Weber/OER carbs conversion to E85?

General engine tech -- Drag Racing to Circle Track

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enigma57
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Re: Weber/OER carbs conversion to E85?

Post by enigma57 »

:shock: 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! :D

Best regards,

Harry
blown265
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Re: Weber/OER carbs conversion to E85?

Post by 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
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Re: Weber/OER carbs conversion to E85?

Post by lc-gtr-1969 »

enigma57 wrote: Tue Jan 05, 2021 11:37 pm 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.
Fumbling around in the shed...
Geoff2
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Re: Weber/OER carbs conversion to E85?

Post by 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
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Re: Weber/OER carbs conversion to E85?

Post by jarmoyp »

lc-gtr-1969 wrote: Wed Jan 06, 2021 6:16 pm

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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Re: Weber/OER carbs conversion to E85?

Post by 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
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rbwhite
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Re: Weber/OER carbs conversion to E85?

Post by rbwhite »

I tuned a vintage car on E85 a few years ago. A 1976 Toyota Celica with 2240cc 20R motor. 12.5CR. I switched back to 110 octane race gas after a year because the dyno results did not improve much, the carbs were developing some corrosion in the bowls and the fuel pump was not getting lubricated and would seize if you let it set for a while. I ran two 45 DCOE's with the following settings:
Main Venturi 40mm
Aux Venturi 4.5
Main jet 210
Air Corr 240
Emul tube F3 or F4
Accel jet 50
Pump Exh jet 0
Idle jet 80F9
Needle valve 300
Geoff2
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Re: Weber/OER carbs conversion to E85?

Post by Geoff2 »

Main jet seems overly large for 40mm chokes, even with E 85 & one barrel per cyl. The 48 IDF comes with 40mm chokes, has 150 MJ.
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