351 Windsor Ignition Timing

[MACH1MUSTANG]

Need some guidance. I have a 69 Mach 1 with a 351W and I'm trying to dial in the ignition timing and fuel mixture. The motor is built up pretty strong with a solid cam and lifters, file fit 11:1 compression pistons, bored .030 over, balanced and a 3 angle valve job. It also has an Edelbrock Performer intake and a 750 cfm Holley with vac. secondaries. This engine really likes octane and timing. I have to run a mixture of 110 octane race gas and premium pump fuel, the intital timing is set at 6 degrees and when I hook the vac advance line back up it goes up to about 26. When I rev it up it appears to go as high as 55 but it runs awesome, great power and throttle response. I thought anything over mid 40's BTDC is dangerous but I was wondering with the set up and fuel I have am I OK? I have also been told while on the dyno is is running rich. Carb has a fresh rebuild and was jetted down a few sizes. Would the race gas effect the dyno fuel air reading? The mixture screws on the carb are only open about a quarter to a half turn, is that normal? Like I said it runs awesome but I just want to be sure I'm not going to damage anything.

Thanks,
Jim

 

[86bluecobra]

What dizzy do you have? Personally i do not think you need the vacuum advance canister. I have my 351w set up to 18 degrees initial and my MSD dizzy has 20 degree advance mechanical in it. So i run 38 degrees. I am thinking of getting there other bushing i believe it is for 25 degrees mechanical timing and then i can bump my initial down so it fires better in the cold.

 

[MACH1MUSTANG]

I just have the stock dizzy but I replaced the points with a pertronix set up. I have 26 degrees mechanical and I have tried it with no vac adv set at 12 initial for a total of 38 but it seems to run a lot better with the adv hooked up. How am I getting more total adv with the vac adv hooked up? I thought total adv was inital plus mechanical? With vac avd hooked up I set timing at 6 inital, getting 26 on vac adv and I'm getting over 50 total.

 

[D.Hearne]

It shouldn't advance at all when you connect the vac hose. This needs to be connected to the port on the pass side of the main metering block.(ported vacuum) It should be able to run on 93 octane premuim with 11 to 1 compression. Set the initial at 12 degrees and see what the total is with the vacuum advance hooked to ported vacuum.

 

[fast4cheap]

unhook the vacum port, you dont need it especially on hipo builds, it was designed for economy driveabily issues in high gear. you will see better performance with out it, 36-38 degrees total timing by 3000 RPM, you can modify the stock distributor by taking the plate the ignitor attaches to off and changing the advance springs, you can pick up these springs from a parts store usually they are mr gasket brand. they are for chevrolets but dont worry all you need are the springs from the kit.

 

[rbohm]

the reason you have alot of advance when you hook the vacuum line up is because you are hooking up to a constant vacuum source. there should be a port on the carb that has a timed vacuum vacuum source, meaning you only have vacuum at that point when the throttle is opened up a bit(aka part throttle). vacum advance is needed on the street when you want performance and fuel economy. leave it hooked up for the street.

 

[fast4cheap]

If you have changed the cam to a larger unit you have altered the amount of vaccum and rpm of vaccum delivery, therfore the vaccum advance will not perform as intended, it is not a must for street use and you threw fuel economy out the window already with the mods, for better more reliable performance ditch the unit and use the mechanical advance only. If you havent changed the advance rate then you may not reach full mechanical advance until 4000 rpms or better. I works on a daily driver, I know from experience.

 

[D.Hearne]

Just because it's a high performance build , doesn't mean it can't get good fuel economy too. If it's tuned right, the fuel efficiency should be there too, as long as you keep your foot out of it and the engine's kept in the powerband while cruising. The dual plane intake & vac secondary carb helps there too. I always run the vac advance, even on my 331 sixpack. It would pull down 16 mpg highway without overdrive (3.73 rear with 28" tires) as long as I kept my right foot under control. It's got a 10.4 to 1 comp ratio and a Ford Z303 cam and it would run with 89-93 octane fuel. No reason that 11 to 1 Windsor couldn't do with 93.

 

[fast4cheap]

I run a 12.1 clevland on 93 and i have no problems I think the large cam bleeds off some cylinder pressure and the closed chamber heads dont hurt either, you are right it can be streetable and high performance at the same time, but the vacum advance becomes useless with large solid lifter cams and just hinders the ability to achieve max tune, I also run no vacum advance on my 83 with I drive everyday, with no loss of fuel economy or drivability, By tunning at the track I know what works, Try a custom mechanical advance tune you will like it.