Stroker timing changes ?

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mbaird

mbaird

mbaird
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So I just finished installing my new 4” stroke engine and I got ti thinking about timing . Nothing changed but the 4” crank . Will my timing curve be different? Piston speed will be faster so will I need to advance my timing throughout the rpm curve ?
Curious…
 
And compression increased 1 point to 10:1
Will the increase in compression offset the piston speed ?
 
So u used the same pistons and rods from a previous build? I presume u used a 360? U have a difference of .420 in stroke. Enlighten us how u accomplished this by not having pistons with a shorter compression distance. Kim
 
oldkimmer said:
So u used the same pistons and rods from a previous build? I presume u used a 360? U have a difference of .420 in stroke. Enlighten us how u accomplished this by not having pistons with a shorter compression distance. Kim
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No.. I used a Scat 4” crank , scat rods and Scat Stroker pistons , I should have said that the only change was the 4” rotating assembly.
 

Once I start driving and tuning I will figure it out but conceptually I was curious.
 
mbaird said:
So I just finished installing my new 4” stroke engine and I got ti thinking about timing . Nothing changed but the 4” crank . Will my timing curve be different? Piston speed will be faster so will I need to advance my timing throughout the rpm curve ?
Curious…
Click to expand...

Yes
 
Newbomb Turk said:
Yes
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The point was to start a discussion explaining why the timing needs to change . Aspects like piston speed , cylinder filling, changes to DCR etc…. Many know that canges are required after a component change but not exactly why . The ability to visualize the process helps us become better tuners .
 
You might work with less initial timing if everything is the same. Might not be much.

Test it out. :)
 
mbaird said:
The point was to start a discussion explaining why the timing needs to change . Aspects like piston speed , cylinder filling, changes to DCR etc…. Many know that canges are required after a component change but not exactly why . The ability to visualize the process helps us become better tuners .
Click to expand...

It’s hard to give specifics because there are too many variables.

But, if you are going from say a 1.85 r/s ratio and you are going to 1.53 you will probably need 2-4 degrees more initial as a baseline.

That also depends on your compression ratio, the fuel you are using, cam timing and even coolant temperature.

You want most of the combustion cycle done by 12-15 degrees ATDC so any time you change the r/s ratio it affects ignition timing.

As a very general rule the lower r/s ratio the more total timing it will want depending on rpm and induction efficiency.

It really takes a a few hours on an engine dyno just to determine what the engine wants for a timing curve.

Then it takes time to screw around and get the mechanical curve to match what the engine wants, while keeping in mind that ALL ignition boxes retard with rpm so you have to account for that too.
 
Mbaird,
To answer your question. Strokers generally have smaller rod/stroke ratios. Before & after TDC, the piston is moving faster compared to a larger r/s ratio engine. This requires ign [ timing ] to be started earlier [ advanced ] so that the burn is completed at the correct crank angle for max power.
 
I set initial to 18* and on intitial drive up the street and back . the engine was shaking pretty bad. That could be the carb as well as the plugs are black . I am setting the floats right now because the carb is dumping fuel into the intake after shutdown.
 
mbaird said:
I set initial to 18* and on intitial drive up the street and back . the engine was shaking pretty bad. That could be the carb as well as the plugs are black . I am setting the floats right now because the carb is dumping fuel into the intake after shutdown.
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Dam, I hope u get that cleared up pretty soon. Good luck 2 ya. Kim
 
mderoy340 said:
Pull the dipstick and if you smell fuel change the oil!
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Years ago I pulled the dipstick on my 340 after a 150 mile trip when it started running badly. The ‘oil’ had become friendly with the coolant and turned a minty-green. It either had a cracked head or blown head gasket….I forgot which. ;(
 
mderoy340 said:
Pull the dipstick and if you smell fuel change the oil!
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I did . Smelled fine . Most every Edelbrock I have has done this to some extent . My theory is that having the jets in the floor of the body makes them susceptible to this . Super sensitive to float height and fuel pressure.
 
The chamber design in the head and the shape of the top of piston are the two main contributing factors to what the engine will want for timing on WOT. You’re going to make peak torque (max VE) at a much lower RPM than before if you didn’t add a bunch of camshaft so your curve will want less advance at the new peak TQ rpm. I’ll render a guess that your all in timing will be similar, maybe 1-2 degrees less than before for max power, and it’ll want 3-4 deg less in the curve around peak torque. All other points in the curve will be about the same. Idle timing likely won’t change much, again if you didn’t change the cam it might not change at all.
 
I was at 16 intitial and 32 total + VA of 18 if I remember correctly. I can try staying at 16 with VA hooked to manifold port or use ported and recurve the distributor.

The heads are EQ magnums ported by IMM . Good chamber …. Nothing else changed
Pistons are Scat with a step dish . Quench is around .040
 
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