Porsche 996.1 cab

Dad's 1983 he kept 3.2, one of his biggest regrets was not bumping it to 3.8.  

It would have cost a whopping $200 more. But he wanted a more rev happy motor. He got it, but there was always the question in hism ind of "what if I'd gotten a bit more torque"

With the Mechanical injection the change would have forced him at the time to go to PMO carbs and that $2-3k upgrade was not in his budget at the time. 

(1983 911sc, A LOT of parts in it.)  I have to put in a plug for WEBCAM racing cams.  Dad had some amazing fantastic support from them everytime he had a question and when he'd call up he usually got to talk to the cam designer.  (993 supersport cams). 

It would be marginally more expensive to go to 3.9 - although we're talking a small percentage of the overall cost.

Essentially I'd need to source a 3.6 litre crank carrier - these have 2mm thicker bearings than the 3.4, helpfully - and of course the crank.

The 3.9 would still be over-square, but "The Internet" tells me that in the 997.1 the 3.8 is less willing to rev than the 3.6.

However, this may be a bit of a strange one as they share a crank, it's bore that increases on the 3.8, and therefore this may have no bearing on things/be BS.

My feeling is that I could build a 3.7 and then rebuild to a 3.9 if it's insufficiently fast for my Senna-like abilities, and that the 3.7 might be a happier unit as the short stroke with the lightweight flywheel would be very free revving.

But, there ain't no replacement for displacement...

plus, do you really want to build that motor twice?  i'd go 3.9, especially since the incremental cost is low, and you're working around other inherent high-rev limitations.  it's not like you'll go give it a boot full of throttle and at 7000 it's going to roll over, pull the blankets off you and say "not now, i'm tired"

Some decisions have been made - staying 3.7 due to 4mm shorter stroke, which is important because I’ve totally lost my mind and we’re going to go for solid lifters, bigger valves, 13mm of lift and a 9,000 rpm redline. I shall be the fastest hairdresser in town.

Finally got the car back, spent 5 hours/300 miles behind the wheel yesterday and it was glorious.

This is an M96 as it comes from Porsche:

Note the unsupported bores - they eventually go oval and then crack.

Here's the block with Capricorn liners installed and the deck closed - this is what we're going to do for my block:

Whilst waiting for that day to come I did a ridiculous little hack which has ended up being hugely beneficial.

Take one Porsche cup-holder, cut away everything 10mm above the plane of the rear/vertical member:

Stick a quad-lock boss on it:

Profit:

(I suspect this will only make sense to people familiar with the first generation 996 and 986, apologies to everyone else).

200 cell cats fitted in an X-pipe configuration and the car now sounds absolutely glorious.

I also fitted the 997 GT3 gear shifter, which replaces all the plastic bushes of the standard one with metal items - very snickety now.

For the LOL's we worked out what the speed would be at max revs in the current gear ratios:

1st  60mph
2nd 95mph
3rd 130mph
6th 250mph

Stock final drive is 3.44, you can buy a 4, but that's still 112mph in third.

Ideally we need 5 - which I suspect will be custom. Anyone got any contacts in this area?

Howling into the void here, but I'll keep updating as I'm a creature of habit.

We've found a supplier who can provide a 4.5 final drive, it'll mean that cruising at 80mph is a bit frantic, but equally it'll make 3/4/5 usable when running out to the redline.

With that said, I went to a track day at Brands Hatch on Tuesday and, rather unfortunately, rang up 102.6 decibels on the marshals noise meter. This was too many decibels for the event, and I was sent home in ignominy.

So! Does anyone have experience of quieting down a car to get it past scrutineering? Many points given to people who have achieved less noise without melting anything (such as the bumper).

In reply to Dammit :

Back when I was racing z cars we used a 90° elbow turned down on tip of exhaust pipe.  Actually dropped dB a bit.  But DAYUM...102 is LOUD.

In reply to Dammit :

Run a real muffler?

Ebay fart cannon plugs work well. Ive made my ouwn for 3 inch exhaust to pass noise, with no appreciable difference in the power.

In reply to docwyte :

I think what made the difference was moving to 200 cell cats in an X-pipe, the exhausts are quite middle-of-the-road:

I think part of the problem is that the car is rear engined - so the noise testing marshal gets the exhaust noise plus the induction noise, and all the running engine noise.

There's also not a great deal of exhaust tip to work with, in terms of bolting on an additional silencer section (this photo may explain my concern for the bumper):

These are the tips:

I don't do a great many track days (this would have been the first with this car), and for normal, everyday driving the exhaust is great - it's very quiet at idle, cruising you can listen to Radio 4 with the roof down, but at high revs it sounds like a sports car should. So! I don't want to change that, I just want to be able to pass scrutineering at the track every now and again, without getting all melty. 

Back at Brands now, clutch in, aircon off, scored 99.7 on the same test.

Magic!

Order placed, engine cases dropped off, 100mm bore/3.7 litres here we come.

One thing that's been entertaining me - the 911 has a range of ~400 miles, the C55 has a range of ~200 miles. Makes the open top sports car the more logical road-trip vehicle, rather than the family estate car.

Engine: 

Everyone knows (or thinks they know!) about the problems inherent to the M96 series of engines, the IMSB is the most commonly talked about (endlessly on the 996 Facebook group it sometimes seems) but there's also bore-score and crank-breakage, plus accelerated big end bearing wear. Terrifying eh?

Well - lets add one more to that. Enter The Tappet Carrier.

These do as the name suggests, they contain the tappets, sit in the head - what's to know?

The problem is that the design isn't great and the material used is crap.

What does that mean? It can mean this:

Porsche actually tried to rectify this when they introduced the X51 Powerkit - which some of you I am sure recall had an additional scavenge pump on one of the heads. This was there in order to remove oil fast enough that under heavy braking the tappet carrier didn't suffer hydraulic fracture.

Now with our engine we want to eradicate the weaknesses that Porsche left, so this had to change.

Therefore we scanned in a tappet carrier:

And went through many iterations of CAD model:

To get to the point where we have something that we can now tweak, and then have machined from billet:

We'll likely have two versions of this - one for standard hydraulic lifters, the other for the solid/mechanical lifters that I'm going to run.

Current bore is 96mm, we are going to 100mm. With the 3.4 litre 78mm stroke crank this nets 3.7 litres. However, the engine builder jjust suggested we use the 2.5 litre, 72mm stroke Boxster crank. This would mean capacity would actually be unchanged at 3.4 litres, but 72x100 rather than 78x96.

Why would we do this?

For a nominal Mean Piston Speed of 20.8 m/s, a 78 stroke would net you 7846 rpm, whereas the same MPS with the short stroke gives 8666 rpm.

In reply to Dammit :

This is very cool. Any plans to market it?

What kind of scanner did you use?

white_fly said:

In reply to Dammit :

This is very cool. Any plans to market it?

Thanks! In terms of producing them, personally, no - however, we've discussed licensing the design to a Porsche engine specialist here in the UK so that they can make them for people - they have the facilities and the infrastructure, I'm a chap with a hobby. 

So they will be available, in two varieties - standard (for the OEM hydraulic lifters) and mechanical (for solid lifters).

(As a side note the head-mounted scavenge pump is NLA from Porsche but there is a company that produces a version, but they have two, one for each head - which somewhat indicates that they don't quite understand what said pumps are for). 

WillHoonForFood said:

What kind of scanner did you use?

A friend of mine is a product designer, he has to scan in products all the time to reverse engineer/reproduce parts for them so I went with his recommendation for a commercial place in the UK. It was ~£150 for an extremely detailed 3D scan that showed all the internal oil-ways etc.

That was then used as the basis for the CAD model - which was rather more expensive as it was days of work rather than a quick trip through the imaging device.

We are going to use these, Jenvey ITB's:

But, because life isn't complicated enough and also to try to avoid the typical ITB power delivery profile of "nothing unitl 4,000 rpm then armageddon" we are going to put the top of each bank of trumpets into one of these enclosures:

And then feed them using a GT3-RS centre section as so:

Pictured here with an X51 intake which we won't be using, if anyone wants one give me a shout, I now have two spare...)

And here you can see why:

We are hopeful that by being able to vary the (effective) volume of the intake tract we can iron out the peaks and troughs inherent in ITB delivery with bare trumpets.

This Youtube video shows the exact characteristic that we hope to avoid:

https://youtu.be/st3WDUYomkk

Ooh, engine porn .

I remember stumping the marshals at Brands Hatch once by showing up with an Integra Type R with a stock exhaust. I think they were concerned their sound meter was broken as no Honda on track could be that quiet.