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IMP Weber carb alternatives - Part 2: Calculations

BoyToys

BoyToys

Well-known member
Super Patron
Thought I would create a new thread as followup to the one where we were discussing Weber alternatives. A head scratcher, get out your calculator.

Key questions: what size carb do I need; i.e., throat and venturi diameter to suit a 1.7 liter V4? Informative link below, but will boil it down here.

Calculations for bore size: .83 x the square root of (Krpm's x one cylinder's volume...which is 425cc).
Calculations for venturi/choke size: .7-.9 x bore size

V4 specs have max hp at 5000 rpms, but I plan to run at no more than 3500 and tune the power (torque) down low to perform well at 2500-3000.
.83 x the sq rt of (3.5x425)= 32mm bore
.83 x 32mm = 26.5 venturi.

Seeing as how the common conversion using Weber 32ICH is unobtanium from where I've looked, the 34ICH with a 27mm venturi should work (#15290.034). The 34mm bore is larger than needed but would suit well for air volumes at higher rpms, like 4000. Massage the correction factor and you can come up with 34mm bore and 27mm venturi.

Caution: I am not an automotive engineer, just an arm-chair engineer...which may make me dangerous.

Here's the link

Performance Oriented

www.performanceoriented.com www.performanceoriented.com
I know....too much information!
 
I'm just an Electrician but I did sleep at a Holiday Inn once

I'm assuming you need down draft carb ???
I got looking for one for my polaris and this popped up for Volkswagon's

link


1707437584878.png
 
I'm focused on Webers only, not some unknown brand made in some country other than Spain that perhaps starts with a C. Yes, must be downdraft. 34PICT's were typically used for dual carb setups on VW's. Would require a lot of rejetting and no idea what venturi size they used. Late in the Ford V4 Essex history they switched to a Weber 32DIF...good luck finding one.
I ran a Weber in my old MGB a couple zillion years ago and became minimally knowledgeable.
I'm just an educated microbiologist with a healthy mechanical aptitude...and 70 years worth of old man wisdom. It comes with age....
 
Good to know! 34ICH can be had in three different venturi configurations: 25mm, 27mm, and 29mm. All of which should work, depending on where you want to maximize your torque.
 
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