cams and carb spacers


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By YellowWing - 15 Years Ago
The time has finally come to pull the 312 out of my 56 Fairlane. Project includes C4 swap and installation of the following.



Set of G heads milled .020"

Reds Headers

Blue thunder intake

525 Demon Jr

MSD distributor and coil

Mummert's Y-265s cam 265 duration (224@.050) 110 separation



Whole bunch more wife doesn't know about Wink



I don't know yet if engine has been bored or what the deck height is. I'm looking more for torque than Hp and have a couple questions.



Thinking about advancing the cam for more low end but how much 2 degrees, 4?



Carb spacer sounds like a good idea and after doing some searches on the forum I know a 4 hole is the way to go but should it be a 1" or 2".



Also looking through the posts I see most recommend richer main jets. Any ideas for a good starting point.



Thanks for your input. Mike as excited as a kid on Christmas eve Smile
By Y block Billy - 15 Years Ago
Yellowwing,

I used a Mummert Y272 cam and advanced it 4* on a 292 .060" over with G heads shaved .020" decked to pistons .010" in the hole, B manifold with 4100 carb and it is very strong on low end torque. had to finally put the 9" rear end in.

Now I need headers and bigger exhaust.

By Ted - 15 Years Ago

It’s usually a good practice to start off with the jetting that’s supplied with the carb and then make adjustments from there.  Every engine is slightly different so what works on one persons engine may not necessarily work on yours.  But with the Isky E4 cam in my 272 and with a 1” high 4 hole carb spacer, I ended up going with larger primary jets in my Road Demon Jr. 525cfm from #58 to #61.  Off idle drivability saw an immediate improvement.

By Richard - 15 Years Ago
Regarding the carb spacer: Why is the four hole preferred to an open spacer.

Thanks,

Richard
By GREENBIRD56 - 15 Years Ago
The Y factory four barrel manifolds are a "dual plane" - and "air gap" - style manifold - both are well known concepts that build torque at low(er) rpm ranges. Use of the four hole spacer not only provides a thermal break between the iron and the carb base plate - but preserves the dual plane chambers of the manifold. 
By 46yblock - 15 Years Ago
Is there a significant difference in insulation between the plastic and fiberlike phenolic spacers?
By Ol'ford nut - 15 Years Ago
GREENBIRD56 (6/22/2010)
The Y factory four barrel manifolds are a "dual plane" - and "air gap" - style manifold - both are well known concepts that build torque at low(er) rpm ranges. Use of the four hole spacer not only provides a thermal break between the iron and the carb base plate - but preserves the dual plane chambers of the manifold. 

Then why does the Mummert manifold and carb spacer have two holes?

By YellowWing - 15 Years Ago
On the Mummert intake and my blue thunder you will notice a divider down the middle of the carb opening. This separates the two plane of the intake. A four hole spacer has material down the center that seals and preserves this separation ( two oblong holes front to back would also work but spacers are not generally made this way). A single square hole in the spacer allows for the free flowing of air between the two planes. Does this help explain? Mike
By grovedawg - 15 Years Ago
YellowWing (6/23/2010)
On the Mummert intake and my blue thunder you will notice a divider down the middle of the carb opening. This separates the two planes of the intake. A four hole spacer has material down the center that seals and preserves this separation ( two oblong holes front to backwould also work but spacers are not generally made this way). A single square hole in the spacer allows for the free flowing of air between the two planes. Does this help explain? Mike




Answers the same question I was wondering about.



46yblock (6/23/2010)
Is there a significant difference in insulation between the plastic and fiberlike phenolic spacers?




Does someone have an answer for this? A difference between plastic, fiber, or metal? I'm sure they transfer heat differently and therefore one is more desirable than the others?
By GREENBIRD56 - 15 Years Ago
There is a particular problem with the four hole style spacer that the slotted version avoids. It maintains the side for side division of the "cross-H" style manifold - but prevents the primary butterflies from being shrouded (?) as they swing down into the cylindrical passage of the four hole spacer.

 

This illustration was created to show a particular problem that occurs when the 4 hole spacer below the carb is stepped (smaller bores) and the primary butterflies swing near the step. On a manifold that has the slot style opening, there is nothing behind the primary to interfere with smooth passage out of the venturi throat. 

My tests with the infared thermometer shows the phenolic spacers to be way superior to the aluminum or pot metal versions when it comes to preventing temperature rise of the carb baseplate.

By charliemccraney - 15 Years Ago
I believe that wood is actually the best at insulating the carb, followed by plastics and probably phenols, then metals.
By Ted - 15 Years Ago
Ol'ford nut (6/23/2010)
GREENBIRD56 (6/22/2010)
The Y factory four barrel manifolds are a "dual plane" - and "air gap" - style manifold - both are well known concepts that build torque at low(er) rpm ranges. Use of the four hole spacer not only provides a thermal break between the iron and the carb base plate - but preserves the dual plane chambers of the manifold. 

Then why does the Mummert manifold and carb spacer have two holes?

Although a four hole design can supply a maginally stronger signal for the carb over a slotted version, Steve illustrates a good point about the shrouding that can take place under the throttle blades.  With this in mind, when the carb base is slotted the intake is still separated down its middle so that the carburetor is halved.  This divides the intake plenum so that the draw thru of fuel within the carburetor alternates from side to side and allows for a higher intake manifold vacuum during part throttle situations.  An open plenum under both halves of the carb essentially makes for a reduced vacuum as the carb now sees open exhaust valves on cylinders that would normally be isolated from the throat of the carb that’s trying to draw fuel.  As a general rule, keeping the primary carb bores separated are good for peak torque values while opening up the plenum under the carb either with an open spacer or cutting on the intake gives a boost to the peak horsepower number while hurting the peak torque numbers.
By Ted - 15 Years Ago
46yblock (6/23/2010)
Is there a significant difference in insulation between the plastic and fiberlike phenolic spacers?
Thermal properties are different.  As a rule, less dense would have superior insulating properties over more dense.  With that in mind, then fibrous phenolic would be better than plastic.  And what Charlie mentions about wood is also correct as when talking to the Nascar crowd, even different wood types for the carb spacers comes to the forefront.