Questions Regarding Siamesed Intake Ports (9 Port Head)

General engine tech -- Drag Racing to Circle Track

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enigma57
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Re: Questions Regarding Siamesed Intake Ports (9 Port Head)

Post by enigma57 » Wed Jul 26, 2017 12:34 am

Thanks, roc! I cannot take all the credit, though. I came up with the design and hand fitted the aluminum filler plugs and carb mounting flanges.

Nick Smithberg (Smithberg Racing) did the welding and machine work. As you say, superb craftsmanship. My 2nd tour of duty in the service, I did quite a bit of welding and brazing and eventually worked my way into NDT work. Inspected a lot of welds to nuke piping systems aboard the fast attack boats.

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And I can tell you that the welding and machine work Nick did on my intake are up to the same standards as the nuke welders did when working aboard the subs back when they were playing chicken with the Russkies in the '70s. None better.

Will keep this thread updated as the intake progresses. Just now, I am concentrating on adapting larger drum brakes to my '57. Then I will rebuild and rejet the carbs to a good baseline tune and mount them so I can figure out throttle linkage, fuel log, etc.

Appreciate your offer to put me in touch with the ENGINE folks down in Brazil. I tried to contact them a while back, but their website was down and I was unsure as to whether they were still in business.

Best regards,

Harry

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Re: Questions Regarding Siamesed Intake Ports (9 Port Head)

Post by enigma57 » Mon Oct 16, 2017 6:18 am

Truckedup wrote:
Sat Apr 01, 2017 6:34 am
Hey Harry, I sold the GMC 302 powered 37 Chevy truck a few years ago... I'm messing with vintage Triumph bikes again and he's a recent photo of me with the two engine land speed racing Triumph I just finished building...

Image
:D Hey Tony! Thought you'd get a kick out of this. Looks like the Roman chariot method of twin engine motorcycle racing circa late 1920's or early 1930's......

https://www.facebook.com/SteampunkTende ... unI4lXW1l4

Best regards,

Harry

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Re: Questions Regarding Siamesed Intake Ports (9 Port Head)

Post by enigma57 » Mon Jan 08, 2018 2:55 am

Finally got back to work on intake and carbs. Have three questions regarding tuned length......

Engine is 292 Chevy inline 6 and because of harmonics issues with these engines, I will limit redline to 5,000 RPMs (5,500 RPMs tops).

Intake I am working up has adequate CSA as cast for 5,500 RPMs max without stalling the port, so that should be OK as it is. Will cam engine for 5,500 RPMs redline.

Now regarding runner length...... The intake I am working up consists of 2 halves (inboard and outboard), which allows me to add a spacer between them to adjust overall tuned length.

Also...... This inline 6 engine has 3 sets of paired, siamesed intake runners (head ports and a couple inches in intake manifold at interface with head where individual runners open into a single siamesed port feeding 2 cylinders).

* Question...... With siamesed runners in head ports...... Can I assume overall runner length to be same as with individual (non-siamesed) runners? (Including length of the siamesed port areas?)

* Next question...... If I didn't screw up the calcs, I get the following runner lengths using 3rd and 4th harmonic for 5,500 RPMs redline (measured from where runners join small plenum beneath each carb to back of intake valve resting on its seat......

Plan A. Runner length 7.5" (intake less head, add 4.0" for headport) = 11.5" (Add 2.5"spacer between intake halves to bring overall runner length to 14")

Intake runner length, 14 inches......

4th harmonic, RPM range from 4,916 RPMs to 5,497 RPMs with peak @ 5,207 RPMs and pulse strength of 4 percent

Plan B. (Add 6.0" spacer between intake halves to bring overall runner length to 17.5")

Intake runner length, 17.5 inches......

3rd harmonic, RPM range from 5,048 RPMs to 5,769 RPMs with peak @ 5,409 RPMs and pulse strength of 7 percent
4th harmonic, RPM range from 3,936 RPMs to 4,401 RPMs with peak @ 4,168 RPMs and pulse strength of 4 percent

* Last question...... It would appear that the longer 17.5" overall runner length would be the way to go, as this would make use of both the 3rd and 4th harmonic (assuming that I have the lateral space in engine compartment for runners this long). Am I correct in this? And would such a long runner present a problem with fuel separation (this is a carburetted engine, not EFI)?

Thanks,

Harry

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Re: Questions Regarding Siamesed Intake Ports (9 Port Head)

Post by mk e » Mon Jan 29, 2018 1:15 pm

enigma57 wrote:
Mon Jan 08, 2018 2:55 am

Plan A. Runner length 7.5" (intake less head, add 4.0" for headport) = 11.5" (Add 2.5"spacer between intake halves to bring overall runner length to 14")

If I'm looking at the pictures right I think you'll need to include the carb and any stack you have in you tuned length calculation. If the runners separate and stay separate then for sure you need to add in the carb, it they separate then rejoin under the carb you PROBABLY need to include the carb in the back because the plenum looks WAY too small to terminate the waves. I think.....
Mark
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Re: Questions Regarding Siamesed Intake Ports (9 Port Head)

Post by enigma57 » Mon Jan 29, 2018 2:00 pm

mk e wrote:
Mon Jan 29, 2018 1:15 pm
...... If they separate then rejoin under the carb you PROBABLY need to include the carb in the back because the plenum looks WAY too small to terminate the waves. I think.....
That's how they are configured, Mark. Very small plenum under each 2bbl carb, then 2 separate runners extend from each plenum as far as the siamesed port area feeding 2 intake valves. I had planned on adding a small balance tube connecting all 3 plenums. Just large enough to smooth idle and off idle operation. Not large enough to share air/fuel mixture between all 3 carbs like a common plenum would.

Best regards,

Harry

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