The Dutra duals touch the bottom of the Offy intake on my slant. I suspect this contributes to the heat soak issues. The bottom of the intake is a cooling/heating plenum to be plumbed into the cooling system.

There are several fixes I have considered:
1. Grind the exhaust flange down so it does not touch.
2. Plumb the coolant into the manifold.
3. Machine the coolant plenum off the bottom of the intake.
4. Fashion heat shields for the exhaust manifolds. My Daughter's Civic has a shield that looks like it might work for one of them. This would require one or both clearance options above.

Thoughts on this?
1.Would coolant at 180 degrees serve to keep the intake cooler than when dry?
2. Would the space created by removing the plenum serve cooling purposes more?
3. Maybe the evenness of temp with coolant would be a good thing.
4. Recommendations for plumbing same? Where would one tap into coolant, both to and from? Heater core delivery hose? Seems it would flow only when heater was running. Maybe in from delivery side of heater and back on block side of heater valve on fender.
5. This is dry flow EFI. What effect does runner temp have on fueling? The air intake temp sensor is before the TB.

Any of the above will require removal and extensive clearance machining of some kind. Thanks for your thoughts. This is a Fall project. I am just beginning to wrap my mind around the project.

Sam

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It is my understanding that the Offy 4-bbl intake is designed to bolt up to the original heat box on the stock exhaust manifold (at least mine is - you can see old soot in it), as opposed to the Clifford 4-bbl intake which is designed to have an optional coolant heated chamber bolted to the underside of the plenum.


The simple soultion would be to grind away the bottom part of the Offy manifold, but you have to be certain about keeping it for EFI use, because absense of the heated plenum will make the intake less suitable for use with a carburetor. The effect of a heat shield could help to some degree locally, but would not be very great, as long as the intake and exhaust runners are fixed with the same bolts to the same side of the cyl. head.

Olaf

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Aspenized

Mine is different. The bottom plenum goes all the across and has NPT taps for coolant.

Sam

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My clifford manifold has the water passage under it. All the offy's I've seen look like what Olaf posted, including the 2x1

I had the same problem as you with my dual dutra duals and clifford intake. I did a combo of both, grind the flange and grind the water passage. Didn't think I'd ever use the water passage. And yes, they were meant to be t'd into the heater core. Not sure what was meant to be done with the water control valve in that scenario.

Sam, could your intake have been modified by a previous owner? Aluminum welds are easy to grind and polish so you don't notice them at all, but there should be traces of welding internally, if it has been modified. Does your Offy have the part number 5270? It is visible on the photo.

BTW: Did Offenhauser ever make special marine versions of this manifold? I would think that aluminum would be a bad choice of material to use in salt water because of corrosion, but it could explain the coolant heating of the intake air, especially when combined with a 'wet' marine version exhaust manifold. If so, you may have a very rare manifold, and one that may be quite valuable! Put away your grinder for now!

Olaf

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Aspenized

Sam, are you sure you have an Offie intake, and not a Clifford? Can you post a picture?

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I'm not sure. I thought it was Offy because Clifford was so hard to get when I was doing this EFI. There is a heat shield over it now, so photos will be hard. I suspect you are right. There are bosses for injectors cast into it. Questions are the same either way. Is running coolant through it useful?

I have a vague recollection that maybe Lou procured this manifold, along with one for him. I remember machining his, but cannot recall where they came from.

Sam

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Offy does not have bosses stock. Sounds more and more Clifford.

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66 Lil' Red Piggie Valiant (Mater Crusher) - Thanks Zilla!!!!! 72 Demon (Number 1 Son's)

That is a Clifford 4bbl with water heat manifold. 45-4500WH PN, IIRC. Offy never made anything with built in water passages.

Yeah, I would grind down the exh manifold flanges where they touch. However, I don't think that's your heat soak issue. The int/exh runners are close or touching right at the head, and there is a ton of iron in those DD exh manifolds. 180 stat will help, I would bet. I have not tried that yet on my car.

I am pretty confident that my heat soak issue is that SOME of the INJECTORS get overheated and give inconsistent pulse widths. This will screw up idle mixture more than at higher duty cycles. Likely the case for you too.

Lou

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Home of Slant6-powered fun machines since 1988

There are a couple of contributing factors that can lead to "vapor-lock" at the injectors on inline engines like slant six (or Jeep 4.0L).

First is ambient heat from the exhaust manifold- you can make heat shields for the intake as well as the injectors.(one fix for Jeeps was to cut a piece of foil/paper hose for thermal-heated air cleaner & fit it around each injector). The newer plastic body injectors seem to do better than the older metal types (like bosch). If you have an electric radiator fan you could devise an "after run" feaure to blow air during hot soak.

A second possible cause is loss of fuel pressure. Most oem fuel systems are designed to maintain pressure for quite awhile after shutdown- typically I like to see 20+ psi after 30 minutes (specs will vary). If your regulator or fuel pump check valve is letting pressure bleed off quickly then it's much easier to boil fuel in the rail & inj.

You want to isolate your intake manifold from the exhaust. The coolant passages in the clifford are there to provide warm-up heat to a carbureted engine to avoid "carb icing", where the fuel can't vaporize properly. I don't think it would provide any benefit to a MPFI setup- it would heat the air during normal ops. Remember, engine coolant temps spike during hot soak as well.

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63 Valiant Wagon
225 - 4 bbl

On my 83 D150 I went from a 195 to 160 thermo.
I have not noticed any downsides. Summer time driving, I have full time hot water heat to the carb base using the head to water pump by pass..

However as you are running a dry intake manifold, I cannot think of any reason to ad heat to the intake runners.

Sam, I liked your idea of wrapping the Dutras in header tape, and I would certainly grind the Dutra flanges so they don't touch the intake manifold.

I lieu of tape there are also high temp coatings that can be applied to the Dutras to contain heat.

Tightly wrapping heat woven tape on cast headers or exhaust manifolds and then clamping down tightly with some sort of exhaust clamp can lead to cracking. A wrap just tight enough to prevent it from falling off under use is best. Double wrap it and some snug hose clamps or such.

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Tom
'86 Alfa Romeo Spider, red "Dinsdale"
'10 Corvette, red "" (no name yet)
'95 Ferrari 348, red "Zoom"
'04 Maserati, black "Evil"
'05 Aston Martin DB9, green "Bond, Treasury bond."
'82 Dodge W150 Power Ram, yellow "E. Valdez"

Offy info: Doug at AAAMarine, who has been trading Offenhauser since the late '50s, have had the same question put before him earlier. He confirms that no special marine version of the #5270 was made.

BTW, Welcome spacecommander!

Olaf

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Aspenized

If I measured the intake manifold in operation with an infra-red gun, the temp there might tell me if coolant would help. If it measures higher than coolant temp by maybe 50 or more, coolant may help pull heat away as well as even out temp.

I will pursue all of these later in the Fall as driving season winds down.

Does the water flow from the water pump through the short bi pass to the head? I wonder it there is room in there to get fittings to route plumbing to the manifold. For what it is worth, the 86 Buick this TB came off of had MPI and coolant passage through the TB. I have never plumbed that.

Sam

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Coolant passages the TB assembly are there to provide heat to prevent ice-up during low temp/ hi humidity operation. The design engineers were trying to insure good engine running during all possible weather conditions (from Mexico to Alaska). Some car makers used TB heating(GM & many Japanese cars), while others didn't (such as Chrysler or Ford)

AFAIK coolant flow is into the pump through the bypass, heater, & lower radiator hoses. Flow is out through the mounting passage into the block.

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63 Valiant Wagon
225 - 4 bbl