when I changed my intake I had to put in a 3/4" spacer so the plunger would not hit the intake. (holley 750).

What if anything does a spacer affect as far as how the engine runs?

thanks

It depends on the spaced used.
A phenolic (not metal) spacer insulates the carb (and fuel mix) from intake temps, thus delivering a cooler (denser) mix to the intake - hopefully.
An open plenum (one big squarish hole) spacer is apparently better at higher RPMs as it in effect, makes your manifold a high(er) rise, increasing intake runner length and (hopefully) velocity.
The 4 hole spacer (holes line up with the carb base butterflies) works at lower rpms to better seperate the primaries and secondaries allowing a better distribution to the cylinders and increasing runner length.

This is what I've been able to gather after my research here and elsewhere, along with some dyno test time on various intakes, spacers, motors, carbs and combos.

My conclusions? Test different spacers on YOUR combo and see what works best for YOU.

I have found the HVH Super Sucker 2" alloy spacer worked better than the 2" Phenolic (plastic) open spacer on my Performer RPM manifold, but the 1" HVH worked better on the Victor Jnr, same Carb, same motor.

Hope this helps. I may not be 100% correct, but like I said, it's what works best for your set-up.

Good Luck!

thanks ghost.

I have a 5/8" aluminuim spacer to be more exact. and it is a " big hole". Not individual holes matching the carb. I do have the performer intake from edlbrock.

So I should be getting one with the individual holes because low rpm and torque required for boat?

21 ft scarab excell.

the open one will work fine on that, they seen to pick up the mid range without loosing top end performance, most run a 1" spacer...