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simvegas
08-23-2007, 04:52 AM
Im now running a big bore and stroker Sr motor.
I was just wondering theoretically (actual tuning we will just move values up/down and recrod and repeat) whether increasing the stroke of a motor would make it like more or less timing then it had before?

Post your theories and give an explanation.

LigouriRd
08-23-2007, 08:53 AM
I don't think the stroke would make that much of a difference, rather I would think that it would depend on the resulting compression ratio. Higher CR would need to run less timing to keep away from the knock threshold. That said the motor would more efficient under low boost and boost would build faster. There are other things that reduce the knock threshold, like reducing sharp edges and hot spots on the pistons. My $.02

smracing
08-23-2007, 09:44 AM
Cam timing changes are needed.

steve shadows
08-23-2007, 06:11 PM
well yeah a motor with larger displacement can handle more overlap for making power.

On ignition timing I would think you would probably have *sorry* higher mbt to hit peak torque.

*im not sure on stroke however, ive heard of timing on maps being effect by bore size on account of the flame fronts characteristics regarding

the size outwards from the spark itself. Stroke downward is a change in overall displacement but and can effect piston speed.

as others said compression ratio is the no.1 concern in an overall change in the engine dynamics, displacement is important in sheer volume (VE) and how much more fuel and how much spark you will need now.

MATT_BACK_VASS
08-23-2007, 06:23 PM
think about it

the higher the stroke, the fastaer the piston is being pulled down / moving down / a t the same rpm... so the piston has less time that it's able to be pushed down by the combustion event.. so wouldn't this mean , if good enough fuel is available, a stroker motor will benefit from more advanced ignition timing than a shorter stroke motor at the same rpm?

tuco
08-23-2007, 08:34 PM
think about it

the higher the stroke, the fastaer the piston is being pulled down / moving down / a t the same rpm... so the piston has less time that it's able to be pushed down by the combustion event.. so wouldn't this mean , if good enough fuel is available, a stroker motor will benefit from more advanced ignition timing than a shorter stroke motor at the same rpm?

Sort of. But it more depends on the Rod/Stroke ratio.

MATT_BACK_VASS
08-23-2007, 09:38 PM
i see.

well iwth a stroker youre only getting a worse rod to stroke ratio unless you get crazy

white98s14
08-25-2007, 04:54 PM
i have a 2.2L 90mm s14 motor...have been running it for 3 years now.I have been running the timing map from Enthalpy power fc maps he posted on here....of course the fuel maps were different.The car doesnt knock with this map.....just bee warned "do not pay attention to the knock warning if you have a power fc" when you have forged pistons you are going to get piston slap noise that the knock sensor thinks is knock and flash the check engine light.the only proper way to set the timing is to tune the torque curve on a dyno.

TheWolf
08-25-2007, 08:16 PM
define worse... a longer rod ratio and longer stroke isn't terrible but here's a brief write up on what changes.

A Long Rod is faster at BDC range and slower at TDC range. It is drawing harder from 90 ATDC so a harder sucking and more port velocity due to the reduced time constraint.

Then with a long rod the piston travels from BDC to 90 BTDC faster than short rod and goes slower from 90 BTDC to TDC. Because of this you could dial in some ignition advance because the piston spends more time at the top but this could also cause detonation due to flame front speeds. The higher octane fuels with their slower burn rates would benifit from this but if this was a 87 octane street driven daily abused car I wouldn't seek the last degree or two of advance.

The longer rod/stroker engine will spend more time with the piston further up in the bore resulting in a poorer angle on the crank but a higher combustion pressure pushing down.

Since the cam's were designed for a 2L and moderatly stock ports it would be wise to retard the exhaust cam some so the benifits of the increased stroke and longer rod are not defeated. It would be something I would explore atleast.

Kingtal0n
08-27-2007, 02:37 PM
It really wont make that big of a difference when your talking .2 or .4 liters here and there. Now compare a 2.4 to a 6.4L motor there will be some fundamental differences to change your baseline...

its all theory and numbers, you need to just see what works, its not like every other person is running around with a 2.2L stroker sr20 these days. Like anything else, trial and error > theory within practical limitations.