I have seen and read all the hype about a 248 degree cam swapped for the intake cam which is 240 degrees. Not only is this a small difference, people were installing at either 3 teeth or 4 teeth offset to compensate for the new cams locator pin being in a different location. Now for all of you who have read and discussed this to death, this isnt for you...keep moving.
I wanted to see how much of a difference it makes at 4 teeth vs 3 teeth vs degree'd properly. Tools used are a degree wheel. AEM stand alone ECU. Wideband O2 sensor. Accelerometer.
here is what I found. I did this to decide if it would be worth it for me or not.
At 4 teeth the cam is severely retarded. It is at 18 degrees passed where is should ideally be. The centerline was at 137 degrees BTDC. That gave a lobe seperation approximately 128 degrees. Way out of time. Car had much less efficiency up to 3100 rpms. It took up to 12% less fuel to this point. After this, the power seams similar and at about 5600rpms it peaks and drops very quickly. Retarding BOTH cams a reasonable amount will shift the power band higher. Moving ONE cam a huge amount just kills the engine and leaves such a small powerband it wouldnt have any applications I could think off.
At 3 teeth the cam is now 21.6 degrees advanced on the crank making the centerline at 97.4 degrees. This is again a seriously out of time camshaft placement. Overlap with the exhaust is too high for a short duration cam. Idle vacuum was at 12in. Up from 19 stock. Terrible high end power. Needed up to 14% less fuel above 4100rpms. No change in power between 1k and 2.5k. Possibly a slight amount more from 2500 to 3500. Again a very poor timing setup for a camshaft.
at 3.6 teeth, I placed the centerline at 121 intake and 118 exhaust. The idle is at 19in. This gives me an exhaust valve closing at the same event the intake valve opens. No overlap (ther is no overlap with stock cams either). There was up to 13% more fuel needed after 2500rpms. The most being between 4000 and redline. None to Slight loss of power at 1000 to 2000 rpms, it felt smoother and revved faster but I couldnt measure anything. Very slight increase from 2000 to about 2500. At 2500 rpms it was noticeable and measurable.
Best thing was the turbo now boosted faster and sooner. 7lbs at 2500rpms vs 7lbs at 3500rpms stock running in second gear. Brake boosting it reach 10lbs at 2700rpms vs 3200rpms. The 248 degree cam is still a mild cam. The 240 degree is definately pretty short and was imo more of a emissions decision than performance. Hence the 232s in the 96 and higher for OBDII. You will not lose much power down low with a mere 8 degrees in your cam, but with a proper degreeing you will gain more power from 2500rpms and up.
Sound was different at idle. Revs faster but in gear slightly slushy at 1000rpms. All this was done at 7 lbs of boost and I measured 15hp more peak. At 18psi I didnt get accurate measures due to wheel spins, but its response was leaps and bounds better than the stock setup.
Granted I adjusted BOTH cam timing but thats what you should always do.
To sum it up, cam swap with just counting 4 or 3 teeth retarded, is just that...retarded. Redrill it with a 1/4 in drill, make a hole exaclty 3.6 (or 3and a half) teeth counter clockwise and you will have a very nice cam combo that works in the ka243de. On the dyno software (desktop) you can see exactly what is going on. If you dont degree your new 248 cam your losing power over stock no matter how you slice up the rpm scale.
