Holley carb experts needed!
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Holley carb experts needed!
Does anyone know what Holley aims for as far as the Air Fuel ratio, say, for cruising at 2500 rpm?
The reason i am asking, is i can't believe the PVRC(power valve restriction channel) is adding so much fuel!
if cruise is 17:1 then 13:1 would need a 30% increase in fuel. even 12:1 would only need a 42% increse. When i compare the jet area to the pvrc, i get +75%(when the power valve opens) on the primary and +169% on the back. I must be making a mistake here so lets figure out what it is. Maybe you have a spare carb apart you can look at? Any books discuss this? Thanks! (this is a street qjet replacement 4165, but others may be similar)
:cheers:
[Modified by Matt Gruber, 3:22 PM 5/28/2003]
The reason i am asking, is i can't believe the PVRC(power valve restriction channel) is adding so much fuel!
if cruise is 17:1 then 13:1 would need a 30% increase in fuel. even 12:1 would only need a 42% increse. When i compare the jet area to the pvrc, i get +75%(when the power valve opens) on the primary and +169% on the back. I must be making a mistake here so lets figure out what it is. Maybe you have a spare carb apart you can look at? Any books discuss this? Thanks! (this is a street qjet replacement 4165, but others may be similar)
:cheers:
[Modified by Matt Gruber, 3:22 PM 5/28/2003]
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Re: Holley carb experts needed! (Matt Gruber)
you must also add in the fuel flow from the idle and off idle circuits that is being used at part throttle that richens up the jet only flow before the PV opens. there is more fuel flow than just from the jet before the PV opens. i can scan you a article that explains air flow vs fuel flow area:chevy
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Re: Holley carb experts needed! (clem zahrobsky)
clem,
excellent point. i missed that completely!
Any idea how much fuel is coming in, in addition to the .060" main jet? What could it be? 10 or 20% more? Any figures in that article?
thanks :chevy
yes i'd like to see that article, but sometimes scans are too small for me to read
excellent point. i missed that completely!
Any idea how much fuel is coming in, in addition to the .060" main jet? What could it be? 10 or 20% more? Any figures in that article?
thanks :chevy
yes i'd like to see that article, but sometimes scans are too small for me to read
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Re: Holley carb experts needed! (Matt Gruber)
The power valve channel restriction is drilled further inside that big ole hole than you are thinking. You can measure their diameter using a set of fine drills. A street carburetor has about 6 jet sizes worth of PVCR, so 16:1 at cruise and 12.5:1 at full-throttle. A race carburetor has about 4 jet sizes worth of PVCR, so 15:1 rolling through the turns and 12.5:1 at full-throttle.
All the fuel for the idle/transfer system comes through the main jets into the fuel well. The main jets aren't restrictive to the idle/transfer system. The idle/transfer mixture is controlled by its own drilled jet combined with the air bleed size. When the main venturii really start sucking, all the fuel flow is stolen away from the manifold vacuum actuated idle system.
All the fuel for the idle/transfer system comes through the main jets into the fuel well. The main jets aren't restrictive to the idle/transfer system. The idle/transfer mixture is controlled by its own drilled jet combined with the air bleed size. When the main venturii really start sucking, all the fuel flow is stolen away from the manifold vacuum actuated idle system.
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Re: Holley carb experts needed! (HeaderDesign.com)
Rodney
that's what i thought; the idle and transition feed thru the main jet, so the total is whatever can go thru the main jet.
i do use numbered drills to check the pvrc sizes. the primary has a .052" pvrc, with a .060" main jet. computing the area of a circle gives a 75% increase in mixture.(feel free to check my math; i'm looking to find my mistakes).
I put a .0235" wire in the pvrc to cut fuel flow by 8.7%, about 1 A/F ratio. Just got back from a test drive; Looks like it really was 75% richer, my A/F sensors are still "stuck" on full rich(12.3 or higher). But, there might be fuel from the accelerator pump making it look over-rich during the test. While this is a TH400, on my 61 4 speed, every time i would let up and shift, when i nailed it again it took nearly the whole gear to clear out the pump shot :rolleyes: Now i am doing a pretty long 1/3 throttle primary only, so i hope the pump shot is not a problem(it's only getting 1/3 stroke) Next i plan to put another piece of wire in there.
thanks for your input :yesnod:
[Modified by Matt Gruber, 8:02 PM 5/28/2003]
that's what i thought; the idle and transition feed thru the main jet, so the total is whatever can go thru the main jet.
i do use numbered drills to check the pvrc sizes. the primary has a .052" pvrc, with a .060" main jet. computing the area of a circle gives a 75% increase in mixture.(feel free to check my math; i'm looking to find my mistakes).
I put a .0235" wire in the pvrc to cut fuel flow by 8.7%, about 1 A/F ratio. Just got back from a test drive; Looks like it really was 75% richer, my A/F sensors are still "stuck" on full rich(12.3 or higher). But, there might be fuel from the accelerator pump making it look over-rich during the test. While this is a TH400, on my 61 4 speed, every time i would let up and shift, when i nailed it again it took nearly the whole gear to clear out the pump shot :rolleyes: Now i am doing a pretty long 1/3 throttle primary only, so i hope the pump shot is not a problem(it's only getting 1/3 stroke) Next i plan to put another piece of wire in there.
thanks for your input :yesnod:
[Modified by Matt Gruber, 8:02 PM 5/28/2003]
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Re: Holley carb experts needed! (Matt Gruber)
Is that a new carburetor? Maybe the previous owner calibrated the PVCR for alcohol :p: . You could do your non-full-throttle tuning with the power valve plug installed. Start lean on the accelerator pump and work up. It's easy to diagnose a lean misfire. Lean misfire will blow the Power Valve if it is installed. The power valve blowout protection won't help you either, since the fuel/air can blow up in the power valve vacuum chamber just like in the manifold.
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Re: Holley carb experts needed! (Matt Gruber)
the length and shape of the entrance and exit of the orifice also controls the amount of fuel that go thru it not just the diameter. the idle circuit is still pulling at full throttle and even sometimes there is fuel being pulled from the accelerator squitter nozzles. the emulsion bleeds in the metering body wells also control the richness. the jets and the PVR are not the only factor involved. :chevy :chevy
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Re: Holley carb experts needed! (HeaderDesign.com)
Well, it is used. But i have 3 of them and they are all the same and show no signs of mods.
I've got a .040" wire for the pvrc; if it is 17:1 cruise it should be 13 pv open. If it is 16 cruise, it will still be too rich.
This is a huge drop in total carb fuel flow so i be watching carefully at WOT.
i think i'll switch back to my custom 13" PV.(now is 10.5") There won't(i hope) be any lean running as it will tip in very early.
I've got a .040" wire for the pvrc; if it is 17:1 cruise it should be 13 pv open. If it is 16 cruise, it will still be too rich.
This is a huge drop in total carb fuel flow so i be watching carefully at WOT.
i think i'll switch back to my custom 13" PV.(now is 10.5") There won't(i hope) be any lean running as it will tip in very early.
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Thread Starter
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From: central FL, near the beach.
Re: Holley carb experts needed! (clem zahrobsky)
well clem, it's only a piece of .040" wire; if you are right i'll get a too lean reading and i'll be looking for something between .023 and .040".
thanks for your advice. :cheers:
thanks for your advice. :cheers:
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From: Fredericksburg VA
Re: Holley carb experts needed! (Matt Gruber)
I just checked a 4180C 600CFM carburetor that I have sitting here. The PVCR is 0.045" for a main jet of 0.060" (63). The area increase is 56% but you have to consider the whole fuel path to get the actual flow increase as Clem said. The flow path is pretty miserable through the PV.
Those PV's sound like they open really early for most engines. People usually start with a 6.5"Hg valve. Why are you using a 13"Hg PV?
[Modified by HeaderDesign.com, 8:13 PM 5/28/2003]
Those PV's sound like they open really early for most engines. People usually start with a 6.5"Hg valve. Why are you using a 13"Hg PV?
[Modified by HeaderDesign.com, 8:13 PM 5/28/2003]
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Re: Holley carb experts needed! (HeaderDesign.com)
thanks for checking.
it is encouraging to see it uses a smaller pvrc. my carbs are about 30 years old. :cheers:
it is encouraging to see it uses a smaller pvrc. my carbs are about 30 years old. :cheers:
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Re: Holley carb experts needed! (HeaderDesign.com)
i started using a 13" PV in my 61. the choke was milled off, the pv works like a cold start enrichment circuit in the winter(at fast idle). With a vacuum gauge you can see, when cold, right where it would stall, the valve opens and it picks right up :yesnod:
But my 72 does not have a hand throttle like the 61, i was going to go back to a normal valve, but with the 10.5 it did ping a little before the valve opened, so i guess my excuse for using it is up to now, it has allowed the use of 87 octane with 9:7:1 iron heads and xe262 cam. this could be because of the excessive rich mixture, so final tune is up in the air for now.(tuning is a hobby for me)
But my 72 does not have a hand throttle like the 61, i was going to go back to a normal valve, but with the 10.5 it did ping a little before the valve opened, so i guess my excuse for using it is up to now, it has allowed the use of 87 octane with 9:7:1 iron heads and xe262 cam. this could be because of the excessive rich mixture, so final tune is up in the air for now.(tuning is a hobby for me)
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Re: Holley carb experts needed! (Matt Gruber)
It almost sounds like the pump shot and the early power valve opening are combining to give you the after shot rich condition. You might be able to tune the part-throttle ping out with an adjustable vacuum advance can instead of the richness. Calibrate the can visually for onset of movement and full advance on the workbench using a vacuum tester. Count turns out from the seated position for each calibration interval. Works well for me. If you are content to always run rich, you might want to add a top-end lubricant to the gas like Marvel Mystery Oil.
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Re: Holley carb experts needed!
i now remember why i use 13" pv's.
(this was 8 years ago and i forgot)
i read some tuning articles that the pv should open 4" below the idle vacuum.
Since i use rather small street cams the idle vacuum is very good, about 16-18 as i recall.
Also climbing the steepest overpass in town, a 65 foot rise over the intercostal waterway, i note 15" while maintaining a steady speed.
i don't know why holley includes 6.5 & 8.5 valves in the kit. i never drive near those numbers; it is either light throttle in traffic, cruising, or WOT :D
(this was 8 years ago and i forgot)
i read some tuning articles that the pv should open 4" below the idle vacuum.
Since i use rather small street cams the idle vacuum is very good, about 16-18 as i recall.
Also climbing the steepest overpass in town, a 65 foot rise over the intercostal waterway, i note 15" while maintaining a steady speed.
i don't know why holley includes 6.5 & 8.5 valves in the kit. i never drive near those numbers; it is either light throttle in traffic, cruising, or WOT :D
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Re: Holley carb experts needed! (Matt Gruber)
so i take it apart and one of the .023 wires is missing :rolleyes:
where is it? in the pv window!
Next i bend the .040 wire into an L so i hope it will stay put. it barely fits into the .052 pvrc and the bend looks like it may further cut flow. it looks silly to even try this, but i want to see a lean condition and work back from that. i'll guess now that a .034-036 wire will be final.
Using the 13 pv again since lower ones make no sense for my driving style. (can you fault an engine for pinging when you are passing a car at 11" wth a 16 or 17:1 A/F?) But as mentioned that vacuum can could be adding too much too soon. it starts at 10" is 1/2 advanced at 12", full at 15" Does that sound excessive to anyone? Thanks again for the comments :cheers:
[Modified by Matt Gruber, 11:45 AM 5/29/2003]
where is it? in the pv window!
Next i bend the .040 wire into an L so i hope it will stay put. it barely fits into the .052 pvrc and the bend looks like it may further cut flow. it looks silly to even try this, but i want to see a lean condition and work back from that. i'll guess now that a .034-036 wire will be final.
Using the 13 pv again since lower ones make no sense for my driving style. (can you fault an engine for pinging when you are passing a car at 11" wth a 16 or 17:1 A/F?) But as mentioned that vacuum can could be adding too much too soon. it starts at 10" is 1/2 advanced at 12", full at 15" Does that sound excessive to anyone? Thanks again for the comments :cheers:
[Modified by Matt Gruber, 11:45 AM 5/29/2003]
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Re: Holley carb experts needed! (Matt Gruber)
Looking back through this post, I think I see the root of your problem. The cast iron head, mild cam, and 9.7:1 compression will need premium gas. You will be able to optimize the fuel ratio and timing with premium, largely recovering any economy lost to the less expensive gas and sub-optimal tune.
I've found that a typical smooth idling street performance engine will use the 6.5 Power Valve, and the vacuum advance will be full-in at 12"Hg and full-out at 4"Hg. The vacuum overlap range of the PV and onset of vacuum advance is a tuning point. Quick accelerating cars may use a higher number PV. Pinging may require higher full-out for the vacuum advance, and/or the next higher PV depending on the in.Hg vacuum that the pinging occured. The two-stage PV's don't have high-flow capability, so watch out for those.
Also, are you sure you are measuring the PVCR correctly? The actual restriction is drilled way down next to the main well. Make sure your drill goes all the way into the well (about 3/4" total travel).
I've found that a typical smooth idling street performance engine will use the 6.5 Power Valve, and the vacuum advance will be full-in at 12"Hg and full-out at 4"Hg. The vacuum overlap range of the PV and onset of vacuum advance is a tuning point. Quick accelerating cars may use a higher number PV. Pinging may require higher full-out for the vacuum advance, and/or the next higher PV depending on the in.Hg vacuum that the pinging occured. The two-stage PV's don't have high-flow capability, so watch out for those.
Also, are you sure you are measuring the PVCR correctly? The actual restriction is drilled way down next to the main well. Make sure your drill goes all the way into the well (about 3/4" total travel).
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Re: Holley carb experts needed! (HeaderDesign.com)
i did expect to use hi-test.
but when i switched to cold air cowl induction, i noticed a big improvement, 87 has been fine for years now. won't know if there is a pinging problem until i get the A/F set right. if it pings with 13:1 that could be a problem, but in the past any pinging was cured(like a bad tank of gas) by reducing initial by 2 degrees.
Also helping is a blocked heat riser and tight quench of.040" with small chamber heads.
Also a study of gas station gas showed 30% put 87 in the hi-test tank and rip us off. And 87 sells fast, less chance of older(stale) gas in slower volume honest stations.
Sounds like you have a good tune for your driving style :cheers:
[Modified by Matt Gruber, 12:48 PM 5/29/2003]
but when i switched to cold air cowl induction, i noticed a big improvement, 87 has been fine for years now. won't know if there is a pinging problem until i get the A/F set right. if it pings with 13:1 that could be a problem, but in the past any pinging was cured(like a bad tank of gas) by reducing initial by 2 degrees.
Also helping is a blocked heat riser and tight quench of.040" with small chamber heads.
Also a study of gas station gas showed 30% put 87 in the hi-test tank and rip us off. And 87 sells fast, less chance of older(stale) gas in slower volume honest stations.
Sounds like you have a good tune for your driving style :cheers:
[Modified by Matt Gruber, 12:48 PM 5/29/2003]
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Re: Holley carb experts needed! (HeaderDesign.com)
as far as measuring 3/4" into the pvrc, i am sure not doing that! i can get about 3/8" in and then i hit a perpendicular channel.
this is a 4165, it uses a different plate not interchangable with others.
this is a 4165, it uses a different plate not interchangable with others.