Roughly, what would the effects of this cam change be?

[WhatSpeedLimits]

I'm in the process of upgrading from cams with a duration of 268in/264ex to 272/272 and was wondering if by looking at the timing charts if anyone could give an idea of what they would expect to happen.

The cams are from the same manufaturer and same lift, just different durations. I made a pic of the charts overlayed so we could see the profile differences.

The intake cam (on the right) is hard to see since it is 'only' open 4 degrees longer (from 268 to 272) and appears to have the the time split evenly on both opening and closing (2 degrees each). It also appears to be mostly different in profile under 8mm of lift..after that the lines converge.

(yes I know it is hard to see at this size)

The exhaust cam on the other hand is gaining 8 degrees total (from 264 to 272) and it seems they put all of it on opening the exhaust sooner..with a little left after holding peak causing closing at a slower rate at first but ending up matching the 264 closing around the 6mm lift mark (from what my untrained eyes can see).

Overlap appears to be about 2 degrees more with the cause being earlier intake opening.

Here is the chart overlay-

http://i164.photobucket.com/albums/u26/powerdubs/CamTimingOverlay-1.jpg

Thanks

 

[Junior37c]

I'd expect:
reduced compression
less peak torque
a broader torqueband
peak torque will occur at higher RPM
reduced maximum cylinder pressure and therefor increased piston life.
better idle quality and vacuum.
increased NOx emissions

All that said, this isn't that big a shift so these changes will be minor.

Do you mind telling what the engine is? I'd like to be able to figure how well that lift will work. Just keep in mind too that an engine is a system, changing one part will affect the function of the other parts. Like your exhaust resonance tuning in this case.

 

[patprimmer]

Seeing as the inlet closes at virtually the same time, there will be no change to compression.

The exhaust opens earlier and therefore extracts a little less power at lower speeds, but reduces blow down pressure at higher speed. It might increase peak power and torque very slightly at slightly higher RPM.

Regards
Pat
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[WhatSpeedLimits]

The engine is a Volkswagen 3.2 24v VR6 although the cams will also fit the 2.8 24v VR6.

Here are the 3.2 head flow #'s that my porter gave to me.

http://i164.photobucket.com/albums/u26/powerdubs/R32FlowChart.jpg

These engines have responded really well to cams thus far. The 268in/264ex cam set gained power over the entire RPM vs the stock cams. The new 272/272 set are finally being produced due to demand by people wanting to see what else we can squeeze out of the engine.

 

[Junior37c]

No experience with that particular engine but looking at the bore/stroke I'd be inclined to go with a shorter duration, tighter lobe centers and more lift. your 25m/s limit comes at 7800rpm, at 13bar BMEP and expecting peak torque at ~6500 so that it can have a nice fat torque curve and continue to make power higher up, I'd be looking for ~320hp by the time you shut it down on the rev limit. by sacrificing powerband you might get as high as 365 reasonably.

 

[WhatSpeedLimits]

I wish cams with more lift was available but they are not. It took about 2 years to convince the cam makers to produce these.

More lift would require different springs and pistons. Most of the guys aren't willing to go that far so the company went with these as a drop-in option.

These engines are already seeing results around 320hp with a peak HP at 6600rpm on the 268/264 cams on the stock heads, stock intake manifolds and 2.5 exhaust.

In an attempt to compliment the 272/272 cams I am about to install I've had the cyl head ported. The car has 2 cats off the headers that combine into 1 exhaust. The size of these pipes and cats are 2 inch stock and I've upgraded them to 2.25 pipes and cats and installed a 2.75 catback exhaust in place of the stock 2.5.

The cam timing is variable on both cams and I have a tuner that can make changes to the timing for me.

Thanks