Blocking exhaust Crossover issues???
 

I see the Procomp, or whatever else it is branded as, intake for a reasonable amount but they do not have an exhaust crossover and are blocking that area off. Are there any issues blocking that crossover? Reversion issues? I know it is best to fill the head to block that area and I would likely be switching to E-heads at some point, but for short term, I am thinking about purchasing the RPM copy procomp intake. Thoughts?

They are fine so don't hesitate to get one.

I had my crossovers blocked off at one point then had them filled....

Helps keep heat away from intake

That was my thought as well, just did not want to create any issues from now till the time I switch heads.

Blocking the holes will not cause any problems. I used the Mr. Gasket intake gaskets with the thin metal block-off plates, on lots of engines. And I used homemade block-off plates, with a couple of factory alum intakes.

Never had any problems, street or race. But I have read that there is a slight performance advantage, when filling the holes. I've also heard that it changes the sound of the exhaust. Can't verify.

So whats the best method to fill the exhaust cross over,. and does it apply to most pontiac cast iron heads... :popcorn:

Molten aluminum pored from the combustion chamber side.

There is no easy way to fill the crossovers in my opinion. To fill properly with molten metal, the heads must be completely disassembled, crossover ports cleaned, preheated and poured with your choice of aluminum, zinc or mix of metals like they use at Mondello. With this method, you need to have a crucible to melt the metal and a ladle to pour it into the crossover. It needs to be done quickly and in 1 pour to prevent it from solidifying in layers that could break loose and work their way into the exhaust valve. Unlikely that it would, but not impossible.

An alternative to aluminum is a high temp resin called Resbond 940HT. This is a powder that is mixed with an activator in a ratio of 100 parts powder to 30 parts activator that can be pored into the port and allowed to solidify. This will provide a nice fill that will withstand 2800 degrees continually. Again, the heads will need to be disassembled and the crossover ports cleaned and scuffed for adhesion before poring in the mixture. This is an adhesive, so cleanliness is important. It is necessary to block off the port at the intake manifold side and pour the mixture through the exhaust valves until the cavity is full. Depending on the temperature of your work area, it will take 24-48 hours for the mix to completely set, at which time you can use sand paper to shape the ports if required. The next step is a final cure in the oven at around 400 degrees for a period of time.

I have never actually poured a crossover full with molten aluminum, but I do know the risks involved. Without proper preheat, it is possible to crack the cast iron due to the rapid heating of the head. I have also seen where the pour solidified in layers, causing small pieces to become loose in the ports. Many people have done and continue to do this with success, but without the right equipment, this can be risky and dangerous. I have used the Resbond to fill the crossover cavities, and found it to be a very easy alternative, but expensive at around $120.

Here is a very good step by step thread from the Olds forum: http://classicoldsmobile.com/forums/...ond-940ht.html

Blocking the exhaust crossover or filling in the exhaust crossover passage in the heads is NOT a good idea for engines that are driven in cool/cold weather.

None of the factory divorced or hot air style chokes will work with that deal either.

If your car is casually driven in warm/hot weather only, then not having a working crossover is OK, but it will still increase the time required to heat the intake up enough so fuel doesn't "glob" up on the runners and come out of suspension.

A working choke is a nice feature on most street driven vehicles, but certainly not a deal breaker if you don't mid "patting" the throttle and waiting a few minutes for things to heat up so the engine will idle without some additional help from the operator.

For "max-effort" set-ups blocked or not having crossovers at all, or a choke of any kind aren't really a big deal. Very few folks call on those vehicles to take you down for groceries in the cold Winter months up North when a working choke and open crossovers become necessary.

My own engine hasn't had open crossovers for quite a few years, since going to the KRE heads, but I did put an electric choke on the carb after not having one for a few years. It's one of the best upgrades I've done in the past 10 years, fires up instantly in any weather, fast idle for a minute or so till it warms up some, and didn't slow it down at all at the track......Cliff

Thanks for the reply's fella's,..

Where can I get some Resbond,.. and could this stuff also be used for some fill in port work on heads and intakes...

My 64 GTO is just a warm climate car here in Michigan,.. I'll probably block the crossover with a small piece of metal,..

Good info...

Since this question was asked in the "street" forum, will chime in.

If I had a nickel for every telephone call we have had in the last 25 years from individuals that have blocked the crossover on street engines, and had cold driveability issues; I could buy Florida and retire!!!

25 years ago, I listened to the same stuff about blocking the crossover and did on my own Pontiac. Ended up fitting a manual choke carburetor to be able to drive the car in town for the first 30 minutes after start-up. And yes, I have a 4-speed; would not like to even think about doing it to an automatic. After warm-up, it runs great!

Jon.

I purchased it direct from Cotronics. Their tech line is helpful and they are familiar with this application.

http://www.cotronics.com/vo/cotr/ca_fastset.htm

Pay attention to the final curing part of that Olds page. Bake out moisture for final shrinkage & hardening. Heads can be heated in a gas grill, or the kitchen oven if your significant other is game.

Jon, I'm with you on this as we are in the "Street" section, and most folks don't realize that heat is actually your friend when it comes to these things, and that the intake is going to heat up anyhow, you are just prolonging the process, and using more fuel the entire time.

I get the SAME calls here, from folks who tried the "trick of the week" and blocked the cross-overs, then wonder why the choke no longer works, and why the engine runs poorly until it reaches full operating temperature and heat soaks a bit......Cliff

Since the exhaust gas that circulates under the manifold is a lot hotter than coolant, wont the manifold get hotter at full operating temperature then the rest of the motor?

I know we have some top tier Carb guys on this thread, but would it make a difference if you are going with a TB EFI setup?

crossover
 

I have two factory intakes. One is bone stock, just cleaned up ports up to match gaskets.
And the second I removed the crossover completely and made blockoff plates.
Well lets just say I preferred the stock one with crossover intact. My Firebird
has good manners cold and HOT with it. Heck the exhaust note changed and
even my kids noticed the difference. The goal was to keep carb as cool as possible
and having to wait 1/2 hour on a 70 degree morning to get smooth idle was a deal breaker.
But the modified intake does make great garage art.

Gerry

Happily driven with blocked crossovers. Resbond-filled is easier overall. Aluminum pour into the intake gasket side worked well for me. I use 0000 steel wool stuffed into the bowls to stop the alumin flow to result in a nice as-cast bowl shape. Easy easy.

Electric choke ought to solve all the Cold warm-up concerns. Yet I use the thermostatic spring with carefull adjust for choke action. Or just been leaving the chokeplate off & deal with a stubborn cold start.

Blocked crossover Benefit is reduced running temps on the highway. Probably reduced ping too. Blocked crossovers are indicated for the hobbiest that affords time and effort to tune the combo, or endure a rough spell during warm-up.

OTHERWISE keep with the other's advice to keep the crossovers unblocked for that high quality cold-start and run-ability.

Heat is your friend with a "wet-flow" intake system. Cool/cold engine parts in the intake tract cause fuel to come out of suspension and require richer mixtures (a working choke) until the parts heat up.

The only reason folks are able to get away with not having a working choke on these engines is how they are used. Most NEVER set out in below freezing or sub-zero weather. It is difficult, if not near IMPOSSIBLE to start one of these engines and have it continue to run till warmed up in really cold weather without a working choke.

You have a fighting chance at that deal if you are using an aftermarket gas-sucking pig carburetor that's putting down way to much fuel right to start with, but with a well tuned carburetor you will find your engine stalling out, and requiring a half dozen or so shots from the accl pump to restart it, then it will stall again and again, running a few more seconds each time until you get enough heat in it so it stays running. (Sound familiar).

The factory really did know what they were doing running exhaust gas thru the bottom of the intake to heat it up quickly. This greatly reduces engine warm-up time, and allows for leaner mixtures to be used for "normal" operation.

The last couple of time this topic has shown up we see opinions from one end of the spectrum to the other. My opinion is that you need to leave the cross-overs open if you have a divorced or hot air style choke system. You need to leave them open if you plan on using the vehicle to fetch your groceries year round AND live where it falls and stays well below freezing for weeks/months at a time.

If you are just pissing around on nice weekends with one of these cars, and almost NEVER drive it in cool/cold weather, it simply becomes a matter of how much you can deal with when it relates to cold start-ups. I personally ran my own engine for a few years without a working choke, and it was fine. I was younger and could deal with having to sit there and do 2-3 pumping the hell out of it restarts, and "patting" the gas to keep it running until it would idle on it's own.

The BEST thing I ever did for my engine was to install an electric choke on the carburetor. Now I have INSTANT starts in any weather, and fast idle for warm-up. I even tested that deal last Winter at -26 degrees outside and it roared to life and warmed up just fine. That same day my Nissan Altima BARELY started, and my 2000 Tahoe refused to start!!!

One thing I will not do here is argue about this topic. All sorts of good theory, and opinions, etc, but it really boils down to personal preference and where you live and how you use your vehicle. IF you are in the dessert in the SW, and it's always hot, you may not need a choke or an open cross-over, and could actually run into scenarios where the added heat cooks the fuel in the carb on hot shut-downs, not sure about that but common sense tells me this could be a potential issue.

I say all that because the factory did not only run exhaust thru the bottom of the intake, they also had an additional heat channel under the carburetor in 1967 (Pontiac's with q-jets) that put heat DIRECTLY on the steel shim under the carburetor. That deal is certainly over-kill, and at the time was probably a good idea to run even leaner mixtures and heat up the fuel some, but in actual use we get enough complaints about those intakes that we recommend to customers to block off the supply holes to the channel under the carb if/when you are having issues related to cooking the fuel out of your carburetor......Cliff

"I know we have some top tier Carb guys on this thread, but would it make a difference if you are going with a TB EFI setup?"

Those are just electronic carburetors, same rules apply. I'm a NOT a fan of any of them to date. I really do NOT like the fact that they dry up the intake in certain conditions. Never all that fond of the factory TBI set-ups either, and have a few great stories to tell about how we've out ran them every place with q-jets and tuned HEI distributors, but that's another topic.

It seems like the aftermarket TBI's are are getting better, but I've cause the demise of so many of them, I'm surprised a few of the companies making them haven't put our a "contract" on me!......Cliff

CLIFF,
Electric choke indeed.
hot manifolf floor for vapor release sounds good. But consider;

I want to propose that even the ice-cold start event though warm-up should show the fuel never touching the manifold floor at fast-idle: pethaps cold-start fuel goes from throttleplate cracks to runner having the demand.
Highway cruise ought to show the same dryness.
Half-throttle through WOT is a sure situation for fuel slamming tne manifold floor.

And surely the valve bowl & long-turn Cyl wall wett with fuel at all conditions, with severity depending on porting efforts aimed at reaching "wet flow" goals.

Any good?