Volvo Community Forum. The Forums of the Volvo Owners Club

Forum Rules Volvo Owners Club About VOC Volvo Gallery Links Volvo History Volvo Press
Go Back   Volvo Owners Club Forum > "Technical Topics" > 140/164 Series General

Notices

140/164 Series General Forum for the Volvo 140 and 164 cars

Information
  • VOC Members: There is no login facility using your VOC membership number or the details from page 3 of the club magazine. You need to register in the normal way
  • AOL Customers: Make sure you check the 'Remember me' check box otherwise the AOL system may log you out during the session. This is a known issue with AOL.
  • AOL, Yahoo and Plus.net users. Forum owners such as us are finding that AOL, Yahoo and Plus.net are blocking a lot of email generated from forums. This may mean your registration activation and other emails will not get to you, or they may appear in your spam mailbox

Thread Informations

Modifying a Stromberg 175 Carb

Views : 1593

Replies : 13

Users Viewing This Thread :  

Reply
 
Thread Tools Display Modes
Old Aug 30th, 2021, 20:17   #11
142 Guy
Senior Member
 
142 Guy's Avatar
 

Last Online: Today 02:22
Join Date: Jul 2020
Location: Saskatchewan, Canada
Default

Quote:
Originally Posted by Burdekin View Post
The dyno guy also said it was spot on, a little rich at max revs was all.
I had a look at your dyno curve when you first posted it and find that comment a little odd. At 5500 RPM your AFR has dropped to about 13.4. That is richer than stoichiometric; but, running a little rich at high engine load typically results in slightly higher horsepower. Most engines are volumetric efficiency limited and adding a little extra fuel helps ensure that all the O2 is used up. Of course, too much is not a good thing because you lose heat in evaporating the excess fuel which starts to reduce power output.

Your dyno guy may be suffering from 'digital EFI think' where it would be easy to tweak specific cells in a fuel map to push that AFR from 13.4 up to 13.7 around 5000 RPM. I suspect the Stromberg doesn't have that ability to adjust fuel delivery at 5000 RPM wide open throttle without having some knock on effects at lower RPM. Your AFR does seem to be excessive at around 2200 RPM; but, if part throttle AFR at 2200 RPM is good then wide open throttle AFR at 2200 RPM may not be an issue.

On the matter of potential modifications to the Stromberg to improve flow, you might want to consider mapping the manifold air pressure during a dyno run. New MPX 4250AP MAP sensors are fairly inexpensive (about $35 Cdn); but, a salvaged MAP sensor from just about any car will likely fit the bill (our local pick and pull salvage yard had a flat $5 charge for any sensor pulled from a wreck). The sensors almost universally have a 0-5 volt linear output and you can usually find the slope calibrations on line. With a 5 volt power supply, an analog input data logger and the sensor you can record your actual static manifold pressure during engine operation. If your manifold pressure is running just 3 or 4 kPa below atmospheric pressure during peak RPM wide open throttle conditions there is probably nothing to be had by beating your self up fiddling around with the Strombergs.

Last edited by 142 Guy; Aug 30th, 2021 at 20:20.
142 Guy is offline   Reply With Quote
The Following User Says Thank You to 142 Guy For This Useful Post:
Old Aug 31st, 2021, 21:44   #12
Derek UK
VOC Member
 
Derek UK's Avatar
 

Last Online: Yesterday 12:33
Join Date: Jul 2006
Location: Chatham
Default

The richness at about 2.2k showing badly on the AFR graph is mirrored slightly on the torque curve. The needles might like a bit of extra meat there but probably makes the car feel lively too. Good set of curves. Smoothing the bridge would I think reduce the atomisation at lower revs and that isn't good.
Derek UK is offline   Reply With Quote
The Following User Says Thank You to Derek UK For This Useful Post:
Old Sep 1st, 2021, 07:29   #13
Burdekin
Chief Bodger
 
Burdekin's Avatar
 

Last Online: Yesterday 21:22
Join Date: Oct 2009
Location: Aberdeen
Default

Quote:
Originally Posted by Derek UK View Post
The richness at about 2.2k showing badly on the AFR graph is mirrored slightly on the torque curve. The needles might like a bit of extra meat there but probably makes the car feel lively too. Good set of curves. Smoothing the bridge would I think reduce the atomisation at lower revs and that isn't good.
Driving the car it hits all the fuel ratios for me. Idle about 13.2, cruise 14 to 15 and full open throttle 12.5. I was going to experiment with dashpot oil as well, using 80/90 gear oil at the moment.

The idea of the porting post bridge is to make the air flow easier the same as at the front of the carb with stub stack at the entrance. It's opening up the area at the outboard side of the piston. Tapering the lower front and rear edges of the piston is suppose to improve throttle response. There definitely is extra Hp to be had with more carb.
__________________
One day I will get rid of all of the rust.
Burdekin is offline   Reply With Quote
The Following User Says Thank You to Burdekin For This Useful Post:
Old Sep 1st, 2021, 14:12   #14
Derek UK
VOC Member
 
Derek UK's Avatar
 

Last Online: Yesterday 12:33
Join Date: Jul 2006
Location: Chatham
Default

Years ago I rounded the front of the pistons on my B16B. Didn't notice any difference. My comment about keeping the bridge sharp was because at that point the fuel is being sucked from the jet so having the smooth airflow changed to "rough" helps the atomised air in the inlet manifold. It doesn't want to drop out of atomisation onto the walls of the manifold. This can happen with the alloy manifold as it runs cooler than the cast iron one. The GT one piece is the best of all of the various one and 2 piece setups. The alloy inlet looks cool but it may be too cool at times!
Derek UK is offline   Reply With Quote
The Following User Says Thank You to Derek UK For This Useful Post:
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +1. The time now is 06:17.


Powered by vBulletin
Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.