weber question

Can you run down draft carbs on a side draft application???

I plan on putting my GTI on a carb diet and was deciding on either maybe hayabusa carbs or the like or webers or the like

Also is 48 and 50 too much?

Yes. But why? Why would you not run run sidedrafts on the GTI? What year is the GTI?

Downdrafts are usually used to solve a space problem where sidedrafts won't fit. Nothing wrong with either application, really.

And as for the 48 or 50, it depends on the HP of your motor. Best thing is to look at what size others use on the same motor/HP build level. If you're going where no man has gone before, then look at the Weber book for displacment/HP/RPM and size it from there. For example, 40 DCOE's work OK on a 1.6L motor, but only up to around 110-120 HP or so, then they start choking the top end and 45's work better. But, 45's don't idle/low speed a 1.6L as well. So "they" say. Race 1.6L motors use 45's or 48's. And Megasquirt rocks.

Don't forget, 40 and 45 are the size of the throttle plates. You can change the airflow by changing the venturi size.

Example: you can run 40 DCOE with 28mm venturis.

Ahhh that's true, the venturis would be good to change.

It's an 85, now the reason why I was asking is I know these were used on V8 and such "top" applications but was wondering if I could use them for side. Now the engine is obviously sidedraft. I won't be using the counterflow setup, I will be using the smarter crossflow ABA head. Now everybody's running 45's DCOE's it seems. I was just asking if the 48 and 50's were too high. And yes Megasquirt does rock, that's why I want to use it.

I was looking at some DCO's

My engine is only cranking maybe a whopping 100 odd bhp and same torque so.....

You know that the downdraft and sidedraft carbs are totally different units right?

DCOE's are the most common sidedrafts.

Downdraft models commonly used are IDA, IDF and DCNF

There is also the DGV and DFV progressive downdrafts.

Shawn

I've owned many a Weber, both sidedraft and downdraft. Currently running 45mm Dellorto DHLA's on the Jensen Healey and the Abomination had a 48mm DHLA.

For street use the DD's are OK but not exceptional, their main advantage was better driveability compared to the worn out SUs, Hitachis etc that they replaced. The drawback to downdrafts is the ~90 degree bend into the intake. Sometimes it's just not worth it; a good (bad?) example is the 'sink trap' adapters to run twin DGV's on a TR6 or 240/260Z. Like this:

FWIW, you can run ginormous sidedrafts on little motors with the aforementioned venturi swaps. The Dell has a better low speed progression system and is thus less likely to cough, pop and backfire at low speeds. The blessing (and curse) of sidedraft Webers and Dellortos is their tuneability. As Colin Chapman said (much paraphrased), 'I don't offer adjustable suspensions because of how bad the average guy can screw up a set of Webers with only a screwdriver'. The lack of a decent cold start circuit makes both of them a beeyotch on a DD. Save the cards, letters, bricks, broken bottles; I know people do it all the time.

I have been wondering about motorcycle carbs on different applications. The biggest concern I have is getting them sized correctly before building a big $$$/time intake. Anybody know of a CFM chart for popular motorcycle carbs? The other thing is that for good low speed driveability you'll need accelerator pumps. That narrows the field considerably.

Of course there is nothing wrong with the applications, but if he wants DCOE's I have seen many applied in older GTI's, Scirrocos and rabbits

ddavidv wrote: Downdrafts are usually used to solve a space problem where sidedrafts won't fit. Nothing wrong with either application, really.

A friend of mine, now dead, (HEY GYPSIE), was a Harley mechanic way back in the day and really biatched about DCOE's on Harleys. He hated them. I forget the exact number, but he used to say there were like 12 different things to adjust on them. I've seen DCOE's and DHLA's on a few HD's. Usually 45's, and not very many. "I heard" the president of the S ons of Si lence MC's in Colorado was the distributor for Webers in that state, or something like that, in the 80's. I saw a lot of So S' bikes with a DCOE back then.

I have a pair of 40 DHLA's on the shelf. Someday I'll find a car to fit them. I bought them originally to go on the MR2's 20v, but I found a AFM and ECU after I bought them and went OEM EFI instead. After selling off the manifold they came with, I have like six bucks in the pair, including air filters and a fuel pressure regulator.

Jensenman, thanks for the advice.

Yeah the VW croud (at least) are using a lot fo the bike carb setups, 700, 900 1300 cc, and all. It is quite interesting and REALLY cheap.

I was just wondering about the downdraft deal because it only made sense that a 90 degree bend vs. the side drafts only would have flow problems but I wanted to use DCO's maybe 40 just with bigger venturis, that way I don't have to have the 45 DCOE's that everyone has.

And they are HUGLY popular on the Rabbit's, MKII's, Scirocco's, etc.

If you've got a big 4-banger, the vibrations can give you a bit of trouble with fuel aeration.

I only ever ran into it with DCOEs on a Toyota 20/22R hybrid motor in a buddies Celica. We had to use the anti-vibration mounts with the big rubber o-rings to stop it.

Shawn

Yeah, I had those anti-vibration things with the O rings and spring washers on my TC Europa Special. The O ring was not installed correctly by the the shop that rebuilt the motor. It drooped down, sucking air. At 110 MPH, it leaned out #3, melting a chunk of the crown off the piston, which rattled around damaging the combustion chamber before blowing out the exhaust port. Be real careful with those anti-vibration setups.

I had the anti vibe stuff on the J-H, it's aluminum spacers with O ring grooves which of course need O rings and Thackery washers (the spring washers Hess mentioned). When tightened as recommended, the carbs could shift in relation to each other which meant every time I drove it the idle would be screwed up because the movement meant the carbs were no longer synchronized. Talk about a PITA. I finally dumped the Thackery washers and using a feeler gauge, tightened the self locking mount nuts so that I have ~.010 gap on either side of the aluminum spacer. I have had zero problems since then.