I am considering a full heat crossover block off plate but I would like to have SOME choke warmth - have any of you done a partial plate? Like a block off plate with a 1/4" hole?

 

Does your Oldsmobile have a radical cam? If your worried about a functional choke don't bother installing block off plates.

 

Slightly bigger cam than stock

 

I put the W31 cam in my spare 455.

For a time I tried to use exhaust crossovers. I fabricated a set from aluminum (beer/soda cans). The exhaust was hot enough that it burned through. I later fabricated a set from tin cans (think canned veggies). The exhaust didn't burn through, but any improvement on the butt-dyno was unnoticeable. I never had trouble starting but my carburetor has an electric choke

Unless you're racing your Oldsmobile, any improvement from blocking the exhaust crossover will be unnoticeable.

 

Down South here the summertime drive is tough with the heat soak on the carb and todays crap gas. Not looking for extra power just less vapor lock

 

I had a '72 4-4-2 while residing in California near Palm Springs (1976-1978) which experienced vapor lock on occasions. Old timer mechanic at the USAF base maintenance shop had me install (plumb in) an additional fuel/vapor filter which solved any vapor lock issues. Something you might consider.

 

A partial blockage of the crossover will just delay the heating, not prevent it. Eventually it will reach equilibrium at the same temperature.

 

I doubt there would be much delay. I have a pyrometer on my 86 Ford truck and exhaust gas is "hella" hot.

 

Your mostly correct. Think about this. Since your using a gas the rate that heat up occurs is determined by mass flow rate. So if you make the holes to the manifold smaller the gross adjustment is in mass. But the intake also has cooling being done at the same time. This cooling can be ambient or depending on driving intake charge. If you have enough intake charge you can counter a heat source with less mass. So there can be a different level of equilibrium that might just be lower. The only way to know is to test. I don't think it would do any harm other than needing more time to warm up.

 

Block it off.
I welded cast plugs into the intake. Recessed it a bit so I didnt have to worry about the mating surface.

The divorced choke works. You have to lighten the spring up. Its cold blooded in 40°F or less temps. It simply needs more warm up time. The choke pull-off may need to be adjusted to pull off sooner.

I also removed the thermo flap out of the ex mani and welded up the holes.(69 ex manifolds with the divider).

I have the stacked aluminum/gasket under the carb.

Left head pipe is wrapped with a heat blanket by the starter. Starter solenoid has the mini Ford style heat shield over it.

ALL hot start/heat soak/farting carb problems 100% mitigated. The engine runs smoother at all temps. Once up to op temp it starts up like a fuel injected car even if its 100°F+ ambient. Reach in-tap-key... varooom.

 

Just blocking it is useless for power. If you fill it with a metal (most use aluminum, we use zinc) and then reshape the exhaust bowls on the middle 4cylinders so they are shaped like the outer ports then weld up the center divider, our dyno testing shows with headers and a high overlap cam we made 39HP. We are going to repeat this exercise, probably in April, but run a smaller cam (with headers and with stock W/Z manifolds). I suspect the gain with less overlap won't be as much and the same with stock manifolds. But we will get the data. We have blocked it off with 0.010" steel and gained 0 HP on the dyno testing. From a choke standpoint, put an electric one on.

jerry

 

I’m with Jerry, blocking doesn’t hurt anything, but to truly realize a gain the crossovers should be “poured” and the bowls reshaped. Don’t want to go through a proper crossover fill? Block them with something that won’t burn through and the carb will see a bit less heat. I agree along Joe’s lines, do it or don’t, trying to meter it will at best only buy time, more likely just cause a rougher warmup only to have the carb heated the same once hot.

I’m not sure that I’ve had a “muscle” car with an active heat crossover in 30+ years. I drive my cars in New England, in cold months, sometimes down to 0*F, with no problem. They all have/had chokes, either electric or manual and I am not a “warmer upper.” Start engine, and drive, if teens or single digits I might give it 30 seconds before driving off. My cars always love the frigid air.

​​​​​​….

 

Duh explained why this does not happen.

Here's his conclusion explained from a slightly different point of view:

The intake manifold temperature--and ultimately the carb temperature--is the result of an equilibrium. The manifold temperature stops rising when the amount of heat added to the intake from exhaust gas equals the amount of heat lost from the intake. The intake manifold loses heat from the cooling action of the surrounding air and from the intake mixture flowing though it, etc. A hotter intake loses more heat.

When you add less exhaust heat to the intake manifold, the intake can only reach temperature equilibrium if it doesn't get as hot. A cooler intake loses less heat.

 

My Performer RPM intake has aluminum blocks welded into the exhaust crossovers. I converted to an electric choke which I do not think works quite as well as the original hot air choke. - close but not the same. Maybe fine tuning could resolve that.


As for any performance gains, I can’t say any have been documented. I do a lot of 0-60 runs and the block off plates showed no measurable improvements using in car measurements.

 

You'd probably have to change the jets on your carburetor and your timing advance to see butt-dyno improvements.

 

I only drive my car from May to October. I live in the Toronto area. During several of those months the heat and humidity can get up to and at times over 100 f. I drive my car as much as I can, heat or no heat. I have C heads with the performer intake and sniper efi. The centre ports are blocked, not for performance but to keep the exhaust heat from going through the intake. I know of a person that does not run blocked off centre ports and his engine is 20 to 30 degrees hotter, always! I drove my car on a 95 degree day and I was going 70mph for a full hour and a half, my engine ran at 165. Same thing going home 3 hours later.
Just my 2 cents, either can or usd.

 

Do you think the .015" turkey tray metal is thick enough to survive as a crossover block off? I have an old one I can cut plates from. Reason I ask is I have a 24 ga (.023") stainless scrap I could use but it is .008" thicker than the post-compressed turkey tray - I'm afraid 24 ga block offs would stop the normal gasket from compressing properly.

 

Why not cut block offs from a tin can? I know those will work. They'd go in the trash anyways.

There may come a time when we have to reuse an intake manifold gasket. It's not there yet, but for a time the intake manifold gaskets for the 6.9l / 7.3l IDIs in Ford trucks weren't manufactured. You can still pull up old threads; in which, guys mention cleaning and reusing the intake manifold gasket.

 

Tin can block off in an otherwise stock, but with headers "E" block, always burned thru for me. If you desire to use that type of heat block off i'd recommend at least the turkey tray metal. I eventually filled my "C" heads exhaust crossover with a powder like furnace cement that you mix with water (sorry, can't recall the trade name). It sets up like a rock and lasted several years on the drag strip and is still to this day solid.

 

Well I was able to use my heavy gauge stainless by milling them down a few thousandths - got The Right Stuff for the front and rear end rails so all good there.

Dumb question - do the intake bolts need sealant like Chevys? All the bolt holes appear to be "blind"

 

IMO, it's best practice to (1) liberally clean the intake manifold bolt holes, (2) clean the bolt threads & (3) apply The Right Stuff to the bolt threads.

 

I've never applied sealer or RTV to the bolts. I also generally cut the turkey tray from the side rails. I guess if you don't want to use a tin can to manufacture exhaust crossover block offs you could always use the turkey tray if you're only sealing with the side rails.

 

Paul, Olds V-8 intake bolt holes are indeed blind--no sealant required.

Clean the threads and bolt holes as Chief said, then you can use thread lubricant for more consistent clamping force.

Just be sure to reduce the torque per the type of lubricant you use.

 

you did the right thing by blocking off the crossovers. the bolts actually need some oil on them, not sealant.

 

Heaviest intake I've ever installed. Good Lord

 

I've thrown several up there...45lbs - 50lbs? And, that's using the turkey tray(s). The last time w/ the bosses misaligned when I bought them. Careful, easy to blow out a hernia on those babies.

 

This is what I used. I ground them down to a good interference fit in the intake crossover ports. The plug surface is a good .030 below the intake surface.Then tacked welded them in. They could be removed. Been in there 26 years.

 

Fel Pro makes the steel intake gaskets with no turkey tray.

MS 9947-1