IcemanG17

Louie
Interesting theory on Porsche turning down the power on the GTS....looking back it makes perfect sense...in 1991 the 3.3 turbo was the top dog making only 315hp.....the turbo 3.6 of 1994 bumped to 355 or 360hp....so a 345hp GTS makes perfect sense. Which many GTS did not make...it seems mid 280whp is normal or around 335 crank hp.....but GT cams + exhaust really brings the GTS motor to life.....332whp is about 390crank hp...so 400 is just around the corner....too bad they didn't do it....it would have been SWEET! Just look at how it keeps making power at higher RPM's instead of dropping off....

Vilhuer

I know one case where 944 S2 cam gear was machined off the cam and made adjustable. It can't be removed from cam due to lobes being larger that hole in gear. Exact same thing could be done to any 4 valve 928 cam but its expensive and difficult job to do it right.

Dennis K

Thanks Louie. I've looked at that dynochart on your website quite a few times. I don't know how many times I've looked over the section about the oiling system mods.

So there are 18 teeth on the sprocket? I'll have to double check.

Thanks Adrian. At you've tried it. Too bad it didn't give any meaningful gains. It would have been a neat trick though . . .

928ntslow

Brian, that's the way I heard it...kinda. Porsche was phasing out the 928 and I think they discovered this in 92 about the time they had already "paid" for the GTS. Used up the parts they had to make the cars and kissed them goodbye. Bad marketing would have been to phase out your fastest, most powerful trend setting car , so you detune it (in the cams) and rewrite the story that it was the intention to bring the rear engine cars into the future all along.

Seems strange that the cams on a GTS aren't that fab. Makes you wonder about the oil issue too. It would be nice to know what actually happened in the board room in the early 90's!

IcemanG17

What any of us would give to be a fly on the wall in some of those meetings....

I still think if Porsche came out with a 5.0L 300+ hp 928 in 1978 when the 911 turbo was 265hp.....things would have been different.....

Then the V8 could have grown over the years to 6-6.5L like the strokers today with variocam to bump the top end power.....or turbos.......

Charles Parkinson

Hi all, Is there any consensus on the "best" cams to run in a GTS ie GT Inlet and Exhaust or GT Inlet GTS Exhaust etc. I do a few track days and sprints in my GTS and could do with as many extra horses as I can lay my hands on. I also assume that to get maximum benefit from any cam changes will need some shark tuner time. Cheers, Charles 93GTS, Sydney.

Louie928

Hi Charles,
I believe the GT cam set would be the best, but that's only because I have used them and they were noticeably better especially at the top end. I don't know how the US '85/'86 32v cams would be. Probably ok too since the consensus is that they work about like GT cams. Probably the least expensive improvement would be to replace the GTS exhaust cams with S4. GT exhaust cams should be better if you can't get the GT intakes cams too.

Dennis K

Mark - I was able to look at a camshaft and it does indeed have 19 teeth. So each tooth is ±18.95º (cam degrees).

Charles Parkinson

Thanks for the input Louie. Looks as if i should start looking for some GT Cams. I have not had the car dyno'd but will do so before changing cams (assuming I can find some). It will be an interesting exercise to see how they change the power delivery as the engine is particularly sweet between 5 and 6.5k rpm on the track with standard cams. Cheers, Charles in Sydney.

mark kibort

I was rounding. whats 1 degree among friends?

so, each tooth is near 38 crank degrees. sounds kind of radical for a test.

mk

mark kibort

85 cams are pretty darn close to the same. same lift and duration. the only difference is a slight timing difference with the intake cam, but its very slight..
the big difference is having to modify the 85-6 cams to fit the exhaust, driver side. (the mod we discussed in prior threads.)

I cant see any reason why the GTS exhaust cam would be better.

mk

Dennis K

You're exactly right. It's the 38 CRANK degrees that I overlooked. After talking to people more knowledgable than myself and thinking about it some more, the bottom line is that this was a bad idea and it ain't gonna work.

Louie928

Charles,
Do dyno the car as it is so you know what you have. As a suggestion before you do anything drastic (costly), set cam timing per the WSM and degree both intake and exhaust cams at cyl #1. Then you know what actual cam timing, lift, and duration you have. I'm not convinced that the WSM has the correct timing data. The GTS intake cam specs show the cam quite a bit retarded from what you'd think it should be. The lobe center is 127 deg where you'd think that 110 might be close. That was Dennis' point. The GT intake cam has lobe centers at 112.5 deg. The cams will advance about 2 to 3 degrees from cold to hot. The GT intake cams is right where you'd expect at ~110 deg hot while the GTS intake would be around 125 deg hot. That's quite advanced and I'm not sure I believe the specs. The GTS intake cam has about 8 degrees longer duration than the GT cam so should be good for higher revs. However the exhaust cam is odd too. It has 9 degrees less duration than the GT cam, and at 196 deg is about the same as an S4. However it's timing is advanced by 10 degrees compared to the S4. The GTS exhaust valve closes too early and that's why the S4 exhaust cam works better.

Using the WSM specs, the GTS cam set is very unusual. The lobe centers are very far apart. The intake cam has good duration and seems suited for high end performance although the timing is too retarded even for that. The exhaust cam has limited duration and timing severely biased toward smooth idle and low HC emissions with no overlap at all. That will kill the top end performance.

I'd suggest doing this. Have the exhaust cam re-ground for 10 deg more duration and 0.5 to 1mm mm more lift. Also, move the lobe centers 12 cam degrees retarded from stock. That will move the intake and exhaust lobe centers closer together. You'll need to cut into the base circle by a mm or so, but use lash caps if you need on the end of the valve stems. You'll need to fiddle around with overall cam timing to get the torque curve like you want, but that's easy with the Porkensioner tool.

Vilhuer

Ultimate solution for 32V cam problems might be closes than we think. See post #23 in below thread:
https://rennlist.com/forums/968-forum/370154-968-cam-vs-s2-cams.html

They are brand new from billets and not welded cams. I chose to do away with the chain drive and I built custom adjustable gears to drive each cam. Its still the same factory crank gear and exhaust cam gear tooth count but two smaller pullies between the two cams to drive them 1 to 1.

I can see two problems in this.

One is mentioned few messages later at message #27. Geting stock distributors to work would complicate things. One way around this could be to put second belt drive to rear end of the heads. This would also maybe buy some more room for larger gears.

Other thing is that heads are not designed to deal with pressure in frontmost bearing surface on intake side of the head and thus bearing surface is possibly too small. This can be dealt with head modifications but things get complicated quickly.

In any case I would look long and hard for setup like that if aim is to make high hp cams for 4 valve heads.

John Speake

Is there any alternative for the Devek B1 cams - I assume these are not available anymore ?