The Stovebolt Site Forums The Shop Area Engine Shop Manifold heat on offenhauser dual intake

So I bought the offy manifold. I bought the langdons twin weber setup.
(posted pic here previous).
After reading a lot on this, I am going with manifold heat.
(don't tell Tom!)
Anyway, I didn't know till after I bought offy that there are two plugs underneath. I read a lot how most weld them, or, possibly JB weld them.
I blew thru one with my mouth, and yes, they leak. Good thing I read cause I would have hooked to water heat and flooded engine bay!
I bought Williiams headers which no longer come drilled for manifold heat.
I drilled and tapped myself. I chose Williams because there is no grinding with Offy intake like with Fentons.
So, here is my question...
Because there is a slight leak in these plugs, is that good so that as heat builds in the intake some is constantly forced out? And, is the amount that may be forced out going to smell in the cab?
Or, do I seal them up?
It seems sealing them up is like trying to blow air into a balloon that will not take any more? Am I wrong on this?

Phil...

Please someone correct me about this if I am wrong however you do not need to circulate exhaust heat you are just using the exhaust to transfer the heat that's why on the exhaust system heat kit I bought from Patrick's only had one pipe (copper line) going to the intake. I also believe the exhaust heats faster than the water system at start up but they basically accomplish the same thing. The goal is to keep the intake from freezing or icing.

As for me I would not want any exhaust leaks. My water systems has a blank off that bolts under the intake where I ran water in and recirculates back to the pump. I am running Fenton not Offy.

Correct. I do not want any leaks either. Just wondering why Offy has those plugs in manifold bottom that leak. I will seal them then.
I too am running a copper line. So it is a heat transfer that is occurring?
It just seems strange to me that it would pipe off the exhaust manfold and not have any escape once it enters the intake manifold. I am not an engineer, I just don't get it..
Phil

I just did this , this week ,I used orignal Fenton headers & fenton intake . also I could not understand why anybody would use offy. because of the plugs. , ( the Fentons do not have to be welded )I don't see any advantage to use the offy.
. Got the fenton linage kit from patrick's , installed it yesterday , the foot feed to the bell crank Monday .
I've got a set of williams headers from National Chev last week . and they had the plugs for manifold heat . did not use them will later on another project . I'm using water hard piped in and out ...
See If you can send the offy. back and get fentons . also I haven't seen any offy. linage kits . If you go with the one line set up , everybody I've talked to says it will work fine ...with either manifold . I would not want any exaust in my cab . Also I did no grinding on either manifold , or the hold down washers wasn't needed ..

Nice Lucky you. I have to do a little grinding on mine to make fit. Ah its a project. I like the look of the Offenhauser but the Fenton's look cool too. I was hoping if I got the same intake and exhaust brand it would have saved me from the grinder. The important thing is to heat the manifold and have no leaks with water or exhaust.

Yes the heat transfer is occurring. Yup I know its weird. I guess you can think of it like a pot belly stove it radiates heat and there is not real circulation either.

good luck with it.

Thanks for input.

Can't send back. I'm stuck with it. I'll have it sealed up. I like the look. Just don't understand how a product can be sold like that. Even though it is designed for exhaust heat, what was the thinking with leaking plugs?

It's like having an umbrella made from window screening!
Thanks guys, Phil...

Hey wanderer, good luck with your. I just ordered the dual exhaust kit from them, less the headers and mufflers for 299.00. Kit is from headers to back including x pipe. Supposedly bolts right up to their headers. Getting excited!
Didn't want glass packs. I"ll see how it sounds open pipe but most likely going with 3 chamber manga flows...

Give a phone call to Tom Langdon @ Langdon's Stovebolt (586-739-9601) he's the 6 cyl guy. He can answer ALL your questions and he has the speed goodies.

Apparently, the manufacturer and vendors give no serious consideration regarding selling the Offenhauser intakes with leaking plugs - "let the buyer beware".

Tom Langdon will suggest water heat, which the Offenhauser intake allows to circulate from end-to-end of the intake (most other dual intakes do not allow this flow from end to end). It works very nicely, as long as the plugs are sealed.

I have also used heat transfer from copper tubes between the headers and the intake. It works very nicely and I do not need to worry about water leaks or coolant-hose breaks. I prefer two copper tubes because, my simple mind likes the symmetrical appearance.

As posted above, the exhaust-heat method provides heat immediately, but the water-heat cannot supply heat until the coolant heats up.

The pros/cons of water-heat, exhaust-heat, and the one vs two copper tube can be argued, but that will not resolve which technique is better - do what you like.

Does anyone know if JB-Weld will hold up to the heat transferred when the exhaust-heat method is used? My Offenhauser did not need to have the plugs sealed (it did not leak coolant or exhaust gases - I used both methods), so I do not have first-hand experience.

Re hot rod John,

Actually I just bought my linkage, heat plate and dual carb setup from Tom. Great guy. He even explained why he preferred the Offy, however, he didn't mention the possiblity of leakage with that product. Not his fault however.

Re Tim,

Yes, like you I'm going with manifold heat, copper also. I'm going to try the JB Weld high heat. Good to 400deg at 600psi. I think it will be fine. I'm going with 1 line. Didn't want to drill 2nd header yet. I want the quick heat. Cold here in NJ and I daily drive it. I'll post pics when setup. I already converted Toms plate with the fittings needed for copper pipe.
Phil...

Tim , Fenton also allows water to circulate from end to end .. (I'm using water , steel or copper tubed in and out .

The Offenhauser internal journal has a divider above the intake-plate; and, it has an internal passage that goes from the plate-opening to the side, and then goes from side-to-side; and then, at the other side, it turns and comes back to the other side of the divided intake hole. This is true circulation.

My Fenton intake does not have a divider above the intake-plate. The internal passages do not go to the side, then side-to-side, and then back to middle. Since there is no divider in the middle, under the plate, I think there is no full side-to-side circulation?

You can get water to go in and out of the plate on the Fenton intake, but it does circulate from end-to-end as it does on the Offenhauser.

My Fenton intake is about 5-years old and I bought the Offenhauser intake from Patrick's about 16 years ago.

Good to know TY

My 2 cents on this topic:

Neither coolant or exhaust heat provided thru tubes from Fenton headers do anything at all. Extensive testing with an infrared thermometer tells me the cylinder head warms and stabilizes intake temperature via the intake runners and this peripheral stuff is just too slow. I'm engineering a heat plate for a friend's 292 with offy 4 barrel intake that will use diesel glow plugs to perform the required task instantly and turn off as soon as heat migration is underway. That was basically the secret to the stock thermostatic system.

So, you measured no heat transferring at all through the pipes from the headers to the intake?

Interesting topic. I'm currently splitting restore time between a 49 3100 and a 72 Karmann Ghia and a common link between both is they both use a single 1-bbl carb and an intake manifold that has long runners. The Engr's of both power plants determined that the intakes be preheated via exhaust gases to get them warmed up to operating temps as quick as possible. Both for performance and economy sake....

The horizontally opposed air cooled VW's intake manifold has a cast-in heat chamber with 2 separate runners that connect to both exhaust pipes on either side of the opposed engine but it is somewhat unique it how they are plumbed. One side is plumbed directly into one sides exhaust right where it exits the head (can be cyl 2 or 4 depending upon orientation). The other side is plumbed into the muffler at a point where the exhaust exits the muffler. Basically it creates a low pressure area at this point which helps to ensure the hot exhaust gases will flow through the manifolds heat chamber. If both sides are plumbed directly at the same point on both exhaust pipes it would only produce a "pulsing" effect and not true flow, which would not provide the heat the proper way does.

Heres a pic of the a stock muffler notice the small pipe running from the manifold connection straight into the muffler. On the other side the manifold connection is directly on the pipe to head connection.

Long story short, it appears that the method used to plumb hot exhaust gases into a dual carb stovebolt manifold isn't optimum for hot gas flow between both exhaust manifold. It "may be" if one header's exhaust is at a higher pressure than the other at any gven time but then again the pulse may not be long enough to get good hot gas flow. I dunno I could be wrong and that won't be the 1st time

Anyways I could be over thinking this but I thought I'd throw it out for discussion sake
Dave

I'll rephrase. IMO they both transfer heat but its too little too late to provide any benefit. The cylinder head (of course) is the heat source and I find convection thru the intake runners happens a whole lot faster than it takes coolant to warm up or push exhaust thru a straw size tube. Most of us are familar with the symptoms of a stuck open heat riser/too much manifold heat so I believe like the stock system heat needs to shut down as soon as the manifold warms. So far it's only speculation but I have a feeling the glow plug approach may solve this issue very effectively.

Interesting ; I know nothing about glow plugs , except they get hot , What if I installed 1 on the intake , where its tapped out for the vacuum ( windshield wipers etc. } power it up with a switch that could be turned off on the dash ....when every thing gets hot turn it off .....

I'm going to install the glow plugs (probably a pair) in the heat cavity at the bottom of the intake which makes no contact with fuel. Directly in the plenum will likely result in an explosion!

I sure don't want that ...

So I sealed my plugs with Permatex multi-metal epoxy stick. Dried like a rock, can't pry it off. Good to 350deg and 3500 psi. Pressure tested today after 48 hr set, I'm good to go. At least for manifold heat.

Dave, ironically, me and a buddy at work were discussing the VW manifold today. He used to work for them as a mechanic years ago.
I originally thought about the pulse effect also, but was told its more of a heat transfer. Now I'm not an engineer, but hers a thought...

Would there be any benefit attaching one header to the heat plate and the other to a line the drops below the header, possibly the downpipe in a welded bung that lets say, enters the downpipe on an angle. Like the VW, would we then get an exhaust heat that pushes heat in, and in a sense pulls the heat out for a more tru flow? Or, am I, we over think all this!
Phil...

The amount of help available from any electrical heating device is proportionate to its electrical load in watts.
If this is 12 volt from your battery (like, to warm it up before you start it) the real cure is an auxiliary battery with a diverter charging circuit (like on R/Vs) so that the aux can be run all the way down without affecting your normal (start/run) battery.
Otherwise, when it's really cold you'll also have a dead battery.

Flow: exhaust gas will always flow from high pressure to low pressure. Heat (hot air, conduction etc.) will always flow from high temperature to low.

Thanks for your input Jeff. I was planning on throwing power to the glow plugs immediately after startup so the alternator rather than battery is doing the work but he will have a robust electrical system so preheating is an option. As I have some familiarity with your experience I would appreciate your input on the following questions:

1. Do you think coolant or exhaust circulation thru the intake after the engine is fully warmed up provides any benefit?

2. Are you aware of other applications where electrical quick heating as proposed has performed and/or failed at the task we are discussing?

Thanks.

1. Yes, when outside air temp is low, but a thermacter-controlled air cleaner (mid smog years) does very well and costs almost nothing. Downside: if original appearance is important, some surgery to hide where the snorkel enters will be needed, as well as a "stove" partially covering the exhaust manifold.
2. it seems to me that the highest (safe!) temperature keeps the electrical load low since the working cycle will be short. What I can't figure is how to insure maximum contact for conductive transfer between the bulb and the manifold parent casting. It doesn't look safe to just stuff it in a tight, bored hole, the bulb probably shouldn't flex at all. If there's an air gap (bulb doesn't touch the manifold except at the threads) transfer will drop off since there's no convection (only radiation). It could be bonded in place with one of those high-heat transfer epoxies, but how to repair if it fails? Should be easy to test using a scrap block: how hot is the other side of the sample when the bulb is lit for X seconds, etc.
Your choice of location sounds right - the mixture will wash over the heated floor and vaporize before following the vacuum signals to the individual ports.

Interesting article: Heat Riser Valves and Manifold Heat Control Devices

Thanks again for input that spurs me to find solutions. I learned a few things about thermal greases/gels that could possibly be used to fill the cavity and distribute heat uniformly. Mounting a standard block heater element instead of glow plugs in the plate might show promise as well but require 110V conversion. Hmmmm......

Thank you for the great read! After reading this article I am convinced the best heat method (for me) is the heat valve flapper method provided by original Chevy engineering. I'm lucky I found a '53-54 Corvette type dual exhaust with the integral heat chamber.

I have used the Fenton headers for 15 years on a daily driver only vehicle year 'round. My only criticism of the two little copper pipes to the bottom of a home-made heat plenum is 'I don't like the way it looks'. By reading the above article I believe that heat will be present initially and then titrated as the engine is warmed, a more ideal situation and one that may yield me another mile per gallon. Actually this could be set up as a lab experiment ala Stovebolt Mythbusters!

Copper can be easily cosmetically changed. Gunsmiths like Brownell sell blackening solution that can be wiped on. I prefer to tin it with low temperature solder which buffs up nicely.

I'll guess it's not the color of the copper pipes that he dislikes but that the loopy tubes don't look like they belong there. I like to call it a "Polish supercharger"

Cosmo, please share differences after switching to the Corvette manifold. IMO you're gonna see way better cold engine driveability and zero loss of performance wide open.

I'm using 5/16 zinc coated steel for water heat ,

Polish Super Charger, and lead tin chrome. Now I am a happy camper...:)

You know, the best thing about these forums is how many have such different opinions. That's what makes it so fun. The way some don't like the copper look and others do. There are ones who want bone stock, the way it came new. There are some who want or get creative.
Some get annoyed when others hijack a post, me, I enjoy all the input as it still generally pertains to questions asked, and, answered.
Me, I'm going with manifold heat. I kinda like the copper look. I am going to have one input going to the bottom plate from one Williams header. And the other line I am going to run a little longer and tap into a 45degree welded bung about 1foot below the collector into the exhaust following this theory.

Flow: exhaust gas will always flow from high pressure to low pressure. Heat (hot air, conduction etc.) will always flow from high temperature to low. As posted by panic.

In this fashion I hope to achieve an in and out heat from the exhaust . I will post pics when I am done. I have the dual carbs from Tom, the Offy intake, Williams headers and the dual exhaust kit for those headers. I should be done sometime around May 5th. Including my swapping out my 216 for a 235. Gettin excited!
Sadly, the 216 is awesome, just cracked block and leaking coolant. Even after good JB weld fix. Phil...