DCR vs. total duration in cam selection..
05-17-2007, 09:53 AM
#1
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DCR vs. total duration in cam selection.. There is always plenty of cam selection discussions on this board. We hear about DCR constantly and that we want low to mid 8.xx dcr. Then we see cam results of large cams with less than optimal DCR but these cams run huge durations and make the numbers.
My question is when does it make sense to sacrifice some DCR for total duration in cam selection?
I believe this is more relevant for a "track" setup vs. a street setup where DCR helps the low end torque needed on the street. That being said then I'd also like to know what criteria is used when specing a stip cam?
My question is when does it make sense to sacrifice some DCR for total duration in cam selection?
I believe this is more relevant for a "track" setup vs. a street setup where DCR helps the low end torque needed on the street. That being said then I'd also like to know what criteria is used when specing a stip cam?
05-17-2007, 12:53 PM
#2
from reading chp and gmhtp, for a street setup you want some torque in the lower rpm ranges, which results in driveability and economy. To do that, you get a cam with less duration and less overlap so cylinder pressure builds better at the lower rpms. But in doing so the engine doesn't breath as well in the upper rpms and you sacrifice max power at high rpms. For the strip, and depending on your transmission setup, you opt for the larger durations and overlaps to make the most hp, and low rpm power is irrelevant because the engine doesn't operate in that range on the strip. What sort of compromise you make between the two is up to how much you plan on driving on the street and what's acceptable. How a dynamic compression ratio numbers compare from cam duration and intake closing I don't know, never really looked into that math. I don't quite know what you mean by sacrificing DCR for total duration.
I'm guessing DCR becomes lower with larger durations? If so, and the motor still makes good #'s then it would be because of the volumetric efficiency of the motor- how well it's able to breath at upper rpms. And that has to do with the design of the heads and intake and how well they flow, not just cam selection.
I'm guessing DCR becomes lower with larger durations? If so, and the motor still makes good #'s then it would be because of the volumetric efficiency of the motor- how well it's able to breath at upper rpms. And that has to do with the design of the heads and intake and how well they flow, not just cam selection.
05-17-2007, 05:23 PM
#3
TECH Apprentice
I've been thinking about this also. Low DCR's equate to less pumping losses at higher rpm's helping the engine to buzz faster. So, even with a turbo motor 7:1 would be just tickety boo 
Unless I'm wrong of course 
Boosted.
Unless I'm wrong of course Boosted.
