Couldn't be happier with the VAC M20 turbo cam

[turbodan]

I decided it was time to stop being a pussy and turn the boost up. I've had a .8 bar spring in there since the initial install in this car and it was cracking open around 150 kpa. It felt quick since it'd been so long since I'd been running a lot of boost. I still need to check the torque on the head studs and valve clearances, so I settled for a 1 bar spring for now. Not a huge increase, but I was hoping it would be noticeable.

I quickly observed that second gear was again completely useless. It would hook up in second most of the time with the .8 bar spring. The 1 bar spring just lights the tires and hits the fuel cut. The ease with which it broke traction caught me by surprise. I started to get scared when it spooled in third. The car has dyno'd in the past at 384rwhp and its never had a problem hooking in third. This evening it was scrubbing the tires at 80 miles an hour. Not on spoolup but as boost built with increasing revs. The datalog shows this was occurring around 200 kpa. I've run 240+ kpa on the old motors and they're never come close to lighting the tires up in third. I was blown away.

Its only hitting 180 kpa when the wastegate cracks open, but apparently the 30 kpa difference brings the motor alive. The cam uses very little exhaust overlap in conjunction with increased intake duration and lift. It may need a certain amount of boost before it really starts working. Other than that all I did was unshroud the intake valves and increase the volume of the cool side of the combustion chamber. I doubt that had a significant effect other than improving resistance to detonation.

[T_C_D]

Sounds great. Who actually makes the cam?

[turbodan]

They're made by Catcams. Specs can be found here:

http://www.catcams.co.uk/acatalog/info_11.html

I didn't know what to think about the exhaust lobe design at first. I figure it works for small turbos with high backpressure by limiting reversion during overlap. For big turbos with more favorable intake/exhaust pressure ratios it keeps boost from blowing through the motor. The stock B25 cam does seem to become less efficient at higher boost pressures.

[Nebraska_e28]

I need to get accustomed to speaking in the kpa lingo.

[europartconnect]

Thanks for the info

[Shadow]

Dyno soon?

[Jeremy]

Any notable difference off boost? Idle or general cruise differences?

[turbodan]

Very little difference off boost. It feels stronger with very little boost, for example when rolling onto the throttle below the boost threshold. Makes the motor feel torquey.

I may dyno soon. I'm going to adjust the valves this weekend and retorque the head studs. If I'm feeling lucky maybe I'll toss the 1.4 bar spring set back in. That would be ridiculous.

[Xenocide]

How's the idle? Any more lumpy? Stock flywheel I assume?

[turbodan]

Stock B25 flywheel. Idles fine. Possibly smoother than stock. They dialed out almost all of the overlap, so as far as idle quality and emissions its probably better than stock.