Power retrictions in the N/A cars

[Alexw]

I've been wondering for a few days what exactly is the problem/restriction from getting more power from the N/A's and fancy a proper discussion on it. I've seen posts often about getting more power out of these cars but its always difficult/expensive/impossible without forced induction. Is it the intake manifold? head design/flow? Exhaust system? "ECU"? Valves/springs?
What are the limitations that stop people from getting more power from these things and how can they be over come? Or is it a combination of everything? For instance would it be possible to get 100bhp/litre out of them, or would that require almost everything to be changed?

 

[Riverside]

In a word, breathing. When Porsche went to get more power out of the 2.5 they made a 4v head & produced the 944S.

At it's most basic a 4v head will allow two small valves to open & close more quickly, so the cam profile can have a longer duration or the engine can rev higher before piston & valve meet without having to fit (power sapping) stronger valve springs.

If I were going to try to get more power from a 2.5NA I'd start with the head. IMO the induction and exhaust systems are very well designed but I'd match the inlet & exhaust manifolds to the head (porting), and generally try to smooth & speed up the airflow, and map the ECU to suit.

The biggest problem you'll face is that, unlike a pinto or A-series, there are not thousands of cheap motors knocking around in old bangers ready to experiment on so the knowledge & experience of tuning these engines is only held by specialists. There's also not that much demand because more powerful versions of the motor are available for relatively little extra cost compared to tuning.

To get a headline figure like 100bhp/lt you'll need to compromise on bottom end power & probably make it slower in the real world. It's an oversquare engine so has potential but the large bore size & stroke will count against it - afaik you need something like 250-500cc per cylinder to get close to 100bhp/lt and still have useful torque lower down, our oversquare big fours are better suited to giving a smooth delivery, which is exactly what they do already []

Good luck, I wish more people would actually try this stuff rather than just saying it can't be done []

 

[Alexw]

Thanks for the great reply! That seems to be the thing said when people ask about increasing the bhp - buy a turbo and mod it!

It doesn't help the price of the cars being so low, for the price of tuning a N/A you could buy a turbo...

 

[944 man]

The head is quite nice: there isnt a deal that you can do to improve it. The restriction is in the inlet tract and particularly the intake and exhaust manifolds. If you remove the AFM and run a MAP sensor, then match the inlet manifold to the head and port the exhaust manifold too, then you should see quite an improvement (after youve maped it, obviously!).

Simon

 

[Neil Haughey]

There was a thread over on PH about supercharging the 968 that I took part in. The long and short of it was that a few simple calculations showed that volumetric efficiency of the 968 engine is actually not much away from the best modern engines. ISTR actually better then the Honda VTEC unit in the S2000. The problem is that compared to the most potent modern engines it runs out of puff too early to produce big HP numbers, same for the S2 engine only more pronounced. Now this is where the problems start as in the last 10 years I have never heard of anyone managing to 'open' up these motors successfully. ISTR Ninemeister tried an individual throttle body set up but couldn't get enough flow from the head. Would probably need material adding back in to the ports to give a more curved inlet path thus improving port velocity, flow allround the valve and high rpm power. This is something I remember reading about motorbike engine tuners doing as they often had the same situation whereby the engine is canted over and the inlet path has to bend round a long way in a short space. Calling Baz Hartech....

 

[morris944s2john]

I would think if your car is feeling a little down on power and it has done a fair few miles, then an overhaul may be in order to bring the power back up.

First step is to put the car on a rolling road and see how many horses it still has left in addition to the one on the bonnet badge.

Then, decoke the head, inspect and grind in the valves, maybe new piston rings. Basically an overhaul on the engine, fuel and ignition systems.

 

[Porka944s]

I posted nigh on exactly the same post as this a few weeks ago, and agreed first port of call was the dyno, 171.9 of the on paper 190 left, 96k on the clock and apparantly its chipped. I am not sure what to do. sell my car for 3k if market allows, find 3k and buy a turbo, bearing in mind i havent got 3k, or keep the car i love and have spent on, try find the 18.1 missing horses and try get a slight gain, in reality its plent quick for 170BHP infact it feels alot faster.

 

[944 man]

With an S it may be as simple as cam timing.

 

[Alexw]

Thats something else I thought about, having the cams reground to be a bit more aggressive. I know very little about cam timing though, if having a different profile cut wouldn't you have to adjust the ignition timing to actualy make it work? Would you delay it slightly as I assume you would leave the valves open longer?

 

[ChasR]

ORIGINAL: 944 man

With an S it may be as simple as cam timing.

This is exactly what my local specialist said about the 16v engines, reckoning it can cost as much as 15BHP. I know that on the Rover K Series engines, adjusting the cam timing can yield around 10BHP.

When Simon (944 Man) means the cam timing needs attention, he is not referring to getting the cams reground, but to setting up the cam timing via a dial gauge on the top of the piston and on the cam lobes in order to dial the cams into their correct position. This process is detailed in the Porsche Workshop Manual with the correct values. Whereabouts in the country are you?

For some reason (I think it would be a waste of money on an otherwise standard S (cam timing has been checked and readjusted on mine), I have had thoughts about throttle bodies to possibly overcome the inlet manifold restrictions that 944 Man talks about.

 

[Tam Lin]

There is also the whole world-car-same-power cat/non-cat issue.

My understanding is that whilst the standard cat-back exhaust system is pretty efficient, the cars were designed to produce exactly the same power in the catted as the non-cat versions. As a result, the non-cat systems are actually quite restrictive. I've fitted an SAR non-cat replacement module, and it definitely benefits mid-range on feel (I haven't had it on a RR yet).

With a MAF from Promax and propper mapping (and exhaust headers that are more efficient & fit RHD, if these exist), I'm hoping to get about as much as you can out of an S2. With an effective ceiling of 6800 rpm, it's never going to post big BHP numbers, though...

 

[zan]

Our cars are using AFM which by itself isnt a bad technology in the 80's but now the MAF or mass air flow meters are far more accurate on metering fueling and removes the AFM restriction. Vitesse sells a kit which the turbo guys love but expensive.

Say MAF kit around 1000 quid =15bhp
Cam varies but say Millridge 500 =15bhp
KNN filter 50 = 3 bhp
Bore & port throttle body 100 = 3 bhp
Free flow exhaust+ manifold 500 =10 bhp


Total damage 2150 41 bhp

Ok these are guessetimates figures, its unlikely you will get 41 bhp but you get the idea. If you add nitro maybe 1k will give you 50-100 bhp more? Safe if tuned properly. Light turbo is another option but will be expensive.

 

[zcacogp]

ORIGINAL: zan

If you add nitro maybe ...

... come back Brett, all is forgiven! []


Oli.

 

[Peter Empson]

In my experience the MAF (SciVision) on an S2 will buy you no extra power (on my car we dyno'd it on the same day, before and after). It does transform the way the car drives (which is far more important) but mainly thanks to the massively improved throttle response.

Before I SC'd mine I was running the MAF, ESS Janspeed exhaust, cone filter, a rolling road remapped chip, head rebuild - the only thing left to do was attend to the wear of the bottom end (after 140k miles at that point). This didn't net me much additional power (222bhp was I think what it dyno'd at) and I'm very sceptical that you can get anywhere close to 250 bhp on an S2 without some serious ££££'s and that would almost certainly make it much less suitable for road use as torque is one of the great things about the S2. Slap a supercharger on and be done with it ;-)

 

[morris944s2john]

QUOTE:- """ORIGINAL: zan

If you add nitro maybe ...

... come back Brett, all is forgiven!

Oli.
""""

You might joke, but actually, for short bursts of power, a nitrous oxide kit would be the way to go to get more power out of a N/A engine as it is an easy bolt on and a 50% power increase is easily accessible. and quite cheap too. Just as long as breathing the stuff doesn't make the driver start incessantly spamming the forum.

 

[Porka944s]

Pete have you ever done a thread about your supercharger id love to hear the story it sounds nuts!

 

[Peter Empson]

ORIGINAL: Porka944s

Pete have you ever done a thread about your supercharger id love to hear the story it sounds nuts!

The original thread is here, I'll try and add some more detail to it soon now I've put more miles on it.

 

[Porka944s]

wow i read all that very intresting, i want one!

 

[Mike_Pollock]

Ive been lucky enough to have had a trip round the (old) GP circuit at Silverstone with the supercharger and can confirm the PUSH you get!
Mike

 

[zan]

The reason you dont get the extra 10-15bhp on a Scivision kit is that the cable adaptor only adjust the MAF signal to suit the DME requirements. You get the extra 10-15 by tuning the ignition , adjusting the fueling to suit and using the best ron fuel you can get.