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Impact Bumpers


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About PorscheApostle

  • Rank
    IB Enthusiast

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  • Interests
    Surfing , kitesurfing , engineering

Previous Fields

  • Current 911
    82 SC sport
  • Daily Driver
  • Lottery Car
    964 RSR
  • Day Job?
    Saturation Deep Sea Diver
  • Drink?
    Yes please
  • Drive of your life
    Bourge St Maurice

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  1. Not sure what your after. Best take it to MB as it sounds like at the least the synchros need replacing. Hope it works out. DBS to
  2. 915 shifters don't share any modern characteristics you would associate with later transmissins such as the G50 as has been mentioned. G50 transmissions have a totally different selecting operation and even the synchromesh is different. On a G50 the transmission always falls into the 3rd 4th plane as it's managed internally on the intermediate plate a sought of cassette that springs the selector into plane. A 915 doesn't work like this and relies on all the bushings springs and setup to be correct to operate correctly A rebuilt(refurbed) 915 with new synchros is just a fantastic experience. It requires a different style of selection. Faster and positive is better as it's physically impossible to beat the synchromesh if it is operating correctly. When down shifting the ability to heal and toe is also beneficial as a driving style. A 915 has Porsche design history and it's a roots in racing setup. It's mechanical, reliable and simple. A great bit of kit and well tested. They are expensive to repair however hence the reason so many people complain about their operation as the are effectively worn out and the sloppy shift further exacerbates the issues. My 2p DBS
  3. Agreed, by why do that on one Bank and then any advantage gained is grossly lost by it working against itself on the other bank? My only thoughts are that mahle have produced these for other manufacturers and for instance a 4 pot or straight 6 doesn't use an apposing bank. Cold clearances are not great on CPS to due to the material used in their construction but appear marginally better than JEs ( I'll need to actually measure this but am away at the min) The construction looks better than JEs but the piston skirt appears less substantial so it'll be interesting to see how they perform in the real world. The build spec sheet is pretty comprehensive with the Cp pistons. Covers a lot but the ring gaps they specify are pretty significant and have to be filed each cylinder. As I mentioned too, the oil control rings are a 3 piece arrangement which I don't think is going to fare well in our engines . I'm busy sourcing a 2 piece alternative. DBS
  4. So for instance here are some Motorsport pistons mahle that have been machined to take advantage of the offset. The compression ratio is high on these so machining the valve pocket had little effect on the CR. Next is a set of 964 pistons which are also offset but symmetrical in the crown so flipping them is possible . The E represent Einlass or intake in German hence the orientation. Last set are 3.2 Carrera which to my surprise were also offset but cannot be flipped for obvious reasons. My point being the offset is wrongly installed by Porsche on 4,5,6 giving no advantage to that bank. DBS
  5. Lol. I'm fully aware of the concept of the offset but my point was the irony of the offset on a single plug piston such as a 3.2 Carrera which has (if you have built one before humps for the flame swirl) it is however offset symmetrically which means the RHS bank is offset wrongly as apposed to it's lower left and upper right thrust. I have done this with Motorsport pistons with the same offset flipped them around and machined the pockets for the intake valves for the intake valve timing and overlap clearance . The concept of the offset is to reduce piston slap. The reason I haven't done this with my CP pistons is I already have them and do not wish to buy new ones. The point being Porsche did not flip them from factory.
  6. Yes and yes . But I had these for sometime now and this was before Capricorn were doing their own pistons. Oddly enough mahle offset their pistons in some really odd arrangements. Like a 3.2 Carrera for instance . If you get the opportunity have a look at a set which are symmetrically offset on an asymmetrical piston crown. very odd. Carrillo will do you a piston to whatever spec you want it just gets more expensive.
  7. I'll get some more photos once it's back with me and off to paint. Tony littlejohn at gtr Motorsport .
  8. Lol. I'm thinking maybe a bit of that yes. It's got a lot of carbon , doors , bonnet , bumpers , roof and wings . It has an integrated ruf style cage too. So it should be lighter 😲
  9. I've actually got both pistons Je's and Carrillo's in this capacity as this is effectively a test bed for others I might need to build in the future. I'll post pictures once I get round to fitting the pistons for comparison. Incidentally when I stripped this one after fitting mahle liners in the 3.8 capacity plus jes I found the gudgeon pins ie (actually the pins) demonstrated a fair bit of wear after 10k miles. That was the previous build .
  10. Combination of the 2 really . The ring gaps demanded by CP pistons albeit it's more critical on the top compression ring, the very fragile 3 piece oil control ring and the short skirt with no gudgeon pin offset can create issues. On JE s you can fit goetze rings as the dimensions are the same. The JE rings are Shyte too imo and I've had success by fitting the goetze ones . Use no oil at all on a couple of 64s I've built now. It's more the cold startup issues and piston slap from cold on the Cp pistons . Unfortunately there's not an ideal solution and the mahle stuff will always be the best for reliability oil consumption etc Proprietary pistons are just that and unless your liners are perfectly round ie replated and honed there's always the chance you'll get a puff of smoke with them from cold as the rings constantly move around in the bores at some point the gaps will be in a position that they align . That said from hot there should be little oil consumption as the pistons expand and mitigate the cold clearance . Problem is there are limited piston and liner options in increased capacities and more exotic arrangements people want to explore. None of which can be warrantied without extensive rnd imho . Set of CP pistons are about 1500 quid landed but a a full mahle set of liners and pistons are a lot more than that so it really is up to what you want from an engine. I'd always suggest go stock or with whatever Porsche RNd as it was proven and works. Only reason I'm going this route is it's my own engine. DBS
  11. I'm actually hoping for the opposite more a blend of the 2 but not easy with 2 port heads and fixed cams . Going to be a road car that I hopefully take to the Alps each year so I'm planning some modern heating and cooling arrangements , ditching the horrendous 964 Aircon system for something lighter and more basic .
  12. That's a long way off. I'm hoping if finances allow a full cargraphics setup but it's getting silly now.
  13. The liners are from Capricorn and the pistons have been made by Carrillo. Have to think a bit left field with lemans style head sealing arrangements which I'll post when I'm done with the the top end dry build . Need to still do the cc'ing and piston to valve clearance checking ring gaps etc as the Carrillo's demand huge ring gaps due to the material they're made from. Skirts are shorter than jes but generally appear to be a better product. Not mad about the 3 piece oil control rings either. I'll post some photos come the assembly . You might have noticed the rs seals in the case as they don't fit in the same place as the standard liners. They are 4.0 l pistons with RSR cams 993 rs intake valves . Heads have been ported to match some itbs that have been in another build on here 🤪 but they might be married to a varioram intake . Ignition system might be COPs ala Robs 64. Aim is torque and lots of it 350bhp and 420nm is my plan . Hopefully ready for Xmas
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