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Old 06-01-2004, 09:36 PM
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timing on a built 406

A good buddy of mine is having trouble fine tuning his 406 sbc. The car runs runs great, and pulls hard, its a 77 olds 442 with a 4 speed. We think the timing is off and we know the carb is running to rich but we would like to narrow down one thing at a time, heres what he says about the motor:
406 sbc, ~10.25:1 comp, 93 octane

Sportsman II heads, straight plug, not sure if 64cc or 72cc, not sure if ported to intake

Torker II intake

Isky Racing cam #201288 for oval track (2800-7000 RPM)
288 deg, .450 in lift with 1.5 rockers at 007 open and .010 close lifter rise
244 deg at .050 lifter rise, no valve lift given

400 cast crank, 5.7" 350 rods, flattop pistons with small butterfly, block and oil pan machined for clearance

1.5 ratio rockers

750 CFM Holley dp

MSD Pro-Billet HEI distributor #8365 with 6AL as $200 rev limitor, Taylor 10.4 mm wires, Autolite #24 plugs. Not sure if plugs are right for engine. Don't know who put them on.

16 lb. flywheel

March pulleys

Built to handle high RPMs and rev fast


Distributor has 21 deg mechanical advance (stock), no vacuum advance. If I remember correctly, base timing is 28 deg. 49 deg total advance seems too high. Runs rich, plugs are carbon fouled and have oil or gas on threads. Otherwise good condition. Too loud to hear any pinging or detonation well. Good throttle response above 2100, runs rough below, may be because of no vacuum advance.



Any help would be great as to what the timning should be on this type of motor.

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Old 06-01-2004, 09:51 PM
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Blob,

I think your timing is fine. The thing to change is the jetting in the carb. You need to lean it out a bit then I think you will run better at lower RPM's.

Why can't you hear any pinging? Is there an exhaust leak? Running headers?

But I do not think you are having a timing problem because you would have white plug ends or maybe even missing spark plug parts if you had the timing too far advanced.

You might check and see if the weights in the distrubtor are lubed so they move easy. This could cause a stumble.

My money is on the too rich carb.

Scholman
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Old 06-01-2004, 09:57 PM
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yeah i think the carb is too rich also, cant really hear pinging probibly cause there is none and secondly since it is so loud the flowmasters and high compression
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Old 06-02-2004, 06:29 AM
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Well, I disagree with the timing being okay. 49 degrees mechanical advance is WAAAYY too much. 49 with vacuum and mech is even getting real high. You are going to want to limit advance to 36 degrees and 38 would be the max. If you are running that much advance, you are loosing a good bit of power and probably getting some detonation.

First, you need to get the carb a little closer. The only reason the engine is running that much advance and liking it is because it is way too rich(as long as you are sure that the timing marks are accurate). Next is to get initial timing set. I cant imagine needing over 20-22 degrees initial if you get the mixture set properly which can be done by setting for the highest vacuum. Then you can do the same with the timing.

Then comes total mechanical advance. I am not familiar with the MSD HEI, but it may have a way to limit mechanical advance to around 34-38 degrees total. If not, you will need to devise one or find you a distributor that does.

After getting the distributor worked out, you can work on getting the carb perfectly tuned. The best way is reading the plugs. You want a light brownish color after a WOT run.

Chris
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Old 06-02-2004, 07:24 AM
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Agree with Chris above. Lock the distributor while you are at it. It's one less thing to have to worry about later.
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Old 06-02-2004, 07:32 AM
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DITTO with Chris.
Timing should be 12* initial and 24* full advance at 3,000 RPM.
The cam and intake is not a correct combination, different RPM ranges matter when building a motor.
The rest he stated is the way to tune in the carb so I will not say anymore.
George
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Old 06-02-2004, 07:34 AM
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timing

49 deg is way to much no matter how you look at it....... The deal with a performance motor is that you will never "hear" the detonation like a stock motor.

Start with 16 to 18 deg inital and no more then 38 total. With those heads and everything set up proper you will probably find that you only need 35/36 total timing for the best performance. Don't worry about the vaccum advance you dont need it.

Double check those numbers you gave us on that cam i think you have the lift wrong @.450

Do you know what plug he is running????

Keith
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Old 06-02-2004, 07:47 AM
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Re: timing

Quote:
Originally posted by k-star
Double check those numbers you gave us on that cam i think you have the lift wrong @.450

Do you know what plug he is running????

Keith
I bet he is right. The circle track rules limit lift and so they make up for it with duration. I run a circle track cam in my 57's 400 and it has an awesome power band, but is real peaky.

Chris
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Old 06-04-2004, 07:27 PM
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not sure on the plug, i think they are autolite 24's maybe? ill talk to him, yeah the guy that biult his motor is big in circle track racing, the motor is very strong, in that big tank it really huals, cant imagain it with a tune up, thanks for the advice!!
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