What are the pros and cons of running a carb spacer? I have read that they help with top end performance, but do they take away from the low end? Im thinking of trying one out but want to read some input first.

The open spacers help with top end power, & the 4 hole help with low end torque. For a street car, go with a 4 hole.

x2 4 hole for the street and open for top end hp.

It makes the intake maniold think its bigger than it really is...some engines like them, some see no gains, or a loss of performance. Every engine is different, a dyno is the only way to see for sure how your engine reacts.

There is a spacer that starts out as a 4 hole & tapers into an open spacer. In every case we have used one on an engine on our dyno it has helped all around power w/o hurting torque or HP.
Below is an example of the spacers Wilson makes, they are also made by other companies.

http://www.wilsonmanifolds.com/shop/index.php?l=product_images&p=9


I have one of these on my engine.

Can I run a 4 hole spacer with my open intake?

sure, the carb has 4 holes so your just just making the carb flange thicker by using a 4-hole spacer..
A tapered 4-hole spacer can provide the best of both worlds

performer rpm intakes require a special unit that has a window machined into it designed to enhance cross-flow across the divider.


Here is my HVH tapered 4-hole with a window..






and the matching intake manifold


On my engine combination the spacer can add up to 40hp..

are all brands different or are spacers just spacers?

open, 4-hole, tapered 4-hole,
they come in varying thickness..

Hmm, thats interesting about the spacer being different for an Edelbrock RPM intake. It must not be "required" because I run a regular tapered 4 hole Wilson on mine, but that is an interesting piece of info. Did that info come from High Velocity Heads? Also, do they charge more for it?

all i can tell you is i used one on "the other project"
and it made a world of difference..
Never compared with a standard open or 4-hole unit so
don't know if it's better, but it works for me..
It's not required for the manifold but it does
compliment the existing setup..
Roughly $135 online..

You may also want to think about phenolic spacers that help keep the carb cooler.

Absolutely, phenolic spacers can add performance by keeping the carburetor cooler, use a fuel cooler to maximize the benefits of a dense mixture...combine all these techniques and you maximise HP with the chosen selection of parts..

is there a specific application one for holley street avenger carbs? all i'm seeing is the 4150 and 4500 series.

or can i just use one of those?

the street avenger is a 4150..
what manifold do you have..?

don't know yet. haven't decided between Holley street dominator, Edelbrock performer,

both of those are low-rise dual-plane intakes, that
motor won't turn enough rpm to benefit from a spacer..

if you were serious about makin power i'd recommend
a 4-hole tapered, but not with those manifolds..

Wow, I have always thought that those carb spacers were just one of those "rip off" products that didn't actually do anything. Guess I was wrong.

How many inches tall of one should I get for my Holley 770CFM Street Avenger carb and Holley Street Dominator intake?

Thanks,
Jason

It depends on the appication...

I was afraid this would happen, just because i run a spacer on my engine some of you might think your engine needs one too.
This is not the case unless your building or have a serious street engine, spacers are designed to add power on top.
the rpm where valve overlap is minimized, air-flow is maximized
and the engine really starts to pull like a freight train on steroids..
This is when the tapered spacer really starts to shine by correcting and shaping the air-flow into the plenum..

If ya gotta high-rise and 270 debgrees of advertised duration ur probably a good candidate for the unit.
Otherwise ur most likely wasting ur time n money..

That's the way i see it dawg..

Hmm, well I don't have a high rise intake, but my advertised duration on my soon to be installed Comp cam is 268/280. Do you think I would be fine without a spacer, or would I benefit from one?

Here is some interesting results about spacers on a smaller engine than mine. Yea, it is a Ford, but interesting results none the less...

http://www.fordmuscle.com/forums/tech-exchange/465957-carb-spacers-dyno-test-1964-falcon-302-a.html

Thanks,
Jason

i'd recommend switching to a high-rise dual-plane...then check out a spacer if ya like what the new manifold does to the powerband....glad to see you researched a little and found out that i'm not just passin gas...lol
15-40hp depending on application

George

So if i have the holley 670 and edelbrock performer, I would probably benefit most if i just got a 4 hole spacer up to an inch, maybe less? It would also be a benefit just for the fact of the heat transfer, right?

It's a street/strip car mostly street. Is it really even worth the spacer in my application?

that would be your biggest advantage, .25" or .5" phenolic..

Sorry for my ignorance, but how do you tell if you have a high rise dual-plane intake or not? Just wondering, because shape and height wise, my intake looks a lot like yours George. Mine looks like it has the same basic style of divider and internal structure as yours does, from what I can tell in your picture anyways. I'll get a picture up later if necessary, at work right now.

Thanks,
Jason

Would a 4-hole benifit me at all on my stock chevy intake (I will put it on my edelbrock later)?

Jess