I have the Street Advanger 4 barrel installed, not vac. advance hooked up right now. City is 9mpg and highway is 12.2mpg. The wide band at idle is a bit rich at 12.5:1. Off idle around town is about 14:1 and highway cruising is more like 14.8:1. These numbers are consitant untill the motor really gets heat soaked (40min plus driving,190* is as hot as it gets.) then the numbers move down a bit, about a full point. Idle 12:1 around town 13:1 and highway cruising 13.8:1. The motor runs with no pinging (none I can hear) at 12* and 25*total (no vac hooked) until its heat soaked and then it will ping at these settings under heavy load. Heavy load is just before the vac secondaries kick in and secondaries in. Wide band reading with 4 barrels open is 13:1.
I understand I can gain some mileage with the vac canister hooked up, but how much is expected? How lean can I go on the primaries. Of course I'll richen the secondaries to compensate for the leaning primaries. Does the idle circuit really play much role in terms of mileage?

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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

About 16:1 for economy cruise.

13:1 at WOT sounds good.

The vacuum advance will help considerablly.

How much time is spent at idle? With stop and go traffic it will have an effect, otherwise not much

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

you built that motor with mileage being one of your goals???

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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.

Install a 170 with a small 1bbl and a carefully-curved distributor.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Are the secondaries on the carb vacuum or mechanical link operated?

Sam

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Lean out yopur cruise and hook up the vacuum advance...and start tuning again.

With my last build I wasn t even close till I got the advance curves straightened out. There are huge mileage gains to be had.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

I concour.

what rear end ratio do you have?

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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.

dumb me! 3.55...

may be a tad high?

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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.

On some 4 barrel carbs there is linkage that locks out the secondaries while the choke is on. You can run a cable to this and lock it out on purpose if you are inventive, and can fabricate such things. Years ago I had a '57 Pontiac with two four barrels on it, that I had done just that with. They were both Carter AFB's. With the secondaries engaged it got about 6 MPG, but with the secondaries locked out, it got about 13-14 MPG. The thing is,with a big cam, to get the engine into the upper RPM's where it is more efficient, you are likely engaging the secondries, and thus using lots more gas.

I don't know the specifics of your carb. Maybe it cannot be done, but it worth looking at. If you can arrange this with your 4 barrel, then you would want to use it for economy only, and cruise. We called the choke cable for this lockout the "fast button". When you pushed it under power, it literally felt like you had been hit in the rear by a truck.

Sam

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My uses/needs of the vehical have changed a bit. I sold my pickup and now only have the work van and 'cuda.

Vac secondaries Sam.

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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

Well, good for the cuda, I'm sure this means not only she'll get to be loved, but you ended up cozy with your car and your new motor.

cruise speed numbers for those MPG readings?
manifold vacuum readings cold/hot for the "bad MPG" area?
power valves are?

you might need to get into carbs now. I'd lean out the primary AND the secondary, but by different means. I'd jet down the primaries, use a different power valve, maybe staged, and will drill the metering blocks so I'd have more emulsion stages, plus maybe drilling the idle and fast air bleeds in order to tailor my carb to my special needs engine. As fas as secondaries are concerned, I'd just add emulsion stages and keep the jetting as is. You might also need an adjustable power circuit restriction.

how's idling, burns eyes?

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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.

Vac advance is CRUCIAL for good mileage, as is the overall mech advance curve. You can gain 15-50% with timing changes. There is no reason you can't get 20MPG hwy with that motor and car.

Lou

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Home of Slant6-powered fun machines since 1988

I found a vacuum advance stamped 11R that I am using which gives me 13 degrees vacuum advance at 2500 rpm. Problem is, I can't find another one.
It picked up the mileage over 4 miles per gallon.

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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

Coast a lot.