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Carb spacer...

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GreggR View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GreggR Quote  Post ReplyReply Direct Link To This Post Topic: Carb spacer...
    Posted: Mar/26/2013 at 3:32pm
I notice that carb spacers are available as both 4-hole (or 2-hole for a 2V) and open designs.

Anyone have a preference?

Is there a technical advantage either way?

Did a search, but didn't find this question addressed...

Thanks
Skating away on the thin ice of a new day.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote whizkidder Quote  Post ReplyReply Direct Link To This Post Posted: Mar/26/2013 at 3:36pm
I'm no expert, but I'd match the spacer to the manifold.
Ron Frost
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Post Options Post Options   Thanks (0) Thanks(0)   Quote nda racer Quote  Post ReplyReply Direct Link To This Post Posted: Mar/26/2013 at 5:12pm
It depends on what your combo prefers.
 
A 4hole can crutch the bottom end on a single plane manifold and a open can hep the top end on a dual plane, etc, etc.
 
I put the low rise Weiand Excellerator manifold (it was brand new and $40) on a smog mill with 2.56 gears and ran 15.2, bought a plenum devider kit for it and dropped to 14.6. Nice crutch for a bad combo.
 
 
A buddy bought a Holley System Max kit for his car and it ran best with the carb directly on the manifold, cause the kit was set up perfect from tha manufacturer. He tried a few diffent spacers and went slower. 11.2s out of a stock bore and stroke 350 N/A not too bad for a dual plane manifold.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 6768rogues Quote  Post ReplyReply Direct Link To This Post Posted: Mar/26/2013 at 6:20pm
Originally posted by whizkidder whizkidder wrote:

I'm no expert, but I'd match the spacer to the manifold.


That is what I do.
Why Ramblers? Chicks dig 'em. Whatever it is, I can take it apart.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tsanchez Quote  Post ReplyReply Direct Link To This Post Posted: Mar/26/2013 at 6:52pm
Like NDA says, it depends on the engine, signal at carb and manifold entry. Most of what a spacer does is add plenum volume. I have had many time that it caused driveability issues, especially with air valve secondary carbs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Red20 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/26/2013 at 7:18pm
I use a 1", 4 hole spacer on a dual plane edelbrock performer intake on a 360 with an edelbrock 650 carb w/ mech secondaries.  I noticed an increase in torque myself.  No numbers to back it up, but my seat-o-the-pants dyno confirms it.  One thing i did was chamfer the edges of the holes on the bottom side of the phenolic insert to help with air flow and reduce de-atomization of the fuel air mixture.  I used a router and 1/8" roundover bit to do that.  Don't know how much it helps, but I can't see it hurting.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WCKAMX390 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/26/2013 at 9:29pm
Used 1" spacer on my 390 ci, 4 spd AMX. Noticed a little better top end. Can't prove it, but felt it. Had to take spacer off because hood would not close and did not want to run hoodless...
1970 AMX, 390 ci, 4 spd, Ram Air, 3.54 posi

2002 Trans Am WS6, ls-1, 6 spd, T-tops, 22,000 mi, ALL factory stock

2012 Dodge Challenger "Yellow Jacket" SRT8, 6 spd, 392 Hemi, 1 of 1000 made
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jarcher401 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/13/2013 at 1:51am
No lie, but on the engine dyno I gained 10hp and 11tq from adding a 1 inch spacer.

600cfm carb
8.5:1 
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Gasket matched heads
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Apr/13/2013 at 11:05pm

Every carb I've ever seen was designed to have a gasket seal over all of the underside except the throttle bores themselves. Alot of the hollowed out spaces under a carb are designed to derive their vacuum from ports carved into the throttle bores, and not just from an open space. Plus, the rough underside of the carb will create extreme turbulance under the throttle plates and around the idle discharge ports.

Most stock intake manifolds have a closed plenum with individual intake bores, though they do eventually combine or have cross-drilled passages between them.  I am always very careful to make sure the spacer matched both the diameter of the intake manifold bores and the carburetor throttle bores to provide a streamlined path of entry. It's worked very well for me.
 
When faced with an open plenum, I would still install a closed spacer while matching the spacer bores to the throttle bores only.
 
Watch out on 327's with factory Holley 4bbls. They have two extra secondary idle discharge ports with their own holes drilled in the manifold and spacer.
 
Any spacer increases plenum volume, and has all the effects on engine performance that a larger plenum poses. Where I live, fuel percolation is the carb is paramount, so I tend to pile on at leat 3/4" of spacers. More than that and the cab is just being heated by convection. 
 
The primary way a carburetor cools itself is by the intake air flowing through it.  If your carb ever gets really hot while driving, downshifting and reving it up to increase airflow helps.  That is also why I believe in cold air intakes when the weather is above 85 degrees. Not for power, but for drivability. I've seen carbs get so hot, the accelerator pump shot vaporizes before it leaves the discharge nozzles.        ....Arizona problems.
 
 


Edited by FSJunkie - Apr/14/2013 at 12:25pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mr. Ed Quote  Post ReplyReply Direct Link To This Post Posted: Apr/14/2013 at 10:38am
I thought the spacer was primarily to insulate the carb from the heat of the manifold. Yes, no?

Thanks!
Mr. Ed
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