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what course of action is indicated? |
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6PakBee
Supporter of TheAMCForum Charter Member Joined: Jul/01/2007 Location: North Dakota Status: Offline Points: 5458 |
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It's a pity you don't have the BSFC numbers. That, IMHO, is one of the first things you want to look at as it is an indication of how efficient the engine is. If it is relatively constant that is a good thing. If it is all over the place, falling, or rising with rpm, then you have some kind of problem. A/F ratio is not the entire answer.
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Roger Gazur
1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6912 |
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From just looking at the dyno run the BSFC must be very poor above 3250 RPM. You can see when the secondary's are opening and instead of seeing the engine leaning out with higher RPM it's drawing more fuel to sustain the the RPM though the run.
The "blocking secondary's" is just stating there is TOO much fuel to burn. That's the O2 sensors connected for the run. It's a nice curve for HP and Torque, but too low on the RPM scale for this setup to be at peak power. It's basically very good at pumping enriched fuel. What was done to stop the "stumble"? Guessing that the secondary's were put in early. Boris is correct, your better off rich. That stated, my first impression if keeping the manual secondary's, is to enrich the primaries and drive out the secondary's to open at a higher RPM. You want the secondary's to open just before the primary's start to lean out. This is definitely not the case looking at the dyno sheet. To elaborate - that sharp "U" between 3000 and 3250 RPM, the goal should be to flatten out that "U". You can see the primary's leaning out very quickly at 3250 RPM.
Edited by Trader - Apr/01/2021 at 6:11pm |
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bikerfox
Moderator Group Joined: Aug/02/2009 Location: USA Status: Offline Points: 4473 |
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I believe that to cure the stumble, the tech enlarged the pump discharge nozzles.
I'll inquire about the BSFC info. Thanks for replying everyone.
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1969 Rebel SST (1970-1987)
1968 AMX (2005-2011) 1969 SC/Rambler (2011-2019) 1970 Javelin (2019 to ?)"Jane" |
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BassBoat
AMC Addicted Joined: Aug/29/2008 Status: Offline Points: 1719 |
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just my 2 cents. You adjust full power AFR by changing the PVCR for the primary and the secondary orifices in the plate which is harder to do. Stock 600 -9 are too lean for single carbs. What are you running now? Adjust the primary jet for driveability. I think messing with bleeds is a smaller fine tuning thing. Full disclosure I tend to leave them alone.
You might find that quarter mile performance is better with a richer, maybe 11.8 AFR than typical 12.5 WOT target for max power. but 10.0 is too rich Edited by BassBoat - Apr/01/2021 at 7:32pm |
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bikerfox
Moderator Group Joined: Aug/02/2009 Location: USA Status: Offline Points: 4473 |
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Thanks for your comments, BB. PVCR is 5.5 and everyone seems to "like" this number, based on the 11" of vacuum. Unsure of what you mean by "Stock 600 -9 are too lean for single carbs. What are you running now?" This 4160 is a 450 cfm carb. The primary jet, reduced from .062 to .059 was due to a rich condition at idle. By the way, this is NOT a quarter mile car. Jane is driven about 95% of the time @ 70 mph.
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1969 Rebel SST (1970-1987)
1968 AMX (2005-2011) 1969 SC/Rambler (2011-2019) 1970 Javelin (2019 to ?)"Jane" |
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bikerfox
Moderator Group Joined: Aug/02/2009 Location: USA Status: Offline Points: 4473 |
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From what I've gathered, BSFC is measured on an engine dyno. I'm doing a chassis dyno.
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1969 Rebel SST (1970-1987)
1968 AMX (2005-2011) 1969 SC/Rambler (2011-2019) 1970 Javelin (2019 to ?)"Jane" |
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6PakBee
Supporter of TheAMCForum Charter Member Joined: Jul/01/2007 Location: North Dakota Status: Offline Points: 5458 |
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Hmm. I guess it depends on how old the chassis dyno is and what features it has. I just did a cursory search on Google and found that BSFC is available on chassis dynos that have a fuel flow input and are configured to calculate BSFC.
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Roger Gazur
1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6912 |
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Am I missing something?
The primary jets have nothing to do with idle mixture. The implication is that the throttle plates are being held open and you need more air for idle. This just adds to AFR complications. Putting back the original primary jets and adjusting the idle mixture for idle quality would be the first step. If you need more air, cracking the secondary's slightly open achieves this without increasing AFR. They used to drill holes in the primary throttle plates, but cracking open the secondary's has the same effect and can be adjusted. Try this with just a screwdriver first and see if your idle quality improves. If you can get your idle circuits working the way they should be, the rest is much easier. |
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BassBoat
AMC Addicted Joined: Aug/29/2008 Status: Offline Points: 1719 |
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The PVCR is the hole that the power valve opens. The 5.5 number you reference is the vacuum at which it opens. How much fuel you get when the power valve opens determines the total fuel. On the primary, there are two sources of main fuel, the jet and the PVCR. If you have too big a jet, you get too much fuel when you are just driving around. If you get the driveability right, then that will tell you the primary jet is right, then you open or in your case close the diameter of the power valve channel restriction to get the AFR where you want it. I would suggest trying to run with the secondaries disabled, and getting the AFR right on the primaries. Then see what happens with the secondaries. I missed that you had 450 CFM carburetors, sorry, so my reference to the -9 secondary plate applied to a 600 cfm 4160. I like to get the plates that allow you to change jetting with conventional jets.
As I understand it, it is typical to have to lean out the carburetors on dual applications. |
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PHAT69AMX
AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5926 |
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What is the Holley List Number of your carbs ?
Edited by PHAT69AMX - Apr/10/2021 at 10:48pm |
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