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Dual Quad tuning tips?

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F-BIRD'88
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Re: Dual Quad tuning tips?

Post by F-BIRD'88 »

No rule says you cannot hand hone the size if a metering orrifice a bit with a drill bit by hand to tweek the flow a bit.
You don't need to own every drill bit ir every size metering jet. Very small changes can have a BIG effect when tuning wirh a AFR guage...
TheGreatPumpkin
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

F-BIRD'88 wrote: Sun Sep 18, 2022 2:42 am No rule says you cannot hand hone the size if a metering orrifice a bit with a drill bit by hand to tweek the flow a bit.
You don't need to own every drill bit ir every size metering jet. Very small changes can have a BIG effect when tuning wirh a AFR guage...
Yup, that's exactly what I'm gonna be doing. At least I know I'm close. The IABs will probably end up being closer to factory spec. Not trusting the gauge all the time was good advice
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

By the way, I did get a fancy PCV valve, I think it should help given my erratic low speed AFR behavior
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

Update: car is running in a decent range. Idle circuit is rich at cruise under 2000rpm, goes lean before the mains come in, and goes significantly lean (1.1, 1.2 Lambda) on light accel. With slightly harder accel, pump shot covers any lean spot there, so I know I'm close, just needs more signal but less IFR. Secondary seems to be opening fine with no lean spot. WOT is rich (0.8 Lambda). Idles at 800rpm with 18inhg vac (idle still hangs up, I have teflon tape for the advance weights). Very thankful for all the help, will continue to give it what it wants. Seems to like the small jet/small bleed type setup, and idles much better that way. Blade settings are well under 0.020 of slot, but again, it idles and runs way better without a high idle. Here's the current tune and where I might go with the settings. I am trying to keep all the jet and bleed areas proportional to each other like the factory setup, just downsized. I've had good results with that plan so far. Lemme know if anything seems obviously out of whack.

TB P: ~0.016 of slot (go to 0.015)
TB S: minimum without bind
IFR P: 0.0225 (go to 0.021)
IFR S: 0.025 (go to 0.024)
IAB P: 0.070 (go to 0.063)
IAB S: 0.018 (ok)
Jet P: #65 (ok)
Jet S: #70 (go to #68)
PVCR: 0.035 (ok)
MAB P: 0.024 (ok)
MAB S: 0.024 (go to 0.023)
PV: 10.5 (ok)
Nozzle: 0.025 (ok)
Cam: Orange #1 (ok)
Spring: Purple (ok)
Total Timing: 36 (ok)
Bushing: Black (ok)
Springs: Blue/Blue (ok)

In other news, temps are still around 200 max. I put on a rad support spoiler and will be increasing the width and height of it as much as I can, will be putting in a hood seal, and will be boxing in the area between the grille and rad to force air into the rad.

EDIT: I will also be checking the emulsion bleed sizes/quantity/location in the QF metering blocks to see if that's causing any rich conditions, and will be relocating the IFRs to the lower position, after doing quite a bit of reading about why that's a good idea. Looks very simple. Anyone have any tips for that?
F-BIRD'88
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Re: Dual Quad tuning tips?

Post by F-BIRD'88 »

To quicken up main startup lower PV to 6.5" vac rated.
or raise fuel bowl float level or decrease MAB sizes.
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

F-BIRD'88 wrote: Fri Sep 30, 2022 5:25 pm To quicken up main startup lower PV to 6.5" vac rated.
or raise fuel bowl float level or decrease MAB sizes.
i decreased the secondary MABs. if i decrease the primary MABs it richens up at high rpm cruise. I'll check to see what my cruise vac is and think about changing the PV, though i do like how it comes in on the highway for passing and stuff, no downshifting needed
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Re: Dual Quad tuning tips?

Post by F-BIRD'88 »

Primary IAB will be between.062" and .070". you need to finetune that to get balance. This is why I hand hone mine to size VS selecting various off the shelf sizes.
IFR may be a hair too small..
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

F-BIRD'88 wrote: Fri Sep 30, 2022 5:39 pm Primary IAB will be between.062" and .070". you need to finetune that to get balance. This is why I hand hone mine to size VS selecting various off the shelf sizes.
IFR may be a hair too small..
was thinking the same thing re: IFR but I gotta try it now that i'm reducing the IABs a lot. i'll let you know what happens. I did the mods to the metering blocks, the QF blocks had an extra 0.028 emulsion bleed, so I rearranged them to look like the stock blocks. I've heard this will help even out the low speed AFR a lot, we'll see
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

TheGreatPumpkin wrote: Fri Sep 30, 2022 5:43 pm
F-BIRD'88 wrote: Fri Sep 30, 2022 5:39 pm Primary IAB will be between.062" and .070". you need to finetune that to get balance. This is why I hand hone mine to size VS selecting various off the shelf sizes.
IFR may be a hair too small..
was thinking the same thing re: IFR but I gotta try it now that i'm reducing the IABs a lot. i'll let you know what happens. I did the mods to the metering blocks, the QF blocks had an extra 0.028 emulsion bleed, so I rearranged them to look like the stock blocks. I've heard this will help even out the low speed AFR a lot, we'll see
Here's the result. Low speed cruise is now rich everywhere, but actually fairly consistent i.e. a flat AFR curve. Tip-in is actually rich now, WOT is lean, I think it also revealed a secondary opening lean spot. Seems much more responsive to the IAB change from 70 to 63 than earlier changes of that magnitude.

Anyway: I definitely need bigger IABs (maybe 68?), go back to #70 main jet in the secondary, secondary IABs up a notch... Trying NOT to mess with the emulsion holes again unless I really have to. I went to a more factory arrangement with two 0.028 holes each side - from top the bottom it's 28/blank/28/blank. That's what the stock blocks were in the Holley 1850 carbs. I will try to give it what it wants!

EDIT: with the IFRs in the low position, idle is more stable. it's just too rich, which mean I should do an IAB increase or throttle blade opening increase, I think
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Re: Dual Quad tuning tips?

Post by F-BIRD'88 »

Why do you now want to jump up to 68 from 63 IAB?
(Its very sensitive to tiny IAB size changes. Hard to define it to a jet size label.)

Just progress up from 63 a bit bigger at a time till its right.. Hand file the 63 IAB with a 1/16" .062" drill bit a hair at a time and try it for effect (air cleaner on)
It does not need to be perfect as long as it stays in an acceptable afr range thru the off idle part throttle progression.
The 2 carbs need not be exactly the same throttle opening nor idle metering.
" WEW"
Thats why the OEM's set them up with progressive throttle linkage on dual plane 2x4 intake manifolds.

Thats why the Edelbrock carbs you can buy specific for their Dual Quad RPM intakes are "Carb#1 and Carb#2 with different part numbers.. 'cause they are not set up the same.
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Re: Dual Quad tuning tips?

Post by TheGreatPumpkin »

F-BIRD'88 wrote: Sat Oct 01, 2022 1:38 am Why do you now want to jump up to 68 from 63 IAB?
(Its very sensitive to tiny IAB size changes. Hard to define it to a jet size label.)

Just progress up from 63 a bit bigger at a time till its right.. Hand file the 63 IAB with a 1/16" .062" drill bit a hair at a time and try it for effect (air cleaner on)
It does not need to be perfect as long as it stays in an acceptable afr range thru the off idle part throttle progression.
The 2 carbs need not be exactly the same throttle opening nor idle metering.
" WEW"
Thats why the OEM's set them up with progressive throttle linkage on dual plane 2x4 intake manifolds.

Thats why the Edelbrock carbs you can buy specific for their Dual Quad RPM intakes are "Carb#1 and Carb#2 with different part numbers.. 'cause they are not set up the same.
Not sure if you caught that but i went from 70 IAB to 63, and at the same time changed the emulsion, which was dumb, too big of a move, so I'm going back to where it's likely much better, nearer to 70
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