Weber/OER carbs conversion to E85?

[enigma57]

Oooops! Right you are, Paul! My screw-up. Converting English measure to metric has always been a challenge for me.

Whilst you were making the change over to metric 'down under' in the early '70s, I was trying to forget Viet Nam and became rather pre-occupied here Stateside with cracking tinnies, fast cars and faster women. Thanks for setting me straight on that!

Best regards,

Harry

[blown265]

No problem Harry- great respect to you sir.
I figured it was just a conversion thing. The only reason I picked it up, is that here in Australia in the early 70s we had a factory built I6 supplied from Chrysler with 3 x 45mm DCOEs, and I was doing some basic hp/ci numbers to see what the carbs' potential was. Most who modify this engine go to a much larger Weber carb, so I was surprised to see the smaller unit/choke making that hp.
Regards
Paul

[lc-gtr-1969]

Agreed. 2.87 HP per cu. in. displacement naturally aspirated held to 7,000 RPMs redline is quite an acheivement.

My concern is the relationship of 47mm throttle bore to choke (main venturi) size vis a vis proper fuel metering. I can see a maximum of 40mm choke size allowing for proper fuel metering ('just'), but 42mm chokes seem a bit much with that throttle bore size unless this is a WOT event only and all else is off the table. With 42mm chokes, I would expect a minimum throttle bore size of 50mm and ideally, 52.5mm .

Best regards to all,

Harry

I have a fair bit of weber experience running 45s and previously would have agreed with your statement- however having recently switched to 48s with 42mm chokes, I am finding the fuel metering is fine, really no need for me to drop back to 40s. I suppose cam / compression / head flow will all factor into the metering ability and choke size. I guess choke selection can be somewhat engine specific... My old engine which ran a different head would not have tolerated the bigger chokes but the newer, higher head flowing, higher compression engine does.

I have not yet tried e85 with my webers but I would not be surprised if F7 tubes worked better with E85 simply as this will help richen up the midrange without the need for a main size which may over supply at the top end. However you wont know until you run it with the F2s.

[Geoff2]

48 Webers with 42mm chokes. Depends which 48s... DCOEs have 42 chokes; IDFs have 40; IDAs have 37.

The 45 DCOE comes with 36mm chokes.

[jarmoyp]

I have not yet tried e85 with my webers but I would not be surprised if F7 tubes worked better with E85 simply as this will help richen up the midrange without the need for a main size which may over supply at the top end. However you wont know until you run it with the F2s.

No, it,s not enough just change the tubes.

[enigma57]

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I see what you mean regarding choke size. Food for thought. The great majority of Webers I see here are DCNF downdraught carbs and variants. I try and stay within 1 step (2mm) of Weber's recommended 1.25:1 throttle bore to choke size when I can. The Maserati carbs in photos above are sized from OEM in that manner.

My first set of 42 DCNF carbs were original to a '74 Aston Martin and had 36mm chokes. A bit touchy to sort out in the lower RPM range, but doable. So I have been using the Aston OEM throttle bore to choke size ratio as a rough rule of thumb when increasing choke size beyond 1.25:1. In hind sight, I may have been overly cautious in so doing. I will take a fresh look at this next time I run into this situation.

Much appreciated.

* My apologies for the double image of the photo above. It just came out that way when I pulled it off my computer.

* The other thing is...... I wanted to post the photo of my little friend there. Had him for 8 years. Sadly, we lost him today. Miss him lots.

Best regards,

Harry