timing
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
That doesn't really help very much. If you have the KB2347, that piston gives 9.3:1 with 76cc heads, and you didn't tell us what heads you have. That piston has a stepped-dish according to Tim, but if that is what you have I'd start at 6 BTDC and work up from there until you get pinging or detonation and then back off. You will probably end up around 10, depending on the gas you are using.
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Senior User
Joined: Sep 2011
Posts: 124
Likes: 1
From: canton michigan
That doesn't really help very much. If you have the KB2347, that piston gives 9.3:1 with 76cc heads, and you didn't tell us what heads you have. That piston has a stepped-dish according to Tim, but if that is what you have I'd start at 6 BTDC and work up from there until you get pinging or detonation and then back off. You will probably end up around 10, depending on the gas you are using.
Thanks ... this is my combination
any recommendation on curve?
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Probably 30 degrees centrifugal will be all you can handle. Maybe 35. And get it in by about 2500. If you limit it to 30 you can bring it in earlier. But you may have to play with initial timing to keep it from pinging.
However, we haven't talked about quench. Did you zero-deck the pistons? What head gasket did you use? Did you have the heads planed?
However, we haven't talked about quench. Did you zero-deck the pistons? What head gasket did you use? Did you have the heads planed?
Laughing Gas
Joined: Aug 2010
Posts: 896
Likes: 55
From: Bothell
Your high rpm timing is more important than idle timing.
What distributor are you running and how much mechanical advance do you have? If it's a duraspark the weights will have numbers on them to say how much advance the distributor will give.
What octane gas do you plan to run? If you have the stock, open chamber, heads you may be stuck with 92 octane. 0 deck with open chamber heads will not give you any quench.
Gary is right, you'll want 30-35 deg advance at 2500 rpm or so... set this and then see where the idle timing lands. If it's WAY off you'll have to adjust the total mechanical advance in the distributor.
Don't be scared if it idles well with 10-15 deg or maybe more.
If you are going to try to run low octane gas then make sure you time the engine with this gas.
If you can't get it to stop pinging with 30 deg advance then step up a level of octane and start over.
Do all of this with the vacuum advance disconnected. After you have the mechanical advance dialed in then you play with the vacuum advance.
I believe I have my 400 running with 15 deg at idle and 32 deg total.
What distributor are you running and how much mechanical advance do you have? If it's a duraspark the weights will have numbers on them to say how much advance the distributor will give.
What octane gas do you plan to run? If you have the stock, open chamber, heads you may be stuck with 92 octane. 0 deck with open chamber heads will not give you any quench.
Gary is right, you'll want 30-35 deg advance at 2500 rpm or so... set this and then see where the idle timing lands. If it's WAY off you'll have to adjust the total mechanical advance in the distributor.
Don't be scared if it idles well with 10-15 deg or maybe more.
If you are going to try to run low octane gas then make sure you time the engine with this gas.
If you can't get it to stop pinging with 30 deg advance then step up a level of octane and start over.
Do all of this with the vacuum advance disconnected. After you have the mechanical advance dialed in then you play with the vacuum advance.
I believe I have my 400 running with 15 deg at idle and 32 deg total.
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