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L20B with U67 head


edekalil

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I have an L20B motor and a U67 head with out any emissions junk casted into it all done up at the machine shop from way back with a mild cam I need to assemble befor I die. After looking here recently at heads I noticed this head does not have the ports for water to go through a intake manifold.

 

IMG_0890.jpg

 

I'm sure all will be fine, since it came off an L20B ( probably off an older motor befor the emissions castings like the head that was on the motor when I got it )

 

I have two carb set ups to choose from to use on it, one is a Mikuni 44ppi I think it's called set up the other is the flat top su style carbs. I guess because this head came from a truck with an L20B not having the ports open for water flow to the intake manifold should not be any problem.

 

Any in put or suggestions please chime in.

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It's definitely not a problem. If you're using the dual side draft amnifold, there are no provisions for water anyway.

 

Back in "the day", we used to tap the water passages and plug them with pipe plugs, even on motors with stock intake manifolds, but then we ran one on the dyno with and without the water cooled intake, and guess what? The cooled intake dyno run made more power. The circulating water does not heat the manifold as was previously assumed, but it actually cools it from the heat of the exhaust directly beneath it.

 

Either way, you should probably build or buy some sort of a heat shield for the dual carb setup. Fuel boils and hot air entering the carbs causes tuning problems, so anything you can do to eliminate or insulate from the heat will be a good thing.

 

I have a template for an old Nissan Motorsports heat shield somewhere in my files. It was originally made for the Datsun Comp (Nissan Motorsports) intake manifold, but works with just about any dual carb setup. If I can find it, I'll take a pic and post it up. We built the shield out of aluminum and then sandwiched in a sheet of asbestos between another sheet of aluminum, then riveted it all together. You can still buy the sheets, though not through Mikuni anymore. If you search for ceramic heat barrier, you will find it.

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I must have an odd setup. My su manifold has the water passages. I used to have an l20b with u67 and flattops, my new 510 has an l20b with w58, so the water passages are in use now. It seems more punchy on the low end, but a little less top end than the old setup. The biggest thing is it idles much more stably with the water cooling. I’ve never had a heat shield on mine, only time I ever had problems was with the u67, when it was 90+ degrees out, heavy traffic, and getting caught at too many lights...it would stumble and shudder for a block or two, then run fine.

 

Matt, I hope you do find that template, I’d like to have a heat shield if only for shits and giggles.

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If dual sidedrafts mikuni or weber set up you don't want the holes in the head. This will be perfect.

 

YOu have a head that had the mated intake manifold and exhaust that was bolted together and used a heat riser flap to heat the carb so the carb(s) don't freeze up.  earlier model cars used a watrer line to heat the intake via a water port.

 

SUs were water heated also and came as such routing of pipes and hoses with those manifolds.. If in a warmer climates one can plug these up if needed

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The coolant flow warms the intake air when cold or in severe cold but cools it by extracting radiant heat from the nearby exhaust or when the engine is warmed up. Basically it keeps the intake air in a narrower controlled temp range so it runs and performs more predictably. 

 

The '75-'77 L20B came with the U67 head. On these engines the exhaust and the intakes are joined together so that hot exhaust can blow up on the underside of the intake to help evaporate the gas falling down from the carb directly above it. There is a bi metallic spring that unwinds with heat and closes a flap gate so the amount of heat can be controlled somewhat like the coil on the choke heater. It was a terrible idea as all other L series used the water cooled/heated intakes and this system was heat only and the parts needed to be contained or the valve would rust into one position or stick. You can't run a header or L16 manifold without addressing the opening in the bottom of the intake. Also there is now no warming of the intake air nor cooling in hot weather.

 

fId8YzE.jpg

 

I had this on my '76. I replaced the intake with a '79 that does have the water cooling and just drilled 3/8" holes in the head and added the extra piping at the thermostat by pass. The exhaust was changed to an L16. You can see the coil spring in that loop of EGR tube from exhaust to intake. Naturally it was rusted solid.

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If you run the SU's drill the holes that cool the manifold.I had problems without the manifold being cooled in the hotter months.Sitting at a light or in a drive through food place it would get too hot and run like shit until i got moving for a couple of minutes.Drilling the head cured the problem.

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