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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.

Image

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

Post by moregrip » Wed Feb 12, 2020 8:20 am

new here, found this thread via google search; great info!

So what did you end up going with?

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

Post by enigma57 » Wed Feb 12, 2020 9:07 am

I love tinkering with Webers. Especially the DCNF series. The siamesed intake port arrangement on these engines precludes modifying them for an IR intake configuration, though. So I decided to build and test 2 intakes.

One will be the 3-carb intake having 3 small plenums, each feeding a separate pair of siamesed runners.

The other is a common plenum type I am modifying to take 2 similar carbs. With this intake, all 3 pairs of siamesed intake runners draw from a single plenum and 2 carbs are positioned to provide equal air/fuel distribution. This intake began life as an ancient Clifford dual carb intake and as such, the plenum volume is a bit large. So I will whittle a hardwood plenum stuffer for it and shape it to aid in getting equal flow to all runners. \[:]V[:]/

The 2 carb intake, I will run a pair of 38 DCNVH carbs on. These were used as singles on 2 litre and 2.5 litre Maserati Bi-Turbo engines in the mid-'80s and unlike DCNF carbs, the DCNVH are fitted with power valves.

The DCNF carbs I will run on the 3-carb intake were designed for IR intake, so must be reconfigured quite a bit to function correctly even with the small individual plenums.

That's about it for now. I was trial fitting the 292 block in my '57 Chevy to work up front engine mounts a while back and discovered a crack in the block. So will be on the lookout for a good standard bore block that will clean up with 0.030" overbore (hopefully). Will get moving on project again this Spring if all goes well.

Best regards and thanks for asking,

Harry

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

Post by moregrip » Wed Feb 12, 2020 11:24 pm

Excellent, please keep the info and pics coming! Very interested.

I'll be starting a 250 inline 6 build soon myself. Stock crank, stock rods, NOS forged pistons running a 194 head, T6 Racing bolt in lumps, Clifford single carb manifold type with a weber 38 DGAS, which I believe will only be good for about 5000rpm or so. Still batting around cam specs but thats the idea, looking for 6000rpm redline finished product.

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

Post by enigma57 » Thu Feb 13, 2020 1:49 am

:D Should be fun! I will follow with interest. Please keep us informed as to your progress.

Regarding the 194 head...... If you don't have it as yet...... Yes, the small chamber head will raise compression some, but the open (bathtub) chamber heads breathe better and shroud the valves to a lesser degree. If you find one that is from '73 or newer engine, it should have hardened exh. valve seats so you don't have to have new seats installed in an older 194 head to run unleaded gas.

The Weber 38 DGAS carb is a good choice for a driver. You are correct, it may limit your top end a bit. The original Italian made versions had 27mm fixed chokes (main venturii). I have heard that the newer Spanish made 38 DGAS / DGES carbs now have 30mm chokes. This will help top end airflow a bit, but Weber did not revise the jetting. So you will need to bump up idle (slow running) jets and main jets a bit...... Possibly decrease air corrector size a bit as well...... Both to suit the larger choke size and to make allowances for 10% ethanol if you cannot get straight, undiluted gasoline where you are.

The 250's are not as prone to destructive harmonics when run above 5,000 RPMs as are the long stroke 292 engines. But don't try and spin the 250 like a 283 or 302 short stroke small block Chevy V-8. Try and enhance the 250's natural torque building ability and cam it accordingly. Use good parts and fasteners throughout and have your machine shop balance the bejavvers out of it. Should give you good service and last a good while if you do that.

You might give Mike Jones a holler when you are ready for the cam. With all the particulars (car, engine specs and use), he should be able to make a recommendation on cam grind. Mike posts here under the screen name CamKing if you need to look him up.

All the best with your build,

Harry

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

Post by moregrip » Thu Feb 13, 2020 3:30 pm

Thank you for the additional info on the 38 DGAS. I'm sure that will come in handy once its time to get to the driving part!

Regarding the 194, yes I already have it. The plan is to deshroud the intake valve such that there will be no additional negative impact to flow. I spoke with Larry at T6 Racing and Mike at Sissells and both indicated the 194 head was a good choice. I've also read many a debate online back and fourth!

Appreciate the hat tip to mike jones, may have to give him a shout. There are a couple of "off the shelf" grinds I've been interested in, one by Isky and the other by Crane.

Yes for sure I'll keep you posted!

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

Post by pdq67 » Thu Feb 13, 2020 6:20 pm

Harry,

SOME guys have been installing home-made SBC cast-iron heads on the old 6-banger by cutting them in the right spots and welding/brazing the pieces back into one long head.

Might think about this and do away with the old bangers head.

Would aluminum LS- engine heads work here also??

pdq67

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

Post by enigma57 » Sun Feb 16, 2020 4:30 am

Good luck with your build, moregrip! If both Larry at T6 Racing and Mike at Sissells believe the 194 combustion chamber can be unshrouded for bigger valves and will work best for you, they should know.

Regarding off the shelf cams for these engines other than sourcing them directly from cam grinders, there are several places to get them including Clifford Research. One of the best selections you will find is from Tom Lowe at 12-bolt.com. Lots to choose from depending upon your needs.......

https://www.12bolt.com/store/c6/Camshafts.html

https://www.12bolt.com/

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Paul, thanks for your suggestion. Much appreciated. I have followed with interest the small block Chevy heads cut down and welded back together with mods to heads and to block. This same mod is covered in Leo Santucci's book. I have also looked at the 12-port heads from Sissel. They are all great stuff, but are definitely out of my price range. And beyond my needs.

For what I am doing, a reworked and lump ported 9-port head should be just fine. This is a road car. Not a max effort race engine. That is why I am building it to make as much average power below 5,000 - 5,500 RPMs as possible. As you know, these long stroke tall deck 292 engines are prone to severe harmonics issues above that and are infamous for throwing flywheels when spun to high.

I blew an OEM nodular iron flywheel in a '55 Chevy once many moons ago. It took out the bellhousing, a good sized chunk of tranny tunnel, dash and windshield when it let go. Fortunately more straight up and towards the passenger side than where my feet were. And no, I wasn't racing nor even turning the engine very high at the time.

By the grace of G-d, I still have both feet. Just a large, odd shaped scar covering most of my right heel where the shrapnel laid a bit of sheet metal from the tranny tunnel over onto my right foot pinning my foot and pushing the gas pedal to the floor. Somehow, I had the presence of mind to switch off the ignition and coast into a gravel parking lot. Still, I don't have any idea how high that 327 spun up before I got the key off. Had to get some guys there to take a tire tool and bend the metal back enough to get my foot free.

Not an experience I care to revisit. That is why I scored a 30 lb. SFI approved billet steel flywheel last year for this engine. Its drilled for a small block Chevy, but I will be running the later fully counterweighted 292 crank that has (6) 1/2" securing bolts rather than 7/16" and 3 locating dowels rather than 1. So will need to have the flywheel mounting holes enlarged and drill the 2 additional dowel holes before having everything balanced.

Regarding the LS heads...... They share same bore spacing as Chevy 194 - 292 inline 6 and small block V-8. Not sure if their head bolt locations would be more difficult to adapt to an inline 6 block than early small block heads, though.

I've got a new set of Edelbrock Victor Jr. heads ported by Mondello for a stroker small block I was building about 20 years ago. If I were to get wild and crazy and cut them up and weld them back together and all the other stuff required to make them work on a 292 inline 6, I would look at using them...... If they're not too big. These things will flow better than 300CFM at only 0.550" lift and intake ports were taken out to same size as a 1209 race gasket. You could park a VW in there! :shock:

Best regards,

Harry

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

Post by moregrip » Sun Feb 16, 2020 10:11 am

Thanks Harry, I figure if both those sources feel the 194 head will perform well then who am I to argue. I'm willing to give it a shot and see; fingers crossed it all works out. The added compression will be nice.

Question, if you had the room, would you be going the DCOE route?

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

Post by pdq67 » Sun Feb 16, 2020 2:34 pm

Truckedup wrote:
Mon May 22, 2017 8:39 am
Harry, the head work used and retaining the Siamese ports may seem out of place to V8 guys..But a properly reworked stock head can support 1.5 HP per cubic...However, I believe it would be very lumpy for street use...
I was a actively involved in the Inliners club for many years...There was talk of Chevy 6's blowing off well modified V8's on the street..I personally never saw any Chevy 6 powered street cars capable of this performance...I think it might be like flat head Ford V8's where the typical street build makes 160 HP but there's always the talk of the few with time and money to make way more power ....I believe a nicely done up 292 with decent street manners might make near 300 HP if reasonable low end power is required...
I know of a '55 Chevy post car that had a hopped up 261 Gimmie in it that ran the 1/8th back when I was in HS. Sucker gave V-8 car's fits.

Something like 5.38 gears, 4-speed and small real slicks.

I want to say the engine came out of a custom '52 Rag-Top. It had split manifolds on it and had the prettiest sound going up and down through the gears, "Smitty" mufflers here.

It flat walked away from my stock '57's 283 2-barrel/3-speed late one Sat. evening while leaving town.

pdq67

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

Post by enigma57 » Sun Feb 16, 2020 4:00 pm

moregrip wrote:
Sun Feb 16, 2020 10:11 am
......Question, if you had the room, would you be going the DCOE route?
That would be the most logical choice, given available manifolds...... Or Dellorto DLHAs. I like doing things differently, though. So I would look into sliding valve carburretors...... SU, Mikuni HSR. Something along those lines. :D

Best regards,

Harry

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