Cam choice question
 

I wanted a little bit more out of my 3.6 so we set out to build a new motor.

Which cam would you chose to put in this engine

These are the specs:

-993 core
-3.9 CMW P&C
-CNC ported heads (45mm)
-Carrillo rods
-52mm intake valves
-43mm exh valves
-Chromolly drilled retainers
-CMW springs
-Jenvey ITBs 51mm tapered 45mm
-MOTEC M600 ECU


IMP CONSIDERATIONS

The engine will go in a street car.

The decision to go with ITBs was based on the goal of acheiving
maximum throttle response.

Torque is also an important factor as the car is NOT a race car.

Peak power was never assumed to be one of the most important criteria for the decisions taken.


In North Carolina we need to pass emissions so that limits the choice of cam (even though I think we can play around with Motec to get a very very lean mapping just for the emission test)

My engine builder is suggesting the following cam:

DC-22



What is your opinion? some fellow pelicans think that it is too mild and with the ITB and the 3.9L displacement I could go much wilder.
Again this is a street motor.

This is a table of DC-22 cams relative to other Porsche and custom cams.

http://www.drcamshafts.com/911profilesprint.htm

I really value your opinions as I am certainly not an expert!

Thanks for our help

Have you read through this thread yet?

John

great read! fantastic...

So according to those equations the DC-22 would give me

Max torque @ 5,100 rpm
Max HP @ 6,700 rpm

Moving to the DC-24 would leave the Max torque at same level (same duration I valve) but move the peak HP further out @ 7,200 rpm.

Am I correct in implying that the DC-24 will give me a slightly flatter torque curve than DC-22 (torque dropping less fast than rpm increase)?

Assuming the overlap between the 2 cams is the same wouldn't the DC-24 be a beter cam?

I'd talk to Camgrinder directly about that question if I were you. It looks like the DC24 has some more exhaust duration and most likely as a result can't be ground onto a 3.0 or a 3.2 CIS cam. In order to fit that extra exhaust duration he may have had to increase the overlap. You'll only know by looking a the specific opening/closing data and graph for the cam. This is the type of detailed question that goes beyond the Cam Selection piece and really should be discussed with Camgrinder.

The DC22 cam has the same intake profile as the DC24, but a smaller exhaust profile. Adding exhaust duration moves the torque peak up. It also increases the overlap. Since mid range performance and passing emissions are a priority, I would stick with the DC22.

Very lean mapping leads to higher NOX numbers. Does your states emission test include a NOX test?

this is what the emission test consists of:


"The Pass/Fail determination is made based on a comparison of the HC and CO readings against the idle emissions standards for that particular vehicle.
The analyzer will test and disapprove a vehicle when the CO or HC reading is higher than the standards in the following charts: "

1981-later CO=1.2 HC=220

Do u think I can pass it?

Matteo:

In NC, as of Jan 1 2006, you only have to go through the safety inspection, not the emissions inspection.

According to the local DMV guy, who told me I could register my race car after Jan 1, as long as it passed the safety exam.

Brian

F'n almost wish I was back in NC again....

Wow.. that's great news... so Brian did u register your race car yet?