Timing Curve

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BobbyB
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Re: Timing Curve

Post by BobbyB »

750 carb drives very good. Secondary butterflies are almost fully closed. Max vacuum in park is 13” hg, 11” hg in gear. Afr about 13 in park, 13.5 in gear. Base timing now 28* total timing 32*.
First drive showed afr about 13 at cruise so dropped main jets from 72 to 70. Jet change dropped afr to about 13.5 at cruise.
Williams suggests increasing IFRs by .002”.
Considering opening secondary butterflies a little first, to see if I can get afr at cruise up to 14 or 14.5. Thoughts?
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Re: Timing Curve

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BobbyB wrote: Sat Oct 12, 2019 5:51 pm 750 carb drives very good. Secondary butterflies are almost fully closed. Max vacuum in park is 13” hg, 11” hg in gear. Afr about 13 in park, 13.5 in gear. Base timing now 28* total timing 32*.
First drive showed afr about 13 at cruise so dropped main jets from 72 to 70. Jet change dropped afr to about 13.5 at cruise.
Williams suggests increasing IFRs by .002”.
Considering opening secondary butterflies a little first, to see if I can get afr at cruise up to 14 or 14.5. Thoughts?
Increasing primary IFR may make the idle and off idle stronger.
I would leave the secondaries alone, especially since you're thinking they might help cruising AFRs.
Set the high speed cruising AFR with the primary main jets.
If you are cruising at very high speeds, 80 mph plus, then with the 3310-1 you could experiment with a light enough spring so the secondaries might crack open. The -1 has secondary power valve so it shouldn't be too rich. But generally leave the secondaries alone for cruising.

IMO. The next thing to check is to go to the drag strip or chassis dyno and see that the AFR stays flat at WOT, full load (upper gears) on the primaries. If not, then trim the primary high speed air bleeds. Then go back and find the jets for best power, then again the jets for lean cruise without surging and if there is a difference, trim the PVCR.
Finally, check the secondaries for best mph at the track or HP curve on a dyno.

Seems like a lot of initial for the duration cam but if that's what you and Baldwin have worked out then that's probably about what it wants.
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Re: Timing Curve

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Mattax wrote: Mon Oct 14, 2019 1:21 pm
BobbyB wrote: Sat Oct 12, 2019 5:51 pm 750 carb drives very good. Secondary butterflies are almost fully closed. Max vacuum in park is 13” hg, 11” hg in gear. Afr about 13 in park, 13.5 in gear. Base timing now 28* total timing 32*.
First drive showed afr about 13 at cruise so dropped main jets from 72 to 70. Jet change dropped afr to about 13.5 at cruise.
Williams suggests increasing IFRs by .002”.
Considering opening secondary butterflies a little first, to see if I can get afr at cruise up to 14 or 14.5. Thoughts?
Increasing primary IFR may make the idle and off idle stronger.
I would leave the secondaries alone, especially since you're thinking they might help cruising AFRs.
Set the high speed cruising AFR with the primary main jets.
If you are cruising at very high speeds, 80 mph plus, then with the 3310-1 you could experiment with a light enough spring so the secondaries might crack open. The -1 has secondary power valve so it shouldn't be too rich. But generally leave the secondaries alone for cruising.

IMO. The next thing to check is to go to the drag strip or chassis dyno and see that the AFR stays flat at WOT, full load (upper gears) on the primaries. If not, then trim the primary high speed air bleeds. Then go back and find the jets for best power, then again the jets for lean cruise without surging and if there is a difference, trim the PVCR.
Finally, check the secondaries for best mph at the track or HP curve on a dyno.

Seems like a lot of initial for the duration cam but if that's what you and Baldwin have worked out then that's probably about what it wants.
Thanks Mattax,

I agree... it seems like too much initial timing to me (but that is why I started the thread & called it "timing curve"). I hope to work on the timing curve to be more like... 20* initial, with 32* total soon.

My current plan is to yank the 750 to increase its primary IFR by .002 (per William). While the 750 is off I will try the 650 Brawler with increased IABs from .070 to .073 & see what it does. All this is based on very limited time to play with the car... & the weather. (Never mind that this is my second favorite hobby... Bowhunting is #1, so, I am on my way to the woods right now!)
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Re: Timing Curve

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Lowered both floats 1/2 turn on 750 carb and tested on 75 degree day. 11” hg max in gear showed 14 afr. Cruise showed 13.5 to 14.5 afr. Car drove great. No WOT.
Pulled 750 carb and put 650 carb on. Only change to 650 carb was .070 IABs out .078 IABs in on primary side.
Adjusted mix & idle screws for 11” hg in gear at 650 rpm. Afr showed 13.7 stopped in gear. Afr was 15 to 17 at cruise. 650 drove good, snappier than 750. Throttle is barely cracked at 55 mph & about 2800 rpm. But, at wot it popped back like it is going too lean. I did not see afr at wot.

I was very surprised that increasing IABs did not require the mixture screws to be opened much more. They were still out only about a half turn to get highest idle vacuum in gear.

Plan to change IAB in 650 carb from .078 to .073. Plan to increase main jets in 650 from .066s to .067s & retest.
William fixed me up with a metering block for the 750 carb that has .031 pressed in IFRs. Current stock IFRs are .033. I plan to drop main jets in 750 carb from .070 to .068.
William wants to see me try a base plate on the 650 that has smaller transfer slots.
I wish I had a data logger...probably need to get one.
Days are getting too short and cold for hot rod testing...having fun though.
Might try disconnecting PCV...
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Re: Timing Curve

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Tested 750 carb with “different” metering block that has .031 drilled IFRs (down from .033s). Also dropped main jets from .070s to .068s.
Highest idle vacuum is still 13”hg in park at 850 rpm & 11” hg in gear at 650 rpm. Afr in gear idling is about 13.5. Mixture screws are out 1-1/8 turns each.
Car drove good with afr of 14 to 15 at cruise but had a small hesitation at 2000 rpm. Still not as responsive as the 650 quick fuel brawler, though.
WOT in 2nd gear was very good, but I did not see afr at wot.

I plan to check float levels and drive some more, and check spark plugs. I expect to increase main jet from .068 to .069 if I still have any hesitation at 2000 rpm.
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Re: Timing Curve

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Checked front float. Raised it a couple of flats, so that fuel just trickled out with fuel pump on when I shook the car. Drove 15 miles to work (the long way). About 68 degrees today. Car drove very well, seemed a little peppier. 2000 rpm hesitation seems to be gone.
Mixture screws are out 1-1/4 turn which gave 12" hg at 650 rpm in gear, which is the highest I have seen. AFR is about 13 at idle in gear.
Cruise showed AFR of 14 to 16.5.
Noticed it feeling lean on a pretty steep hill at about 2500 rpm in high gear, maybe 25% throttle. No hesitation.. but it seemed like it was very close to it., about 10"hg, AFR showed about 16.5... should I increase main jets from 68 to 69, or go with a higher power valve? Current power valve is 6.5.
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Re: Timing Curve

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Go up one # on the MJ. You might first try another flat or two on the float level.
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Re: Timing Curve

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As the cruise AFR is progressively leaned out, tip-in response often becomes 'stretchy', not an actual stumble or even sag, but less than-expected acceleration. Short of the onset of misfire, the degree of this that you can accept and tune to affects your vehicle's highway fuel economy.
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Re: Timing Curve

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Tuner wrote: Thu Oct 24, 2019 3:44 pm Go up one # on the MJ. You might first try another flat or two on the float level.
Thanks Tuner, Will try another flat on the float and see what happens.

How do you choose power valve #s?
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Re: Timing Curve

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BobbyB wrote: Thu Oct 24, 2019 3:42 pm..
Noticed it feeling lean on a pretty steep hill at about 2500 rpm in high gear, maybe 25% throttle. No hesitation.. but it seemed like it was very close to it., about 10"hg, AFR showed about 16.5... should I increase main jets from 68 to 69, or go with a higher power valve? Current power valve is 6.5.
Do you mean when tipping in from 10"Hg. or to 10"? If the former, a higher number PV should help.
Felix, qui potuit rerum cognscere causas.

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Re: Timing Curve

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MadBill wrote: Thu Oct 24, 2019 6:57 pm
BobbyB wrote: Thu Oct 24, 2019 3:42 pm..
Noticed it feeling lean on a pretty steep hill at about 2500 rpm in high gear, maybe 25% throttle. No hesitation.. but it seemed like it was very close to it., about 10"hg, AFR showed about 16.5... should I increase main jets from 68 to 69, or go with a higher power valve? Current power valve is 6.5.
Do you mean when tipping in from 10"Hg. or to 10"? If the former, a higher number PV should help.
I agree with MB. Try a get a couple of numbers lower than cruise vacuum.

I will wait for tuner to give his thoughts.
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Re: Timing Curve

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MadBill wrote: Thu Oct 24, 2019 5:42 pm As the cruise AFR is progressively leaned out, tip-in response often becomes 'stretchy', not an actual stumble or even sag, but less than-expected acceleration. Short of the onset of misfire, the degree of this that you can accept and tune to affects your vehicle's highway fuel economy.
Thanks Mad Bill,

You have described exactly what it is doing.
At 55 mph on flat ground, vacuum is about 16 to 18 in hg. As you approach a significant hill throttle response is excellent and vacuum drops very little. Afr goes from 14.5 ish to 16 ish. As the hill get steeper “stretchy” is the perfect word...the throttle becomes less and less effective as vacuum drops to 10ish in hg. Afr get up to 16.5 or so. More throttle will take care of the hill just fine but there is not a direct relationship of throttle opening to torque.
Once the power valve opens at 6.5 in hg there is more than enough torque.
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Re: Timing Curve

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MadBill wrote: Thu Oct 24, 2019 6:57 pm
BobbyB wrote: Thu Oct 24, 2019 3:42 pm..
Noticed it feeling lean on a pretty steep hill at about 2500 rpm in high gear, maybe 25% throttle. No hesitation.. but it seemed like it was very close to it., about 10"hg, AFR showed about 16.5... should I increase main jets from 68 to 69, or go with a higher power valve? Current power valve is 6.5.
Do you mean when tipping in from 10"Hg. or to 10"? If the former, a higher number PV should help.
Cruise vacuum is 15 to 18 in hg, so as throttles opened vacuum is dropping “to” 10ish in hg.

Thanks
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Re: Timing Curve

Post by BobbyB »

Raised front float 2 flats.
Mixture screws in 1/4 turn to 1 turn out total each.
Car drove great a 68 degrees.
Idle Afr 13.5 in gear at 11in hg 650 rpm.
Cruise 14 to 15 AFR at cruise on small rolling hills. Mostly steady at 14.5 AFR.
Still seeing 16 AFR on bigger hills with vacuum dropping to 10 or 11 in hg, but much stronger and not as “stretchy” as Mad Bill said. Raising front float 2 flats made much more improvement than I expected.
Very strong at WOT in first and second gear. AFR showed 11.5 to 12.5 at WOT up to 6000 rpm. Vacuum fell to almost zero at WOT so, I guess 750 cfm is plenty big for my 347.
Still try going up from 68 to 69 main jet?
Increase power valve from 6.5 to 7.5 or 8.5?
Thanks for all the help.
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Re: Timing Curve

Post by ClassAct »

BobbyB wrote: Sat Oct 26, 2019 9:53 am Raised front float 2 flats.
Mixture screws in 1/4 turn to 1 turn out total each.
Car drove great a 68 degrees.
Idle Afr 13.5 in gear at 11in hg 650 rpm.
Cruise 14 to 15 AFR at cruise on small rolling hills. Mostly steady at 14.5 AFR.
Still seeing 16 AFR on bigger hills with vacuum dropping to 10 or 11 in hg, but much stronger and not as “stretchy” as Mad Bill said. Raising front float 2 flats made much more improvement than I expected.
Very strong at WOT in first and second gear. AFR showed 11.5 to 12.5 at WOT up to 6000 rpm. Vacuum fell to almost zero at WOT so, I guess 750 cfm is plenty big for my 347.
Still try going up from 68 to 69 main jet?
Increase power valve from 6.5 to 7.5 or 8.5?
Thanks for all the help.

Power valve opening depends on cruise vacuum. IIRC, somewhere you posted you had 15-16 inches of cruise vacuum. If that's the case, you need a 10.5 power valve.
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