Evo 8: JUN 272 vs S2, if cost was no issue
Oct 23, 2012, 01:27 AM
#6
With regard to the published specs, the JUN 272 and GSC S2 appear very similar.
Both the JUN and GSC have comparable effective duration (235 vs 232 respectively).
Both are ground on similar lobe centerlines (108/115 vs 107/113).
Both feature similar valve lift (10.8 vs 11.2mm).
Both cams are ground to favor power in the upper rpm ranges, and will give a lumpy idle. Both require upgraded valvesprings to deliver best power and longevity.
The valve lift difference is small, but an unported EVO head cannot respond to anything greater than ~10.5mm lift anyway.
Any further differences would be in the cam lobe profiles.
Both the JUN and GSC have comparable effective duration (235 vs 232 respectively).
Both are ground on similar lobe centerlines (108/115 vs 107/113).
Both feature similar valve lift (10.8 vs 11.2mm).
Both cams are ground to favor power in the upper rpm ranges, and will give a lumpy idle. Both require upgraded valvesprings to deliver best power and longevity.
The valve lift difference is small, but an unported EVO head cannot respond to anything greater than ~10.5mm lift anyway.
Any further differences would be in the cam lobe profiles.
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Oct 23, 2012, 02:39 AM
#8
What constitutes overcamming is mostly a factor of effective duration and overlap, whereby increasing either beyond a certain point results in more power being given up under the curve than gained elsewhere. Ideally, one would want the smallest cam set that delivers the most power under the curve for any application. That being said, generating max power for a 5000-8500rpm power curve differs in optimum valve timing than a curve that spans from 6500-10,000rpm.
As for increasing lift beyond ~10.5mm with stock ports, the head simply cannot deliver greater airflow.
Additionally, larger displacement (e.g. 2.3-2.4L) engines with longer strokes and short rod/stroke ratios are somewhat less sensitive to longer effective duration due to slower piston speeds around BDC. Those engines can use a little more valve timing than a 2.0-2.1L longer rod engine.
As for increasing lift beyond ~10.5mm with stock ports, the head simply cannot deliver greater airflow.
Additionally, larger displacement (e.g. 2.3-2.4L) engines with longer strokes and short rod/stroke ratios are somewhat less sensitive to longer effective duration due to slower piston speeds around BDC. Those engines can use a little more valve timing than a 2.0-2.1L longer rod engine.
Oct 23, 2012, 05:54 PM
#10
S2s idle better than the JUN cams. The ramp rate on the JUNs is more aggressive than the S2 which favors larger displacement a little better but all in all they are very similar for power production. Greg did some replica JUN cams (in a customer car here now actually) since JUN didnt seem to have the repeatability in their cam grinding that a CNC grinder can offer.
5000-8500 is more than a stock block needs, 5000-8000 is more the working range and even then that is really dependent on turbo. Having dyno'd some other aggressive cams vs the S2 it would seem that the S2s will deliver similar power on gas without sacrificing down low. I have seen definite gains from S2s over S1s in the same car with the same turbo, its all about what it is being used for and if its MIVEC or not. In this case since its non-MIVEC, power under the curve is more mechanically dictated than in a IX.
aaron
5000-8500 is more than a stock block needs, 5000-8000 is more the working range and even then that is really dependent on turbo. Having dyno'd some other aggressive cams vs the S2 it would seem that the S2s will deliver similar power on gas without sacrificing down low. I have seen definite gains from S2s over S1s in the same car with the same turbo, its all about what it is being used for and if its MIVEC or not. In this case since its non-MIVEC, power under the curve is more mechanically dictated than in a IX.
aaron
Oct 25, 2012, 05:01 PM
#14
Evolved Member
What constitutes overcamming is mostly a factor of effective duration and overlap, whereby increasing either beyond a certain point results in more power being given up under the curve than gained elsewhere. Ideally, one would want the smallest cam set that delivers the most power under the curve for any application. That being said, generating max power for a 5000-8500rpm power curve differs in optimum valve timing than a curve that spans from 6500-10,000rpm.
As for increasing lift beyond ~10.5mm with stock ports, the head simply cannot deliver greater airflow.
Additionally, larger displacement (e.g. 2.3-2.4L) engines with longer strokes and short rod/stroke ratios are somewhat less sensitive to longer effective duration due to slower piston speeds around BDC. Those engines can use a little more valve timing than a 2.0-2.1L longer rod engine.
As for increasing lift beyond ~10.5mm with stock ports, the head simply cannot deliver greater airflow.
Additionally, larger displacement (e.g. 2.3-2.4L) engines with longer strokes and short rod/stroke ratios are somewhat less sensitive to longer effective duration due to slower piston speeds around BDC. Those engines can use a little more valve timing than a 2.0-2.1L longer rod engine.
Oct 25, 2012, 05:08 PM
#15
More time spent (duration) over 10.5mm will still always make more power. It doesnt flow much more when lift is over 10.5 but it doesnt flow less either. Running the most you can then at that point will make more power to a point.
In practical application an S3 on a stock turbo will loose below 6500 vs an S2 and gain once its above that. Even then it was only 20whp peak so the losses down low dont math out in favor of the gains up top. On a larger turbo car it would "lose" down low anyway since its not making boost at lower rpm but will benefit at high rpm where the car is making peak power.
In practical application an S3 on a stock turbo will loose below 6500 vs an S2 and gain once its above that. Even then it was only 20whp peak so the losses down low dont math out in favor of the gains up top. On a larger turbo car it would "lose" down low anyway since its not making boost at lower rpm but will benefit at high rpm where the car is making peak power.