Ok I finally got started. This project will be similar to the PAW type tunnel ram manifold. Twist is its going to have 3 AFBs.
I got a pair of manifold spacers which will act as the head flanges. I got some 2" ID X 1/8" wall aluminum tubing to form the runners. As it works out the circumference of a 2" circle is almost the same as the perimeter of the stock 392 port. I ground down a chunk of iron bar stock to make a tapered mandrel for the final port shape.
First I squished the tube end in a vise to make an oval, Then turned it 90 degrees and squshed again to try to make the rectangular port end. What you get is a rather anemic shape so that's when the tapered mandrel comes in. Hammer that puppy into the semi formed tubing and with some back and forth between the mandrel and the vice I got a decent port shape. You can see there is some degree of taper in the runner as it goes from fully round to the rectangular shape needed. I don't know yet if this is a good amount of taper or if it should extend further up the runner for a more gradual change in cross section. But if you look at stack injection you'll see the shape changes from rectangle to round within a short distance, so I might be OK with this.
To make a slower taper would require much more grinding on the bar stock. I suppose its possible to form the whole runner into a rectangular shape but that might beyond the limited tooling I have. The area of a 2" circle is a little bit greater than the area of the rectangular posrt size so maybe I'll get a little bit of a funnel effect, dunno for sure.The runner I expect to be something like 4-6 inches long. That's alot of work with a 6" grinder. Plus the pressure needed to ram the mandrel thru the tube might require a hydraulic press. More pics in next post
12-Pak Tunnel Ram fabrication
Moderators: scottm, TrWaters, 392heminut
12-Pak Tunnel Ram fabrication
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Re: 12-Pak Tunnel Ram fabrication
In these pics you can see the taper I mentioned. Also can see how close the formed tube fits the intake spacer port. Any overlap can be trimmed after welding.
Oh, welding. I still have to teach myself how to MIG weld. I never let not knowing something stop me from trying.
Potential problems I see so far are the bolts. Not alot of room for bolts, even if I use just four bolts per head. I'll have to look around for a good answer. I'm also thinking about the heater hose outlet. Not sure what to do there. I'm planning on a remote electric water pump to show off the pretty Moon Timing Cover I bought, hate to cover that up with a regular pump. Maybe its best to go ahead and drill and tap the flange for a fitting. If I end up running the heater hose from the front of the motor(more research needed) I could just plug the fitting.
I'm also thinking about this...my exhaust crossovers are filled. Maybe I could make a water heated gizmo under the plenum for a little better driveability. Might be possible to control the flow so it could be shut off when not really needed. Dunno if that's even worthwhile.
Also thinking about the plenum. Smaller plenums are better for throttle response, larger better for top end power. I've read the rule of thumb is the plenum should be at least the displacement of the motor, sometimes twice as much. Sounds big for a crisp throttle but again, more research needed. With a total of 1200 potential CFMs I don't know that a big plenum is needed. The primary venturis are pretty darn small so maybe each carb has 150-175 CFMs with just the primaries. On the face of it, it sounds like a workable combo.
The plenum will be long, I have to make sure I leave enough clearance for the distributor. I'll have to wait til the block comes back amd I buy a dist. Obviously the smallest diameter dist cap would be benficial. But the higher the plenum(longer runners) sits the less the dist may be a problem.
All stuff to think about while I should be working. good thing I can't fire me.
If anyone has thoughts, suggestions, experience they'd like to share I am ALL EARS. For example if someone has a plenum available to measure its volume that would give me a baseline from which to explore. This is my first time doing something like this so I learn as I go.
hnaks for listenign to me think out loud.
Oh, welding. I still have to teach myself how to MIG weld. I never let not knowing something stop me from trying.
Potential problems I see so far are the bolts. Not alot of room for bolts, even if I use just four bolts per head. I'll have to look around for a good answer. I'm also thinking about the heater hose outlet. Not sure what to do there. I'm planning on a remote electric water pump to show off the pretty Moon Timing Cover I bought, hate to cover that up with a regular pump. Maybe its best to go ahead and drill and tap the flange for a fitting. If I end up running the heater hose from the front of the motor(more research needed) I could just plug the fitting.
I'm also thinking about this...my exhaust crossovers are filled. Maybe I could make a water heated gizmo under the plenum for a little better driveability. Might be possible to control the flow so it could be shut off when not really needed. Dunno if that's even worthwhile.
Also thinking about the plenum. Smaller plenums are better for throttle response, larger better for top end power. I've read the rule of thumb is the plenum should be at least the displacement of the motor, sometimes twice as much. Sounds big for a crisp throttle but again, more research needed. With a total of 1200 potential CFMs I don't know that a big plenum is needed. The primary venturis are pretty darn small so maybe each carb has 150-175 CFMs with just the primaries. On the face of it, it sounds like a workable combo.
The plenum will be long, I have to make sure I leave enough clearance for the distributor. I'll have to wait til the block comes back amd I buy a dist. Obviously the smallest diameter dist cap would be benficial. But the higher the plenum(longer runners) sits the less the dist may be a problem.
All stuff to think about while I should be working. good thing I can't fire me.
If anyone has thoughts, suggestions, experience they'd like to share I am ALL EARS. For example if someone has a plenum available to measure its volume that would give me a baseline from which to explore. This is my first time doing something like this so I learn as I go.
hnaks for listenign to me think out loud.
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Re: 12-Pak Tunnel Ram fabrication
Dunno what happened the mandrel file but here's another try
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Re: 12-Pak Tunnel Ram fabrication
It gets expensive real quick, but using a Jerico belt drive distributor moves the distributor to a forward facing unit, clearing the intake manifold nicely. I will see if I have any photos which I could post.
I discovered some years ago that vacuum secondaries are a challenge to get to work right on engines with a lot of cam. I think, though, that using Carter AVSs for the end carbs would be a good way to start your experimentation. I look forward to seeing your results.
-Andy Carlson
Ojai CA
I discovered some years ago that vacuum secondaries are a challenge to get to work right on engines with a lot of cam. I think, though, that using Carter AVSs for the end carbs would be a good way to start your experimentation. I look forward to seeing your results.
-Andy Carlson
Ojai CA