Jim M.

A friend and I (both 93 GTS's) are considering the installation of 968 intake valves and S3 cams in our GTS's.

The questions of the day are:
1. Do the stock pistons need to be notched to accomadate the larger valves?
2. What about the increased lift and duration of the S3 cams? Will that force deeper notching even with stock valves?
3. If the pistons are notched will they need to be re-balanced?
4. If notching is necessary then we will also need new rods. Both engines have the weak, non-reusable 1-L rods. So this becomes a very slippery slope very quickly.

Any BTDT's out there please chime in! Your input is appreciated.

sidehatch

Sounds cool but i would get nervouse playing around with all that.

RyanPerrella

Jim,

I am no expert here but think i can handle this one

No the pistons dont need any modifications, only the heads and their seats.

The S3 cams do need to be modified but i dont know specifically how, I do know they are apparently the same as GT cams but they are longer physically so must be cut down or something like that.

I know Roger was talking about replacing rods in his car which he will keep at 5.4L. I would replace those i guess. Please do tell, what rod manufacturer your using and what those were going to run.

And it was a pleasure to meet you at Sharktoberfest last month

Cheers

Imo000

Same happens when you tie your shoes, right?

Vilhuer

Maybe as stock versions are meant for 2mm smaller valves. But its just 1mm difference so it should be fairly easy to remove even by rounding sharp corners away with Dremel. I had exhaust side of 968 pistons done to 39mm also as they have unequal size notches from the factory unlike 928 pistons and on drivers side of the V8 exhaust notch is on intake side and wise versa.

As piston notches are basically same for S4, GT and GTS I think same depth is ok for S3 cams also.

Never heard anyone balancing pistons. How would it be done even? If enough material is removed from them crank could need to be balanced but small largening of notches should not affect weight that much.

Porsche says whenever rod nuts are opened 1R rods should be replaced with 2R. I'm sure many have reused 1R without problems. Depends on use I quess. New rod nuts and bearings are good idea obviously.

RyanPerrella

I wonder what Sunset charges for the Set of 2R rods

I wouldn't be surprised it they were really damn cheap honestly, Of course they could be damn expensive too. Maybe someone should call and see before just assuming they would be like a billion dollars per rod cause zee come from zee factory

byrdman454

Kibort mentioned this a while back in an old thread about modifying S3 cams...

the mods, as was mentioned is $400 by elgin cams. one bearing surface is lengthened to fit the S4 heads. (exhaust cam on the driver side is the only change, plus the ends are cut off, due to no bearing surface at the firewall side needed in the S4 heads)

Vilhuer

https://www.928gt.com/p-24047-92810300804.aspx

$175 x 8 = $1400. This gets right into custom rod $ territory. Add few $ and all of the sudden its stroker money. Just need crank, pistons and block and that it.

RyanPerrella

no offense, but if thats what they charge, then i imagine Sunset is half that

I am going to call now that i have the PN

UPDATE: $131.10 per rod x 8 = $1050

Not to bad honestly, considering thats all that has to be replaced. sure custom rods are almost that price, but you spend a fortune on everything else. For a simple rod swap in the early GTS's, thats not too bad.

There are 850 plus rods available in Germany too

Jim bailey - 928 International

So enough "spare" rods to do 106 GTS engines....

Jim M.

Thanks Erkka, sometimes we can't see the forest for the trees. Your advise is always dead on.

RyanPerrella

yes, sounds like they prepared for a recall that never came or something huh?

That did sound like a HUGE number to have in stock for a 15 year old car.

BC

One of the front bearing surfaces on the S3 cams must be lengthened. All cams then must be cut off at the back (I guess you don't NEED to do it, but we do).

Even S3 cams with more lift than stock do not need deeper flycuts. But the width may need to change as mentioned.

andy-gts

I think I recall Mike Simard of Simard tools doing a small batch of billet cams...never heard much from him except I want a set!... may be he will chime in and give us an update!
andy

IcemanG17

This is the ideal solution......but pricey at about $3k a set!! Plus whatever it costs to get them ground and heat treated

In general GTS motors have incredibly mild cams.....and respond VERY well to GT cams..... Around 330+ whp with just the cams.....

With 85-86 cams modified to fit would be similar....of course having those reground by elgin would be a monster....maybe 400whp?