928ntslow

So Marc, are you saying that a cam swap alone is not going to provide anything of worth?

Tom. M

what interests me is the combo of GTS intake and S4 Exhaust..or is it the other way around.....supposedly this is the combo to have. We will be testing this combo ..and others at some point up here....Adam B is currently running a set of GTS cams in his essentially stock S4...once that get dynoed....he'll swap out one of the cams for a S4 cam..and retest... and likely run a combo in his "big" motor too....we'll see....

No hype...just numbers....

later,
Tom
midlman@rennlist.net
89GT

Lagavulin

That would be very informative!

The GTS intake does have the most duration of the 4v cams. However, the 85-86 and GT exhaust are the same spec-wise, and are bigger than the S4 exhaust. But we all know by now that the 85-86 driver-side exhaust will not fit without mods.

So the 'best' combo based upon longest duration numbers alone would be the GTS intake and GT exhaust. On a 5L S4 engine, that big GTS intake which holds the intake valve open much longer (..25 crank degrees vs. the S4's) will bleed cylinder pressure and should noticeably cut down low-end power production, but should give more top-end. On a bigger motor, I would think that the lost low-end power would be desireable since it is now moved on top where there is more hook-up.

With that said, installing the GTS intake would be a 'cheap' way to lower one's dynamic compression ratio for a blower motor without having to pull it apart (..I have a thread on that subject somewhere).

It is interesting to note that the GTS cam specs are nearly identical to the 996's, but the 996 does use 'VarioCam' to advance the intake timing to 'get back' the lost bottom end, smoother idle, emission-friendlier, etc, and retards it back to take advantage of the healthy top-end the timing provides (..overly simplified, I know).

That will be great!

Fastest928

Keith,
GTS to GT cam swap is a quite a good boost in top end...but you may not gain any mid range torque, but not lose any either..although it will feel like a loss while driving.

It is a good simple gain, coupled with other mods, makes quite a difference!

Plus all the reliability of stock....

Happy Turkey day!

Marc
DEVEK

atb

Tom wrote:

Definitely need to just get this done. I've got the feeling I'm going to probably have to dyno the GTS cams twice. The car has lost a significant amount of bottom end with the cam swap (I don't think the 5L has enough static compression to make the cams work). After dynoing the GTS cams, but before swapping in the S4 exhaust, I'm planning on double checking the cam timing. The new cams went in at the same time Tom and I did a t-belt/H20 pump change on the car, so the cams are probably off-time a little bit. If they are off I'll retime them and get the car dynoed once again. Need to make this a priority, I'll try to get the first dyno run done in the next couple of weeks.

Dubai 94GTS

I second Doug Hillary. Pitting occurs when both moving surfaces weld (micro-scale) than move away ripping of the surface. This will occur because the surface temp is very high (dis-coloring will occur; blue) or the surface pressure is very high.
I think a good lube that has a strong surface tension and high visc can reduce or eliminate the phenomena; otherwise it is a serious design problem. Pls correct me if I am wrong; synthetic oils do not have more surface tension than mineral oil; they just last longer because they are more thermally stable and hold their characteristic better at extreme tempr.