Polara_68

I'm wondering if it would be of benefit to partially block
the heat crossover passages of a cast-iron 4-bbl intake
on an LA 318?

By partially block, I mean to install, in each side of the passage,
a block off plate that has a 1/4" to 5/16" hole in it,
as is done on some other "Brand X" smallblock V8's..

I know that keeping the intake charge cooler helps make more power,
yet the heat crossover is needed for driveability on a street-driven car,
especially with the cold weather we get around here, and this car
does get driven in colder (Fall & Spring) weather from time to time
(and even occasionally in the frigid Winter).
But most of it's usage occurs in the warmer Summer months.

The engine in question runs well at present, cold or warm,
and seems to warm up & reach operating temperature fairly quickly
no matter how cold the weather
(I do not know the temp rating of the present thermostat).
As for the heat-riser valve in the exhaust manifold - it appears
to be inoperative -while quick to warm up, it does not seem to run
excessively hot in the summer, so I presume the heat-riser valve
is in the Open (or at least mostly open) position.
(The heat-riser valve in stock exhaust manifolds is thermostatically controlled
to be open when the engine is warm and closed when the engine is cold -
when it's closed it diverts the exhaust from the passenger side mainfold
thru the heat crossover in the intake -
but there is always a portion of the hot exhaust gasses passing thru
the crossover in the intake, even when the heat-riser valve is open).
I will make certain the heat-riser valve is completely Open
when I drop the Y-pipe to install the dual exhaust.

I will be installing a carb with an electric choke, so manifold heat
will not be needed to open the choke.

My theory is that limiting, but not totally eliminating,
the flow of hot exhaust gasses thru the intake crossover may produce
a little more power (when the engine is warm), without harming cold-weather driveabilty..
cold-weather driveabilty is important to me (and it does get cold around here..)

I realize the power increase may be small, but every little bit helps lol..

I'm seeking your thoughts (pro or con) on the viability
and effectiveness of this idea, and also hoping to hear from folks
as to the best methods to fabricate/install block-off plates like these
(fail-safe methods that will not lead to vacuum leaks, and/or will not
result in the block-off plates coming loose eventually).

I know we have some very knowledgeable
and experienced Mopar Maestros on here,
and I'm looking forward to your thoughts on this..

thanks!

deadkelly

the gain maybe small but i block mine off . but all so it never gets as cold over here . yeah a small hole maybe a good compromise good luck .

scotts74birds

Yeah, no one ever froze to death in oz. For the absoluutely small gain that would be found by that, not worth the time or drivability. Guess I'd leave it for now. Bigger gains to be found elsewhere.

deadkelly

couldn'd you use a felpro blocked off gasket & drill a small hole in that ? there f all work in that ?

theomahamoparguy

well, if your heatriser valve in the exhaust is mostly stuck open or the bimettalic spring is old causing the heatriser valve to stay open than i feel the crossover passage is about probably only about 40% -50% effective. I mean its working yes (to put some heat in the bottom of the manifold) but the majority of the ehaust gasses are going out the tail pipe. It would be kinda like removing the heatriser valve alltogether. This is how my car is. no heatriser valve but the crossover passage is open. I live in nebraska and do drive it in the winter, have NO problems. I bet if I blocked the crossover I probably wouldn't have any problems either. I use a manual choke. These are just my thoughts. I never did like the heatriser because it is restrictive in the exaust passage, and it really sucks when they stuck shut.