Porsche Enthusiasts Club Forum

I've been reading up as much as I can on engine mods etc while I plan what to do with my 2.5NA Lux - which I'm thoroughly enjoying for the most part. It's quick enough for the driving I do but how much of the 163BHP remains is anyone's guess - I'd like it back and a little more if possible.

So while I'm getting through all the list of little things that JMG pointed out in their excellent free inspection, I can't help but wonder why I would sell this 944 Lux for another bag of uncertainty to do this all over again. Yes I know that the Turbo seems to be everyone's holy grail and modifications to the 2.5NA are easily overlooked because of the availability of those 944's - but decent ones cost a fair whack more than I've got to play with and I certainly don't want a cash hole. I also like the idea of something different and I'm not really after masses of horsepower because I just wouldn't use it. In fact I just saw this week that the 944S 2.5 16v has 190BHP - that's the kind of gains I'm looking for from my humble NA.

This brings me to my latest discovery that some owners in the states are upping the displacement of the 2.5L 8v to 2.8L - I've yet to find what hp gains are had with that conversion and what it exactly entails besides crankshaft work. Has anyone done this or do you perhaps have a definitive explanation of this conversion?

What about fitting a 16v head in place of the 8v 2.5L - is that possible, and if so what's involved?

thanks!

The 2.8 conversion needs different rods so is not cheap. Personally it is probably better to convert to an S2 lump. S2 engines used to be big money but have now got cheaper & with an S2 loom & DME should be a fairly easy conversion & easy to maintain.

The S produces max HP and Torque well up the rev range, to get any noticable differnace between it and a lux, requires driving it like you stole it ! Below 4500 rpm I would say they are pretty much the same despite the S higher output figures. Assuming your engine is sound and hasn't lost too many horses over the years, you could do worse that trying one of Promax's chip's. They are only £100 and I believe they may accept sale or return if not happy (you would need to confirm with them). There was a recent thread on PCGB from a chap who tried one in his Lux.

My advice would be to get everything in tip top condition then chip the car. The promax chip made a world of difference to my lux, like night and day. Try that first. After that if you wan't a faster car, buy a faster car! Imo the lux engine when chipped is great, its smooth and torquey and more than fast enough to propel you swiftly around UK roads. Not too bad on the old juice either.

Agree with Jim that if you can find a fit S2 engine with a rotten body that would be the cheapest & easiest way to upgrade. You could also drop a fit turbo lump in complete. But the first thing to do if you want your 8v to go like it should is to pay for some dyno time & see where it is to start with. Your wasting money fitting chip sets in if you don't do this. My car would have suffered permanent damage had I done this. When your dealing with cars as old as this you just can't drop a chip in & fix it. It may go better as the chip will add fuel but it may also make the mixture rich enough to wash the oil off the bores! Chip sets can be good but should always be checked on the dyno!!! I gained 28hp at the wheels with one hours dyno time. Stock chip. The guy on the rollers has to know what hes doing though. I also know somebody who put an S2 lump into there lux & it made less power at the wheels than my 8v. It costs around £50 to check your fueling. Cheaper than a new engine. My car had a full service record from one of the specialists that some of you guys swear by & a 4.5K engine rebuild. It was still only putting 112 at the wheels when I got it.

Spot on. Hence my comment about sound engine and lost horses.

This is good stuff guys, thank you. With the long weekend coming up I'm planning on doing a full service (plugs, air filter, engine oil & filter) with new Dizzy & Rotor and tranny oil. It makes sense doing that before a chip. What other things will get it to tip top condition prior to a Dyno run?

@ J.J how much hp did you have after your 28hp gain? Are you back to the 163 stock or above it now?

You dont necessarily need dyno time, you could also fit a wideband sensor. This will let you analyse your own fuelling and decide if the car is running as it should.

Most of the benefit from re-map/chips to our engine will come from changing ignition advance. This means higher cylinder pressures and more chance of knock, so you want to make sure your not running too lean.

How much was your dyno time?

Like everyone else I think the 2.8 conversion is not worth it and an S2 or Turbo lump would be a much better choice. If your engine needs a rebuild then it might be worth uping the spec a bit to run a turbo. At least then you'd know exactly what condition everything is in. I think you've got to look into and decide what you want to end up with. You could waste alot of money refreshing your engine only to dump it later on for a different lump.

If you do increase the power significantly remember to do the brakes and suspension too.

But the sensor will not give to the years of experience of a good dyno operator

I don't think you need that level of expertise to determine if your AFR is OK. You need their expertise to get it tuned properly, but that is essentially what you are getting from a chip albeit for an engine similar to yours rather than identical.

Problem with mine wasn't the AFM! If you have the right software you can do it with a laptop on the road. So long as plod doesn't get you!
All engines are different. A chip set will work only if everything else is right. Very rarely on cars of this age will there be no other issues. It may only need an injector clean. A new FPR or damper. Is the fuel pressure correct? Will a wide band tell you this? I don't have anything against plug in chips but they have to be checked properly. Usually there used instead of a dyno session rather than in conjunction with one which in my experience will never get the best out of them.
Mine will go back on the dyno as soon as I get the race head bolted on. Along with the rebuilt gearbox & the new water pump. Just wondering if I can get a custom inlet manifold past the accountant. Need a couple of flanges machining then a bit of fabrication. Trouble is once you start where do you stop.........

A wideband will tell you if your fuel pressure is wrong as incorrect fuel pressure will mean that the DME is not injecting the ammount of fuel it thinks it is. This means the car will run either rich or lean. They are a good bit of kit to have in a car, they are really usefull for diagnosing running issues.

Clever bit of kit. But don't you need a lambda sensor? Surly the dyno is cheaper! Though I'd like one of those to mess with.

I emailed Clark of the famous & fabulous site bearing his name, as he'd done a 2.8L conversion on his 951, and this is what he had to say:

"Hi Steven,

Realistically, about the most you could expect out of upgrading to the 2.8L
is about 15 additional horsepower.

It's a much greater advantage on the Turbo because in addition to the
increase in displacement you also get a big increase in exhaust flow to the
turbocharger which provides for faster spool up and reaching and maintaining
the peak horsepower longer.

I honestly don't believe the bang for the buck you would get out of
increasing the displacement on a NA engine is worth the cash layout.

You could probably add a supercharger to your car for about the same price
as a displacement increase and get a much larger increase in horsepower.

Hope this helps.

Regards,
Clark"

Nice chap! 15hp gain is not worth it at all. Supercharge!