Pistons speeds are limited to the design and strength of the rod materials and rod/stroke ratio. @8000 rpm a 100mm stroked engine will have a piston speed of ~5250ft/min or 26.7m/sec. It would be very interesting to see what G loads are applied to the rods are if I could find my spreadsheet. By comparison a 95.5mm stroked engine = 5013.123 ft/min or 25.467m/sec Stock 2litre 92.8mm = 4871.391ft/min or 24.747m/sec.
so thats roughly a 8% increase in piston speed between the two so by that logic the pistons in the engine with the 100mm crank would be travelling at the same speed at 7,360rpm as the pistons in the engine with the stock crank at 8000rpm what is that actually going to mean though? should the rev limit then be set to 7,360?
@8000rpm the 8% looks small but when you consider your rods are being subjected to 2125 vs 2290 Gs things start to look different. And I have not even considered the piston weights yet! This does not even consider what what sine/cosine forces would the rod be subjected to as it recirpocates from power stroke to exhaust stroke at this level of acceleration and load from the piston. At 7425rpm the piston speeds between stock stroke and 100mm are similar and the Gs are lower for the 100mm at 1972. Again the maximum sustained Gs would be subject to rod quality and material. This would determine to some extent where to set your max rpm.
I don't know the crank specs but early VW LT van's used a 2.4 and 2.7 4 cylinder diesel engines which may of had a longer crank than 95.5mm.
They are different engines though - I'm pretty sure it's a longer engine, so that would rule it out. No harm in just checking though, folklore is one thing etc...
Lots of possible reasons... poor basic machining/bore finish, poor quality pistons/rings, high rod/crank ratio increasing side loadings... a combination of some or all of the above.
I think there is an academic playoff here, as surely anyone running 84mm bores is on forged pistons, with the implicit oil usage this brings anyway? Surely poor machining/pistons can't be put into an oil usage theory of a 'given' bore size?
Different alloys in the forged pistons have different expansion rates. There are a couple of types generally used in after market stuff. Only takes some machinist to get it slightly wrong with the clearances and it is the same as running with 200k on the engine. That's miles not revs!
After yesterdays Rolling road day Bargate showed an ideal bore and stroke NASP combination with 245.5bhp @ 8000rpm and 191 lf/ft @ 6500 rpm from a 83.5mm bore and 92.8mm stroke. I wouldn't go anymore than than if you was a 8000k screamer engine build.
Arround 223.7 bhp @ Wheels , Sambo will be posting the power Graph's fro, Sambo's RR Thread Bargates mad Rocco, 16v on itb-s sprint car 11.9 sec,expected power 255 bhp, very torquey at 191 lb/ft at 5800 rpm
I would rate that at 255-258 all day long. Same with yours... I see it made 182 atw's in another thread... thats a good 210-212hp.
Hi Eurospec made the 99mm stroke then later the 100mm cranks. A mate of mine owned a 16v KR that had the bore taken to 83.5mm and a 99mm crank squeezed into it. 2168cc running on Kjet limiter at 7200rpm. The car ran surprisingly well despite the rod ratio,however the BE bearings took the beating and would be changed at every service interval as a precaution. The motor had Ross pistons iirc and non std rods fitted. Amazingly there was no wear to the pistons or bores. Seeing that I have been gifted with that block I plan a 8valve conversion with a 6250 rpm limit. Ciao
Yes, both those cranks are 95.5mm stroke. The rod angles are far from ideal when fitted to a short block. There may well be clearance issues too, both with the crank and rods, and pistons will need machining too. You can actually get a kit for fitting a diesel crank to a petrol tall block. That sort of says it all for me.
where can i get me one of these kits? I thought the 9a was a tall block? -im using the s2 pistons too by the way
S2 pistons? Are they not 81mm. 9A block has an 82.5mm bore. Basically the kit for the tall block includes 159mm conrods with a 20mm pin instead of the std 21mm. This means that the short block pistons with their shorter compression height will reach the top of the block because of the extra stroke on the diesel crank. S2 pistons sounds like you are going to be running forced induction?
ive just bought some AUDI 2.3 20V/ 7A /S2 TURBO PISTONS & CON RODS. these are 82.5 - same as 9a, and are forged as standard. im running Throttle bodies on the front - but am playing with the idea of feeding the engine with a turbo as well(like the skylines). When i heard about the diesel crank I thought it would be a good addition as well. Any thoughts?
Turbo or NA will be the thing you have to decide on first. This will determine the CR you need to aim for. ITBs and turbo are really not that common a mix. The single plenum seem to cope fine on some very high end machinery.
