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462hemi
timing issues


O.K. guys. Here's the lowdown. I've been trying to get rid of a part throttle ping for the longest time now and it is driving me nuts. I have a 462 (bored and stroked 392) with 10-1 compression using KB pistons and 6.7 rods. The cam is an Isky grind, 480 lift, 290 duration and 108 LSA installed straight up. I have the Hot Heads 4 barrel intake with a Holley 850 VS carb. I'm using a Mallory Unilite mech only distributor (sb Mopar adapted for the hemi). I have been fighting this part throttle ping ever since the beginning (around 3000 RPM). I have tried several of the Mallory curves thinking its the advance curve, still pings. I've used power valves from 6.5 up to 9.5, still pings. I am currently using a "custom" power valve that I have reworked to open at about 12" vacuum. (My idle in gear vacuum is 14-15"), still pings. The only thing left for me to do is use a long curve that not fully in until well after 3500 rpm. I've brought the curve in early and late but no difference. Would a vacuum advance distributor work better (I'm thinking about the transition from cruise to part throttle). Any ideas?
Bill
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on: Wed 24 of Jul, 2013 [20:07 UTC] reads: 28225

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author message
oldboy
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Re: timing issues
on: Thu 15 of Aug, 2013 [02:17 UTC] score: 0.00
Bill,
Hey thats great news! Im really happy the puzzle has been solved.I am going to do the timing numbers and see if i get the same result. It almost seems too easy, but i will do it.
It sort of goes against everything ive read, but i will be glad to have a fix.And also an inexpensive one at that.
Waiting to reinstall my rear axle, then im on it. Will post then. Thanks again. Im really glad this has worked out.
Russ.

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462hemi
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Re: timing issues
on: Wed 14 of Aug, 2013 [19:33 UTC] score: 0.00
Russ, just got back from visiting my carb guy today so here is the latest. He went for a ride so he could here the ping first hand. When he did he said in his opinion that the ping was caused by the cam creating maximum cylinder pressure at 3000 RPM. He also said that the only way to cure this is to reduce the timing. I asked him if 100 octane fuel would stop the ping. He said it would stop some but not all, the only cure would be to reduce the timing. After he adjusted the carb (I should learn to leave things alone, LOL) he concentrated on the timing. After all is said and done we ended up with 24* total (14* initial and 10* distributor). I originally had 8* and 28*. He said that some early hemi'swill like maximum total advance of 28 - 30 but not all. Mine is a perfect example. Now it purrs like a kitten, idles great, has excellent throttle response, runs cooler and most likely will get better mileage (we'll see about that). In fact I think the Hemi is operating better than it ever has. So if your problem is the same as mine try adding a little to the initial and reducing the total. Keep me posted...
Bill

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462hemi
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Re: timing issues
on: Mon 12 of Aug, 2013 [02:08 UTC] score: 0.00
Billm, here's the stats of my engine,
cyl head vol = 110 cc's (the only variable in the equation, if they were 105cc's the compression would be 10.45 - 1.

piston head vol = 4587.56 cc's
gasket thickness = .038"
gasket bore = 4.030
cyl bore = 4.030
deck clearance = -22
stroke = 4.525"

using KB290 .30 over pistons and a 5/8 stroke. I used the United Engine and Machine calculator. 10-1

Tmorton, that is exactly what my carb guy said, he thought that it could possibly be the cam creating more compression as it reached the 3000 rpm mark.

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billm
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Re: Re: timing issues
on: Tue 13 of Aug, 2013 [00:54 UTC] score: 0.00
Hi Bill,

Thanks for the information. Some of your numbers don't make sense, but from what I can find about the pistons, and using a stock (published) deck height of 10.865, your compression ratio should be about 10.85:1. That's not too bad, but may be too high for the octane used.
The fact the the engine pings at 3,000 RPM make sense because that's where the engine is developing peak cylinder pressure. This is a partially a function of the cam. If you put a stock cam in the engine, it would probably ping like crazy at low RPM. If you put a really wild cam in it, the pinging wouldn't appear until a higher RPM.
I assume you've got a timing tape or degree marks on your harmonic balancer. Beware of timing tapes, since they rarely match the circumference of the balancer. Anyway, you should plot your mechanical advance curve by running the engine (with the vacuum advance disconnected) in increments of approximately 250 rpm from idle to the point where the centrifugal advance is maxed out. The curve should be smooth. If not, something in the distributor is sticking. Aim for a maximum advance (initial plus mechanical) of 28 to 32 degrees at about 2500 RPM. If the engine still pings, you need a higher octane fuel. If your car is street driven, do not leave the vacuum advance disconnected. Vacuum advance has nothing to do with your pinging, and greatly improves engine efficiency under part throttle conditions.
Again, my recommendation is to try a higher octane fuel. I believe your pinging problem will disappear.
Let all of us on the Hot Heads site know your results.
Bill


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tmorton
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Re: timing issues
on: Mon 12 of Aug, 2013 [01:51 UTC] score: 0.00
If you want to verify your compression ratio you can always get a burette and measure the volumes at TDC and BDC thereby ending speculation on that issue.

Another possibility for the pinging may be the result of the cam you are using. Performance cams usually tolerate higher compression ratios because the overlap lowers the actual compression pressure at lower rpms. However your cam may be resulting in higher compression pressure at the 3000 rpm range (that extra air brought in from the higher lift and greater overlap has to be peaking at some point). the point being comparisons with stock hemi engines goes out the window when the cam is changed.

Regardless of the cause, once you verify that the mixture is rich enough (check it with an exhaust gas analyzer) the only cure left is to retard the timing.

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billm
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Re: timing issues
on: Sun 11 of Aug, 2013 [17:52 UTC] score: 0.00
Hi Bill,

I ran some numbers of what your compression ratio should be. Since you mentioned running connecting rods 1/4" shorter than stock, I assume you've got a 1/2" stroker crank. If so, your true compression ratio should be about 11.6.1 To make a 462 Hemi with a 1/2" stroker crank would require a 4.085 bore, which is pretty big. If you've got a 5/8" stroker crank, the bore would be a more reasonable .030 overbore, but the KB pistons probably wouldn't fit without machining their top surface. If that's the case, nobody but your machinist knows your true compression ratio. I think you need to run racing fuel in your engine. No amount of fiddling with the distributor advance or fuel curves is going to solve your pinging problem.

Bill

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billm
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Re: timing issues
on: Sun 11 of Aug, 2013 [15:53 UTC] score: 0.00
Hi Bill,
Here is my two cents.
Do you know for a fact that your compression ratio is 10:1? You mentioned using 10:1 KB pistons, but with your longer stroke your true compression ratio should be much higher than 10:1. Did you do the math to calculate your actual compression ratio? If so, your problem may be a simple lack of octane in the fuel. Have you tried running a 100+ octane racing fuel? I believe if you try a tank of racing fuel your pinging problem will go away. Everything you've written supports this theory. Timing and fuel curve changes can only do so much if the compression ratio is too high for the fuel octane used.
You didn't mention your bore and stroke, but I'll run some calculations to estimate your true compression ratio and post it later.
Bill

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462hemi
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Re: timing issues
on: Sat 10 of Aug, 2013 [17:44 UTC] score: 0.00
Moparruss, I have checked TDC twice using the piston stop method and it is dead on, Ma Mopar would be proud, LOL.
Tim, in regards to your post, I did have this engine build by a professional shop which boiled, magged etc the block and heads. As far as octane rating, I'm using 94 octane. I have experimented with the timing curves, it doesn't seem to make a difference. What I find funny is that no matter who you talk to regarding these early Hemi's they are all in agreement that the timing should be 30*, no more no less and all in by 2500. What did make a difference was reducing the timing down to 26* but it still pinged (only not as much). I know the '58 letter cars had different casting numbers for heads (don't know what the physical differences between heads for a letter car and a New Yorker are) and used a larger cam (435 I, .442 E for 300D, .389 I & E for New Yorker). Timing was 6* BTDC for both however the New Yorker had 20* mech advance at 4800 while the 300D had only 13* at 2100 RPM. Not sure why but the difference between the 2 are marginal IMO. I'm going the check the carb and get that set up first and if I have to run at 26* or 24* total, so be it. Don't know how all these other guys are running 30*+ and get away with it (if they are, that is). Thanks Russ and Rocketman for your input, I will post my results next week sometime.
cheers
Bill

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moparruss
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Re: timing issues
on: Sat 10 of Aug, 2013 [00:04 UTC] score: 0.00
426 Hemi,

I've been following your post for a while now and I just now re-read all of it. Just a suggestion - have you "dead stopped" the engine on #1 cylinder to confirm that the mark on your crank damper is in fact TDC when it lines up with your timing pointer? I have found the marks can be off with aftermarket dampers. If it is off you could really have more advance than you think.

Just a thought,

moparruss

author message
rocketmantim
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Re: timing issues
on: Fri 09 of Aug, 2013 [19:10 UTC] score: 0.00
> O.K. guys. Here's the lowdown. I've been trying to get rid of a part throttle ping for the longest time now and it is driving me nuts. I have a 462 (bored and stroked 392) with 10-1 compression using KB pistons and 6.7 rods. The cam is an Isky grind, 480 lift, 290 duration and 108 LSA installed straight up. I have the Hot Heads 4 barrel intake with a Holley 850 VS carb. I'm using a Mallory Unilite mech only distributor (sb Mopar adapted for the hemi). I have been fighting this part throttle ping ever since the beginning (around 3000 RPM). I have tried several of the Mallory curves thinking its the advance curve, still pings. I've used power valves from 6.5 up to 9.5, still pings. I am currently using a "custom" power valve that I have reworked to open at about 12" vacuum. (My idle in gear vacuum is 14-15"), still pings. The only thing left for me to do is use a long curve that not fully in until well after 3500 rpm. I've brought the curve in early and late but no difference. Would a vacuum advance distributor work better (I'm thinking about the transition from cruise to part throttle). Any ideas?
> Bill

Bill, here is more on your part throttle detonation problem.
Detonation is casued by several things. I will list those things and potential solution based on the information you have provided. I have looked at original centrifugal spark timing curves for 392 hemi engines as they were built in 1957 and 1958. The New Yorker version of the 392 with a single four barrel carb used a different advance curve that the 300C or 300D versions. I'm sure this was done for a good reason but it is unlikely that we will ever know exactly why. At 3000 RPM, timing for a 392 was at 20 to 26 degrees BTDC. That number includes an intital timing of 6 degrees BTDC. Following are the most frequent causes of detonation.
1. Detonation can be caused by too much spark timing; The solution is to reduce spark timing, but know how much you have before making changes.
2. Detonation can be caused by lean mixture; The solution is to richen the mixture, but you must know in advance that fuel pressure and supply are adequate. Use a fuel pressure gauge at the carb inlet (or as near as you can get to the inlet) to determine that you have at least 4 psi at 3000 RPM during your acceleration.
3. Detonation can be caused by inadequate octane quality. You should be using a minimum of 91 octane (pump posting number) or higher if available in your area. If knock still persists, the solution would be to use a mixture of 100 octane unleaded with some of your highest available pump gas. Try a 50/50 blend to start with.
4. Detonation can be caused by high compression ratio. Your engine with 10:1 CR may be marginal on street gasoline. The solution is to reduce the CR, but...........before you tackle that job, visit options 1, 2, and 3 above.

I think that you have a quick advance curve that most of the aftermarket distributor manufacturers use for racing applications. Since yours is not a race car, using a slower curve would be adviseable Your street engine may be happier with a little less timing and the addition of a vacuum advance unit that will help throttle response at part throttle and improve fuel economy.

On old engines like the early hemi, there can be lots of scale and rust deposits in the cylinder head water jacket. These deposits reduce the ability for the cooling system to work properly. Hot spots can develop and detonation becomes an issure. Chemical cleaning with acid reduces this problem. This is a job for a professional shop. This type of cleaning also takes care of the rest of the unwanted deposits like oil and sludge. When rebuilding an engine it is best to have the block cleaned like this also.

I have been around and involved in cars/racing since the late 1940's when I first went to races with my Dad. I am a hands on engineer and worked for a major oil company for 39 years doing fuels and lubricant development. I not blowing any smoke and can back up what I've said with proven theory and real-world testing. Hope the ideas are worthwhile for your application.

Tim













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oldboy
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Re: timing issues
on: Fri 09 of Aug, 2013 [17:48 UTC] score: 0.00
>Bill,
I will cettainly stay tuned.Got my rear axle apart now for service, so wont be back on the pinging issue for a couple weeks.
i wish to have no pinging eventually at all. I expect to hunt between carb adjustment and further experimentation with timing, distributor springs.
ultimately i wish to go with a power adder as i have posted in past months, but not until this issue is resolved.
Wish i knew a racer/ experienced type who could tell me what the engine is saying.
Btw this month hot rod has interesting related article in the back of the mag.

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462hemi
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Re: timing issues
on: Fri 09 of Aug, 2013 [00:18 UTC] score: 0.00
Russ, I spoke with Bubba about the distributor/timing issue. He said to me that when he gets a Mallory distributor he doesn't change springs at all. All he does is bend the spring post of the loose spring so that it isn't loose anymore. That would be the stiff spring that comes in later in the advance curve. Well I put the distributor back to the way it was originally and I did what he told me to do and guess what. IT STILL PINGS. So I went and talked to the carb guy. I am going to take my car over to his shop next week and between him and I (mostly him) we will try to figure this out. The carb guy said that it could be the cam, that when it gets to around the 3000 rpm mark it starts to build up compression pressure which would cause ping. Anyway I will post my findings but it won't be till sometime next week, I'm working nights this weekend. Stay tuned for this continuing saga...

Bill

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oldboy
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Re: timing issues
on: Thu 08 of Aug, 2013 [13:23 UTC] score: 0.00
Bill,
if you would be so kind to post your findings, once completed
I would be greatful. I understand you are running a mallory dist. Im running the msd. Still got light pinging, still going to experiment with advance springs and timing until satisfied. Car runs well otherwise, but like you, the pinging is driving me crazy. Thanks, Russ.

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462hemi
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Re: timing issues
on: Sun 04 of Aug, 2013 [23:57 UTC] score: 0.00
Well I'm going to take George's advice and talk to Bubba. I don't know enough to keep doing this trial and error thing any longer. Since retarding the timing helped greatly I'll concentrate on that. If there's a spring combo that will work, it's probably the one I haven't tried yet, lol. I took the Wiilys to a show and shine today and it worked pretty good, I was surprised. There's an excellent carb guy about 30 minutes away from me. He's next on my list to talk to (after Bubba). I'll keep you posted.

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oldboy
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Re: timing issues
on: Sun 04 of Aug, 2013 [02:50 UTC] score: 0.00
Bill, you are mentioning a fuel problem. I had thought the same way. Changed out a good holley vacuum secondary carb .750 cfm for an Edelbrock vac. Secondary w/ same cfm.small change, maybe only in throttle responce. Pinging was still present. Next i found my fuel pressure was all over the place, switched to a better electric pump, no change. Fuel pressure crazy. Turned out to be a faulty reading with a liquid filled guage. Switched to a "dry " guage, and that solved the wacky readings. Also installed a adjustable regulator with return line tto the tank at this time. Pinging was now slightly less but not gone. I think the remainder lies in the timing- Russ

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462hemi
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Re: timing issues
on: Sat 03 of Aug, 2013 [22:51 UTC] score: 0.00
Here's an update. I put my initial advance at 12* and set the distributor at 14*. This brought my total down to 26*. I left the same curve in the distributor. It seemed to get rid of a lot of the ping however it is not completely gone. When it does ping it is for a very short duration. I still believe it is carb related. I can't see going down on total advance any further. This is were I'm at now, a little better but not there yet.
Bill

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oldboy
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Re: timing issues
on: Sat 03 of Aug, 2013 [03:31 UTC] score: 0.00
Bill, by the way i am currently running without vacuum advance.
Vacuum advance made the problem worse.

author message
George
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Re: Re: timing issues
on: Sat 03 of Aug, 2013 [14:12 UTC] score: 0.00
Contact "Bubba" at 1-888-809-3835, if it's a dizzy problem he can sort out your dizzy. Bubba's Hot Rod Shop.

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462hemi
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Re: timing issues
on: Fri 02 of Aug, 2013 [18:55 UTC] score: 0.00
I keep thinking its fuel related so I took out the power valve and locked it open so it does not close and took it for a drive. The current curve in the distributor is a 2 stage (purple and brown spring) which isn't fully advanced until 3200 or more. The locked open power valve should have solved the problem if it was a fuel issue however the ping is still there although it seemed better (I think). So now my next venture is to play with the advance curve, maybe to have to curve (purple and orange spring) come in at 800 RPM and be fully advanced at around 3500+. (This is a 2 stage curve as well). We can't be the only ones experiencing this, are we? The OEM curve is 6* btdc with 10* centrifugal advance degrees @ 2400 RPM of distributor plus 11* of vacuum advance for a total of 27*. Maybe we should be using the factory curve instead of the hi perf curve.
Bill

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oldboy
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Re: timing issues
on: Fri 02 of Aug, 2013 [18:04 UTC] score: 0.00
Hey, 462hemi., i too have experienced the timing you have described. My 392 is 10::1 with msd distributor. Running premium fuel.
I am currently running 12° initial, with 30° total timing. This is working out best so far.
I am however still getting pinging also. Motor runs well otherwise, but heavy throttle produces a noticable ping. Light gradual throttle and there is no noticable noise.
I am going to continue to experiment with distributor curves, with the various springs and stop to bushings the msd has.
Good luck. If you have found a solution i would like to hear about it.


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