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what course of action is indicated?

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6PakBee View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 6PakBee Quote  Post ReplyReply Direct Link To This Post Posted: Apr/01/2021 at 4:31pm
Originally posted by bikerfox bikerfox wrote:

Thanks for your replies.

There's no vacuum info given (although it was 11" @ idle) and no BSFC that 
I can see, although when the car was being dynoed I vaguely recall that acronym
on the screen.  Yes, there's room for secondary blocks and I've thought about 
going that route.  There is no surging going on and a stumble was fixed.


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.
Roger Gazur
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Apr/01/2021 at 5:21pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote bikerfox Quote  Post ReplyReply Direct Link To This Post Posted: Apr/01/2021 at 6:33pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote BassBoat Quote  Post ReplyReply Direct Link To This Post Posted: Apr/01/2021 at 7:27pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote bikerfox Quote  Post ReplyReply Direct Link To This Post Posted: Apr/01/2021 at 10:05pm
Originally posted by BassBoat BassBoat wrote:

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

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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Post Options Post Options   Thanks (0) Thanks(0)   Quote bikerfox Quote  Post ReplyReply Direct Link To This Post Posted: Apr/02/2021 at 12:57am
Originally posted by 6PakBee 6PakBee wrote:

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.

From what I've gathered, BSFC is measured on an engine dyno.  I'm doing a chassis dyno.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 6PakBee Quote  Post ReplyReply Direct Link To This Post Posted: Apr/02/2021 at 7:48am
Originally posted by bikerfox bikerfox wrote:

Originally posted by 6PakBee 6PakBee wrote:

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.

From what I've gathered, BSFC is measured on an engine dyno.  I'm doing a chassis dyno.


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.
Roger Gazur
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Apr/02/2021 at 8:32am
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote BassBoat Quote  Post ReplyReply Direct Link To This Post Posted: Apr/02/2021 at 9:56pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Apr/06/2021 at 10:14am
What is the Holley List Number of your carbs ?

Edited by PHAT69AMX - Apr/10/2021 at 10:48pm
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