Carb sapcer differnce

[Nima]

Can anybody explain to me the difference between open carb spacer with the one with 2 or 4 openings?
Thanks

[shuttermutt]

Originally Posted by Nima

Can anybody explain to me the difference between open carb spacer with the one with 2 or 4 openings?
Thanks

I'm no expert, but here's what I understand...

4 Hole
A 4 hole spacer, as you might expect, has one hole for each barrel on the 4 bbl carb. Most folks will tell you that a 4-hole spacer is probably the best match for a dual plane manifold such as the Edelbrock Performer series or most Chevrolet factory intakes. This design helps to maintain (or potentially increase) the vacuum signal to the carb while slightly increasing your overall intake volume and reducing your charge temperature. Depending on a whole big list of factors, you may notice a bit more bottom-end torque.

Open
An open spacer, on the other hand, is often cited as the best match for an open plane manifold such as the Edelbrock Victor or Holley Dominator series of intakes. They will definately increase your overall intake volume and reduce your charge temperature, but you may have difficulty at lower rpms largely due to a weaker vacuum signal. Again, depending on how your engine was built, how you operate it and about million other factors, you may notice a bit more "umph" at the top-end, but at the potential cost of some bottom-end torque.

Now, there are some people that have installed spacers and swear they pick up a ton of horsepower. Sure, okay... it might happen, but I've got my doubts. For everyone that claims a big horsepower boost, there are probably 10 others that will say they didn't notice any difference whatsoever. Ultimately, there's only one way to find out, isn't there?

I put a 4-hole phenolic spacer under my Edelbrock 1406 after describing what others here on the board diagnosed as a vapor lock/heat soak problem. Basically, all the fuel was getting "boiled" off in my carb after I turned off the key. The 2-inch spacer fixed that completely. Well worth the $30 investment if you ask me.

I experimented with a 1-inch spacer as well. I'm betting it would have cured the hot start problem as well, but I didn't notice any difference whatsoever in the "seat-of-the-pants" dyno. Contrast that with the 2-inch spacer which did produce a noticeable difference. Specifically, the throttle response is a bit crisper and the engine doesn't seem to have to work so hard when I stomp on it from mid-low rpm (1500-2000).

My personal recommendation would be to experiment if you can. I was fortunate enough to find "the cool guy" at the auto parts store that actually let me install both the 1-inch and 2-inch spacers before I paid for one. I don't know if you'll have the same luck, but I do think it's worth the hassle of buying both and returning the one that doesn't perform as well. Hopefully, you'll hit on the right combo.

Oh, and while we're at it, do yourself a favor and go with phenolic. Phenolic is a thermoset synthetic resin that's frequently reinforced with glass cloth or other flexible materials. It's very dense, has very good mechanical strength and is quite heat resistant. Avoid plastic for your spacer as it has none of these desireable properties. Aluminum is okay, but overpriced and you lose the heat resistance. Wood has the best heat resistance, but it requires periodic replacement or maintenance.

For more information, I'll refer you to this website which does an outstanding job of describing intake design and talks a bit more about carb spacers. Yes, it's Mopar-centric, but the principles apply to Chevy and Ford engines, too.

Good luck!

[Nima]

Thanks for good explanation.Appreciated.

[Tynee]

Wow, VERY nice explaination. Thanks from all of us who didn't ask the question, but now understand a bit better.

[shuttermutt]

I aim to please!

[chickenwing]

I say thank-you also. I have the 1406 then a 4 hole tv cable plate from Bowtie Overdrives then an open wood 1" spacer. I'll cross over to the 4 hole 2" phenolic. Hopefully this will aid my tuning woes.

[shuttermutt]

Probably not FAQ worthy, but I'm glad I can help. Good luck!

[cableguy0]

also if you have an open plenum intake such as the victor jr victor or dominator a 4 whole spacer will help your engine in the lower rpm ranges to get back some of the torque lost with the open plenum. the 4 hole spacer "tricks" the engine for lack of a better word to act as if it has a dual plane down low but with the performance of an open plenum up in the higher rpms