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Timing Curve

General engine tech -- Drag Racing to Circle Track

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Geoff2
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Re: Timing Curve

Post by Geoff2 » Fri Oct 04, 2019 6:05 am

Reducing idle timing is NOT the way to get the transfer slots [ TS ] positioned correctly. Give the engine what it 'likes' for idle. Theeeen, tune the idle cct.
TSs almost closed off is ok, but better to primary blades open a little further than secs if both P & S TSs are closed off.
The IFRs are sized for off idle, TS operation, the transition from idle to main cct. Not sized for idle. The reason Holley 4bbl carbs have a sec idle system is NOT because it is reqd for idle purposes; it so some fuel always flows from the sec side to keep the fuel fresh in the sec fuel bowl.
You could block the sec IFR & IAB so that the carb only idles on the pri idle system; then, close off the sec blades to reduce airflow at idle; this will require opening the pri blades slightly to compensate. Lots of 4bbl carbs have idle ccts ONLY on the pri.......& idle just fine: Carter/Edel AFB/AVS, QJ, TQ.

BobbyB
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Re: Timing Curve

Post by BobbyB » Fri Oct 04, 2019 6:58 am

Firedome8
What is “falters or runs splashy”?
Could it be my “28 degrees at 2000 rpm (a lttle erratic at this rpm)” something is definitely happening at this engine speed in park!
What IFR should I try first from the .030s ... .028?....025?...or .020?
Thanks everybody. It sounds like nobody thinks I should reduce base timing.

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Re: Timing Curve

Post by Firedome8 » Fri Oct 04, 2019 8:48 am

BobbyB wrote:
Fri Oct 04, 2019 6:58 am
Firedome8
What is “falters or runs splashy”?
Could it be my “28 degrees at 2000 rpm (a lttle erratic at this rpm)” something is definitely happening at this engine speed in park!
What IFR should I try first from the .030s ... .028?....025?...or .020?
Thanks everybody. It sounds like nobody thinks I should reduce base timing.
Falters or runs splashy Is my verbage for not very smothe. I usually go up in size and work back, you can make a large jump just to see what happens. The post on shutting down the sec idle comes from a great source and should be paid attention to. Timing should be steady. Possibly more timing in conjunction with closing the sec down.
Do you have a pcv. Are the plugs clean and what heat range?

Look at above posters past comments on this and timing effects on idle, good information.

Vizards holley book bill mentioned is a click away and is a good resource.

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Re: Timing Curve

Post by BobbyB » Fri Oct 04, 2019 9:05 am

Firedome8
Yes I have PCV valve with 3/8 hose into back of carb. Seems like a HUGE vacuum leak to me. I am considering choking the PCV hose down some.
HOW THE HECK DO YOU KNOW WHAT PCV VALVE YOU NEED? Thais one is from a 74 Torino 302.
Plugs are NOT CLEAN!
Heat range is as specified by Head manufacturer AFR
Just put in .025 IFR and 6.5 power valve. I will try to test it today if I can.
I believe secondary idle is essentially shut off since no transfer slot is showing.

SNW Vette
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Re: Timing Curve

Post by SNW Vette » Fri Oct 04, 2019 12:55 pm

Hi,
Here is an adjustable PCV valve. It will help you get a reasonable PVC flow for your setup.
Good luck, Steve

M/E Wagner Performance #DF-17, Dual Flow Adjustable PCV Valve

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Re: Timing Curve

Post by Firedome8 » Fri Oct 04, 2019 1:28 pm

BobbyB wrote:
Fri Oct 04, 2019 9:05 am
Firedome8
Yes I have PCV valve with 3/8 hose into back of carb. Seems like a HUGE vacuum leak to me. I am considering choking the PCV hose down some.
HOW THE HECK DO YOU KNOW WHAT PCV VALVE YOU NEED? Thais one is from a 74 Torino 302.
Plugs are NOT CLEAN!
Heat range is as specified by Head manufacturer AFR
Just put in .025 IFR and 6.5 power valve. I will try to test it today if I can.
I believe secondary idle is essentially shut off since no transfer slot is showing.
Maybe a fresh set of plugs , sometimes the recommended heat range is very conservative so you do not burn down the engine.

Geoff2 suggested blocking sec air bleed and ifr , try it .

A good test is worth a thousand opinions.
Smoke Yunic.

GARY C
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Re: Timing Curve

Post by GARY C » Sat Oct 05, 2019 2:50 am

If one reinvents the wheel... Is it still round?

Maybe I am misunderstanding this post but 90 hundred million bazillion (not a real number) people have shown/proven tunes for this type of application and yet everyone wants to start in left field and then try to wonder why they are having issues?

What am I missing?
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!

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Re: Timing Curve

Post by BobbyB » Sat Oct 05, 2019 7:30 am

Lizardracing wrote:
Thu Oct 03, 2019 3:29 pm
4V vacuum secondary carbs don't have four corner idle so the valves should be shut. All idle A/F must go through the primaries. Ideally. Opening the secondary on these carbs is like adding a controlled air leak. A tiny bit prolly won't hurt but thats air not be accounted for and too much of it means you the carb loses control of the idle mixture and the screws aren't very effective.
More base timing typically helps, not makes it worse. Set you timing and leave it until the carb is working good and really close, then if you wanna, try a timing change and play with the carb again. Don't go back and forth or you'll be chasing your tail.
The only QF carb I've had needed some IFR work to be right.
Lizard, did you have to increase or decrease IFR?

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Re: Timing Curve

Post by BobbyB » Sat Oct 05, 2019 7:40 am

MadBill wrote:
Fri Oct 04, 2019 12:58 am
[quote=BobbyB post_id=829723 time=<a href="tel:1570153869">1570153869</a> user_id=20834]...Mad Bill you understand my original question and the basis for it. Am I off base with thinking I might be better off with more open butterflies and more transfer slot?
You may be able to bandaid things by juggling slot exposure but when the calibration is right as above, the mixture will remain steady as the revs are slowly raised.
Here's a snippet of the tuning process from David Vizard's Holley book, but there are at least half a dozen other good ones available and you really should take advantage of one or more of them; it just takes too many words to get into all the details in a forum post. (I started to post the preview but realized it was running into a dozen pages...):
https://www.musclecardiy.com/performanc ... ion-guide/
[/quote]
Thanks Bill, I have the book and have talked to the author a little about IFRs and carb tuning a while ago... I am a pretty slow learner and poor reader... Trying hard to do this right and not destroy my new engine. Nobody answered what IFR to try so I put in .025 in place of .030.
Did not test yesterday but will try to today, though temps are much lower. Might wait til tomorrow. Plenty of other stuff to do.

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Re: Timing Curve

Post by BobbyB » Sat Oct 05, 2019 10:49 am

GARY C wrote:
Sat Oct 05, 2019 2:50 am
If one reinvents the wheel... Is it still round?

Maybe I am misunderstanding this post but 90 hundred million bazillion (not a real number) people have shown/proven tunes for this type of application and yet everyone wants to start in left field and then try to wonder why they are having issues?

What am I missing?
Gary, Are you saying I am starting in left field? If so, how?

GARY C
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Re: Timing Curve

Post by GARY C » Sun Oct 06, 2019 7:53 pm

BobbyB wrote:
Sat Oct 05, 2019 10:49 am
GARY C wrote:
Sat Oct 05, 2019 2:50 am
If one reinvents the wheel... Is it still round?

Maybe I am misunderstanding this post but 90 hundred million bazillion (not a real number) people have shown/proven tunes for this type of application and yet everyone wants to start in left field and then try to wonder why they are having issues?

What am I missing?
Gary, Are you saying I am starting in left field? If so, how?
Just trying to figure out if you are wanting to tune it (power/economy?) or trying to do something that no one else has done or does?
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!

BobbyB
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Re: Timing Curve

Post by BobbyB » Sun Oct 06, 2019 8:41 pm

GARY C wrote:
Thu Oct 03, 2019 4:28 pm
Is 25 total?

I would increase initial timing until I get the highest idle vacuum at desired idle speed and then limit total to 34 and start there.
To do this, I would have to reduce initial timing because idle speed was too high. This was the basis of me starting this thread.

GARY C
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Re: Timing Curve

Post by GARY C » Sun Oct 06, 2019 8:43 pm

BobbyB wrote:
Sun Oct 06, 2019 8:41 pm
GARY C wrote:
Thu Oct 03, 2019 4:28 pm
Is 25 total?

I would increase initial timing until I get the highest idle vacuum at desired idle speed and then limit total to 34 and start there.
To do this, I would have to reduce initial timing because idle speed was too high. This was the basis of me starting this thread.
you can't reduce idle speed at the carb with the idle screw?

I don't use the assumed .020 transfer slot theory, (decades old bandaid for a bad idle circuit and wrong timing curve.) I adjust both the primary and the secondary to use the idle circuit to idle, (you may still start to see the transition slot depending on engine combo) that way I have all of the transfer slot to transfer. If you are idling off of the transfer slot then you idle circuit is not metered to idle for your engine. The carb gas 4 circuits for smooth transition and fuel metering, strangle everyone wants to use the transfer circuit for idle and the intermediate circuit for wide open throttle.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!

BobbyB
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Re: Timing Curve

Post by BobbyB » Sun Oct 06, 2019 9:27 pm

GARY C wrote:
Sun Oct 06, 2019 7:53 pm
BobbyB wrote:
Sat Oct 05, 2019 10:49 am
GARY C wrote:
Sat Oct 05, 2019 2:50 am
If one reinvents the wheel... Is it still round?

Maybe I am misunderstanding this post but 90 hundred million bazillion (not a real number) people have shown/proven tunes for this type of application and yet everyone wants to start in left field and then try to wonder why they are having issues?

What am I missing?
Gary, Are you saying I am starting in left field? If so, how?
Just trying to figure out if you are wanting to tune it (power/economy?) or trying to do something that no one else has done or does?
Trying to get best of both with clean plugs and a long lasting strong engine.

Today I got about an hour to test and make changes.
Quick Fuel 650 Brawler Carb was changed from 5.5 PV to 6.5 PV. IFRs down from .030 to .025.
Opened front (only) mixtures screws to 1/2 turn ( from 3/8 with 030 IRFs) and engine started right up.
While it warmed up, I sprayed carb cleaner looking for a vacuum leak but found none.

After warm up I turned mixture screws in a little at a time but saw almost no change from 12” hg & about 13 AFR. Idle speed was about 950 rpm. Finally with front mixture screws fully closed idle speed dropped to about 900 rpm. Front butterflies were fully closed. Engine was idling at 900 rpm on secondaries only with no rear transfer slot showing.
To verify this, I sprayed carb cleaner in to the primary venturies with no change in idle. Spraying carb cleaner into the secondary venturies stalled the engine. I repeated a few times to be sure.

Based on this, I closed the secondary stop screw another half turn. This brought the idle speed down to 600 rpm in park. I then opened the mixture screws 1/2 turn and opened the idle speed screw to get 850 rpm in park. Adjusting the mixture screws I got 13”hg maximum in park.

Driving the car 20 miles on country roads it ran great. The tiny hesitation from stop signs on flat ground was gone. Afr at idle was about 13 in park, 13.5 in gear at 650 rpm. Cruise afr was 14.5 to 15.5 . Up hill, with PV open, AFR was about 13.

I approached WOT in 2nd enough to open secondaries about 25%. (Based on how much my zip tie slider moved on the secondary rod) the engine pulled well and showed about 12.5 AFR.

Pulled plugs after cool down and they looked a little better, but the 2 rear plugs were a little wet shiny... I think it was fuel based on their smell. (When I pulled plugs a couple days ago, plugs 2 & 6 were wet.)

Overall, I think I am making progress. Car drives fantastic with really nice throttle response. Trying to get it perfect.

Thanks for all your input.

GARY C
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Re: Timing Curve

Post by GARY C » Sun Oct 06, 2019 10:26 pm

A cpl things that have been noted here over the years is that AFR readings and reality are rarely the same thing, I am not sure if you can gain anything from reading plugs with the exception of a wide open throttle cut, people that have taught on this subject will tell you that just driving back to the pits after a track pass destroys anything you can learn from plugs regarding air fuel.

I always wondered if you put an aftermarket AFR system on a modern day production vehicle would it read what one thinks it would?

It sounds like you are going in the right direction, just keep in mind that even the rate at which your secondaries open are going to affect you AFR's, a head wind or tail wind will effect the load your engine has to deal with and will effect your readings and tests, same with temp and humidity, cars in front of your are beside you will effect the load your engine has to deal with and change readings.

You really need a consistent test parameter that you can do over and over the same way every time to evaluate what changes do what, the biggest problem with something that reads real time on the road is that it is impossible to recreate that real time over and over.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!

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