Re: full ign advance less than 30
[Re: Pacnorthcuda]
#2989395
11/26/21 07:28 PM
11/26/21 07:28 PM
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Joined: Dec 2014
Posts: 5,886 ohio
ruderunner
master
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master
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ohio
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This ^ something doesn't sound right. 30 degrees shouldn't ping under light load.
Angry white pureblood male
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Re: full ign advance less than 30
[Re: dragon slayer]
#2989407
11/26/21 07:46 PM
11/26/21 07:46 PM
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Joined: May 2003
Posts: 6,566 Downtown Roebuck Ont
Twostick
Still wishing...
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Still wishing...
Joined: May 2003
Posts: 6,566
Downtown Roebuck Ont
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Are doing this with vacuum advance off or on? If you have vacuum can on, you adding more advance during your test. Not at WOT. Kevin
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Re: full ign advance less than 30
[Re: Hangtowner]
#2989447
11/26/21 10:04 PM
11/26/21 10:04 PM
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Joined: May 2019
Posts: 6,289 nowhere
Sniper
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nowhere
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What is so magical about the usual 34 degrees? The amount of timing needed is dependent on the combustion chamber efficiency. In order to get the most effect out of the combustion event timing needs to occur at a point where the engine can get the most out of it. In the case of our cars that is about 34 degrees BTDC. The more efficient the chamber design the less timing that is needed. An LS1 takes about 27 degrees total as an example.
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Re: full ign advance less than 30
[Re: Hangtowner]
#2989462
11/26/21 10:36 PM
11/26/21 10:36 PM
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Joined: Aug 2003
Posts: 43,228 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,228
Bend,OR USA
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What spark plug brand and heat range, part number on the plugs? How old is the fuel in the tank?
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: full ign advance less than 30
[Re: Cab_Burge]
#2989512
11/27/21 09:17 AM
11/27/21 09:17 AM
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Joined: Jan 2021
Posts: 993 rust belt
Moparite
super stock
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super stock
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rust belt
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What spark plug brand and heat range Just what i was thinking! Also where is the vac line to the distributor hooked up to? Not familiar with your carb but you want the vac only when you are on the throttle. If you hook it up the other way you will get advance at idle. Pinging is not always from timing, Hot spots(plugs sharp edges) in the combustion chamber can ignite the fuel prematurely causing pinging. With that amount of compression you should run super or something with a higher octane rating.
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Re: full ign advance less than 30
[Re: lewtot184]
#2989524
11/27/21 10:20 AM
11/27/21 10:20 AM
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Joined: Jan 2003
Posts: 4,733 Moved to N.E. Tennessee
GomangoCuda
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Moved to N.E. Tennessee
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i think the real culprit is too much cylinder pressure for the gasoline used. that 268 intake lobe probably closes the intake valve at 60-62 degrees ABDC, combined with 10.25:1 compression, way too soon. i bet if you did a compression check that thing is blowing around 200psi or more; if the engine is healthy. i had a 9.3:1 440 blow 190+ with a comp cams 268 intake lobe and it wasn't a happy combo. closing the intake valve that early may work ok on 8:1 but i believe the sweet spot is around 70ABDC. keep in mind that for every .010" of carbon build up the static compression ratio will raise about 1/2 point with a 440 and .010" isn't a lot. of course other checks like verifying TDC on the dampner should be done too. Agree that may be too much compression for that cam. Also - is there any useful quench? what is your deck height? Head gasket thickness? Which Eddy heads - big chambers or small chambers? Is that 10.25 comp ratio an actual calculation or just what the piston maker calls their piston? It could be even more than you think. What octane gas? What carb and what have you done to it? it could be going lean and causing the ping. 4200# and 3.08 gears is contributing to your problem.
Last edited by GomangoCuda; 11/27/21 10:37 AM.
In theory, there is no difference between theory and practice. In practice, there is.
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Re: full ign advance less than 30
[Re: lewtot184]
#2989599
11/27/21 02:46 PM
11/27/21 02:46 PM
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Joined: Jan 2003
Posts: 1,761 Windsor, ON, Canada
Diplomat360
top fuel
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top fuel
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Posts: 1,761
Windsor, ON, Canada
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i think the real culprit is too much cylinder pressure for the gasoline used. that 268 intake lobe probably closes the intake valve at 60-62 degrees ABDC, combined with 10.25:1 compression, way too soon. i bet if you did a compression check that thing is blowing around 200psi or more.. . Yup, that's what I'm thinking as well. That is a fairly small cam which will build pretty good cylinder pressure given that high of a static CR and the cam IVC event. Check out Wallace Racing DCR Calculator for a better feel how your current 10.25 and the cam IVC pan out. Typically it is said that up to 9.5 DCR is about the max for a 94 octane pump gas. For a comparison, here are the results for my SB 360 build which used a 238/244 @0.050" hudraulic flat tappet cam in a blueprinted 10.5:1 static CR motor:
Static compression ratio of 10.5:1.
Effective stroke is 2.91 inches.
Your dynamic compression ratio is 8.72:1 .
Your dynamic cranking pressure is 182.97 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 8.72 :1.
V/P (Volume to Pressure Index) is 162
The actual cranking compression pressure I was seeing on that engine was 185-195 psi, so I consider the above DCR numbers to be pretty close. That combination ran on 91 octane pump gas, very fast ignition advance (mechanical), 21 initial that topped out at 35 deg. Factory iron heads, chambers polished, using NGK BKR6E-11 spark plug, V-Grove (#2756).
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Re: full ign advance less than 30
[Re: Hangtowner]
#2989615
11/27/21 03:35 PM
11/27/21 03:35 PM
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Joined: Jan 2006
Posts: 8,162 USA
360view
Moparts resident spammer
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Moparts resident spammer
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Posts: 8,162
USA
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fresh 440, 10:25 compression with Ebrock performer aluminium heads. Lunati 268/274 cam. 4200 pounds and 3:08 gears. With the standard Mopar distributor with big and little springs, it pinged at full throttle at 4000 rpm which is 30 degrees(about 5 degrees initial). I put the FBO plate in it, changed springs for full advance at 3400 rpm. With the plate set for 16 degrees crankshaft and 15 initial, now it pings at 3000 rpm. I can now keep backing off to find out where it doesn't ping and that will probably be well below 30. Did we just build this engine with too much compression even for aluminum heads? What is so magical about the usual 34 degrees? What is the fuel being used? Octane, Anti-Knock Index, etc A 1995 Magnum V8 with SMPFI will ping on at least one cylinder with scantool measured 28 degrees of total advance at full throttle and 4000 rpm at 90 degrees F at 480 feet above sea level elevation with ‘Regular” Sunoco gasoline (87 AKI on the gas station pump) but actually about 85 AKI when tested. With 93 AKI Sunoco in the same conditions it will not ping. The high swirl, heart shaped Magnum V8 combustion chamber with quench clearance of about 0.087 and 62% quench area is more Octane tolerant than the older wedge 440 chamber. Knocking on a 440 V8 30 degrees of total advance at 4000 rpm wide open throttle 92 AKI gasoline - maybe 180 degrees of coolant temperature? would depend on intake air temperature .... near certain to knock at 90 degrees F/ 70 degrees F Dew Point .... unlikely to knock at 32 degrees F/ 30 degrees F Dew Point The Performance Trends Engine Analyzer 3 computer program can make an educated guess at this, taking into account Dynamic Compression Ratio, Volumetric Efficiency, and exhaust pipe back pressure.
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Re: full ign advance less than 30
[Re: Hangtowner]
#2989689
11/27/21 08:32 PM
11/27/21 08:32 PM
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Joined: Jun 2003
Posts: 72
Hangtowner
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I made a mistake on the cam. It is a Lunati 262/268 so milder than what I first posted. Worse situation for 10.25:1 with 91 octane, I suppose I forgot to mention that I am at sea level also.
Last edited by Hangtowner; 11/27/21 08:34 PM.
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Re: full ign advance less than 30
[Re: Hangtowner]
#2989693
11/27/21 08:48 PM
11/27/21 08:48 PM
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Joined: Nov 2007
Posts: 21,831 Kirkland, Washington
Pacnorthcuda
Too Many Posts
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Too Many Posts
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Posts: 21,831
Kirkland, Washington
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I made a mistake on the cam. It is a Lunati 262/268 so milder than what I first posted. Worse situation for 10.25:1 with 91 octane, I suppose I forgot to mention that I am at sea level also. And your advancing the cam 2 degrees works against you too…..the problem is you have an early intake valve closing event….the cylinder is sealing early and you are building compression…big time. I run about 200psi with 10.2 and stealth heads, Lunati cam (the one with .493/.513 lift) and I get away with it at about 34 degreees mechanical (also have vacuum) but I do have quench.
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Re: full ign advance less than 30
[Re: Pacnorthcuda]
#2989780
11/28/21 10:04 AM
11/28/21 10:04 AM
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Joined: Jun 2008
Posts: 3,916 usa
lewtot184
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learn how to do the math on a lobe profile and try to find something that closes the intake valve 70-72 degrees ABDC. to keep duration down you'll need something with a 112-114LSA. the summit 6401 might work. it's actually 280/290 seat timing on a 114LSA; closes the intake valve at 72 degrees ABDC. may not be a 100% cure but much better than what you have. it's difficult to find anything that doesn't have a 108-110LSA anymore. with a heavy car/tall gear valve and ignition timing will be the key.
as i think more about this a stock magnum cam would be better than the lunati. they have a 115LSA and close the intake valve in the mid 70's range ABDC. they are not 268/284 as the factory claims. they have a long closing ramp that the factory doesn't claim all of. true seat timing is close to 276/292.
Last edited by lewtot184; 11/28/21 10:37 AM.
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Re: full ign advance less than 30
[Re: Hangtowner]
#2989875
11/28/21 03:37 PM
11/28/21 03:37 PM
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Joined: Aug 2011
Posts: 2,864 Pattison Texas
CSK
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I made a mistake on the cam. It is a Lunati 262/268 so milder than what I first posted. Worse situation for 10.25:1 with 91 octane, I suppose I forgot to mention that I am at sea level also. If its lean AFR it can make it ping & rattle fix that 1st
Last edited by csk; 11/29/21 09:27 AM.
1968 Charger COLD A/C Hilborn EFI 512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim 2020 T/A 392 Stock 11.79 @ 114.5
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