Blocking the heat crossover, IN the head.

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Bad Sport said:
True, but that's mo money. I already have a nice set of heads.

I have never done this, but it is an old hot rodders trick and is still common practice today with old school engine builders. The claim is that it increases the port flow for those two exhaust ports, essentially making them more equal to the other 6 ports.
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Yep!
 
RustyRatRod said:
If you plan on street driving it at ALL I would leave that passage open.
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Nah. Don't need it. I blocked mine and one of the best things it prevents is that dreaded Mopar crank-crank-crank no start when it's hot outside and the engine is hot. My Barracuda could literally start hot at a touch of the key. Maybe a half revolution before it lit off.
 
lilcuda said:
Nah. Don't need it. I blocked mine and one of the best things it prevents is that dreaded Mopar crank-crank-crank no start when it's hot outside and the engine is hot. My Barracuda could literally start hot at a touch of the key. Maybe a half revolution before it lit off.
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Kinda where I was at with it, the new modern design aftermarket heads don't have that cave in them.
 
I'm telling you for a FACT I have tested it and you can't find 1 HP. NOT 1. You are pissing away your time. But don't tell me it works if you haven't had flow bench and dyno time to back it up.

I decided to work a Sunday one time and a pontiac "guru that wrenched at the shop I was at spent the entire day filling his ports. Went to the flow But being the hard boiled book reader he was, he spent the money to test on the dyno and found zero. Nothing. I asked him if he liked working for zero.


You can spend way less time and make gains than doing this deal

Some guys only learn by doing. Just post VERIFIED results.
 
Well, who do you believe.

I spoke with a very well known engine builder/head porter on the phone today and he said do it, it will help.

Sure is a controversial subject, lol. But, that's why I posted it.
 
Bruce, you sure do put a LOT of worry on a LOT of the wrong things, IMO.
 
To block off or not to block off that is the question. Drivability wise a working heat passage is a plus, especially during warm up and in colder climates. Blocking it off is a plus for hot soak/ restart problems and it keeps the paint from burning off the intake at the carb base. If it's burning the paint, it's getting damn hot! tmm
 
I block them off, worth it to me. Street manors are good. There is a reason why head and manifold manufactures go to the trouble and expense to cast performance heads and manifolds without that crossover . I use stainless sheet .021 thick. I cut a piece the same exact shape as the opening but .100 larger on all sides , use contact cement to glue them to the head over the opening, let that set up and use your usual manifold gasket . NEVER had any issues at all doing it this way since 1987. had it apart many times no issues. To me that is THE easy way, no melting old pistons,..no grinding in ports,..same gaskets. Shims .021 thick will not create any leaks and is far enough from the ports to not cause any issues there. 20 min. you can do it. JMHO. With experience.

Terry
 
Bad Sport said:
Well, who do you believe.

I spoke with a very well known engine builder/head porter on the phone today and he said do it, it will help.

Sure is a controversial subject, lol. But, that's why I posted it.
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Then go for it. I most certainly don't know much, but I know I have tested it more than once. There was ZERO power in it. Didn't find any driveability in it (which is quite subjective in itself) either.

Some guys do stuff because it makes them feel better. I got over that in the last decade of the last century.


FWIW if you tape off the exhaust hole in the head face and flow the port, you will find ZERO flow gain. Then you can block it off inside the port (with some screwing around) and you will get the same zero result.
 
Yeah, I don't expect to gain much from it if I do it, my main goal is to close off the crossover. Every time I have done it using a gasket, it blows right through.

It does make me wonder why so many guys do it though. Not necessarily here, but other forums I have been on. AND, I must say I haven't seen any documented proof either.
 
I would think it's a given that anything you do to reduce heat to the air intake would increase the power of a motor. Why else would the performance intake manifolds do away with that heat crossover passage? Intercoolers obviously have proven to substantially increase HP. Back in the day we used to put dry ice under the intakes on big block Mopars and run a cool can trying to squeeze as much power as we could out of them (at the drag strip).
 
If you are running headers, or stock exhaust manifolds with the butterfly removed, then there will not be much flow going through the passage. The original exhaust manifolds had a butterfly valve in one side for a reason. It would be closed when cold and therefore create more restriction on the one side, so the exhaust gasses would be forced through the port under the manifold. As the engine heated up the bi-metal spring would open the butterfly valve. Then there should be little to no flow going under the intake.

I remember the intake manifold from a 1968 383 2 barrel, the passage was almost completely plugged with soot. That probably insulated it pretty good from heat.
 
If you read up on gasoline engines, you'll see gasoline cannot burn unless it's in a vapor form. HEAT is a part of that process. That's the main reason for the exhaust passage, not "just" cold weather operation.
 
RustyRatRod said:
If you read up on gasoline engines, you'll see gasoline cannot burn unless it's in a vapor form. HEAT is a part of that process. That's the main reason for the exhaust passage, not "just" cold weather operation.
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Well, that begs the question as to why everyone recommends blocking the passage, and the aftermarket heads do not have that provision at all.

Ain't disagreeing with ya, but the conversation sometimes go in twelve different directions, lol.

Always room for edjamacation!

I always was under the impression a cooler charge was a denser charge.
 
In street applications, you want the best atomization possible for good drivability and mileage. In a race application, such as aftermarket heads and intakes with no passage, fuel atomization isn't as important.

I'm not saying it "might not" pick up 1 or 2 HP under the right circumstances. But it's very unlikely in a street car. I know for me there are a "TON" of other places I would look other than the cross over. It's just not worth the extra effort.
 
1967 'cuda said:
I would think it's a given that anything you do to reduce heat to the air intake would increase the power of a motor. Why else would the performance intake manifolds do away with that heat crossover passage? Intercoolers obviously have proven to substantially increase HP. Back in the day we used to put dry ice under the intakes on big block Mopars and run a cool can trying to squeeze as much power as we could out of them (at the drag strip).
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What he said. exactly right.
 
Bad Sport said:
I always was under the impression a cooler charge was a denser charge.
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A cooler charge means denser air, which increases the oxygen available for combustion. Hence intercoolers on turbos and all the cool air intake devices like hood scoops. But that does not change the amount of fuel by itself. The 0 HP increase test results from the dyno may well have been without the engine heat soaked and definitely not under a hood in a hot engine compartment, and so any HP increase due to denser air would not have been seen; it would only have checked the effect on exhaust flow.

But all that of has little meaning for the amount of fuel in the air; the optimum temps for good fuel vaporization and suspension works against air charge density so you're always balancing. Hence the hard cold start by the poster from CO with the Airgap. My son and I selected a Performer intake over the Airgap exactly so that it would warm up and run better in cool temps, even without the crossover. And thus all the exhaust manifold intake air heaters for air that you have seen on cars.

Modern fuels do have lower vapor temperatures so the need for a heat riser has decreased somewhat. If you only do fair weather driving, then you ought to get by with no crossover heat in most locations. But, I personally would not mess around with it beyond a good block plate. Easy enough to pull out later if you change your mind.
 
nm9stheham said:
A cooler charge means denser air, which increases the oxygen available for combustion. Hence intercoolers on turbos and all the cool air intake devices like hood scoops. But that does not change the amount of fuel by itself. The 0 HP increase test results from the dyno may well have been without the engine heat soaked and definitely not under a hood in a hot engine compartment, and so any HP increase due to denser air would not have been seen; it would only have checked the effect on exhaust flow.

--Also that cooler denser charge needs to be compensated with an A/F ratio change, like when you add a sealed hood scoop and need to jet up

But all that of has little meaning for the amount of fuel in the air; the optimum temps for good fuel vaporization and suspension works against air charge density so you're always balancing. Hence the hard cold start by the poster from CO with the Airgap. My son and I selected a Performer intake over the Airgap exactly so that it would warm up and run better in cool temps, even without the crossover. And thus all the exhaust manifold intake air heaters for air that you have seen on cars.

Modern fuels do have lower vapor temperatures so the need for a heat riser has decreased somewhat. If you only do fair weather driving, then you ought to get by with no crossover heat in most locations. But, I personally would not mess around with it beyond a good block plate. Easy enough to pull out later if you change your mind.
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Another point about the manifold heat, with my air-gap after driving around for 10 minutes or so (after it's warmed up enough to stay running, usually 3-5 minutes or less in anything above 35* or so) if I pull over and put my hand under the intake plenum it's pretty hot to the touch. This takes longer if I drive it on the highway due to the constant airflow outside and inside the intake. Also I've noticed that the intake plenum gets colder when the car is first started cold due to the vacuum in the intake (lower pressure = less heat). Again having that dual-snorkel air cleaner with the heat riser hooked up makes a big difference in how fast it warms up.

I think this winter I will buy a heat-gun to pre-warm the plenum when I go out in cold temps. I'm worried that I have already caused undue wear to my rings from liquid fuel pooling on the plenum floor from all those extra-cold starts and that's the real issue to be concerned about. I also put in a block heater when I built the engine but when I put in my shorty headers it blocked it so I couldn't hook up the wire.

Bad Sport were those gaskets that burned through made of steel? And what happened, was it like a small hole that developed or did it start leaking to the outside? Inquiring minds :D
 
MOPEkidD-3 said:
Bad Sport were those gaskets that burned through made of steel? And what happened, was it like a small hole that developed or did it start leaking to the outside? Inquiring minds :D
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Yes, metal. When I changed intakes, it had blown slap through it.
 
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