Humm... where to start.. lol Lot's here to digest. It's obvious to everyone now that I like stirring things up a bit. Yeah, I could've just said, "ready made" instead of "ready made in China", but that's now how you get a handle on who you're talking to.

Dan, yeah, I made and tend to make a lot of assumptions, but I was already clear on the fact that you'd have no problem correcting any bad guesses. I did say "but *if* you think a boycott..." So the preaching of my own opinion was conditional from the get-go. And I did take it for granted that you live in the U.S., not sure why. But, that was an unfounded assumption. In any case, no offense intended on any front.

Concerning my apparent, self-appointed expertise... I've already remarked that the reason I'm here is to learn about an engine, of which I have very little knowledge or experience. That said, most engines obey similar physical rules, something I do know a bit about. On the reread, my statements concerning the function of the manifold heating system do sound overly authoritative. I haven't done the research yet, but apparently there are forces at play in the slant intake system that run counter to usual laws of thermodynamics governing nearly all other engines installed in the majority of motor vehicles ever manufactured. Thank you for pointing that out. I am very interested in finding out this information. For what it's worth, my intuition was that the extremely long and unequal runner length of the manifold *might* cause a lean condition in the outermost cylinders, i.e., a flat spot or stumble on immediate throttle opening. Accelerator pumps wouldn't help much, too far away, unless they had help with atomization, so bring on the hotspot. Am I close? The rest of the time, particularly at cruise, atomization shouldn't be a problem given the extreme airspeed through the manifold (3.7 liter breathing through two 1.5" venturies at WOT, and a lot less at part throttle).

Anyway I more or less dismissed all of the above for a couple reasons, first, I don't plan on stabbing the throttle much, if at all. I've got an '92 FJ1200 ABS that makes over 140 rear wheel hp, when I'm in the mood to feel some acceleration. What I want from the van is decent fuel economy at highway cruise, and I'd quickly give up a little driveability around town to get more mpg's at cruise. Otherwise, I have bought a van with a V-8, and saved you some annoyance and entertainment. So, if the objective is MPG's, then anything that contributes a colder, denser charge that allows more ignition advance before detonation is where this header project should head. And a hotspot goes again this line of thinking. Am I right? BUT, again, there's more here than meets my inexperienced mind, so we'll see where I went astray.

Okay, sure I'll take a stab at a proof here (pardon the format, it's been 30 years since I took symbolic logic):

(a) The preheat is required while the engine is running, even when it's at operating temperature because there's a phenomenon constantly cooling the engine even at operating temp; then,
(b) the engine never, does not require the preheat when running because it's either cold or at operating temp and both conditions require the preheat; therefore,
(c) the preheat is regarded as a "must have to run, period" sort of thing.

In fact, near as I can interpret, nearly everything in your response--not just what I've quoted--drives towards the assertion that you can't get do without the preheat and have a decent running slant. Have I missed something here? And, yes, there is a third operating condition "overheat", but I hope we can agree that we are not involving that parameter in this discussion.

I'm a former homebuilder and now a residential contractor (semi-retired). Those words have more truth than just about any client is willing to accept, unfortunately--unless you're being paid by the hour.
I too have owned dozens, and still own and drive a few, carbureted cars. Working with a choke--usually manual--and nervous pedaling the accelerator for an extra squirt when needed is pretty much second nature, and kind of a lost art nowadays. I mentioned my high school ride elsewhere, '70 T/A with a built RAIII 400. In my memory I can still hear the 2-3 second stream of gas from a full stroke of the Holley 850 DP. Press the pedal to the floor a couple times, a couple turns from the starter, and WHOOM! Enough thunder from the garage to piss off the all the neighbors on the block. haha I had straight pipes off the headers to two California Turbos cut-off right in front of the rear axle. Nothing compares to that sound. Still raises the hair on the back of my neck just listening to 'em on youtube.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Yes, a slant six can run without intake manifold heat, but it causes problems that can be masked by tuning and self-delusion. Fuel will still fall out of suspension while the car is running and puddle on the intake floor. This causes premature engine wear and poor economy. Just ask the V-8 guys who have a car that runs great when the exhaust crossover is working but then runs terrible when the exhaust crossover in the intake gets clogged with carbon. Yes, aftermarket V8 intake often have the exhaust crossover eliminated, but again, the problems from no intake manifold heat are tuned away, even though the underlying reasons why manifold heat was ever used still exist.

But it is your car. You feel free to do whatever you want to it.

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Casually looking for a Clifford hyperpak intake for cheap.

Thanks for the reply, Reed. I've done some research on the site since my last post, and noticed that you appear to be one of the primary, resident technical guru's here. Obviously I got off on the wrong foot with Dan, my fault there.

Anyway, yes, I realize I was wrong. There is very definitely a cooling phenomena at work here that frankly in all my years of working on cars, studying engine technology, etc., I've never either heard of, or at least didn't pay it enough attention. I'm an import mechanic primarily, and most of my experience is with fuel injection, or carburated cars where manifold length is short and direct, often with multiple carbs. But this does help explain why Trans Am ran like crap part throttle with a Torker II mid rise manifold. I have no doubt I'd blocked off the manifold heat.

It looks like manifold heat is even more important in the slant because of the short distance from the throttle plate to a 90 degree bend, not to mention the unequal length intake runners. I've also learned that, yes, you need a lot of heat to get the job done. There are several threads besides this one that touch on the idea of using electrical heating or engine coolant. I get that surplus exhaust or coolant heat is the only way to go when running at operating temp. Too much heat, however, and you lose power, boil the fuel out of the carb at shutdown, and lower the threshold for detonation.

So, now I'm wondering, does anyone have any data on how much heat is required (ideal temp of intake manifold, for example) at highway cruise to overcome the manifolds fuel/air distribution issues? Assuming you install headers, it seems like using a coolant supplied heat exchanger with some sort of thermostatic regulation would be ideal, and not ridiculously difficult to engineer. This could be supplemented by a resistive electric heating coil--or tape --during cold startup and run, until the coolant took over.

Let us engage in a thought experiment.

I don't know how much a cast iron intake manifold weighs, but they are a hefty chunk of metal. Lets assume one weighs 40 lbs.

How much energy does it take to raise a given mass of cast iron one degree Fahrenheit? Fortunately, these calculations have been done by people more qualified than me. Looking HERE, we see that the specific heat capacity of cast iron (the amount of energy it takes to raise the temperature of a given mass of cast iron one degree Fahrenheit) is: 0.110 btu/lb-F. 40 pounds at 0.110 btu/lb = 4.4 btu to raise 40 lbs of cast iron one degree Fahrenheit.

Great. Now, lets assume you are starting your engine on a reasonably mild morning with a temperature of 55 degrees Fahrenheit. That was a warm summer day where I grew up in Alaska, but opinions may differ. Lets assume you want to heat the intake manifold to around 150 degrees to allow the gasoline the ability to vaporize if it falls out of suspension and hits the floor of the intake.

150-55 = 95 degrees. It will take (4.4x95) btus of energy to accomplish this on our hypothetical engine (and this is not taking into account the effects of the air rushing through the inside of the intake or being blown across the exterior of the manifold). So, on our hypothetical intake it will take 418 btus to heat the intake to regular operating temperature.

Then the question becomes how fast do you want those Btus to be introduced to the intake. Obviously, you want to bring the intake up to operating temperature as fast as possible. Lets assume you want to give the motor one minute to have the intake reach operating temperature.

So our hypothetical engine power consumption just to heat the intake =

418 Btus in 60 seconds.

1 BTU = 1055.05585262 Joules

We want to input 441,013.345 joules in 60 seconds

Watts = joules/second

Example
What is the power consumption of an electrical circuit that has energy consumption of 90 joules for time duration of 3 seconds?
P(W) = 90J / 3s = 30W

So we need the following watt consumption:

441,013.345/60 = 7,350.22242 watts. Just say 7350.

Watts = Amps/volts

Lets assume you have nigh on zero voltage drop in your charging system and your battery and alt are top notch and you have a full 14.5 volt output at all times.

7350 = x Amps/14.5 volts

amps required for heating the intake = 7350 X 14.5

You would need an alternator capable of 106,578.225 amps to heat the intake manifold enough in one minute from 55 degrees Fahrenheit to vaporize gasoline.

Now, bear in mind that 7.35 kilowatts = 9.86 horsepower, roughly 1/10th the stock output of a slant six.
Kilowatt to horsepower converter

Then you also want to be able to maintain the intake temperature during engine operation. Once the intake manifold was heated the amp draw should lessen significantly, but some input of heat would still be required.

Now remember, I am not a scientist or engineer, I am a lawyer. I love math and science, but there is a reason I did not pursue them as a career. Check my math, make sure I didn't mess up somewhere, but I think I did OK. The above calculations make a large number of assumptions and disregard many real world factors that will affect how this hypothetical engine would operate.

In terms of getting the intake manifold up to operating temperature quickly and maintaining that temperature easily while the engine is operating, exhaust heating is really the best way to go. Unlike electrical heat tape, the exhaust is up to full heat as soon as fuel is combusting. Also unlike electrical heat tape, using exhaust to heat the intake will put no extra load on the engine. Any electrical heat tape, especially one that you are calling on to provide 418 = Btus, will have a massive amp draw on the alternator which will, inturn, have a horsepower draw on the engine. At the same time, the engine will already be producing hot exhaust no matter if there is an electrical heat tape system or not.

For the majority of the life of the internal combustion engine, every major automotive manufacturer (a) heated the intake manifold (b) with exhaust gases. Exhaust gas heating is the most effecient and simplest solution to this problem. MPEFI eliminated the need to heat the intake because intake manifolds are no longer "wet" and carburetor icing and fuel condensing in the intake tract are no longer a problem.

But I can say that even if you ignore everything I say about anything, Slantsixdan and Joshie225 know worlds more about building engines and the slant six than I do. I mostly like to run my mouth and repeat what I read. Listen to them long before you listen to me.

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Casually looking for a Clifford hyperpak intake for cheap.

Reed: Thanks for suggesting some thinking on what is required, that gives an idea of what is needed.

Unfortunately, I would like to suggest a correction (my apologies, but one if the things I do lately is teaching basic electric circuits): power is equal to voltage times current (P=V*I). So the current is around 500 Amps (which is still a bunch, like a starter?)

Your power estimation is still correct, 1/10 of the Slant HP (believe me you handle math better that some people trying to become "engineers"guys I've seen around).

Well, you can extend the warming up period to 2.5-5 min, and put that in 200-100 amps.
Then you need to check how much power your resistor can deliver... before burning and so.
You know your battery can help you for a while, but sucking 100 amps for 5 min will put a stress on your electric system and battery (specially if you still have ll the current flowing through the alternator gauge).
And you have not included heat losses due to airflow (maybe if you wrap the intake manifold with insulator, like when protecting a sprinkler pressure vacuum breaker valve during winter...)

It is "possible" to do it, but not necessarily a good solution. Of course, car companies avoid all this hazzle and loss of efficiency and reliability with a proper design using the exhaust gases.

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/6 Dodge Charger 69
...there's nothing like using the "Search" link above to solve most of your problems...

Thanks for correcting me. I havent studied electronic circuits since basic electronics in high school, and that was over 20 years ago now.

But we came to the same conclusion. The exhaust manifold heating system is a much more efficient and simpler design.

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Casually looking for a Clifford hyperpak intake for cheap.

I had to do a double take. I thought that i stumbled into a BMW board, what with all that math and stuff. If the OP is really an import guy, he should already know that all inline Japanes engines with carburators had water heated intakes, including that aforemention 280ZX.

Which means that we can throw numbers like the BMWrs if we want to, but we prefer to keep our discussions grounded

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/6 Dodge Charger 69
...there's nothing like using the "Search" link above to solve most of your problems...

My defense is that it was too many units to convert for me to keep it all straight. Especially late at night.

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Casually looking for a Clifford hyperpak intake for cheap.

I recognize that most intakes have a heat source. What I was not aware of is the evaporative cooling effect, and consequent need for manifold heat for that reason. Until now, I'd assumed that the heat was provided primarily as a cold running assist. Based on what I've read, the cooling effect is not as detrimental where the carb has a fairly straight shot into the intake port of the head, i.e., side draft webers, etc. even though the factory may provide heat.

Evidently you don't know much about imports yourself, or at least not the 280ZX, or you'd know it was fuel injected.

Interesting you mention BMW. When I owned my shop, a fair percentage of my clientele owned BMW. It's one of the handful of makes I would flat out refuse to own, unless someone else was paying the repair bills to keep it on the road. More expensive to operate than Land Rover, and that's saying A LOT.

No, I am not an import guy. The only Z car that I have owned had a 350 in front. I haven't open the hood on our Kia Rio, it gets 30 to 35 mpg and that is all I care about. All maintence is done on extended warranty. I think it has a plastic intake manifold.

Most of the BMWs around here are owned by obnoxious 20 something's. They are lowered down so far they are barely drivable along will mufflers you just wonder why.

But then I have owned cars that were lowered so far they were cool. They also had cool mufflers. Nothing like those punk BMW kids, nope nothing like them at all.