Wow.
Wait Dan Connor? Is that a Dan Connor in the Chicago land area?
Wow.
From previous information:
N54 are
Intake 245deg 9.7mm lift
Exhaust 261deg 9.7mm lift
N55 is
Intake: 255* / 9.9mm lift
Exhaust: 261* / 9.7mm lift
I have the N53 cam specs saved somewhere, I'll see if I can find them.
There were quite a few assumptions being made so I purchased an N52 cam and measured it against an N55 cam. The numbers help give a much better idea of how the cam swap will affect an N55. Quite a few of the assumptions in this thread are wrong... including some of my own. Post #67 mixes up the pictures. N55 is left and N52 is right. Post #107 has a lot of assumptions that don't seem to hold true. What I did find with my own measurements was that while the N52 and N55 share very similar exhaust cam profile in their respective engines, there are some other part differences that will produce much different profiles when the cams are swapped.
View attachment 32656
You can see the previously stated roller ratio of 1.64 can't be true (based upon my measurements). Resulting valve lift would only be 9.27mm. We know the exhaust valve lift for all three engines is 9.7mm so we can use that information to deduce the actual rocker/roller arm ratio for the N55 to be 1.72. It was hard to measure this ratio by hand because as little as 1/64" difference can swing the ratio from say 1.68 to 1.71. The math is simple though and the cam measurements are pretty accurate. 5.65*x=9.7 ==> x=9.7/565 ==> x=1.72. Do the same basic math for the N52 cam and you get a rocker arm ratio of 1.66.
This is important because the ratio play a direct roll in overall valve lift. Multiple the lobe lift provided by the N52 cam by the N55 roller ratio of 1.72 and you get a resulting valve lift of 10.03mm (5.83mm * 1.72 ==> 10.03mm). This is an increase of .33mm lift over stock N55 cam. The exhaust valve will also open earlier and close later. How much? That is not something I plan to try to figure out. It would require more measuring equipment and time than I have.
The general theory would be that more duration and lift out of the exhaust valve could potentially increase whp at high rpm while sacrificing a bit of torque down low. How much? certainly not 100whp. This kind of cam change would be chasing 10whp at best is my assumption. Maybe on an 800whp build you might pick up 50whp... That is reality of making small changes to the exhaust cam especially so with leaving the intake cam stock. Exhaust port restrictions are still there as well.
There are also a few things that need to be considered when doing the swap such as, Spring travel/bind, piston to valve clearance, hydraulic lifter preload/travel, torque on the cam ledge, etc. Most of which might be considered moot since it's a working swap. Stock springs have the travel from what's been measured by others... not too sure what kind of issue might pop up with the lifters.
here is a link to the pics and spreadsheet: https://drive.google.com/open?id=1R-GaBRBd7Gw6xIL5_GlULuCk3DTbD2O1
Maybe @CobraMarty or someone like @MOTIV Motorsport can be so kind as to share some opinions/speculation?
If you send me the N55 exhaust cam, I can measure duration directly off the cam itself with my setup. Also, if you have an extra N55 roller arm, I would like to measure it myself and compare it to a N54 roller arm.
I would say is that earlier exhaust valve opening and increased lift can't really make up for poor exhaust flow.
That statement is false. You can open the exhaust valve 5-10 degrees earlier and close the valve at the same or 2-3 degree later and get lots of top end. It is all about reducing pumping loss and you can help this by opening the exhaust valve several degree earlier to achieve more power. This is where the duration on the exhaust cam comes into play.
I understand that, but, you're talking about an n52 cam swap not a custom cam... these are symetrical cams. If you're getting into lift sooner you're also going to be staying in lift longer, or am I off base with that statement?
All N52, N54, N53 cams have asymmetrical cam profiles, this was validated when I measured them. Even visually I can tell that they are asymmetrical, so I did not need to use any equipment to come to this conclusion. I'm 100% confident that the N55 cam is also assymetrical, based on the fact that 99+% of all cam profiles from all OEM since the late 90s are assymetrical.
The N52 and N53 exhaust cam has more duration than the N54 exhaust cam see post #162.
FYI, google "mikeseli cams" let me know if you have any other questions.
I look at the torque curve, no more peak, just carried out further. This is good!!
The one other thought is the drop off in power after 4800rpm on the stock cam N55 is due to valve float.
With the N52 cam and N55 rockers and the additional 0.3mm lift, that brings the valve spring closer to 'binding' and this decreases the harmonicsof the valve spring and this in and of itself will decrease/delay valve float another 5-800rpm and thus extend the power curve.