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Zenith 38 39 NDIX ?
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JeeWee
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PostPosted: Wed Dec 25, 2019 2:20 am    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

you can easily convert your 38's to 32's with swapping the throttle bodies out, just source a set of throttle bodies and you are fine. other diameter venturis etc is available as well
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PostPosted: Wed Dec 25, 2019 3:34 am    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

JeeWee wrote:
you can easily convert your 38's to 32's with swapping the throttle bodies out, just source a set of throttle bodies and you are fine. other diameter venturis etc is available as well


Yes and no ....Yes.. he /you can do that just buy 2 new rebuilt kits for 32 ndix that has the correct accelerator pump yes there are two different types .. no on venturis there nothing he can do with venturis on those 38/39 ndix body's the venturi on those are cast to 28mm I believe so there gonna have to stay that size or machine for bigger venturis the 32 body's have removable venturis , he would also need to buy 2 32ndix controls pump levers the one on the 38/39 are longer do to the fact the 38/39 ndix have a fatter base the 32s have a thinner throttle body to body gasket ....
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Alstrup
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PostPosted: Wed Dec 25, 2019 6:05 am    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

JeeWee wrote:
Hey Alstrup, I think I have to agree with you. I would love to test both the 32's and 38's on my motor and see what differences are shown on the dyno. Ok I have 8,0:1 CR, ww okrasa cam, 1448cc etc, and have to say they do better then expected in low RPM's. I am running stock WW orkasa valve size 33x28 But it might be the case the 32's do better then 38's, but I came across these and thought it would be so cool to run 38's. There are a couple of guys running 40's (weber/solex) on 69,5x80mm combo's so I thought let's give it a try.

Anyhow what venturi size would you run on 38ndix on such a setup?

Hello.
Alright, for an engine just shy of 1500 cc. with the WW cam the stock 28 mm venturi in the 36/38 mm carbs are not that far off. With the extra displacement you also get the chance for meore static compression, and while 8-1 is not especially high it makes a significant difference to the 7,3ish CR possible without doing something drastic with a normal Okrasa kit (1286 cc)

Speaking of difference in engine behaviure. Not so long ago I was approached by a guy that had built his own Okrasa engine out of a WW kit. Unfortunatly 2 pistons was damaged due to some foreign debris entering the engine. So it had to be taken apart, cleaned and fixed. Thatīs where I came in. He was basicly satisfied with the engine since it gave him a better driving experience than a stock 1200. Since we had to invest in new parts anyway I persuaded him to do it "my way" which meant taking a set of late model 1200 dome pistons and then further machine the pistons to protrude 1,25 mm into the chamber, leaving a "pocket" opposite the spark plug so there would be no intereference there either. Also, one of the seats were nicked just a little, so we performed a complete competition valve and seat job. Then he put it back together. Now the engine has 7,8 CR and he says that it is almost hard to believe that it is basicly the same engine. It is much more responsive now and pulls way better than before. Idle stability has also improved.
I will admit that it is a lot of work to get 0,8 more CR, but to me it is worth it.
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PostPosted: Fri Dec 27, 2019 5:51 pm    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

You can make a big carb smaller but you can't make a small carb bigger.. At Bonneville the carb system of choice is Empi repro 48 ida.s . They work amazing. I know it seems wrong but it works. If it was not for the rules at bonneville I would run Kadrons or ict's on smaller 36 hp builds but on a big engine I wish I could run 40 dcnf.s or 36 dellortos
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PostPosted: Fri Dec 27, 2019 6:20 pm    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

AirCooledClassics wrote:
You can make a big carb smaller but you can't make a small carb bigger.. At Bonneville the carb system of choice is Empi repro 48 ida.s . They work amazing. I know it seems wrong but it works. If it was not for the rules at bonneville I would run Kadrons or ict's on smaller 36 hp builds but on a big engine I wish I could run 40 dcnf.s or 36 dellortos


I wouldn't begin to argue with you about the efficacy of a carb on a bonneville engine because I have never been there and run that course...But thats kind of comparing apples to oranges. A pure bred bonnevile engine is designed to run WOT, not be a daily driven traffic engine.

putting 48 IDAs on a 1200-1300cc MILDLY built okrasa engine is not such a good idea (not implying you said that specifically).

The 38's will work yes, but if it were my engine I'd still opt for 32s. just my $.02 though.
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Frederik
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PostPosted: Sun Mar 15, 2020 5:54 pm    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

I've been thinking if i should try and trade or sell the 38/39 carbs and try to find a set of 32 instead. Buy I think I will do this instead

First build
WW okrasa kit
And just use the ww okrasa solex copies
77mm domed pistons
Stock crank and cam
Speedwell 1.25 rockers

But I've started to collect parts for a next build
80mm AA p&c
BBT cam
(WW crank, not bought)

And then try and see if I can get use of the 39NDIX pair.
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PostPosted: Wed Mar 25, 2020 4:40 pm    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

you could easily run engines of that size using only ONE 32NDIX
single or dual, they work great!
especially if you look into some of the modifications that can be done with them.
25 & even 26mm venturies are out there or could be easily made.

www.356carburetorrescue.com in US.

http://www.riechertmotorentechnik.de/Vergaser/Duesen/duesen.html
reichert has jets and goodies.

i'm sure there are some specialists in EU as well, seeing as the NDIX was used in multiple applications.

i love them! best carb ever Very Happy
never got to play with the bigger ones Sad
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PostPosted: Thu Feb 25, 2021 6:55 am    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

Frederik, near carbs.

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PostPosted: Tue Mar 09, 2021 10:48 pm    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

I agree wholeheartedly about running a single 32 NDIX on the right size motor. I somehow stumbled into putting one on a 1200 with a big bore kit and small EMPI cam in dune buggy in the 70's. Everything seemed affordable those days, even on a high school budget. Anyway, it was great, reliable in every way and I knew nothing about it and never touched anything but the idle.
Later it came off and I had a German expat mechanic install it on my new-to-me '71 bus. A NY winter was a case of special handling of the manual choke. Move the arm by hand before starting, let it warm up, move the choke to full off and drive. Simple enough and always worked. It was driven cross country from NY to OR during the fuel shortages. As I recall we got consistent mpg (I don't remember the numbers, but we didn't cuss about it) and, again, not a lick of trouble.
I have a sp 1600 in a bug now and if I could afford a 32 with manifold it'd be grand.
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PostPosted: Thu Jun 24, 2021 8:48 pm    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

I've put my 1448cc WW okrasa engine on the bullshit detector:

Image may have been reduced in size. Click image to view fullscreen.


got the proper jetting and impressed with the results, already 100nm at 1500rpm. With the 38ndix mounted still a lot of torque at the low end!

68,68DIN hp oh yeah!

I love this engine!
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PostPosted: Sat Jun 26, 2021 1:18 pm    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

Dancing
Looks like you have some intake reversion in the 1700-2100 rpm area. Did you notice if the carb sound was "snapping" in that area? If you want to pursue it you might want to install intake tracts to help reduce the reversion (Actually improving the intake port energy)
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PostPosted: Mon Jul 05, 2021 3:57 pm    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

Alstrup wrote:
Dancing
Looks like you have some intake reversion in the 1700-2100 rpm area. Did you notice if the carb sound was "snapping" in that area? If you want to pursue it you might want to install intake tracts to help reduce the reversion (Actually improving the intake port energy)


Hi Alstrup, you are right, this caught my eyes as well that the curve is not really smooth in that area. I have not heard the carb snapping.

On one of the carbs the throttle shaft is not 100% straight. I only did 1 run as it is a new motor. Need to fix the carb so it might run smoother. because it had idled for a long time and 1 of the valves doesn't shut fully, I suspect that one of the spark plugs if fouled, when i came home I replaced it and it ran way better.

I am curious after your idea to install intake tracts, how do they look like? I have not heard of these before honestly, and I am always open for feedback en new learnings. I will put it on the dyno again on the 28th of august. Perhaps I can incorporate your feedback.
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PostPosted: Tue Jul 06, 2021 2:25 am    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

Here you go: https://www.precisionmatters.biz/backstory-zenith-power.php Scroll down and they turn up
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PostPosted: Tue Jul 06, 2021 2:33 am    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

On second thought, It is most definitely an intake reversion. Assuming the fuel delivery (AFR) is within reason it kinda looks like the the intake is rather efficient right there. By adding stack and/or changing the intake length you may very well be able to smooth that out so it keeps "the good line" further.

If you take the heads off to perform a valve seat job I will definitely recommend that you get a performance valve job done to them. On an engine like yours I would not be surprised to see a 5 hp improvement with even better torque.
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PostPosted: Wed Aug 25, 2021 1:49 am    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

https://www.precisionmatters.biz/velocity-stacks.php

Gotcha, you mean those. I do agree that these might help.

The May 1977 Hot VW's Zenith NDIX carb article stated: 'If using an air filter that mounts atop the carb, be certain that there is at least four inches of clearance between the top of the carb and the top of the air filter. This is for gas standoff wichi is acutally the gas/air mixture taking place out the top of the carb. If the top of the filter is not at least four inches, the gas/air mixture will hit the top of the air filter and cause solid droplets to form on it.'

I don't have these stacks now, which is a pity, as I have a dyno session on saturday.

I will keep you updated, and yes I am very interested in your research on how to make the okrasa heads flow better. I love the use of the Ferrea valves, really good stuff. I now use the stock valve style and they look horrible in terms of flow.
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PostPosted: Wed Aug 25, 2021 3:08 am    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

I got one more 39 NDIX (now have 2x 38 and 2x 39) so the 39NDIX was not a one off modification. Still not sure for what it was used on originally (simular but not the same as Unimog, Hotchkiss etc) but where I got it from I suspect some military used veicle.

They are made by Zenith Stromberg, France.

Comparison next to a Porsche 32 NDIX

What I still havn't found any other model NDIX to have is the valve in the throttle body (blue arrows). The level (bottom arrow) opens up a brass valve (middle arrow) venting the connection between the two ports to air (top arrow).

39mm looks to be as big as the port can get
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Red arrows are difference I've spotted. The 39/38 carbs all miss this two "screws", what are they? (Holes not drilled or tapped so not really missing)
Image may have been reduced in size. Click image to view fullscreen.


Vacuum port prepared (vacuum signal to distributor possible?)
Image may have been reduced in size. Click image to view fullscreen.


39 NDIX to the left, 32 NDIX to the right.
Image may have been reduced in size. Click image to view fullscreen.
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PostPosted: Wed Aug 25, 2021 11:18 pm    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

Nice carbs bro!
These 2 missing screws are there to hold the venturi's in place. On 32 carbs they can be exchanged. On my 38's they are solid and can not be exchanged, therefore no screws needed.
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PostPosted: Thu Aug 26, 2021 1:00 am    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

Thanks, thats explains it the vents are solid on my 38 and 39 carbs as well.
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PostPosted: Thu Aug 26, 2021 7:35 am    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

Frederik wrote:
Thanks, thats explains it the vents are solid on my 38 and 39 carbs as well.

Yes. That is a real pity. The 38/39īs could easily have been a very nice carb ugrade along with more displacement.
We did make a CNC program to increase the solid venturi size, because we had a customer who wanted to try and use them on a modded 1720 cc. 356 engine.I forget which size we got it to. Iīll have to check the file. I - think - 30 mm. But, we also ound that the larger venturis didīnt help that much unless the top o the carbs were modified, so the venting bar was removed and new venting tubes made. That, along with the above mentioned stacks bumped power with a whopping 10 hp and something like 4% increase in torque.

I you are really into making power with these carbs the right thing to do is to swop the 38/39 mm throttle body over to the 32īs and then make a set of 32 mm venturiīs and of course make the modifications to the upper carb. Then the theoretical hp peak will be something in the neighbourhood of 130 hp. IRL most likely around 125 hp due to the intake turbulence just over the venturiīs.

JeeWee. I you have a chance to make that before you go on the rolls again, you can take a simple piece of PVC tube and cut to about 50 mm total length and strap on the carb so you have something like 35-40 mm above the carbs. Then you can get an idea about whether it has the desired effect on your engine. There is a good chance that the local home depot has some PVC drain pipe in the right diameter, or close which you can make them from.

Edit. Just checked. We made the 36 bodies to 32 mm venturiīs.
That particular 1720 pulled 110 hp and 153 Nm torque.
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PostPosted: Thu Aug 26, 2021 8:55 am    Post subject: Re: Zenith 38 39 NDIX ? Reply with quote

Alstrup wrote:
But, we also ound that the larger venturis didīnt help that much unless the top o the carbs were modified, so the venting bar was removed and new venting tubes made. That, along with the above mentioned stacks bumped power with a whopping 10 hp and something like 4% increase in torque.


Like this? One my carbs has the wenting bar missing. But it is not a modification, they are cast that way/ factory "modification". Don't know how they sorted the venting on it..
Image may have been reduced in size. Click image to view fullscreen.


The "shiny plug" to the left is also a mystery to me
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