Ultimate F7? FAO BenR/Stan

[unrealneo]

I was reading earlier about the Sodemo, Solution F etc F7R (short stroke to reach higher RPM) and mean piston speeds etc....

Would I be right in saying an F7P is a better starting point for ultimate power over a F7R? ....If you were starting from a production block that is!

Of course that may depend on how far you can bore the F7P.

What's the max you could bore the F7P to reliably?

I am of course assuming that the reason those unit reach 280-300bhp n/a is due to the RPM they can reach?

[unrealneo]

[Winston]

Drooooooooooooooooooool :P

[stan]

The casing as designated by F7P/R is irrelavant when it comes to over-boring, as the spacing between cylinder centres is the same. The max overbore i think you would get away with is 84mm, tho this would need a "special" gasket to aid sealing on the reduced material between the bores.

As for power, yes, it needs to be revving alot higher than std to achieve those power figures....hence the short throw crank.
The cylinder head would need to be up to it flow wise, with attention payed to combustion chamber, valve area etc etc to promote flow and burn rates at high engine speeds....would be quite intresting to see proper pics of it!!!
The engine will be totally revised in terms of geomtry, component materials (and coatings etc etc), with only the outside of the casing as Renault intended it! everything is critical...aerodynamic properties of conrods, crank....geometry of reciprocating mass, ratios beteen rod length and stroke, friction between bearing surfaces etc etc etc etc...theres so much to consider that u cant even begin to skim the surface on a forum!!

[BenR]

If your starting from scratch then the F7R is what you want.

You can only realitically bore the F7's out to 84mm, the cylinders are too think and close together. The current trend is reversing (as it always does in cycles) and to run as long a stroke as you physically can make work.

With material advancements the piston speeds are becomming less and less of an issue. This means you can run longer strokes, more beneficial conrod angles. And when restricted to capacity you can run a smaller bore and control the burn more efficiently, wasting less energy waiting for the flame to propagate accross a 10mm or so bore.

RPM is only one part power production, and the higher you go the harder things get to keep things flowing. I personally would stroke the crank further to something like 98-100mm, run a piston with a 28-29mm comp height, drop the rod length to 142.5mm etc.

You could still keep a r/s of about 1.425 and rev to about 9500-10,000.

use some of my 35mm valves and work hard on the flow abilities......320-330bhp is on the cards i'd say.

[BenR]

I am of course assuming that the reason those unit reach 280-300bhp n/a is due to the RPM they can reach?

Saying that, the BTCC 19's used to reach 280bhp at 8500rpm so its not the the sole reason.

[unrealneo]

[quote="BenR"]and rev to about 9500-10,000.
[\quote]

With a stroke even longer than a standard F7R?

For how long?

A standard F7R reaches 25m/s mean piston speed at around 8000rpm IIRC.

I've read that even F1 cars dont go much above 25m/s?

Or is my information out of date?

[BenR]

average speeds mean dick and all.

an S2000 has higher mean speeds than an f1 car, but the accelration rates are totally different. F1 pistons reach their peak speeds in a much shorter time than road cars.

Its all about materials nowadays, i know friends in the states that are running 106mm cranks at 10,000-11,000rpm and 93mm crank to 15,000rpm. All on 2.3-2.7ltr honda 4 pots making over 390-400bhp NA.

[stan]

With material advancements the piston speeds are becomming less and less of an issue. This means you can run longer strokes, more beneficial conrod angles.

In terms of power density, i think the main problem with increased piston speed isnt a mechanical one dictated by the ability of the piston itself, but the sheer lack of time-scale at high rpms for a full burn to be achieved.

As always its a pay-off....you reduce bore diameter in order to promote high speed burn ability, but you reduce capacity and valve area.

[unrealneo]

average speeds mean dick and all.

an S2000 has higher mean speeds than an f1 car, but the accelration rates are totally different. F1 pistons reach their peak speeds in a much shorter time than road cars.

Its all about materials nowadays, i know friends in the states that are running 106mm cranks at 10,000-11,000rpm and 93mm crank to 15,000rpm. All on 2.3-2.7ltr honda 4 pots making over 390-400bhp NA.

Do you have any pics or videos for me to drool at?

That is all, thanks. :D