944 Turbo - interference design

[mavebloke]

Hi, newbie here, please be gentle! I'm considering trading up from my Alfa 145 to either a 944S2 or a 944 Turbo. I read somewhere that the 944 Turbo isn't an interference design ie the valves can't contact the pistons if the cambelt fails, due to the lower compression ratio . Is this true? If so this may influence my turbo vs S2 dilemma. Any advice appreciated, ta!

[Pavlo]

No its not, the valves do hit the pistons. It is possible to convert it to non-interference though.
Thats why you should always make sure the t-belt was changed and the car was maintained when you buy the 944/951.
Rennlist forums are very nice about porsches, this is where i spend my time at. Within 30 min you will recieve at least 1 replie. And there has been a thread on there recently on converting to non-interference engine.

[mavebloke]

OK, thanks, I'll check out the rennlist forum

[carsonmx114]

how can you make a interference motor a non-interference motor? i would think you would have to make major changes and give up alot of power.

[pnoiSR20]

Hey im new to the ENTIRE Porsche thing. i was just wondering though......what are the specs for the 944 Turbo and what exactly is the difference between the Turbo and the S2?

Im sorry if i annoy any of u guys, im just new to the Porsche scene.

[Pavlo]

carson- the pistons need to be changed/modified so that when T-belt breaks the valves don't hit it.
pnoiSR20-Turbo is 2.5l turbo, using kkk k26 turbo charger, and turbo s uses k27/6 hybrid or k27 (not sure), it makes around 230 hp (227 i think) and the turbo s 247hp (not sure once again).
The S2 makes around 210 +- 10hp. It is a 3L NA motor.

[930guy]

Why not just change your cam belt when recommended and not worry about it?

[carsonmx114]

thanks for the info. i just figured anything you did to make more room in the combustion chamber would lower your compression ratio.

[930guy]

that is true but why would you want to lower your compression ratio? That means less power!

[mavebloke]

Yeah, I realise it lowers your compression ratio a bit, I originally asked because a non interference design makes cambelt condition less contentious when buying a second hand car. I'm not sure that small change in compression ratio makes that much difference in a turbocharged car anyway; don't you just shove the boost pressure up a smidge, so you end up getting the same mass of air into the cylinder? When you're off boost, you just have the throttle open a bit further for the same power.

[carsonmx114]

yes the lower the compression the higher the boost potential but i would agree with 930guy changing the pistons is alot more work than changing the timing belt. i'm not trying to be smart or anything but i got my first 944t in 92 and the one i've got now in 96, i've never had any valvetrain problems at all. don't let fear of timing belt trouble stop you from owning a great car. buy the car, buy a service manual, put on a new belt, enjoy the car and don't worry about it again for 60,000 miles.

[mavebloke]

Cool

[930guy]

On a regular 944 turbo-how are you going t "up the boost a smidge" with out spending all kinds of money on a boost controller?

[mavebloke]

Dunno... to be honest, my original question about interference design was just because I was trying to decide turbo vs S2, and that might have been a deciding factor. If I do get a turbo I will of course look after the cambelts. However, if someone goes to the trouble of changing the engine to non-interference, I would have thought that changing the boost a bit would have been simple by comparison; it's just a spring loaded wastegate isn't it? Do you need to go to the expense of a boost controller, or can you get slightly stiffer springs?

[930guy]

944 use a vacuum system to control the waste gate-the springs are not easily replaced.