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2 x 1 intake Questions
https://slantsix.org/forum/viewtopic.php?t=59615		 Page 1 of 1
Author:  JohnnyDees [ Sun May 08, 2016 11:36 am ]
Post subject:  2 x 1 intake Questions
Has there ever been a 2 x 1 intake (slant six) that was not two separate sets of runners? What would be the pros and cons of one plenum area for the 2 carbs?
Author:  Joshie225 [ Sun May 08, 2016 11:55 am ]
Post subject: 
Do you understand how plenum volume affects carburetor operation?
Author:  JohnnyDees [ Sun May 08, 2016 12:40 pm ]
Post subject: 
I have a basic understanding that a larger plenum area can help HP and torque if the carb setup can handle it
Author:  SlantSixDan [ Sun May 08, 2016 12:55 pm ]
Post subject:  Re: 2 x 1 intake Questions
Quote:
Has there ever been a 2 x 1 intake (slant six) that was not two separate sets of runners?
Somebody might've hacked together such an item, but no, I'm pretty sure no such item was ever commercialised.
Quote:
What would be the pros
None.
Quote:
and cons
All.
Author:  '67 Dart 270 [ Sun May 08, 2016 7:23 pm ]
Post subject:  love your succinct and no nonsense answers...Dan
...reminds me of that scene in Terminator when he's asking the clerk for all the guns and ammo, and the clerk says, "what's it gonna be" and the terminator says, "all"

b
Author:  SlantSteve [ Mon May 09, 2016 4:55 am ]
Post subject: 
Probably not for a slant six,but plenty of hot Holden sixes here on Oz ran them, some as factory fitted options. Worked pretty decent, no real difference from a 2 bbl slant intake except the dual carbs probably give better distribution. To this day they are a very useful intake for the Holden six fans.
Author:  Joshie225 [ Mon May 09, 2016 8:07 am ]
Post subject: 
Quote:
I have a basic understanding that a larger plenum area can help HP and torque if the carb setup can handle it
Read more, a lot more, if you want to understand what's going on and the ramifications of the changes you might make.

With the intake manifold split into two separate groups of runners you have, essentially, a pair of three cylinder engines. Look at the firing order and you'll see that each set of three fires at even 240° intervals. With a small plenum, and conservative valve timing the carburetor has a strong, pulsating signal. In fact when you go with a pair of 1 bbls the proper jetting is usually down 2-3 jet sizes. With a larger plenum the pulsations are damped and the carburetor meters less fuel. To get an idea of how much the pulsing flow (and the pulses go both ways) means to the carburetor look at the throttles and venturis of the carburetors on individual runner intake systems compared to a plenum manifold.

With a pair of 1 bbls on a plenum manifold you slow the air through each carburetor and the metering doesn't function as intended and you might have a tough time transitioning from the idle and transition circuits to the main circuits and experience a bog. I had this when I put a big 2300 series Holley on a Super Six intake in high school.
Author:  NorEaster [ Fri May 20, 2016 9:17 pm ]
Post subject: 
In comparison, going to dual carbs on a single SL6 manifold, has advantages over running dual intake manifolds, esp. when there is a balance tube in the manifold. In example: the Offenhauser dual 1bbl which may still be available. It came with the linkage to convert to dual carbs.
I have no info on how this set up compares to the 2-bbl intake but I'll bet you can find someone who's done the Offy and get their input.

The Offy has the potential of better duel distribution with positioning each carb to feed 3 cylinders w/o fully treating the the engine as if it were two 3 cylinder motors sharing a block since it has a balance tube connecting the runners.

And, I believe the Offy was cast to accept machine work to convert to fuel injection. The carbs would then serve as throttle plates for air metering. A possible 2nd/next step.

FYI, the engineers at Chrysler did a dual 4bbl SL6 test engine. Got gobs of torque but reportedly couldn't get it to idle.

Note the recommendations already made on jetting and exhaust.

You can't beat the return on investment from improving exhaust flow. Dual 2" would be fine for what your doing. 2-1/4" is your upper limit. Oversizing exhaust can reduce heat scavenging and actually reduce engine efficiency.

Plenty of good info on exhaust already on the forum.

If staying with a single exhaust manifold, you might want to research running a single inlet/dual outlet muffler. I think you'll find running a smaller outlet size than the inlet will work best. Such as 2-1/4 single inlet with dual 2" outlets.
A little porting work on a factory single exhaust manifold to smooth flow would be a nice idea.

Look at your torque curve. It's determined by cam grind. There are different torque curves in different years.
In example:
My SL6 is in a 1980 van. Torque peaks @ 1600 and stays flat up to 2600. Earlier years often had torque peak later. Too much fuel too soon will just waste gas and may bog the motor.
Author:  NorEaster [ Sat May 21, 2016 4:44 am ]
Post subject: 
Thanks for your reply, Dan.

Agreed, esp. on the exhaust. It would provide the benefits of improved breathing of a single 2-1/4" system with the esthetics of the dual exhaust look which seems to be of interest.

My SL6 project plans are to run a dual exhaust system back into a dual inlet/single outlet muffler placed close to the rear axle. My objectives are maximum torque and fuel economy keeping the low rpm torque curve I already have. It's a work truck which never sees more than 3,000 revs.

In my view the SL6 is a cost effective alternative to a Cummins 4BT conversion. I'll post my project on the forum when time permits.
Author:  Doctor Dodge [ Sat May 21, 2016 7:38 am ]
Post subject: 
Another issue with multiple carb / common plenum intakes is all the A/F turbulence that happens underneath each carb.

This mixture/flow "chaos" can hurt or help... and it keeps changing with RPMs / CFM rates.

The bottom line... this type of setup has a lot more complexity and expense.

I am sure that all the airflow paths & related turbulence can be simulated with today's computers but in the end, compromises are made to get all those carbs to work well together when feeding into a common plenum.

Just my 2 cents...
DD
Author:  SlantSixDan [ Sat May 21, 2016 11:24 am ]
Post subject: 
Quote:
Agreed, esp. on the exhaust. It would provide the benefits of improved breathing of a single 2-1/4" system with the esthetics of the dual exhaust look
True, but much bigger benefit to be had with a 2-into-1 system than with a 1-into-2.
Quote:
My SL6 project plans are to run a dual exhaust system back into a dual inlet/single outlet muffler
Much better :-)
Quote:
My objectives are maximum torque and fuel economy keeping the low rpm torque curve I already have. It's a work truck which never sees more than 3,000 revs.
How much work are you up for? There's a great deal to be gained with thoughtful camshaft selection and dial-in. And is yours presently running a 1bbl or a 2bbl carb?
Author:  NorEaster [ Sat May 21, 2016 1:33 pm ]
Post subject: 
Exhaust plans include Doc's manifolds, (assuming I can get them?) feeding the 2 into 1 system. X over pipe. Probably dual cats.

Presently the Carter 2bbl. Long term goals include Turbo / EFI.
Turbo(s) to be sized for low rpm results.

I plan to stay with the 1600-2600 torque curve as it suits the use of the vans. (Towing & hauling tools.) A B350 Maxi (9,900lb. GVW) will follow after I finish the B100. The Maxi will need the turbo more than the B100.

I think I'm hijacking this thread. I should start my own on my projects.
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