slate blue

Hi to all, I was just alerted via email about the new 928 carbon fibre intake. They have now done the intake testing on the dyno and racetrack. Well done BTW guys. Now one of the issues raised was wait till the titanium valves and alike are added. Can't wait to see the hp readings then.

Well I doubt the high rpm potential of a stroker motor at any time, it won't matter what valves it uses, as the problem is in the bottom end. the piston speed at say 7500 rpm will be monsterous. It would be faster than an F1 motor. The loads on the rods would be bolt streching. It might hold together for a short time but that engine will a grenade. Just my thoughts.




I wouldn't use titanium in a street motor either as doesn't heat cycle well at all, but wait for the new hollow stem valves that are comming next year at around $35 a piece.

BC

where are those valves going to come from Greg?

Also - The mass of the rods and the pistons can be reduced so that 7000 would do just fine I would think.

slate blue

Hi Brendon the mass would need to reduced so much that pistons would last a very short time. Think about this, I work out that if I dropped the weight of the piston down to a little less than 500 grams pins rings included, going off the Porsche set redline, that the load on the conrods would be the same as the factory motor when I revved it to about 7750 rpm. The factory redline is approx 6800 rpm. Now the factory piston weight is 720 grams and the stroke is 85.9 mm.

So if you can see how much I had to drop the weight of the piston to just increase the rpm a thousand revs. Now those pistons are very high tech to weigh what they do and have some longevity. I don't think you'll find a piston weighing less unless it is a MMC piston. The load on the rods increases at the square of the piston speed. Remember what was needed to achieve the extra 1000 rpm now add into the equation almost an extra 10mm in stroke an you'll now get what I'm talking about.

Hope this helps.

Greg

Jim bailey - 928 International

Greg the big stroker engines typically run aftermarket "Chevy" rods like Carrillo , Pauter etc. with the very strong bolts....the cranks are strong billet units .

Fastest928

about 7200 rpm is max for a stroker engine using the absolute best components for an endurance engine..

Marc
DEVEK

slate blue

Thank you Jim and Marc for your replies, yes I will take your word Marc on 7200 rpm, the email I got mentioned 7500 to 8000 rpm, and as I eluded to in my previous post that is just way to fast. The maxium piston speed would exceed the speed of the BMW f1 engine currently revving at 19,000 rpm.

That engine Jim uses Mahle MMC pistons and Titanium Pankl rods and a crankshaft that is as light as a feather. I seen that crank on tv and it was compared to the M3 6 cylinder crank and it was half the weight and the race engine was a v10.

The cylinder bores also can be an issue as I have spoken to the people who coat the F1 Cosworth v10 race motors and one of the critical factors is lubrication at these engine speeds. It cuts wear and friction and of course delivers more power as a result. If you look at say the m3 piston which attains piston speeds nearly as high as the F1 engine it also has a low friction coating applied by Mahle, likewise most bike engines have a similiar coating.

Not trying to be pendantic just imformative and helpful, that is what this list is about.

LT Texan

Hey Greg,

Where do you get the info re F1 engine piston speeds? I would have figured stroke and rod length to be highly classified info.

slate blue

Well Dan I have a few sources actually and most are in the public domain. First BMW website: The site details the technical aspects of the BMW M3 engine and in particular talks about its piston speed being almost as fast as their F1 motor. The dimensions for this motor are commonly available. I believe from memory the stroke is 87 mm and revs to 8000 rpm. They even discussed a specific distance the piston travelled in a second.

From this you can extrapolate quite a bit of info about the F1 engine. Also they was a show on that the BMW technical director discussed the 2000 series motor and showed it's internals. Other info comes from my contacts in related fields and racing journals.

P.S I tried to post a link to the page which can do a number of mathermatical tasks in relation to engine calcs. but unfornately it was down.

Cheers Greg.

chris928

Ti 928 valves can be had from Del West:

http://www.delwestusa.com/manufactur...ium_valves.asp