Theoretical Max BHP

[Syed Shah]

Well 22B certainly was looking more at the real world, but he was in agreement with Iain, who was simply looking at things from a mathamatical perspective.

Alex, see my post on the previous page about real world results (using large displacement engines).

[Mycroft]

As this thread is being taken down this route, perhaps the "MORE CUBES" engineering has its final resting place here;
http://www.vlewis.net/loader.html

The cheesy music is very appropriate, don't you think, lol.

[Syed Shah]

Link not working for me

So, answer the question Iain, which will mak more power, a 2.5ltr 6cly, or a 5.0ltr 12cyl???

[somberg]

Quite amusing that link Mycroft

2300 HP @ 1900 RPM, 65 liter (gulp ) displacement.

2300 / (1.9 * 65) = about 18,6 HP per 1000 RPM per liter

Not bad, when comparing to a

Golf TDITDTTDTI producnig 150 PS at say 4000 RPM, 1.9 liter (?)

150 / (4 * 1.9) = 19,7 PS per 1000 RPM per liter

Frankly I don't quite understand your problem Syed. Your question cannot be answered because there are too many unknown variables involved.

[JohnA]

Originally posted by Syed Shah
...displacement would yield worse results on drag cars etc. ..Not true.

OK, I'll try and explain this to you (how I see it, anyway)

First of all we're not talking simply about displacement, but "displacement per cylinder"
You can have a 20cc cylinder (Honda made a 6 cyl 125cc motorbike) and a 800cc cylinder (Suzuki DR BIG)
However, the size of the air molecules and the atomised fuel remains the same.
Also the generation of the combustion chamber technologies are the same.
You can't really expect the same combustion efficiency in a 1cc cylinder as in a 1000cc cylinder, can you? After all the flame propagates at the same speed, irrespective of cylinder size.
If anything, the huge cylinder has a lower chance of mixing the fuel properly, no matter how it swirls or tumbles it.

On a similar concept, you cannot have 100ft insects flying around, because they would be much too larger than the air molecules they displace (in order to fly)

On a different note, the fact that you can't rev a big cylinder as easily as a small one, doesn't help either

[Syed Shah]

Originally posted by JohnA
OK, I'll try and explain this to you (how I see it, anyway)

First of all we're not talking simply about displacement, but "displacement per cylinder"
they displace (in order to fly)

That was all I was getting at, Mycrofts statement that displacement is counter-productive, only applies on the volume of each cylinder.

A large displacement will give better results, than a smaller one, with the same bore+stroke.

Now, if the bore and stoke are held constant, like in my example, the only way to increase displacement is more cylinders. And this will create more power.

[Mycroft]

Thank-you for the mail on this matter.

I have Syed on my ignore list in an effort to avoid a 'handbags at dawn' incident, anyone who knows me well will understand why.

To re-state my position on here would be pointless because it was in my first post in this thread, but so that there is no confusion over what I, Ricardo, Lampredi, David Burn, Peter Setzer, Carol Shelby and most importantly David Vizard all agree on I will copy and paste it here to save you all the trouble of going back a page;
.............
Syed, efficiency palys a part in this, the theoretical ideal is a chamber size somewhere between 380 and 450cc smaller than that and the revs have to be very high up and torque goes up that way also so not a nice motor to drive.

The 1JZ and the RB25/26 were designed around this theoretical ideal.

Getting 100bhp/ltr is quite easy for cars with small cylinder displacement but try getting 800hp from an 8ltr V8, the efficiency drops off quite remarkably as that displacement heads to a litre per cylinder, put simply I believe David Vizard [probably the closest any man I know that deserves the title Guru] says that the same 'work' on a 1 ltr/cyl motor that releases 100hp/ltr on smaller displacement motors will return you 88hp!

Mathematically, he is spot on.

I even left in the awful spelling mistake that offends me.

[Syed Shah]

Well, the example I used would have a cylinder size of 418.2cc, so thats fine.

I never said anything about an 8cyl 8ltr car, I know it would be inferior (for a start, anything more than 5krpm would be OOT for it).

For a set cyl volume, more cyl = more displacement, more power and the same rev limitation.

[JohnA]

Originally posted by Syed Shah
For a set cyl volume, more cyl = more displacement, more power and the same rev limitation.

...Assuming that you end up with a cylinder configuration that can rev properly (without huge counterbalances)

The straight six is inherently smooth indeed - how would you "increase the displacement" in this case?
Not realistic is it?

[Syed Shah]

Simple, increase the bore slightly.

[alex h]

Originally posted by Syed Shah
Simple, increase the bore slightly.

Yes but if you go above 450cc's per cylinder it becomes inefficient....which was the point.

so 6x450 = the max = a 2.7 is the biggest you really want.

No body disagrees that more cubes=more HP but too many can be inefficent per cylinder. The question was max theoretical HP on a RB26DETT well for the max cc's-best effciency it looks like a 2.7L is best.

So what point are you trying to make that we didn't read about 4 pages ago?

[Syed Shah]

Originally posted by alex h




No body disagrees that more cubes=more HP but too many can be inefficent per cylinder.

So what point are you trying to make that we didn't read about 4 pages ago?

Well done for stating the obvious, what I already said, no need to repeat it.

BTW, Mycroft states that more displacement is bad full stop.

[alex h]

Originally posted by Syed Shah


Well done for stating the obvious, what I already said, no need to repeat it.

BTW, Mycroft states that more displacement is bad full stop.

FFS what's your f***ing point.
Other than turning a thread into a "I want the last word" farce?
We all know what's being said....but you forget that BBS's are first editions of thoughts and so if things arn't worded perfectly then try reading between the lines.

End of story. Think this has gone as far as it can.

[JohnA]

Originally posted by Syed Shah
Simple, increase the bore slightly.

Increasing the bore doesn't give you any extra cylinders. You just get the same number (and configuration) of cylinders, just bigger ones. And we've already discussed this.
(I can see why Mycroft abandoned the thread now...)

[Adamantium]

To be fair syed did say that he would increase the number of cylinders maintaiing the ideal volume per cylinder.

In this situation you would get more power yes, but you would have much larger rotating inertia and at this point frictional losses increase drastically, so you wont simply get double the power despite maintaining a close to perfect volume/cylinder figure.

in mycrofts defence, you have picked on the fact that he didnt say increased capacity per cylinder produces deminishing returns, but we all knew what he meant. Dont mean to be rude but it was a silly point to argue as surely you can see that mycroft is a little better versed in these matters than the rest of us and knows what he is talking about, so I dont really see the point in chasing him to get him to admit he made an error in how he communicated what we all understood anyway.


Rather than putting this one to bed I was hoping to throw it in another direction.

On reading this months evo magazine I saw gordon murray (who I have massive respect for) utterly slate the idea of turbo charging.

I appreciate that a normally aspirated engine is a purist way to go, but had wondered if he had considerd the benefit of forced induction from the point of view that it enables you to generate enormous power while crucially keeping weight down. in itself a very important consideration in terms of performance and handling.

I think there is enough electronic jiggery pokery available to by means of variable geometry turbo chargers, anti lag, twin scroll etc, nitrous to remove lag entirely. and boost control can deliver a linear power delivery if required. These systems may complicate things and add weight but I dont see why ultuimately it would be wrong to use a small power plant modified in such a way as described above to produce the power and torque in a way which mimmicks a large NA engine. Only downside I can see is longevity.

You also get the added advantage of much more torque, whereas the likes of the mclaren F1 has to make do with a lowly 470lbft, compared to 631bhp.

can someone show me where I have gone wrong except for by not maintaining a purist viewpoint?

[323GT-R]

I read that piece too, I took the comments he made regarding turbo engines to be in the context of the overall 'feel' of driving the engine, ie that an N/A engine would have a better and more progressive throttle response and generally a flatter torque curve. I think he was also having a bit of a swipe at the Bugatti 1000HP target, a purely HP target where the F1 was designed to be the ultimate driving car.

His comments on supercharging being better than turbo charging were interesting...

[Syed Shah]

Well, since 22B has ended that saga, lets continue........


For the NA/Turbo arguement;

i personally think that for an all-out race car, NA is best: balanced power delivery. The problem is that to get that much power from an NA engine, it has to rev very high (look at F1 for example), and this in turn leads to a very short engine life. But for a race team, this is not much of a problem.


With the low weight they have, race cars dont need absurd (1000bhp+) power figures to be extremely fast. So, with this in mind, NA is the best route, on a light race car.

But, this does not apply to most of us,

We have heavy cars, that need much more power than a race car to go at the same pace. We also can't rebuild a road car engine every 500miles. So we can't rev as high. To make high power without revving to 15000rpm+, we need forced induction. Which is why the turbo option is better for us.

So, he is right from an all-out racecar viewpoint. But for a road/drag car, forced induction rules.

[Adamantium]

errr mclaren f1 has same redline as m3, ie circa 8000