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Weber 40 question
http://forum.porsche356registry.org/viewtopic.php?f=1&t=45862
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Author:  Robert Reed [ Mon Apr 09, 2018 3:41 pm ]
Post subject:  Weber 40 question

Hey Guys, I have a set of 40IDF’s on my Super 90, and wondered how much the air horns do for it.
I am still trying to get this car back on the road and ordered a new set of air filters for it; they were on the carbs but new filter base won’t allow them to go back.
The horns are 42mm tall and I assume they add a little ram effect to the engine.
Would like to hear your input on the question.
Bob

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Author:  Tim Berardelli [ Mon Apr 09, 2018 5:30 pm ]
Post subject:  Re: Weber 40 question

Just trim the excess material off the base to provide the required clearance for the air filter elements. A small cut-off wheel on a Dremel type tool will "do the trick".

Author:  Robert Reed [ Mon Apr 09, 2018 5:47 pm ]
Post subject:  Re: Weber 40 question

Tim
Thank you for the suggestion, unfortunately with this air filter base I don’t believe that it will be that easy a solution.
The top hold-down bolts are located midway length wise which places them exactly in the wrong location for doing that.
I was just trying to determine what effect removing the horns would have. I certainly don’t intend to race the car, and doubt I will be revving it past 5k.
Bob

Author:  neilbardsley [ Tue Apr 10, 2018 5:03 am ]
Post subject:  Re: Weber 40 question

Robert Reed wrote:
Tim
Thank you for the suggestion, unfortunately with this air filter base I don’t believe that it will be that easy a solution.
The top hold-down bolts are located midway length wise which places them exactly in the wrong location for doing that.
I was just trying to determine what effect removing the horns would have. I certainly don’t intend to race the car, and doubt I will be revving it past 5k.
Bob


I have horns on both my 40 idf engines. They are both used on the street and I rarer too rev beyond 5k but they make a difference in torque. I think you might be better using some horns which are more open and will fit under your filter. Like these.

https://www.ebay.co.uk/i/322657061719?chn=ps&dispItem=1&adgroupid=13585920426&rlsatarget=pla-142413585906&abcId=&adtype=pla&merchantid=113632889&poi=&googleloc=9072497&device=c&campaignid=207297426&crdt=0

I think the larger opening creates better flow. I choose about 4cm because any longer wouldn't fit under my filter but I think that longer is even better for lower revs? I think that is a 2d graph in the 356 performance book that maps distance from head to rev?

Author:  Tim Berardelli [ Tue Apr 10, 2018 6:30 pm ]
Post subject:  Re: Weber 40 question

Robert,

Please post a picture of your air cleaners. Maybe we can figure out a solution. One really good reason to use velocity stacks is that if any hardware gets loose, the engine won't eat it or them.

Tim Berardelli

Author:  Robert Reed [ Tue Apr 10, 2018 6:56 pm ]
Post subject:  Re: Weber 40 question

Tim;
I did some reading on the net for airflow on the Weber’s and decided rather than cut up the original air horns that I would just order some that are individual horns. I also read where the trumpet style are much better for smoothing out the flow. Apparently the straight horns tend to “pack-up” the air coming into the carburetor. Hated to chop up the old air horns anyway, so this seems a better option; the new stacks are the same height as the old.
Thank you for your support,
Bob

Author:  DonCichocki [ Tue Apr 10, 2018 8:23 pm ]
Post subject:  Re: Weber 40 question

Robert,
Here are my Weber 40's with, I think 1 5/8" tall, velocity stacks in conjunction with K&N air filters. I did a little notching with a round file on the flange of the stacks as I had a little interference with some components on the top of the carb. They fit inside the filter fine. Hope this helps.

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Author:  Robert Reed [ Tue Apr 10, 2018 9:32 pm ]
Post subject:  Re: Weber 40 question

Don;
You must be omniscient, that is exactly what I ordered this afternoon. Same height even.
Bob

Author:  neilbardsley [ Wed Apr 11, 2018 5:43 am ]
Post subject:  Re: Weber 40 question

DonCichocki wrote:
Robert,
Here are my Weber 40's with, I think 1 5/8" tall, velocity stacks in conjunction with K&N air filters. I did a little notching with a round file on the flange of the stacks as I had a little interference with some components on the top of the carb. They fit inside the filter fine. Hope this helps.


That is almost exactly my setup but your engine is cleaner :)

Author:  Robert Reed [ Tue Apr 17, 2018 9:24 pm ]
Post subject:  Re: Weber 40 question

Guys; just wanted to let you know that I did resolve my issue.
I got 4 individual velocity stacks and thought I’d post a pic.
I really do appreciate the time and effort y’all put into responses to questions being asked; it’s truly invaluable!
Bob

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Author:  neilbardsley [ Wed Apr 18, 2018 3:10 am ]
Post subject:  Re: Weber 40 question

Cool. Did you consider going up a little in size in the main jets? I bought some 2.5 larger but haven't tried them yet. I figured that the better airflow meant I might now be running a little lean on the main circuit. I guess you will find out when you road test.

Author:  Robert Reed [ Thu Apr 19, 2018 1:50 pm ]
Post subject:  Re: Weber 40 question

Neil,
I basically just replaced what was there height wise, and doubt that there was that much difference to warrant change to the jets. So, the answer is no...
Bob

Author:  Kerem Ustunkaya [ Sun Apr 22, 2018 2:25 pm ]
Post subject:  Re: Weber 40 question

DonCichocki wrote:
Robert,
Here are my Weber 40's with, I think 1 5/8" tall, velocity stacks in conjunction with K&N air filters. I did a little notching with a round file on the flange of the stacks as I had a little interference with some components on the top of the carb. They fit inside the filter fine. Hope this helps.


Hi Don,
Are you happy with your velocity stacks and KN configuration?
Was it easy and issue free to jet and tune ?
What is your engine specs and jetting in your IDF 40s ?
As a matter fact, I have posted a new topic/subject today regarding to my tuning/jetting issue and reached to this subject via my subject. You may find it interesting as well.
Regards,
Kerem

Author:  DonCichocki [ Mon Apr 23, 2018 8:28 am ]
Post subject:  Re: Weber 40 question

Kerem,
I find the K&N filters and stacks fine. Better than the stock Porsche filters and the stacks seem to help jetting at lower RPM's.
I don't think the filters effected the jetting as I can't feel any difference with them on or off.
My engine is a late "C" with a 1720 Shasta P/C combo and Weber 40 IDF's. I'm in the process of returning it to a stock "C" cam but it had a modified "SC" cam in it so the jetting I'm posting might change.
I ended up with: 135 main, 55 idle, 210 A/C, and F11 emulsion tube with the top 2 holes soldered up. By soldering up the top 2 holes the main circuit comes in sooner and eliminates the Weber stumble. There are MANY combinations that people have come up with that work, this is what worked for me.
Also get rid of the Weber manifolds and get a set of Solex manifolds and adapter plates to mount the Webers. The Weber manifolds are made to use with 40IDF AND 44IDF so the opening is way too big for the 40's. My Weber manifolds measured 47mm at the carb flange!

Author:  Kerem Ustunkaya [ Mon Apr 23, 2018 11:04 am ]
Post subject:  Re: Weber 40 question

DonCichocki wrote:
Kerem,
I find the K&N filters and stacks fine. Better than the stock Porsche filters and the stacks seem to help jetting at lower RPM's.
I don't think the filters effected the jetting as I can't feel any difference with them on or off.
My engine is a late "C" with a 1720 Shasta P/C combo and Weber 40 IDF's. I'm in the process of returning it to a stock "C" cam but it had a modified "SC" cam in it so the jetting I'm posting might change.
I ended up with: 135 main, 55 idle, 210 A/C, and F11 emulsion tube with the top 2 holes soldered up. By soldering up the top 2 holes the main circuit comes in sooner and eliminates the Weber stumble. There are MANY combinations that people have come up with that work, this is what worked for me.
Also get rid of the Weber manifolds and get a set of Solex manifolds and adapter plates to mount the Webers. The Weber manifolds are made to use with 40IDF AND 44IDF so the opening is way too big for the 40's. My Weber manifolds measured 47mm at the carb flange!


Hi Don,
Many thanks for your kind reply.
You have a very nice engine with the 1720 Shasta P/C combo. Did you have any mods to the cylinder head where the cylinder edge meets the cylinder head? The reason I am asking this, if I am not wrong larger bores can cut into cylinder head and may cause a crack in time especially if the engine is driven hard. I believe this is the case with any large bore cylinders but I am not sure.
You are right, Weber manifold will effect the gas speed. Is the Solex manifolds and the adapter plates somehow available ?
Best regards
Kerem

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