Advance curve prestolite Chrysler 318 |
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67 ski nat
Platinum Member Joined: July-19-2018 Location: Santa rosa Status: Offline Points: 1181 |
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Posted: October-23-2019 at 6:07pm |
Had my original prestolite ibm-4109 on Chrysler 318 run on an old school distributor machine (looks like a 60-70’s record player with strobe lights around edges)
Wanted to see what oem distributor in the boat was set at for advanced curve to match with new pertronix springs and compare Boat ran fine so knowing was good base start. 1500-2500 @ 5 degrees 2500-3000 @ 10 degrees 3000 - 3500 @ 14 degrees max Looks like the bronze springs in pertronix d241800 kit is match, the next step up are the silver springs, 10 degrees more at same rpm (too much??) |
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MrMcD
Grand Poobah Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3594 |
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A safe number for a 318 is 35*, for old 318 with Iron heads we are talking about Total Timing.
The amount received once the distributor is fully advanced. The curve you show above is not giving much timing. With a total mechanical of 14* you would need an initial timing setting of 21* to reach the total advance number of 35*. I think that is too much initial advance for good performance. Each engine configuration can vary slightly and if you add a performance cam you will need more base timing. Does your engine have a performance camshaft? With a 318 modern information says you want full timing all in by 3,500 RPM. This means your distributor mechanical advance should be fully advanced by 3,500. In a boat you always want a strong idle, dropping a boat in gear fully loads the engine and we all know an engine that stalls at the boat ramp is no fun and not safe. Most say 10-12* initial works well for a 318 but I dont know this engine so you will need to establish what initial timing works for your engine in your boat for a starting point because a strong idle is so important. You may find 5* BTDC works or you may find 15* BTDC works best, I would try a few settings and see what the boat likes best at idle for initial timing and build from there. Once you think you have a good initial timing setting test it a little because sometimes what works well at idle initially may be hard to start after a shut off. Once you determine a good initial setting do the math and set an advance curve that provides 35* at 3,500. It should stop advancing at that point. The springs you choose will determine at what RPM the advance comes in. I think a steady advance from idle to 3,500 max woud give the best performance. If you bring it in too fast in a boat you will have pinging or detonation issues which rob power. So if you have an initial timing of 10* and max of 35* at 3500 RPM your distributor would need to be limited to giving 25* mechanical advance. 10* initial + 25 Mechanical = 35* total. There may be a Guro out there that can hand you a timing map that gives great performance in these old 318 marine engines but if not you will need to do a little trial and error to get your perfect curve. Vacuum advance is never used in boats, in boats even in cruise mode there is significant load on the engine so vacuum advance would not work and is never added. |
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67 ski nat
Platinum Member Joined: July-19-2018 Location: Santa rosa Status: Offline Points: 1181 |
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Thanks much for great information. I think your correct 14 max is not enough
My manual recommendations 12.5 initial. So that’s only 26 total You and others have convinced me to leave the silver springs in pertronix, they max at 24 degrees at 3500, so 36 total sounds better I will be aware of pinging etc. perhaps I was missing out on performance with old distributor with only 14 degrees This timing stuff is part magic |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10669 |
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You might think this is a silly question, but are those numbers showing "distributor degrees "or "engine/crankshaft degrees" of advance? Typically something like an old Sun distributor machine tells you "distributor degrees" which have to be multiplied by 2 to get "engine/crankshaft degrees" Also, I don't know why you have numbers that appear to ratchet their way up You should be able to plot a curve with advance at every 500 or so rpm easily enough and with weights and springs controlling the advance, the advance at 1500 degrees isn't gonna be the same as at 2500 like you show for example. If you're not sure on distributor vs engine/crankshaft degrees, put the new Pertronix on the machine and plot it's curve and you'll know if you have to double the machine readings I seem to think you have a LA/LM 318 engine and the manual in the reference section gives 2.5 degrees BTDC for an idle setting. The manual for the older Polyhead M318 gives a spec of 12.5 degrees Just checking to see what you're using for a reference So the big question is are you reading"distributor degrees" or "engine/crankshaft degrees" ? |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10669 |
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Just to clarify a little
If you have 2.5 degrees initial at idle (LM 318 spec) and you double your 14 degrees max you'll have a distributor that has 28 degrees of crankshaft/engine advance added to your 2.5 initial for a total advance of 30.5 degrees which is right about where Chrysler probably wanted you to be for low octane regular gas on a heavily loaded engine in a boat. The advance limiting slots in the distributor advance plate usually would limit you to about 28 degrees crankshaft/engine advance on a Prestolite from that time period. Over the years they changed, and the slots were shorter but for you that doesn't matter So ........like I said earlier, verify whether your numbers are distributor or engine/crankshaft degrees. Your 14 at full advance makes me think you're reading distributor degrees on the machine |
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JoeinNY
Grand Poobah Joined: October-19-2005 Location: United States Status: Offline Points: 5693 |
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You lost me here Ken, I have seen the engine and distributor RPM referred to when putting a distributor on a machine and confusing people but engine and distributor DEGREES are only different as they relate to rpm and I don't think he could be getting it wrong to get his 14 to really be 28. On a typical 4 stroke the distributor is only turning half as fast as the engine. So if the timing would be all in at 3500 engine rpm the distributor running at 1750 on a machine should have all the advance. But even if you screw that up and run the distributor at 3500 rpm you will still only have all the advance? |
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67 ski nat
Platinum Member Joined: July-19-2018 Location: Santa rosa Status: Offline Points: 1181 |
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I do understand both your comments. I’m hoping machinists doubled for me since he also gave me 3300 (could it be 6600). He may have doubled one reading but not other I will ask him today and report back also will ask about large gap in rpm 15-2500
Boat did appear to run fine with prestolite and he said it was so tight and balanced it did not need rebuilding not sure which distributor I will use now as backup Mine is first year LA/LM. I have both books and just notice one shows 12.5 vs 2.5 for LM Gonna try 2.5 initial. thanks keno |
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67 ski nat
Platinum Member Joined: July-19-2018 Location: Santa rosa Status: Offline Points: 1181 |
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Ok my machinist says his distributor machine shows both engine and distributor rpm and those low numbers are already doubled .
I will accept his numbers for now But will time initial to 2.5. See if she starts easy smooth With ‘silver’ medium springs that shipped in pertronix (5 to 24 advance mechanical) |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10669 |
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Well, my reply to the above stuff is that distributor advance is half of crankshaft advance measured at the harmonic balancer since the distributor rotates at 1/2 of crankshaft speed. Or in other words you have to double the distributor advance.
I think I'm not the only one that thinks this if you do some reading of the stuff linked below link So if your distributor is turning at 1000 rpm's (meaning the engine is at 2000 rpm's) and the distributor advance is 8 degrees as an example, then the reading at the harmonic balancer which we get with our favorite kind of trusty timing light will be 16 degrees. One way to visualize this is with a distributor with the cap off and a known advance curve Let's say it has 24 degrees of mechanical advance like that new Pertronix Daryn has Make a reference mark where the rotor is pointing at the housing and now turn the advance mechanism to full advance without the shaft moving and make another mark See if you got 24 degrees of movement or 12 degrees of movement You can check how many degrees by measuring the circumference of the housing and measuring the distance between the 2 reference marks and doing a little math. I'm going out to measure one now I'll be back in a while For Daryn, ask your mechanic if his machine reads distributor degrees or engine degrees or both maybe You could also put your new distributor on the machine and see what it tells you. |
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MrMcD
Grand Poobah Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3594 |
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If you time it with a dial back timing light or adjustable timing light you will see exactly what is going on with the engine running. These timing lights really help dial in total timing in your running engine.
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10669 |
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Well, that didn't take long
That's what my wife usually says Measured a new Mallory that.s set for 26 degrees max advance and when I did the measurements from my last post and did the math, the rotor turned right about 13 degrees. I could put up all the numbers if somebody wants but that's all for now |
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JoeinNY
Grand Poobah Joined: October-19-2005 Location: United States Status: Offline Points: 5693 |
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You are blowing my mind Ken - here I was thinking I was pretty good at turning a distributor a few degrees and getting the timing I wanted to workout but really I have only been turning it half as far as I was trying to and getting lucky
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10669 |
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I had my mind blown equally as much the first time this got explained/demonstrated to me Joe
I thought the same about those little nudges or sometimes I made way to big a nudge and did some head scratching. |
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67 ski nat
Platinum Member Joined: July-19-2018 Location: Santa rosa Status: Offline Points: 1181 |
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Echo joe in ny. That explanation of rotor degree measurement s borderline brilliant , actually really help.
Unfortunately I have cheapy light may need upgrade I will say opening the doghouse on the lake and fiddling with distributor and advance really not my favorite I set pertronix in hole immediately after old was.out to avoid confusion so it is set. Hindsight should taken him both to compare. His machine had James Bond type knobs ; 4,6,8 cyl Gm/Chevy/ford/aux Stroke Volts 6/12 Thanks much for all your support. I’m kinda feeling comfortable starting it Saturday |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10669 |
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Last time somebody used the word borderline to describe something I did, it wasn't followed by the word brilliant.
Good luck with the timing, I'd be shooting for 8 to 10 BTDC at idle which with the Pertronix distributor with the stock silver springs and no limiters will give 32 to 34 degrees at3500 rpm. and higher. with a decent curve. Then you could adjust from there if you were feeling adventurous I figure you still have the Pertronix instruction sheet with these numbers, based on previous comments about different spring colors Since you won't exactly have a lot of timing marks on the flywheel you'll probably be needing one of those new "star wars" timing lights just to get it set at 8 to 10 BTDC at idle |
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67 ski nat
Platinum Member Joined: July-19-2018 Location: Santa rosa Status: Offline Points: 1181 |
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Well pertronix has good reputation for this Chrysler marine d2418 I understand they did research too and silver springs good stock advance. The copper and bronze maybe for more racy and a de-tune option. Hopefully in good hands
I like your approach makes sense and professional Yes a fancy light is in order, however book does says 2.5 degrees,(not 12.5 ) You like 8-10. To start still ? If the motor starts and runs great I will ‘edit’ my previous post and delete word borderline |
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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Kinda like this one on ebay. Best money you can spend Innova 3568 New-open Box (see Pictures) INNOVA 3568 Digital Timing Light |
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Keep it as original as YOU want it
1978 Mustang (modified) |
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67 ski nat
Platinum Member Joined: July-19-2018 Location: Santa rosa Status: Offline Points: 1181 |
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Thanks Duane
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10669 |
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Not a whole lot of research Every Pertronix billet distributor is shipped out with the silver springs for 24 degrees mechanical advance at 3500 rpm with a good curve to get there. if you do the 8 to 10 initial and leave the stock springs you'll probably be plenty happy with that setup Those Chrysler numbers of 2.5 and 12.5 would be to go with different curves that have about the same endpoints. Do you know what the initial timing was set at when you got the boat? |
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67 ski nat
Platinum Member Joined: July-19-2018 Location: Santa rosa Status: Offline Points: 1181 |
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Hi power out in north Santa Rosa now. 50 mph winds. Fire close by I’m being evacuated
What’s important is I got off work early Friday. Hooked up fake lake and turned key She fired right up. Let it warm and she sat down at original idle before prestolite extraction. Super happy she runs again Thank you Hindsight: get baseline initial timing with prestolite before removing Have discussions on forum before removing I will get fancy light and see where I’m timed at before real lake test under load |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10669 |
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That's a good idea Glad it fired right up for ya' Maybe I should have used a different choice of words like "started right up" |
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