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347 how much mechanical advance at what rpm
Ford factory 5.0 block stroked to 347 cid
10.5 compression Edle performer rpm heads - port matched to gaskets intake and exhaust cam 236/242 @0.050" .575" lift at valve LSA 110 intake Edle Vic Jr single plane Running premium 93 octane pump gas What would you recommend the total (base + mechanical) advance be and at what rpm would you want it all in buy. I am puzzled that Ford, on the 89-93 Mustang GT 5.0, the WOT timing table is: RPM Deg Adv 1000 - 8 1800 - 18.5 2150 - 21.5 2600 - 22.5 3500 - 22 5000 - 26 Talked to a dyno tuner who said a stock 5.0 typically makes best power on premium gas around 28 deg. I didn't get an rpm. Even that seems low to me. |
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As I have learned, the initial timing / idling depends partialy from the cam.
On my 302/CR 10.5 the comp cam duration is 244/244 @ 0.50. Made first the basic tuning on the holley carb. Important:Transfer slot measure SQUARE. Start the engine and turn the distributer until you arrive to the desired idling RPM. On my case 850/900 rpm. Initial timing shows 20°/21°. From there set the mech advance at 33°/34° be 3000/3500 RPM. Comparing with the timing table from Demom Carburation the initial timing of 20°/21° looks ok. Rico |
Total timing depends on a lot of things, including the compression ratio and chamber design. I've had modern head designs just require 28 degrees and some older stuff do best at 38-40.
The edelbrock head doesn't have the most efficient chamber design, but if it were me trying it, I'd aim for around 34-36 total. You can always pull a spark plug and see where the band is on the ground strap and that will get you close. |
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That is the timing numbers I was thinking, but I'm a concerned about detonation.
My biggest concern is not being able to hear pinging over the side pipes and wind. I was thinking about how to rig a stethoscope to the engine that I could wear and drive. The link to the plug reading is very interesting. I'm trying to think how I could do a long full throttle run and then shut it down and let it cool off to pull the plugs. When I first saw the Ford WOT timing table, I assumed that it was being added to the base timing. 32-36 deg seemed about right. I have been assured by one expert that it is not being added to the base. Its only getting 22-26 deg from 3500-5000 rpm. It does explain why I can roll out of the throttle and at about 3/4 throttle feel a big surge in power. I can roll into the throttle and break the tires loose in 2nd gear, but if I stomp it, it will not. Its because there is a significant drop in timing when it switches to the WOT timing table. The normal timing table is based on load and with the MAF scaled to 19/36 of actual air, it thinks the engine is at a much lower load and pulls in more timing. |
Every engine combo will be a little different.....you just have to try different settings and see what works best for you combo....
My 331 stroker made the most power across the power band at a total timing of 30 degrees on the dyno.........with 22 degrees of advance,I set my initial/idle timing at 8 degrees and had the total timing all in by 2500 rpms.... I'd start at a total of 30 degrees and slowly work my way up,adding 2 degrees of timing at a time and see how things go......... David |
I've never heard of a typical inline valve head and their various chamber designs benifiting from anything less than 34 degrees, regardless of stroke or bore. When a Yates type canted valve C-3 head is being used with thier shallow tight chambers and dished pistons much less timing lead is required they are MUCH more efficient.
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There are lots of inline valve heads that like 28-30 degrees total. Has to do with a modern chamber design.
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Which ones?
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Pretty much any trick flow head, inline or twisted wedge, some AFR, there are others. All your modular ford heads are way down there, your ls heads, etc.
Chamber design is a lot of it, compression ratio is a lot of it. My last sbf with high port TFS heads was at 28, last sbf with track heat TFS was at 30, some of my fe stuff likes 32-34. |
I like to use a speed wrench and spin the distributor around two, sometimes three turns from TDC (depending on conditions and how aggressive I wanted the engine to be) then I would add about 35˚ just for good measure. Seemed to work pretty well most of the time.
Ed |
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As Brent said, a lot of factors go into determining how much total timing any engine will need to make the best power....... David |
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