Big manifold hole & Smaller carb throat.

[Bruce]

[Eaallred]

[thetravman]

[Pat D]

[krusher]

[Lionhart94010]

I can understand that some samba contributors may make their living based on the research they have worked hard to get… And it is their prerogative & Understandable if they do not want to tell us everything they know; I cant blame them for it, however it is always a great pleasure when a member with a greater understanding helps enlighten us all with more than just a “yes it will” or “no it wont” :0)

Getting back to the subject at hand; it seems that it should be possible for an enterprising person to make sets of different inserts to fit in the “Big hole manifolds” with different diameter pipes that would fit under the carb and get close to where they naturally narrow in the manafolds to see if there is any appreciable difference for any specific engine setup… (I’d do it but have too many projects already)

(This might be a Product idea worth patenting ;0)

Thetravman,

For your planned mild 1600-1776 engine, it might help to look at what VW and other MFG’s did for their stock setups that are similar to what you are going to have, your post is under “Performance/Engines/Racing” and the advice that you are getting may not be what is best for your application…

My (unprofessional) guess is that for your application having a close matching size(negative not positive) between your intake manifold and carb base would be best; and that you may want to pay special attention to your manifold length and the velocity stack/air cleaner setup to make sure they compliment the rest of your engine’s setup :0)
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Current VWs 71 T2 Westy SO-72/6(Miami), 71 Crew Cab, 2015 GSW TDI
Other owned VW’s 59, 68 1500s, 69 & 71 Bug’s; 72 & 73 S-Bug’s; 67 Westy, 67 Deluxe, Other 71 DC, 72 KG GT that now lives in Australia, 12 JSW TDI, 2015 GSW TDI, 2023 Tiguan
VW technical information sights
thesamba - www.ratwell.com - www.shoptalkforums.com/ - www.vw-resource.com - http://www.type2.com/
http://bobhooversblog.blogspot.com/ - www.aircooled.net/gnrlsite/resource/articles.htm

[thetravman]

I want to believe that IDF's can be mild and fairly fuel efficient. IDF talk is found in performance/engines/racing.
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Have your car serviced at your local aircooled repair shop today.
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[mharney]

They can. It just depends on how you jet them and what you put them on. There are other factors too, smooth linkage action goes a LONG way to taming carbs, believe it or not. Getting everything else in tune matters a lot too.

I got 28mpg on dual 48 IDFs on my 2332 without really even tuning for mileage.. I tuned for power where I wanted it, and put my foot in it quite a bit. Idle jets are a major component to mileage figures and I paid little attention to those when I set it up.. I think they hovered around 55-57 on mine, which is about right, but I never tried to take to into the lean no man's land.

[redhot]

The Germans looks to think otherwise... So, which is the best, and why?

CSP Type-1 Weber IDF Manifolds

These CNC Machined Manifolds are available in 40mm,44mm and 48mm and will provide a much better mixture flow than the universal Manifolds. They are reinforced for port matching and each Pair comes with German made Gaskets in the right diameter and a complete fitting kit with metric Hardware.

* Made in Germany
* CNC machined
* Available in 40mm, 44mm and 48mm for maximum flow
* Reinforced for Port matching
* Quality Gaskets
* Metric Hardware
* Good Body to Manifold Clearance


http://www.csp-shop.de/cgi-bin/shop2/shop_main.cgi?func=start&wkid=48086022079

[veedubnut]

Has anybody looked at a single plane manifold for a V-8, say like the Victor Jr? It has a giant 4inch square hole in the middle and 1000 cfm throttle bodies seem to love it...just my 2c...

[GTV]

I'm no engineer but the one size fits all manifold thing has always bothered me. So I conferred with Porsche engineers by measuring the manifold from a 356/912 engine that mounted 40mm Solex PII carbs.

And the answer is:

Approximately 40mm.

Huge surprise

One size fits all manifolds work good enough for the masses and are cheaper to produce. It's about profit margin, nothing else.
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EMPI Power Rules!

[modok]

Thinking often amounts to nothing. Try it both ways then we have something to think about, if you haven't, then I don't know what we got to discuss besides your imagination, which is limited.

I know of four reasons a larger size can work better.
There's a good possibility Pat has a different theory.
I get the feeling that explaining it would achieve nothing!!

[mark tucker]

different applications need different things as do different engines witch falls into the different applications category.all aspects need to be considered.

[74 Thing]

[Brian]

I had similar concerns on this. Modok had some good notes
https://www.thesamba.com/vw/forum/viewtopic.php?t=694866
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Wash your hands

'69 Bug
'68 Baja Truck
'71 Bug
'68 Camper

Only losers litter

[bugguy1967]

He’d have to re-remember what he was talking about from four years earlier...
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"A petrol engine can start readily, run smoothly and give every appearance of being in good order, without necessarily being in good tune." - Colin Campbell, "The Sportscar Engine"

[modok]

yep, don't remember
I still don't know for sure what would be THE best. It is possible that there is even more power and drivablility to be found with different shape intake manifolds.
Phenolic insulators matched to the carb bore work well, offsetting the carbs towards the middle so the the low hanging side of the throttle plate lines up with the wall, works well.

I think the reason carbs like a larger bore below the venturi is it gives better "fuel shear"
Just by dry flow you would not need the the throttle bore to be more than 15% larger than the venturi, but actual real world up to 50% larger WORKS great, so it has to do with the FUEL, not the air flow. Why do IDAs kick ass? there are reasons. it's not just for show! BUT FOR THROTTLE CONTROL...biG THROTTLES, NOT SO GOOD, very touchy, so you can see why it can make sense to have below the throttle larger. How much larger, where, what shape, hmmm, you tell me!

Say, if you had a manifold where right below the carb the passages tilt 15 degrees toward eachother, then neck down, THEN curve toward the head....I'd like to try that

[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
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Flow Through a Curved Conduit

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

[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!

[74 Thing]