engine and drivetrain Best Dual Sidedraft Carb Setup?

[NickVyse]

So I'm close to swapping my 38/38 in the NK for twin sidedrafts. Hoped this thread would help me choose between my pair of early DHLA40, a pair of DHLA40E with a prescription from dellorto.co.uk to suit my engine (very helpful people and good value too) and the solex 40's from my tilux parts car.

 

I bought the emissions carbs first, then read the earlier dellorto were more tuneable and a good deal came my way, and then I got the non-running tilux. If the solex don't leak around the spindles then perhaps these are the way to go as the linkage is all there and the jetting should be just about spot on.

 

But reading about the benefits of the emissions dellortos has me full circle. 

 

Any opinion other than suck it and see (pun unintended)?

 

​(BTW, one of the best and most informative threads for a long while, should become an FAQ article just as it is)

Edited June 9, 2014 by NickVyse

[TobyB]

 

 

This is pure magic

 

Pure something.  Magic wasn't the first thing to pop to mind...

 

 

 

 using every drip of fuel efficiently without ANY waste in circuit cross over where one is going after the other

 

 

Phew.  There's probably some understanding under the verbiage, but it's getting lost in the 'pure magic'?

 

Anyway, feeding the idles off the main circuit DOESN'T automagically put a switch in there- it just means that

as the main starts to feed, the idle's inhibited.  So you've traded one characteristic for another.  And need to tune

accordingly.  And that explains the emulsion needs, too, to an extent.

 

Sorry, I'd missed that they were Del's- my numbers were for Weber, and for large chokes in a smaller carbs...

 

 

 

 with this simple technique you can tune anything from a 1300 to a 2000cc without really doing anything

...but if you're not doing anything, then you're not tuning, are you?

 

I've moved the same set of carbs to 3 or 4 engines, and it always surprises me how little re- jetting carbs need 

for quite- different demands.  I ran the 45's on the street car (bone stock motor, exhaust, ignition) just to baseline them, and I don't

thing ANY jet changed by more than 5 when they went on an 11:1 race motor with headers, exhaust, real ignition, etc.

And it went leaner on both airs and mains (I seem to remember)

 

Which makes some sense- mixture is mixture, and the design of carbs inherently tries to keep the ratio constant...

 

(but yes, there IS some magic in there.  It's pretty cool...)

 

t

[bazju]

I'm starting my dual side draft build now. I have the kit from TEP as a base and will be documenting the best I can everything I do to get it set up. I plan to tune with a wideband, and set it up for a mix between power and economy. I have never worked with carbs before, but have done some serious research. Most of my experience is with megasquirt, so this is a bit of a change. 

 

That being said I'm already a bit let down by what I received from TEP. I'll see if they fix it before giving too much detail. If not I'll adapt and overcome. Pretty excited though!

[Harv]

Jason, what are you using for chokes or venturies or whatever they call them?

My 912 did that sorta and when I went to 32's from 28's it made a world of difference.

John.

Edited June 14, 2014 by Harv

[NickVyse]

Jetting/chokes for dellortos:

 

For an early euro Tii spec engine with the a schrick 292, Matt from http://www.dellorto.co.uk gave me this as a starting point for 'N' designated dellortos. These are the later emissions carbs.

 

Venturis 34mm

mains 162

idles 62

7848.3  Auxilary venturi

130  emulsion tube

80  starter emulsion tube

 

For the earlier 'Universal' dellortos then he recommended the following:

 

33 or 34mm chokes will work, with 34s use:

 

142 mains

180 airs

7772.5 emulsions

7850.1 idle holders

55/58 idles

35/40 pumps

 

with 33 chokes use around 138 mains

 

This is just passed on knowledge as I haven't got round to swapping my 38/38 weber yet.

[Rustpile]

I got this suggestion for a stock engine with 45s and megajolt ignition, sound OK?

 

34 chokes
135 mains
58 idles
7850.1 idle holders
40 pumps
7772.5 emulsion
180 airs

[AceAndrew]

need more info (cam, compression, elevation).

[Rustpile]

Stock E21 cam(264?) stock pistons. 8,5:1? Sea-level. Oh, and I run 95 octane unleaded, is that OK, or should I use an additive? Could spring for 98 unleaded as well, or even 99, but that is expensive stuff. (2,80 per liter, or $10/gallon)

Edited June 19, 2014 by Rustpile

[Simeon]

Would not put 45s on a stock engine, particularly to choke them down. Go with 40s and save (some) money. Don't worry about any hi-test fuel with a stock CR either. 

 

Sidedrafts are cool but you may be better off with a downdraft Weber instead. 

[Rustpile]

Would not put 45s on a stock engine, particularly to choke them down. Go with 40s and save (some) money. Don't worry about any hi-test fuel with a stock CR either. 

 

Sidedrafts are cool but you may be better off with a downdraft Weber instead. 

 

Sure, but I already had the 45s, and they are on the car now.

[zinz]

Buy a decent header and start shopping for a new camshaft... a 292 at a minimum.

Your engine needs to be able to digest all that those 45s will be feeding it. Sounds like you have a handle on the ignition-side of the equation. But I think you will be disappointed in how the engine behaves until it is able to properly ingest and exhaust that bigger air/fuel mix.

Read more here... http://www.bmw2002faq.com/topic/143658-updated-carbs-cams-ignition-etc-geting-the-mix-right/

[Rustpile]

I am uncertain to how true this actually is, I know it is what most people and shops say, but logic. Sidedrafts should not require a hotter cam to work, or a cool header. Thinking of the engine as a huge air-pump, we have added more potential air on the intake side. The engine only takes what is can use however. And sidedrafts are completely adjustable. I know that I might need to spring for a cam and headers, but for now, I am going to try to keep what I have. Scope creep. I run the euro header, I think that is similar to the US tii-header. I ported it a bit as well, so it should be reasonably good. I don´t really want a different cam, I think. I rarely do high-rpm rally driving. i drive it to work in the summer, and to buy ice cream with my girlfriend.

[Simeon]

Sure, but I already had the 45s, and they are on the car now.

 

Sorry, not clear from your original post. Are we talking DHLAs or DCOEs?

 

As you say later,they are infinitely adjustable (within limits) and certainly you can choke them down and tune from there but this process is usually easier when starting from a carb better suited in size. 

 

General advice is get a good book so that you understand how they work and what each jet does in terms of progression and fuel supply. Team this knowledge with a WB sensor to work out what is best for your engine. Be prepared for lots of missed ice cream eating opportunities. 

[76ohtwo]

I don´t really want a different cam, I think. I rarely do high-rpm rally driving. i drive it to work in the summer, and to buy ice cream with my girlfriend.

If that's the case, you probably want 40s or a 38/38 downdraft. Your best bet for a seasonal daily driver is a 284 cam and 38/38; it will probably produce more power than 40s. 40s and the cam would also be a good combo. I haven't heard of anyone running 45s with a cam any lower than 304

[Kidasters]

Quick update:  got the intake back from the machine shop yesterday (took me a bit to get there - just too busy).  Their work is excellent.  If I wasn't so lazy, I'd go take a picture and post it.

 

I need to get motivated and go start the pull and head re-install.  I dream about being as good a photographer as Gerock, but I'm not....