Does anyone have photos of diagrams of modifications to the inside of the intake manifold that will help make better fuel distribution? This would be to help with the lean condition inherent on cylinders 2 and 5.

Thanks

Joel

What intake manifold are you working with?
DD

Offenhouser

I run an Offy.

First, trace the port opening in the head, and verify the gasket you have matches that. It should if your buying mainline gaskets. Not sure what's out there these days.Chinese crap might be different. Stick with flepro at a minimum. Victor Reinz is my choice.Regardless, match the intake to the head and gasket.
So, gasket match the Offy to the gasket. In most cases, you'll find it is smaller than the opening in the Head intake matched gasket/template.

Carefully match the openings in the offy to match the template. Make the increase in size gradual.

I was amazed at how much smaller the Offy intake was than the ports. And I say that, as the ports should be larger. Doesn't matter, velocity is what you need, as the ports are close to water. Be very cautious about making the ports bigger. If you don't know, don't. Look up Doc's Band saw cut heads if you want an eye opener. The pics can be accessed through he Engine part of the forum, look for Frequently asked Questions, and then search there.

The Clifford has a much better match, and has a larger intake runner cross section as it doesn't choke down. That's why it's the better drag racing manifold.

I would rate the Clifford short ram better than the Hyperpak for that purpose. If you're road racing, then the Hyperpak offers better performance in the engine operating envelope. If youre running over 5000 rpm, the Hyperpak is not the manifold to use. The Clifford short ram rein's supreme. That said, I don't have one in an NA build. The Offy is much more street-able.

CJ

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Part of Tyrde-Browne Racing

Are you seeing lean 2 & 5 after WOT runs or from part throttle "street driving"?
I assume you are running the carb. orientation with the primaries facing forward, correct?
If you are concerned about even WOT distribution, try "side-ways" carb mounting.
For better fuel distribution on the street, lots of intake manifold heating makes for better distribution and MPG.
After that, it gets down to controlling any remaining liquid fuel, traveling along the walls and floor of the manifold.
DD

Seems I'm having trouble getting my replies to show up. I replied to CJ earlier today and it looked like everything went through after I clicked submit but the reply isn't showing up. I replied to doc's last reply and it disappeared too.

Of course the last reply went through.
I haven't checked the plugs at the track. I do have a lot of hard street miles on it and several cold starts. #1&6 plugs are sooty black. #2&5 are white and #3&4 are nice and light tan. #1&6 never looked that black and sooty with the bbd manifold on it.

Would it help if I cut the center 4 holes out of the offy manifold and got a better adapter for the AFB? The holes in the adapter plate don't line up well with the manifold or the carb. Maybe I just need a better adapter?

Cutting-out the 4-holes will hurt more then help.
Are you heating the Offy manifold?

Black #1 & 6 is usually the result of a "wet" manifold's "boundary effect" were the mixture first travels down to the floor of the manifold and then moves out to the outer walls of the manifold, Once there, any liquid fuel tends to to stay out at the wall(s) and then follows along the wall and into the adjacent cylinder.
Having a nice "hot spot" on the manifold's floor, right under the carb. will hopefully vaporize any liquid fuel hitting it, getting that fuel into "suspension", before it has a chance to move out to the boundary walls.
DD

I have headers so I have no heat on the manifold. You're probably right about that. Maybe the shape doesn't work as well for cold fuel distribution as the BBD manifold.

I found the correct adapter for the offy. I had put it up with the stainless valves I had bought about 17 years ago. It's shaped alot better than the one I had. Hopefully it will work a little better.

Joel

Heating the manifold is usually the fastest / easiest solution for distribution problems but there comes a point where intake manifold heat starts to work against you.
One example is when everything is really hot. (a hot day, a hot engine and having to make "hot laps", like the final rounds of bracket racing or the final "all-in" laps of road course or track work.
Water heating can be a good compromise and allow a simple way to shut-off the heat ( with a valve) when you do not need it.

No intake heat... then you need to think about ways to move the liquid fuel to where you need it. (and away form where it is not needed)
Note: Any liquid fuel inside an intake manifold is not good and hard to manage.

Manifold floor plenum "dams", plenum to runner entry porting work, and / or diversion "turtles" are all ways to direct the liquid fuel into a different runner.
My work with the Hyper-Pak intakes showed that placing small angled dams on the plenum floor, right in front of the # 1 & 6 runner entries helped direct some of the liquid fuel into # 2 & 5 runners. The dam in front of #6 needed to be taller then the one in front of #1.
DD

Maybe related, I hate the flat floor under the carb design. I can't see how that can have any good performance/tuning outcome. I don't have a fuel distribution problem with port EFI. But I built a simple epoxied in manifold floor turtle/air flow diverter. I figured whatever restriction it fosters, I could make it up with the turbo. I'm toying with using the Clifford floor "heating" plumbed chamber as an iced water cooled intercooler for 1/4 mile jaunts.

that could be an interesting reverse application of the water ports. I bet in Florida that's needed. even more efficient if you run the cold water during cool down too while sitting in pit spot / staging lanes!



Greg

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http://www.youtube.com/hyperpack

I'm working on putting together a low tech flow bench using the Dave Vizard model in his head porting book. I plan on mounting the intake and carburator and doing some testing from cylinder to cylinder to see if there's any difference between the six cylinders. I'll try some mods to the intake to see if anything helps or changes the flow percentage. It will take a while to get data since I'm slow with my projects. I'll post any results as soon as I get them.

That would be interesting, but GIGO still applies. But I wonder what interaction there is between cyls as they their flows rise and fall, but not sure how one could account/test/measure that if they wanted to accurately.

Regardless, your test will only increase our collective knowledge I suspect unless there is some wayback Mopar test flow data discovered.

I wonder if doing some 3d solid modeling in inventor with CFD analysis would be beneficial?


Too bad I just cant sit at the confuser all day and sketch up that stuff!


Greg

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