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Old 08-19-2008, 07:03 PM
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Blower Motor - Timing - Spark Plugs: Need Clarification Please

I know this has been asked numerous times, but I just do not seem to get it. So, here it goes again. Sorry...

Again, the engine is a 502 with an 8-71, I am fouling plugs rather quickly. The spark plugs in it now are AC Delco Rapidfire #4's. Carbs are set good. Every where I read, and have been told here, set the initial timing 16 to 18 degrees.

At first, I set the timing to 12, runs great and very strong, but fouled the plugs. Car was not driven much at all, but still the plugs were extremely black.

I changed the plugs out, with the same as above. I went ahead and attempted 16 degrees, but the black smoke and raw fuel was extremely bad. I stopped there.

I have a question about going two steps colder on the spark plugs, I ask and ask, but it does not make sense as to why. How is going with a colder plug going to help this? It would make since going to a hotter plug.

Do you think that a colder plug and keeping the timing at, lets say 12 to 14, would be better? Borti stated he went 1 step hotter, and it would better for the street.

Now, I did call the blower shop - they said two steps colder, went to a race shop where I get my fuel - they said the same, called NGK tech support - they too said colder plugs.

Give me some advice please. It is irritating me...

Thank You,

Jason

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Old 08-20-2008, 07:31 AM
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BUMP

Maybe somebody that knows this stuff will see this today. Need some help guys...

Jason
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Old 08-20-2008, 03:29 PM
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Still no takers???
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Old 08-20-2008, 04:20 PM
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if the carbs were really "set good" you would not be haveing a problem with spark plugs.

What carbs, what cam. details matter.

fouled plugs and black smoke indicate a extremely rich AFR and or a severe ignition issue.
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Old 08-20-2008, 05:55 PM
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Quote:
Originally Posted by F-BIRD'88
if the carbs were really "set good" you would not be haveing a problem with spark plugs.

What carbs, what cam. details matter.

fouled plugs and black smoke indicate a extremely rich AFR and or a severe ignition issue.
Yes, it is very rich. I have determined I need 16 to 18 degrees advance. I backed off the timing some, that is when it got crazy rich. O.k. I will take the advance back up, but my question is, how does a colder plug make things better. In my head, that tells me it would burn less fuel. At least that is what "everyone" is telling me. The only thing I can come up with is, more advance will bring me to a leaner state, and the colder plug keeps things in check (cyl. temps, etc). I am basically just trying to understand it all, before I pull the plugs again.

Gap - I was able to do some research today while "at work" and found that I should keep the gap for a blown engine .030 to .035. I was thinking of opening it up to .050 to .055. From what I understand, that would be incorrect to open the gap up.

I am just trying to figure how this all works out, and of course, in my head it works out backwards.

Thanks F-Bird,

Jason
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Old 08-21-2008, 11:47 AM
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How much total advance do you have??? This is the important thing. I'd guess you should set the timing at around 32-34 total at about 2800 rpm and let the initial fall where is might. If you have low compression I doubt it will kick back even at 14 initial. I like to run a separate ignition switch and get the motor turning before lighting the fire.

Your carbs are very rich. I'd set up the carbs with manifold referenced power valves. Try not to wash the cylinder down too bad or you may scuff a piston or contaminate the oil with gas.

As for plugs my thought is to run about stock possibly one range colder untill you run enough to start showing some real heat on them. If you have room I'd run and extended tip too at least for starters.

With that big motor and light car it's hard to run it long enough and hard enough to create a lot of heat so you are mainly dealing with part throttle.
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Old 08-21-2008, 02:18 PM
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Total is about 32.5 to be exact, yes, one of them fancy little timing lights.

It seemed to do real well with 12 degrees, but noticed that my plugs where extremely black. So, that is what started this thread. I put a new set of plugs in, and was going to adjust the timing. I moved it some, then started loading up - this is where the heavy richness in the original post came from.

What I am really searching for is the whole, "needs to be 16 to 18, plugs two steps colder, etc."

Basically, I ordered some NGK plugs, two heat ranges colder than the AC Delco Rapidfire #4's. I will put them in this weekend, and adjust the time to about 16 degrees and go from there. What should the gap be? Is .035 good?

I am finally going against what my head thinks, and realizing that more advance is leaner, and with colder plugs this helps with cylinder temps and at the same time keeps from detonating - I guess.

Correct me if I am wrong.

Jason
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Old 08-21-2008, 04:51 PM
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If the plugs are fowling I think you want to go hotter not colder

Chet
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Old 08-21-2008, 06:27 PM
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See, that makes sense to me as well, but as the experts put it, that is wrong.

Again, the only thing that makes any sense to a colder plug, is for more advancement. I am trying to figure this out before this weekend. I do not want to be chasing my tail back and forth.

Jason
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Old 08-21-2008, 06:56 PM
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First thing get these mis concepted tuning rules out of your head.
More advance does not "make things leaner" More spark timing advance starts the fuel burn sooner.
"Hotter plugs" retain more combustion heat and tend to burn off combustion deposits (run cleaner) But tend to cause detonation and preignition at WOT.
Cooler heat range plugs resist over heating the tip, protecting against detonation and priignition (burn't pistons) at WOT.
The (proper) heat range of a spark plug is a complex subject depending on how you use the motor etc etc.

To fire up your blower motor and get it running and broke in a normal passenger car heat range plug gapped at .035" is just fine.

Once you get it all running good (in the drive way) you will want to select the proper heat range plug for WOT use. Supercharged motors make more combustion heat and pressure. So you want to run a spark plug that will resist overheating under power. So you want a slightly coooler than stock heat range plug for your application. About 2 to 4 to heat ranges cooler than the same motor without a super charger.
Engines with non stock hi performance cams (particularly blower motors) need a lot more spark timing at idle than a stock motor does, yet want less total timing. So a stock distributor timing curve will not work.
What camshaft is in this motor? what power valve are in the carbs. have the carbs been modified for blower use (boost referenced power valves)
Once a spark plug is fouled, it is junk (reguardless of its heat range)
So if you fouled the plugs up you will need to start with new spark plugs.
Need details of your motor to tell you how to set it up.
I would not bother tryiing to start the motor until you have dialed it in better
as all the fuel wash will just kill the rings and more spark plugs.
Again from what you have posted, you need to get all the false tuning assumptions out of your head and start fresh. Someone along the way mis informed you severly. Don't take that personally, we aren't born with this knowledge. You need to stop, regroup , change a few things and try again.
I can help but need details on your build.
Are you sure the ignition timing pointer is installed correctly (verified true TDC), it is very very common for this to be out of wack, especially with replacement parts. Accurate spark timing is uber-critical on a supercharged motor. Inacurate timing pointer/balancer timing mark alignment makes it very hard to tune and can easily result in costly engine damage.
When set up properly super charged motors run very well and do not foul spark plugs. But the set up is different than a non super charged motor or a stock motor.

Just to set things straight. If you fouled the plugs, its because the carbs and ignition timing is not set right. Not because the plug is "hot" or "cold".

Last edited by F-BIRD'88; 08-21-2008 at 07:14 PM.
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Old 08-21-2008, 08:53 PM
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Thanks.

First, it ran great with the 12 degrees and #4 plugs. Did not run hot, or have any drivability problems, but keep in mind, it only idled alot vs. driving. It has not been opened up. The plugs were fouled, and I put new ones in. They have only been fired one time, and are o.k. now.

I was just going back through the info. that has been posted here before, and all of the things that Hampton, Dyers, The Blower Shop, and BDS have to say, and it all points me in the same direction - 16 to 18 degrees initial, 32 to 34 all in by 2500 to 3000. That is all understood, my question was how does a colder plug make a difference. You answered it completely, thank you. See Below
Quote:
"Hotter plugs" retain more combustion heat and tend to burn off combustion deposits (run cleaner) But tend to cause detonation and preignition at WOT.
I did also purchase a new set of NGK's, two ranges colder than the #4's.

As for your questions:
Cam - Hyd. Roller, lift .527" I .544" E, 224/234 at .050", 110 lobe centers.

The carbs are Mighty Demon Blower Carbs. I do not have the power valve info with me now, again, they have been matched. I do have them boost referenced.

Starts great, no pump, fires right up, idles good, but obviously better warm - with current timing and plugs.

As for ignition pointer, it is correct. Again, the engine has run great before and after blower install.

Total timing is in at 32 degrees, by 2500 RPM.

Thank you very much for your explanation, you have verified what I was "studying up on". Again, the engine ran great before the blower, installed blower, no change in plugs, ran great, of coarse with the timing advancement on initial set up. I am trying to fine tune, and will install the new plugs, and advance the timing from 12 up to 16 - 18.

Much Appreciated,

Jason
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Old 08-21-2008, 09:29 PM
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You'll find it idles much nicer with as much timing at idle as it wants.
Most likely 26 or so degrees. So, if the motor wants 32deg at full andvacne and 26deg at idle you need a very short advance curve limited to 6deg.

26+6=32. This requires than you tear down the distributor and modify the mechanical advance curve stop so that the distributor only advanceds the timig by 6deg with rpm. You cannot achieve this curve by swapping advance springs and bushing. you must tear down the distributor.

As a tuning exersise and to prove my point, temperairly lock the mechanical advance frozen. Set the timing at 32deg, reset the carbs idle speeds and idle fuel mix screws for best idle once the motor and supercharger housing is fully warmed up. Go for a ride. Go for a week.... idle, stop, go idle in gear out of gear restart hot cold.

if the motor needs 34deg to make best power under boost or 30deg under boost or 36deg under boost than that is what it needs.
Find the best idle timing that the motor wants (more idle timing (26+ish) allows your to close the carb throttles down further to get a clean idle and quick throttle response.
Now create the timing curve the motor wants.

I'll bet it wants 24 to 28deg at idle and 32 to 35deg at WOT under full boost on pump gas.

You cannot achieve this range with the distributor set up with 20deg if internal mechanical advance (12 idle and 32 max timing)
If you just move the idle timing to 18deg you will have too much max timing under boost for pump gas.

Start with the timing locked out at 32deg, find out what the motor wants for max timing under full boost. (around 32 ish on pump gas) and what it requires for idle timing . if it wants 32deg at idle also for best idle , leave it locked out a 32deg full time. Often this is the case.

I would use a non projected tip spark plug. What is the NGK plug that fits your 502BB heads?
Your plugs will stay clean ( mild color) if your main jets are right.

If when the timing at idle is 26 to 32deg BTDC and the idle speed is too fast:::
You may need to remove the carbs. Flip them over and reset the throttle blade opening at idle for all 8 barrels.
You want the idle transfer slots all even and all barely showing under the throttle blade edge at idle. You may have to do this more than once to get it right. Should idle clean at 800-900 neutral and only drop a little when put in gear. (if you have the right torque converter)

Again, if the motor wants 32deg at idle, give it 32deg at idle.
If the motor is hard to start hot with this much idle timing, install a ignition power interupt switch to releive the starter cranking load and or install a MSD "starter Saver" auto crank spark retard box or a ignition boost retard box that has this cool built in auto fuction. Be sure you have the correct starter mount rear brace on your starter motor.

Last edited by F-BIRD'88; 08-21-2008 at 09:41 PM.
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Old 08-22-2008, 07:09 AM
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F-Bird,

I printed this out. I will start plugging away at it this weekend. We will see what she likes. Even at 12 degrees, starts great cold and hot. I will start with 16 degrees, and the new NGK plugs, and move on from there.

Thanks again, I will post the outcome...

Jason
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Old 08-23-2008, 10:03 PM
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re: Blower Motor - Timing - Spark Plugs: Need Clarification Please

If your are to rich you need to lean out the jets and idle mixture... You also need a CD ignition. Timming will only increase or decrease vac.. Causing the power valves to come in hurting the plugs more... You are way to rich check the basics float level, etc..... I have seen carbs with spray tubes on the acc pump fuel sucked right out of it... The fuel pressure on a pull through carb only needs 6 # no more !!!

My holley DP 650' s on a 6-71 468 10" vac at 900 rpm have 71 pri and 78 on sec, 30 cc shot pv is 6.5 . Timming is 18~ at 900 7.2 comp... 12 # boost...


Hope this helps

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Old 08-24-2008, 07:08 AM
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Well, set in the new NGK plugs, two steps colder. Set timing to 16 degrees. Starts cold and hot, easily, idles great, responds great, just like it did before. I am leaving it where it is for now, to set a second baseline from the original plugs and 12 degrees timing. I am feeling happier again.

Again, it was not huffing and puffing, but I do also need to realize, I never really drove the car. The two times I did, it mainly idled around the neighborhood with only a touch of the pedal to get to a coast. I opened it up one time about 1/4 to 1/2 throttle and it scared the poooop out of me . So this in itself is enough to foul some plugs.

I am thinking of getting it out later today, slow roll it some, take it out to a back road and open it up a little. This will keep it happy, I HOPE!

I have also made a little log book, scratch pad noting the specifics on plugs, timing, etc. from the very start. Hopefully this will help me keep track of where I started, when I have problems, and when I have made changes. This way, never back step.

I will keep the board posted on the outcome...

Thanks Again ,

Jason
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