Cam Timing with Supercharger
05-23-2011, 05:05 AM
#31
this is a very good read and makes sense on how sideways made more power
http://www.superchargerperformance.c...and-cam-timing
Your exhaust system and exhaust back pressure:
If you have a stock log type exhaust manifold, with a close coupled cat, with a dual cat exhaust system, small exhaust tubing, and a couple of restrictive mufflers on your car then it is possible at peak power to have upto 10psi of back pressure.
If this is the case, my first recommendation would be to upgrade to a high flow, low pressure exhaust system because of the potential power gains; however, I do know that some of our readers have cars that they are setting up for their parents or for dual use where their partner or the laws in their location …etc are really strict when it comes to any added exhaust noise or any aftermarket exhaust. In this case, where exhaust upgrades are not an option, then you must select your camshafts, and tune your cam timing to where you have ABSOLUTLEY the minimum possible amount of overlap. If you have significant overlap, then the more you rise above about 4500 rpms the more your supercharger will suffer and the more power you will waste. If the supercharger is geared to 7psi of boost for example, then during overlap, the cylinder sees 7psi of boost on the intake side, and 10psi of back pressure on the exhaust side, the net result is that air will flow from the high pressure zone (the exhaust) to the lower pressure zone (the intake) and so your cylinder will start to fill with exhaust gases. As the rotation continues, the exhaust valve will close and overlap will end, and the intake valve will stay open for the remainder of the intake stroke (for the rest of the duration of your intake cam), and the rest of the cylinder will fill with fresh air.
What happens here is that we get a cylinder that filled for 30* of overlap with exhaust air, and then filled for another 210* (of the original 240* of duration for a typical street cam) with fresh air.The result is a cylinder that is only 85% filled with fresh air or an engine that is literally 15% smaller in displacement On the other hand, if our supercharger is geared for 18psi for example, then during overlap we will have 18psi on the intake side and our exhaust back pressure of 10psi on the exhaust side, the net result of this overlap is that our supercharger is effectively only producing 8psi worth of differencial pressure between the intake and the cylinder and so we are only going to get a power boost of 8psi during overlap. So, during those 30* of overlap the supercharger is only effectively producing 8psi of boost, and after that once the exhaust valve closes, the supercharger will be able to go back to operating at full boost for the other 210*. The net result is something like 16psi of boost so 2psi (or about 12%) of our power was wasted.
http://www.superchargerperformance.c...and-cam-timing
Your exhaust system and exhaust back pressure:
If you have a stock log type exhaust manifold, with a close coupled cat, with a dual cat exhaust system, small exhaust tubing, and a couple of restrictive mufflers on your car then it is possible at peak power to have upto 10psi of back pressure.
If this is the case, my first recommendation would be to upgrade to a high flow, low pressure exhaust system because of the potential power gains; however, I do know that some of our readers have cars that they are setting up for their parents or for dual use where their partner or the laws in their location …etc are really strict when it comes to any added exhaust noise or any aftermarket exhaust. In this case, where exhaust upgrades are not an option, then you must select your camshafts, and tune your cam timing to where you have ABSOLUTLEY the minimum possible amount of overlap. If you have significant overlap, then the more you rise above about 4500 rpms the more your supercharger will suffer and the more power you will waste. If the supercharger is geared to 7psi of boost for example, then during overlap, the cylinder sees 7psi of boost on the intake side, and 10psi of back pressure on the exhaust side, the net result is that air will flow from the high pressure zone (the exhaust) to the lower pressure zone (the intake) and so your cylinder will start to fill with exhaust gases. As the rotation continues, the exhaust valve will close and overlap will end, and the intake valve will stay open for the remainder of the intake stroke (for the rest of the duration of your intake cam), and the rest of the cylinder will fill with fresh air.
What happens here is that we get a cylinder that filled for 30* of overlap with exhaust air, and then filled for another 210* (of the original 240* of duration for a typical street cam) with fresh air.The result is a cylinder that is only 85% filled with fresh air or an engine that is literally 15% smaller in displacement On the other hand, if our supercharger is geared for 18psi for example, then during overlap we will have 18psi on the intake side and our exhaust back pressure of 10psi on the exhaust side, the net result of this overlap is that our supercharger is effectively only producing 8psi worth of differencial pressure between the intake and the cylinder and so we are only going to get a power boost of 8psi during overlap. So, during those 30* of overlap the supercharger is only effectively producing 8psi of boost, and after that once the exhaust valve closes, the supercharger will be able to go back to operating at full boost for the other 210*. The net result is something like 16psi of boost so 2psi (or about 12%) of our power was wasted.
05-24-2011, 03:46 PM
#32
I saw your post, just havnt had tiem to devote to two huge paragraphs haha. Im going out with my tuner tonight to modify my maps for the J's header. Once I am done Ill be going to King for a base line dyno run, then Ill install my keys to see my gains!
06-01-2011, 03:07 PM
#35
I just got my car tuned on teh dyno with the js, but not the keys (ran out of time). I gained approx 13whp with the header, so now I'm sitting at 379whp. Ill be installing the keys and getting a street tune, once the street tune is done Ill schedule another dyno tune session.
King Motor sports is having there dyno day in 2 weeks, I was thinking of throwing the keys in, street tuning it and then doing 3 baseline runs to see my gain, but Ill just pay to have them tune it on the dyno to see the true gains I get. Im hoping for a 5whp gain.
King Motor sports is having there dyno day in 2 weeks, I was thinking of throwing the keys in, street tuning it and then doing 3 baseline runs to see my gain, but Ill just pay to have them tune it on the dyno to see the true gains I get. Im hoping for a 5whp gain.
From 364whp to 379whp.
06-02-2011, 03:14 AM
#38
I think rom now on people should type next to the number exhaust and intake, so nobody gets confused.
Ill be running -1 intake, and +2 exhaust.
Sorry for the typo! 15whp gain is NO JOKE! The belt had to be tightended, and now Ive maxed out the tensioner, so I should probably buy a new belt for it.
Ill be running -1 intake, and +2 exhaust.
Sorry for the typo! 15whp gain is NO JOKE! The belt had to be tightended, and now Ive maxed out the tensioner, so I should probably buy a new belt for it.
06-02-2011, 05:59 AM
#39
Former Sponsor
Which header is that with? Only change was that and had stock before I am guessing? Very nice! Makes me think I have lots to gain with my setup which is oem header and a 60mm HKS dual exhaust.