Porsche Enthusiasts Club Forum

That's interesting about the Arrow cranks on the Cossies? Not sure what size the standard Cossie cranks are compared to the 944 version. There's always been a bit of speculation over lightening our cranks. I wouldn’t have thought that by lightening the externals that the crank would suffer any more flex? Many years ago when doing my first 3L motor I was sourcing parts in the U.S. and I had the crank sent away for a medium lightening. It came back as a full knife job. A lot of water has gone under the bridge since then and many motor builds later that crank is only now about to get put under stress on the 3.1L 8v racemotor. Interestingly at the same time that the crank was sourced, some Arrow rods were also sourced and are in the same motor now. So I would have thought they'd still have some drawings for a 944 in their system. I don't have the dimensions but they would be to make a 3L and above motor depending on bore. I was also involved in a 16v build that was going to have a custom Arrow Crank. It never quite got to the point of it being ordered but I didn't think that it would have been at the same weight of the stock version. On another note, I'm 99% certain that the custom cranks that MMount gets made in the US are substantially lighter than stock. Might be finding that out for sure sometime in the future.

I had been told that its not good to try and hone Alusil as its difficult to get the rings to bed in? There are quite a few posts about this. Most people seem to either nikasil coat the blocks of put in liners? Has anyone successfully managed to hone/deglaze the cylinders and get new rings to bed in properly?

The guy I was going to use to put in cast liners was going to do to for £300 labour plus parts on top.

Hi Patrick, Have just had a read of the How to get 400hp NA thread and it seems Michael Mount used a standard crank in that build, revving to 8500rmp. They do say its a 968 crank which is a little lighter, but it looks identical to me.

Cheers Tim

Interesting. I'll have to re read that thread. It's been a while. Nice car of Henk's but he's bought a Cup car now and the 944 has been relegated to the shed.

Yes, you can hone Alusil but whoever does it must have the right tools. That's the advantage of a ductile iron sleeve. They are more resiliant than the stock Alusil bore but if you manage to damage one you can have it honed more easily plus you have a wider choice of pistons and don't have to worry about coatings.

That sounds quite reasonable, but Id suggest talking to Kevin or Alex Eacock at EMC. Kev will set you straight with regards to honing Alusil blocks and be happy to give you a price. Im sure that you are familiar with their experience and success with these cars.



Simon

Something that has always concerned me about liners is their stability. If youre using an open deck block then what keeps the tops of the liners true? Is it just the clamping pressure against the head?

My extensive research suggests there's only 2 or 3 companies in the UK that have the Sunnen hones and know how to lap an Alusil block correctly. To CNC machine a block correctly for liners I've found 1. That doesn't mean other people cant do it but I wouldn't want to pay someone unless they have a track record to prove they know what they're doing.

Id be interested to hear who they were Paul?

Hi 944man, The liners I have had made for this build are called a step liner. You bore the block to size but leave a step in the bottom of the block. The liners are then press in and up to this ledge. The top face of the block is the faced so they are perfectly flat. The liners are then bored to suite your pistons. Any good machine shop would carry this out.

Cheers Tim

Thanks Tim. That locates them at the bottom then, but what holds the tops in place? There must be substantial forces involved - can you do anything to make it closed-deck, even partially?


Simon

The original bore wall of the S2 block are around 9mm thick, the liners are 2mm thick which leave 7mm of the original bore wall to support them. Tim

Of course! Id mistakenly presumed that the whole bore was removed.

*feeling foolish*

Thanks Tim.

Very impressive project. It can often be a big advantage having no preconceptions.

I would have thought the detonation threshold will be raised with the 16 valve head.

Do you have more details on your crossover pipe modification? At what boost level do you think it becomes a restriction?

Have you thought about keeping 2 split-pulse pipes right up to the turbine housing, and running a twin-scroll T3 turbine housing? It would possibly clean up the flow and maybe help spool-up.

Twin scroll turbos are brilliant, but they require voodoo to make them actually work. Let me rephrase that: Ive driven manufacturers twin scroll turbo cars which were brilliant. Ive never seen a twin scroll added after-market, though.