3.? Liter 16 Valve Turbo Thread
09-20-2007, 04:52 PM
#121
Actually there are hp/tq gains because you can tune the intake to exhaust timing – less overlap is better for a turbo engine.
The challenge is that you have to come up with special cam and crank gears. The stock cam gear is too large a diameter to have two of them side by side. If you change the cam gear diameter you have to change the crank gear to keep the same drive ratios.
The other challenge is that the second cam gear will hit the hood if you leave everything else stock. Also – no belt covers unless you want to fabricate some.
Even with all that - in my opinion, if you to put together the best set up then that is the way to go.
The challenge is that you have to come up with special cam and crank gears. The stock cam gear is too large a diameter to have two of them side by side. If you change the cam gear diameter you have to change the crank gear to keep the same drive ratios.
The other challenge is that the second cam gear will hit the hood if you leave everything else stock. Also – no belt covers unless you want to fabricate some.
Even with all that - in my opinion, if you to put together the best set up then that is the way to go.
09-20-2007, 05:58 PM
#122
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you need the gears (cam and crank) an the belt as a matched set.
If you look up Rolex's thread there are some pics from last spring....
If you look up Rolex's thread there are some pics from last spring....
09-22-2007, 08:35 PM
#123
Drifting
I know the cam gears and crank gear must be replaced with some 'one-off' units, but can't you use an exhaust cam for the intake side as well?
I would like to try a twin-gear setup some time in my life on an S2/968, but didn't know how smart of an idea it would be. So how is everyone running twin gears if they hit the hood? I would imagine they are building a rasied hood, but I haven't seen any shots of it.
What kind of gains can be had from going to this setup on a turbo 16v (theoretically speaking)?
I would like to try a twin-gear setup some time in my life on an S2/968, but didn't know how smart of an idea it would be. So how is everyone running twin gears if they hit the hood? I would imagine they are building a rasied hood, but I haven't seen any shots of it.
What kind of gains can be had from going to this setup on a turbo 16v (theoretically speaking)?
09-23-2007, 12:52 AM
#124
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i don't think twin belt gear is the answer use just one on the exhaust and then shim the chain tensioner up to change inlet timing . yeh it will take you longer but how long does one spend on the 3 replacement ones? and you realy wont be forever changing the timing .
But on the positive using a timing belt set up from a 2lt twin cam will result in a slower water pump wich may be good on the track .i will go electric water pump so its not for me
But on the positive using a timing belt set up from a 2lt twin cam will result in a slower water pump wich may be good on the track .i will go electric water pump so its not for me
09-23-2007, 01:03 AM
#125
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I know the cam gears and crank gear must be replaced with some 'one-off' units, but can't you use an exhaust cam for the intake side as well?
I would like to try a twin-gear setup some time in my life on an S2/968, but didn't know how smart of an idea it would be. So how is everyone running twin gears if they hit the hood? I would imagine they are building a rasied hood, but I haven't seen any shots of it.
What kind of gains can be had from going to this setup on a turbo 16v (theoretically speaking)?
I would like to try a twin-gear setup some time in my life on an S2/968, but didn't know how smart of an idea it would be. So how is everyone running twin gears if they hit the hood? I would imagine they are building a rasied hood, but I haven't seen any shots of it.
What kind of gains can be had from going to this setup on a turbo 16v (theoretically speaking)?
09-23-2007, 01:43 AM
#126
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The timing chain is not a weak link. Not maintaining the pads on the tensioner is the weak link. Its easy, maintain the car and it will go forever.
The only reason for twin cam gears is for using two custom cams (one intake, one exhaust cam) and timing them properly.
09-23-2007, 03:07 AM
#127
Drifting
Yea, but correct me if I'm wrong, the specs on the exhaust cam are different, so it would technically be a "custom" intake cam. I haven't ever seen a true custom intake cam for my car that has a mount for the second cam gear; the demand simply isn't even close to needing to bother with it.
The chain isn't a weak link, which is true...but the whole system together adds up to be weak. Anything can happen with those parts. I'd rather break a belt and bend some valves, then break a pad/tensioner/pipeline/chain and ruin the whole head completely.
The chain isn't a weak link, which is true...but the whole system together adds up to be weak. Anything can happen with those parts. I'd rather break a belt and bend some valves, then break a pad/tensioner/pipeline/chain and ruin the whole head completely.
09-23-2007, 08:13 AM
#128
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not impossible to go twin cam gears the 2 cam gears and crank drive gear are smaller than standard 944 (full set of 3 from a 2lt jap) the water pump pully stays the same size therefor the drive ratio of crank to water pump .
I believe the cams are both very similar you can see by looking that the lobes are symmetrical which is often a problem in other things
I believe the cams are both very similar you can see by looking that the lobes are symmetrical which is often a problem in other things
09-23-2007, 11:40 AM
#129
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not impossible to go twin cam gears the 2 cam gears and crank drive gear are smaller than standard 944 (full set of 3 from a 2lt jap) the water pump pully stays the same size therefor the drive ratio of crank to water pump .
I believe the cams are both very similar you can see by looking that the lobes are symmetrical which is often a problem in other things
I believe the cams are both very similar you can see by looking that the lobes are symmetrical which is often a problem in other things
The issue with using Japanese pullies is, You better know what works and stop bench racing. There is a point where the crank pulley gets to small and you WILL skip the belt! I have heard from people who tried this and they have bent valves experimenting with different sizes. IMHO, Its not the best way to do a twin gear setup. As far as cam profiles go, both the exhaust and the intake cams on the 16v heads are tiny and have no lift what so ever. The only way to make a real cam is to grind one from new billet or weld and grind an existing cam.
09-23-2007, 02:49 PM
#130
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09-23-2007, 04:02 PM
#131
I know a N/A 3,0 S2 which has a 944 S exhaust cam installed. Owner says it's a better exhaust cam than S2's original one. How about 3.0 turbo engine with 16V head, would a S-cam be a good alternative also with charged 16V engines?
10-02-2007, 01:23 PM
#132
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i gave up thinking about cams as you cant get solid numbers i will graph my own but i feel i've got better ways to spend my time and money . i don't think cam tinkering is as cost effective on the 16 valves i will start with timing them .
10-02-2007, 01:34 PM
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The reason why you can't get solid numbers is because nobody has made any and posted results. There are a few people I know that have had decent success with regrinding them but the problem with the stock cams are, there is not enough lobe to get a decent amount of lift.
10-02-2007, 02:19 PM
#134
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hmmm but only looking for 500 hp with a good flowing head do you think it is worth spending 1000 on a set of custom welded cams ? i would only realy want the big mid range that a 8v has the 16v seems to flow aple at 7000 rpm even with its tiny cams . I will give it more thought after i graph my cams and see exactly what they are . I'm kind of against putting something together with less than 230 degrees advertised .
I would lash out and spend up if i were confident of seeing an extra 50flb acrosss a 3000 band
I would lash out and spend up if i were confident of seeing an extra 50flb acrosss a 3000 band
10-02-2007, 02:54 PM
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