Big manifold hole & Smaller carb throat.

[nextgen]

I had the beautiful original CB tall manifold on my 914 but when I went to the Cali Style Upright Conversion I had issues adjusting the carbs. Even cut the manifold so then would work. Helped but not good. The late Joe of Oregon Performance told me to buy from RedLion. No clue if they are still around. Difference was the original were aluminum. The smaller are Cast Iron. No big deal but I liked the Aluminum better.
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email: [email protected]
The TYPE IV UPRIGHT CONVERSION MANUAL
BEETLE MAGNETIC DEFLECTOR SHIELDS
LETS TALK DUBS https://www.youtube.com/results?search_query=joe+cali+ghia https://letstalkdubs.libsyn.com/ep-200-joe-cali-ty...qI3xJTCzjs

[67 Sunroof]

I just read through all of this-it’s fascinating!
I remember back when I was messing with Honda Civic’s in the 90s that the Acura Integra motor had a Plenum with butterfly valves and 8 runners similar to Ford’ idea WAAAAY back in time. There were short runners and long runners in the intake manifold. When you hit say 5700 rpm’s the butterflies would activate and open up and that would allow the air to run through the longer plenums for better flow at high rpm’s. Pretty cool
That motor redlined at 9100.
Another cool thing I learned was anti-reversion headers and “stepped” headers.
Anti-reversion had a lip at the beginning of the flange to keep exhaust gasses from being sucked back into the head.
Stepped headers would start small and gradually get larger as it got further away from the head to keep torque.
And scavenging cylinders...
Adjusting the valves so they had the slightest overlap would help “scavenge” the cylinder. It would suck FRESH air in and force out the “spent” exhaust gasses from the cylinder to help it ignite better.
I also learned that a pent roof design was superior because it would force the air/gas into the “squish” area and allow a more efficient burn.
I’m FAR from the smartest cookie in the book but engineering fascinates me.
I learned ALOT from Larry Widmyer from ENDYN. The man was a genius.
Thanks to Pat for being here. You don’t HAVE to divulge your secrets and what you have learned over the years. It’s taken you years to test and develop and I totally agree with your stance.
But,
Before you leave this planet........PLEASE PLEASE write a book to pass on to us less wiser people so we can utilize it in our builds!
Haha
Thank you!

[oldschool5er]

[oprn]

[ralf]

[BarnFine]

Dual 2 barrel carbs are going to respond much differently than a conventional engine with a joined manifold to a single carb. Some notes from the usage of multiply carbs on a v8 give us an example.
"Compare this to a conventional 4-barrel arrangement. Each cylinder is connected to a common plenum, and the carb can be as much as a foot away from each cylinder. When a cylinder valve opens, the entire column of air reaching back through the manifold back to the carb must begin to move, and that takes time, which affects throttle response. Furthermore, that cylinder must pull air and fuel from a carb that is designed to deliver air and fuel to 8 cylinders, not just one. Contrast that to one which provides a dedicated barrel to each cylinder and can therefore be optimized for that cylinder rather than compromising in order to be able to serve 8 cylinders."
Let's think about a dual runner intake used on modern engines. For low RPM torque we use a long skinny runner, for air speed. As we move into a higher RPM and would normally start starving the cylinder for air we move to a fat short open runner.
Now let's consider acoustic supercharging properties of an intake. While the air is moving we have a column of air moving into the low pressure area of the cylinder, when the valve closes this air (which is still moving) is going to bounce back off the valve and hit the air moving in behind it. This creates a pressure point of air behind the valve, the air will resonate. If the valve opens at the right time (RPM) we get an additional boost of air into the cylinder.
The design of the intake, it's length and size, will determine at what RPM we will get this benefit. Now imagine how this affects having a larger port up the intake runner which can act like a chamber. You can actually calculate the correct length and size of a runner which would be beneficial to someone planning out his power band.

[Wreck]

I was going to try making a Plenum that joins both runners ,a bit like a turbo set up , and then put the carbs on top so both throats can feed each cylinder . with a big 1 inch balance pipe .
I think it would also help reversion plus in my case my 48 Dells are maxed out with 42mm vents and I feel they still don't flow enough . that way I could come back down in vent size so the carb works better . that was my theory anyway . I decided to change to EFI so won't try it.

[Wreck]

[ralf]

maaan thats cold right there..

def understand though...

and yeah shipping might not be practical and the waiting time if it means your bug will be parked the whole time

tell u what...

while its cold LOL u can actually do a template of the carb gasket base etc and figure out a pattern that offsets it ... not enough to need it welding or adding another tang, but maybe it could be possible to restud the same flange and just leave the "originl" stud holes vacant and it wont affect things right?
_________________
Flow Through a Curved Conduit

porting my SP head for my brother's project
https://youtu.be/OS_mVjQuqgk

[oprn]

[ralf]

omg... dont tell me u went against "porsche engineers' ?


LOL but my point exactly...
_________________
Flow Through a Curved Conduit

porting my SP head for my brother's project
https://youtu.be/OS_mVjQuqgk

[AlteWagen]

I noticed a reduction in fuel stand off when going to a larger bore manifold flange. I originally had some early offset CB manifolds with the small opening but needed some straight manifolds for the new linkage I got which had the larger 48mm bore. At upper rpm (4500 and up) I could see a lot less fuel 'fog' above the carbs with the larger manifolds. I originally thought it may have been due to the 'straight' manifolds but as a youngster I didnt do anymore research as it did run better and I just kept driving it.

Fast forward a couple of decades and I noticed the same when working with some kadrons. This time it was a large port on the head but a smaller manifold port that left a 'ledge' hanging over the head port. Again noticed a lot less fog on the upper rpm range.

This time I did a little reading and saw that others have also seen similar results and that it helped reduce the reversion caused by the column of air smacking the closed intake valve.

I know its not scientific but visually and SOTP told me there were improvements.
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Grapes of Wrath $200 Engine Rebuild
Official Dual Carb Thread
Cylinder Head Quick Reference Sheet

[ralf]

[oprn]

I doubt I have room for spacers as the air cleaners are already too close to the body. If anything I would like to make these manifolds shorter.

[ralf]

or just have a 1/2 inch aluminum flange/base cut

drill and tap for the current spacing.. countersunk it with bolts

then dril and tap new studs.. bam! u got urself offset LOL



can go extensive by slightly tapering the flange bore to suit etc or just bore it to 44mm LOL
_________________
Flow Through a Curved Conduit

porting my SP head for my brother's project
https://youtu.be/OS_mVjQuqgk

[modok]

I had to have some material added to extend the inside ears, the outside I plugged with 1/8 pipe plugs and moved over.

[UK Luke 72]

Pull the studs, weld, reface and tap new holes probably .
Or slot the carb holes?
_________________
2276 Beetle build https://www.thesamba.com/vw/forum/viewtopic.php?t=670744&highlight=2276+beetle+daily
2276 EFI Conversion https://www.thesamba.com/vw/forum/viewtopic.php?t=689172

[74 Thing]

[oprn]

I have 40 mm carbs on 44 mm manifolds. So you are saying that if I shifted the carbs slightly in board toward the engine centerline there could be an improvement?

And it would keep the right air cleaner from rubbing on the body! Sounds like a win/win to me!

[ralf]

interesting cool points modok....

i must admit... earlier on (a few years ago) i always thought manifolds perfectly matching the carb bore was best...

atleast in every paper we see and read it says its best... heck we have the way over used term of "port matching" too LOL! so why not?


until very recently (mind u its not vw lol so dont hate me so much)

we had a fully dynoed car/engine that sported a 70MM throttle bore... it was fine and good..

(odd story owner had to downgrade) so he moved to 62mm... oddly enough the manifold was already ported for 70mm.. so it was mismatched? as per modok explained...

but oddly enough 4-5k rpm improved... and the top end = peak power keept trying to hold on hehehe... and previous peak power was 8,700rpm...

so we assumed it was good peak right? until the downgrade of throttle.. peak power hovered form 7,500rpm to 9,000rpm.. so it was a table top! i was surprised myself...


so going back to vw... production ease yes but Pat D may know something more than most.. and the usability etc...

we havnt even touched the factor that modok mentions... wet flow is of different volume than dry flow aka.. it may need slightly more space after the vents....




but hey... portmatching rocks. on paper and by the book its what it says LOL
_________________
Flow Through a Curved Conduit

porting my SP head for my brother's project
https://youtu.be/OS_mVjQuqgk