it'sallGood

In a Hemmings mag Dec 2016 I read this article about 66 442 Lancing Lightning that included this "the intake featured a pair of clever exhaust heat-riser block-offs, one on either side of the center carb. The owner could unscrew the block-offs and rotate them 90 degrees, changing from street to strip without disassembling the engine". How does this work?

dbater

Only on the L69 tri carb intake can you remove the heat riser block off plates and reposition to block the flow of exhaust beneath the center carb.

it'sallGood

I have the L69 option 400. Any reason not to leave the block offs in that position?

dbater

Depends on the climate, cold weather the heated air beneath the manifold aids in cold starts,choke operation and overall combustion. But if you find the engine will be running hot for most of the time you will be fine with them in the closed position.

joe_padavano

Yeah, OK, this one unfortunately didn't make it to production.

dbater

Sorry, should have added that I was aware of…. Looks like a valuable piece of history!

joe_padavano

Unfortunately not one of the pieces in my collection, but I know where one is.

66-3X2 442

Yes we do.

it'sallGood

So my curiosity got to me and as the article in Hemmings described for racing reinstall the block offs quarter turn to eliminate heating fuel to center carb. When I pulled my block offs noting no gasket and very little gasket maker if any which makes sense that this could be done on a race day and put back easily. Nope. Luckily I got some high heat gasket maker and two sets gaskets on hand. After some clean up I installed a gasket and a bit of Gasket maker on an let marinade over night. Driver side block off leaks. So disassembled and cleaning up a bit more now. Question is metal to metal? Use a gasket? use gasket maker? Just curious to see what works for you all since the article suggest quick change metal to metal.

66-3X2 442

That is a machined surface with no gaskets or sealer just like the exhaust manifolds. You can file the intake and block offs if there is pitting and use some high heat sealer.

it'sallGood

sounds right I appreciate the answer, it makes the most sense of the options

Jims48

I have a 66 442 with tri power that has the heat riser block offs. I understand you can change them to cut off heat to the intake on the middle carb. What is the reason that change should be made? How does that impact performance? I get questions from people all the time about those riser block off and I would like to be able to respond with an intelligent answer
Thanks
Jim

joe_padavano

Cooler intake air is denser, which makes more power. The exhaust crossover under the carb is intended to warm the incoming air during cold engine operation to promote fuel atomization. Once the engine is warm, it really isn't needed. Blocking off the crossover is primarily used by drag racers who need the last few hundredths of a second in their elapsed times. Blocking the crossover to lower inlet air temp is worthless unless you also rejet the carb to take advantage of the denser inlet air. In any case, you are unlikely to feel any difference on the street.

66-3X2 442

Tell them that's where you hide your drugs, the cops never look in there. Seriously that was good thinking by the Olds engineers back then. Just as Joe said the colder the air charge the more HP.

Koda

"Uh, dispatch, the engine smells like a meth lab, but I can't find it."

Jims48

Thank you Joe for a very good explanation. I can at least explain this to anyone who asks.
JIm

Vintage Chief

Rallye469

I can see the block offs working for about 10 minutes at the track(which I assume is what they were made for).
But after that, I imagine the manifold gets heat soaked and it wouldn’t matter much.

Am I off with my thinking?

rectifier

I'm afraid to try to loosen the hold down bolts for fear of them breaking off ! Besides,I drive my junk year 'round as long as there is no snow or rain.

dbater

Broken bolts and frozen block off plates, it's a job best left for when you have the manifold on the bench.