Need help figuring out vent size and jetting for my 1776

[Ghunter]

Have a 1776 here's the build sheet...
W110 cam
Stock ratio rockers
Panchito 044s from cb 40x35.5 valves
Port matched intakes
8.3:1 compression

I had some 36 dells with 30mm vents and the motor use to pull very strong all the way to 6k

Unfortunately they are leaking into the motor with the car off fouling up my oil, I have a set of new hpmx 40s i had put on and tuned but I noticed they're a loss of power in my mid to upper range,

The 40s have 28mm vents and I belive close to stock jetting mains might be bumped up but I'd have to pull them apart to find out,

My main question is should I go with 30mm or 32mm vents and jet accordingly or should I be able to see the same power with the 28 vents and different jets[/quote]

[Ghunter]

I guess I could add, it's got stock gearing with 205/65r15s in the rear
Mainly street driven but moved closer to a track and would like to take it to some test and tunes

[Lingwendil]

Maybe 30mm vents. What exhaust?
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[Ghunter]

1.5in sidewinder with 2 or 2.5in muffler

[Ghunter]

Also pulled jets out mains are 115 airs are 200 not too sure about idles they could be 52 or 55 I remember I changed them but not sure if I switched back or not when I took them off

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I had a similar size cam in a high compression 1776 wth ported 40x35.5 valved with .60 idles/1.35 mains/200 airs/28 vents. Cb’s latest Panchitos flow quite well, but you’re pretty low on compression. I would think you would be in the range of 55-57 idle, 1.25-1.30 main, and I would keep the 200 airs with the standard 28 vents. The bottom line is you’re just going to have to get some jet sets and experiment. Everyone can speculate what size “it will be” but they are all just educated guesses. When you do get it tuned in, please post your results for others to use as a guideline?

[Danwvw]

Yes dells can leak gas through if the floats hang up and gasohol tends to boil out of dual carbs on air cooled engines when metal head to manifold gaskets were used. I finally put a gas shut-off solenoid on my tank to fuel pump line.

I would think the 40x35.5mm heads need 30 or 32 mm venturi's to really perform at higher rpm. Yes the original jetting sounds lean to me.
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[Ghunter]

okay well if i goto 30 or 32mm vents, where should i start with jetting im at about 1250' up from sea level

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I would keep the 28’s. That cam will start to flatten out around 5000-5500 rpm. Anything you would gain in the upper rpm range, you will loose drive ability in the bottom rpm ranges. If it’s going to become a track car 60+% of the time, by all means, try the bigger vents. If you are driving it more, I would think the standard 28’s will have a little nicer street manners. It would be one thing if the engine was a large stroker that the displacement could carry the load in the bottom rpm ranges, but I would think it would significantly change the bottom rpm behavior with a 1776. Going from a stock heater box 1 3/8 header to a 1 1/2 heater box 1 5/8 header changed my 1776 drastically.

[modok]

main jet should be 4.2 times venturi size to start,
with 200 air, fine tune from there as needed.

Going to the max vent size the carb can handle you often end up with a lean spot at 1/4 throttle, thus will usually have to go to a larger air jet size, 210 or sometimes 220......and a step larger main to match the larger air jet to make it all work. What is the max the carbs can handle? 32? 33?

Progression ports on HPMX are not exactly the same as 40idf-70, hopefully in a good way but I don't really know.
The hpmx should in theory be able to run a 32 or 33mm venturi but..... assume nothing! How big you can go will have to be found by trial and error.

31mm venturi and 130 main seems to be the right size for many mild VW engines.

34 would be a better match for what those heads could flow, but probably too big to match the rest of the engine, tho it might work if you had 44mm carbs.


Maybe.... drill the jets to 1.32 and adjust the venturi size until it's right?
I know that's totally backwards to adjust the venturi to suit the main jet, but, probably would work just as well, or probbly better.
Weird but true.

[Ghunter]

If I wanted to have my vents opened up I'd just do that on a lathe correct? I wouldn't need to reprofile the contour?

Just cut the hole bigger and smooth the transition?

Obviously going to try bigger mains before anything, but if I'm still not getting the pull I had before, bigger vents seems to be my next option

[modok]

A basic venturi has a leading angle of 22 degrees and a trailing angle of 5-7 degrees. Meaning "off centerline" like you would set the lathe compound slide.

That may need to be changed a little to make it actually all fit, but you basically can't go wrong sticking to the classic form. If 5 degrees will make make the bottom a razor edge then I guess we go down to 4 degrees, ect....
The entry can be more of a raduis but I don't think it makes any huge difference.

The section that is bored straight to be the smallest point, should be perhaps 2mm wide and located so the bottom of the aux. venturi is even or just 1mm downstream of the smallest point.

more trouble that it's worth, unless the ones you bought are made wrong......
Last time I bored some I went 0.1mm overesize on one, and was all upset about it but, actually that's 2x more accurate than most of the ones I ever bought.
Some of this chinese stuff I wonder... maybe the size marked is what size the wished it was? Trust but verify. Jets and vents too.

And BTW hpmx take the same venturi as 44idf,

(Not the same as the weber 40 idf commonly sold)

[Ghunter]

Yeah thats why I was asking about opening them up, cb performance sells 32mm as the smallest for 44 idfs, and everywhere else I'm looking wants 20$+ per vent

[modok]

Yep, that is a bit odd isn't it.
You'd think empi would be selling a lot of venturis but I guess they don't.
Some of the e-bay sellers are very good.
I got some very nice emulsion tubes from a seller in the Check Republic, just as good as Italian, a venturi is a simpler part.

[Ghunter]

Looked last night I found some that are coming from the Czech Republic and they do look very nice if bigger mains doesn't solve my issue I'm definitely going with those

Found a .125 drill bit measured with calipers, might try drilling the mains and giving her a test drive

I'll report back

[j-dub]

What about fixing the DRLAs?
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[Ghunter]

Would love to just I'd want it done correctly, haven't done any research into who does it still and is reputable, only one drains out but it'd be nice to have them both freshened up

[Ghunter]

Took her out for a spirited drive just now bigger mains definitely helped a lot now I just gotta fine tune my linkages stumbles a bit off the get go and is popping thru the carb sometimes when I blip the throttle

[74 Thing]

You can contact Rick about the DRLA rebuilds
https://www.thesamba.com/vw/classifieds/detail.php?id=1792064

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The jet sizes are actually metric, so a 125 main jet is 1.25mm. This would actually be .049 in inches. If using an 1/8 inch .125 drill bit you are making a 318, or 3.175mm jet.