Expected Power Output

[James_M]

Hi All

I wonder if I might ask for some advice (again).

My 1994 968 Sport (125,000 miles and mechanically stock) needs a new back box. So, naturally I have ordered a complete Janspeed system with sports cat, as well as a ProMax chip and K&N panel filter while I was at it. This lot won't be fittted until next month so since I had some spare time before the PCGB novice trackday yesterday I took it to Surrey Rolling Road where it could only muster 213bhp.

Given the car's age and mileage should I be disappointed with this and where should I start looking to see if I can find the missing ponies? The dyno guy said the fuelling was spot on so it's not that.

As far as I know (and my specialist hasn't mentioned anything) the car is mechanically sound and I have replaced all the usual suspects over the last few years. Is it likely to be simple cylinder wear or something similar?

I have read that standard 968s rarely produce the full 240bhp but 213 seemed a bit light to me all the same.

Cheers

James

 

[Big Dave]

The main place for the "ponies" to escape is the valve seats in the head. Over the miles they wear out / get carboned up + dont seat correctly letting out some compression. It helps to get a head job done , ie head off ,valves reseated + new head gasket....
Im sure Paul F wuill be along soon, as he had this very job done at Hartech a few moons ago... It restored his missing horses...

 

[paulf968]

James -- hi (I've arrived!)

There is no reason why any 968 should not be able to make 240bhp - my road car with the same mileage as yours does just that but did show 220bhp when tested a while back before some work. Your reading is certainly low and if we assume it's accuracy then I would want to know what was going on.

As Dave says the usual point of weakness if all the mechanical bits and timing have been set correctly is the valve seats. A dynamic compression test of some sort is now required, where figures comfortably over 200 psi should result -- if not then it is head off time to correct things.

Also what oil are you using? anything thicker than a 10W-40 will sap a lot of strength in oil shear on the crank. In seeking to get 240 bhp -- I changed from 15W-50 to 10W-40 and found the last 7 bhp I needed!

You could give the guys at NineX a ring -- they are nearby and Andy Duncan knows a lot about getting the best out of a front engined Porsche (he preps cars for the PCGB race series)

 

[James_M]

Thanks very much Paul and Dave

I've not heard of NineX and Googling them hasn't come up with much. Can you post a link or phone no. please? Where are they?

I'll call my regular specialist (whilst sitting down) to ask about the cost of valve seat work. Can you suggest what I should be expecting?

I still had a whale of a time at the PCGB novice trackday and shall we say 'several' much more modern cars had to get out of my way on the pit straight []

James

 

[paulf968]

NineX -- Andy Duncan -- 01628 633 088

say you got the name from me -- as I see him at every PCGB race meeting -- he borrowed my tin snips last weekend!!

NB diagnosis, then head off job, with a light skim and valves re-lapped -- sorry but unlikely to be much change out of £700

get it diagnosed, then sorted, then get on them trackdays and surprise a few people!

 

[Paz]

Do the heads get ported too?

 

[paulf968]

no they don't as Mr Porsche got it right first time! -- although I have not tried it myself (the PCGB race regs do not allow it) --

I know one guy on here who has worked very hard to extract more than 240 out of his engine -- he has had some success doing such things BUT it is really hard work to get bang for buck

 

[Paz]

Over engineered in true Porsche style.

Did you get my PM Paul?

 

[Big Dave]

Paz.
As Paul has mentioned. Its not realy worth all the effort of doing the porting, as it doesnt realy improve things much...
And if you get the porting wrong, it can actually cost you some "horses"...
I know of a few people who have had there heads ported + in my opinion wasnt worth the effort + cost..£££££££££
A compression test is well worth having done though. This will then tell you the health of the top end of your engine...

 

[frogisland]

Completely agree with Dave and Paul. Considering the mileage that you have i would consider your position fairly normal - you have to expect some wear and hardening of seals. The head gets quite coked up also. I bought another head when i had mine done (have a spare 968 head sitting in the garage) replacing cams, followers, reseating valves etc. Unless you intend to keep the car along time or have cam issues then leave it as it is. It is not a cheap thing to do to take the head off etc.

I know of a couple of cars that had basic mods such as airbox/filter, chip/mapping, injectors cleaned and getting around 250bhp (various rolling roads). I had mine rolling roaded before the head refresh and was very healthy. (my cams and followers were on their way out - lost the case hardening on a couple of cams causing wear on the followers, so decided to take the head off and replace with a reconditioned spare head that i had)

Just a point of detail - it is not normally valve seat wear, if this is the case you would have additional issues that take some £, moreover it is the seating of the valves.

Some photos that might interest you

JP

 

[frogisland]

 

[frogisland]

 

[frogisland]

 

[frogisland]

 

[Paz]

Thanks for all your help guys []

 

[James_M]

Many thanks to everyone for their advice. Here's a brief update.

Compression test and cylinder leakage test have shown the engine (valves and piston rings) to be fine, there is very little leakage. More than fine considering the mileage and according to my mechanic.

One other suggestion since I've had the car back is that the throttle isn't fully opening. I have noticed that with the pedal fully depressed there is still scope for the widget at the end of the throttle cable to move further and on the face of it open the throttle further. Is this the norm? Will moving the widget further round actually achieve a wider throttle opening? So far I haven't had chance to take up the last part of the travel by hand with the engine running to see if the revs increase further.

All thoughts on the above and any other suggestions as to where my missing horses have gone will be much appreciated.

Cheers

James

 

[Big Dave]

The best way to see if the throttle is fully open is,,
To remove the maf unit + the rubber snorkel that is connected to the throttle body, then ask a friend to push the accelerator pedal all the way down..[ with the engine switched OFF by the way.] Now look into the T body, The butterfly you can see in the T body will move + youl be able to see if its fully open... If not then wind the bolt / stop down behind the accelerator pedal, or adjust the throttle cable....
Hope that helps.