Brainstorming ideas for coolant crossover on Air-Gap intakes

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MopaR&D

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I'm running an Air-Gap intake on my Magnum-headed 360 and always had tuning issues with the fluctuations in temperature of this manifold. After adding a functional hood scoop with the air cleaner sealed off, even on a warm day the incoming cold air being sucked in causes my intake to cool down... Goes like this: Engine is cold, start it up, intake gets colder from vacuum; I start driving stop & go around town and over time engine heat makes its way up to the intake and warms it up. I get on the highway or a long road with a higher speed limit say ~45 mph and the intake actually gets cold AGAIN, I can pull off the road and the plenum is cold to the touch.

So what I want to do is make something to allow the intake to be heated from engine coolant. It's not a new idea, I know Ford did it with a lot of their production engines and it is actually a lot more efficient than using exhaust heat. What I want to do is make some small metal box or wide flat tubular device to somehow adhere to the bottom of the intake plenum and just route the heater outlet through it. Any ideas guys? Looking for max heat transfer while still being feasible, I don't have the equipment to prototype a billet aluminum part lol.

And before anyone says "get a regular RPM intake" again I'm running Magnum heads which have no provision for exhaust crossover even if there was an intake for Magnums which had it. And I don't want to use exhaust heat anyway.
 
One thing to remember is even with the Magnum heads, you will have more heat to the plenum on an rpm intake just from the oil splashing on the bottom of the runners even without the crossover. Just not sure what non air gap intakes are available for Magnums.

If you can put a tube of some sort underneath and attach it somehow, then run a heater hose on it, it likely will help. I have had the same issues in late fall with the air gap on the 318 in my Dart. An electic fan with a temp switch helped it get up to temp sooner in the cold.
 
One thing to remember is even with the Magnum heads, you will have more heat to the plenum on an rpm intake just from the oil splashing on the bottom of the runners even without the crossover. Just not sure what non air gap intakes are available for Magnums.

If you can put a tube of some sort underneath and attach it somehow, then run a heater hose on it, it likely will help. I have had the same issues in late fall with the air gap on the 318 in my Dart. An electic fan with a temp switch helped it get up to temp sooner in the cold.

That first part is true, if I upgrade my engine with aftermarket heads in the future I will probably go with the LA intake bolt pattern for the much bigger selection. I could run an RPM intake with no crossover and it would probably stay warmer overall and be more consistent after the engine is warmed up.

For the time being I've thought about just pulling off a heater hose and re-routing it under the plenum to see if it does anything. Wouldn't cost anything and totally reversible.
 
That first part is true, if I upgrade my engine with aftermarket heads in the future I will probably go with the LA intake bolt pattern for the much bigger selection. I could run an RPM intake with no crossover and it would probably stay warmer overall and be more consistent after the engine is warmed up.

For the time being I've thought about just pulling off a heater hose and re-routing it under the plenum to see if it does anything. Wouldn't cost anything and totally reversible.
Khalid: No heat riser port,on E/Q heads... My LA bolt pattern heads,still had a sealed heat riser crossover port...Isn't gonna happen... The heater under the plenum,is interesting...In the 80's,some OEM carbed setups,used "heat grid " gaskets.. Electrical controlled,would preheat the air/fuel mixture for emulsification...Not aware ,of an four barrel application,just some info.
 
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Maybe use a small trans cooler under plenum. Block the bottom of cooler with sheetmetal and the heat will rise. You could also use a heated air intake with the vacuum/temp control on the snorkel that everyone throws away.
Here's a pic of a dual plane Magnum M1. You can see the water channel that runs from the thermostat area back to the plenum floor. MP does not make this intake any longer.

intake m1 pics 004 (640x479).jpg


intake m1 pics 003 (640x471).jpg
 
Maybe use a small trans cooler under plenum. Block the bottom of cooler with sheetmetal and the heat will rise. You could also use a heated air intake with the vacuum/temp control on the snorkel that everyone throws away.
Here's a pic of a dual plane Magnum M1. You can see the water channel that runs from the thermostat area back to the plenum floor. MP does not make this intake any longer.

View attachment 1714963603

View attachment 1714963604
I plan on running both hoses under the intake when I get around to hooking the heater up. why not try that and see if it does anything? I don`t expect much, but some heating.
 
The small fluid cooler is a good idea, I could cut down the fins and use some thermal conductive paste like the stuff for attaching heat sinks to computer parts.
 
If you just want warm air/fuel mixture , why not just UNseal the air cleaner from the hood scoop and let it breath hot underhood air? Or is your idea to be able to turn the heat on and off when you want?
 
I googled elevation Ft Collins and see you are at about 5000ft.
I wonder if you are experiencing Icing in the venturies.
Icing usually occurs at temps closer to freezing, at sealevel, but is not uncommon at temps even above 60*F, depending on the humidity.
A lot of initial timing will cause the butterflies to operate at very small openings,which promotes icing.A large venturi, and or a small cam may also lead to icing. If you have all three,you may have a recipe for icing.
You may benefit from; less initial advance, a spreadbore carb,and/or more cam.This will get your butterflies open a little further, and perhaps minimize the icing.5000ft also needs more Scr. A 9/1 motor will struggle to make heat.
Another option is a heated carb-spacer, like they used to put on certain Fords back in the 70s
Another option might be a deflector to prevent the rad-fan from blowing under the plenum
I gotta tell you tho, The very first winter I had my combo together, I ran it deep into October, with no problems, and no choke. 360/292-508cam/AG-750DP/aluminum heads/ 900ft elevation/TTIs. Timing was 14/34@3400. Yeah it was a little cold blooded for a couple of miles. But a 205*minimum running temp and a thermostatic clutch-fan, put some heat in her in just a short while.

What are your cam specs? Do you know the ICA? How 'bout the compression ratio, or cylinder pressure numbers.
 
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You could run your heater hoses or make a copper tube heat exchanger that comes off your heater hoses that runs under the intake. You could even get real trick and put a heater shut off valve in line to shut off flow once you are at full temperature.
 
I have a feeling that any of the ideas about heating it with coolant is going to fall short of making any difference at all, because of the surface area of the aluminum and volume of air going through it.
You are going to have to heat the intake with oil from underneath to many any difference.
 
I have a feeling that any of the ideas about heating it with coolant is going to fall short of making any difference at all, because of the surface area of the aluminum and volume of air going through it.
You are going to have to heat the intake with oil from underneath to many any difference.
I think it would be fairly simple to fab air dams to block most air from flowing through the gap. That coupled with coolant fed copper rubbing would definitely go in the right direction
 
I don't think you need to actually heat the intake that much. If you can keep the carb warm, and get the fuel to stay in the aircharge, that would go a long way.
I had a 340 once that gave me trouble.I coiled a brake-line tube around the center pair of primary tubes, and connected that to an unused manifold port at the front of the AVS carb.That solved my winter driving problem.This engine did not have the AG. I think it was more or less stock.
 
I googled elevation Ft Collins and see you are at about 5000ft.
I wonder if you are experiencing Icing in the venturies.
Icing usually occurs at temps closer to freezing, at sealevel, but is not uncommon at temps even above 60*F, depending on the humidity.
A lot of initial timing will cause the butterflies to operate at very small openings,which promotes icing.A large venturi, and or a small cam may also lead to icing. If you have all three,you may have a recipe for icing.
You may benefit from; less initial advance, a spreadbore carb,and/or more cam.This will get your butterflies open a little further, and perhaps minimize the icing.5000ft also needs more Scr. A 9/1 motor will struggle to make heat.
Another option is a heated carb-spacer, like they used to put on certain Fords back in the 70s
Another option might be a deflector to prevent the rad-fan from blowing under the plenum
I gotta tell you tho, The very first winter I had my combo together, I ran it deep into October, with no problems, and no choke. 360/292-508cam/AG-750DP/aluminum heads/ 900ft elevation/TTIs. Timing was 14/34@3400. Yeah it was a little cold blooded for a couple of miles. But a 205*minimum running temp and a thermostatic clutch-fan, put some heat in her in just a short while.

What are your cam specs? Do you know the ICA? How 'bout the compression ratio, or cylinder pressure numbers.

This is exactly what's happening or at least 2 out of the 3, I have a 750 Street Demon on top of my 10.5:1 360 with a tiny 213/220* @ .050" Voodoo cam and the carb does get very cold; noticeably more than my old 625 cfm AFB which had smaller primaries. With this new carb I'm basically driving around with the idle circuit the majority of the time. I did get the bigger carb with the intention of upgrading to a bigger cam so that will come at some point but I can't say for sure when (need to get some 3.55 gears beforehand and I don't really have the $$$). Luckily the carb has the plastic main body which helps and I have a 1/2" wood spacer under the carb.

I have been driving it around with the air cleaner unsealed and it does help a bit but I can tell it still needs more heat in the intake. I looked at small coolers for power steering etc. on Summit which seem promising, I think I'll just get one and figure out a way to flatten the fins on the sides so there's more area to conduct heat to the intake. I already have a valve in one of the heater hoses I use to switch it off in summer time.

AJ is right it doesn't need much heat and any little bit helps, this past winter I got the idea to hit the intake with a heat gun for about 10 minutes before I started the car and as it was running, even a small increase in temp made it run better.
 
That's a pretty good combo.
With a Lunati 10200701 having specs of 256/262/112 in at 111 the ICA would be about 59*. On a 10.5-360, the Dcr would come in at 7.72(corrected to 5000ft) with 153 psi cylinder pressure. The math says at sealevel a 550 carb would be a good all-round choice. At 5000 ft it should be more than enough.
Since you have run the smaller carb too, how would you compare them?
If you set this smaller carb up to run at 5000 ft it will not like to run down at 1000 ft, so the bigger carb could be set up to run there. And then 15 minutes later you will be ready to go.


I wouldn't go more than one size bigger with a FT hydraulic cam, on account of any bigger and it will loose Dcr fast, and that means the bottom-end gets soft, and that leads to a higher stall TC, and probably gears. A bigger cam will make more power on account of it will pull in more air at higher rpms, but the trade-off is at the other end.
Having said that, a swap in cam types, will give you one or two camsizes bigger, with the same 59* ICA. So a solid FT, or a roller would work. But I think a small roller like that would need to be a custom cam. So you would probably be left with a solid-FT.
You are on the right track with attempting to run the fresh air.The engine will make more power on the denser air, and at 5000FT this is a challenge.If you can figure out a way to keep the icing away, you will be in good shape.
With your current cam, and at your altitude I can totally see a stock TQ/C.I. intake working.The iron intake will be much slower to change temperature, and the TQ with smaller primaries will run with the butterflies open a little further.
Just remember to reset your T-Port sync with any carb change.
If you currently have 3.23s I dunno if I would be in a hurry to buy 3.55s. Especially if you can already spin the tires with the smaller gear. But if you have less than 3.23s, swapping to 3.55s will cause the car to cruise with a smaller primary opening, again.
So in conclusion; If it was my car, and I could not solve the icing in any conventional way, I would be shopping for a CI/TQ set-up.

Just for kicks,tho, I would first try running a tankful through her with max-strength gas-line antifreeze. The isopropyl-alchohol kind. If your problem is at all icing related, this will kill it.
Good-luck!
 
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If icing is truly the prob. Would it not be easier and more effective to do as the factory, and just run a "stove and tube" down to the headers, and supply warm/hot air to the air intake, with a vacuum door to open/close scoop air source as nec.

jmo
 
AJ I'm currently running 2.94 gears with 28" tall tires. I know based off the numbers I have to be careful with a bigger cam but I'm gonna go with a custom grind for sure. I intend to drop in 3.55s first and once these tires wear out go with some shorter 27" Nittos on 17" rims. I know you said my theoretical cranking compression is only 155 but I have a feeling it's much higher than that; even with only 8* initial advance the engine kicks back hard on the starter when hot, so much so that I had to wire a killswitch into the ignition circuit so I can crank the engine first with no spark then fire it off once it's already spinned up in the right direction. One of these days I just need to get off my lazy *** and do a full compression test lol.

To others talking about the factory style air intake with the warm-air valve, I actually do have one of those and was running it for a couple years but 2 problems now, it is noticeably more restrictive than my open-element K&N piece. Also it will no longer fit under the hood with the 1/2" spacer under the carb which I'm going to keep (made a big difference in tip-in response). I still have it and will use it if the need arises again but according to David Vizard's experience and research I've been reading in his books, the most effective setup regarding heat control of the intake is to keep the air and fuel cold going in but regulate the intake manifold heat to around 160-200*F. This makes sure the fuel stays atomized as it flows through the intake and absorbs the heat from the intake runners; keeping air and fuel cold before entering the intake maximizes the density of the charge going in as we all know.
 
Yeah at 5000ft you need all the air you can get, and the colder, the denser.
If you are having a hot kick-back on the starter,at 5000ft, with 10.5 Scr,and 8* initial; the kb might not be compression.

I ran my 367 with a 223* cam, at 11.3 Scr(aluminum heads), and at 900ft, with 14* initial. With the mini-starter I had no issues, even at 205* minimum running temp.
So perhaps one or more of the parameters are off.
The biggie would be your elevation.
For example; correcting 10.5Scr for 4000ft your Dcr might be 7.92/158psi.
And at 900ft I get;8.54/174psi, at 59* ICA.
So maybe verify your local elevation. I got the 5000 off the net, so who knows if that is correct!
 
I think where I live on the eastern edge of town is closer to 4000 feet, I'm a solid 15 miles from downtown Fort Collins which is visibly closer to the mountains.

I'm just gonna check my cranking compression it's the only way to know for sure (IF the gauge is accurate) and it's something I should have done long ago in the 4 years this mill's been running.
 
Khalid: No heat riser port,on E/Q heads... My LA bolt pattern heads,still had a sealed heat riser crossover port...Isn't gonna happen... The heater under the plenum,is interesting...In the 80's,some OEM carbed setups,used "heat grid " gaskets.. Electrical controlled,would preheat the air/fuel mixture for emulsification...Not aware ,of an four barrel application,just some info.

Tim (and others) I seriously considered using something electrically heated but I like the idea of using the engine coolant, it's a good heat source because the temp stays pretty constant but it puts out a lot of heat energy since it's contained in water. The bigger "cooler" I can fit the more the intake will be heated but not to too high a temp

I did see an old electric heat grid carb spacer thingy for a small Olds V8 (2-bbl of course) somewhere on the web, might be a good idea for people running Super 6 intakes on their slants with no intake heat...
 
BTW, copper and aluminum are not electrolytically compatible so you will get corrosion (even in dry CO) if you put them in contact. So I would be thinking stainless or aluminum for the tubing. If you air seal up the area, then the epoxy and tube idea may work out.

I still wonder why not just switch to the Performer intake and have it heated normally from underneath with the oil and get rid of the open air under the plenum.....
 
BTW, copper and aluminum are not electrolytically compatible so you will get corrosion (even in dry CO) if you put them in contact. So I would be thinking stainless or aluminum for the tubing. If you air seal up the area, then the epoxy and tube idea may work out.

I still wonder why not just switch to the Performer intake and have it heated normally from underneath with the oil and get rid of the open air under the plenum.....

Thanks for the tip on the metals I had a feeling that might be an issue but didn't really think about it till you mentioned it, I will keep that in mind.

And once again lol, I'm running Magnum heads so there is no "regular RPM" intake I can run. If I had heads with the LA intake pattern I would not have put an Air-Gap on in the first place, it was my only option with the Magnums. Tim that's what I meant with regards to aftermarket heads, if/when I upgrade my heads I am definitely going with LA intake pattern so I can run a non-Air-Gap intake and at least get the heat from the oil splashing underneath.
 
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