YOU have a CRACKED INTAKE MANIFOLD!

[@TheLM1961]

Jim, you make very good educational videos about the GMC MH. I bought a 73 four years ago, which I completely rebuilt, and now I can also say it, it is absolutely necessary to block the crossover, because the heat break, but also as can be seen in your earlier video, the heat at the bottom of the turkey tray burns the oil, the burnt oil coal can clog the channels and the oil pump and destroy the engine, I have learned, and saved my engine by doing that, many thanks.

[@motorhomerehabranch]

I’m glad you acted on it, please pass the word…. I feel like the telephone operator at the CDC!

[@ryanjones7468]

Thank you for the great and informative video! I have watched older videos which you recommended the block offs but never really understood why until now. I don’t have a gmc motor home yet but it is one of my life goals for the future. I remember being a kid in the late 70’s and early 80’s and seeing them and thinking they looked so futuristic. Just curious would this apply to other Oldsmobile built v8’s from the 70’s and 80’s or just the toronado/motorhome drive line. Thanks from up here in Canada.

[@arielsquare4]

Jim do we reuse the turkey tray? I did a toronado and did not reuse it, worked fine

[@motorhomerehabranch]

Pitch the turkey tray. No need besides you are using the fiber gasket

[@markcollins457]

Are there any down sides to blocking off the cross over.

[@motorhomerehabranch]

Not that I have seen

[@blakenorman4822]

my 85 la 318 2 barrel kept fouling spark plugs in a day, wouldnt start or run, put new plugs in several times and it would fire right up and run a day or so and then foul out again and again, put 2 new 2 barells on too, no help, finally put new 4 barrel intake and new holley 600 on and has been running strong for the last 6 months now, crazy stuff, could have been my factory intake was just clogged up or cracked?

[@motorhomerehabranch]

Very possible. Vacuum at idle would be a giveaway

[@guineapigzed]

Then the exhaust needs a balance pipe?

[@fwaynedavis]

No. This is way too restrictive and small to do that. It was solely to provide heat to the carburetor to facilitate good warmup, especially in cooler climates. It's the same on most vehicles of the period. Any respectable engine builder has always eliminated this crossover as its drawbacks severely outweigh the need to take a little longer to warm up an engine till the idle is smooth. Also there was a flapper on most factory exhaust manifolds that closed when cold (im not sure if the GMC had this). It forced hot exhaust to traverse this small channel to rapidly heat up the carb and fuel. When new this worked OK, and the flapper would open after a short warmup period and all was good. You don't "need" these at all. Just baby the warmup a bit, then let it breath as cool as possible. If you are using fuel injection this is an absolute must to block this off.

[@guineapigzed]

@@fwaynedavisthanks, That wasn’t my question. The lecture said it was to balance the exhaust.

[@wilfredvanvalkenburgh2874]

The stock GMC motorhome does not need an exhaust balance pipe since it is a single pipe design. An H pipe would help a dual exhaust system, but the GMC "Y"s off to a single pipe system.

[@motorhomerehabranch]

You have that in the “Y” pipe. Mufflers are involved so don’t backfire…. the mufflers may blow out

[@motorhomerehabranch]

@@wilfredvanvalkenburgh2874you’ve got it man, thanks