Wideband Demon Tuning / Graph

enkeivette

enkeivette

Well-known member
Joined
Mar 30, 2008
Messages
990
Background:

383ci/ AFR 195cc/ 9:1/ 110LSA/ 239in 245ex. duration/ 576in 594ex. duration. 10lbs of boost (centrifugal). Mech fuel pump, boost referenced. 18 degrees initial, 24 total (Thanks to BigBird) 91 octane.


Here's what I've done so far, jet wise. (Pump cams (green& blue) discharge nozzles (40s w/ hollow screws) 6.5PV (8" @ idle)

80s in the primary, 94s in the secondary. - 11:1 cruise 15:1 WOT

Changed the high speed air bleeds from 39s to 28s. Brought the WOT AFR down to 12:1

Installed 75s in the primary, 88s in the secondary. No change. (Guess the metering blocks didn't flow enough for the 88s/94s.

Installed 67s/80s. Lean spit like crazy. 14.5:1 cruise.

Installed 69s/80s. Lean spit no longer occurs in the lower rpm, but still present at mid rpm. 14:1 cruise.

Adjusted the idle mixture screws. 14.7:1 cruise & idle.

Installed 73s (Don't have 71s)/80s & readjusted idle mixture screws. Car idled at 14.7:1, then I let it sit for 20 mins while I hooked up the rpm wire for the LM2. Turned it back on, idled at 17:1, then 19:1, and up and up till it stalled. :cussing:


23vahqt.jpg


So I readjusted the idle mixture screws and it's sort of stable now at 14.7 again with a cruise in the high 13s and under boost she is in the low 13s. I could leave it as is, but I'd like to lean out the cruise a bit more and get it around 12 under boost. Still haven't gone WOT, don't want to till I get it around 12 under boost.

There is no longer a lean spit btw.

I'm thinking about buying and installing 71s and 84s. What do yall think? (No I will not spend $50 on a jet assortment kit, I'm poor and stubborn.)
 
There are many wiser tuners than me but if you are trying to lean the cruise you need to give us cruise rpm at least. You are only going to hurt parts if you do not get the light throttle fixed with t-slot and idle fuel restrictor/air bleed changes. If you lean the main jet out enough for light cruise it will be too lean to transition / run on main jet before the power valve opens up. Wicked lean spike.
 
You're taking the "shotgun" approach to your tuning: Change a bunch of stuff and see what happens. You need to take a much more methodical and rational approach to your tuning with an understanding of the tuning variables and effects. A few things to keep in mind and to abide by when you tune:

  • Jetting and high speed bleeds affect WOT and high power mixture with little or no effect on cruise mixture. You cannot tune cruise mixture with jetting on a BG or Holley carb.
  • Make any changes in about 10% intervals, otherwise you will likely "overshoot" your tuning. You made a high speed bleed change from 39 to 28 in a single step - that's a 30% change in high speed air bleed diamater, which gave you a 48% change in metering area of the bleeds(!!). I've never seen a carb that was off in its calibration by over 48% as delivered from the manufacturer, so you can see my reasoning that your change is not likely reasonable, and you are compensating for other issues through this radical change. This will trickle down to problems in other areas.
  • Idle mixture screws, IFR sizing, and low speed bleeds affect idle and cruise, independent of jetting.
  • You have to maintain an 8-jet split in sizing between primary and secondary sides at all times in order for the carb to delivery equal air/fuel mixture on both ends of the carb. You had a 14-jet split at one time, which would really screw up mixtures.
  • enkeivette said:
    No I will not spend $50 on a jet assortment kit, I'm poor and stubborn.)
    Click to expand...
    Your chances of hitting the tuning right with whatever parts you have on hand are slim-to-none. If you want to do this right, you need to buy a complete jet assortment in the usable range along with airbleeds in a +/- range on both sides of the high and low speed bleeds.

Here is what I would do:

Concentrate on tuning one paramater at a time. Always tune for WOT mixture first and forget about idle/cruise.

Install the .039 high speed bleeds. Run primary/secondary jetting at 77/85 as a start. Run your float levels in the middle of the sight glasses (not the bottom line). Make a WOT pass and see what the numbers are. If you need to go richer to get a target A/F at WOT in the low 12's, run the pri/sec jetting up evenly, maintaining an 8-jet split between the two up to a maximum size combo of 83/91. If this is still running you lean, drop the jetting back to 77/85 and drop the high speed bleeds from .039 to about .036. This is a 14% change in flow area (not diameter) of the bleed and is all you want to do in a single step. Then, re-perform the testing up to the maximum 83/91 combo. If it still won't hit low 12's, drop the bleeds another 3 sizes and do it all again.

Once you get the WOT where it needs to be, set the idle mixture for best quality idle and see what the cruise mixture ends up being at this point. If you're rich, increase the low speed bleeds from .070 to .074. This will give you a 12% increase in flow diameter of the low speed bleeds and will significantly affect cruise mixture. You have to re-set idle mixture with each low speed bleed change. Re-perform as needed to get cruise in the low-14 range.

Keep in mind, if you have any ethanol additives in the fuel in your area, your mixture must be richened at cruise and idle. Most areas run about 15% ethanol in the gas. With 15% ethanol, you have to run an A/F mixture at idle/cruise of 13.8:1 - you cannot run 14.7.

Lars
 
Last edited:
lars said:
Keep in mind, if you have any ethanol additives in the fuel in your area, your mixture must be richened at cruise and idle. Most areas run about 15% ethanol in the gas. With 15% ethanol, you have to run an A/F mixture at idle/cruise of 13.8:1 - you cannot run 14.7.

Lars
Click to expand...

Glad you tossed that in. I was wondering about that. Our gas is pretty much 10% ethanol everywhere, so I ASSUME about 14:1 would be in there, correct?
 
With 10% ethanol, stoichiometric is 14.2:1. On a performance application, and for best throttle response, you want to stay a few decimal points richer than that, so I'd shoot for high 13's to 14.0.
Lars
 
Thanks Lars. I'll give him the $50.:idea:

1) We really need to set up a "Tuning for beers, West Coast."

2)OR, I neeed to schedule my vacation around yours. We keep taking them the same week.:search:
 
big2bird said:
Thanks Lars. I'll give him the $50.:idea:

1) We really need to set up a "Tuning for beers, West Coast."

2)OR, I neeed to schedule my vacation around yours. We keep taking them the same week.:search:
Click to expand...

OR we could invade Colorado.

Fixed that.

:withstupid:
 
This is a blow-thru supercharger system and not a draw-through, right? You can't use a "GC" carb in a draw-through application without a severe WOT lean condition since the PV won't open.
Lars
 
OK, I'll return the leaner primary jets. Yes this is a centrifugal supercharger.

I ran the .039 high speed bleeds with 80/94 then 80/88 jets. Under boost it spiked over 15:1. If I install the .039s again, with even smaller jets, I'll be back in danger territory, I have no doubt.

I read 11 pages of Motorheads tuning thread on the Innovate forums, he has a very similar long block with almost the same carb. I watched him slowly move up the high speed air bleed size till he landed on .028s, which is why I decided to make the huge leap. My WOT was waaay off (as we all saw from my blown up piston), just as his was, so I didn't feel that incrimental changes were necessary.

My idle is tuned to around 14.7:1 via the idle mixture screws (I try to stay away from ethanol stations). But my cruise AFR drops to about 13.5:1, what should I do to correct this? Will I be able to increase my cruise AFR about a point with the .074s IABs and then readjust the idle mixture screws to get a 14.7 idle AFR again?

Law school is $36K a year for tuition alone, that's why I'm not spending money. Don't have any. When I'm out in a few years yall can give me crap about being cheap.
 
lars said:
. . .

Keep in mind, if you have any ethanol additives in the fuel in your area, your mixture must be richened at cruise and idle. Most areas run about 15% ethanol in the gas. With 15% ethanol, you have to run an A/F mixture at idle/cruise of 13.8:1 - you cannot run 14.7.

Lars
Click to expand...

Carbs are still a bit black magic to me. Where do you plug your laptop in?

In all seriousness, this is great info, I even understand some of it in princple.

enkei and I live in SoCal. It is my understanding CA has seasonal fuel mixes (some kind of CARB/AQMD thing). I don't remember how many or what they are exactly, but it's part of the reason fuel is more expensive out here. Bottom line, it is possible the ratio of alcohol in fuel mixture may actually vary over the year, though I'm not positive.
 
Vettezuki said:
lars said:
. . .

Keep in mind, if you have any ethanol additives in the fuel in your area, your mixture must be richened at cruise and idle. Most areas run about 15% ethanol in the gas. With 15% ethanol, you have to run an A/F mixture at idle/cruise of 13.8:1 - you cannot run 14.7.

Lars
Click to expand...

Carbs are still a bit black magic to me. Where do you plug your laptop in?

In all seriousness, this is great info, I even understand some of it in princple.

enkei and I live in SoCal. It is my understanding CA has seasonal fuel mixes (some kind of CARB/AQMD thing). I don't remember how many or what they are exactly, but it's part of the reason fuel is more expensive out here. Bottom line, it is possible the ratio of alcohol in fuel mixture may actually vary over the year, though I'm not positive.
Click to expand...

The seasonal mix is oxygenation level, if you buy that.
Mobil just went 10% ethanol.:push:
Shell claims nitrogen enriched. (I thought NOX was verbotten).:confused2:
Chevron I THINK does not use etahanol. The Techron is good stuff too.:thumbs:
The rest, I lose track. Too much Wallstreet BS on commercials.
 
big2bird said:
Vettezuki said:
lars said:
. . .

Keep in mind, if you have any ethanol additives in the fuel in your area, your mixture must be richened at cruise and idle. Most areas run about 15% ethanol in the gas. With 15% ethanol, you have to run an A/F mixture at idle/cruise of 13.8:1 - you cannot run 14.7.

Lars
Click to expand...

Carbs are still a bit black magic to me. Where do you plug your laptop in?

In all seriousness, this is great info, I even understand some of it in princple.

enkei and I live in SoCal. It is my understanding CA has seasonal fuel mixes (some kind of CARB/AQMD thing). I don't remember how many or what they are exactly, but it's part of the reason fuel is more expensive out here. Bottom line, it is possible the ratio of alcohol in fuel mixture may actually vary over the year, though I'm not positive.
Click to expand...

The seasonal mix is oxygenation level, if you buy that.
Mobil just went 10% ethanol.:push:
Shell claims nitrogen enriched. (I thought NOX was verbotten).:confused2:
Chevron I THINK does not use etahanol. The Techron is good stuff too.:thumbs:
The rest, I lose track. Too much Wallstreet BS on commercials.
Click to expand...


FWIW, every single tuner I've ever talked to said Chevron is the best gas to use. I think their primary reason though was consistency of octane rating.
 
Vettezuki said:
big2bird said:
Vettezuki said:
lars said:
. . .

Keep in mind, if you have any ethanol additives in the fuel in your area, your mixture must be richened at cruise and idle. Most areas run about 15% ethanol in the gas. With 15% ethanol, you have to run an A/F mixture at idle/cruise of 13.8:1 - you cannot run 14.7.

Lars
Click to expand...

Carbs are still a bit black magic to me. Where do you plug your laptop in?

In all seriousness, this is great info, I even understand some of it in princple.

enkei and I live in SoCal. It is my understanding CA has seasonal fuel mixes (some kind of CARB/AQMD thing). I don't remember how many or what they are exactly, but it's part of the reason fuel is more expensive out here. Bottom line, it is possible the ratio of alcohol in fuel mixture may actually vary over the year, though I'm not positive.
Click to expand...

The seasonal mix is oxygenation level, if you buy that.
Mobil just went 10% ethanol.:push:
Shell claims nitrogen enriched. (I thought NOX was verbotten).:confused2:
Chevron I THINK does not use etahanol. The Techron is good stuff too.:thumbs:
The rest, I lose track. Too much Wallstreet BS on commercials.
Click to expand...


FWIW, every single tuner I've ever talked to said Chevron is the best gas to use. I think their primary reason though was consistency of octane rating.
Click to expand...

I was told the same thing 20 years ago, but the reason given was that Chevron did not use any ethanol nation wide, and that ethanol tore up the seals in fuel injectors. Likewise, ARCO was the worst for deposits and such.
 
enkeivette said:
Law school is $36K a year for tuition alone, that's why I'm not spending money. Don't have any. When I'm out in a few years yall can give me crap about being cheap.
Click to expand...

I am not waiting to give you crap. I will start now.:tomato:
For the paltry sum of $50, your trying to circumvent the tuning process.
Lars has given you the DEFENITIVE process and science on how to do this properly back from square one, the logic behind it, and HOW to do it.:1st:
You asked for help, and we listened. Now you want to justify skipping around the steps.:bonkers:
PLEASE reconsider that what he is saying is the right way, buy the jet kit, and go thru the steps as stated. Otherwise, further guidance is rather pointless, huh?:goodnight:
 
Correction, Motorhead ran .026 HSABs.

And no, air bleeds are a different size. IFRs are even smaller.

Bird, I have:

94s
88s
84s
80s
78s
75s
73s
71s which I'm returning.
69s
67s
65s

Do you really think I need to spend $50 on a jet kit to fill in a few of the odd sizes?

I was asking for advice more so to lean out the cruise. Didn't realize that jets were independent of cruise AFR, now I know and now I can install a jet/ HSAB combo that I know will yield a 12:1 under boost while leaning out my IABs idle mixture screws & IFRs need be.

So I am taking his advice on the cruise tuning. I was trying to tune my cruise AFR via the main jets, so thank you Lars for the heads up.

To explain my shotgun approach to tuning and my funny jet sizing, I was tuning for years without my wideband. So I kept increasing jet size (up to 80s & 94s!!!) because I kept going lean at WOT. I basically maxed out the jet size and I needed to change the HSABs or drill the PVCRs, there was nothing left to do! BG does not know how to setup their carbs. Skim this Innovate thread and see how many people have the same problem, fat at cruise and dangerously lean at WOT.

http://www.innovatemotorsports.com/forums/showthread.php?t=3509
 
Last edited:
Finally, I totally agree that decreasing the size of the HSABs slowly (3 sizes at a time) would be the best thing to do, after maxing out the jet size.

Oh... I think I see, if I run a slightly smaller HSAB (like a 36) Lars is saying that my jets might bring me down to where I need to be. So I guess if I maxed out the jet size with the .039 HSABs, I might not with .036 HSABs, or .033 HSABs, is that it?

What's the difference? Isn't AFR just AFR

What will go wrong if I have a 12:1 AFR with 28 HSABs & 75/83 jets versus a 12:1 AFR with (ex.) 33 HSABs & 80/88 jets?
 
Last edited:
You must log in or register to reply here.
Top