The Stovebolt Site Forums The Shop Area Engine Shop Heat riser or heat drifter??

In the stock setup for our Stovebolt’s, the exhaust is
diverted so it flows directly up against the floor of
the intake manifold for the first few minutes and
then as the butterfly opens the majority of the
exhaust (95%) flows straight out the exhaust pipe
unless more heat is called for. In which case the
thermostatic bi-metal spring, if properly adjusted,
partially closes the butterfly diverting more heat to
the intake.
When we get rid of the stock exhaust manifold in favor
of a cast iron header or any header as far as that
goes the only options are to run a pipe over to
a ‘dead end’ plate or run coolant thru a heat
exchanger plate.
The first one, the pipe, has always seemed to me, to
be nothing much more than a decoration since it is,
just as I posted, a ‘dead end’, with none of the
exhaust gas flowing across the bottom of the intake.
The tube simply serves as a small path to transfer
heat by conduction. This does very little for a fast
pre-heat after initial startup nor does it seem
adequate to maintain heat once the engine is up to
operating temperature. The original design was meant
to heat the floor of the intake fast so that fuel
vapor rather than raw fuel enters the engine and to
maintain adequate heat to the floor of the intake.

The second attempt, which is circulating coolant under
the intake has its flaws also. Coolant is regulated
at 160° to 180° as it exits the engine but by the time
it would reach the bottom of the intake it would be
considerably less because the hoses act as heat
exchangers also. And, as has been discussed before, it
would take 10minutes or more for the coolant to reach
temperature, which would not satisfy the design
criteria for rapidly heating the intake floor.

Considering these facts it would seem that splitting
the original exhaust manifold even though it isn’t as
efficient or as pretty, might be a better choice after
all.
So….are we wasting our time and money by installing
these inefficient methods of heating the intake when
we install aftermarket headers, or would we be better
off just running without a method of raising the heat
to the intake??

Denny Graham
Sandwich, IL

Two thoughts come to my mind. First, splitting the exhaust is to improve the flow out of the engine. How one does that might make some difference...but not much, I think. And second I agree that both a heat rise pipe and coolant under the intake are somewhat too little and too late. The question I would want answered is how much better if any are the aftermarket split headers than a well made split stock exhaust manifold? If there is little to no difference flow wise then it would seem that modified stock would get the most with the least as it were. The Fenton type do look good but if there is no gain and little advantage cool won't make you run stronger.

The high heat from the exhaust does a couple of things just as you mention, one it helps cold start ups, and two, it keeps the fuel vaporized. I have run engines both ways, with no heat and full heat ( no flapper valve). The full heat was never a problem and always ran better then no heat, even when hot out side. Race cars are a different animal and cannot be included when discussing street driven cars or trucks. I suspect full heat also lets the mixture flow quicker, since hot gases are lighter.

With the small amount of air flow the inline engines make at normal driving speeds, any type of exhaust will do a good job of getting it out of the engine. I built a header type manifold for my 250. Six short pipes into a tapered pipe which ended up being 2 1/2" at the outlet. The front pipe was 1 3/4" which blended to the tapered piece. It was all smooth and nicely done with no sharp corners or jagged welding. It sounded better, seemed to run better, all was good. I had no heat under the carbs ( three of them ). I took it to the local drag strip and made five runs. all with in a short time. All five were very close to each other, 17.98 @ 72.6 mph - 18.0 @ 72.9 mph. It would make a great bracket racer! Next week I went back with a stock 1 barrel and exhaust just as GM delivered it, guess what it ran? 17.97 @ 72 mph, I couldn't believe it. Five more runs all the same.

What I found was the engine had plenty of exhaust pipe and the stock manifold was good enough for how hard I was running the engine. I let it shift at 4500, no need to push it any farther as the carbs were at there limits anyway. From transmission back, I used the same exhaust system, 2" single pipe, through a 2" quite muffler with 2" full tail pipe.

I started thinking about what had happened and went looking for some answers. Using my dad's $400 computer based engine analyzer I started plugging in numbers and data from my truck and recent drag race results. I came up with fairly mild 155 hp flywheel, 125 hp rear wheel engine. This is just what I was guess it had due to mph, and weight calculations I had done. So with this data I started changing the header design. To make the most horse power and torque in the rpm range I had used, the primary header tubes needed to be 1 9/16" diameter, 36" long, going into a 2 1/2" collector about 18" long. The very small and long pipes was key to high torque which is what moves the truck. To get higher hp, I needed shorter larger diameter pipes. The program had cast headers as a choice along with log style manifolds, both of which showed the same out put. On most engines we looked at on the program, cast headers were a option and almost every time, they showed very little gains over stock log type manifolds on V8's. Another factor is the exhaust port, this is what limits flow, not the manifold or pipe. If the exhaust can not get out of the head, pipe size doesn't make any difference. In my case, the head was ported with about a 14% gain in exhaust flow over stock ( I used a bigger exhaust valve).

Joe

I can understand getting heat to the intake floor in a stone cold engine. But once up to running temperature I don't see it a problem when running Fenton split manifold without any heat transfer. I'm talking in fair weather not in the middle of winter. But then again I've been wrong before.

If you keep the intake hot, the fuel droplets will stay atomized. When a fuel mixture hits a cool or cold surface, it sticks and pools on the floor. If the floor is scalding hot, it vaporized right back and continues down the runners.

In a warm dry area, you won't see a problem, but add in some humidity and cooler air, you get big time icing and stumbling.

Joe

Denny,

I almost completly agree with you! Everything but the not pretty part as I think mine come out pretty good.

Yeah I'd agree with you, Curt. John

Any plans on making any more of those, Curt?

I'm using water heat now (since last weekend) and it doesn't take a whole lot of time to heat the intake. 5 minutes on the outside. I haven't actually measured the temp, but it isn't going to lose a whole lot of temp in 24" of rubber hose. When I had exhaust heat, the flapper never worked for 30 years and I didn't even know it was there for most of that time, I wedged into the heat on position once, dear lord I thought it was going to explode. Heating it too much isn't good either.

Well, as usual, If I mince words and don't type my usual three
page post then there is always some misinterpretation. No where
did I say that the Fenton or Williams headers are not "pretty".
What I was referring to was the "heat pipe" being "nothing much
more than a decoration."
Has to be the exception to everything brokenhead. The engineers
wouldn't have wasted all that effort on the heat riser for all
those years on all those millions of cars and truck if it wasn't
needed. Of course, there are some people that are better
engineers than those that designed the Chevy six during it's
80 year run.

Denny Graham
Sandwich, IL

Does anyone have a copy of the dyno information from Inliners.org from a few years back? There was a bunch of testing done on a 250 and 292, seems exhaust was one of them.

Joe

I think they turned out pretty good too.
Will that exhaust manifold fit a stock 216 and if so do you sell them?

Dave

No doubt it was a lot more fun discovering this at the drag strip as opposed to making a flow bench adapter plate, documenting effect of alterations, and digitizing/dissecting the head.

There was an inliner who made nice split manifolds and whose work I tried to emulate but stopped some time ago. I believe this was because only about one third of those that exist are suitable for welding and you would soon run out of material. Heavy use (overheating) makes the iron brittle and exposure to the elements (rust) prevents success. I may do a few locally if provided with good cores but other than that it's not really feasible as much as I think this is the best method and would like to provide this service to stovebolters. I once hinted at providing the machined flange, elbow, and instructions in an old thread where all you needed was an old fart welder but all I heard was crickets

Also, The 250/292 factory exhaust manifolds are not good candidates for dual modification due to their design but that's moot as far as 235/261 flow. Frank McGurk's HRM article documents the difference the dual Corvette exhaust manifold showed over stock which IIRC is was significant especially when combined with other modifications.

I once hinted at providing the machined flange, elbow, and instructions in an old thread where all you needed was an old fart welder but all I heard was crickets

I have two old fart welders, a Lincoln AC buzz box and a Lincoln 250AS DC welder. Just not sure I have the skill to weld cast iron or not... Some say it is tricky to weld, others say nothing to it.
Those TIG welds you do look purty though.

John








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Been real busy and didn't have a chance to look at your album
Curt. Veeery nicely done. I'm sure I haven't seen those
pictures before but I've made a folder for them and will
definitely study them closely.
I've worked as a machinist and as a welder as we had a welding
fabrication/machine shop in the family for many years and have
worked in and around the field most of my life. I don't have the
machining center but I do still have a couple of Bridgeport's
and am set up with mig, tig and stick welding capability.

Got most of it from the pictures, the only question I have, as
most guys that have welded cast iron might have, is, did you do
the welding and what method and filler did you use???
Preheat the casting I would imagine? And I've found that after
welding cast iron it's really hard. The difference between the
as cast metal and the welded section has always been a concern
with me because of the way it hardens up. The flange and sch. 40
close elbow are straight forward but I would like some info how
you made it up to the casting.
Please fill us in on any more details you can think of.

Denny Graham
Sandwich, IL

perhaps amongst all of us we could gather some information on the various intake heating methods. I.E. using infrared thermometers everyone could measure the temp of the intake at a given spot. For example, once I get my new radiator in I could provide the temp on a water heated intake, and so on for other people. I am not so certain the engineers designed the exhaust heat/flapper system because it was the absolute best. As with pretty much anything, accountants "design" the machines the engineers just make it work. The beauty of the exhaust heat/flapper was it was extremely cheap to build, and if it failed it would most likely fail in the "heat off" position and like me, most people would not even be aware that anything had occurred. And I have driven it in 10-15° below weather and noticed no inconsistencies. I do know that I don't know the optimum temperature to run an intake mixture. But I do know the water heat made an incredible difference in the heat of the intake directly under the carb, and started heating in just a couple of minutes (at least the way I have it plumbed in) whether or not it is the "best" temperature I don't know. However Tom Langdon if I am not mistaken was actually an engineer at GM at one time and would/should know, and he recommends water heat. That being said, there are other methods that seem to work, at least satisfactorily. (meaning there isn't one CORRECT answer)

I don't know if the engr's back in the day discovered they could improve the ICE's efficiency by heating the intake manifold directly under the carb by individual trial and error or if someone had documented it and they all subscribed to it but it's clear the American and German ICE engr's back in the day believed it did and implemented exhaust heated intake manifolds into their ICE designs.

Even tho the Stovebolt 6 has a temperature sensing heat to manifold regulator and the ACVW boxer 4 doesn't they both utilize heated air primarily at the junction where the downdraft carb meets the intake manifold and splits directions to improve ignition efficiency.

Since the ACVW doesn't have heated coolant circulating throughout the engine it's understandable why heated exhaust is used but the Stovebolt 6 has both heated sources and the engrs used heated air.
Was it cost or efficiency that drove that decision?
It's pretty Obvious that single carb'ed engines w/long intake manifolds work better when heated at the carb to manifold junction.
As already posted I would think heated air will heat up the manifold quicker than heated water but heated water would still be more desirable than having no heated manifold.

How about dual or triple carbs? Do they need manifold heat?
On the ACVW that goes to dual carbs the consensus is no. The manifolds are much shorted and very close to a heat source (the head) so warm up time is greatly diminished. Also of note is most of the duals are 2 BBls and don't even require a choke to start a cold engine. So after a very short warm up period dual carbed ACVW boxer 4 ICE's work very well without manifold heat and chokes....

In a Stovebolt 6 w/dual carbs we're still looking at somewhat long intake runners that are open and exposed to the cooling air of the radiator fan. In this case it seems to make sense that intake manifold heat will improve the engines efficiency.
Air or water is again more desireable than not.

What about 3 carbs? With each carb mounted directly over the intake runner that feeds the heads intake port?
This would almost seem to be the best method of increasing the engines efficiency and perhaps doing so without heating the manifold.
The engr's must have thought this back in the day when they designed the Blue Flame 6 for the 1st Vetts.

Course finding new carbs that will work w/the Stovebolt 6 in the tri-mount is the question and problem. There are several small venturi/adjustable jet 1bbl & 2bbl carbs widely available for the smaller ACVW boxer 4 and I wonder if anyone has tried any of these newer carbs in a Tri-mount Stovebolt 6 config?
And if so did they find it necessary to heat the intake manifold?

Anyways I'm rambling, good topic.
Dave

When referring to an "old fart welder" I'm not talking about equipment but an individual whose has been holding a stinger 10+ hrs a day for 40+ years. This process is all about procedure which presents no challenge for those with that experience. I machined and fit up the components and closely observed the old fart who does this:

1. Warm the casting gently to 200-250 f. Just enough to get the sweat out of it and get the molecules moving as he said. An oven can be used which will heat it evenly as dwelling in one spot with a torch can induce brittleness/cracking.

2. He used a stick welder with UTP FN-85 rod and if IIRC it was 1/8" dia. Here's the product info on the filler material. The elbow is steel so this is a case of joining dissimilar metals and possibly why this particular rod is the ticket.

3. Beads were short; no more than 3/8" long and immediately he would peen the weld as well as the surrounding area with an air hammer set very low with a blunt tip. He would actually "push" the weld to flatten/spread/shape it as it cooled but the primary purpose was to prevent stress buildup.

4.Welding/peening were both done in about 20 second bursts for probably 100 times. He paced himself in such a way that each bead he put down was maintaining preheat for the next.

5. When he finished I wanted to dress it up a bit with a grinder and was told that the breeze/exhaust could potentially ruin it and that it had to immediately be wrapped in a welding blanket and left undisturbed for a minimum of 6 hours. (burying it in kitty litter or vermiculite are acceptable alternatives). He had some type of muffler/diffuser? on his air hammer to prevent blowing on the part and didn't want open doors or fans anywhere near the process.

6. As the welds were shaped with the air hammer there wasn't much to do to smooth it out. I just used a rat tail file to blend the elbow to the casting.

This process worked flawlessly several times so I hope some of you can make use of it successfully.

We welded a cast iron Harley head. Used heat from a rose bud, Wire feed welder and, had no issues after we figured it had to be placed into an oven. The cooling caused uneven shrinking, that was the problem. Sand, kitty liter, oven, whatever, just keep it slow. I do like the peening idea, that, I will keep in mind.

Thanks Curt. I've welded a lot of chrome molly so I'm familiar
with what a breeze can do to a hot weld and the necessity to
cool a weld in an alloy slowly. I'll look into that filler,
thanks for the tip. I've tig welded cast iron using a Eutectic
filler rod but it got so hard a file wouldn't touch it, had to
grind it to shape:
http://www.pbase.com/dennygraham/image/136649996

Denny G

I never saw the need for a heat riser for the Hillbilly intake I built for a 302 GMC.

https://plus.google.com/photos/1081...79269253230710993?authkey=CLPIwcnBxZvuPg

I made cuts with a band saw, bolted the pieces to a complete manifold for a jig, heated her up and started welding. It was one of my first projects when I bought my first Millermatic 200 around 30 years ago. I had to true it up with a belt sander. It's been on several engines. I've had a few fires in a carb when my linkage wasn't right, but for the most part it made a 302 really come to life.