Cam discussion-I pray
06-17-2005, 01:03 PM
#1
TECH Enthusiast
Thread Starter
Cam discussion-I pray I am just learning about cams and wanted to learn a bit about what specs affect engines in different applications. While I have chosen to use a forced induction application becuase the specs have observable consequences that aid in this cam discussion, this is posted as a tech question in the internal engine section for 2 reasons. 1: I am not interested in this discussion turning into a forced induction war and 2: it is a cam-valve event discussion that may and I hope, will steer away from the first application (forced induction) that I used to get the topic going. I am not in the know on the topic and wanted to weed through why certain 'exceptions' seem to work so well.
I'll start my question off with a request to avoid flames if you read something you disagree with in this thread. I would like you to avoid hijacking this thread for a forced induction 'I read it somewhere' tournament on who read more about forced induction.
START:
Two very good successful tuners that do a lot of forced induction work use 10.1:1 compression with full boost to get near 650-700rwhp with the d1sc and f1r ati units. I know a lot of people are already screaming here since the widely held belief is that you have to be in the 8.5:-9.5:1 but that is not my discussion/question. Since those tuners do it successfully, that will be a discussion elsewhere.
The issue here which has to do with boost bleed-off and cylinder pressure (it will apply to all applications but is very easy to illustrate with forced induction since boost is measurable). With cams, what specs have what relation to boost. Andy at A&A in California uses a 224 single pattern cam on a 114. Many of these cams (there are so many versions available from different sources) would have near a 69* Intake closing ABDC and on an engine with 10.1 static compression ratio would yield a dynamic compression in the 7.8:1 range.
PUHLEEZE DON'T HIJACK MY THREAD WITH WHY YOU THINK HIS COMPRESSIONIS TOO HIGH OR YATA YATA YATA....I'm not interested in the application.....this is a cam question for me to learn about cams and what the valve events do to ALL applications. I am citing this example to use as a basis for a discussion for my enjoyment nothing more.
If a cam with more overlap on a narrower LSA were used you would have an earlier intake closing point and less bleed off. What would happen to using a bigger cam like that? (I don't care if it is a bad aplication, I want to know what happens...ie I would want to see why it is bad). I see the static compression would remain the same and the dynamic compression would likely be higher. To further illustrate, the gt2 cam has a lower dynamic compression than a 224/227 114 TR cam would for the intake closing point difference in the same application. Daring to go into forced induction territory, if Andy were to use the stock 02 Z06 cam with an intake closing point of 80* a static cmopression of 10.3:1 would still yield a lower DCR than his currently applied 224 single pattern cam. Keep in mind please that I don't care if the application is better or worse, I want to know what happens if the spec is changed on the selected cam. I don't want to hear I tried that cam and lost 55 rwhp.
Now before I get flamed for not being a know it all with the subject, my hope here is that someone can teach me about the exhuast event and let me know what in the cams mentioned above are affected by exhaust reversion, and why headers lower the boost psi in some applications. Is it the overlap/ early opening of the exhaust valve?
OK, so the questions are --how does the exhaust opening event on bigger overlap cams affect bleed-off (why does improving exhaust flow by adding headers lower boost?? and....Does the intake closing point of the selected cam allow you to use more static compression since the DCR is lower with a later closing point?
I'll start my question off with a request to avoid flames if you read something you disagree with in this thread. I would like you to avoid hijacking this thread for a forced induction 'I read it somewhere' tournament on who read more about forced induction.
START:
Two very good successful tuners that do a lot of forced induction work use 10.1:1 compression with full boost to get near 650-700rwhp with the d1sc and f1r ati units. I know a lot of people are already screaming here since the widely held belief is that you have to be in the 8.5:-9.5:1 but that is not my discussion/question. Since those tuners do it successfully, that will be a discussion elsewhere.
The issue here which has to do with boost bleed-off and cylinder pressure (it will apply to all applications but is very easy to illustrate with forced induction since boost is measurable). With cams, what specs have what relation to boost. Andy at A&A in California uses a 224 single pattern cam on a 114. Many of these cams (there are so many versions available from different sources) would have near a 69* Intake closing ABDC and on an engine with 10.1 static compression ratio would yield a dynamic compression in the 7.8:1 range.
PUHLEEZE DON'T HIJACK MY THREAD WITH WHY YOU THINK HIS COMPRESSIONIS TOO HIGH OR YATA YATA YATA....I'm not interested in the application.....this is a cam question for me to learn about cams and what the valve events do to ALL applications. I am citing this example to use as a basis for a discussion for my enjoyment nothing more.
If a cam with more overlap on a narrower LSA were used you would have an earlier intake closing point and less bleed off. What would happen to using a bigger cam like that? (I don't care if it is a bad aplication, I want to know what happens...ie I would want to see why it is bad). I see the static compression would remain the same and the dynamic compression would likely be higher. To further illustrate, the gt2 cam has a lower dynamic compression than a 224/227 114 TR cam would for the intake closing point difference in the same application. Daring to go into forced induction territory, if Andy were to use the stock 02 Z06 cam with an intake closing point of 80* a static cmopression of 10.3:1 would still yield a lower DCR than his currently applied 224 single pattern cam. Keep in mind please that I don't care if the application is better or worse, I want to know what happens if the spec is changed on the selected cam. I don't want to hear I tried that cam and lost 55 rwhp.
Now before I get flamed for not being a know it all with the subject, my hope here is that someone can teach me about the exhuast event and let me know what in the cams mentioned above are affected by exhaust reversion, and why headers lower the boost psi in some applications. Is it the overlap/ early opening of the exhaust valve?
OK, so the questions are --how does the exhaust opening event on bigger overlap cams affect bleed-off (why does improving exhaust flow by adding headers lower boost?? and....Does the intake closing point of the selected cam allow you to use more static compression since the DCR is lower with a later closing point?
