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Technical discussions specific to 1964-1967, 1968-1970, and 1971-1973 Classic Mustang. Discuss all tech related to in-line six cylinder and V8 powered Vintage Mustangs here.

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Unread 01-20-2011   #1 (permalink)
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Default New 347 Up and Running but question about the Timing?

I finally broke in my new 347 stroker a few weeks ago and it runs and sounds great! I do have a question about the timing. I am using the MSD Pro Billet Distributor, Blaster 2 coil and 6AL box. I want to correctly set the initial timing, total timing and timing curve for this motor.

I have a 300 duration cam shaft with 10.5 to 1 compression so my idle is set at 1100rpm. Because of the light car and a 4 speed toploader, I have the 2 lightest springs in the distributor to obtain total timing by 2500rpm's or so.

I have a slight hesitation when I hit the throttle off idle. I would like to get the timing correct before I begin tuning the carb. I currently have my initial timing set at 16* BTDC and total timing at 37* with a 21* mechanical advance bushing. Should I change the mechanical advance bushing from 21* to 18* giving me timing in the range of 16*/34* or 17*/35*?
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Unread 01-20-2011   #2 (permalink)
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what heads and combustion chambers do you have?
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Unread 01-20-2011   #3 (permalink)
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16 deg is a lot of initial timing, as long as the engine is not pinging you are probably all right, it might cause the engine to be hard to start when it is hot. Dist mech advance is usually in dist degrees and not engine degrees. Watch you temp as increases in timing will cause the engine temp to increase. Hesitations on take off are usually initial ignition timing, accelerator pump setting, float level setting, etc. Good Luck.
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Unread 01-21-2011   #4 (permalink)
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Rarely do SBF like more than 34* total timing. There are more that like less than like more. The only way to know is to tune it on a dyno or accurately time multiple runs at wide open throttle.
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Unread 01-21-2011   #5 (permalink)
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Thanks everyone.

Cindy- I am running ported and polished 190cc Pro Comp Aluminum heads with a 60cc combustion chamber, flat top pistons and zeroed deck height.

Rex- I thought 16* initial timing sounded high as well but I have read that with my cam duration being what it is, a good initial timing is between 16* and 18*. The car starts without any issues at all, although heat is not an issue since it is 40 degrees or so in the garage.

PaulS- I agree that some dyno time would resolve all issues, but unfortunately I am still in the building process of this V8 conversion. I am almost done but still in the process of redoing the rear suspension and building the 9" rear so the car is not drivable yet. From what you said about 34* total timing, I am guessing I need to change my mechanical advance stop bushing from 21* to the 18* bushing. As it stands with a 21* curve, a total timing of 34* would result in a 13* initial timing. That sounds a little low. With an 18* curve, that would allow a total timing of 34* or 35* with an initial timing of 16* or 17*. Does that sound better?

Any 347 owners with input?
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Unread 01-22-2011   #6 (permalink)
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you have a pretty good setup john. this is a case of less = more. run the 18 degree limiter, at 14/32. a small efficient chamber will need less total timing, probably 32 total. i have dart heads on my 408, they have a very good combustion chamber. i bumped mine from 32 to 34 and lost a couple of hundredths. like paul said, with testing/dynoing you will really find out what it wants.
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Unread 01-22-2011   #7 (permalink)
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Hi,
I'm running a re-curved OEM dizzy with Pertronix. I had it setup to be "all-in" by 3100. It has 23 deg built in with a total of 37. I have run as much as 16 initial when dynoed. My CR is 10.6 with no signs of pinging. My rig ((334) was last dynoed at 392 RWHP at 6100, with 400 RWTQ @ 4400. As far as pinging goes, it's going to depend on your dynamic CR (influenced by the cam events). Each engine will be different as to what it's going to like, to run it's best. I will say, have run as much as 40 degrees total, with great response from the engine.
Again, each engine is different as to how it responds.
With that being a new engine, you won't really know what it likes until you get it on the street and or the track and Dyno.
Hope this helps a little.
Happy Motoring!
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Unread 01-24-2011   #8 (permalink)
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Thanks for the responses. I know the best way to tune the car in on a dyno but since I am unable to do so now, I thought I would do my best to get it as close as possible. I will keep working on it.

Thanks again
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Unread 01-24-2011   #9 (permalink)
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The best you can do without the dyno is to set your timing with the engine running at 3500 rpm to 34* BTDC. Be sure to disconnect and plug the vacuum advance hose and then reconnect it after your done.
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Unread 01-25-2011   #10 (permalink)
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Thanks Paul. With the 21* stop bushing in right now, I am at 15/36* with all in by 2500 or so. I will change the bushing to the 18* and try 16/34* to see if I notice a difference.

As for the carb, I am running a Holley Street HP 750 Double Pumper with mechanical secondaries. I checked both floats and they appear to be adjusted correctly with the car as level as I could get it (on jack stands while building the rear and suspension). Next to check would be checking the 4 corner idle mixtures screws with a vacuum gauge, right? I tried to adjust by rpm yesterday and got it close. From the factory, the front 2 screws were out 1 1/8 turns and the rear 2 were out only 3/8 of a turn. Shouldn't they all be equal? All 4 now adjusted out 1/2 turn. That gives me the highest rpm but I still have a slight hesitation.

Any suggestions?
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Hi,

It's quite possible to have different settings on those mix screws. Due, in part, to the characteristics of your intake and engine pulses. So, go by what the vac gauge is telling you. If you are running a dizzy with a vac, then you have approximately 10 deg additional to factor into your timing settings. It will allow you to run a high initial setting then dial-back the mid-range. What rear ratio, are you running?
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Unread 01-25-2011   #12 (permalink)
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Quote:
Originally Posted by kenash View Post
Hi,

It's quite possible to have different settings on those mix screws. Due, in part, to the characteristics of your intake and engine pulses. So, go by what the vac gauge is telling you. If you are running a dizzy with a vac, then you have approximately 10 deg additional to factor into your timing settings. It will allow you to run a high initial setting then dial-back the mid-range. What rear ratio, are you running?
Keeping all the screws out the same amount is best for an even mixture. Since the engine only responds to the average mixture you could run two open 4 turns and the other two open 1/2 turn but if you adjust them out and in the same amount it will be fine.
The vacuum advance has nothing to do with setting the initial or overall timing. It is not used when cylinder pressure is high enough to make a difference (at wide open throttle or when vacuum is below a certain point.
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Unread 01-26-2011   #13 (permalink)
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Thanks, I appreciate the info. Unfortunately, I am a little more confused.

Quote:
Originally Posted by kenash View Post
Hi,

It's quite possible to have different settings on those mix screws. Due, in part, to the characteristics of your intake and engine pulses. So, go by what the vac gauge is telling you. If you are running a dizzy with a vac, then you have approximately 10 deg additional to factor into your timing settings. It will allow you to run a high initial setting then dial-back the mid-range. What rear ratio, are you running?
Kenash -
What exactly is a "dizzy"? I am guessing it is a type of distributor. I am running an MSD Pro Billet Distributor. Additionally, if you adjust all four idle screws out the same amount to obtain the highest vacuum, why would you make any further adjustments to just two of the screws? I am sorry, I am not very familiar with carbs. As for the rear, I am building a 9" with 3.55 gears.

Paul-
Could you explain a little more about the vacuum advance? (ie. what it is and what it does? etc)

Thank you all!
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Unread 01-26-2011   #14 (permalink)
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Quote:
Originally Posted by JPM1221 View Post
Thanks, I appreciate the info. Unfortunately, I am a little more confused.



Kenash -
What exactly is a "dizzy"? I am guessing it is a type of distributor. I am running an MSD Pro Billet Distributor. Additionally, if you adjust all four idle screws out the same amount to obtain the highest vacuum, why would you make any further adjustments to just two of the screws? I am sorry, I am not very familiar with carbs. As for the rear, I am building a 9" with 3.55 gears.

Paul-
Could you explain a little more about the vacuum advance? (ie. what it is and what it does? etc)

Thank you all!
Hi JPM,

"dizzy" is just a slang word for distributor. I find it easier to type. Does your dizzy have a vac canister? There is a lot of technical information available on engine vac, how to read it for tuning and it's affect when used for timing purposes.
Each engine is different. It take es hours of both road and dyno tuning to find the "sweet spot".
My engine is a 333 making 392 RWHP at 6100. (400 RWTQ at 4400). It likes 16 deg initial for a total of 37 by 3100 Rs. My static CR is 10.8. I run full vac with 6 degrees adjusted. I have excellent un-interrupted power in the 35-4400 range.
But, these specs may not work for you. Heads, cam and a stable valve train play major role in getting the most out of your combination.
Happy Motoring!
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Unread 01-26-2011   #15 (permalink)
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JPM,
I don't know off hand if your pro Billet distributor has a vacuum advance or not.
The vacuum advance is a metal housing that has a spring and diaphragm that holds timing in the static position. It uses a hose connected to your carb or intake manifold to advance the timing when vacuum is above a certain level. (when cylinder pressure is lower because of part-throttle conditions). You have to disconnect the hose from the distributor and plug it when you set the timing.

In the picture note the yellow "can" attached to the distributor with the black hose running to it. That is the vacuum advance.
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New 347 Up and Running but question about the Timing?-engineleft01.jpg  
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