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71' carb spacer project.

walkman

Active member
Joined
Jul 9, 2003
Messages
33
Location
ca
Corvette
1971 Stingray Bridgehampton Blue
Ok, sorry it took to long to get back on this. Here are the facts & numbers. I changed out the stock intale manifold to a Edelbrock 2101 aluminum. I wanted to put a 1" spacer under carb. For every 10 dreeges lower in temp = 1% in hp gain. A 1" spacer WON'T fit, BUT a 3/4" will. I have at lease a 1/2 to 3/4 clearance from the hood. I had the 1" phenolic spacer cut down to 3/4". You can use the same fuel line to the carb and the same choke rod. Here's the trick to the choke. Take the thin housing cover over the spring off and turn the rod that's goes to the spring around/reverse, It works like a charm. Here are the temp # using a Tel-Fast non-contact thermometer. Before intake runners 229 after 152. Exhugst 361 before 303 after. I also have ceramic coated shoryt headers. Temp readings 469 before 352 after. Hope this helps, anyone with question please ask. Pic's let me know.
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
The spacer has no effect on intake air charge temperature, which is what determines the "10*F reduction = 1% power increase" equation. Temperature of the outside runner surfaces doesn't matter much - what matters is the temperature of the air entering the carburetor.

:beer
 

grumpyvette

Well-known member
Joined
Apr 17, 2001
Messages
841
Location
Loxahatchee, FL, Palm Beach co
"what matters is the temperature of the air entering the carburetor."

while IM reasonably sure you meant the AIR TEMP entering the CYLINDERS, after travaling thru the intake runners and carb , I totally agree that a 3/4" carb spacer won,t change the temp of the air much in the cylinders, what it might change slightly is the atomization and fuel/air distribution patterns.
generally a spacer tends to add plenum volume, loose some low rpm tq and gain a bit of high rpm peak power, but not in every case, Ive see both noticable improvements and very noticable losses in power
 

walkman

Active member
Joined
Jul 9, 2003
Messages
33
Location
ca
Corvette
1971 Stingray Bridgehampton Blue
I differ in opinion from your statement. A 3/4" phenolic spacer's insulating properties will lessen greatly the heat transferance from the intake manifold to the carb's base. I can prove that with temp. #'s. The 10* referes to the temp. of the air/fuel mixture. With a blocked off exhaust cross under runner and the spacer the air/fuel mixture going into the engine is cooler. That's a fact. GM has that cross under runner under the carb TOO heat the air/fuel mixture and get it off choke faster. When I changed maniflods I blocked it off, that's why they give you thoes little tin squares in the gasket package. You can't cool the ambient air, BUT you CAN cool the air/fuel mixture going into the engine. That's why they used Cool Cans and spacers ( other than metal spacers) in drag racing. Plywood spacers were the best. Pack the Cool Can with dry ice to cool the coil of tubing in the can that had gas/fuel in the tubing. The cold gas mixing with the ambient air AT the carb lowered the air/fuel mixture temp.
 

walkman

Active member
Joined
Jul 9, 2003
Messages
33
Location
ca
Corvette
1971 Stingray Bridgehampton Blue
Your right it won't by it's self change the temp much. But it will lower the air/fuel mixture by 10*, and that's what we are talking 10*
 

walkman

Active member
Joined
Jul 9, 2003
Messages
33
Location
ca
Corvette
1971 Stingray Bridgehampton Blue
Maybe my temp. #'s for the runners were misleading. That was the differance between cast iron and aluminum intake. Not because of the spacer. But the spacer will lower the temp of the heat transferance from the intake to the carb. Again we are only talking 10*
 

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