New Summit Pro Hemi Cams. I need advice on giving good phaser tuning instructions.
Hi fellas, it's Brian from Summit Racing. We have new 2009+ Hemi cams ready for release.
1.) 5.7 truck cams
2.) 6.4 truck cams
3.) Turbo Cams
4.) Supercharger cams
5.) Higher lift automotive naturally-aspirated cams with limited VVT
6.) "Big Guns" for pistons with valve reliefs in the 232 to 251 duration range
We're asking customers to bring you the cam cards with the four valve events and centerlines and doing our best to stress the importance of adjusting the phaser table BEFORE startup.
Here's where it's a little weird. I'm finding some manufacturers do their best to hide specs and I guess that's somewhat understandable. It's troublesome because it can result in a lot of bent exhaust valves if the phaser table isn't corrected prior to initial start. Comp, TSP and FRP do a good job with Duration, LSA and Advance. Those can *at least* be entered into the Summit Cam Timing Calculator to generate the Intake Opening, Intake Closing, Exhaust Opening and Exhaust Closing Valve Events. Some of the bigger cams are locked out with the intake open a few degrees btdc and the exhaust closing a few after and that's fine too. For those who will enable VVT, it's probably safer to never let exhaust closing go much further retarded mechanically than 0 ATDC to keep the exhaust valves from tagging the pistons.
I've gone through a lot of threads here where the valve events weren't thoroughly calculated prior to folks being given phaser advice. Two cams with seemingly the same duration and LSA can have drastically different events if cam advance is different.
Here is an example with the 6.4 Scat Pack Cam. 215/221 121 + 13. This converts to 0 I/O, 35.5 I/C, 64.5 E/O and -23.5 E/C. A little close on the intake but the phaser doesn't advance so that's fine. Even with a 14 degree phaser limiter, exhaust would never get closer than 9.5 btdc.
Here's one of our new cams though and I'll show you where it could cause trouble.
SUM-5723 5.7 TRUCK STG. 3 218 int. / 224 exh. 112.5 LSA, 3.5 ADV, -4 Overlap, 0 I/O, 38 I/C, 48 E/O, -4 E/C
This particular cam couldn't ever tag an intake valve BUT if a 14 degree phaser limiter alone is used with no phaser adjustment, the exhaust closing would be 10 ATDC and would likely crash.
I'm considering adding a note that states: "Hemi cam phasers start at full physical advance and retard from there. In general, this increases intake valve clearance and reduces exhaust clearance as the phaser retards. It is safest to set the exhaust closing point no later than TDC. If you see -8 degrees exhaust closing point on the cam card, you MUST limit total phaser travel to 8 degrees maximum before initial start to avoid catastrophic damage. Most cams will perform best with maximum advance from idle to peak torque and taper from there to redline. It is the engine builder's responsibility to check piston to valve clearance during the initial cam install to insure it matches the cam card value."
What are your guy's thoughts on this? I need to keep the message simple. As much as I wish everyone had your tuning abilities, that isn't the case and I try to keep our customers out of trouble. I also don't want customers putting these cams in and having them perform poorly due to loads of physical cam retard when they shouldn't have. I don't know if they understand they shouldn't run the engine AT ALL if the table hasn't been adjusted. Rather than trying to express it to them as a exhaust centerline difference (because they don't know the duration difference), it seems giving them a maximum value would always be safest if 138 is *always* the exhaust number.
Thank you for your help with this. If I've completely missed the ball on something or my knowledge of the phaser itself is incorrect, please let me know. It's very appreciated and we try to get these things right out of the gate! -Brian Nutter, Summit Racing R&D guy.
