Intake Manifold Bypass

Jim Dewar

Supporter
I have noticed on the forum many engines don't have this coolant bypass configuration. RF supplies this injection manifold with these holes predrilled to eliminate steam pockets. I am using a 4 barrel carb and noticed from the gallery many cars don't seem to need the modification and I don't want to remove the manifold to modify if it's not necessary. Any experience would be appreciated! Thanks, Jim
 

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Jim,
If you don't have the holes on the intake manifold near the back of the engine don't worry about them.
On production engines those holes on the intake manifold are used for many things.
Supply/return coolant to/from the heater core, supply/return coolant for the throttle body, coolant temp sensor for the computer, temp sensor for temp gauge, etc.....

RF might use those hole for something else besides eliminating steam pockets.
 
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Ron Earp

Admin
They are good to have for just what you indicated, the elimination of steam pockets and making sure the cooling system is solid with water. I'm 100% convinced some say the standard water pump won't cool because they haven't bled their systems properly and this is one of the ways to make sure you get a proper bled and remain in good shape. In the standard RF the engine lies forward at about a 10 degree angle so it was prone to trapping air at the back of the engine with no good way to escape. Most stock 5L installs in passenger cars have the engine tilted back about 3 degrees or more, so it isn't likely to be a problem there.

I drilled and tapped these into my 4bbl FunnelWeb intake manifold. You might have good results with out them, but a lot of folks use them.

R
 
I totally agree with Ron, but from experience will recommend that these pipes should be no greater than dash3 bore. I run them as individual pipes back to the expansion tank. Frank (you do not need to remove the manifold to drill and fit either )
 

Jim Dewar

Supporter
Thanks Guys, I was certain of your response. Frank, Please explain the teaser on the end. (you don't have to remove the manifold) Shavings in the coolant jackets?
 
Jim,

My experiance has been only positive with the bleed lines, it is a setup that RF did, even supplying a modified water intake with the nipple welded in. Ron, I agree that it most likely was a fix created because of the engine being angled down at the front and might not be needed on other cars. With that said, RF80 ran very cool with this mod never coming close to running hot so if nothing else it did not hurt the car and allowed it to be fully bled.

The vents did not come already installed on this manifold, I drilled and taped the holes and used dash6 lines. The dash6 size was the size used by RF. Frank, could you give your reason for dash3 as a maximum size?

Lastly, since the vents go right into the water jacket how do you drill them without putting chips into the engine?

Peter
 

Ron Earp

Admin
Lastly, since the vents go right into the water jacket how do you drill them without putting chips into the engine?

Peter

I suppose you could do a lot of grease, tap 1/2 turn, pull, clean tap, and repeat and get by. But, It is only 12 bolts and some sealant to pull the thing and do it right.

R
 
Thanks Guys, I was certain of your response. Frank, Please explain the teaser on the end. (you don't have to remove the manifold) Shavings in the coolant jackets?

Just position the shop (wifes) best vacuum cleaner nearby while drilling /tapping. If its noisey enough you wont hear her yelling til your done!

Jac Mac
 
Perhaps pressurizing the coolant system with a little air would be enough to push the nasty bits out???

I'd worry more about mssing the coolant passage.

Brian
 

Steve C

Steve
GT40s Supporter
Guys...I don't want to speak for Frank but, I believe the reason he suggessted AN3 lines was same reason I used AN4's ( not larger) on my SPF Cobra with an engine that sits pretty level...I wanted the rear of block to be free of air pockets but, not allowing a large ammount of water to bypass it's normal path. On my carbed Windsor I come out of the Weiand manifold at bosses at rear and merged lines to a hole tapped in front of manifold just before the outlet neck....so in effect I have less return dia due to merge into one AN4 than 2 AN3 returns ( just enough to insure rear always free of steam pockets)....Let's see if Frank agree with my rational... Steve
 
Steve, that's exactly what Frank told me when he looked at my car - he was concerned about coolant bypassing the block and not cooling the rear of the engine sufficiently. I think an orifice of some sort in the -8 (-6?) steam line would be even more effective, and less expensive to plumb.
 

Jim Dewar

Supporter
OK, I just removed my intake drilled and tapped 3 = 1/8 NPT holes since Frank won't share his secret procedure! Thanks Guys for the opinions, Jim
 
My 4XWeber manifold has only the front water passages connected through the manifold and discharging- the rest are blocked. Are steam pockets a concern with this configuration?
 
Usually only if your engine has a nose down attitude as fitted. The likelihood of air locks in the head coolant passages is greater with front mount radiators where the system cannot self bleed thru the top hose. The small -3 lines advocated here can be routed to the header tank to vent any trapped air, but are not large enough to create any loss of coolant flow thru the radiator.

Jac Mac
 
Jac Mac is right, the purpose is only to vent trapped air/relieve steam pressure rather than redirect water flows. I connect the Dash3 pipes to the header tank, and with the cap off you will be amazed just how much water they return flow from the engine, anything larger, and I have tried dash4, reduces the correct path of water flow through the cooling system, which could be more detremental . I use this system on all of trhe cars we build here. Frank
 
Frank,

I bow to your engineering talent and experience and would consider adding a restriction in the line. I do have a question and that is, since total flow would be limited by the smallest area of restriction, would the 2 -3 lines equal one -6 in total flow?

The only true answer to the value of the mod comes from use and I still stand by the fact that during several track days in South Florida with air temp in the 90F range and over 90% humidy, engine temp remained rock solid at 190F even after a 15 lap session. I will state that this applies only to that car and engine and that I have no proof that without the vent the engine would run any hotter. I did add it to the new motor in RF80 because I don't think it does any harm and might be adding benefit.

Peter
 
One -6 will have approx twice the flow or x section area of two -3 lines. One other point to bear in mind is that while you may bleed the system at initial fill , small leaks at the water pump seal or in the return line from radiator to pump can allow air to be drawn into the system when running along with localised boiling at hot spots within the block / heads and any leakage past the head gaskets etc all serve to create air pockets.

Jac Mac
 

Ron Earp

Admin
You guys run that thing to a header tank, or to the thermostat housing? I've seen both done, but having not owned a runnign version of either is one better than the other? I'd think the header tank would be good.
 
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