Is there any harm being done if your getting a lean surge at cruise or is it just annoying? I dropped two jet sizes today because I was running pretty rich in this 90* heat, as the car was last tuned at 65*-70*. Rich condition went away but I am knocking on lean surges door if I go any lower. Also I am considering add in a SuperTrap type of homemade device to the tail pipe tip to knock down the noise some more. With the noise I can't reasonable listen to the radio or answer the phone if a customer is calling. It just not very professional to be screaming in to the phone with a load exhaust in the background. With that being said, if I lower the exhaust noise (restrict) will the engine run richer if nothing else is adjusted? Another words, if I am getting a slite lean surge and I restrict the exhaust a pinch, will the lean surge likely go away?
In conclusion: Is a lean surge harmful at cruise and will adding more exhaust restriction help get rid of it?

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

Your conducting business in your 'cuda? Your my hero!

I would use dynamat or a cheap knock off to deaden the sound. I assume you have your exhaust all the way out the back? Why would you hear a drone in the cabin?

Sorry I can't help with the lean surge.

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Chris'
Autobody
Restoration
Service

Any thoughts on the lean surge?

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

Lean surge is like jerking and jiggling your car back and forward like someone is shoving/pushing on a rope. Goes away if throttle positions changed.

But "regular" shaking, I'm not sure.

Cheers, Wizard

Brennan,

Are your plugs burning white? no color at all?
or is one partially fowled from running rich causing it to fade in and out.
What temp does the engine run at?
What # jets are you using in the 390?

Restricting the exhaust is only going to make it run hotter and make the lean surge worse.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Lean conditions can be hazardous to stroker motors. (High speed detonation.)

Running too lean can actually cost you fuel too. You'll find yourself in the Power Valve more often.

You bumped it two jet sizes; Bump back up one and see how it behaves.

CJ

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Part of Tyrde-Browne Racing

Will lean surge hurt the engine " at cruise and light throttle" = NO.


Drive you crazy driving it, yes, kill fuel mileage, yes.



Can you change the IFR in your carb ? If so go up one or two sizes, if not you can go down on the size of the idle air breed and it will richin your cruize up enough to get you out of the lean surge and still keep the smaller main jets so your not to rich at WOT, and hard pull mid throttle
( enough throttle to open power valve).



Also get you a Magnaflow muffler and your car will be a lot quiter, and even flow more and perform better, than all the other mufflers out. Much better than a flowmaster if thats what your running, and it might even totally kill the drone. Infact if you are running flowmasters its will be a night and day diff on the sound, and performance.


Jess

I am very close to a lean surge now. Under some conditions (slite down hill cruise) there is only the slightest hint of it. (15.1:1) The fuel around here is going to going to "not more than 10% Ethanol" shortly and I am assuming the lean surge will manifest itself for sure then. True?. Also I am already running the Magnaflow muffler. It was my understanding that the SuperTrap muffler tip could be used to adjust the fuel ratio and little, or is that only on 2 stroke engines? My hopes are when the Ethanol is blended I could choke up the exhaust tip a bit and kill some of the noise and cause it to run a little richer. No?

PS water temp -160* stat, gauge reads 170*

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

This won't be helpful, but most cars produced in 73 & 74 had factory lean surge, and terminal hesitation. The damn things were practically undrivable with all the air pump & recirculation plumbing need to meet the emission regs of the day. Cats & computers cured the problem...

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

The problem in the 1974 models was the acc. pump lever being not calibrated correctly and an undersized jet in the Holley 1945... in the 1974 318's with the BBD, and incorrectly set float was problematic since the A-bodies with this option tended to die going around corners or on quick stops...

-D.Idiot

step up one jet size and be a tad rich instead of being a tad lean. You have lots of things to lost if you run your mill lean. Money, time spent dialing it in... how many MPG does 2 jets sizes can cost you? 1? c'mon!

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Well, two jets seems to be a big deal. Drove from Orlando to Palm Coast and got 9.7 MPG. AFR Gauge showed around 11.0:1 most of the time and dipped down into the 9's on the slitest decel and caused the engine to stumble a bit. Changed the jets filled back up and headed home. Got 14.6 MPG and the gauges showed 14.8 most of the time and dipped down to 13.2 a slite decel and then creeped back up to the 14.8. Both directions were with traffic flow anywhere between 75-90mph. (I am a third lane driver)
PS I decended about 90ft in elevation from Orlando to Palm Coast

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

Nice data reporting Cuda. It would be interesting to see if your plugs were colored after that run at 11.0 Supposably the best "power" jetting is around 11.5 to 12.5 for engines with "power adders" i.e NO2, etc, it appears you were a tad under that even. Time for laughing gas?

The theoretical stoichometric ratio for complete burn of gasoline (yada yada yada) is ~ 14.7, so you were well under that until you re-jetted. I understand that best power is around 12.8 to 13.2. I think you are fine at 14.8 if it performs ok.

FYI, I was reading an ancient Chilton's Manual that had a quote about the Chrysler Lean Burn system--they (Chrysler) bragged about the Lean Burn computer leaning out the mixture to around 18:1 A/F ratio. Of course they also bragged about this meaning they needed NO other emissions controls (lik air pumps, cats, etc). Oddly enough my Slant had ALL of that stuff (so it seems that the Lean Burn still left much to be desired)!

I wonder if you should try leaning things out a bit more perhaps. With an A/F gauge installed you can tell right away what the effects are. I take it the performance after leaning the jets was better? The effect on your mileage is pretty profound--and the 90 foot elevation change had nothing to do with it (unless the Slant was happy about the beach).

Anyway, great reporting and data collection. That tweak can save you real dollars at ~$4 a gallon...

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Slanted D150

hmmm

how many emulsion stages has your present primary metering block? usually if that's responsive to that little step down in jetting your fuel bowl level ain't right for your engine. You need either more emulsion stages or a larger air bleed in the high speed air bleed.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

http://tinyurl.com/ynkktz I am using the block on the left.
http://tinyurl.com/23enlg I am using no high speed air bleeds.
Fuel bowl level is set at the bottom of the brass plug window.
If I go any leaner I start getting the lean surge. What are the physics behind the lean surge?
The jet move really surprised me too. What Really surprised me was that it was running a perfect 12.9 full throttle and a 13.5 steady cruise this winter at 65*. Now its 90*+ and it was running pig rich. I know the air is thinner, but dam.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir