I searched through the archives but couldn't find anything that satisfied my quest.
I'm getting ready to pop my intake manifold (cast iron high rise) in order to install a set of Rhoads lifters in it and maybe some full roller rockers. My question is - can I block off my crossover passage completely and still have a divorce choke that works?

As it is now, it opens a tad too early (in my opinion) and when the engine touches the 200 degree mark it starts to run poorly..the loss of power is noticeable.
At the very least I was going to include a restrictor plate into the intake gasket, but I could swear I read somewhere that with a cast iron intake I could block the passage off completely and still have a functioning divorced choke.

P.S. I live in a relatively warm climate.

"can I block off my crossover passage completely and still have a divorce choke that works?"
Been there done that, gave up. The divorced choke requires more heat than it will get with the cross over blocked so you will have the choke overchoking the engine for miles before the choke will come open.
The restrictor plate in the cross over may be a good comprimise.

As stated dont block it,bad move for street application,but restictor plate may work out ok.

Also,run an oil shield under intake if it doesnt already have one to lower intake temp to help keep power up when motor is heated up.

Lastly ,200 deg isnt that hot and the power should not drop that noticeably at 200 deg,maybe at 220 & above on these older design motors but not that much at 200 deg F IMHO. Is your motor possibly getting tired and looses comp when hot or it needs better tuning and is possibly running rich A rich mix can be ok with cold or semi warmed up motor but when heated up to full op temp at 200 thats when an over rich mix could cause power to drop off.

Scott

Thanks for the perspectives thus far. The valley baffle shield is one I thought of and it is a very good suggestion because it will keep the overall temperature of the manifold down - somewhat, whereas the crossover is more focused under the plenum.
I'm even thinking of purchasing a solid gasket or one with a block off, and drilling that out to a size smaller then that of the "restrictor" versions.

A couple of things causes me to suspect the manifold is getting too hot. My engine mixture was good with the previous quadrajet (light tan plugs), but while I was tweaking and improving the carb, I fractured the darn casting by peening the check ball seat too hard. So I went ahead and purchased one from Sean Murphy, but I've yet to check the plugs since. Still, it wouldn't make a difference since the situation was the same with the other carb.

Another thing is, the engine does have a very slight valve rattle--at times. Given all of the above, I suspect that because my mixture is so good, the additional heat is causing the problems I'm experiencing...very slight and sporadic detonation and perhaps vapor locking(?).

I've used a divorced choke stove very successfully on my RPM manifold/Q-jet setup. I just epoxied it to the manifold, made an appropriate linkage, and it worked great. The choke, once it is about half open, has very little effect at low throttle openings.

Another thought/question, do you have headers? Stock exhaust with the heat riser thing? So long since I had that piece in my hands I can't recall its proper name but back in the day the right side exhaust manifold had a valve in it that was closed when the engine was cold and forced exhaust up thru that heat riser duct.
The generic, nice drivability route is to have that functioning and when the engine is cold that valve forces exhasut thru the duct, carb & divorced choke all warm up nicly.
The Hot Rod approach is nuke that valve (or install headers) and not much exhaust goes up thru the intake manifolds duct, or block the duct.
The Edelbrock manifold have a casting defect that cracks & opens up when hot and gets oil from the valley into the heat duct, makes them burn oil like crazy which is why I blocked the heat riser and can not make a divorced choke work. It is frustrating to me as I would like to run one as the electric choke of the Edlebrock carb will not clear the Cowl Induction air cleaner when on a 454 (it will on a 350 as you can use a spacer to raise the air cleaner up from the carb. Proper fix for mine is a Holly or Quadrajet

Up here in cold weather country you know really fast when your crossover gets blocked up with carbon. Age can put enough carbon in the crossover that it blocks it, and cold weather drivability gets really bad. A cast iron manifold needs the crossover to function properly. Interestingly, aluminum manifolds don't need it because aluminum has far superior heat transfer and the choke functions just fine without the crossover.

Another thought/question, do you have headers? Stock exhaust with the heat riser thing? So long since I had that piece in my hands I can't recall its proper name


I believe its called a "heat riser". I have headers and plan to stay with them.

Here's some eye candy...

http://pages.sbcglobal.net/vonik/_uimages/chevelleengineresized.jpg

Interestingly, aluminum manifolds don't need it because aluminum has far superior heat transfer and the choke functions just fine without the crossover.


That may be what I read before. I'm actually not sure if he had specified the type of manifold he had.

Up here in cold weather country you know really fast when your crossover gets blocked up with carbon. Age can put enough carbon in the crossover that it blocks it, and cold weather drivability gets really bad. A cast iron manifold needs the crossover to function properly. Interestingly, aluminum manifolds don't need it because aluminum has far superior heat transfer and the choke functions just fine without the crossover.

Interesting! My deal, I have an Edelbrock manifold & headers, as the manifold has a casting flaw that allows oil into the crossover I have it blocked. Having recently made the 350/454 conversion to get the air cleaner/cowl induction fit proper I had to toss a spacer that had been on top of the carb. Now the CI aircleaner hit the Edelbrock choke so I thought Iwas going to be clever and use a divorced choke. I made an arm for the choke shaft and a link from 1/8" rod, all fitted up nice, ran the engine for 3 or 4 miniutes and the choke had harly moved so I declared it to not be receiving sufficent heat and removed the setup (curently have no choke and contemplating options) and your indicating I should have let it run longer??

Interesting! My deal, I have an Edelbrock manifold & headers, as the manifold has a casting flaw that allows oil into the crossover I have it blocked. Having recently made the 350/454 conversion to get the air cleaner/cowl induction fit proper I had to toss a spacer that had been on top of the carb. Now the CI aircleaner hit the Edelbrock choke so I thought Iwas going to be clever and use a divorced choke. I made an arm for the choke shaft and a link from 1/8" rod, all fitted up nice, ran the engine for 3 or 4 miniutes and the choke had harly moved so I declared it to not be receiving sufficent heat and removed the setup (curently have no choke and contemplating options) and your indicating I should have let it run longer??

Three or four minutes is not nearly enough time for the engine to heat up sufficiently to greatly affect the choke.

My electric choke would have been 3/4 open in that time