the "newer" style cam

[running_cold924]

is it worth changing to? since the 951s use the pre-86 cams, would the newer cam help give any more power? being 3 degrees more advanced? and this would be a drop in cam as well being it is still a stock cam.

pros/cons?

[running_cold924]

other question....would I need a different chip then?

[nize]

specifically what cam are you talking about?

[running_cold924]

just the later style cam(after 86) when they gave the stock 944 a little more juice, they also changed camshaft profile to slightly more agressive( advanced timing) all the 951s use the cam before the cam mentioned above(from 84-85.5)

[landrover88]

well after riding in your 951 last weekend I don't know why you want it to be faster.

I thought your ride was Super quick.I had to kick my N/A in the A** the whole way home.

Dave

[kdjones2000]

About the only difference I have heard between the later NA cams and the stock 951 one is that the NA has slightly longer duration. I have heard nothing about it being with more advance.

Several people have put the NA cam into their 951's for this reason, although I have no first hand knowledge of how much benefit it gives.

Hope it helps a bit...

Keith

[running_cold924]

thanks dave!!! sorry you had to beat your n/a.....

kd- thats all I could find about what I wanted to do. its just that no-one has had any real claim as to whether it make a difference or not. I guess it is duration, not so much advance then. just trying to see if anyone else had any proof.

[wild man]

I haven't looked at any of the specs for either cam, but does the the late N/A one have any "overlap" due to it's longer duration? If it does, then THAT is the reason it is NOT a recommended upgrade for the turbo.

[running_cold924]

well, like I said, I just was wondering if anyone on here has done this swap...I saw a page with cam durations(comparisons) done between the 2...I will see if I can find it.

[robm-951]

I have a late cam in mine. IMHO, I think it does provide a very small increase. I don't think it's worth a lot of effort or money. I don't think I would bother unless you needed to do cam tower seals.

[running_cold924]

thanks, thats just the kind of answer i was looking for.

[wild man]

Since I got no answer to my question regarding overlap, I'm going to have to assume no. It doesn't sound like there is very much difference between the 2. But now I'm curious why I haven't seen any other threads regarding 951 cam upgrades. I understand it is difficult to squeeze any more performance out of a turbocharged engine via a "better" cam, but are there any aftermarket options available for this part (for street use)?

[333pg333]

http://members.rennlist.org/951_racerx/
This should give you a bit of info that you're after. I believe from what they say, that the n/a cam gives you longer duration but not by enough to warrant going through the expense of doing this mod just for the sake of it. Going up to a properly specified larger cam will be noticeable but you may have to upgrade other parts as well.

[running_cold924]

YES!!! that's the page I was looking for! I could not find it for the life of me, thanks 333pg333!
just click camshaft diagrams on the left and it shows you the cam comparisons.

[wild man]

Thanks for providing the link. I see that the exhaust opens 4 degrees sooner, and closes 4 degrees later on the late camshaft, upping it's duration from 220 to 228 degrees. The early one is 4 degrees away from having any overlap, which would be undesirable in a forced-induction engine. The late one is 0 degrees away, which is as close as you can get, but still acceptable. What doesn't make sense to me, is why the early one closes the exhaust at 3 degrees BTDC, and why they chose to use that one on the turbos. Everything tells me that the late one would be the better choice. At the very least, I think that it would spool the turbo faster and sooner. Does it have to do with emissions, maybe? I have a complete cam tower assembly in my cellar, but I don't know, off hand, which cam it has in it. Is it possible to tell, without pulling it out? If it is the late one, I would not be above swapping it into the 951 at some point in time. There is no doubt in my mind that it IS the better camshaft to use, for both the N/A , AND the turbo. But could swapping cams cause my lifters to go south?

[wild man]

Now that I've had a few hours to think about it, I've come up with what I believe is a plausible explanation of why they did not use the late camshaft in the turbo cars, which, by definition, ARE late cars. I believe that closing of the exhaust valve before the piston reaches TDC is a way to achieve a form of emission control known as EGR (exhaust gas recirculation). By allowing some of the now inert exhaust gas to "dilute" the incoming air/fuel mixture, combustion temps and EGT's are lowered, thereby reducing the NOx (oxides of nitrogen) levels that are emitted from the tailpipe. But what lower EGT's also means, is that there is less chance of suffering from the dreaded "collapsed exhaust pipe" syndrome. But this syndrome is far more likely to occur in tracked cars, where boost is on for extended periods of time. For this reason, I would recommend AGAINST running a late cam in a car that is raced. But for a car that only sees street use, the late cam appears to be a viable option.

That said, the question becomes, how much difference does the extra 8 degrees of exhaust duration make? I would love to see a dyno chart comparing the 2 cams in a turbo car, with all else being equal. I think there is also a possible improvement that won't show up on a dyno chart. And that would be improved low-end to mid-range throttle response. But it may show up on the chart as higher torque in the low to mid ranges (if there even is any improvement, in that regard). Does anyone know if any sort of performance comparison has been made between the cams, in a car running, say, 15 or more psi of boost?

[running_cold924]

i'd love to see that as well, that's the whole reason i made this post

[wild man]

Well, I know that the difference in a turbo, where the mixture is under pressure right at the valve, waiting to flow in, would be far less dramatic than it would be in a N/A, where the mixture has to be drawn through the valve by the piston.

But my curiosity now does the better of me on this. So IF the spare cam that I have IS a late one, I've got no problem playing the role of the guinnea pig, to see if it "feels" any different. But it's not likely that there will be any dyno comparisons. Best hope for number comparison would probably be stopwatch timings for 60-100 runs (3rd gear, kicking boost in at around 50).

The only issue I have concerns about, is premature lifter wear, since they will no longer be mated, once the other cam goes in.

[running_cold924]

yes, true. the other cam box you have, no lifters in it?

[nize]

Originally Posted by wild man

But it's not likely that there will be any dyno comparisons. Best hope for number comparison would probably be stopwatch timings for 60-100 runs (3rd gear, kicking boost in at around 50).

wild man; this test will be a waste of time without before/after dyno comparisons.

you'd also want to monitor a/f to see what the changes are (if any).