Greetings All,

Opinions, please, on the various methods to block off the exhaust crossover passage inside the intake manifold on a V8. I'm talking about the passage that routes exhaust to warm up the plenum under the carb. In my over-inflated opinion, this was desirable with fuel chemistry of the day when our vehicles were new and we each still had a full head of hair. Modern fuels are much more heat-sensitive, and my engine has had some issues. I blocked off this passage several years ago (and did a few other minor things) to reduce heat reaching the carb, and all has been well since then.

I'm getting ready to install a reman 351W in my truck, and will soon be swapping over the intake manifold and other bits. The swap has been stalled due to monsoon rains, but I'm hoping to get as much ready ahead of time in anticipation of a decent break in the weather.

When I previously blocked off the passage, I used some stainless steel (.030 thick?) across the opening in the gaskets, with high temp RTV around the edges of these homemade inserts. This seems to have worked well, but it was kinda persnickety to fit these extra pieces.

I've also read of people tamping the passage full of heavy aluminum foil. I'm kinda leaning in this direction, mostly for ease of installation.

I've even heard of filling the passage with a special heat-resistant type of mortar, such as used for furnace repairs. I've actually seen this on one engine I worked on, but don't plan to go to that extreme.

So whaddya think? Gasket inserts? Foil? Something else?

 

I'd use firewool but because I can access it.
it definitely can handle the heat.
Not sure if you want to spend money on it, it isnt too pricey but it all adds up. Youd probably have a lifetime supply as well.
I think another name for it is kaowool?

 

Not a Ford but a v8 that used a metal pan gasket.
I used part of the old gasket and cut 2 squares that fit in the raised part of the gasket. I used a little RTV as glue to hold them in place till the intake was installed.

I think I would stuff the ports full with tin foil and use a tin can to make block offs as it is thin. Just use a little RTV to seal it is all.
Dave ----

 

You could use block filler or, just buy an aluminum intake for under $200.

 

I seem to recall back in the 1970's the Mr Gasket intake manifold set came with a block off plates. Anyone else remember that ?

The Al intake is a good idea too.

 

I'm not familiar with this stuff. Got a brand name or something I could research?

I'm still running the stock 2bbl carb. A matching manifold is available, but kinda rare. I hate to fork out that kind of cash because it could work against me. I'm in the People's Republic of Oregon and am subject to emissions testing (for the truck, not me personally). As long as the truck passes the tailpipe sniffer, they never even open the hood. In theory it should pass just fine, but if not, a visual inspection is part of the next steps. Some aftermarket manifolds may be okay, but I haven't researched it. And I certainly couldn't swap to a more common 4bbl set-up and expect to pass a visual inspection, if it ever came to that.

 

I've seen this on a Chevrolet (still available from Mahle and Felpro), but am not seeing anything for Ford.

The Chevrolet set came with several plates. Some had a hole in the middle to restrict flow, others were solid and blocked all flow. The instructions detailed which plates were installed for which model.

 

Hard Block or Thermosteel seems to be the filler of choice for a lot of builders looking to block off the egr passage. Filler will completely block off the passage, eliminating any chance of blow through. Better gas mileage, cooler charge, better performance.

 

You have no problems in the winter blocking these passages completely off? I blocked them completely off on a chevy I had, and it made the engine extremely cold natured and hard to get going in the morning. I went back to a restrictor plate in each side and it was much better. But I still had to run the stock aircleaner with the heat from the exhaust manifold running into it. I had another engine with no heat to the aircleaner, but it had a working heat riser that blocked the exhaust manifold on one side and forced the exhaust under the carb till the water temp got to 100 degrees. This system worked good, that engine would not run well either with the heat riser de-activated and the air cleaner not hooked into the heat system.

 

I've run like this about 7 years with no issues. Hard to quantify, but the engine feels a little cold-blooded in the winter until driven a few miles, but this is not unexpected. Not severe by any means, and not really a big deal.

This engine has no control valve for exhaust flow through the passage. It was full open at all times on both sides. If pressure was balanced on both sides, there'd be no differential and thus little flow through the passage. It's got a single exhaust, with a Y pipe. In theory the crossover should not have got too hot, but apparently it was as I had lots of heat-related problems.

I do have the stock heated intake with the shroud on one exhaust manifold. I rigged up a remote thermometer just before the air filter element, and confirmed it's working properly.

When I pull the intake manifold, I'll be curious to see how my block off plates have held up. For all I know, one or both may have worked loose.

I remember hearing hot rodders would rig up a sliding shutter plate. The plate extended up above the manifold a little bit, enough to grip with pliers. You could loosen the mount bolts and slide the shutter up or down as desired to regulate flow. Sounds kinda cool but I wonder how durable it was. I'd suspect it was prone to external leakage at the top, too.

 

Having the heated air into the aircleaner explains why you are getting by.

I went to the car show at Hershey Pa in 2018, one of the events was some of these old race cars making a lap around a track they have there. There was a cold snap that year, it was about 40 ish degrees outside, and half of them could not make the run. You could hear them in the pit area trying to get them started and warmed up and some of them just would not run. That's what you get with full race stuff with no heat in the intakes.

 

I have heard of that but I dont know if anyone makes them like that now days?
Not all ALM. intakes have them bloced off.

I would stuff the foil in the passage and make block offs from a tin can like I posted and be done with it.
As for passing smog I dont know how that will change with the block off done?
That heat helps vaporize fuel for a complete burn but you may be ok if you drive it and get the motor nice and hot first.

With that also said being it is kind of damp and cool I dont know how blocking off the cross over will work on keeping the carb from icing up?
A good working factory air filter assy would help on this.
Dave ----

 

There are some intake manifold gaskets with metal plugs to block off the exhaust cross over. Not all sets come with them I think Fel pro makes a set but its not your basic number, Fel pro how ever only had one set for my 292 that came with those plugs with a small hole drilled in the middle as a restrictor to try and prevent intake manifold paint burn due to the heat of the exhaust crossing over. I tossed them out as they were not on the original gaskets and never had paint burn since I used Por15 engine red.

I couldnt help on the gasket for a 302/351W how ever as I got the basic set as my AFR 165 Renegades lacked the exhaust cross over in the first place.

 

Be done with it? Have we met? My head is swimming with various schemes to make little adjustable guillotine shutter plates so I can tweak the amount of heat transfer. Shut off in the summer when too much heat is a factor, and partial flow in the winter when a little extra heat would be beneficial. So what if I was happy with the present set-up! Should I just give up? Was it over when the Germans bombed Pearl Harbor?

 

I had to abandon the adjustable shutter/guillotine idea. The valve covers stuck out too far and got in the way.

I found Fel-Pro's 1262 S-3 gasket set was perfect to permanently block the crossover passage. It has a metal core, similar to a head gasket, so should stand up to the exhaust heat:




Link to Fel-Pro 1262 S-3

The literature says this set is designed for "large race ports", but the openings were the correct size for the stock heads and manifold on my 2bbl 351W (VIN code G).

I did not use the cork pieces for the ends. I used rubber pieces I had from another set. If this gasket set does not hold up to the exhaust heat, I'll come back and update this thread.