My engine is in the workshop having new piston rings, head sealing rings, turbos and head overhauled. A leak down test revealed over 10% on most cylinders - approx 25000 miles since my last engine build, so it shows how these 500+ hp outputs wear the "consumables" pretty quickly. Interestingly, the engine still felt as powerful as ever on the road, I think the turbo engines will mask the leakage by using the boost to maintain the air mass required for the programmed power output.
I tentatively faxed RS Tuning to find out if they had any developements which I could use whilst the engine was stripped. Surprise surprise, I can spend some more money on new "Evo" turbos and cams and crate the motor back to Germany for remapping to give around 25hp more.
Whilst I was discussing this with my workshop, it transpired there was a 993 GT2 EVO 1 intercooler lurking about in the stores room. This I/C is the same thickness as the stock 993tt I/C but it has about 25% more surface area and utilises the pressure sensing type induction -I seem to remember the race cars giving 520hp with restrictors using this set up.
I am currently using a Cargraphic/FVD/TTP I/C which although bigger does not cool any better than stock.
I am waiting to hear from RS whether this GT2EVO1 I/C in conjunction with pressure sensing induction and their new turbos and cams is the way to go and how many wheelbarrows full of Euros they will want.

 

I have a question for you:

If the engine was running stong and your computer wasn't throwing any faults, why did you feel it was necessary to pull it apart. (I don't have a good handle on leak-down percentages and what they mean in actual functioning of the engine.)
I'm curious because I have a 500 HP TT and I'm interested in what kind of longevity I might expect. It's my daily driver and just turned 30k

Thanks,

Scott.

 

Scott
I'm sure others know more about these leakdown figures. but I believe more than 8% is out of tolerance. I think one of mine was 15%.
I wanted a modification done by a guy over here, Mike Tilson, which involves stripping the engine down up to heads off, so I asked for the leakdown test to sort of justify doing the tear down - a bit stupid I know, but I needed an excuse, just like I am trying to find an excuse to pay for another 50 horses.
As far as the longevity of your motor, I think it depends what sort of boost it is seeing. Remember for factory longevity, the stock 993tt ran 1.1 overboost maximum and around 0.7 bar at peak power.

 

Yup. It's amazing how quickly 500 gee-gee's seems normal.
"If enough is good and more is better, then too much should be just about right" anon.

 

I'm no expert, but I don't think 10% leakdown is panic stations - but like you said, you were looking for an excuse to tear it down....strength to your elbow (I expect you'll need it to lift your wallet )

 

TB993tt
Just had a leak down on my 993tt and one of the cylinders showed a 12% loss. MY motor has 8000 track miles, and lately seemed a little off against some modified tt. I agree with you that turbo motors mask some of the problems on the street. I visited Porsche Motorsports (PMS) to get advise and some answers and it seems no one I've spoken too, really knows what the leakdown numbers should be. PMS says rebuild the GT 2s every 45 hours. At that rate I'm on borrowed time. My shop says that the other cylinders are OK with the lowest being 4% and not too worry with one at 12%.
Next, I had my oil analysed to see if that would turn up anything. "We suspect the engine is OK"
Like you I'm probably going to tear the motor down
and it maybe its time for the 3.8 evo pistons and cylinder.
On a final note, the GT2 evo1 entercooler was something I considered when I built my engine, until PMS quoted me $12k US. I passed on that and went with the Andial cooler which has worked great. If anyone has factory data on leakdowns numbers, I'd like to know.

 

Jim
I think I have been innaccurate in describing the intercooler I am considering as GT2 EVO1 - From checking my Paul Frere book, the intercooler I am looking at is actually the origional GT2 racing intercooler not the EVO, this used the same inlet system as the EVO but was a "side to side" unit as opposed to the "back to front" design of the Secan EVO unit. The GT2 cars with this unit were rated at 465hp @ 5700 rpm using a max boost of 1.05 bar and restrictors 2 x 34.2mm. This is a way short of the GT2 EVO which was 600 @ 7200 rpm , 1.2 bar using 2 x 36.6mm restrictors. I am hoping that there is efficiency (read power) to be gained by the racing inlet system utilised by this type of I/C.
maybe its time for the 3.8 evo pistons and cylinder
The thought had crossed my mind also, if I am paying for a full engine power mapping session. There is a tt race engine next to mine in the workshop which is being built up with 3.8s with a target hp of 650+ (Secan I/C) and I avoided asking the price of those 3.8s

 

An update:
RS Tuning reckon that the GT2 race intercooler (pre Secan) will give no benefit compared to the stock one. Their turbo and cam package would yield a further 25 to 35 hp but at the expense of a slightly lumpy idle and a lot of Euros. I decided that the cost of 315 Euro per hp was too much and also I was worried about altering the nature of the engine - bigger turbos and more radical cams giving more lag and more "peaky" delivery.
Whilst in pieces (a depressing sight ) all tolerances have been checked. The rods are apparently out of shape and we are going to put in Carillo's to cope with the torque. Other "consumables" will be piston rings, timing chains, fully reconditioned heads, new flame rings, turbos reconditioned. I am also trying a clutch package by FVD which is a pressure plate rated at 980NM and a stock organic RS clutch disc. FVD say they have someone using this set up in a 900hp car, I previously used a sintered disc with torsion springing which held the torque but always made one feel wary of trips involving stop go traffic.

 

TB
I would be interested in your feed back on the FVD clutch package. I tried a semi-race disc with a GT2 prssure plate which was impossible on the street. Clutch Masters modifed a GT2 pressure plate with 20% more clamping force which has held up quite well for street and tack. It seem if your pulling over 750NM the clutch becomes a weak link.

 

Jim
I will let you know how this clutch package turns out.
I visited my engine again last friday and it is now ready for rebuild.
Those conrods were actually slightly bent, you could quite easily see this. I am assured the Carillos won't bend - they seem to be beautifully made, a bit nice to be hidden away inside. The surface of the barrels have been skimmed to remove some roughness caused by flame leakage. There is evidence of some subtle porting work in the intakes but the valves are stock size. The heads and barrels have a groove about 2mm wide to accept the new flame rings which are apparently to RS's own specs made in aluminium -they feel very light weight and flimsy, particularly when you think what their job is. Annoyingly the turbo pipes need renewing AGAIN -this is the 4th set I have gone through, they seem to perish around the top where they attach to the intercooler inlets. The turbos have been fully recond. and repainted like new.
with a bit of luck I may be back on the road this week end

 

TB,

Can you summarize the engine parts that were excessively worn? I understood the turbos, turbo pipes, connecting rods, piston rings, and barrel surfaces. Were their other items, like valve guides, valve seats, valves, chains, chain guides, pistons, cylinders, cams, etc? This information is very valuable to 993TT owners with engine mods.

Also, do you have the latest turbo pipes? Ruf uses the new factory part with the red reinforcement rubber on both ends. He also uses a special "smooth" clamp with screws on both ends (see photo).

<a href="http://boards.rennlist.com/upload/ruf9.JPG" target="_blank">http://boards.rennlist.com/upload/ruf9.JPG</a>

 

Bill
Thanks for the info on those Ruf fasteners. Yes I have got through 2 sets of the orange ended turbo pipes.
The parts which were most worn were the piston rings. The valve guides were replaced as part of the head recon. but I'm not sure how worn they were. The valves are the original ones but I don't know if they would have been reground as part of the recon. What was interesting was evidence of some subtle inlet porting work by RS. There was quite a bit of leakage around the head to barrel which is doubtless down to the big mid range boost. I am concerned about the conrods bending since the rods they fitted to the early 993tts (mine is May '95) were "special" in that they were weight matched and reinforced as used in the GT2 racers, so it makes me apprehensive about the later "production" rods, but again it is probably the boost which caused this problem.
The timing chains had stretched but the pistons,bores,cams were all to spec. Part of the rocker gear had broken (not sure what exactly and it can't have been crucial since the engine ran fine pre tear down) this maybe a result of the high rev limit (7100rpm with hydraulics) or just bad luck.
I feel that if you run over 1 bar boost and use the performance then you have to expect some degree of rebuild every 15 to 20,000 miles if you want to keep the motor in optimum fettle.