DDK - Die Deutschen Klassiker

Well, I now consider the turkis delight to be ‘run in’.
I’ve covered hundreds of road miles in the car and indeed I’ve already done a trackday.
So, I felt it was now ready for some fine tuning.....

In fairness to the Nicks (Mr Moss & Mr Fulljames) they had simply built the engine and installed it. The car was running with best guess settings and carbs straight out of the box from PMO. The car wasn't an easy drive at low revs and only really came alive at high revs. Everyone agreed, "run it in and then we'll set it up properly"

I’d been very happy with the engine as it came but I realised that once loosened up it would benefit from careful and knowledgeable attentions.
Therefore Nick (Redtek) caught up with me a few weeks back and kindly set the timing with the engine in the car and improved things markedly. After having had the ignition timing adjusted properly at Castle Heddingham the car was noticeably better on the drive home.

Now I felt it was time for a rolling road session at Bob Watson Engineering.
Bob needs little introduction to many on this forum, his expertise and experience is evident and everyone speaks very well of him. I’m a fan now too.



To track back a little I’ll explain that the engine is built on 7R magnesium cases, correct for an early seventies 911.
Porsche managed anything between 130 bhp (the 'T') to 190 bhp (the 'S") from the 2.4 engine. With the '73 RS they stretched the capacity to 2.7 litres and attained 210 bhp. Therefore by the simple expedient of increasing engine size to 2.9, as with my engine, I’d expect to realise 225 bhp or so. Plus, it has been twin plugged which wouldn’t increase power output per se but does allow a higher compression ratio meaning we could achieve maybe 235 bhp? Or more?

However all parties were somewhat disappointed when the car took to the rolling road and revealed a rather modest 234 bhp.

Which does need qualifying in that I'd been delighted with the performance of the car before hearing the numbers but the print out left us rather deflated. It seemed a rather ordinary output. Pretty much the power expected but not remarkable.

No matter, it meant Bob could work his magic.

After many hours of skillful adjustment the output was transformed. Bob had the car on the rolling road for several more sessions and eventually reported 253 bhp. Fantastic. Although that wasn't Mr Watson's appraisal. He conceded that the engine had a rather large flat in the output around the 3,500 - 4,500 rpm range. So, probably fine on track at near maximum revs but perhaps a bit off the mark on the road at more modest revolutions.

So, Bob kept the car a few more days and changed more jets and even emulsion tubes. At this stage I must thank Nick Fulljames for his help working in conjunction with Watson Engineering. Also deserving of praise are Tuthills for their expertise and help with lending parts. I believe their assistance proved invaluable.
Bob methodically went through all permutations and even changed the exhaust to a standard back box in case that was affecting things (it wasn't, the current exhaust was pronounced good). Even the spark plugs were changed and further improvements gained.

Finally the call came through.... 260 bhp! Woo hooo!

260bhp!

However, that's not the end of it. The results show an impressive maximum torque (Nm) of 274. That is at 5,750 rpm but more notably the torque is solid and even all the way from about 3,000 rpm to 7,500 rpm. I had originally specified an engine with a good spread torque rather than a high-revving 8,000 rpm screamer and the guys have delivered on that superbly (we've set a sensible 7,500 rpm limit although I've heard it whispered that it's capable of surviving at eight).

And so, I'm delighted. It couldn't get any better. Could it?

Well, yes, it did get better.

Bob volunteered that he had some accurate scales so I'd asked him to weigh the car.

Now, I hadn't built it to be ultra light but I was keen to keep it trim when specifying the configuration. Hence the magnesium engine cases and gearbox, the aluminium engine lid, the fibreglass front wings, the fibreglass bumpers (front & rear), the Lexan rear quarter 'glass', the lightweight amber engine 'tin ware' and stripped out interior.

I don't like the increasing weight of many of today's modern cars and we strove to build a light and nimble sports car.

I secretly hoped the car would be under 1,000 kilos. So, imagine my delight when it topped the scales at 940 kilos (without petrol).

I couldn't quite believe how light the car had become. Whilst weight saving had been important, this is not a seriously stripped out racer and after all it does have some big wheels and weighty tyres. The car retains a glass rear window (and side windows), still has a steel bonnet and a chunky roll bar is fitted. Change some of that and be more ruthless in removing carpets, etc and you'd easily trim further kilos but this car leaves me with a happy balance between practical road car and extreme circuit racer.

The result is a car that enjoys a power to weight ratio of approx 275bhp per tonne. That's better than a brand new 911 Carrera. In fact about the same as a Carrera S. So, nearly 40 years on and mankind has developed a 911 to equal my seventies hot rod. Of course the modern car has cup holders and Herr Thom Thom but I'll settle for the aural delights of mine and forsake a few creature comforts. The drive home was great fun.
See you at a trackday soon.....

Ferry Man wrote: Imagine my delight when it topped the scales at 940 kilos (without petrol)...........and enjoys a power to weight ratio of approx 275bhp per tonne.

It's amazing what a good 'old fashioned' mechanic like Mr Watson can squeeze out of these old girls......great result Paul

Martin

That's a very healthy output Paul and it's good to see Bob working his magic again

Interesting to see the latest developments on the car.
Did the power output vary much with the exhaust in it's different configurations ?

just read your write up today in GT purely porsche Paul while waiting for some checks on our school bus. Cool

Need to weigh my RSR and get on a rolling road now....

Fantastic results Paul.

260bhp at 960KG - just mind the driver doesn't take it over the 1,000KG

Any graphs from the rolling road ?

Ian

Highfield wrote:Any graphs from the rolling road ?

Yes, I've got records from 5 different sessions on the RR.
I'll post a couple up later.

sd wrote:Did the power output vary much with the exhaust in it's different configurations ?

Very interesting that one.
I'll reveal more about the increase when I put up the graphs.

Bob works his magic again, great result Paul, stunning final result

Highfield wrote:just mind the driver doesn't take it over the 1,000KG

Ooh, that hurt Ian. I nearly missed that comment, can you give me any dieting tips?