Inliners International Forums General Discussion Hi Performance Best 4bbl manifolds for inline sixes?

Our project has come to the point where we've decided we should be going with a single 4bbl. But it will require that we build a manifold.

What kinds of manifolds are producing the best results on inline sixes?

Side draft Weber type manifolds are producing more power than a single 4 bbl.

Are you looking for more top end power?
Off idle,part throttle,full throttle acceleration?

MBHD

What engine?
Why build?
What results?

I think full throttle acceleration is the aim more than anything... we do have access to triple Weber manifolds if we want to go that way, but we want to try a good 4bbl setup.

The engine is the Hemi 6 and 'why build' is answered by saying that we don't think there's a conclusively good one available.

You would be better off running 3 2 bbls. Like some Webber IDA's IMO.

It's pretty hard to beat the torque,,,broad power range of a nice side draft set-up w/just a single 4 bbl.

MBHD

Hank, what is the fuel economy comparison between the sidedrafts and the single 4? I'm thinking sidedrafts could help me put a 250 into a '55 Stude and give enough hood clearance.

I'm seriously disposed to finding out what kind of 4bbl intakes work well on inline sixes...

We're pretty much up with it on the options, they're covered, but we want to do the best possible job of a 4bbl intake and see how it runs.

So who can tell me what works in that line?

I see what you mean - not familiar with what's out there for the hemi.
Starting with an existing aftermarket 4 bbl., the volume can be increased somewhat with a simple tall spacer, and the runner length extended to get some useful inertia fill (if not an actual tuned length) by just splicing in a section between the flange and the plenum entry, but a complete re-make (changing runner entries and distribution) is a lot of work.
IMHO a side-draft, especially IR (Weber DCOE, Mikuni PHH, Dell'Orto) is easier to design and fabricate than a 4 bbl., because internal plenum shape and volume is less important and easier to control. Also easier to play with the length with flanged stubs, etc.

If you find or use a good/correctly sized DCOEs,you should get better fuel economy as long as you can stay out of the throttle,which is really hard to do B.T.W.
If you drive aggresive,,the 6 barrels will gulp quite a bit of fuel,so all bets are off for mileage in that scenario.

Look for DCOE'S that have multiple transition holes near the throttle valves like about 4 as an example. This will give you better driveability & throttle response.

A set of 40 MM carbs will work even if you can't find some 45's.

You can change the choke tubes for more power if you want or smaller choke tubes which will give you better mileage when properly jetting.

Once you get the corrct emultion tubes,jetting the rest is not too difficult.
But it does take some time, & need extra jets to know which way to go on the jetting.

But w/todays wide band readers readily available, that alone will take out the guess work involved to properly tune.

MBHD

Does anyone use a dual plane-style manifold on an inline six with a 4bbl?

I think the Pontiac sprint 6's were dual plane from the factory?

MBHD

I don't have a Sprint to examine, but there's no tell-tales of multi levels or dividers visible.
The asymmetrical runners are interesting, though - the 5-6 runner is much larger and with a different entry radius than the 1-2.

Ray, the old Port O Sonic design from Edelbrock had divided runners.....if memory serves me corrrectly the top fed from the primaries and the bottom fed from the secondaries.....I have no experience with that design and have only seen one; might have been one of those ideas that looked good on paper but didn't work in practice.....fats

?
Do the pontiac sprint manifolds match/mount to a chevy head?

One member here had adapted it to fit the Chevy head,later,,,I think it had developed vacuum leaks though.


MBHD

Okay... something interesting happening here...

Any chances of any pictures of the Pontiac Sprint manifold?

Ks from Wichita... that does sound odd, wonder what they were aiming at? Probably gas speed on part throttle. Yes, that's very interesting, but when it got to the engine ports it would suddenly have full cross-section and slow down? But you could, I guess, put dividers down into the ports as well.

http://i418.photobucket.com/albums/pp263/eldo6770/OHC6MTRS014.jpg

MBHD

Isn't your hemi engine a individual runner design? Not siamesed intakes.
If that is the case, a manifold with equal length runners to the flange of carb base is the best option. The are formula's around to calculate the lenght of runners for picked RPM running designs. The problem with the inline engine is the length that all must be stretched out to reach the middle. It is hard to get equal lengths. It seems to me a runner length of around 15" is really good for optimun tq around 5k rpm, can't remember the cross section size. Shorter runners will move the peak tq higher in rpm. Tom

Thanks Hank.

Yes, they're individual ports...

21.875" centre to centre of the front and rear ports.

Thanks for the Pontiac pic... does anyone know if the runners are split up inside them?

OK go on ebay and search up this item number. 360256821536
Looks like individual ports at the head and also dual plane.
Looks like a clifford sort of on the outside anyway.

Also here is the one piece dual exhaust manifold with large heat runners to the sideways carby. Also with individual ports.
360257209908

I think there is a Q-jet for one on there too. I think it has the numbers.

Don't see dual plane.

Port-O-Sonic = Offenhauser

I do see a carby turned sideways...

That's a no-no for us. We have to avoid fuel surge problems in corners.

The manifold referenced is not the Offenhauser Port-O-Sonic (similar to the Edelbrock Torquer etc. single-plane), but the Offenhauser "Dual-Port" (runners are separated upper and lower).
It was produced for the Ford 240 & 300 BB6, AMC 232 & 258 L6, and the Toyota Land Cruiser L6, and many common L4, V6 & V8, but no other L6 engines.

Ray, I believe that was the theory; keep the airspeed up through out the rpm range....if memory serves me correctly they were divided top to bottom so you still had the bolt boss to contend with and dumped into the common port.....this was conceived during the gas crunch of the 70's so that probably explains a lot.....fats

You are most correct Panic; looked at too many manifolds over the years and memory isn't what it used to be.....info probably irrelevant to the question anyway....fats

But - thanks for bringing it up, since I had to research it to get the answer (my memory is not so great, either!).
IMHO it's a useful idea under certain conditions (obviously not racing-only), but wasn't really popular for the L6.
Just a guess: the D-P L6 manifolds were only for 12 port engines, since the effect is partially reduced when the primary-only runner meets the siamese opening and "and dumped into the common port" in the 250/292, etc.

The concept is good for light throttle cruising in terms of airspeed and fuel vaporization but the addition of what is effectively two more walls and the ensuing boundry layer flow issues would probably offset any gains; at any rate it wasn't pursued very far so that should tell us something......fats

The one I had back in the late 70's had been narrowed on the front and rear runners, It was on a 258 that Glen Self built and I was running it in a 65 El Camino on the street, it would lay waste to a good running 350, it would have been undriveable without a standard tranny.

By the way, here's a new slant 6 manifold made in Australia:

http://www.pentastarparts.com.au/sunshop/index.php?l=product_detail&p=2555

Not sure, but I think it also has the carby turned sideways.