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Plenum on a multi carb intake manifold for an inliner?

General engine tech -- Drag Racing to Circle Track

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Plenum on a multi carb intake manifold for an inliner?

Post by PackardV8 » Sun Apr 14, 2019 7:10 pm

Image[/img]I just stumbled across this photo of a home-built intake manifold. FWIW, I've built several intakes for inliners and it never occurred to me to use such a large plenum. Balance tubes were always common, but it seems the tunnel ram has gone retro. Your thoughts?
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Re: Plenum on a multi carb intake manifold for an inliner?

Post by modok » Sun Apr 14, 2019 7:38 pm

I like it!

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Re: Plenum on a multi carb intake manifold for an inliner?

Post by FC-Pilot » Sun Apr 14, 2019 7:50 pm

I never thought about building a tunnel ram when I rebuilt the tractor engine for my grandpa. Opportunity missed on my part.

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Re: Plenum on a multi carb intake manifold for an inliner?

Post by rfh » Sun Apr 14, 2019 8:20 pm

The problem that we have found with our inline six cylinders using manifolds like this is the balance between the carbs being big enough to handle the piston flow demand Vs the the carbs being too big at wot and losing the vacuum signal to the carbs.I would suggest removing the carbs over cylinders 2 and 4, put plates to cover those holes and checking the throttle responce with just two carbs hooked up.A vacuum port in the manifold and a vacuum gauge will help greatly

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Re: Plenum on a multi carb intake manifold for an inliner?

Post by chevyfreak » Mon Apr 15, 2019 3:01 am

That just looks so cool.
I have never build a 4 carb intake for a inline. So cant say how the responce will be.
I did a 2 carb on a chevy 6 there it favours the stock type runner size with one barrels. Did the 3 x1bbl but stock type intake. No tunnel ram types.
Currently buzy on a big plenum 4bbl intake for my 266 inline chevy. Will see if the bigger plenum gives my uphill.
Havent tested yet.
Intake looks like a fat W.
Just playing to see what effect it has. I build it in such a way that if it fails i can change it to fit a blower and re use intake.

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Re: Plenum on a multi carb intake manifold for an inliner?

Post by PackardV8 » Mon Apr 15, 2019 12:37 pm

chevyfreak wrote:
Mon Apr 15, 2019 3:01 am
That just looks so cool.
Agree, and that's paramount for most of those type builds. On a flathead six Studebaker Champion, I took two SU carbs from a BMC 4-cyl, added a third leg and had the best intake I'd ever tried.
Image I couldn't sell it to the customer, "It just doesn't have the look I want."

He went with an Offenhauser 1 x 2 which performed less well but had the look.
Image
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Re: Plenum on a multi carb intake manifold for an inliner?

Post by RevTheory » Mon Apr 15, 2019 12:50 pm

Shouldn't have any fuel standoff issues :D

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Re: Plenum on a multi carb intake manifold for an inliner?

Post by F-BIRD'88 » Mon Apr 15, 2019 12:56 pm

I would have made the intake runners much longer.
Like a Chrysler slant 6 intake. Lots of mid range torque.

Most good old straight inline 6 are not real high revers
So tune the intakes and exhaust for big torque boost.
(Longer runners and exhaust primaries)
Joe Sherman's rule of thumb on TR plenums.
Big carbs= shorter plenum
Small carbs = taller height plenum.
Ideally you'd want to make a adjustable prototype test plenum. Adjust carb height and plenum volume with plenum spacersand carb spacers.

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Re: Plenum on a multi carb intake manifold for an inliner?

Post by F-BIRD'88 » Mon Apr 15, 2019 1:08 pm

If the combined 4 carb cfm seems too big. Group the 4 carbs (eg 2 and 2) with twinned but connected plenums to allow using progressive linkage. This layout is still a TR but does allow you to lengthen the runners.

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Re: Plenum on a multi carb intake manifold for an inliner?

Post by F-BIRD'88 » Mon Apr 15, 2019 1:14 pm

On your straight tube plenum you could add a U shaped tuning pipe that connects both ends of the plenum. Now tune that pipe length just like a trombone slide to tune the plenum volume. And then play with carb height spacers+/- to get the carb height on the plenum right.

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Re: Plenum on a multi carb intake manifold for an inliner?

Post by PackardV8 » Mon Apr 15, 2019 3:16 pm

F-BIRD'88 wrote:
Mon Apr 15, 2019 12:56 pm
I would have made the intake runners much longer.
Like a Chrysler slant 6 intake. Lots of mid range torque.
Most good old straight inline 6 are not real high revers
So tune the intakes and exhaust for big torque boost.
(Longer runners and exhaust primaries)
Agree, but most times when asked to fabricate an intake, it's about what looks 'right' and then mostly about what will fit under the hood and always about how much it's gonna cost.

Interestingly, the Slant Six came about to keep the length short via small bores. The 170" for the Valiant/Lancer would fit under hoods straight up, but Mopar also wanted a 225" "RG" version as optional and also for the full-size Plymouth, Dodge and trucks. The resultant 4.125" stroke made the RG too tall, so the characteristic 30° slant of the cylinder block and the long intake was copied from the 1952 Mercedes-Benz 300SL.Image This enabled vehicle stylists to lower hoodlines, and also made room for the water pump to be mounted with a lateral offset, significantly shortening the engine's overall length.
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Re: Plenum on a multi carb intake manifold for an inliner?

Post by chevyfreak » Tue Apr 16, 2019 3:09 am

When i was hunting for pics to get ideas what some did for intakes i found this one. Dual plane for inline 6 with 4bbl. For chevy inline. Dont know if a dual plane wil work on them, because of the open intake ports.

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Re: Plenum on a multi carb intake manifold for an inliner?

Post by mag2555 » Tue Apr 16, 2019 7:57 am

Despite the Plenum I bet at lower rpm it acts like a IR set up and there reversion issues which will be compounded by having 4 carbs.
I guess your well on the road to find out !

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Re: Plenum on a multi carb intake manifold for an inliner?

Post by PackardV8 » Tue Apr 16, 2019 11:52 am

mag2555 wrote:
Tue Apr 16, 2019 7:57 am
Despite the Plenum I bet at lower rpm it acts like a IR set up and there reversion issues which will be compounded by having 4 carbs.
I guess your well on the road to find out !
As mentioned, most old inliners aren't going to live at much above 5,000 RPMs. Thus, long duration/big overlap cams aren't usual. At what cam duration/overlap would you feel reversion would become a problem with an IR intake?
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Re: Plenum on a multi carb intake manifold for an inliner?

Post by mag2555 » Tue Apr 16, 2019 12:25 pm

What cid motor is that where looking at?

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