The Official 356Talk Forum

DonCichocki wrote:Matthew,
I think you're mistaken. The DRLA40 had a 40mm throttle plate where a DRLA36 has a 36mm throttle plate.

No I don't think so. I have worked on both sizes. Also, its the venturi and not the throttle plate I am referring too.
https://www.cbperformance.com/category-s/129.htm

Both the Weber and Dellortos have changeable venturis. I'm saying a DRLA36 has a 36mm throat while the DRLA40 has a 40mm throat, I'm not talking vents.
http://www.carburetion.com/Dellorto/Del ... p#DRLAdiag
See #11 in the above parts diagram.
If you have a stamped DRLA 40 and a DRLA 36 I'd love to see the size of the throats compared where they meet the manifold.

Here's what I'm talking about. In the photo you'll see a DRLA40 logo with a 40mm throat. If you can show me a DRLA36 with the same throat I'll eat a large serving of humble pie.

Is this the new carb from Italy, Don ?

Hi Don, did Jeff finally turn you to the Del dark side? Where did you get them? For your engine the 36mm throttles might be better.

Don has seen the light, Cliff. Remember, "they just work."

Here are the dyno graphs and info for Mike's 1883. I've noted Del or Web for carbs. The first run was with the Dels as delivered. Next was with the Dels optimized for jetting and corrected timing. The Web run was the final run with Webers. All test were done with equal head temp.

Thanks for posting the data for all to see, John and again, my thanks for sorting out the engine.

A point I would like to make: John is known for his concours level restorations but he and his staff also do phenomenal engine building and maintenance.

Mike

Cliff,
I'll be trying 30mm vents in a DRLA40, same as with my old Italian Weber IDF40 using 30mm vents.
Gotta keep busy!

1883 cc 10.3:1 twin plug, Dellortos 40 33mm custom venturi.
Mike, Curious if you know the adjusted jetting on the Dellortos running on the dino (best results), just for comparison sake.

Looking at the graphs you see what you would expect changing from 40mm/28mm carbs to 44mm/32mm carbs with one exception, with the size of the Webers being so much larger it is a bit surprising that power below 4200rpm is not less with the Webers. There are some aspects of engine performance that can't be measured on a dyno though. The very first run must have showed a dangerous condition since it was aborted very early. Dyno room cleanups are annoying

Greg: no we didn't make any changes to the Dellortos while on the dyno. Once we determined the venturis were 28mm, we decided to go with the proven 44mm Webers.

Cliff: you are right. The dyno gives us objective data but my seat of the pants tells me the changes were a big improvement. When tested with the Dellortos, the A/F read flashed RED when it leaned out especially under load.

Mike

If anyone is interested, I have a 1720/912 case/ Solex motor for sale. Maybe 2/3000 miles, and built in our shop. It has been my "Spare Tire" for a number of years, and only used once. Pellow look, but easily changed. Everything done right of course.

……………………………...Jim.

Here is a graph from an 1883 that I built. The numbers are taken at the rear wheels which is approximately, best guess, 15% below the crankshaft output. Devide by .85 to get crankshaft power, or close, maybe.

Note that the relationship between power and rpm is much different on the two different dynos. The relationship between the two axis of the graph changes the appearance of the curves and can confuse things when comparing results from different dynos. On the Dynojet you can adjust that to get the look that you like. Still, looking at the overall shape of the curves tells a lot about an engine.

Those curves do look quite different, Cliff. Have you found the differences are due to the dynamometers or the engine set up?

Mike