The Forward Look Network
The Forward Look Network
Search | Statistics | User Listing Forums | Chat | eBay | Calendars | Albums | Skins | Language
You are logged in as a guest. ( logon | register )

Downsides of wiring the Carter WCFB 4bbl velocity valves open?
Jump to page : 1
Now viewing page 1 [50 messages per page]
View previous thread :: View next thread
   Forward Look Technical Discussions -> Engine, Exhaust, Fuel and IgnitionMessage format
 
56D500boy
Posted 2023-07-22 9:13 PM (#630891)
Subject: Downsides of wiring the Carter WCFB 4bbl velocity valves open?



Expert 5K+

Posts: 9900
500020002000500100100100100
Location: Lower Mainland BC
.
Besides potentially increased fuel consumption if I don't keep my foot out of it.

There is still the choke "interlock" that keeps the secondary butterflies from opening until the choke is fully off.

I just don't get the need for the velocity valves and while I was playing with my spare Carter WCFB I held the velocity valve counter-weight "open" while I observed the throttle travel and the opening
of the primary and secondary butterflies (I am working on my PCV adapter plate). The velocity valves seem like overkill.

REFERENCE:

https://www.mymopar.com/downloads/mtsc/086.pdf



Edited by 56D500boy 2023-07-22 9:27 PM




(TechnicalSericeDocumentNo86_Pg16_Secondary-VelocityValves.jpg)



Attachments
----------------
Attachments TechnicalSericeDocumentNo86_Pg16_Secondary-VelocityValves.jpg (66KB - 49 downloads)
Top of the page Bottom of the page
PolyJ
Posted 2023-07-23 1:49 PM (#630905 - in reply to #630891)
Subject: RE: Downsides of wiring the Carter WCFB 4bbl velocity valves open?



Veteran

Posts: 143
10025
Location: Denver, Colorado, USA

56D500boy - 2023-07-22 7:13 PM . Besides potentially increased fuel consumption if I don't keep my foot out of it. There is still the choke "interlock" that keeps the secondary butterflies from opening until the choke is fully off. I just don't get the need for the velocity valves and while I was playing with my spare Carter WCFB I held the velocity valve counter-weight "open" while I observed the throttle travel and the opening of the primary and secondary butterflies (I am working on my PCV adapter plate). The velocity valves seem like overkill. REFERENCE: https://www.mymopar.com/downloads/mtsc/086.pdf

Hey Dave,

Aside from ensuring both the secondary throttle valves and the secondary velocity valves are correctly centered and operational as designed, I wouldn't fool with the velocity valves for a street car. With the velocity valve configuration, there should be two idle ports in one of the secondary throats--one below the throttle valve and the other above it but below the velocity valve as the manual page you display shows. While the primary throttle valves are open but before the secondaries kick in, the two idle ports work in conjunction as air bleeds to produce a smooth transition from only the primaries functioning to the secondaries kicking in. The secondary velocity valves, their weight, and two idle ports are calibrated by design to assist with easing on the secondaries allowing for enough velocity to build and better atomization to avoid bogging when the secondary circuit kicks in. It's a lot of monkey motion compared to an AFB, AVS, and Holley 4150/4160, but it's a key part of the secondary circuit in your WCFB.

While racers pretty quickly abandoned the WCFB once the AFB and Holley 4150/4160 came about in 1957, those racers who were stuck with the WCFB carburetor prior to 1957 or to meet class rules would bend the secondary velocity valves to either make the angle more aggressive or less aggressive to fit the engines needs under the racing conditions. They would also grind down the velocity vavle weight or add weights to the valves to modify the pressure needed to open the velocity valves. These adjustments to the secondary velocity valve system are delicate and largely lost to time since the WCFB hasn't been a mainstay in performance circles for over 60 years. I would expect someone who doesn't have an engine dyno or extensive experience tuning WCFBs at a track is more likely to do more harm than good fooling with the secondary velocity valves. If I ran a WCFB, I might temporarly tie open the velocity valves just to see what would happen, but I expect the engine would be prone to bogging at part primary throttle and when the secondaries begin opening.

Top of the page Bottom of the page
57chizler
Posted 2023-07-23 3:43 PM (#630908 - in reply to #630905)
Subject: RE: Downsides of wiring the Carter WCFB 4bbl velocity valves open?



Expert

Posts: 3776
20001000500100100252525
Location: NorCal
The consequence of running without the secondary velocity valve is, as Justin noted, a noticeable bog when the secondaries are opened. The primaries have the accelerator pump to enrich the mixture when airflow increases with throttle opening but the secondaries don't have a pump so the velocity valve restricts the airflow at throttle opening to prevent an over-lean condition that causes the bog. As the airflow velocity increases it overcomes the counterweight(s) on the velocity valve and allows more airflow without the sudden lean condition.

In theory, the velocity valve might not be fully open even at WOT...depending on the engine's airflow demand.
Top of the page Bottom of the page
Jump to page : 1
Now viewing page 1 [50 messages per page]
Jump to forum :
Search this forum
Printer friendly version
E-mail a link to this thread

* * * This site contains affiliate links for which we may be compensated * * *


(Delete all cookies set by this site)