Has anyone blocked their intake manifold exhaust crossover? I've talked to a few guys who say it lowers the running temp and makes it easier to start after sitting for 20-30 minutes. Two problems I am currently having.

NOT a good idea as far as MPG and general street-manners.

If you are having hot-start probs .. just insulate the carb from the hot intake.

Depends on your local climate. If you live and drive in a year-round mild climate, it can work fine. But, not great in Winter/cold climates. Fuel is not atomized as well, so fuel-economy / emissions are worse.

I live in Southern California and it works fine on my '71 Charger, but I'm not expecting great fuel economy and it rarely gets really cold here, even during winter months.

I have aftermarket cast iron dart heads on my 400 sbc and they don't have a heat crossover. I drive it in 15 degree weather during the winter and it runs fine. I do have to let it warm up a little longer before trying to drive off, but that is normal for any carbureted engine when it's cold out. Having an electric choke that is set up right is key.

My brother fills the openings in his heads with zinc alloy that he buys through Dick Miller Racing.

With the junk fuel available these days I blocked mine to help the hard starting.. I haven't noticed any loss of mileage.. But it has improved the starting...

Considering all the aftermarket aluminum heads don't have the crossover I have to wonder how much it helps. I figure eventually the intake will get good and hot just from heat transfer through a hot engine. Probably not as hot as it was with the exhaust flow but enough to still get good fuel vaporization. May just take a little longer to get the intake up to temp.

i did mine on my six pack

Exh crossover serves 3 functions
1. Heat the intake charge to help emissions and cold drivability
2. provide heat for the bi-metallic choke stat
3. provide exhaust gas for EGR systems

NONE are required for even a mild build! Most carbs have electric chokes,perf engines don't use EGR and who cares about cold drivability? BLOCK IT OFF!!

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It's about 1/2 inch thick so I might try to file it down to half that and see if it will fit.

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Maybe you should consider (or fabricate your own) carburetor heat-deflector plate:



Here's the Post:



I had a vapor-lock/carb-heat problem, so I bought/installed one under the carb on my '71 Charger. Holley makes/sells them, but I don't see it at Summit Racing or on Holley.com, though it may be there someplace (Jegs, etc.) Or, make one out of Aluminum sheet.



Here is a photo of one on a Chevy from the internet above.

Or this one a Moparts member fabricated out of "Plexiglass?"

Similar Moparts Post

I weld my intake crossover shut. Thats the way I block them as I never run the crossover on my muscle cars. But I dont drive them when it gets real cold like below 40 to 50 degrees. Blocking that will help your problem some. I had some hot soak loading up when it gets over 95 here so I installed one of the 1" plastic type carb spacers. It solved the problem completely. You can just see it as it is the black spacer under the carb. I would block it if I were you. Ron

Block it.We have all ours blocked.Neither has chokes and I run a Dominator on mine.How many people drive their cars in the winter?They were installed to heat the intake when these cars were daily drivers.That and if you worry about gas milage get a Prius.My 440 gets maybe 4 MPG.That and my aluminum heads now dont have any heat cross overs.Rocky

Are you still running stock manifolds with an exhaust butterfly valves? You can likely block it, and never notice the slightly extended warm up time until the fuel stops collecting along the manifold and intake runners, which can cause a temporary lean condition on initial warm up. You will also noticed improved drivability once warmed up. Mopars like cool dense air, which I have always referred to as horsepower air on those foggy chilly mornings.

I blocked it on my old VW engine at one time. On our VERY cold sub 50 degree days here in California, it used to ice the carb and cause stalling, because the carb was mounted so far from any other heat source.

On our beloved V8's, heatsoak from the heads and valley of the motor prevent that in all but the coldest climates.

I can't do this on my slant 6 though, because it would likely have cold start/drivability problems on all but the warmest days without the heat from the exhaust to keep the fuel from collecting along the inside of the intake on start-up. The nearly instant heat from the exhaust, really helps vaporize the intake charge and gets the engine running smoothly quickly. After the first 5 minutes though, the same heat begins to rob me of performance. I've used heat shields to try to make this issue less noticable and aid with hot start issues. It's been pretty effective. Much more so than the infamous "fuel line mod" touted by some slant 6'rs...

Hey 383man,

I was going to PM you to see how you were turning those high 11's with a 383. Now that I see under your hood I don't have to ask that question.

Beautiful car. Saw the burnout photo on the 62-65 Mopar site.


Butch

An oval track friend told me he has always packed furnace cement into the cyl head cavity.

....... My 440 gets maybe 4 MPG.
....if you worry about gas milage get a Prius.

THIS is something I would not be proud of !!

Your 440 is soitenly NOT fuel efficent ... I would think you could "cruise" with a furr-real Pro Stock car and get better MPG than that ..

Performance and fuel mileage and efficiency CAN come-together ...LOOK at some of the newer cars .... the FIRST being the recent Corvettes.

IIRC ... a dead-stock OEM vehicle that runs in the 11's ...and gets nearly 30 mpg.

VERY impressive ...IMO.

Doc I built a race car not a fuel economey car and yes its street driven.With 12.5 pistons almost .600 lift cam and Dominator its not fuel friendly.Fast but not fuel efficent.So like I said if you want fuel economey get a prius.How many of these cars here actually get driven?I mean daily.My kids 300 does and he gets probally 12 or 14 mpg and its a 62.Thats if he keeps his foot out of it.Rocky

I'm running stock intake and manifolds. I'm thinking of just installing a valley gasket that has the exhaust crossover holes blocked. That sounds like the easiest way to do it for me.