Raising compression
12-07-2012, 12:07 PM
#61
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Thanks Shawn. I had that impression but I know that Josh and Sid had been dealing with those issues over time. Sounds like the cylinder stabilisation has helped cure that...along with good tuning.
12-07-2012, 01:55 PM
#62
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...and keeping CR lower. Not exactly sure what Sid's final CR was but IIRC it was just a little higher than stock.
12-09-2012, 10:44 PM
#63
Rennlist Member
Thomas - it really depends on the kind of fuel used; the turbo used; the engine specifics (bore, stroke, which head, ect), even the type of load the engine will see...
But to not just leave it in ambiguity, we have pushed pretty hard in Sid's car. His car has a nice big turbo (slightly bigger than a GT35r), and is a stroker setup, still using the 8v head, massive intercooler, and running E85 with a 5th injector injecting fuel right before the throttle-body, which further aids in cooling the intake charge. Sid obviously runs my 3D mapping, but I can pull out just the 16psi column data to show as an example: (and yes, this is a LOT of timing lead)
But to not just leave it in ambiguity, we have pushed pretty hard in Sid's car. His car has a nice big turbo (slightly bigger than a GT35r), and is a stroker setup, still using the 8v head, massive intercooler, and running E85 with a 5th injector injecting fuel right before the throttle-body, which further aids in cooling the intake charge. Sid obviously runs my 3D mapping, but I can pull out just the 16psi column data to show as an example: (and yes, this is a LOT of timing lead)
Do you think the additional stroke of Sid's motor, thus lower rod/stroke ratio, is a factor in his motor liking more timing?
http://victorylibrary.com/mopar/rod-tech-c.htm
12-09-2012, 11:02 PM
#64
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Absolutely; that and the quench setup.
With the added stroke, the piston acceleration is higher - therefore needing more timing lead.
Give me a min, and I'll post up a bit more info..
Ok, here is a graph for the 951 vs your first stroker (and Sids):
And here is the one for your upcoming motor:
As you can see, the added stroke (everything else remaining equal) increases the piston acceleration notably... This changes the necessary spark-lead, as the faster accelerating piston will be rising faster, essentially giving less "time" to build combustion pressure (obviously I'm simplifying some). In-fact, it might not be immediately obvious, but at the same crank-angle, the verticle position of the piston will be different in a stroker compared to factory...
With the added stroke, the piston acceleration is higher - therefore needing more timing lead.
Give me a min, and I'll post up a bit more info..
Ok, here is a graph for the 951 vs your first stroker (and Sids):
And here is the one for your upcoming motor:
As you can see, the added stroke (everything else remaining equal) increases the piston acceleration notably... This changes the necessary spark-lead, as the faster accelerating piston will be rising faster, essentially giving less "time" to build combustion pressure (obviously I'm simplifying some). In-fact, it might not be immediately obvious, but at the same crank-angle, the verticle position of the piston will be different in a stroker compared to factory...
Last edited by Rogue_Ant; 12-09-2012 at 11:26 PM.
12-09-2012, 11:26 PM
#65
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12-09-2012, 11:43 PM
#66
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Great info, Thanks Joshua. Amazing the forces taking place.
