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advanceing camshaft . does it affect ignition timing?

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Post  maverick172 May 27th 2023, 8:27 pm

so i advanced my camshaft 4 degree and i used to run my engine at 27degree total timing now i have it at 26 degree and i am getting some run on , so i am thinking of backing it to 24 or 25 degree to try it , just curious if advanceing the cam affects ignition it seems too on my comnination

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Post  supervel45 May 27th 2023, 9:18 pm

Usually run on is caused by heat and or poor fuel quality. Never heard of advancing a camshaft doing it.

I suppose way out of wack rotor phasing might cause or aggravate it, and maybe advancing the cam would affect that a little. I'm not sure on that but, it would be good to check the phasing anyway.

I quess you idea of backing the timing down would eliminate the rotor phase deal somewhat if it is a problem.

Also you will build more dynamic compression by advancing the cam, so there's that. It may want less timing for the fuel octane.

supervel45

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Post  rmcomprandy May 28th 2023, 9:46 am

maverick172 wrote:so i advanced my camshaft 4 degree and i used to run my engine at 27degree total timing now i have it at 26 degree and i am getting some run on , so i am thinking of backing it to 24 or 25 degree to try it , just curious if advanceing the cam affects ignition it seems too on my comnination

Advancing the camshaft will increase low speed cylinder pressure, (with effects similar to slightly raising the compression ratio).
It appears you must have been right on the edge to start with so, a better fuel will usually cure that issue.

Rotor phasing means nothing when the ignition is OFF.

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Post  maverick172 May 28th 2023, 10:08 am

rmcomprandy wrote:
maverick172 wrote:so i advanced my camshaft 4 degree and i used to run my engine at 27degree total timing now i have it at 26 degree and i am getting some run on , so i am thinking of backing it to 24 or 25 degree to try it , just curious if advanceing the cam affects ignition it seems too on my comnination

Advancing the camshaft will increase low speed cylinder pressure, (with effects similar to slightly raising the compression ratio).
It appears you must have been right on the edge to start with so, a better fuel will usually cure that issue.

Rotor phasing means nothing when the ignition is OFF.

ya thats kinda what i thought .. so on the edge of predetonation"? you mean

i will try some octane booster
or a slight mix of race fuel with pump gas
ya i did a quick dynamic compression calcaulation and it raised it like .25% went from 8.25:1 too 8.5:1

so i removed my power valve from my front primary on a 1050 dominator and trying differant jetting i notice midrange it is kinda rich i can tell obviously from eliminating that power valve circuit what afr should i tune to at wot or cruiseing speed ?
i heard to jet up like 8 jets if you remove pv. factory was 84prim 94 sec 5.5 pv
i am at 93prim 93 sec and no pv now . i think my vacumm was to low to properly use the pv that i had .
i am in the 13's in idle circuit mid cruise i go too 10's which is fat rich and wot hard to tune on street but going to take to track and try tune that best ..

maverick172

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Post  maverick172 May 28th 2023, 10:17 am

supervel45 wrote:Usually run on is caused by heat and or poor fuel quality. Never heard of advancing a camshaft doing it.

I suppose way out of wack rotor phasing might cause or aggravate it, and maybe advancing the cam would affect that a little. I'm not sure on that but, it would be good to check the phasing anyway.

I quess you idea of backing the timing down would eliminate the rotor phase deal somewhat if it is a problem.

Also you will build more dynamic compression by advancing the cam, so there's that. It may want less timing for the fuel octane.

ya kinda what i thought might have to runa bit of octane boost in it or mix some race gas ..
surprised it raised my dynamic compression .25point went from 8.25:1 to 8.5:1

ya ideally i want to run the most timing i can with still haveing max power than back it off a degree .
btw this is on the 521 i got it all back together pumped to get it out to the track and see what it runs now..
ps i had my wife step on the throttle when i put my carb back on and noticed the butterflys where only open 3/4 way so maybe my "turd of a engine " maybe not such a turd afterall the gas peddle was bottomed out on floor and was not getting full throttle . i could of swore i checked it when i put engine in this winter but i guess not .

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Post  rmcomprandy May 28th 2023, 12:16 pm

maverick172 wrote:
rmcomprandy wrote:
maverick172 wrote:so i advanced my camshaft 4 degree and i used to run my engine at 27degree total timing now i have it at 26 degree and i am getting some run on , so i am thinking of backing it to 24 or 25 degree to try it , just curious if advanceing the cam affects ignition it seems too on my comnination

Advancing the camshaft will increase low speed cylinder pressure, (with effects similar to slightly raising the compression ratio).
It appears you must have been right on the edge to start with so, a better fuel will usually cure that issue.

Rotor phasing means nothing when the ignition is OFF.

ya thats kinda what i thought .. so on the edge of predetonation"? you mean

i will try some octane booster
or a slight mix of race fuel with pump gas
ya i did a quick dynamic compression calcaulation and it raised it like .25% went from 8.25:1 too 8.5:1

so i removed my power valve from my front primary on a 1050 dominator and trying differant jetting i notice midrange it is kinda rich i can tell obviously from eliminating that power valve circuit what afr should i tune to at wot  or cruiseing speed ?
i heard to jet up like 8 jets if you remove pv. factory was 84prim 94 sec 5.5 pv
i am at 93prim 93 sec and no pv now . i think my vacumm was to low to properly use the pv that i had .
i am in the 13's in idle circuit mid cruise i go too 10's which is fat rich and wot hard to tune on street but going to take to track and try tune that best ..

If you are intending to mix race gas with pump gas, be sure it is lead free race gas as tetraethyl lead, (TEL), and alcohol don't work well together.

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Post  supervel45 May 28th 2023, 1:22 pm

maverick172 wrote:
rmcomprandy wrote:
maverick172 wrote:so i advanced my camshaft 4 degree and i used to run my engine at 27degree total timing now i have it at 26 degree and i am getting some run on , so i am thinking of backing it to 24 or 25 degree to try it , just curious if advanceing the cam affects ignition it seems too on my comnination

Advancing the camshaft will increase low speed cylinder pressure, (with effects similar to slightly raising the compression ratio).
It appears you must have been right on the edge to start with so, a better fuel will usually cure that issue.

Rotor phasing means nothing when the ignition is OFF.

ya thats kinda what i thought .. so on the edge of predetonation"? you mean

i will try some octane booster
or a slight mix of race fuel with pump gas
ya i did a quick dynamic compression calcaulation and it raised it like .25% went from 8.25:1 too 8.5:1

so i removed my power valve from my front primary on a 1050 dominator and trying differant jetting i notice midrange it is kinda rich i can tell obviously from eliminating that power valve circuit what afr should i tune to at wot  or cruiseing speed ?
i heard to jet up like 8 jets if you remove pv. factory was 84prim 94 sec 5.5 pv
i am at 93prim 93 sec and no pv now . i think my vacumm was to low to properly use the pv that i had .
i am in the 13's in idle circuit mid cruise i go too 10's which is fat rich and wot hard to tune on street but going to take to track and try tune that best ..


Randy is correct on the rotor phasing when the key is off. I would still check that anyway to see where you are at.

When I said remove the power valve from your Dominator, I also said to use it only for a Track Carburetor.

IE: WOT Likely at Launch on a Transbrake or Close to It, until the Finish Line. Jet for Highest MPH and Also Guage Spark Plugs.   REASON ON CHECKING SPARK PLUGS: Some Cylinders May be LEANING OUT!!!

I'm not going to get into Accelerator Pumps here but, Keep in Mind You Get Less Pump Shot the Higher Rpm you Stage the Car. I have seen a Double Pumper with a High Stall and A Brake E/T Faster with the Back Pump Arm Disconnected. Just Keep That in Mind when Tuning. Seriously Don't Do it on Your Combo. Cool

I suspect your jets will fall between 92 and 94, Square Primary and Secondary.

A lot of Dyno charts I have seen or 13.1 or so A/F ratio. Of course type of Fuel Plays a Role. Not Saying that is Best for Your Combo Either. Also Keep in Mind Highest HP on a Dyno A/F Ratio's Don't Always Equal Fastest Track Times. It's a Very Good Starting Point Though.

Yes Full Throttle Carburetor to Pedal Helps E/T's. Wink

The PVRC or Power Valve Restriction Channel Diameter will determine how much the jet has to be increased if a Block Off Plug is Run. For Race Only as Above Jet Square is the Old School Rule. Unless it's an L-88/ZL-1, Then Cross Jet. Wink

Like I pointed out some of the Jet Numbers have the Same Drill Hole Size Number and the Flow is Slightly Different because of the inlet/outlet angle cut. You can fine tune with them.

If you only have ONE Holley Jet Kit, it also Comes in Handy Knowing This, especially when trying to get Close to Square Jetting.

For Street/Ecomony/Drivibitly I would throw most of what you read about PVRC and Jet Sizing and A/F Gauge Readings Out The Window, as I Said Before. Go By Seat of the Pants and Fuel Economy. Jet Lean on the Primary's until you get a surge at Steady High Way Speed, and then Jet up the Primarys 2-4 Jet sizes. Then Go after the Secondary's for Best Performance, Preferably at the Race Track for Highest MPH and or Very Lastly E/T.

^ In the Old School Method accelerator pump cams and shooter sizes were always used as Band Aids over Re-Sizing PVCR Channels and Considered good enough for Tip In drivability for Hot Rods. At the Level your Combo is at I would stick to it, as the gain is not worth the pain in my opinion.

The Reasoning on Highest MPH in old school tuning, I believe, is Because of Street Cars Without High Stall Convertors and/or Gears, Depend on the Accelerator Pump Circuit so much to get Off the Line, and are Also usually Traction Limited, Which Effects E/T More Then MPH, and 60 foot Times Greatly Aid ET, (especially on shorter tracks), So MPH is a Better Re-Flection of HP. I may have misphriased that a little but it's the general idea.

^ You do need consistent passes to gauge MPH Jetting Gains at the same track, same day and same weather conditions ect.. No wheelspin or EVEN wheel spin/speed between passes, is the goal though. Tire spin on a pass can show a Higher MPH with a Higher 60 foot time and have a Slower ET, if previous pass had perfect traction and a Lower 60 foot time, Slower MPH and Quicker ET. That may not make sense to you but, it happens and you need to be aware of it, WHEN USING THE mph Tuning Method. It's not Fail Proof.

Hence Work on 60 Foot as a Secondary Part of your Tuning Program. For the Carburetor side that would be mainly the Accelerator Pump System in this case. You Don't have a Power System/Power Valve to Contend with anymore, since it is blocked for Race only Application. affraid

This Assumes you picked the Correct Power Valve Based off of actual Vacuum during Driving Conditions, Not at Idle. This is Only for a Dual Use Street/Strip that I mentioned before. Like I said I would Dedicate the Dominator to Race Only if you are Serious on Best Performance and get a 4150 to play with on the Street.

Once if you get further into RACE Tuning the Dominator with air bleeds, throttle slot sizing, IFR's ect. and get it right, if you go that far, you will not want to play with it for Street Drive ability. You'll see.

Always Re-Check Your Float Levels After Changes, With the Engine Running, Just Because.

And Despite what is Normally Said Sometimes/MostTimes the Idle and Main Circuit can Both overlap in some cruise Situations, and Dominators are Nortourus about Transfer Slot Length of the Idle Circuit.

As for as the Dieseling, Ford used a Solenoid to close the throttle when they key was turned off as throttle blade position also affects Run On.

Did you Re-Adjust your Idle Speed?

Did you adjust your Idle Mixture Screws any?

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Post  Mark Miller May 28th 2023, 11:11 pm

Is this engine in a Race Only car or Street and Strip Car IMO if it's street driven any at all i prefer using a front Power Valve?

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Post  maverick172 May 28th 2023, 11:30 pm

supervel45 wrote:
maverick172 wrote:
rmcomprandy wrote:
maverick172 wrote:so i advanced my camshaft 4 degree and i used to run my engine at 27degree total timing now i have it at 26 degree and i am getting some run on , so i am thinking of backing it to 24 or 25 degree to try it , just curious if advanceing the cam affects ignition it seems too on my comnination

Advancing the camshaft will increase low speed cylinder pressure, (with effects similar to slightly raising the compression ratio).
It appears you must have been right on the edge to start with so, a better fuel will usually cure that issue.

Rotor phasing means nothing when the ignition is OFF.

ya thats kinda what i thought .. so on the edge of predetonation"? you mean

i will try some octane booster
or a slight mix of race fuel with pump gas
ya i did a quick dynamic compression calcaulation and it raised it like .25% went from 8.25:1 too 8.5:1

so i removed my power valve from my front primary on a 1050 dominator and trying differant jetting i notice midrange it is kinda rich i can tell obviously from eliminating that power valve circuit what afr should i tune to at wot  or cruiseing speed ?
i heard to jet up like 8 jets if you remove pv. factory was 84prim 94 sec 5.5 pv
i am at 93prim 93 sec and no pv now . i think my vacumm was to low to properly use the pv that i had .
i am in the 13's in idle circuit mid cruise i go too 10's which is fat rich and wot hard to tune on street but going to take to track and try tune that best ..


Randy is correct on the rotor phasing when the key is off. I would still check that anyway to see where you are at.

When I said remove the power valve from your Dominator, I also said to use it only for a Track Carburetor.

IE: WOT Likely at Launch on a Transbrake or Close to It, until the Finish Line. Jet for Highest MPH and Also Guage Spark Plugs.   REASON ON CHECKING SPARK PLUGS: Some Cylinders May be LEANING OUT!!!

I'm not going to get into Accelerator Pumps here but, Keep in Mind You Get Less Pump Shot the Higher Rpm you Stage the Car. I have seen a Double Pumper with a High Stall and A Brake E/T Faster with the Back Pump Arm Disconnected. Just Keep That in Mind when Tuning. Seriously Don't Do it on Your Combo. Cool

I suspect your jets will fall between 92 and 94, Square Primary and Secondary.

A lot of Dyno charts I have seen or 13.1 or so A/F ratio. Of course type of Fuel Plays a Role. Not Saying that is Best for Your Combo Either. Also Keep in Mind Highest HP on a Dyno A/F Ratio's Don't Always Equal Fastest Track Times. It's a Very Good Starting Point Though.

Yes Full Throttle Carburetor to Pedal Helps E/T's. Wink

The PVRC or Power Valve Restriction Channel Diameter will determine how much the jet has to be increased if a Block Off Plug is Run. For Race Only as Above Jet Square is the Old School Rule. Unless it's an L-88/ZL-1, Then Cross Jet. Wink

Like I pointed out some of the Jet Numbers have the Same Drill Hole Size Number and the Flow is Slightly Different because of the inlet/outlet angle cut. You can fine tune with them.

If you only have ONE Holley Jet Kit, it also Comes in Handy Knowing This, especially when trying to get Close to Square Jetting.

For Street/Ecomony/Drivibitly I would throw most of what you read about PVRC and Jet Sizing and A/F Gauge Readings Out The Window, as I Said Before. Go By Seat of the Pants and Fuel Economy. Jet Lean on the Primary's until you get a surge at Steady High Way Speed, and then Jet up the Primarys 2-4 Jet sizes. Then Go after the Secondary's for Best Performance, Preferably at the Race Track for Highest MPH and or Very Lastly E/T.

^ In the Old School Method accelerator pump cams and shooter sizes were always used as Band Aids over Re-Sizing PVCR Channels and Considered good enough for Tip In drivability for Hot Rods. At the Level your Combo is at I would stick to it, as the gain is not worth the pain in my opinion.

The Reasoning on Highest MPH in old school tuning, I believe, is Because of Street Cars Without High Stall Convertors and/or Gears, Depend on the Accelerator Pump Circuit so much to get Off the Line, and are Also usually Traction Limited, Which Effects E/T More Then MPH, and 60 foot Times Greatly Aid ET, (especially on shorter tracks), So MPH is a Better Re-Flection of HP. I may have misphriased that a little but it's the general idea.

^ You do need consistent passes to gauge MPH Jetting Gains at the same track, same day and same weather conditions ect.. No wheelspin or EVEN wheel spin/speed between passes, is the goal though. Tire spin on a pass can show a Higher MPH with a Higher 60 foot time and have a Slower ET, if previous pass had perfect traction and a Lower 60 foot time, Slower MPH and Quicker ET. That may not make sense to you but, it happens and you need to be aware of it, WHEN USING THE mph Tuning Method. It's not Fail Proof.

Hence Work on 60 Foot as a Secondary Part of your Tuning Program. For the Carburetor side that would be mainly the Accelerator Pump System in this case. You Don't have a Power System/Power Valve to Contend with anymore, since it is blocked for Race only Application. affraid

This Assumes you picked the Correct Power Valve Based off of actual Vacuum during Driving Conditions, Not at Idle. This is Only for a Dual Use Street/Strip that I mentioned before. Like I said I would Dedicate the Dominator to Race Only if you are Serious on Best Performance and get a 4150 to play with on the Street.

Once if you get further into RACE Tuning the Dominator with air bleeds, throttle slot sizing, IFR's ect. and get it right, if you go that far, you will not want to play with it for Street Drive ability. You'll see.

Always Re-Check Your Float Levels After Changes, With the Engine Running, Just Because.

And Despite what is Normally Said Sometimes/MostTimes the Idle and Main Circuit can Both overlap in some cruise Situations, and Dominators are Nortourus about Transfer Slot Length of the Idle Circuit.

As for as the Dieseling, Ford used a Solenoid to close the throttle when they key was turned off as throttle blade position also affects Run On.

Did you Re-Adjust your Idle Speed?

Did you adjust your Idle Mixture Screws any?

i played with the settings a bit on the idle circuit but it basically ended being the same i should just left them alone ..
just timing differance but going to try some octane boost and see try bring octane to 98 and go from there

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Post  maverick172 May 28th 2023, 11:30 pm

Mark Miller wrote:Is this engine in a Race Only car or Street and Strip Car IMO if it's street driven any at all i prefer using a front Power Valve?

well it is a street and strip car . but this engine is more performing almost more strip would like it little more streetable ..

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Post  maverick172 May 28th 2023, 11:31 pm

supervel45 wrote:
maverick172 wrote:
rmcomprandy wrote:
maverick172 wrote:so i advanced my camshaft 4 degree and i used to run my engine at 27degree total timing now i have it at 26 degree and i am getting some run on , so i am thinking of backing it to 24 or 25 degree to try it , just curious if advanceing the cam affects ignition it seems too on my comnination

Advancing the camshaft will increase low speed cylinder pressure, (with effects similar to slightly raising the compression ratio).
It appears you must have been right on the edge to start with so, a better fuel will usually cure that issue.

Rotor phasing means nothing when the ignition is OFF.

ya thats kinda what i thought .. so on the edge of predetonation"? you mean

i will try some octane booster
or a slight mix of race fuel with pump gas
ya i did a quick dynamic compression calcaulation and it raised it like .25% went from 8.25:1 too 8.5:1

so i removed my power valve from my front primary on a 1050 dominator and trying differant jetting i notice midrange it is kinda rich i can tell obviously from eliminating that power valve circuit what afr should i tune to at wot  or cruiseing speed ?
i heard to jet up like 8 jets if you remove pv. factory was 84prim 94 sec 5.5 pv
i am at 93prim 93 sec and no pv now . i think my vacumm was to low to properly use the pv that i had .
i am in the 13's in idle circuit mid cruise i go too 10's which is fat rich and wot hard to tune on street but going to take to track and try tune that best ..


Randy is correct on the rotor phasing when the key is off. I would still check that anyway to see where you are at.

When I said remove the power valve from your Dominator, I also said to use it only for a Track Carburetor.

IE: WOT Likely at Launch on a Transbrake or Close to It, until the Finish Line. Jet for Highest MPH and Also Guage Spark Plugs.   REASON ON CHECKING SPARK PLUGS: Some Cylinders May be LEANING OUT!!!

I'm not going to get into Accelerator Pumps here but, Keep in Mind You Get Less Pump Shot the Higher Rpm you Stage the Car. I have seen a Double Pumper with a High Stall and A Brake E/T Faster with the Back Pump Arm Disconnected. Just Keep That in Mind when Tuning. Seriously Don't Do it on Your Combo. Cool

I suspect your jets will fall between 92 and 94, Square Primary and Secondary.

A lot of Dyno charts I have seen or 13.1 or so A/F ratio. Of course type of Fuel Plays a Role. Not Saying that is Best for Your Combo Either. Also Keep in Mind Highest HP on a Dyno A/F Ratio's Don't Always Equal Fastest Track Times. It's a Very Good Starting Point Though.

Yes Full Throttle Carburetor to Pedal Helps E/T's. Wink

The PVRC or Power Valve Restriction Channel Diameter will determine how much the jet has to be increased if a Block Off Plug is Run. For Race Only as Above Jet Square is the Old School Rule. Unless it's an L-88/ZL-1, Then Cross Jet. Wink

Like I pointed out some of the Jet Numbers have the Same Drill Hole Size Number and the Flow is Slightly Different because of the inlet/outlet angle cut. You can fine tune with them.

If you only have ONE Holley Jet Kit, it also Comes in Handy Knowing This, especially when trying to get Close to Square Jetting.

For Street/Ecomony/Drivibitly I would throw most of what you read about PVRC and Jet Sizing and A/F Gauge Readings Out The Window, as I Said Before. Go By Seat of the Pants and Fuel Economy. Jet Lean on the Primary's until you get a surge at Steady High Way Speed, and then Jet up the Primarys 2-4 Jet sizes. Then Go after the Secondary's for Best Performance, Preferably at the Race Track for Highest MPH and or Very Lastly E/T.

^ In the Old School Method accelerator pump cams and shooter sizes were always used as Band Aids over Re-Sizing PVCR Channels and Considered good enough for Tip In drivability for Hot Rods. At the Level your Combo is at I would stick to it, as the gain is not worth the pain in my opinion.

The Reasoning on Highest MPH in old school tuning, I believe, is Because of Street Cars Without High Stall Convertors and/or Gears, Depend on the Accelerator Pump Circuit so much to get Off the Line, and are Also usually Traction Limited, Which Effects E/T More Then MPH, and 60 foot Times Greatly Aid ET, (especially on shorter tracks), So MPH is a Better Re-Flection of HP. I may have misphriased that a little but it's the general idea.

^ You do need consistent passes to gauge MPH Jetting Gains at the same track, same day and same weather conditions ect.. No wheelspin or EVEN wheel spin/speed between passes, is the goal though. Tire spin on a pass can show a Higher MPH with a Higher 60 foot time and have a Slower ET, if previous pass had perfect traction and a Lower 60 foot time, Slower MPH and Quicker ET. That may not make sense to you but, it happens and you need to be aware of it, WHEN USING THE mph Tuning Method. It's not Fail Proof.

Hence Work on 60 Foot as a Secondary Part of your Tuning Program. For the Carburetor side that would be mainly the Accelerator Pump System in this case. You Don't have a Power System/Power Valve to Contend with anymore, since it is blocked for Race only Application. affraid

This Assumes you picked the Correct Power Valve Based off of actual Vacuum during Driving Conditions, Not at Idle. This is Only for a Dual Use Street/Strip that I mentioned before. Like I said I would Dedicate the Dominator to Race Only if you are Serious on Best Performance and get a 4150 to play with on the Street.

Once if you get further into RACE Tuning the Dominator with air bleeds, throttle slot sizing, IFR's ect. and get it right, if you go that far, you will not want to play with it for Street Drive ability. You'll see.

Always Re-Check Your Float Levels After Changes, With the Engine Running, Just Because.

And Despite what is Normally Said Sometimes/MostTimes the Idle and Main Circuit can Both overlap in some cruise Situations, and Dominators are Nortourus about Transfer Slot Length of the Idle Circuit.

As for as the Dieseling, Ford used a Solenoid to close the throttle when they key was turned off as throttle blade position also affects Run On.

Did you Re-Adjust your Idle Speed?

Did you adjust your Idle Mixture Screws any?
i should note i have only 4 too 5 vaccum at cruise speed and i had a 5.5 pv in there

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Post  supervel45 May 29th 2023, 1:09 am

^ If that was the case your PV was always Open, and running full fuel, IE Mains and Power Circuit.

^You would have to drop down to a 2.5hg. or Lower and Gamble it won't close at WOT as I mentioned before in the other thread, to have any benefit if you are pulling 4-5hg at cruise now.

What I was getting at on re-tuning the Idle mixture screws, is you may be able to raise the Idle RPM, by adjusting them, and then lower the Throttle screw to close the Butterfly's more and Keep the same Idle RPM.

Also you might play with that at 27 degree's also and see if you get any improvement.

Another Thing that may have Some Affect on all of this , is How far the Secondary Blade Setting is Open. Probably Not but, it is worth noting.

You can turn it off in gear also, in a pinch.

You should do a cranking compression test to see where you are there, and also for future reference.

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Post  maverick172 May 29th 2023, 8:00 am

ya as i rev it higher seems to loose vaccum altogether . so when that happens the pv closes again so basically it only opens in the mid range?
ya i played with the butterflys . you can barely see the transfer slots so they are not open very far but i will try get them closed a bit more .
ya i can shut off in gear but would rather a good tune that i do not have too
supervel45 wrote:^ If that was the case your PV was always Open, and running full fuel, IE Mains and Power Circuit.

^You would have to drop down to a 2.5hg. or Lower and Gamble it won't close at WOT as I mentioned before in the other thread, to have any benefit if you are pulling 4-5hg at cruise now.

What I was getting at on re-tuning the Idle mixture screws, is you may be able to raise the Idle RPM, by adjusting them, and then lower the Throttle screw to close the Butterfly's more and Keep the same Idle RPM.

Also you might play with that at 27 degree's also and see if you get any improvement.

Another Thing that may have Some Affect on all of this , is How far the Secondary Blade Setting is Open. Probably Not but, it is worth noting.

You can turn it off in gear also, in a pinch.

You should do a cranking compression test to see where you are there, and also for future reference.

maverick172

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Post  supervel45 May 29th 2023, 7:09 pm

^When you Rev. the Engine Under Load, and the vacuum falls Below what the power valve is Rated For, the power valve Opens, and lets Fuel Flow, to richen the mixture. KEY WORD LOAD.

Try to remember it is a N/O Normally Open Valve, Until ENOUGH Vacuum is Applied, To Over Come it's Spring Rating and Close It.

Try to think of it in terms of an electric N/O Relay and replace Voltage Applied to the Coil, with Vacuum applied to the PV Spring. Except ass backwards... On the Electrical Flow through the Contacts versus the Fuel Flow through the Valve . It may make it easier to remember. Neutral Yes Valving and Switching can be a hard brain tease if you don't work with it a lot.

For all Practical purposes on Power Valve Understanding in the real world, It might be better to just consider it N/C Valve, (even though it's not) with the Engine running with High stock type vacuum, at Idle and Cruise., THAT is Closed Most of the TIME. Open ONLY at Higher Loads and WOT or when the Engine is OFF. In a High Performance engine the Vacuum SCALE is just in smaller numbers but all the principles are the same. Say instead of 18" stock idle, 9" Perfomance idle. As a general rule you could divide the two previous numbers by 2 and be in the ball park for PV sizing and live happily ever after. In your case it would be 5=2.5 and call it good as long as your Manifold vacuum can Never go over that at extended WOT, which is not very likely.


^As with everything there can be an exception. Some may run a power valve that is open at IDLE. They are usually on the Fringe of the Spectrum and an Anomaly.

Ford use to advertise it and I believe Holley, as an Economizer Valve, when they came out. It may have started on the T-Pot/Holley Thunderbirds.

What kind of water temp are you running?

Did you try the Water Wetter and see if it Helped lower it any?

The cooler it runs to a point the better with run-on and detonation issues.

PS: On those Transfer slots, be careful, if you cover them completely you may get a hesitation. It's a little bit trial and error type deal.

^You will also want to reset your idle mixture screws when adjusting blade position, as transfer slots work in conjunction with the Idle Circuit. You probably already knew all that but, I just wanted to double check.

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