Hi had a question for you guys alright i got this chevy 350 that i pulled out of an suburban its in pretty good condition with very low miles.what i have done is this.i have put the motor into my chevy monte carlo the motor is bone stock except for a set of headers and an aluminum intake by holley,also what i have done is this. the intake is an square flange set up for an holley carb but the only thing that i had was an quadrajet carb so i had to purchase an 1 inch spacer for that set up which fits perfect.my question is this i already had an 1 inch spacer from an previous motor that would fit perfectly on top of my spacer i just purchased.would it be a problem to run both spacers which would give me a total of two inches?  

Kind of thing you have to try to find out. Spacers do several things; they increase the volume of the plenum and change the flow pattern as it transitions into the plenum and from the plenum into the manifold's passages.

Increasing plenum volume does several more things. First more volume tends to dampen reversion pulses, a good thing. But it also tends to dampen "signal" which the carb needs for proper metering, a bad thing. It also provides a larger reservoir of mixture that any cylinder may draw from, a good thing.

Raising the carb can improve flow into the plenum and from the plenum into the passages by reducing the shear angles the flow has to make from the carb base into the plenum. This can help keep the major flow along the top of the passages and on into the ports. This helps cylinder filling. However, it's more effective to raise the entire passage pattern as is done with a high rise manifold.

The last thing is a negative which simply put is you might run out of vertical space to close the hood, but that's what scoops are for.

Bogie

I was kind of reading over the post and i was kind of wondering about reversion pulses i have never heard of that before could somebody explain?  

i know you sent a feeler out for the info from bogie, but i looked up a definition to maybe help in understanding reversion. really there are a couple factors that contribute to it and are quite complicated, one being that the simple reversal of airflow within the inake port caused by the fast moving intake charge reverse pulsing off of the backside of the intake valve at the moment the valve returns to the seat and stops intake flow. meaning as the flow column is initiated ( by the valve opening and, with the piston lowering in it's cylinder, it causes a low pressure area within that cylinder ) as air/fuel rushes in to balance the newly "found" low pressure area, the column of air filling the cylinder is really picking up momentum. when the intake valve snaps back to it's seated position this column of air stacks up on itself behind the intake valve causing a high pressure situation to appear within the valve bowl portion of the intake port. the "pulse" is the high pressure of the bowl area returning as a wave to the plenumn to restore balance throughout the intake.

so really, the action within the intake manifold is turbulent - back an forth, stoping and starting... hope this helps, good luck!

-another source for the pulse is the degree of overlap ground within a given cam. tight lobe separations, say 106* ish and tighter... cause the reversion to be far more noticable. this is a situation where the lobes being ground closer together have a greater degree of overlap. overlap is the hang time in degrees that the exhaust valve is still open and allowing high pressure exhaust gas out ( both by the expansion of the burnt mixture, and the rising piston within the cylinder displacing the spent air/fuel ) and the  intake valve opens prior to the exhaust valve closing. at lower engine speeds overlap allows exhaust gas to sneek into the inake, ( just as a minor pulse ) causing slow rpm cylinder fill efficiency problems, and driveability problems. and a really lopey, rumpity, type idle with no idle vacuum.  much of this is why so often manufactures stress the application for the cam to be advised by various help sources offered by the manufacturers. this keeps less experienced builders out of the trouble they'd fall into putting together incompatable parts. and ensuring they enjoy the engine they build. 

Sounds like good definitions to me!

Actually the reversion pulses can be so strong, in some instances, that it causes a backward flow thru the venturi and a standing fuel cloud will actually form above the carburetor.

Bogie

Man that was complicated i think i better leave this topic alone thanks anyway!!! and good luck sumpton_13