TheSamba.com :: View topic

Mon May 12, 2014 7:32 pm

Does anybody have a good way to heat the stock dual port manifold with with oil? I'm going to be running a 34 pict 3 with a 30mm venturi and I want as much heat as possible.

Would it work to pull or cut out the stock heat riser pipes then run some copper tubing through the cast piece then attach fittings to the ends for lines?

Mon May 12, 2014 7:40 pm

Well the Engine oil is slow to warm up at all so it will not offer you any benefit during warm up then the exhaust gas is really hot like 1000 Degrees F or something and that would cause your engine oil to overheat I would think. Just make sure it's breathing warm air off the heads through the stock air filter set-up.

Mon May 12, 2014 8:50 pm

I was planning to do away with the exhaust part of it altogether and just use oil alone to heat the manifold. One reason for doing it would be that I was going to run a header and any header I've had didn't seam to heat the manifold enough.

Mon May 12, 2014 10:29 pm

It's so crazy it just might work!

Exhaust is much hotter, but less dense, so by the time it goes through the heatriser it is cool enough to touch. You may actually get more heat out of your oil idea, making the intake manifold 200ºF. Great for fuel economy, terrible for full throttle power. But I bet you could make a thermostatic system to keep your intake manifold cooler, let's say 100ºF, if that's what you want.

Could you clean out the stock heat riser tube real well, cut the ends off and hook up to that? If you do use copper tubing you could glue it on with silicone to aid heat transfer.

Or stick with exhaust heated heatriser system but with the proper modifications to the headers.

Mon May 12, 2014 11:18 pm

I doubt it, the size of the pipe and small amount of interface will limit the rate at which heat can be transferred to the manifold at the lower temperature. If you look at water heated manifolds on non-VW engines you will note the size and format of the ports required to transfer enough heat.

But I'm more than willing to let you try - please post results of your experiment here, whether you succeed or fail.

Mon May 12, 2014 11:56 pm

Quokka what your saying makes sense. I think I would have to coil the tubing around the intake tightly to transfer enough heat.
I'm not too conerned about high rpm power. I'm trying to build a nice balance between mpg, power and longevity.
I've been doing a lot of reading and it seems to be the main problem with a center mount carb is keeping the intake hot enough to keep the fuel atomized.
The hotter the air, the better the atomization, the less fuel required to make the same boom.
I guess i can run some copper tubing through the heat riser of an old spare intake and pump hot oil/water through it and see how it warms the intake.

Tue May 13, 2014 12:05 am

it's easier than most think to make the exhaust heat work. Just pry the needed tubes and flanges off some stock muffers and bend em to fit and weld together.

Tue May 13, 2014 4:12 am

I would think wrapping with copper pipe and then maybe doing a heat wrap over the pipe to hold it in would get you a lot of heat.

Tue May 13, 2014 4:31 am

I'd just go dual carbs and forget the hear riser all together.

Tue May 13, 2014 4:50 am

My Manx has a tri-Mil with a turbo muffler. No tap for exhaust feed at #2 cylinder. I tapped the exhaust at the outlet end of muffler and piped it under the manifold, and piped the other end right out the back of the car. Looks not so great, but DAMN did it ever fix the issue of icing! I put it on the outlet to get all 4 exhaust pulses instead of just one. I lost a little heat because I am further away from the cylinder, but I gained a LOT because I'm getting all 4 cylinders exhaust and not just #2.

Tue May 13, 2014 7:56 am

Glenn wrote: I'd just go dual carbs and forget the hear riser all together.

X2 Make your life easier.

Tue May 13, 2014 10:22 am

Axitech wrote: My Manx has a tri-Mil with a turbo muffler. No tap for exhaust feed at #2 cylinder. I tapped the exhaust at the outlet end of muffler and piped it under the manifold, and piped the other end right out the back of the car. Looks not so great, but DAMN did it ever fix the issue of icing! I put it on the outlet to get all 4 exhaust pulses instead of just one. I lost a little heat because I am further away from the cylinder, but I gained a LOT because I'm getting all 4 cylinders exhaust and not just #2.

Yeah, the main reason a lot of aftermarket exhausts' heat risers don't work well is that both ends of the pipe are next to the exhaust ports in the heads. Exhaust pulses bounce back and forth between the two, but there's no real airflow through the pipe. One end of the pipe needs to be in a lower pressure point further along the exhaust, in the muffler like stock, in the collector, or even just open to air like yours (louder though) so exhaust gasses will want to flow in one direction though the pipe.

Personally, I think modifying the exhaust to make the heat riser work in this way is easier and certainly more proven than attempting to heat the manifold with oil.

Tue May 13, 2014 10:32 am

bdub475 wrote: Quokka what your saying makes sense. I think I would have to coil the tubing around the intake tightly to transfer enough heat.
I'm not too conerned about high rpm power. I'm trying to build a nice balance between mpg, power and longevity.
I've been doing a lot of reading and it seems to be the main problem with a center mount carb is keeping the intake hot enough to keep the fuel atomized.
The hotter the air, the better the atomization, the less fuel required to make the same boom.
I guess i can run some copper tubing through the heat riser of an old spare intake and pump hot oil/water through it and see how it warms the intake.

Unless you have it hooked up to the engine with the engine running you won't get correct results. Fuel vaporizing causes it to cool the manifold. Without it, the manifold will heat up to whatever temp the fluid is that is heating it.

Tue May 13, 2014 11:08 am

Glenn wrote: I'd just go dual carbs and forget the hear riser all together.

X-3

VW put a single carb on for budget reasons. Porsche never messed with one because they knew it was a headache. In the late 50's Porsche stopped using dual singles because in many ways they suck. Corvair never messed with one except on the turbo. I don't know what old Subaru's did. Any time you have two heads far from each other running a single carb is a problem.

The two best two things done to a vw is a oil temp dipstick and two carbs. I do not understand why so many people want to mess with singles.

If you want to run a single carb run a completely stock engine or you will have to do lots of fabrication. A header does not add much power to a stocker anyway.

Dan

Tue May 13, 2014 12:07 pm

[email protected] wrote: In an ideal MPG designed system, the fuel will be added to the air, and heated up, and given TIME to absorb it and evaporate. This obviously means a very long heated intake, with the FI or carb a ways from the cylinder.

I know a lot of guys feel that dual carbs or fuel injection will get you the best fuel mileage because it's easier to make the A/F ratios in every cylinder all the same. But I feel that if you are going for fuel mileage then you are going to be running at some rediculously lean A/F ratio any way, and 15.5:1 in one cylinder and 16.5:1 in another isn't going to make that much difference. The more important thing is that you get as much heat and vacuum as possible to vaporize all the fuel.

If you really want fuel economy, then:

[email protected] wrote: If you were really hell bent on making the most MPG, you'd mount the carb in the front of the car, with a HEATED INTAKE running all the way to the engine. You'd also have a cam that provided the most vacuum at your driving speed. The combination of the heat and the vacuum would vaporize every molecule, and would allow you to jet it leaner than a "normal" engine, since the chamber would see the same amount of combustible fuel in either case. And for you McGyver's out there, consider routing OIL thru your intake preheat tubes, you'll heat up the intake and cool the oil at the same time! :-)

Tue May 13, 2014 12:27 pm

oil is fine to heat the intake, AFTER IT TAKES 30 MINUTES TO WARM UP. Exhaust is great because it works within seconds of starting the engine, AND the amount of exhaust is proportional to how much heat you need with the throttle. Oil lags this by a LOT, which is another reason not to do it.

Tue May 13, 2014 12:43 pm

Seeing how the intake runs cooler than oil temps at running temps could a guy run both oil and exhaust? The exhaust heatrisers would provide immediate heat and the oil would eventually make more heat.

Of course you would have to make your own oil heatriser set up.

Tue May 13, 2014 1:19 pm

then you are using the exhaust to heat up the oil, right?

Tue May 13, 2014 1:47 pm

[email protected] wrote: then you are using the exhaust to heat up the oil, right?

Well, yes and no.

During warm up, yes, since the exhaust should warm up the intake manifold faster than the oil should warm up. Might be a good way to warm up the oil quicker.

During normal running, no, because the exhaust shouldn't heat the intake manifold up over 200ºF. If I string another tube along the intake manifold full of oil, and the intake manifold is 100ºF and my oil is 200ºF then the oil should cool and the intake manifold should warm up even more. Even if the hottest the intake manifokd gets with just the exhaust heat risers is 200ºF then it won't be heating nor cooling the oil.

But I better do a few tests first to make sure the heat from the exhaust won't make the intake manifold heat up over 200ºF, perhaps on a hot day up a hill. Because if it does, it will be heating up my oil and the oil will be cooling down the intake manifold instead.

Tue May 13, 2014 1:57 pm

Do what GM did, draw your intake air for the carb from over the exhaust- you'll have more heat than you know what to do with. I've seen a least one system where a guy had the flap valve as well, where WOT runs caused it to take in only cool air.