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Separating SU intake manifolds

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I've been trying to remove the coolant line between the intake manifolds with no success. There are nuts on both sides but they won't loosen. I've used PBblaster many times and have used heat several times. Anybody managed to get these apart? Any chance they are reverse threaded? I'm also having trouble with the hose fitting that lines up with the coolant tube but is on the "outside" of the manifold.

Thanks for any help.

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I have the same problem. The fittings compress an o-ring to make the seal. The threaded mating surface is in the intake manifold. The fact that you cannot rotate the intake manifold on the tube indicates there is corrosion between the fitting and the tube.

BTW I tried to pass water through the passage using rubber tubing and a funnel and it only passed a drop or two. Using a wire, there appears to a blockage at the front of the rear manifold. My bores cope shows a small hole that appears rusted shut.

The parts manual shows a thermostat behind the rear manifold that is supposed to shut when hot. But I have no indication when it was adopted. Any information about the system would be appreciated.

Edited by djwarner
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Steve, thanks for the heads up. My early Z does not have the carb circuit, just the manifold circuit.

After completing my engine overhaul, oil consumption has gone to zero, but I was still accumulating soot around the exhaust. So I turned my attention to my Weber DGV carbs. Turns out the idle jets are way too rich. I have been working with the techies at Redline, getting tons of help.

The main guru there told me that I needed to re install the heating circuit. As he explained it, the carbs do not produce a vapor, but droplets of fuel. When a cold engine idles, the vacuum created chills the manifold. The droplets of fuel will "wet out" on the cold surface like the outside of a glass of iced tea. The main effect is to lean out the mixture. The choke is designed to help enrich the mixture to replace the fuel dropped on to the cold surface.

After hearing this, I noticed the Cannon manifold adapters got very cold when idling. These adapters allow the downdraft DGVs to couple to the side draft intake manifolds. To complicate things more, the fiber isolaters normally between the manifolds and SUs blocks heat flow to the Cannon adapters as the engine warms.

When I found the heating tubes blocked, I began to consider alternatives. The Cannon adapters have their own heating passages cast in, but there is no easy way to connect tubing to the cast bosses. I pulled out my IR thermometer and found the adapters were chilling about 30 degrees F as it idles.

All that aside, I am in the middle of tuning the carbs with some interesting findings. I will also be converting the DGVs from a two barrel progressive carb into a two barrel synchronous operation. According to Redline, this will boost hp 10-15% most noticeably in the mid range throttle regimes where we live 90% of the time. Right now I'm waiting for jetting kits an linkages. I'll document my results in another thread.

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If I remember correctly the water tubes are steel threaded into aluminum intakes. With water inside you get terrible galvanic corrosion making them hard to separate later...

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I just separated these a few days ago, but mine came apart without too much fuss. As others have stated that nut is on a male fitting that threads into the manifold. They're all normal right-handed threads. FWIW the fittings between the manifolds are M16x1.5 and the fittings on the outside of the manifolds are 1/4" BSPT (British Standard Pipe Tapered - close to NPT but not quite, and not to be confused with British Standard Pipe Parallel).  


Use a flare nut wrench and keep hitting it with PB Blaster and heat. You can use a cheater bar on your wrench but just be careful with them because they're hollow fittings and can shear. I sheared one off in my balance tube as well as my EGR fitting down in the exhaust manifold. Like any other stuck bolt apply torque in both directions as you try to break it loose.


If you're looking for plugs for these, McMaster-Carr has an assortment of BSPT stuff. I got some brass hex-socket plugs, even though there's no real need to plug these holes since I've removed coolant flow from the manifolds.

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