Carb Spacers and their effects

[Heckeng]

Ok Don, I'm throwing a quarter in the coffee can!

 

General question on carb spacers and I didn't want to hijack the other thread where you were talking about them. I've been looking at the phenolic spacers for a heat insulator, and that had gotten me thinking in general.

 

If you have a dual plane intake with a division in the center, should you use a 4-hole spacer? I ask because if you have a division in the intake, and use an open spacer, you kind of defeat the purpose of the intake design performance wise right? I had thought about getting a 4-hole for the low-mid range boost, but I really don't need that, so I ordered a 1" open. I haven't put it on yet, but wanted your (or anybody elses) opinion!

 

Also, what do you think about using the spacers for heat insulators, worthwhile or just a gimmick?

 

Ok, I think there are 3 questions in there, so I'm up to $0.75

 

You probably remember, but here are the basics of my car:

 

454 with 230/236 HR, demon 750dp, ~2800 ATI stall, 3.55 gears with 28" tire

[502ci]

I have tried the phenolic 1" spacer in the picture.

 

I currently have a dual plane intake on my 502 that has a slight area removed on the divider (factory).

 

The car ran immediately 1/10th slower at the track.

 

I kinda blame the fact my open air filter top was now up against my hood, restricting air flow.

 

I removed the spacer at the track and my times increased back to normal.

 

Mine was a bad test with these factors involved.

 

I believe in normal circumstances it would help.

 

[Guest]

Bill have you ever tried a 2" 4 hole spacer with your dual plane intake?

 

here is mine

 

[Guest]

As a heat insulator, questionable on a street car due to duration of exposer to abient underhood heat. Drag car maybe of some benefit. I have never used a phenolic any heat insulating spacers. Always used aluminum, less chance of vacuum leaks due to different thermal expansion rate of the diffierent materials.

Spacers on dual planes is a tricky matter some work some don't. Only way to tell is to try it. Some engines don't like big plenum volume and some don't. The four hole won't help much since the divider normally dosen't seal to the spacer.

You do have to retune when add a spacer, not just adjust the carb bet retweak the whole setup.

In 502's case it most likley was turbulance problem created by the droped divider combined with heads that are small, 290 cc runners, on a 502 ci engine. He needs to be in the 320/325 cc range. When you run a head that is small on runner for the given ci it can create a intake velocity that is to high. No matter the engine size once you reach the point where the air is traveling at to high of a speed it begins to bounce around the interior of the ports and becomes its own restriction. When this happens you negatively effect the cly fill and therefore power drops.

The dropped divider may be just low enough that the air flow merged between the carb and the dropped divder causing the air charge to slam into the divder and be disrupted.

Water and air have the same basic flow properties, Take your garden hose and spray it at the narrow end of a 2x4. The water does not flow smoothly around it, it changes directions to the sides and some turn back the direction it came from.

Knife edging doesn't work well either for air, A smooth radius of the divider will be best.

 

Basic rule of thumb is that if your combo likes the spacer then you are restricted in the intake tract. Could be heads or manifold. Some plenum/divder designs just plane don't work with any spacer.

Don

[Heckeng]

Thanks guys, Back to Jegs it goes! Glad I didn't open the packaging yet!

[kc8oye]

I want to throw somthing into the mix here..

 

I'm running a QudraJet *Ducks the flying debris*

 

on a Cast iron intake (don't ask) it's a GM Crate engine (I got it used) factory intake and mine came with a 1/4" or so open spacer/gasket type setup on it.

 

When I had my previous engine (305 with edelbrock performer intake) I found the engine ran much worse with the spacer-gasket under it then just a plain paper gasket.. I was just curious if this was like rice was saying.. or not where that extra little gap between the throttle bores and the divider creates bad turbulence or not? (I can't find my spare plain paper gasket to test the diff) but I'm not real happy right now with the way my carb is behaving.

[Guest]

Carburetor Spacers:

 

Carburetors spacers can be a very useful tuning aid when working on your streetcar, or racecar. A spacer can be used to move the torque and power-band where it is more usable in your application, or they can be used to help work out inefficiencies in your combination.

 

4-Hole Spacers. As a rule of thumb a 4-hole designed spacer (4 individual holes one under each barrel of your carburetor) will increase your throttle response, and acceleration. They can also move the torque and power-band down in the RPM range. This is accomplished by keeping the air and fuel flowing in more of a column, which increases the air velocity. This can be a perfect addition if your vehicles throttle response is not as good as you’d like, or you’re getting passed when you pick up the throttle coming off of the corning. A 4-hole spacer can also help make up for something in the intake tract being larger than optimal (too large of a carburetor, cam, intake, etc.)

 

Open Spacers. As a rule of thumb an open designed spacer (1 big hole underneath your carburetor) will decrease your throttle response, and acceleration. They can also move the torque and power-band up in the RPM range. This is accomplished by increasing the plenum area, which will help in the higher RPM’s. This can be a perfect addition if your vehicle has traction problems when accelerating, or coming off of the corner. A 4-hole spacer can also help make up for something in the intake tract being smaller than optimal (too small of a carburetor, cam, intake, etc.)

 

Combination Spacers. A combination spacer (half 4-hole, and half open) can give you the best of both worlds. Increasing your throttle response, and acceleration over not using a spacer, and increasing or broadening the torque and power-band.

 

Plenum Dividers. A Plenum divider does as the name implies divides the plenum in an open plenum intake manifold from side to side. These are generally used to help prevent fuel slosh from side to side in high G load Oval-Track, or Road-Race applications. It is common on certain engines to have lean cylinders do to fuel slosh. A SBC oval track engine running on methanol can run lean on cylinders 3 & 5 while cylinders 4 & 6 will run rich. A plenum divider can help eliminate this.

 

Spacer thickness. Varying the thickness of your spacer will affect how it affects your engine. Normally the thicker the spacer the more of an affect if will have on your combination. Meaning if a ½” thick spacer helps you a little a 2” thick spacer can give you more of the same affect.

 

Spacer Material. There are many different types of materials used for manufacturing spacers. They all have pro’s and con’s. Wood for example is a great material as far as thermo efficiency, but can wick fuel, which is not safe. Plastic, or composite spacers are also very good at not transferring heat, but are not as strong, and can be harder to modify. Generally Phenolic fiber, or Aluminum is preferred. Phenolic is very good at not transferring heat, but can be hard to modify. Aluminum is not as good at heat dissipation, but can be ported or modified easily to work on specific applications.

 

Spacer Tuning. Since each spacer will react differently on each combination there is not a right or wrong type. Spacers are a great tool to have to help dial in a new combination, or tune your racecar for varying track conditions. Swapping out a spacer is a very simple change that can have great impact on the drivability of your streetcar, or racecar. Having a couple types, and thickness of spacers around is always a good investment.

[Heckeng]

Tech@bg, good to have you here. I think that it is very respectble that BG takes the time to help answering these miscellaneous questions on forums. Also, nice writeup on spacers.

 

If you're allowed to tell us, Who are you from BG? Are you the only one who will be responding with this username? Just curious if you are by chance Eric, or another BG guy that I'd talked to on the Innovate Motorsports site!

 

Welcome aboard, and thanks for the reply!

[Guest]

Multiple guys will respond. Right now we're monitoring about 250 boards, so we're not on all of them as much as we'd like to be until we can increase our staff some more.