[dataway]

Intake gaskets don't come with the exhaust blockoff I think they did in the old days ... so I made the one in the photo below.

It's about .030" stainless ... no lip that fits under over the exhaust gasket like others I've seen but fits nicely in the opening. Think this will suffice? Might have to tack it in place with some adhesive to get the intake on, but looks like it will work.

I plan on only installing one on the drivers side so the choke stove will still get some heat, but hopefully not roast my intake paint or boil my fuel.

Do you think it will hold up, not burn through around the edges or something.

[surfsama]

I did that on both sides (my carb had an electric choke) with no problems.

The trick is to make sure the plate thickness takes into account the gasket crush depth when you torque-down the intake bolts. You don't what it to be a high point or too low.

[dataway]

It's tad low right now, probably .005-.010" ... wonder what the crush thickness is on these gaskets. Don't want it to rattle around in there either.

[Kenth]

Heat from the crossover channel is one of three factors that helps atomize and vaporize the fuel to a combustible gas.
The other two is velocity and amounts of gas..
If you reduce or take away heat you need to add fuel and rpm´s correspondingly to compensate.
In other words you loose driveability and economy.

This means less or nothing for a race engine running WOT 1/4 miles all day long.

FWIW

[Schurkey]

...and is extremely important if the vehicle is driven in cool or cold weather. 'Course, lots of hobby cars never get run when the weather isn't beautiful.

Exhaust-crossover heat makes the engine warm up a lot faster, though.

[shaker455]

Originally Posted by dataway

Intake gaskets don't come with the exhaust blockoff I think they did in the old days ... so I made the one in the photo below.

It's about .030" stainless ... no lip that fits under over the exhaust gasket like others I've seen but fits nicely in the opening. Think this will suffice? Might have to tack it in place with some adhesive to get the intake on, but looks like it will work.

I plan on only installing one on the drivers side so the choke stove will still get some heat, but hopefully not roast my intake paint or boil my fuel.

Do you think it will hold up, not burn through around the edges or something.

[steve25]

On the head side perimeter of that steel I would apply a thin bead of high heat red silicone gasket maker!

The faster you warm up a motor the sooner the running clearances are the way they should and then the least ware will take place, and the fastest way to warm up a motor is to drive it !

[dmac]

Originally Posted by Kenth

Heat from the crossover channel is one of three factors that helps atomize and vaporize the fuel to a combustible gas.
The other two is velocity and amounts of gas..
If you reduce or take away heat you need to add fuel and rpm´s correspondingly to compensate.
In other words you loose driveability and economy.

This means less or nothing for a race engine running WOT 1/4 miles all day long.

FWIW

I thought that keeping the intake cooler helped keep the air cooler and more dense- increasing efficiency. Probably different for where you live, how far you drive, etc.

[Tom Vaught]

Originally Posted by dmac

I thought that keeping the intake cooler helped keep the air cooler and more dense- increasing efficiency. Probably different for where you live, how far you drive, etc.

Most of that BS "benefits"passed on from year to year all disappears when you actually get into it.
Engine needs to have the fuel in a vapor not "rivers of fuel" wandering around on the floor to individual cylinders.

The reason why the calibration needs to be richer is because more fuel is condensing (becoming liquid rivers) on the floor of the intake and not going into the engine as a vapor so the intake charge initially is leaner. Adding more fuel just covers up the poor distribution now in the intake manifold. A choke makes a carb a/f ratio RICHER by taking away air vs the fuel still being metered.

Where you live, how far you drive does make some difference. Even with blocked intake gaskets some heat eventually warms the intake due to "reversion" (exhaust flow back into the intake on every combustion cycle due to a camshaft event called OVERLAP).

But drag racers can see a small benefit because they are running the engine a very short period of time vs any engine driven on the street.

Personally I think the mod is just kidding yourself on any real street car.

Tom V.

[dmac]

A lot of 'myths' I grew up on are being disproven. Lucky I wasn't emotionally attached to most of them. Even things from 'only' 20 years ago, when I seemed like I was reading everywhere to block of the crossover. . Now the only reason would be to compensate for head/gasket mismatch.

[Tom Vaught]

Hey, if the Gasket Companies could sell you a blocked heat cross-over package vs you using a factory intake gasket, they got your money and you were happy, whether it worked on not. All that rough running had to be from all of that colder air making more power in the engine.

Tom V.

[dmac]

Originally Posted by Tom Vaught

Hey, if the Gasket Companies could sell you a blocked heat cross-over package vs you using a factory intake gasket, they got your money and you were happy, whether it worked on not. All that rough running had to be from all of that colder air making more power in the engine.

Tom V.

Plus I loved the smell of unburned gas in the exhaust and the occasional burst of flames and backfiring from the exhaust when taking my foot off the gas/decelerating.

[4zpeed]

Originally Posted by Tom Vaught

Most of that BS "benefits"passed on from year to year all disappears when you actually get into it.
Engine needs to have the fuel in a vapor not "rivers of fuel" wandering around on the floor to individual cylinders.

The reason why the calibration needs to be richer is because more fuel is condensing (becoming liquid rivers) on the floor of the intake and not going into the engine as a vapor so the intake charge initially is leaner. Adding more fuel just covers up the poor distribution now in the intake manifold. A choke makes a carb a/f ratio RICHER by taking away air vs the fuel still being metered.

Where you live, how far you drive does make some difference. Even with blocked intake gaskets some heat eventually warms the intake due to "reversion" (exhaust flow back into the intake on every combustion cycle due to a camshaft event called OVERLAP).

But drag racers can see a small benefit because they are running the engine a very short period of time vs any engine driven on the street.

Personally I think the mod is just kidding yourself on any real street car.

Tom V.

Originally Posted by Schurkey

...and is extremely important if the vehicle is driven in cool or cold weather. 'Course, lots of hobby cars never get run when the weather isn't beautiful.

Exhaust-crossover heat makes the engine warm up a lot faster, though.

Originally Posted by steve25

On the head side perimeter of that steel I would apply a thin bead of high heat red silicone gasket maker!

The faster you warm up a motor the sooner the running clearances are the way they should and then the least ware will take place, and the fastest way to warm up a motor is to drive it !

^5 Absolutely agree, thanks for sharing!


Frank

[dataway]

Wow... I didn't think it would be this controversial. I'm just looking to split the difference between toasting the intake into a rusted mess, vs. ... a few minutes more for the choke to pull off.
Not like I'm going to drive this car to work on a 20 degree day. And I'm not looking for any HP ...

I'm just thinking the system was designed for a daily driver and this is going to be a weekend warrior ... so fast warm up is not a huge issue.

[Kenth]

Originally Posted by dmac

I thought that keeping the intake cooler helped keep the air cooler and more dense- increasing efficiency. Probably different for where you live, how far you drive, etc.

Cool air to the carb may be beneficial if calibration is up to it.
The carb and intake though needs the heat for reasons above.

And, it is the temperature of the engine that matters to make a combustible mixture of the fuel, not outside air temperatur,

[Kenth]

Originally Posted by dataway

Wow... I didn't think it would be this controversial. I'm just looking to split the difference between toasting the intake into a rusted mess, vs. ... a few minutes more for the choke to pull off.
Not like I'm going to drive this car to work on a 20 degree day. And I'm not looking for any HP ...

I'm just thinking the system was designed for a daily driver and this is going to be a weekend warrior ... so fast warm up is not a huge issue.

You may add the wear factor of running the engine cooler than intended, flushing raw fuel into the cylinders and oil.
This is true for all combustion engines.

[Cardo]

So is there room for compromise here? What about blocking one side like Dataway is proposing or partially blocking both to reduce flow? My heads are at SD Performnace waiting in line, and i had full intention of having the crossovers filled - I still think that there is too much heat up there at full temp. I always had problems with my last car with the fuel wanting to boil off. The fuel bowl would be empty the next day after parking the car after a full warm up and drive. I like Dataway's idea but maybe drill a 1/4 inch hole in the middle?

[carbking]

Blocking the heat crossover on a street engine REQUIRED me to install a carburetor with a manual choke.

As the youngsters say: " been there, done that, would NEVER do it again!".

But I do like the manual choke.

Jon.

[Tom Vaught]

Originally Posted by Cardo

So is there room for compromise here? What about blocking one side like Dataway is proposing or partially blocking both to reduce flow? My heads are at SD Performnace waiting in line, and i had full intention of having the crossovers filled - I still think that there is too much heat up there at full temp. I always had problems with my last car with the fuel wanting to boil off. The fuel bowl would be empty the next day after parking the car after a full warm up and drive. I like Dataway's idea but maybe drill a 1/4 inch hole in the middle?

If you go to the trouble to have "Piston Aluminum" melted on a crucible and properly filled into a cast iron head cross-over passage then there is a tuning benefit for a race type engine
as now the headers work somewhat better. And of course heat is leaving the engine vs crossing back and forth over the engine when the center cylinders fire. Mod was done in the 70s. With that deal and other mods you can get on average a pretty good 260-270 cfm head for racing. Stock Edelbrock head out of the box will flow similar numbers with no mods and less weight.

But some still like the Old School approach to making power.

Tom V.

[Formulajones]

I've experimented with this deal quite a bit on a few different engines. Mainly I go back and forth with it the last few years fighting heat soak issues with this crappy pump fuel we have. We daily drive these cars so I experiment with things like this to find the best drivability.

Some things I found on different applications.

One of my BBC's I blocked the heat cross over with an aluminum intake. I found cold weather driving a bit tempermental, didn't like idling until the engine was completely warm, usually after shutting it off and heat soaking it. In the summer it was perfectly fine. I later installed the OEM cast iron intake, opened up the heat cross over, and immediately had vapor lock issues if the engine sat and idled for any length of time when ambient temps got above 90 degrees. As long as you were moving it was fine, but man it was a pain in the rump when idling in traffic. That intake just got too hot for the crap pump fuel we have.

On my 69Z with it's factory aluminum intake, I left the heat cross over open, mainly because I still run a factory divorce choke. To date, driving the car in town on 100+ degree days and it's shown absolutely no sign of vapor lock or heat soak issues. I've come to the conclusion the aluminum intakes are much better at dissipating that heat. It idles all day in traffic without complaint.

On my RAIII Pontiac, I ran the OEM cast iron intake for decades. I had the cross over blocked, and still used the divorce choke. It still produced enough heat to work the choke, that is until ambient temps dropped to around 35-40 degrees. After extended highway driving it would cool enough to kick the choke back on, but idling in town for a minute or 2 would kick it back off. It was a borderline situation that wasn't too big of a deal.
I later opened the heat cross over back up, and that cold weather choke issue was gone. However this car never experienced any vapor lock issues...ever, even with it's iron intake. I think the better intake design that let some air flow under the intake helps with that, because on the chevys I had all kinds of issues with iron intakes and pump gas. Pontiac is more like an air gap so to speak.
Right now I'm trying a RAIV intake on the car, with a separate heat cross over so it still works the divorce choke but it keeps all that heat out of the intake, plus the intake is aluminum so that's another heat bonus.
So far I'm liking the results, no issues in the summer 100+ temps here. I can shut it off and heat soak it, fires right off no problem, no vapor lock issues at all. But I'm still waiting for temps to cool off enough to see how it runs when it's 30-40 degrees outside. I know the choke will still work fine, but as long as it doesn't exhibit odd cold weather drivability or cold weather idle issues, I'll call it a success.

I will say this. I use a wideband on the cars and try to run as lean of an idle mixture as I can get away with. With more heat in the intake I can run the mixture much leaner with no drivability issues, even out to 15:1 or more AFR. Cool that intake off and I need to bring the AFR down a bit for best idle quality.