PC,

      It's not entirely BS. I've seen major differences between factory and aftermarket manifolds. I've even cast a few, some of which worked and some didn't! The fact that they're aluminum has very little to do with Horsepower, that's mostly a weight issue. Most factory manifolds are designed to be predominately torque producers and CHEAP to build. The second part being very important to the bean counters. Aluminum has historically been much more expensive than iron, so most intakes and heads and blocks are cast iron. There are some exceptional intakes out the, one being the Blue Thunder for the Y block. Incidently, it was designed by John Mummert.

Frank/Rebop

Bristol, In ( by Elkhart) 

I've heard all the b.s. that the Car Craft and Hot Rod magazine people repeat about aftermarket aluminum intake manifolds making 'more power' than a factor iron intake. I'm not impressed. They always talk about peak horsepower as if that's all that matters. I suppose if you're trying to get an extra 5 hp out of an already overstressed C***y 350, well, there you go. Besides, it makes their biggest advertisers look good.



If you really want 500 hp, why not start with a 500 cubic inch engine?



The same goes for heroic efforts to isolate the carb from engine heat; much ado about nothing. Too much hype and not enough common sense.



I usually try to figure out what the original engine designers and tuners were doing, what their goals were, and shoot for the same thing. In the case of carb heat isolators/spacers, I think you first have to look at what kind of intake manifold gaskets you have. Some have bigger holes for the crossover, some have smaller holes. I'm going to guess that the ones with bigger crossover holes also came with fiber isolators. The bigger holes pass more exhaust gas, making the intake hotter. This would want a better heat insulator.



If you have an intake with the small crossover hole, an aluminum spacer would probably be fine.



I think the real concern with heat and carbs is vapor-lock. Insulated fuel lines would help with that. Otherwise, I think you want some heat under there to vaporize the fuel.

Best regards,



Paul Menten

Meridian, Idaho

Dan,

        Reducing this to a simple thought. Cold air is denser, has more oxygen, and make s more power. The air and the fuel passing through the carb tend to cool it off. The intake manifold, which is bolted to the engine, and heated with an exhaust gas passage, tends to make the Carb warmer. Worst case, it actually will boil the fuel in the bowl! Insulating the carb from the manifold works. Wood (!) or plastic seems to work best, the original Ford spacer on my F code is Bakelite. If we are going to talk Alaska, or Indiana winters, then we need some heat to prevent Freezing. (Aircraft, carb heat.) The freezing is created by the expansion of the air below the venturii.     

Frank/Rebop

Bristol, In ( by Elkhart) 

I suppose the question needs asked - if given the opportunity to stand barefoot on an iron plate heated to 180° F (very conservative number) - would you stand on an aluminum pad or phenolic?

Seriously - I think the issue has to do with the ability of the inlet air to drive down the temperature of the carb and fuel bowls (while trying to avoid the fuel vaporization temperature). I can recall some instances (while living in humid Ohio) where conditions were so damp, it "iced" the carb in my truck and stalled it. The aluminum spacers might lose heat quickly in the passageway exposed to airflow - but everywhere else, they are conducting heat very nicely thankyou. The phenolics may not lose much heat to the airflow passage - but they don't transfer heat quickly and directly from bottom to top either.

Aluminum manifolds have a lot of inherent conduction too - and the "air-gap" type, exposed runner designs, etc. are designed to keep the aluminum "insulated" in open air. By doing so the designers make the direct heat conduction path as small as possible. There are some aluminum spacers that have considerable "air" in them too - so there are other ways of dealing with the conduction issue, I know.   

 
 Steve Metzger       Tucson, Arizona

Steve,

"Thermal isolation" an interesting concept.

While "thermo-dynamics" is certainly outside my field of expertise, I have to wonder why there appears to be much controversy re: the best material for a spacer?

No amount of insulation will prevent materials exposed to high temperature for extended time from eventually equalizing. While fiber may slow this process, the reverse would have to apply. Once any material has achieved a set temp., wouldn't it's ability to DISSIPATE heat become the overiding factor? Superheated fiber would tend to maintain it's temp. The required thicker gaskets on either side of an aluminum spacer would also provide a significant degree of isolation. The charge of supercooled/atomized fuel rushing through an aluminum spacer would tend to lower it's temp faster than fiber due to enhanced dissipation, while hot fiber would RAISE the temp. of the mixture. Would fiber lower fuel-bowl temp. at the expense of mixture charge efficiency? (My head is spinning!)



Though I hesitate to stray so far afield, this reminds me of the controversy re: stock vs. closed fiberglass fan shrouds:

While the aftermarket fiberglass shroud may pull more air through the radiator when idling in traffic, would it not also RESTRICT the amount of air at highway speed? If the vast majority of your driving was HIGH-SPEED, would not the fiberglass shroud be detrimental if your cooling system was borderline adequate?






6 VOLTS/POS. GRD. NW INDIANA

hey gary

mate id love to fly up but ive detailed 2 busses this week after shampooing 100 bus seats  plus 1/2 doz cars & the mainline my arms dont want to work anymore & i had to work today  its not the mainline i can polish that fast more like magna's falcon's & commodores the mainline takes me abouy 20 mins seriously though if you can get hold of some of that polish get it its so easy to use ive put it on a whole car gone & had lunch come back & taken it off 1/2 hour later it also makes faint scratches vanish

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover

John -

I think that the thick Holley gasket does just what its supposed to do - provide a thermal break without changing the tuning effect of the "180°", twin H-patterned intake manifolds. Direct contact with the carb base is eliminated and the fore and aft extensions of the gasket provide a "shadow" for the bowls - saving them from line-of-sight heat radiation from below. There are some versions around that use stainless reflectors for the same purpose - including one that is sold by GMPP (I believe). Aluminum isn't really too good at being a thermal isolator - its so good at conducting heat, it often chosen for use in heat exchangers and radiators. People also need to be mindful of the small throttle bore holes in a stock Ford ECZ 9425-B manifold - they are more like 1.438 diameter - versus the 1.56 holes in the Holley gasket. Those steps are hard on airflow.

Temp control of the exhaust heated manifold is also an old trick available to those who wish to try. Blocking or partly closing the exhaust crossover port is a time honored method of driving down the heat. There are "truck" intake manifold gaskets available that have built in restrictors. If the manifold gets too cold - street driving can suffer in some weather conditions.

I believe any benefit of adding an isolated "ram tube" effect between the carb and manifold (a tall four hole spacer) gets lost when the air column enters the common chamber below and gets driven against the floor.

 
 Steve Metzger       Tucson, Arizona

Hood clearance aside, is there an advantage to going higher with the spacer... .5", 1", 2"???  Without knowing any better I replaced a .5" 4 hole plastic with a 1" open aluminum spacer.  I am now aware of my mistake and I'm going to replace it, but I want to do it right this time.  THANKS!

Edit: Is this product worth trying? - http://www.jegs.com/webapp/wcs/stores/servlet/product_10001_10002_11598_-1

- John

John: Lake Forest, IL



'57 Fairlane 500 - Looking better every day.

Gary,



Another option would be the aluminum spacer used for PCV conversion (sold by '55/56 T-bird parts suppliers). Though I don't know if aluminum is used because it dissipates heat better than fiber (it could just as easily CONDUCT more heat?), or is easier to manufacture/work (I applied black radiator paint to mine).

6 VOLTS/POS. GRD. NW INDIANA

Dan, If my memory serves, which might be doubtful, you should check out Moroso part number 64946.  I think that is what I bought.  It matches your manifold size and then you can open up the top as shown in that thread.  I hope this helps.

Jan  Urbanczyk  Major USMC Ret.

                                                                 Bowie Maryland