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Discussion Starter · #1 ·
I remember seeing something about adding a crossover line to the rear ports of the manifold for improved cooling. I cant remember the engine in question, maybe BBF, and I cant find much on search. I have the manifold off of my 455 right now, so now is the time to drill/tap if it will help. Is a crossover necessary/helpful on an Olds? Or should I not waste my time?

I also thought if I do a crossover, I could add a valve that I could open when I put the boat in the water, and it would help burp the air out of the system. Then close it obviously as soon as water reaches the valve. Overkill?
 

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Jet boat service
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I did alot of this in my circle track days on small block chevys. We drilled and tapped the rear of the intake over the water ports on the head and ran the -4 lines up to the T stat housing and tapped in there. Self bleeding. The idea was to get the air pockets out of the heads at the rear of the engine so the individual cylinder temps were more likley to be equal . Or , as close as possible anyway.. We even drilled the blocks in the center , just under the head deck and ran inlet water to this point where the exhaust valves are next to each other on the siamesed head of the SBC. Jim :D
 

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Sit N' Spin
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I always wondered if it would work better to have an intake made with the T-stat crossover relocated to the rear of the block so that the water would flow from front to rear. One would think that with this design the water flowing from one end of the block to the other would simply push the airbubbles out with it.

Wouldn't be practical in an auto application (would be a bitch to get to unless it was a sidewinder on a front wheel drive) but that wouldn't be a problem in a boat.

Whaddya think Jim? Think I should flip my intake manifold around and try it out? :D :D
 

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E-7 Sheepdog (ret)
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I remember seeing something about adding a crossover line to the rear ports of the manifold for improved cooling. I cant remember the engine in question, maybe BBF, and I cant find much on search. I have the manifold off of my 455 right now, so now is the time to drill/tap if it will help. Is a crossover necessary/helpful on an Olds? Or should I not waste my time?

I also thought if I do a crossover, I could add a valve that I could open when I put the boat in the water, and it would help burp the air out of the system. Then close it obviously as soon as water reaches the valve. Overkill?
Necissary, no, the engines have run perfectly fine 40 and 50 years without it.

Helpful, I think so.

There is supposedly a "dead spot" in the coolant flow at the top rear of the engines since water flows in the front mid-block, flows up all across the block, into the heads at the same time all along their length, and then flows fwd thru the heads.
I say "supposedly" because I doubt much real, tested evidence exists of this, BUT, it makes plenty of sense, and seems reasonable, it "passes the smell test".
My Edelbrock Performer RPM Air Gap manifold for my Chevy came with threaded ports in the front and rear crossovers at the corners of the manifiold described this as their reason and purpose, so I headed to the hardware store for hardware and put 3/8" lines threre.

I know people from threads on herer who run an overboard dump line from the back of the heads instead of piping them fwd. to the front crossover. Same cat, different skinning method.

Did it do any good? No way to tell.
It did not "fix" a "problem" per se, becasue I had no "problem".

Engine ran happilly in stock trim from 1978 to 2004.
Engine has run happilly since 2004 after the modification.

Did it do any harm? No.
Was it difficult? Not a bit.

I think valving stuffed in there is an overkill, yes. An un-needed complication that I did not, and would not, bother with.

Best of luck.
 

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Discussion Starter · #5 ·
Sounds like the best setup may be similar to Lowriders - except instead of bringing the rear manifold water forward, the rear manifold could dump into the left riser, and the front manifold could feed the right riser? Or might there be pressure differences, enough to mess with flow?

I can understand the dead spot idea. I guess I never thought much about the actual direction that the cooling water flows in the block, but you are right that there is nothing stopping it from looping from front inlet, up the frontmost left and right cylinder jackets, and right back out from the tstat housing. So the entire rear 6 cylinders could be "dead spots" technically, and the further rear, the worse probably. A front outlet and rear outlet makes a lot of sense from that standpoint. I wonder if there are pressure/flow differences enough that may cause an issue if it was plumbed that way.
 

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E-7 Sheepdog (ret)
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Is this even an issue with an open cooling system?
I sincerely doubt it, but, some folks think they are "preventing" one.

Maybe, maybe not, no way to know for certain.
 

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What if you drilled and taped your manifold at one of the rear crossovers and installed a temp gauge? That should give a idea of temp diff in the manifold front to rear. If temp is lower by quite a bit would indicate air pocket (try to read steam) just a idea??? What you think?:(:(
 

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Captain Rehab
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I'm building a stroker SBC myself and have the Edelbrock Performer RPM Air Gap as well and was considering blocking off T-stat water outlet and plumbing from the front corner water outlets to a tee in the rear water outlets and then to dump. Same theory in effect,just taking the T-stat exit out of the equation.Comments?

Thanks
 

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Sit N' Spin
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If you're gonna do it that way, you'd be better off not joining together with a T and running 2 dumps.
 

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Captain Rehab
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That's what I'm saying. Block off the t-stat outlet and on the front water outlets on each corner,come out with a 90* elbow,run outlet line to rear of engine,have a tee fitting screwed into rear water outlet and off it to dump.This setup on each side.The tee screwed into rear port.
 

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Jet boat service
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I don't think that this is really an issue for jet boaters. In the circle track world we were always trying to eliminate the possibility of detonation on very high compression motors. At the end of a 30 lap main event we could be running at 220 or better. Not so with jet boats. Jim ;)
 
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