I've recently purchased a 1980 D-150 pickup truck with a slant and I'd like to put the super six setup on it. I'm new to the slant six world, so bear with my dumb questions.

. Anyway, I'm not sure if I need to replace my exhaust manifold. Its a standard manifold, but, it does not have the "power valve" with the counter balance. Someone took it off and just plugged the holes where the shaft for the flapper was. What is the purpose of this valve? The Haynes manual says it should open when the engine is revved. Does it help keep the carb warm? Do I need to put it back on for any reason?

The previous owner(s) also cut off the smaller diamter exhaust pipe about 2 inches from the exhaust manifold mounting flange and then welded on a 2" diamter pipe which runs all the way out to the tail pipe. Is this sufficient to ge the benefits of the 2 barrel carb and manifold?

Also the emissions stuff has been removed so I don't have to worry about that.

I've found a couple people who have the super six setups for sale but if anyone else out there is selling them, please let me know.

Thanks for reading,
S

The exhaust manifolds are the same with either set up. The heat riser is fine if you live in a cold climate and need extra carb heat. I took mine out when I switched to an aluminum intake and electric fan. It warms up very quick with out it. The coldest it gets here in the winter (Pacific Northwest) is 10 degrees.

It would be better to run 2 1/4" exhaust all the way back. Many trucks and vans came with 2 1/4 head pipe.

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Aggressive Ted

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74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

I have Dutra Duals, and no heat riser on the rear modified manifold. I live in south Texas, so its not an issue.
You will probably be fine without it.

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"Ja, Ich fahre ein altes auto."
'78 Volare 225
'67 Charger 318

The exhaust manifold heat riser valve does not affect the warmup of the engine, and removing the valve plate does not leave the intake unheated. The heat riser valve is not for "extra carb heat"; in fact it's not for carb heat at all. That's the job of the thermostatic air cleaner. The heat riser valve is to regulate the temperature of the intake manifold floor. With the valve, cold and hot fuel economy and driveability are going to be better. With the valve plate removed, cold and hot fuel economy and driveability are going to be poorer. While the cold driveability difference is only really ugly and obvious in very cold conditions, and the hot driveability difference is only really ugly and obvious in very hot conditions, these differences are present, and the fuel economy difference is significant, in all conditions.

Note that "intake connected to exhaust, no valve plate installed" is not the same case as "intake not connected to exhaust".

If you decide to replace the manifolds for whatever reason, it is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions. Also get one of the electric choke kits.

Get rid of the Haynes manual; if it hasn't already steered you wrong with incorrect information, it's only a matter of time. Get a factory service manual instead.

Exhaust pipe diameter: If you're going to rework the exhaust, use a 2¼" headpipe. If not, the present setup will do until you're ready to replace it.

"All the emission stuff has been removed" could easily mean some beneficial systems and components (such as the heat riser valve) have been disabled or mutilated.

Exhaust manifolds themselves: Same for 1bbl vs. 2bbl setup.

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