blocked heat risers are great for WOT operation. For part throttle use leave the heat riser passages open. The heat helps atomization. At WOT turbulence takes care of atomization. The reason an engine runs poorly when cold is a lack of atomization. Most of the fuel is out of suspension so the flame front doesn't burn evenly and smoothly. It's like there are a relatively few, widely separated, large droplets of fuel in the combustion chamber. Once there is some heat built up then the fuel atomizes when it comes in contact with the hot surfaces of the intake and combustion chamber. Then the flame front burns evenly and quickly. You have a large number of minute droplets of fuel even distributed thoughout the combustion chamber. Also, at part throttle when the air/fuel mixture exits the carb it has to make a hard turn into the intake runners. The fuel droplets are heavier than air and can't make this turn and fall out of suspension. When they hit the bottom of the hot intake they atomize and proceed to the combustion chamber. On a cold intake the fuel runs along the bottom of the runner until it hits the chamber.
Cold blooded means whats been said in the last few posts, it dont want to run right until it warms up. Try it and you will see
Interesting viewpoints. I drove a tunnel ram small block with dual fours hanging out of the hood through multiple midwest winters during high school several decades ago. Used a trash bag to cover the carbs up during heavy snow or rain when parked and just drove it through the snow or rain otherwise. There was no provision for heat risers, nor did I have any problem starting or driving the car. It might not have been optimal, but I did have a heck of a lot of fun...
r. seghi, you are right in accepting ray jays explination if you are talking about stock vehicles but do not overlook the fact that heat has diminishing returns on performance. that is where taking measures to cool the intake charge comes into play especially in performance engines. it is an old method but it works , and is mostly for wot applications as ray jay said. on the street it often does lead to cold start problems and rough idle until operating temp is reached. i think you are right to leave the passages open if you are dealing with a primarily street driven vehicle.
The heat transfer from the heads/block to the intake manifold, as well as that of the coolant will keep the intake "warm enough" (like the Nascar 210*). Putting 1000* exhaust gas to your intake hurts performance, and does NOTHING good except for operate the choke, and automatic chokes are for girls.
Another thing, you only get a lot of exhaust flow through the crossover if you have a working [ or stuck ] heat riser valve. Since most hot rods don't have the heat riser valve the riser passages don't get super hot.
I've restricted them by tack welding old rocker arm nuts inside the passages in the heads, right next to the exhaust ports. That way the heat can still get to the intake, but less of it. It works good in warm weather, but it's slow to get it warmed up enough to drive in winter. But having done it twice, I probably wouldn't do it again. Instead I'd just go with the gaskets that have the restrictors in them. One other thing is that both of these engines have manual chokes, and are "street" engines.
I kinda remember some intake gasket sets that came with some restrictor plates that had small holes in them, maybe3/8". Remember, once you get the throttle wide open you have a lot of relatively cool air and fuel flowing through the intake passages. This cools the intake runners right down. The heated crossover only has a large effect at part throttle operation, right where you want the motor to run smooth and clean.
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