Rear Crossover on intake manifold
 

Anyone ever put a rear crossover tube on the back of the intake manifold to help eliminate hot spots in the cooling system (heads) and have a more even water temp. You would run a tube from one side to the other with a T in the middle and run a small discharge hose overboard.

Mike

I ran tubes from the rear passages up to the front passages. I'd think your's would work better. Just didn't want to add any dump ports in the hull.

Can't view you pic, but I get the idea. I think running a dump would help with high water pressure also. I peg the gauge at wot.

Nice lines:D

I have run mine from the rear to the front 3/8 lines work well. Others I have known to just dump them over board. Dyno testing proved without mild and up built BBCs didnt last long without the mod.

I agree with it lowering the water pressure. I did not have a pressure problem, so it wasn't a factor on my setup. I know of 1 member who did dump the rear jackets into the exhaust tubes at the transom for a cleaner look and to control his pressure.

My current boat also pegged the WP gauge at 3500rpm. Stock 502MPI's. Easiest fix was the Merc relief valves.

OK - you guys confused me, would you do this mod to lower water pressure or reduce temperature hot spots in the heads? Uneven temps would be my concern.

Do it for both. Thats my idea anyway.

We have been doing that for years. I usually run # 8 Aeroquip hose from front to rear. As discussed earlier this mod works very well for equalizing chamber temps. It will never hurt you.:cool:

On my Scarab I ran a #12 from the rear to the front T ing into the front then going to the headers.

My Hustler Whipples came with a 1/4 line dumping overboard.

I guess its releaving steam/air pockets.

Scarab pick ya kinda can see the #12 T fitting on the front

I also have done for some customers as Dean is doing. The -8 line works well. Really cools the back of head down quite a bit. I dont dump them over board, I do that using a blow off valve on the sea strainer. Merc I think made a blow off for its motors a few years ago. It fits inline on the side or back of the motor. Do you have a transom mount pickup or just the drive?

I also had temps that would go up to 170 and then drop down to 140 within a few minutes.So I ran a 1/2" line off the rear of the manifold and it completely stabilixed my temp at about 130.I have a 142 thermostat and I have drilled holes and all but for some reason,maybe aluminum heads,the only thing to work was the dump.I also had high pressure but the merc valve that US1 told me about worked perfect for that.I have the CMI E-Top headers,does any one know how much water they can actualy flow thru them?In other words I know there is two one inch hoses per header,I am only using the lower hook up and not the top.It seams like there is no way two one inch hoses could dump enough water out those little hoses at the end of the tail pipes.

Thanks Nordic95

Did you run the 1/2" line from the rear to the front of the intake, same as the the other guys?
Mike

No I took 1/2" line and dumped it over board.Right now for testing reasons I have it tied into the 1" line for the Merc. water dumps I have out the side of the boat.Everyone thinks its my bilge pumps running all the time and they run over to ask if the plug is in.Now that I know it worked great for temp control I will add two dumps out the back of the boat and let it dump onto the drives for extra cooling.

Nordic95

so you can't just run a line on the back of the intake around the dist. to the othe side of the intake tying the back or the engine together

In my case the two 6AN hoses run to the front crossover heads were removed and inspected before intallling . Valves showed hot on all four corners number 7 cylinder being the worst. Number two was a close match to 7. Also noticed the head gasket the lower water transfer hole in the block didnt match with the head on mumber 7 and no 2 cylinders at least in my 88 block havent check some of the new stuff. I ground out the block so the holes were not restricted as the others are not. Upon runing this combo with then ith the wwater to the front crossover found stagger jettig was no longer necessary and all plugs read the same. The engine ran a bit hotter at idle and low no wake speeds but within normal range as the boat speeded up temps would go down slightly bassicly the opposite of before the mods. Heads were later removed and valves all looked the same.

I am in the middle of making this modification now.. I would rather not drill into the back of the boat.. If I run an 8an line from rear to front on each side, where do I plug in the sensors? Water Temp, High temp buzzer and Water Pressure?? thanks

I'm running an MPI intake and you can't drill them so I tapped into the back of the heads and dump mine on my outdrive. fixed my pressure also.

I've been followong this thread. I'm building a 400 sbc with a weiand 177 would this work for me? it is a siamese block which does not circulate water between cylinders. so I have had cooling problems on #7 and #8 cylinders in the past in n/a application on my last engine went to closed cooling and 14lb cap still a little on the hot side on #8 cylinder. some of my circle track friends run a line between #7 and #8 accross back of block. also brodix and dart have manifolds that are tapped on all four corners from factory,evidently for that purpose

+1

are guys still doing this? also is it imperative to do it on both sides of the intake? i may do this on my 496's and have a t fitting on one side or the other with a pressure relief valve. seems sensable.

I always do it. However, I dump the lines overboard. I not only use it to eliminate any steam pockets at the rear of the heads and intake, but I also use it to control water pressure. I will start out with a #4 coming out of each side. They run to a tee and dump overboard. If I need to get rid of more water, then I will up the hoses to #6. My dump hose is a #10, so I can go up to (2) #8 hoses from the rear of the intake to control water pres.
I do not run a check valve on it because I want it to flow water all the time. You could run hoses to the front of the engine, but then it will not work to help in controlling water pressure. That is always not nesseccary, but it is nice if you need it. You must run a hose from each side of the rear of the intake since there is no crossover to tie the 2 sides together.
Eddie

Thanks Eddie,
So if I understand you correctly don't really bother tieing into the front jackets. only rear. Makes good sense. Also like the idea of dumping if out and forgeting about the pressure valves. Those are known to NOT always work either. Also as long as were on the sub what is ideal pressure again?
Thanks
John

Can I get away with drilling my intake after I have it installed?

Theoretically, It would just be minor metal shavings that would exit with the water, but ???????????????

Sure. No problem. The few little shavings won't hurt anything.

Eddie,

Will the lines from the back of the intake affect the cooling cooling of wet exhaust?
Thanks
Mike

Is there still a benfite to do this even if you have a circ. pump?

I'm running #6's to a "y" connector, then a single #6 overboard. Helped me lower water pressure a few lbs. and control the temps! :)

Also, I put the dumps on the side of the boat so I could peer overboard to confirm I'm pumping water at any given time. :)

The only way it would affect the cooling of the exhaust is if you have very low water pressure now.


Yes, it will still benefit you by not allowing steam pockets to form in the back of the engine.

Eddie

Yes I know this is old, but going through reading stuff.

Would this still work if I ran the hoses to the back of my exhaust wherer I have another place I can remove the plug and put in another fitting?

Yes, I have mine dump right into the extra fitting on my Stainless Marine exhaust manifolds.

cool will do that during this rebuild.

IMHO This thread contains some very bad information and mis-direction. There are way too many variables to the question "Rear Crossover on intake manifold". Let's assume that a BBC is the motor in question. Variables:
1) Block generation
2) Head Model/manufacturer
3) Head gasket manufacturer
4) Crossover or recir pump
5) Any modifications to any of the above

What I see in the thread is a "cookie cutter" approach to water circulation and distribution. Simply does not apply here.

Ok, I have been reading this thread and I'm thinking about doing it. Gen4 427 .60 over AFR 265CNC heads, 10.5:1 comp. Stainless marine GenIII exhaust, Weiland Stealth intake, No circ pump, but a crossover with bypass, steam holes drilled? Engine has yet to be painted or installed, Should I go ahead and do the rear crossover with a T, just in case I have pressure or steam issues, I'm all about doing what I can to extend the engine life, and reliability.

All it needs to be is a dump for steam Air pockets to get out small lines -4 if you go to big then the t-sat will not work right if using one.

I installed a rear crossover but i ran my #6 lines to the front of the intake manifold. I also have a crossover with a bypass and a 140 thermostat with 3-3/32 holes in it. Engine water temp. stays right about 140 and water pressure at cruse about 18lbs.

did you run one for each side?

Yes. I also checked the temp of the heads with a infered thermometer and they were withen a couple of degrese.

have any pics?

Im not shure how to do that. It says may not post attachments.