Open carb adaptor vs. 4-hole adaptor - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ED67C20 · 02-28-2009, 11:57 PM

I have a stock Q-jet spreadbore intake with an eddy performer carb. Right now I am using a Mr. Gasket open carb adaptor. It is just an open square hole for the throttle plates. Is there any performance or gas mileage difference with the edelbrock 4 hole design. The holes seem to be port matched. Just wanting opinions before I fork out $50. Thanks, ED67C20

Longhorn Man · 03-01-2009, 12:11 AM

there are way too many variables, and they are very very aplication specific. Car Craft did a shoot out probably 10 years ago, had 10 or so spacers all tested on one engine. one spacer would make 10 extra horses, and anoother would just rob hood clearance. The same spacer on another engine would make a huge improvement.
There is just no way to say for certian other than to stab it and see what it does.

**67 cst swb** · 03-01-2009, 01:52 AM

It is best (in my opinion) to use an adapter that has seperate ports for each barrel... I sell a "tapered port AFB/Holley to Quadrajet adapter. It promotes smoother transition from carb to intake... Look for it at your local speed shop...
Bryan

ChevLoRay · 03-01-2009, 10:11 AM

Get a phenolic material spacer and it will cut the heat transfer between the intake manifold and the carburetor for a cooler-running mixture.

**67 cst swb** · 03-01-2009, 11:06 AM

you are correct about the phenolic material spacer, but no one to my knowledge makes a phenolic "adapter" from an AFB/Holley flange carb to a Quadrajet manifold.

ED67C20 · 03-01-2009, 04:00 PM

Thanks for all of the advice. I am wondering if I go to a performer intake will I still need the adaptor. Or maybe the performer EPS is the one I should get. It knd of makes more sense to put the money to a good intake instead of $50 into an adaptor.

mrh33916 · 03-01-2009, 04:12 PM

In general i've always heard that a open spacer makes more power at high rpm, cuts low end torque and sometimes causes a hesitation just off idle. For a daily driver I would stay with a four hole design.

ChevLoRay · 03-01-2009, 04:52 PM

Quote:

Originally Posted by 67 cst swb

you are correct about the phenolic material spacer, but no one to my knowledge makes a phenolic "adapter" from an AFB/Holley flange carb to a Quadrajet manifold.

Guess I had a brain puffle......never gave any thought to whether or not they are available with a mix of installation possibilities. Thanx

02-28-2009, 11:57 PM	#1
ED67C20 Registered User Join Date: Aug 2006 Location: spokane, washington Posts: 37	Open carb adaptor vs. 4-hole adaptor I have a stock Q-jet spreadbore intake with an eddy performer carb. Right now I am using a Mr. Gasket open carb adaptor. It is just an open square hole for the throttle plates. Is there any performance or gas mileage difference with the edelbrock 4 hole design. The holes seem to be port matched. Just wanting opinions before I fork out $50. Thanks, ED67C20

03-01-2009, 12:11 AM	#2
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Open carb adaptor vs. 4-hole adaptor there are way too many variables, and they are very very aplication specific. Car Craft did a shoot out probably 10 years ago, had 10 or so spacers all tested on one engine. one spacer would make 10 extra horses, and anoother would just rob hood clearance. The same spacer on another engine would make a huge improvement. There is just no way to say for certian other than to stab it and see what it does.

03-01-2009, 01:52 AM	#3
67 cst swb Senior Member Join Date: Nov 2001 Location: Rapid City, SD Posts: 2,281	Re: Open carb adaptor vs. 4-hole adaptor It is best (in my opinion) to use an adapter that has seperate ports for each barrel... I sell a "tapered port AFB/Holley to Quadrajet adapter. It promotes smoother transition from carb to intake... Look for it at your local speed shop... Bryan __________________ My Trucks: 1967 Chevrolet Short Wide Box 327 TH350 9" w/3.90 gears paint will be White - Current Project 1967 Chevrolet Custom LWB 283 TH400 3.73 Posi, no-AC, no-PS, no-PB, bench-seat, small-window - mostly orig driver 1967 Chevrolet CST LWB originally a 327 TH400 3.73 Posi AC PS PB, had Buddy Buckets, Small Window - parts truck 1967 Chevrolet CST LWB, 283 MT 3.73 had Buddy Buckets, Panoramic Window - parts truck 2001 Chevrolet 3500 2WD Crew Cab Dually 8.1L Allison White

03-01-2009, 10:11 AM	#4
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Open carb adaptor vs. 4-hole adaptor Get a phenolic material spacer and it will cut the heat transfer between the intake manifold and the carburetor for a cooler-running mixture. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

03-01-2009, 11:06 AM	#5
67 cst swb Senior Member Join Date: Nov 2001 Location: Rapid City, SD Posts: 2,281	Re: Open carb adaptor vs. 4-hole adaptor you are correct about the phenolic material spacer, but no one to my knowledge makes a phenolic "adapter" from an AFB/Holley flange carb to a Quadrajet manifold. __________________ My Trucks: 1967 Chevrolet Short Wide Box 327 TH350 9" w/3.90 gears paint will be White - Current Project 1967 Chevrolet Custom LWB 283 TH400 3.73 Posi, no-AC, no-PS, no-PB, bench-seat, small-window - mostly orig driver 1967 Chevrolet CST LWB originally a 327 TH400 3.73 Posi AC PS PB, had Buddy Buckets, Small Window - parts truck 1967 Chevrolet CST LWB, 283 MT 3.73 had Buddy Buckets, Panoramic Window - parts truck 2001 Chevrolet 3500 2WD Crew Cab Dually 8.1L Allison White

03-01-2009, 04:00 PM	#6
ED67C20 Registered User Join Date: Aug 2006 Location: spokane, washington Posts: 37	Re: Open carb adaptor vs. 4-hole adaptor Thanks for all of the advice. I am wondering if I go to a performer intake will I still need the adaptor. Or maybe the performer EPS is the one I should get. It knd of makes more sense to put the money to a good intake instead of $50 into an adaptor.

03-01-2009, 04:12 PM	#7
mrh33916 Project '67 454 Join Date: Jan 2009 Location: Columbia SC Posts: 283	Re: Open carb adaptor vs. 4-hole adaptor In general i've always heard that a open spacer makes more power at high rpm, cuts low end torque and sometimes causes a hesitation just off idle. For a daily driver I would stay with a four hole design.

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