some input would be great....

I have a Mighty Demon 750 with Annular legs and mechanical secondaries.

At WOT I am running between 14-14.5:1 on my A/F

I have been under the impression that about 12.5-13:1 is optimal for max HP

I called Barry Grant today and the tech stated there that there is no true A/F "perfect" setting to go for... some engines work better at 10:1 and some work better at 16:1.....

Any input on that statement?

The Tech also stated that "Pinging" would not be affected in any way based upon A/F... but I was under the impression that a Richer A/F would deter "Pinging"???

Any input on that statement?

The Tech also stated that WOT tuning for A/F should be judged by the look of the plugs.... Now i know if the plugs are black its way to rich, and if the plugs are melting, its to lean.... but what will i see going from say, 14:1 to 13:1... anything?

Any input on that statement?

Currently my Jet size is 70 up front and 77 in the rear...


any input or comments are welcome... thx,

 

I have run a Mighty Demon with annular boosters on a dyno (420 ci small block) and found the carb to be very lean out of the box - about the same number you are seeing. I jetted the carb up 4 jet sizes front and back (maintaining an 8-jet split pri/sec) to get the A/F into the 12.5 range. This increased power by 22 hp.

Each engine is a little different, and "wants" different setups, but you can't tell that without a dyno. Without a dyno, getting WOT in the 12.5 range is a safe bet for producing good power. I just ran a different small block on the dyno, and it produced better power at 13.2 than it did at 12.5. I've had other engines kick butt when jetted all the way down to 11.5:1. Go figure.

If you're on the ragged edge of detonation with a lean mixture, a richer mixture will lower the combustion temperature slightly and may move you away from detonation.

Lars

 

DO NOT TAKE ADVICE FROM BG TECH. I've never gotten any worthwhile advice from them, ever. It's so bad that if I have carb part ques now I will call Holley Tech.

I've been tuning my Mighty Demon 750 since 2005, I had the same problem. Super lean at WOT. I spent a full year messing with the jetting only to get my car back on the dyno to find that it still had a 15:1 AFR at WOT. Taking advice from MOTORHEAD and what I read on the Innovate forums, I ended up changing my high speed air bleeds. I went all the way down to 28s, motorhead went with I think 26s. My WOT AFR instantly dropped down to about 12.5:1.

If you find that upping the jetting will not cut it, tune with the HSABs. You can read through my tuning thread if you want: http://motorgen.com/forum/showthread.php?t=5985

Scroll down to the first graph and you can see the huge difference.

 

How do your plugs look after a spirited run? You are looking for a light tan. Does it ever lean pop going down the road at highway cruise speed?

I was never able to get my 750 demon to run with that small of jets even up here at 5000 feet. I jetted down to 74/80 for racing at sea level with .100 holes drilled in each pri throttle blade. But then again I never pulled out my stock down leg boosters and installed Anular like you say you have. So we are not comparing the same thing.

Annulars are made for lower rpm good signal and they don't meter well once you get into high rpm with high air speed over the boosts. another thing is annulars disrupt the air flow as much as 25-30 cfm on flow bench testing. For most people they are the booster of choice.

Read up on annular boosters. I did and i decided that the down leg stock booster hand polished like every NASCAR carb was the way to go

http://www.barrygrant.com/demon/defa...e=29&specs=29d

 

That's contrary to what I've heard. Annular carbs make slightly more power in the higher rpm.

 

Thank you... very interesting.... BG said go up 2, you went up 8, ...

Engine: 383 sportsman II/ ported polished & port-matched, RPM roller cam, rr&beehive, RPM intake, 750 mighty annular, long tube, borla, MSD, 10.5:1, 16*initial 36*max,

So, this is making me think go going up 4








Wow... a lot of reading...got through half of it but will finish the rest tonight tomorrow... a lot of reading

how difficult was it to change the air bleeds?

I can see a wide band A/F meter is going to be a must



plugs look very clean.. lightly tan.. Runs great, no popping, just runs great... Just want more, and I understand I may be able to squeeze out some lost hp if I do this right.... my standard RPM is around 3K.... rev to 6500 .....

thx george... I will read this after the gym...

 

just one thing here: *****::toeta p: now im

 

I think I had about 88's in my primary and 96's in my secondary and my Demon carb still went lean at WOT, almost no change from factory jetting A/F wise at WOT except the Vette went a little faster because my wallet was lighter from filling up all the time.

Took me a long long time to figure these things out, I had to drill out my PCVR's, not much only a tiny bit and as stated above I change my HSAB down to 26 from 39, (somebody's got a good memory) and now I run stock jetting 76 / 84 and all is well.

The Barry Grant tech is right about one thing, there is no magic A/F numbers for you motor ( forget about 14.7:1 means nothing ). You have to tune the carb to what your motor likes. Although most Gen 1 small blocks that are warmed over tend to like things on the rich side. Mine cruises just under 14:1 in the high 13's, anything over and I lean surges / misses

 

So, you guys think I should leave the jets alone and change the HSAB.... ok... where is the HSAB... and is it a 817ch to replace?

got to get a wide band...



yea, when i went from the 750 edelbrock to the 750 mighty demon, and lost 2-3mpg... and gained 15tq

 

How do you know where your A/F is if you don't have a wideband ?

Probably one of best things I have ever bought, without it I may have blown up a few motors. Both my Holley and Demon went lean 16:1 or more at WOT.

At cruise and idle everything was fine, so the plugs were the correct color, I wouldn't know it was going that lean if not for the LM-1.

Try jetting up a few sizes first. Playing with air bleeds would come later. They are easy to change if your carb has screw in bleeds

 

Last dyno run before i changed to the beehive springs... trying to make sure everything is in line for another dyno run with the new springs, and i want to get the A/F correct first...

I have no problems changing the jets, done it many times on a holly and this is not much different... but have never changed these HSAB.


lars... is the RMP range i operate in better for the anulers (sp) or not? thx

 

Here is an article of interest.

http://www.chevyhiperformance.com/te...uel_sight.html

 

Air bleeds are easier to change than jets.

This guy is pointing at one with the aerosol straw. There are high speeds and low speed air bleeds on each corner, the high speed bleeds will have a smaller ID.

 

Thx..... I read the article from the link gkull sent me also, and I was able to see them there also.... thank you both!!


so, should i even change the jets? or just go directly to the air bleeds? from what I have read so far changing the jets is a wast of time

the dyno CMS is 1.5 hour drive, so I am trying to figure the best rout, so

but changing air bleeds on the dyno look easy..... would hate to lose a bleed down the hole though!!!1

are these bleeds the same on a holly also? never worked with bleeds before.... got to order some .... what size would you suggest?

paul

 

More reading.

http://www.carcraft.com/techarticles...own/index.html

 

That was very good... I will stick with the annular....

but it seems that they did not have much luck with jet changing either, and it was the air bleeds that they went for also...

What would you suggest for a change in the air bleeds?

Just got off the phone with BG again... ask what would be better to change, the jets or air bleeds.... they insist that 2 sizes up in the jets first, then... a reduction in the bleeds.... ?!??!?!1/

 

Air bleeds work just like fuel jets, but instead of controlling fuel flow they allow more air in. Air bleeds can be adjusted three ways. The low-speed bleed is for idle; the mid bleed is for partial throttle; the high-speed bleed is for WOT. Mostly though, the mid can be adjusted for driveablitly since it pertains to partial throttle situations. Air bleeds change or reform the fuel curve. A large air bleed jet leans out the mixture. Example: If a good fuel curve is present but leans out slightly in the higher rpm, you can change the high-speed air bleed to clean up the fuel curve.Idle mixture adjustments change the air/fuel mixture.

Turning them "out" or "in" will either fatten or lean out the fuel mixture.

Stock Demon air bleeds diameters:

VENTURI SIZE:
1.400

1.425

IDLE AIR BLEEDS:
.070

.070

H.S. AIR BLEEDS:
.039

.039


always jets first.

Quote:
Experimenting with air bleeds is not recommended and should only be attempted by an expert carb tuner. Countless hours of testing have been performed on expensive flow stands to obtain the proper bleed size for a given calibration. It is unlikely that a better air bleed calibration can be obtained, however the 4150 ULTRA HP Series are equipped with removable air bleeds.

Here is some basic knowledge of how air bleeds work.

The main or high-speed air bleeds affect the entire range of the main-metering system. The purpose of the main metering system and main air bleeds is to emulsify the fuel before entering the discharge nozzle to be discharged into the air stream in the venturi. The fuel/air mixture becomes leaner as air bleed size is increased. Decreasing the size of the main air bleeds will decrease pressure across the main jet, which in turn will pull more fuel through the main system creating a richer fuel/air mixture.

The main or high speed air bleeds also act as an anti-siphon or siphon breaker, so fuel does not continue to discharge or dribble into the venturi after airflow is reduced or stopped. At high speeds, the fuel/air mixture must be on the rich side to prevent damage to the engine.

The idle system supplies fuel at idle and low speeds. The idle system requires a richer mixture than at cruise speed. Unless the idle mixture is richer, a slow and irregular combustion will occur, known as a rough idle. Decreasing the idle air bleed size richens the idle mixture by increasing the pressure drop in the system. Increasing idle air bleed size leans the idle mixture by reducing the pressure drop across the idle air bleeds. The same conditions can be created by backing out the idle mixture screws, which will increase the pressure across the idle air bleeds, pushing more fuel from the idle well creating a richer fuel/air ratio. The idle mixture screw is the only adjustment recommended for controlling the idle fuel/air mixture richness or leanness.

 

Air changes: You will be the one to ask after all this knowledge

http://www.carcraft.com/techarticles...eds/index.html

 

No, there's a guy named "Tuner" on the Innovate site forum, forgot more than most know about Holley's or any carb, this guy is an old timer but a fricken genius, go to the site and look him up. If you get a chance to pick his brains about something feel privileged

 

iagree: They have a bunch of knuckleheads there at Barry Grant. if you challenge them they get a bit argumentative.