-5 on rear cylinder timing?

[hivolt132]

Can anyone tell me what this feature is used for. I realize its for fine tuning, but while reading hemi designs startup procedeure they suggest going to -5 degrees on the rear cylinder. My setup is very similar to theirs so I have been using their tech. startup advice. They also suggest a total timing of 30-32 and not the 35 that is stock. I can understand why the total would be decreased but not sure on the rear cyl. -5? Maybe its for easier startup or safer when preventing detonation. I am a little nervous to use it because crane hi-4 says dont change it unless I have a specific reason to. Now that I have gone to a .040 head gasket my comp. should be 10.5:1 has any one used this comp. ratio without detonation issues? Kind of high for a street engine, right?

[jurneyman]

First if you could fill in a little more information, about the type,and size of your motor it would help me to give more specific answers to your questions. To the initial question of the retarding the spark an additional 5 degrees, I hope I don't
make this more confusing, but this is one of those paradoxes where the obvious
isn't what it seems. I am going to start right from the beginning so hang with me. The H.D. V-Twin motor has an irregular firing pattern resulting in uneven intake pulses. the time for filling the rear cylinder is 90 degrees less of crankshaft rotation then the time for filling the front. the front intake valve opens and closes, followed very closely by the opening and closing of the rear intake valve. Now here is were it gets interesting, I have found most of the time people believe that with the longer time the front cylinder has it gets more of the mix, but here is where it isn't the way it seems. Now if this is taken into consideration that the time interval between the filling of the front cylinder and the rear cylinder is less then the time it takes between the filling of the rear cylinder and the front cylinder. This difference in the intake filling results in the rear cylinder gaining from the momentum of the air/ fuel mixture that was initiated from the filling of the front cylinder. This condition actually uses the opposite cylinder to pack more mixture into the rear and that may increase the compresson that could lead to detonation and retarding the spark lessons that chance. There is much more to this, but I want to see if I stated this clear enough to understand, before I continue. I know what is in
my mind doesn't always translate to explaining it clearly.

[hivolt132]

On page 2 of engine mods please see: "NEW POST SAME QUESTION". WRITTEN BY ME HIVOLT132 THERE YOU WILL FIND EVERYTHING TO ANSWER MY QUESTION WITH PICTURES.

[jurneyman]

I didn't see that your previous posts were related to this motor because they were under a different title. I would like to see if anyone can see a problem
using the woods cam with the intake at 20/40 and the exhaust at 42/18 with
a duration of 240 degrees, in a 95" inch motor with 10.5 -1 compresson I just
think that the corrected compresson is going to be to high with this cam to
run on 93 oct. without detonation problems. I haven't been following every post
so if I missed something with this combination fill me in.

[Amer_ninja]

I dunno I ended up with +4* rear cylinder offset on my 98"/37g build using Dewey's heads at 9.8 CR. Thats what gave me the best power/TQ on the dyno. I'm using the crane ignition with 0* initial and an advance slope of 7. I don't have any pinging but I use 91 octane fuel. It will kick back or stall the starter on hot days after a gas stop. Bumping the starter first, them laying into it solved that problem (so far).

[hivolt132]

Well, I spoke to Bob Wood and he personally recomended that cam. I do not know much about static compression or dynamic compression. Just basic stuff. Nor do I know a lot about cam numbers just some basic stuff. As far as putting all of these parts together it should be a setup that will work together. I ran the bike today and boy it sounds good, but not under any load by driving it. I set the squish at .040 , supposedly larger squish (.060) or more will result in detonation even with lower compression, thats why I went back in there to correct it. I originally used the SE .065 head gasket. I dought the squish is set too tight now. Even when I rode it the first time I did not hear any pinging. But this is all why I am wondering about the -5 on the rear cylinder. Hemi Design recomends it.

BTW I am a journeyman lineman. are you also?

[GRock]

ninja has it exactly what its for...... rear cylinder timing offset. Depending on the pipe, cam, head combo; you can smooth out and get the most power out of the combo by offsetting the timing. With the wood cam, try 3 degrees for a little better initial and hot soak start, and to smooth the low end and idle. That cam will run with that compression, although she will be a little pissy after hot soak. But ninja button trick helps.

G

[hivolt132]

Originally Posted by GRock

ninja has it exactly what its for...... rear cylinder timing offset. Depending on the pipe, cam, head combo; you can smooth out and get the most power out of the combo by offsetting the timing. With the wood cam, try 3 degrees for a little better initial and hot soak start, and to smooth the low end and idle. That cam will run with that compression, although she will be a little pissy after hot soak. But ninja button trick helps.

G

plus or minus 3?