I have a 122 with a b20 from a 1800 and a 36 32 dgav weber carb. I really don't like the mechanical fuel pump that the car has now. Is it poss to ad an electric fuel pump and a nicer bigger fuel filter with the weber setup? Thanx

Sure, it's possible. I'm using a Facet solid-state pump back by the fuel tank (big filter of your choice goes between the tank and pump), and a Holley fuel pressure regulator in the engine compartment. The fuel pump is wired from the ignition circuit through a relay and an in-line fuse.

Fuel-injected B20s have a block-off plate that covers the hole where the mechanical fuel pump ain't. Find one of those. Note that you do NOT want the electric fuel pump from one of those cars -- it puts out way too much pressure (around 50-60 psi). The Facet pump puts out 10 psi, and you want to regulate that in the 2-4 psi range for your Weber.

Also note that the mechanical fuel pump you now have can pump more fuel than a DGAV can flow... if the engine is built out at all beyond stock, the downdraft carb is limiting your power.

This is what my engine is built right now. Mahel forged pistons with 40 over bore, light pushrods, k cam, dual valve spings, stainless valves, machined crank, hd oil pump, all the good seals and rings and of course the weber. So your saying I should use a diffrent carb then???

DGV/DGAV:
1 32mm throat, 1 36mm throat
2 long intake runners, 2 short
airflow turns 90 degrees going into the manifold, then goes around various bends

Pair of SU HS6:
2 44mm throats
intake runners equal length
airflow goes almost straight into the head

Which will flow more?

Yup, the Weber is strictly for people who don't know ay better.The SU's have more potential.

Regards


Pete

The weber isn't sufficient for your B20. A set of properly tuned stock SU HS6 carbs would increase performance considerably. A set of weber sidedraft DCOE carbs will do even more, but with a significant drop in fuel economy.

I had a set of the stock SU's that came with my orginal b18 and I could never get them tuned right so I decieded to use the weber setup. Is there a big performance diffrence between carb setups. It might be my daily drive again and use it for some autocross thats why I'm finishing it off now.

I'm not saying the DAGV is junk -- I ran a DGV for years in a mild performance motor and liked it. It will give you good power through the midrange, but not at higher rpm. It's probably OK for short autocross circuits where speeds don't get much above 40 mph.

It definitely will run better than worn-out SUs, but not ones that are in good shape and correctly tuned. SUs with wear around the throttle shafts cannot be tuned (although people will fiddle with them daily for years before realizing that). Once put into good shape and tuned with the right needles for the application (KD or possibly DX needles for your motor, would be my guess), they don't need much attention at all.

For best combustion efficiency, you want the intake charge to go past the intake valve at maximum velocity. Turbulence in the airflow is the enemy. The more bends the air has to negotiate, the more turbulence you'll have. For an inline motor, therefore, side-draft carbs always have the potential to flow better than downdraft carbs.

Weber side-drafts (or similar) will potentially give more power than SUs, but they are expensive and a #### to get set up right. They really want to have serious air horns on them, which means taking a great hunk out of the inner fender to make them fit. They *can* be tuned for excellent fuel economy, common wisdom to the contrary.

Hi Phil,

I like the look of your airbox. Is it an off-the-shelf item, or did you build it? What is it made of? I'm about to get my 142 back with its rebuilt motor (usual overbore/cam/2x45DCOE) etc and I know that my engine builder will be using god airhorns, but just sock-filters. I'll be making an airbox, but any tips are very welcome.

Regards

John

John, the box was made for me by Jonathan Panitz in Annapolis for around $150. It's made of Kevlar. I'll hunt down his contact info if that interests you.

What we *should* have done, in hindsight, is put the holes in the lid (removed in the pic), attach that to the carbs, and then turn the box on its side and attach it to the lid. That would make it a lot easier to get the horns on and off.

The intake tube is 3" PVC sewer pipe (should be smooth inside, whatever you use), and exits forward of the radiator bulkhead into the biggest K&N cone filter I could make fit. Crude but effective. I JB Welded a stub of the same pipe into the box, and the upper 90-degree elbow just slips over that, so it can move slightly as the engine moves.

The air horns are handmade by Unitek in Sweden. I don't think much of the Weber factory horns (swapping the new ones on put me back at square one on the jetting -- aaaarrrgh -- but that's an indication of how much better they flow), and TWM doesn't offer any for 48s that are long enough for our particular concept.

Steer clear of the sock filters, as they don't filter the big vent hole above the horns. That's actually an air intake for the emulsion tubes, not just a vent. Air entering there goes into the motor as part of the intake charge.

Hi Phil,

Thanks for that. I think my carb guy has already sourced air horns, but your advice on the vent holes above the horns is very timely.

I'm in Australia, so if it's custom made, I'll chase someone down here to make a box (or do it myself) because the chances of something being perfect first time seems remote, and freight back to the US/Australia a few times will be prohibitive.

Kevlar is an interesting choice - what made that the material of choice? Weight? Strength? I had thought of doing it in aluminium or fibreglass. I had also thought of using flex tube to the front to cope with engine rocking. Doesn't your rigid tube cause any problems? And 3" sounds huge - especially compare with the original little tube the 142s had to feed the strombergs. The bigger tube sounds like a very good idea, but I do think flex tube has advantages, or do the concertinas muck up the airflow too much?

regards

John

I was offered a choice of fiberglass, aluminum or Kevlar, so I went for Kevlar on a whim. It turns out to be light, rigid and easily worked, as I found out when I went from 45s to 48s and had to open up the holes.

To get the features in the right place initially, I mounted the carbs and did a pencil rubbing on a long piece of paper. This is then easily transfered to the material of your choice.

My main purpose was simply to feed the engine cool outside air instead of hot engine-compartment air, and also to have a graceful way of mounting an air filter compatible with the long horns, so I'm not very clear on the theory of the thing beyond that. What I've been told by several people is that it works sort of like an exhaust system in reverse -- once air in the tube is set in motion, it's mass that tends to keep moving, and that reduces the pressure drop at the carbs -- it may even supply slight pressure in some conditions. That's why the smooth tube is important... you wouldn't use accordion tubing in a hi-po exhaust system, right? In my case, the exhaust is 3" diameter, so that seemed appropriate for the intake as well.

I can't vouch for the accuracy of that theory, but it makes sense intuitively. I had originally wanted to put a rubber flex coupling in the tube somewhere, but there simply wasn't room to fit one in. There is a certain amount of float built into the tube/box junction, so I've had no problems there (I've got some hefty foam rubber wired around that junction so dirt can't sneak in).

One downside is that it's useful for tuning purposes to be able to hear the pitch of the intake roar, and there isn't any audible from inside the car...

Hope this helps.

You might need some different needles to get the SU's tuned just right on a B20. My PV has a 2.2 liter B20 with a stock D cam (almost identical to the K cam, the K is a 'smog' cam with a bit less duration) and it ran fairly well with the stock needles that came with on the B18. Rhys sold me a couple of slightly richer neeles and it opened up some full throttle high rpm power. Tuning SU's is a bit of a black science, it took me a while to learn how to get the engine to purr with them. Leaking, sloppy worn throttle shafts, however, will stymie most attempts at tuning.

Since then I've put on a set of DCOE 40's which make more power and have better throttle response. So far they use more gas too, but 1/2 of that is probably me just driving it faster. >:^)