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Old 07-19-2011, 10:46 AM
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Final tuning of my vortec headed 355.

Hey guys.... I was wondering if you can look over my timing curve and tell me what you think... Its a 355 sbc with flat top hyp pistons. Cam is an edlebrock performer rpm... compression is around 10:1 fuel is 89 octane. 3200 stall converter and 3.73 gears. intake is edelbrock rpm with a 650cfm thunder series carb. The initial timing is right around 12* mechanial is 21* and its all in around 3200. There also is a vacuum canister on the dist. its a msd pro billet distributor with a msd 6 box. I don't have the driveshaft yet so cant really test while driving or under load. Thanks for all the help. The plugs are a little on the dark side. The fuel pressure is at 6.5 psi... So after i get it on the road and with the driveshaft i'm gonna run it beat on it some to set the rings and see if the plugs come around. Thanks for your help!

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Old 07-19-2011, 11:34 AM
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There are 7 or 8 different RPM cams, which one do you have? cam specs are a big consideration for timing settings. If you are at 10:1 scr then you should be around 225 @ 50 so 12 seems a bit low on the base timing. Vortecs like about 32-33 total degrees advance without considering vacuum advance so your pretty good on the total, if you raise the base up some you will need to limit the mech advance to keep total under 34.

Whcih MSD dist part #?

I always limit the vacuum advance too, about 12-14 total no more.

The fuel pressure should be limited to 5.5 psi maximum, I run my eddy carb at 5 psi with a regulator no issues at 5 psi.

And yeah the only way to get the tune right is driving it under various load conditions

2 more of my cents
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Old 07-19-2011, 11:41 AM
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Quote:
Originally Posted by Custom10
There are 7 or 8 different RPM cams, which one do you have? cam specs are a big consideration for timing settings. If you are at 10:1 scr then you should be around 225 @ 50 so 12 seems a bit low on the base timing. Vortecs like about 32-33 total degrees advance without considering vacuum advance so your pretty good on the total, if you raise the base up some you will need to limit the mech advance to keep total under 34.

Whcih MSD dist part #?

I always limit the vacuum advance too, about 12-14 total no more.

The fuel pressure should be limited to 5.5 psi maximum, I run my eddy carb at 5 psi with a regulator no issues at 5 psi.

And yeah the only way to get the tune right is driving it under various load conditions

2 more of my cents

Sorry forgot they made the roller versions also.... its the hyd flat tappet.. i think 7102. .448/.510 308 and 318 were some number i remember. Ill make sure i turn down the fuel pressure... might explain the black plugs cause i didn't have that issue last year with the smog heads.
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Old 07-20-2011, 08:13 AM
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use about 25 initial, 34-35 total, and add about 10 more with the vacuum advance.
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Old 07-20-2011, 10:25 AM
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yep need way more base timing, the duration @ 0.050 is 234 in/244 ex on the 7102 and you will need every bit of 10:1 scr, the black plugs may clean up some with a better idle burn at 20+ initial and manifold vacuum advance adding 8-12 at idle, give it a try, don't forget the mech/vac adv limit on the dist. The MSD box may have startup retard feature so you can get it cranked over hot at such a high initial.
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Old 07-20-2011, 10:36 AM
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that makes sense cause when i snap the throttle real quick it seems like it has poor throttle response.... I have the day off so maybe ill pull the distributor apart and change the timing. The box does not have a start retard.
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Old 07-21-2011, 02:05 PM
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The bushing with the least amount of advance that came with the distributor is 18*. Will I need to buy a kit to get less mechanical dance out of it. I heard vortec heads like around 32* total. So with 18* mechanical i am limited to have initial be around 14*?.... looks like I will need to get an advance kit with different bushings........ the msd dist came with six different advance curves. Any idea what's best? I have it set now to be all in around 3200
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Old 07-23-2011, 10:01 PM
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bump.......anyone?
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Old 07-31-2011, 06:29 PM
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well i finally got the driveshaft in and got it going up and down the road today! I had to adjust a couple valves when I got back and top off the transmission fluid. I noticed a large cloud of smoke in the rearview mirror when I would jump on it.... Could this be just becuase the rings havent sat yet? Also I noticed a hesitation could this be my timing issue? or possibly fuel related? the plugs are rather on the rich side but i would rather start out there and lean it out as I go. All input is appreciated thank you!


Also how do you guys like to set your rings.... I have been told to keep it in first and slowly take it up to like 5000-5500 and let off the throttle quick and let it pull on the high and create high vacuum and also to beat on it

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Old 08-01-2011, 06:15 PM
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anyone please? Im having issues keeping it running under load due to the low vacuum and it starts pulling timing out and eventually stalls. Do I just need to adjust the idle to work in gear? I still think I have some timing issues but idk how to fix it??
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Old 08-01-2011, 10:04 PM
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Quote:
Originally Posted by 454C10
use about 25 initial, 34-35 total, and add about 10 more with the vacuum advance.

I hate to quote myself, but this is what you need.
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Old 08-02-2011, 03:57 AM
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Quote:
Originally Posted by 454C10
I hate to quote myself, but this is what you need.
Yeah I get that. But I don't have any bushings for 10*. Ill look into a start retard box if I can afford it this year because there is no way I will be able to start it at 25*. Also I was wondering which adjustable vacuum advance goes to my msd pro billet distributor. Summit has a bunch for different style of advance canisters.
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Old 08-02-2011, 04:48 AM
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I have no idea how a car would start with 25 degrees of initial timing. That would eat a starter right up.

As far as the running of the car. Lean it out in the idle circuit. It will respond better to throttle tip-in. In your case you are running an Edelbrock carb, and they do not have near the features that a Holley-based carb has. I can't help you there. Basically you lean it out in the idle circuit. Then as you step on the gas, you make sure the pump nozzle is discharging adequate fuel. Very easy to check on a Holley. The main jets are what the car is running on at WOT and those can be checked with an afr meter or some track time/reading of the plugs after a pass. You want the car running crisp, not rich. Once you tweak it a bit and get it better, change out the plugs again. Plugs are a disposable tuning aid.
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Old 08-02-2011, 06:26 AM
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Quote:
Originally Posted by zildjian4life218
Yeah I get that. But I don't have any bushings for 10*. Ill look into a start retard box if I can afford it this year because there is no way I will be able to start it at 25*. Also I was wondering which adjustable vacuum advance goes to my msd pro billet distributor. Summit has a bunch for different style of advance canisters.

Looks like the msd distributor can use the standard style vacuum advance canister.

You can modify your current distributor by welding up the advance slot or by drilling and taping in a small screw as a stop. A 6-32 screw should do it. A drill and tap for a 6-32 should be cheap (get a high speed steel set, not high carbon). Do a search how to limit the mechanical advance in a HEI.

Cranking pressure is much lower in your engine due to the big cam. It should turn over with 25 initial. Try it now, just turn the timing up and see if the stumble goes away and if the starter can do it. If you like it, then make the modifications.
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Old 08-02-2011, 06:36 AM
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looks like you vacuum advance is already doing 10 degrees if this is your distributor.

http://static.speedwaymotors.com/pdf/547-8365.pdf

also the most you can reduce the mechanical advance is 18 degrees (according to the manual). so use the most reduction, set the initial timing to 20 to 22 degrees then total would be 38 to 40 degress. And the vacuum advance will add 10 more. Try this set up. If it still stumbles then add more accelerator pump.
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