Fuel consumption...no not a tree hugger, just FMI

[Wietse]

From what i understand from the article mentioned in here is that for power you want to have a 12.8-13.2 figure.
Yesterday i also set the idle mixture screws again and got it at 14.2, which is close enough i guess, idles very nice now..just ticking over.
I am quite sure my idle screws are 1 turn open, most likely even less then that.
When monitoring the AFR readings, specially after changes made it becomes obvious that once you got the cruising figures better, you have to be careful you don't lean it out at heavy throttle.
It really is a matter of balance and an AFR meter is priceless imo if you want to play around with fuel settings.
For any readers interested, spend the money and install one. When i started i knew absolutely nothing about carbs and fuel settings/adjustments and i think it is really worth to be able to learn all this and tune your car yourself. (also FBBO member helping out and created my learning curve)

Regarding your hesitation and sky high lean figure might be sorted by adjusting the pump shot.
I got my pump arms set that once you just operate the linkage it sprays fuel, a little late and it stumbles.
As per manual you should have a certain clearance, but it is easy enough to adjust this by visual only.
Down the line, these engines are better off running on the rich side, as you mentioned that once getting too lean that mighty V8 power gets kinda lost.

I am still doubting a bit on my timing, i've been running it at 18* initial for some time and went to 20* now.
When adjusting to me it felt it wants more initial, just by listening how it run and left it where i felt it runs very strong and checked the timing with the light it was at 24* but to me this is a bit high.
Mechanical advance is 18* and all in at 2500 rpm, so i woud end up at 42* total which kinda scares me. (no vacuum advance installed)
Then again, i am running 98 octane pump gas which should allow me to go quite sharp in adjustments without causing ping issues.

 

[rlem1977]

I installed an AEM gauge several years ago. I chased the magical 14.5 number for quite awhile, thinking that was the right number for clean running and decent performance.
Maybe I am chasing a ghost. I have a 440/493 with 10 to 1 compression, Edelbrock heads and RPM intake, 2" headers, the MP 528 Solid cam with 1.6 rocker arms. The carburetor is a Demon 850 vacuum secondary. I have #83 primary jets and #92 secondaries. I have found that by adjusting my idle mixture screws to 1 turn out or less, it will idle in gear in the 14 to 14.9 range, cruising down the road at 13.5 give or take. It does hesitate off of idle and the gauge shows it goes off of the charts LEAN, 18.0+. Once past that stumble, it runs okay but is a little down on power. If I adjust the idle mixture screws to more than 1 turn out, say 1 1/4, the idle numbers go below 14. I took advice from others that the 14.5 number is the target for idle and cruise but I'm catching on that my car seems to run stronger with a richer mixture.

Not sure the inner workings of the Demon. Been chasing the same thing only with a Holley 4160. Tech support suggest changing the power valve to 4.5 from 6.5, and stiffen secondary spring. Trial and error, though.

 

[Wietse]

6.5 Power valve looks pretty standard on these carbs.
Changed mine to a 5.5 as i only get 9-9.5 vacuum at idle.

As Kern Dog mentioned it is only when he steps on it he gets the lean out and after picks up again.
To me sounds like the pump shot is a little late, had the same little hick up but after setting the pump more tight it has not came back.

 

[Kern Dog]

Not sure the inner workings of the Demon. Been chasing the same thing only with a Holley 4160. Tech support suggest changing the power valve to 4.5 from 6.5, and stiffen secondary spring. Trial and error, though.

The Demon carburetor is essentially the same, mechanically. The higher the power valve, the later the enrichment occurs.

 

[rlem1977]

6.5 Power valve looks pretty standard on these carbs.
Changed mine to a 5.5 as i only get 9-9.5 vacuum at idle.

As Kern Dog mentioned it is only when he steps on it he gets the lean out and after picks up again.
To me sounds like the pump shot is a little late, had the same little hick up but after setting the pump more tight it has not came back.

Yuup, mine only has around 10 vacuum at idle, slight hesitation when romped on from idle, but catches up quick.
So much to tweek between squirters, cam, pump shot.

 

[Wietse]

Unless you are racing it on the track that adjustments are not that critical i guess.
But it does is interesting to get it all set right.
All i really care is to make sure it gets a good mixture and doesn't run lean, with all potential disasters following from that.
Other side is that it runs insanely rich and burning fuel for nothing.

 

[Mebsuta]

Basic, beat up old 383 RR with 3.91 and 4 spd, driven in traffic in the suburbs: about 10 mpg.

 

[Wietse]

I think with a manual 4 speed you will be having a better milage overall, very nice combo though!

 

[Jeff_383]

I think with a manual 4 speed you will be having a better milage overall, very nice combo though!

my worn out, stock 66 383 4speed and 3.23's gets about 15-18 driving all around

 

[Wietse]

The car has been running fine all the time recently and i am quite comfortable with it.
During constant speeds the AFR sits around 11-12 which is quite rich.
After reading up on carbs etc. i learned that actually this Holley 4-bbl double pumper with mech. secondary is actually a carb that performs best for racing purposes, which is not really my intention.
Running a carb with vacuum secondary seems a better choice for my usage of the car for "cruising" with some random hard driving and hard launches.
Also, my ignition does not have a vacuum advance.
I am considering to add the vacuum canister for a start and adjust the timing if needed. (MSD vac. can should add 10 Deg max.)
After i am thinking to change out my carb for a new 4-bbl carb, but this time with vacuum secondary and a electric choke.
What would be a good choice as a replacement?
Currently i have a Holley 750, 4150 model. Not sure about the list number, it used to have a choke horn but that was cut off. (thats where the list number is located)
Guess i could stick with a 750 CCM size, i found the Holley 770 CCM (Ultra) Street Avenger, would this be a suitable carb, or should i step down to a 670 CCM...don't think so though.
Or a Quick fuel Street HR series 780 CCM?

Engine is a 440, Edelbrock performer RPM intake, cam specs unknown but looking at its stubbornness to idle normal and poor manifold vacuum i guess it has a decent duration.

 

[Johnpat]

I run the 770cfm Street Avenger on my 427
Corvette,love it.

 

[Don Frelier]

An AFR of 11-12 at constant cruising speed is WAY TOO RICH!
Shoot for around 13.8-14 for power, I've run as lean as 15 on the highway sounds like a different engine altogether.

 

[Wietse]

An AFR of 11-12 at constant cruising speed is WAY TOO RICH!
Shoot for around 13.8-14 for power, I've run as lean as 15 on the highway sounds like a different engine altogether.

Yep, i already changed the primary jet for a smaller size but when demanding power (on primary only) it leans out (within limits) so i cannot reduce anymore.
For power i was told to stick around 12.8 - 13.2
Therefore i want to improve things during cruising speeds by adding a vacuum advance.
Later on move over to a new carb with vac secondary's.

 

[Don Frelier]

12.8-13.2 is for wide open throttle

 

[moper]

MPH varies by engine, driver, car, and location. A 440 with bolt ons in a B body that's mixed use I'd expect to see at least 15mpg. Most of that will be from proper tuning for all throttle openings which is where great tuners separate from average. Another good percentage of mpg is alignment and tire pressures. Radials should be put within a couple psi of max, and the alignment should be checked.

 

[moper]

Examples: 422" small block making 475hp based on weight and mph, with 2500 convertor and 3.23s, car is 3900lbs with driver, gets 18+ mpg in mixed driving. 496" big block, dyno'd at 480hp at the tires, 2200 converter and 3.23s, 3800lbs with driver, gets 16mpg in mixed driving. My own 440" 6bbl Cuda, 2800 convertor, 3.91s, got 19mpg as a daily driver. Was only on the highway s couple times a week. My 340 4sp Cuda - 3.23s, mild bolt ons, passed emissions, ran in the 13s, and got 18mpg being driven hard (my late teens...).
The reason EFI is gaining popularity is people don't have the knowledge, of care to learn it or keep up on the tuning as weather changes. I don't consider ignorance a problem so not meant to sound derogatory, just stating the truth. If tuning is a problem, by a Sniper or some other self tuner and stick it on the car.

 

[Wietse]

I am not getting 15mpg by far, keeping in mind the 4.10:1 axle ratio that will never happen.
But thing is, my car is more set for racing then street, therefore i want to modify it for street application.
So reinstating the vacuum canister and going for a new carb with vac. secondary i believe is the way to go.
An electric choke is also a must for the ease of starting as now it is a bit of a grumpy monster starting it cold.

Would it be a problem to go from a 750ccm to a 770ccm 4bbl carb?

 

[Wietse]

The reason EFI is gaining popularity is people don't have the knowledge, of care to learn it or keep up on the tuning as weather changes. I don't consider ignorance a problem so not meant to sound derogatory, just stating the truth. If tuning is a problem, by a Sniper or some other self tuner and stick it on the car.

Very true, tuning is very important and that is why i want to learn and be able to do the tuning myself.
Doing the job and learn something to remember, why take the easy route with EFI?
Just by curiosity i wanted to know what MPG others are getting and from that determine if mine is a drinker or not. (if it is i could not care less)
But as i go i realise that my car is not set up for its intentions, so i am just looking for some advice from others.
In the end i am hoping to have a healthy 440 that has the power and in the meantime gets a AFR of 14 - 15 AFR during cruising, thats what i class as a well tuned in engine.

 

[hangn0ut]

You absolutely need vacuum advance for best mileage. Accelerator pump should have zero clearance. Pump shot needs to be instant throttle is touched. That clearance figure is for wot. Amount of travel left before things bottom out. With a power valve main jets used for cruise far. Power valve channel restrictions used for getting wot far. Suggest sa designs book supertuning Holley carbs. Lots of good info. Cheap price. $20. well spent.

 

[Wietse]

Hello gents,

This weekend i was at a racing expo nearby where i live, the shop i bought the car from asked me if i would like to show my car there on his stand...which i really liked! (picture )
Anyway, looking around i found this stand selling carbs, and for the first time got to hold a Holley Sniper EFI unit which impressed me.....
So now slowly changing my mind if i should go EFI and forget about all hassle and have a trouble free setup with an EFI unit.
Now looking at the Holley Sniper EFI 550-511K master kit which comes with everything what is needed.
Just wondering on the fuel supply, can i use the original fuel pick-up tube and the return from the original tank?
Plan is to use the hose included in the kit and run a supply and return from engine to tank.
Rest of the job should be no issues.
Currently the engine is supplied with a 750 double pumper Holley on a Edelbrock performerRPM manifold.
I did read people state this EFI unit does not like dual plane manifolds, while others claim to have no issues at all.
Car remains for cruising and some random street racing, traffic light fun.
Anyone uses this or similar kit with the original fuel tank pick up?