Chris White

The stock block is solid cast Alusil. Nikasil is a surface treatment used in 911 and other applications but not in 944 blocks.
Sleeving is a repair or modification where the damaged or worn Alusil block cylinder is bored larger and a sleeve is inserted to provide a new ‘wear surface’ The sleeve is then bored and honed to fit the piston.
If you want to keep the stock piston size on a worn/damaged engine then sleeving (either Alusil or steel) is the only option.
“resleeving’ would only be done on a sleeved block that was damages.

Chris White

Thom

Thanks.

I want to go oversize in a 3.0 block with fine cylinder walls but they obviously won't accept the pistons as they're 0.5 mm too large.
Will the cylinders have to be rebored then resleeved or will "only" reboring and honing the cylinders (without resleeving them) be enough for putting in said oversize pistons ?

Given that the block is cast Alusil I do not understand the need for resleeving cylinders if rebored cylinders will have the same surface finish as resleeved cylinders after honing is done.

Chris White

You just need to bore and hone to the 104.5mm size – make sure you use the Alusil compatible process.

The sleeving using Alusil sleeves is a repair process for damaged cylinders that won’t ‘clean up’ with over sized pistons.

Thom

Thanks Chris.

Markus951

Can't you control Variocam with something like this?

http://www.iraterides.com/sportcompa...&idRef=Froogle Apex-i

I mean full standalone is must anyway, but in case standalone cannot handle the variocam, could this do it?

It sounds really interesting how would Varicam will work on turbocharged configuration. Add individual throttle body's nice turbo etc..


Markus

Markus951

968 cam profiles are pretty mild, and its pretty similar on/off system on BMW's with vanos. In my ECU i have dual vanos contol so I can make a timing map for both in and exhaust cam. In porches case for intake cam only..

And if there is a desire for more power webcam sells profiles for S2/968 engines witch are designed to work with variocam!
http://www.webcamshafts.com/porsche-auto.html

Does anyone know, what's the story with stock valvesprings, are they ok for turbocharged application or not?

Markus

TurboCab

Controling the Variocam in the 968 is not as complex most people think. It is just a solenoid activated device. You can do it even manually with a switch, if you like. The important thing here is when to activate it, and under which operating conditions.

fast951

If anyone has a need to control the Variocam baed on RPM, Boost or whaterver we have the means to control it.

Cory9584

Im curious about how much it would cost me to sleeve my extra 2.5 block to 104mm? Would there be any downside to using a 2.5 vs 3.0 block or is it all the same once you put sleeves?

Chris White

Usual ‘kit’ price – 2.5 block sleeved, bored and honed to 104mm with new JE pistons, rings and wrist pins - $2750.

The 3.0 block is a little stronger, has windage holes between 1&2 and 3&4 cylinders and the sleeves in a 3.0 can go out to 106mm. The 3.0 block also has clearance for a 3.0 crank – the 2.5 does not.

Chris White

Markus951

Porsche VarioCam

VarioCam was designed primarily to increase torque and power through the rev range, a good side effect is that it also helps to reduce hydrocarbon emissions to a high degree in the 968's exhaust.

The VarioCam operates between 1500 and 5500rpm, and will vary the timing of the inlet camshaft in relation to the exhaust camshaft this has the effect of increasing the overlap and so increases torque.

At the appropriate time the engine management system will send a command to the VarioCam solenoid to move a control piston, oil pressure will then flood a cylindrical chamber and this applies pressure onto the cam chain tensioner, varying the timing.

This system can adjust the cam timing by as much as 15deg., which enhances the torque by up to an extra 6lb ft. When 5500rpm is reached and more bhp is needed rather than torque the system goes into reverse, this can then release an extra 5bhp.

Anyway, take this engine as an example..
Both have been presented here in this forum before.
Vids;
http://www.rescueforce.com.au/images/expose-car.avi
http://www.rescueforce.com.au/images/race-pi.wmv
+ link to some info about this car!
http://autospeed.drive.com.au/cms/A_1327/article.html

What kind of affect shorter rods can have to an engine like this? What affect it will have beside the squish area. The rods will see more stress but it has been done before..anyone?

What ive seen some stroker kits on run S2 crank + shorter rods and that combo works out pretty good!

There is one more great project with variocam:
http://65.61.16.109/forum/topic.asp?...91&whichpage=4

Markus951

hmm

If we are talking about stock bores, stock cilinders and shorter rods.. What kind of power this engine could take?

I mean when choosing a turbo this is what my thouhgts are:

let's say goal is 550hp @ crank with good low end.

GT30R with 1,06 Ar should be able to do it do to the reason that 968 engine is really efficent. The problem here is tht this turbo should be pushed as far as 1,8 bar to get that kind of power. But for everyday use its a bit too much boost and high heat for aluminium bores. It will do good low end spoolup etc. This turbo is quite dull under 1.3 bar - at least this is what I found out on 2.5 liter 8 valve engine.. If you want to make power with that turbo you'll have to push it far..

GT35R with 0,63 AR should be able to do it as well but with less boost. There is a danger for surge but I doupt it will happen do to efficent engine! But we are facing more backprssure here with high egt= danger to aluminium bores. But it would definitely be good compromise between spoolup and top-end.

with 0.82 AR what I think is the best choise. You are able to make 550hp with low boost (lets say 1.3-1,4 bar) It will have 0 backpressure, witch will keep the egt down. Variocam would help in the low end a bit and its good safe power with 1,3 bar boost and no backpressure...

Comments?

Duke

My calculations show surge with GT35R/0,63 ar on the 8v heads. Haven't tried it with the 16v.
That combo is quite often referred to as a bad/surge combo.

You have nothing to win with the 1.06 over the 0.86 ar on a GT30R.
The kind of boost you need to take advantage over the bigger ar would outflow the 30 compressor.

Tom M'Guinn

Also, the 3 liter blocks require that you modify the coolant port on a 951 head, or use a head designed for the block. Some 3 liter blocks also have piston squirters, not found in the 2.5.

Markus951

Seems that this shop here selles Rod + Piston combo for 968 engine with desired compress ratio! Does anyone have experience with this shop`?

http://www.importperformanceparts.ne...o_porsche.html

968 3.0 4 Any Pauter Rods ROSS Billet/Forged Pistons COMBO-10 $1459