This is exactly what happens when engineers get together and play the "what if?" game. Both myself and our development partners 4T have been speculating about an increase in capacity for some time, but because we are happy with the performance of our 103mm cylinders the discussion revolved around fitting a new stroker crank. Thus it came as no surprise after being pushed by customer demand for something a little more special (than a 109bhp/litre 3.8??) and you let them know your ideas, all of a sudden a couple of orders drop in and (fanfare) away we go on phase 2.

The crank is just the start of the job, we have the following items actually in design/manufacture at the moment:

1. Stroker crank with 80.0mm stroke to give 3999.5cc on 103mm bore.
2. Lightweight steel rods.
3. Revised 103mm piston to suit extra stroke.
4. Billet steel hollow race camshafts, extra lift on intake, superfinished lobes.
5. Billet steel followers, special coating to eliminate wear, revised geometry for 15mm (0.600") lift on the intake valve.
6. Revised valve spring/retainer to suit additional lift.
7. Carbon/CNC alloy throttle body set with airbox.

Obviously all of the above will be designed to get the best from the 9m/4T billet cylinder head, but it is definitely as far as we plan to develop the aircooled engine. Based on current power levels from the race 3.8, we think that a totally reliable 440-450bhp is possible, although the complementing idea behind the 4.0 litre is to be able to achieve 100bhp/litre in engines that can be comfortably be used on the road.

Obviously I will do my best to keep everyone posted as the work progresses.

 

The crankshaft ?
All new or an old one cut / weld ?

 

Ahhh ... so that's what happened to John Boggi's engine

 

You got there before me!

 

WOW! Sweet!!!

 

Come, come lads, would we do this to you??

Brand spanking new machined from EN40B billet steel, hardened & tempered then gas nitrided to a surface depth of 0.5mm minimum. In other words good enough for F1, F3000, Indy, Touring Cars .....

The intention is to make them a drop in for the GT3 engine as well, so they will have the smaller big end bearings and revised oiling of the later engine which will be good for 9000rpm. The 964 & 993 will require custom rods to run the crank in any case, so we can take advantage of the smaller bearing to slim down the width of the big end and avoid the oil pump clearance issues when using Carillos or similar.

The target price for the cranks will be around £3000 (+VAT) which compares very favourably with the price of standard Porsche cranks in the UK.

 

very nice! can't wait for the updates...

 

Best not tell Christer about any of this eh ? !!

 

And the question that always comes to mind when I read about another great Porsche "mod", why didn't Porsche do this themselves? I think I remember reading that they thought there would be cooling problems if the displacement got any larger? If you've solved it then great work!
I'm not even going to ask the cost of the whole new engine but I'm sure this would be the reaction.

c

 

Cooling a 450bhp n/a engine is technically easier to achieve than a 450bhp turbo, so since Porsche sanctioned a 450bhp option for the 993TT and GT2 there is absolutely no issue with heat at this power level.

The logical answer is that Porsche did not do it themselves because they did not have to for the power levels they deemed sufficient for the average Joe. The cynical answer is that since they were not capable of designing the cylinder head correctly, what chance did they have with the bottom end? I'll let you chose the answer that fits your needs.

 

Or buy a Turbo and play with that !! or fit a turbo motor in a 964. Hmmm , thats a thought !

All the best

Geoff

 

You are right, slapping in a turbo motor is the cheap and easy way to high hp, but it is not the route that everyone will choose because a big hp number is not the only goal.

This development path was chosen for the 9m/4T race engine to fit in with international racing class limits for naturally aspirated engines, the plan being to keep the lightweight 964/993 race cars up (& beyond?) the performance of the GT3 in the 3.5 to 4.0 litre class. However that said, because the crank will fit a GT3 I think it will only be a short time before we do a similar number on the watercooled engine.

The bonus for us is that we have good customers who understand the advantages of a high hp naturally aspirated engines for both road & track use and are now benefitting from our latest developments. Yes this comes at a fairly high price, but if you want the best it always does - ask Robert Linton!

 

And the advantages are? No lag?

c

 

Hi Colin,

Cool sounding mods. You should post in the 993 section as well as some of them are too lazy to come over here.

Cheers,

David

 

"And the advantages are? No lag?"
The advantages are no fixed rear wing (needed for the intercooler) that detracts. Especially on cabrios. But if you want to go seriously extreme, I am sure Colin could use most of the same components to cobble together a 4 litre turbo with Motec that makes everything else look like it's standing still.