86 2.5 Heated Intake

[TheDirtyJeep401]

Would re routing the coolant hoses that run into the intake effect anything?  I’ve got a leaking manifold/intake and while I have it all apart, i was going to block off the passages in the intake manifold and running a 91+ 2.5 water pump that doesn’t have the outlet for the manifold heater. Hoses would be re routed like on a MPFI motor. 

Is it worth the time and effort? 
Or is it something that shouldn’t be deleted and it will hurt performance if done?

 

Just curious on if anyone else has done it. I know the MPFI motors don’t have it, but I know running TBI means the intake runs cooler and that’s why the coolant passages are there. But figured that much heat would be hurting it, rather than being beneficial. 
 

[eaglescout526]

I mean the fuel will probably evaporate too fast from the heated manifold that’s not as cool as the engine but you can give it a shot as I have never heard of anyone doin this to a Renix set up. 

[TheDirtyJeep401]

5 hours ago, eaglescout526 said:

I mean the fuel will probably evaporate too fast from the heated manifold that’s not as cool as the engine but you can give it a shot as I have never heard of anyone doin this to a Renix set up. 

It’s got me wondering. I’ve got an extra intake that I was looking and and thought about it. I know older GMs that had TBI had the same thing. But other TBI set ups don’t. I have a feeling in the summer it would be no problem, but in the winter, it might not want to do much till it’s warmed up. 
 

I kind of want to try it for “scientific purposes” but really don’t want to pull off. Put back on. And possibly pull back off back and install again. 

[eaglescout526]

I mean to each company is their own way. I can see it being a benefit as the fuel would have better atomization in the chamber if there was no coolant running through it to keep it the same temp as the engine, but it is also aluminum. I feel that the winter it wouldnt struggle that much as long as you have the preheater tube set up and it would help there but other wise winter wouldnt be much different even if coolant was flowing through it.

[gogmorgo]

I have a hard time imagining you're not already heating the intake with the heat radiating directly off the exhaust right underneath, at least by the time the coolant is warm enough to do anything. I don't expect warm coolant is going to be doing a ton of cooling in the manifold either. If you're running a block heater it might help to pre-heat the intake a little to prevent fuel dropout on particularly cold starts, but I guess you'll never know until you try.

[pizzaman09]

The reason vehicles have heated manifolds or throttle bodies is to prevent icing.  It's a very common issue on piston powered airplanes and can also be an issue in cold weather on automotive engines.  The air flowing through the intake brings down the temperature of the intake walls, and ice can form.  This can cause issues like stuck throttle plates and restricted airflow.  The heat is basically a defrost system.  The air flowing through is going so fast that it does not pick up an appreciable amount of temperature.  When you spray cold atomized fuel into the intake charge it has an excellent evaporative cooling effect, if you want to keep your intake charge cool, keep the fuel cold and make sure your cold air intake is actually pulling in fresh cool air.

[cruiser54]

The heated intake manifold likely had to do with emissions in all types of weather. 

Fuel and air traveled together through the manifold.

 

I only experienced "icing" on my Nissan Patrol with an aluminum one barrel to two barrel carb adapter. The mechanical fan blew a ton of cold air on the adapter and caused issues. My Redneck solution was wrapping  the adapter with ethofoam insulation held on with zip ties. Worked great. 

 

MPFI only air travels through the intake. 

 

I say try it. Couldn't a guy just loop the hoses together in the name of science? 

[Eagle]

Before we had throttle body injection, we had those old things called "carburetors." I don't think I can count how many cars I've owned with carburetors, and that's not including the other cars my parents and grandparents owned. Like throttle body injection, the fuel mixes with the air in the carburetor and they travel together through the intake manifold.

 

I've never heard of a carbureted car or truck that had a heated intake manifold.

 

[eaglescout526]

1 hour ago, Eagle said:

I've never heard of a carbureted car or truck that had a heated intake manifold.

Supposedly the 2.5L carb had this as an option of the sorts according to the parts catalog. 

[TheDirtyJeep401]

Looking around on other AMC inline engines since there isn’t a lot out there for the 2.5. The 4.2 has the same thing, coolant line coming from the thermostat housing, and out the back to the heater core. But if you look at an aftermarket manifold, like an offenhauser, it does not have coolant ports or passages. 
 

That’s about the only thing  I’ve found so far on something with a similar style coolant set up with aftermarket intake option, even though it’s carbureted, the set up is the exact same. (About the only thing I can find in comparison since the 2.5 never got a “performance” manifold)

 

Makes me wonder more since after market got rid of it. And those bigger manifolds for running bigger carbs are just going to cool it down even more with more air and fuel. 

[pizzaman09]

It's pretty unlikely to hurt to try bypassing it.  I bypassed the coolant heated throttle body on one of my 90s BMWs with no ill effects.  

[gogmorgo]

16 hours ago, Eagle said:

Before we had throttle body injection, we had those old things called "carburetors." I don't think I can count how many cars I've owned with carburetors, and that's not including the other cars my parents and grandparents owned. Like throttle body injection, the fuel mixes with the air in the carburetor and they travel together through the intake manifold.

 

I've never heard of a carbureted car or truck that had a heated intake manifold.

 

Is that not what the little dryer duct thing coming off the exhaust manifold was supposed to be for even though none of them were ever hooked up?

[Eagle]

On 4/16/2023 at 2:45 PM, gogmorgo said:

Is that not what the little dryer duct thing coming off the exhaust manifold was supposed to be for even though none of them were ever hooked up?

 

I have no idea what you're talking about. I've never seen a car with a "little dryer duct" from the exhaust manifold to the carburetor.

[howeitsdone]

I think he’s referring to a pre-heat tube 

 

[gogmorgo]

14 minutes ago, Eagle said:

 

I have no idea what you're talking about. I've never seen a car with a "little dryer duct" from the exhaust manifold to the carburetor.

 

7 minutes ago, howeitsdone said:

I think he’s referring to a pre-heat tube 

 

Yeah that. Is it not for heating intake air?

[Gojira94]

On 4/15/2023 at 10:04 PM, Eagle said:

I've never heard of a carbureted car or truck that had a heated intake manifold.

 

 

SBC example- a very small number of very early (1950s) SBC heads had a center water crossover, but the vast majority just carry heat from the lifter valley through a dry center port, or even just radiant heat from the intake face of the center of the head. Prevents carb icing. Mainly an issue above the 45th parallel...

Most SBC manifolds for both 'early' and 'late' heads still retain the crossover, including the TBI engines from 87-95. Separate and distinct from any EGR provision on a SBC intake.

[Gojira94]

21 hours ago, Eagle said:

 

I have no idea what you're talking about. I've never seen a car with a "little dryer duct" from the exhaust manifold to the carburetor.

 

GM had a butterfly 'pre-choke' of sorts on their thermostatic air cleaners ("Thermac"). The stove pipe warmed the valve, which closes partially in the snorkel section of the air cleaner when it's particularly cold. As the engine warmed up, the valve would close, removing the air restriction + warmer radiant heat from the exhaust manifold, that aided in very cold starts. Last used on the GM TBI trucks in '95.