Dellorto DRLA 40 modifications

[Alstrup]

[Don Cichocki]

Alstrup,
Stock Dansk exhaust. Stock "C" cam, 215 degrees duration intake and exhaust @.050", 9:1 CR, 1720cc, stock heads, red line 5,200 rpm. Basically a stock 1720cc 356. I rarely take it over 5,000rpm, just want a good, torquey street engine. Maybe DRLA36's would have been a better choice but it's getting to the point where it's very driveable without going PIG rich like most 356's are set up.
I can see going back to 55 idles and larger mains to make it more responsive, who cares if it's rich at WOT as I rarely go there.
Might try 190 A/C as its jetted now just to see results.

[W1K1]

[Alstrup]

W1K1. Both make a difference. On the 356 the CDI makes a very noticeable difference at idle and just over simply because you get a better spark so the burn gets more complete and you do not have to jet it so rich to make it run decent with the Hemi chamber.The programmable part with vacum makes the largest (noticable) difference from say 1300 rpm to whenever the cam comes into its comfortzone on the particular engine. In this area you can really boost the throttle response, - and improve power some, because you can dial it in rather accurate. (You can do this with an SVDA and Dells too, but it takes for ever to do. With a programmable you can come a long way with a couple of hours and then maybe an hour or two fine tuning lateron.
On a type 1 based engine with good heads the difference in the lower rpms with CDI is less noticeable apart from better starts and calming down during warmup. And again the programmable ignition with vacum can help you increase driveability significant in the "off cam zone"

One of the things to be aware of when doing this is, that sometimes the timing curve looks totally crazy when youre done, and you start wondering if you missed the ball completely or it is for real. Mostly it is for real. I guess you can say that the more radical the engine is the more radical the timing curve can be. Personally I do not like the 019. It is too slow for most VW engines. So if you have a running engine with a 019, even a CB Black box along with a proper coil and wires will make you able to have a totally different engine when youre done.

Don. OK. The Dansk muffler isnt exactly helping I´m sad to say. That´s most likely why it is richening up so hard at rpm. The original 356 & 912´s did that too. I think because there was some built in cooling by richness in a stock engine to help keep the heads at decent temps down the Autobahn.
You might want to save up for one of these: https://aapistons.com/collections/porsche-exhaust-...uper-style That will help your lower to midrange torque a lot, and give you a couple of ponies more on top plus give you a more predictable jetting.

[Erik G]

I put a bursch on my 912 1720 with 40 dells and it was a noticeable improvement 2500 rpm's and up. down low, no difference at all. I do like the sound better as well
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[modok]

no, 36mm carbs would have been worse.
I am glad you took the path less traveled as it's more interesting.

Testing emulsion tubes I have not been able to come up with near as much scientific explanation as I'd like......rather ends up just like scripture from the "Passani bible"

Such as, the deeper down the well the air holes are, the more fuel they bring with them. exc
Which is true.

One thing I have learned is the passage from the emulsion well to the nozzle is a point of restriction.
The window of flow area at the junction from the well to the 5mm passage is only 10 sq mm. because it is BLOCKED by the emulsion tube, only a 0.8mm gap.


There may be a useful rule that for flow area, the passageway should be no less than 3x the air added, which would explain why larger than 180 air results in unstable operation, because 2mm air jet approaches breaking that rule.

Seems likely I was able to use 2mm air jet on my custom tube because I reduced the top diameter of the emulsion tube to 6mm, this increased the area of the window to 12 sq mm, although that's probably the LIMIt anyway, because the nozzle is only 15 sq mm

Of course I also moved most of the holes far down the tube, but it took BOTH to make it work.


ALSO
Locating any air holes too close this 5mm passageway may create unstable flow. Which may be something you have just demonstrated.

The DRLA emulsion tube having a PAIR of large top holes, there is a 40% chance that one of the holes will be too close to the "window" when installed randomly. Add that 1mm washer.... now we're really gambling!

Which means that it may be necessary ti INDEX the emulsion tube. HOW?
It stays stuck to the holder. Mark a dot on the holder, remove, rotate the tube the way you want it to be, re-install.

So you could try indexing them so the two top holes are on the sides, that MAY help, OR
Solder closed one top hole of a #2 tube, and install the emulsion tube so the now singular top hole is toward the middle of the carb, so it is "deeper" in the well, and will that make a difference? oh yes, it will.

How these darn tubes work is still very foggy, but i am fairly sure that experimenting with the top holes and NOT indexing the emulsion tubes, you probably will get random results. In fact, I believe that's why some of the results you have here seem random.

[modok]

AND, concerning the #1 emulsion tubes!!

there is a 1 in 5 chance that installed randomly, the top hole will be IN the 5mm passage, essentially, placed AFTER the restriction.
i just did an experiment to see if it matters or not

YES IT MATTERS!

I'm not sure what to do about it yet, but, they goofed. it's goofed up design OOPS

weber and dellorto still have a lot to learn from eachother. i intend to make the ultimate hybrid

[Don Cichocki]

You know Modoc I almost considered making a Dell e-tube based on a F-11, then said NAAAA!
I'd like to hear from anybody who messed with the progression holes.
Nobody ever mentioned sizes of the six DRLA 36 holes.
You mentioned the Weber 36 had a nice even progression hole arrangement and worked well, something to consider.
I do see a rich spike right off idle, just opening the butterfly then it settles down. No pump squirt! Wonder if it's the jump from 1.00mm to the 2nd hole at 1.40mm?
Maybe I'm being too picky?

[Alstrup]

It IS a mechanical fuel delivery. It can NEVER be, and have never been totally even. If you want that, go with Electronic fuel injection in closed loop. Even then the AFR sways up and down within about 1,0 afr. Be carefull not to start shooting sparrows with canons. If you are in an acceptable window without serius spikes, and the engine runs nice and smooth, be satisfied. Especially the 356 engine will never be really good on that account unless you go twin spark ignition. A lower Compression version like yours, with much less shadow on the piston can, as I menthioned earlier, come a long way with an upgraded ignition system.

[Zed999]

[Don Cichocki]

Zedd,
Never hooked up a vacuum gauge so don't know.
I was hesitant about raising the float level like Alstrup mentioned but since I tried everything else I gave it a shot. It definitely helped the transition. Raising the e-tube was NG. The #.1 e-tube was NG. The #.3 is similar to the #.2 but the outside diameter is .3mm smaller. It helped with the transition and right now it's very driveable, the A/F is well within range. Like Alstrup said I think I'm being too picky. Might try a 190 A/C to see what it will do with my present setup.
Are you tuning with a wideband A/F gauge? Until this year I was tuning by seat of pants and you might feel like you're good but the gauge will tell you how far off you are.

[Zed999]

After reading this thread, going back up venturi size and raising the fuel level is on my list.

I don't think you're being picky, but I do think Dells do one thing well and are great at resisting all attempts to do something else! I have wondered whether I should try some Webers as they seem (only from reading) more pliable.

I don't think you need a vacuum gauge, smaller vents bring the mains in sooner due to the faster air flow. Manifold vacuum disappears when the throttle is opened far enough. That lean hole is between the two when neither jet is being sucked on enough. For me in my bus it's typically just where I'd be cruising in heavy traffic, around 35-40mph in top gear and is very annoying. So I either have over rich idle jets or strangle it with small vents (so far).

The best it ever went was ironically when I guessed the jetting and vents from driving and cht with no afr...then I read the lean tune AFR thread...kind of wish I hadn't because once you know...

[modok]

36 drla have the same hole pattern as all the DRLA models
100, 160. 160, 180 180


You have the oddball model that is different.

[Don Cichocki]

Modoc,
I thought the 36 Dells had 6 holes? I see the new Empi Dell clones have 6 so assumed the originals had 6 also … my bad.

[Wreck]

I spent a long time experimenting with emulsion tubes , soldering up holes and drilling others trying to lessen a bad reversion phase (4000 to 4600) . I listened to the tutorial by David Vizard on youtube on emulsion tubes and tried to follow his advise ,hoping I could lean out that rich phase .

I found that just a simple change from .2's to .3's just richened the whole main jet circuit but kept the same graph . Which makes sense since the only difference is the smaller step, the holes are the same .

At various stages I've tried soldering up all the holes and drilling a couple in the step to see where that changes the mixture . I gave up in the end and reverted back to .2's and plan to switch to EFI .

Has anyone tried extending the secondary venture up to the top of the ram tubes like an IDA one to help with reversion ?

[[email protected]]

FWIW, reversion can be lessened by using a larger venturi. Many large cammed engines run better with bigger venturis because of this.
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[modok]

Reversion at 4000-4500..... need to fix the exhaust system.
It's "rich" yes and no, not really rich.

You lean it out enough to make the wideband look good, and you'll be running too hot. Good luck with the efi

Extending the aux vents helps LOW rpm WOT,
I can go WOT it at 800 rpm.
However, in order to make that work, you also have to get the exhaust system right for the engine, or make the engine right for the exhaust
see "golden ratio"

[modok]

Anyway THANKS guys, for sharing what the .3 tubes do.
It's exactly what I expected,
but they just as often do the opposite of what I expected so wasn't goona jinx it.

f-11 tube for a dell? weber aux vent in a dell?
That is entirely possible.
The trick is you have to do both, and while it's a very silly thing to do, it is possible.

You can probably also MAKE a f-11 ish tube for a dell by re-arranging the holes in the "turbo" tubes, the step is in the right place and the diameters are close enough. it will have to be scaled to account for the smaller main well and nozzle size.

[Alstrup]

Why blame the carbs for a problem with the engine set up? There are things that even a fuel injection can´t remedy.

[modok]

i agree Torben,
Perfectly designed engines with perfectly designed exhaust systems,
carbs bolt on and go, perfect.....but

I also know that everybody doing that.... is purely a fantasy and is never going to happen.

There will always be bad exhaust systems and unbalanced engine combos.
I can give away all the "secrets" and it won't matter because they aren't secret, just nobody asks. What size are your transfer ports?? is it secret?

jetting around exhaust reversion...no thanks, but
working on this "lean hole" is GOOD research, any tricks learned here, we can also use to run BIGGER vents.