Valley pan cross-over block??

[69XP383]

I'm going to be installing a new intake manifold on my 383...was hoping to find a Edelbrock DP4B in good shape but I found/bought a "never installed" Edelbrock performer on e-bay for $88.

I'm going to replace the tin valley pan gasket since with a Fel-Pro set (the one on the engine now is semi-rusted) and I see that they are selling the valley pans with the exhaust gas cross-overs blocked. Is it OK/beneficial to block these crossovers with the new set, and why/why not? What is the purpose of the crossover (I'm assuming it heats the maifold for some reason...choke maybe...) or should I opt for the stock valley pan? I think there is a holley 650 on the stock manifold that I will be using on the new intake; it has vaccum secondaries and is a manual choke model.

Also have Copper, Red, and Black RTV for the gaskets, which is best to use?

Brian

[deputycrawford]

You can use the heat block off Felpro gasket number 1214. The cross over was to heat the manifold for emissions. Blocking it will give you much cooler intake charges and a slight more power. More will be noticed when the engine is built to a higher standard.

[69XP383]

OK, thanks...

I figured it was something along those lines. Was hoping to find a Performer RPM or better intake for cheap, but the engine won't be built for some time after car is finished. I figured that going to a high performance intake without any engine mods. might actually cost me both $ and horsepower in lieu of getting an $88 new intake.

Brian

[deputycrawford]

     You will get better info from Firefighter, Chryco and many others but I believe the RPM intake will do fine on stock engines. It will breath up top and not give up almost anything down low. You will just want to get the taller throttle bracket from Mancini Racing. Just tell them you have the RPM intake and they will send the part.

[John_Kunkel]

The cross over was to heat the manifold for emissions.

If so, why is there a crossover in manifolds from the fifties when there were no emissions standards? Think "driveability".

[firefighter3931]

The block off intake gasket helps to keep manifold temps lower....which in turn keeps the fuel cooler and helps prevent vapor lock and ultimately increses power. A cooler intake charge is better. 

The RPM manifold will require modified throttle and kickdown linkage. It is an excellent manifold that does everything well....strong bottom end power and good breathing wide open. 



Ron

[deputycrawford]

John, I guess I was a little too vague with that statement. I believe the manifold was heated to help fuel atomization for driveability. I thought it helped with emissions later on. I guess I am stating things I don't fully understand again. Please fill me in on the crossover theory. I am interested.

[John_Kunkel]

When it comes to the crossover, what's best for performance isn't necessarily best for driveability. Blocking it is usually best for WOT performance but low speed atomization suffers and warmup takes longer.

[ITSA426]

I always thought the only reason for the heat crossover was to let the automatic choke strip get warm enough to open the choke. 

[firefighter3931]

Here's my  fwiw ;

The crossover was designed years ago when fuel quality was much better than it is now.  The problem with today's gaz is that it's primarily formulated for fuel injected engines....meaning it's supposed to be under pressure at all times. Carburated engines operate under vacuum so that's where the problems start. The new stuff boils much easier than the old stuff and poor performance/vapor lock is often the byproduct of high carb & intake manifold temps. Trust me, the manifold gets plenty warm with the heat crossover blocked....i've checked them with an infrared heat gun. I also checked the carb using the insulating base gasket and saw a 20* decrease in running temps (both tested at the same time).

The crossover block off gasket was originally used on the aluminum manifold 6-pack engines to help improve drivability and dieseling issues on shutdown. 

Personally, i would not run an aluminum intake manifold without the crossover blocked off.




Ron

[plum500]

A quick cheers to all who take the time to ask the questions and those who respond. There's been a few threads in the last few days that have been extremely relevant to my situation. Not to mention the wealth of information this board offers all around.

[supserdave]

I wonder if an aluminum intake with cross over blocked would be at around the same temperature as a cast iron one with cross over open?