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Discussion: Camshaft Tuning


Roland@pcmtec
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Here is a snippet of a response sent to someone enquiring about issues with their vehicle. The vehicle was an NA with unknown injectors and large camshafts, the user reported various drivability issues.

The response covers why installing known injectors is a must and also why you should only install camshafts that a workshop has recommended or previously tuned. If not you are expecting the tuner to do weeks of work in a few hours, the result is the cars drivability will suffer.

Quote

 

Firstly is the VCT system locked or still operational? If it’s still operational it is common for the steeper ramp rate and higher lift to cause the VCT actuators to fail to reach setpoint. This is especially true when the motor is hot and hence oil pressure is lower. We have heard of this causing the compression to drop so low the motor will not even start and it sounds like there is no compression at all (very fast start). Some of the bigger workshops have devised modifications to the VCT gear to make it work with big cams (by increasing the mechanical preload on the system). The alternative is to remove the VCT system, however this will kill your low end and midrange power.

Next one is injectors. If you have unknown injectors this makes the tuners job very difficult, especially if they cannot figure out what they are and have to scale the injector by trial and error. Given what a tune costs (~$800-1500) this means they have less than an hour to do this job, very challenging. If you have known injectors with known data their job is much easier and they will get much better results. Finally you may have high flowed injectors, these will often never flow correctly at idle and low load, in these instances you cannot fix the issue. This is why we recommend you use injectors that your tuner has previously tuned and recommends. This is usually the more expensive flowmatched injectors with known data.

Now the camshafts. Personally I would never put aftermarket cams in a vehicle unless it was an 800kw drag monster. They are very time consuming to tune and go backwards over the stock system in almost all places other than high rpm. If I was going to put camshafts in a vehicle I would install a high lift, moderate duration and no overlap camshaft. The reason being is the stock VCT system is very versatile, you can command huge overlap with the stock system (see the ghost cam videos on our forum and facebook page). On an NA you can command as much overlap as you want at high rpm which is going to net you gains.

Now if you still must have camshafts and the VCT preload is working (and the VCT still active) the next issue is tuning speed density. The big workshops who sell their own camshafts spend weeks of R&D developing the tune for these camshafts to get idle, return to idle, low load, cruise etc as close to factory as possible. This literally takes days to weeks of tuning to do. They can then use this tune as a base tune for each customer meaning for the $800-1500 you are paying you get a great tune.

If the tuner has no idea what cams are in the car, or has never tuned them before they have to somehow do 2 weeks of work in a few hours. The reality is unless they have done it many times before it is very challenging for them to get you a good tune in this time. The results can often be quite poor.

IMRC valve. To top it off on an NA vehicle they run a variable butterfly valve in the intake. This means the tuner now has double the maps to tune. This further increases the time requirement to tune the vehicle over say a turbo.

Personally I would re-evaluate why you need camshafts, if you do need them use a known camshaft that the tuner has previously tuned and has a base tune available for. Also ensure the VCT preload system has been modified to suit or removed/locked. If the camshaft is locked using our custom OS with map vs rpm makes the tuners job a lot easier as it makes it closer to a traditional 2D VE map you see in cars with no variable camshafts.

 

 

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