4 Barrel intake for Nissan V6

[BenE64]

Hi, Im looking for some opinions on the best way to build a plenum to adapt to the existing runners on a Nissan V6, I am looking to use a 390HP at this stage, It is what I have.

VG33E lower intake.jpg

After some discussion elsewhere I am at this stage leaning towards a cross ram style set up with 3 cyls of each bank crossing over to the other side, either a straight extension or slightly curved to reduce height a little. I am thinking of either fully dividing the plenum or having it divided lower down and open under the carb, The firing order is 1,2,3,4,5,6 so I was thinking separating odds and evens would stop the cyls robbing each other and even out the distribution a little.

Looking at pipemax I am getting a runner length of 12.3in 3rd harmonic or 9.7in 4th harmonic, due to room i am thinking 4th is the best option. that means approx a 2in extension on the runners

I have found a sectioned view of the cyl head online which shows the inlet port, not sure if there is much I can do up top in the manifold to improve the air flow into the port but if there is I would appreciate the suggestions.

VG33_OWO_Intake small.jpg

[T-flow]

If your trying to use that lower it may not be optimum. But you could build a bread box with a carb flange.

What does the head layout look like?

[Caprimaniac]

I was wondering, are the intake ports siamesed? And the manifold is for 3x webers?

I see Offenhauser has some straight 6 4- arrel intakes, might look into those?

[BenE64]

vg33 front on.jpg

Another photo, swiped of internut. I can cut the lower section up and weld runners to it but i was trying to avoid if possible due to a broken milling machine and time.

[BenE64]

I was wondering, are the intake ports siamesed? And the manifold is for 3x webers?

I see Offenhauser has some straight 6 4- arrel intakes, might look into those?

Not siamesed, removed the horrible EFI top section.

[BenE64]

Thanks GLHS60, i had seen those but cant get them here and dont want to pay for one and the shipping. I have a bit of lee way to raise the intake up so thought to take advantage of that. Tried to draw one up but this explains it better, how would something like this be optomised for a single entry carb? Would the extra runner length be worth the effort of more complex design? Would the bread box plenum work ok with the uoside down V floor

DSC00053.jpg

[1972ho]

here's another

[wwmtlineman]

I saw one on a car at Bonnevile, maybe he will respond

[BenE64]

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This is what it turned into. Its ugly but not as bad as the photos make it look! Started off with delusions of grandeur, had a pretty tig welded box layed out then realised it was 2 x more volume than the engine. Due to the bottom runner section layout i just did the best i could for now. Runners are to pipemax specs for csa and entry sizes etc. 4th harmonic. Plenum volume ended at 2/3s engine volume in the hope of not losing to much bottom end. I ended up dividing the plenum in the area umder the carb its open at the ends. Playing with my big extractor fan seemed to be more even that way. Not very scientific!

[Newold1]

If it were me and I was trying to use a carb, I would buy two of these Weber 46IDA Porsche units off a Weber rebuild shop and fabricate some simple adapters to bolt down to your existing heads.

s-l225.jpg

You will be able to set your inlet length with standard Weber end bells and the 46MM throttle bores should more than satisfy your Nissan' s V-6 valve, port sizes and CFM needs. They will be fairly easy to tune and linkage is very straight forward and when done will look "Very Cool" and have a workable height on top of the engine.
I suspect your crazy runner plenum/single carb "rube goldberg" unit will not produce the best workable power and you'll probably drive yourself crazy trying to tune with possibly only mediocre results! Remember with a carb the air/fuel mix starts at the above the throttle plate and crazy shape manifolds tend to drop fuel out and cause other possible engine issues. JMHO and manifold fabrication experiences.

[BenE64]

I looked very hard at the weber down drafts, but at $12k-$20k i would have many other options including a better car to start with! My budget doesnt extend that far for this project unfortunately.

It doesnt look as bad in real life.

Base plates and runners are fairly straight to the port. It would be better if i had time and equip to build a new bottom section from scratch.

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Thanks for the comments though. Im under no illusions it will be the best. Being prepared for the worst never hurts. If you have any suggestions on better shapes though that would be appreciated. Have welder will modify!

[dwilliams]

Can you install the injectors and fuel rails in the original locations, or are you going to move the injectors somewhere else?

Clearance looks awfully tight, there.

[BenE64]

Can you install the injectors and fuel rails in the original locations, or are you going to move the injectors somewhere else?

Clearance looks awfully tight, there.

Its staying carburetor now. Those last photos where just to show that it wasnt quite as convoluted "rube goldberg" amazing machine as it looked when finished.

[Newold1]

I totally understand the high dollar problem with using the three throat Porsche Webers. Had no idea that they have gotten so pricey. You could still think about three 48IDA Webers mounted transverse across the engine. I see they can be bought for $150 to $200 each ready to run. Again inlet runners pretty simple fabrication and throttle linkage not a big issue. You might want to look at this possibility before you go to far down (time wise) the single 4 barrel plenum concept. You might also want to consider thicker aluminum pipe material for the runners and then do some heavy porting to better curve and shape the runners internally as all those hard corner transitions on the sectioned pipe you are using is going to play a lot of havoc with air/fuel mixture flow. "AIR/FUEL MIXTURES DON'T LIKE HARD CORNERS AND SHARP EDGES!" Just some thoughts

[BenE64]

Where the first pipe transition joined the oem cast section i pad welded the sharp side outside radius internally and then ported as you suggested. The photo where you can see down the runner port was before I cleaned it all up, there are turns but they are as smooth as i could make them. That said i am hunting a spare lower manifold for future upgrades. The manifold has cooland ports adjacent to each inlet port which makes a quick fab job impossible. Need serious time on a milling machine. I will keep an eye out for some decent down drafts. I cant even buy a gasket kit for $200 dollars where i live. I built a single side draft weber on a 4 cyl recently and the cost of jets chokes and emulsion tubes for 1 carby gets out of hand let alone 3. Every jet change is $60, $180 for a set of emulsion tubes would hurt. Will need to begin slowly accumulating parts for that to be achievable. Id probably just change back to efi.