LUCKY DAVE

Uhh, guys.......hate to burst you bubble, but 165 hp/liter is standard output for bone stock sport bikes strangled by California legal emissions and quiet mufflers, burning 87 octane swill. The best race prepped versions are making 250 hp/liter.

Brian Morris

But that's doesn't take displacement, stroke and rpm into consideration.

The limiting factor for a 3L 4 cylinder car engine is going to be RPM. At 88mm stroke the 3.0 would be at 25 m/s at 8500 rpm.

1L sport bikes can turn a whole lot faster.

ritzblitz

Yeah bikes arent the same when they are making that power at 17k rpm...

If you search on youtube pocono 944, thats the car ive seen that makes 300bhp and revs to 9k rpm.

pete95zhn

There was an article in Excellence ( #175, August 2009 ) about this racer, the claimed power was 350hv @ 8500 rpm. 140 hv/l.

Some details has been leaked about the engine mentioned in title, and it's turning to be based on a S2 block...apparently displacement is between 3.2 and 3.6l and the head is milled from billet, so in that case it's a totally different animal...
I'll keep you posted if facts comes out.

Brian Morris

I didn't see the Excellence article, my figures from the builder were from 2004. It seems like 140 hp/l is pretty much the limit for state of the art engines of this size.

If it is actually 3.2l and a true one off custom engine then it seems like 450 HP is possible. The specs could be something like:

106 mm bore x 91 mm stroke = 3.2l

91 mm @ 8500 rpm = 25.8 m/s - which seems possible with a custom crank.

So 3.2l x 140 hp/l = 448 HP

333pg333

I think this is the same car I have heard of. Not sure of power, but damn they've got to be 335's up front!
So you're a comedian now that I'm over here. hahaha

67King

Not enough valve area. For comparison, I did consulting type of some work for an acquaintence with a 3.0L 6 cylinder. It had 12 33mm valves, for a total valve area of 103 square cm's. It made 306 at the wheels, so figure 350 at the crank. Race fuel, 13.5:1 CR. The new engine isn't done, yet, I'm thinking we may pick up 25-ish HP, and we put 34mm valves in it.

The S2 has 37mm valves, total area 86 square cm. The 968 has 39mm valves, 96 square cm. While the Porsche is over square versus the BMW being undersquare, which will help, even with 39mm valves, it is still shy of the valve area for one that may see 375 if we're lucky.

I just don't see it being anywhere near 450 horsepower. A 3.0L may do it, but it would take probably 10-11,000 RPM, and much bigger valves. Very unlikely, IMHO, that a 4 cylinder could do it.

pete95zhn

King, for general info, is there a common formula for counting theoretical max power output in relation to valve size?

My past 8V engine had 4x 48mm inlet valves = 72 cm2 valve area.

lee101315

Well, the internals were designed for that. The crank for the S2 weighs something like 55lbs, have fun modifing it for 17K rpm. Likewise, try modifing a sport bike engine for low end torque and doing what the S2 engine does.

I never said impossible. Just very expensive.

Brian Morris

Here is a page that discusses valve size and power:

http://www.pumaracing.co.uk/PP03.htm

He uses a mulitplier to determine power potential. His standard multiplier for 4V heads is 10% but then when calculating for a "F1" engine he uses a multiplier of 25%.

The formulas show NASCAR engines generate power using a 20% multiplier - and that's with 2V heads. I checked a few other high hp engines and they generate anywhere between 15-20%.

To generate 450 HP using a mulitplier of 15% you'd need around 43mm valves. I checked a few engines with 106mm bores and they can fit 43+ mm valves. It may not be possible to modify the stock heads enough to fit the big valves - that would be a reason to use a custom billet head.

67King

Kind of. But I'm never comfortable with that kind of stuff. A pretty good rule of thumb is that you assume the average air velocity in the intake stroke cannot exceed 110m/s. That is through the port, which is about 5-10% smaller than the inner portion of the seat. On big 2V's, the seat may be 3.5mm (making, for eample, your 48mm valve have a 44.5mm ID on the seat, and your port would be around 40mm). Another rule of thumb I've heard is 65m/s through the valve face (where you'd figure 48mm diameter in the calculations).

All that will give you, though, is RPM at peak power. To figure out a good power number, you'd need to know the thermal efficiency (better known as ISAC - or Indicated Specific Air Consumption) and the mechanical efficiency (FMEP - friction mean effective pressure).

Those are rules of thumb, though. I did a lot of analysis on that engine I referenced, which is why I felt good using it as a baseline.

bdesai7

lots of NOS

Cole

FWIW some of you guys are way high on your rpm numbers for 1 liter sportbikes. Most modern sport bikes hit peak power more around 12-13k not 17k. For example Yamaha claims 180 crank hp @ 12.5k for a998cc displacment.

ritzblitz

Good call, thanks.

How about a 600 though? Either way it will take high rpms to make 450bhp out of a 3 liter engine hah

V2Rocket

so why not build a 360HP 2.0L??! lol