Why do the AJ8's generate more power than the Speed Six?

[PipeNslippers]

It seems that the Speed Six struggles to break the 400 bhp barrier, where as you regularly see AJP8's achieving these figures?

I have also read that the AJP8 can be taken out to 4.7 with air flow capicity to spare in the head..?


But..the Speed Six is a DOHC / 4 valves per cylinder design..versus the AJP8 which is a SOHC / 2 valves per cylinder design (which should be less efficient)..

I can only put this down to the smaller size of each cylinder or a hotter cam..but I hear the AJP8's are also more torquey?

Any insight?

[steviejasp]

Extra 500cc helps i would have thought.

[Byker28i]

Cerbera owner pokes head in, smiles knowingly, strolls out...

[PipeNslippers]

steviejasp said:

Extra 500cc helps i would have thought.

The following thread highlights the figures below:

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

So there are some like for like engine size camparison between the AJP8 and Speed Six:

Graham - Cerbera 4.5 426.3bhp, 360 ft/lbs
FrmYardPants - Cerbera 4.5 410bhp
Fubar - 4.5 Cerbera 406bhp 365ft/lbs
Ridds - 4.5 Cerbera 390bhp
D14AYS - 4.5 Sagaris 386.9 bhp 345ft/lbs
Byker28i - Cerbera 4.2 - 380.7 bhp 330 ft/lbs
Noisy - Cerbera 4.2 - 377.7 bhp
Pmessling - Cerbera 369bhp
GT6K - Cerbera 4.5 365bhp
Demondad - Cerbera 4.2 364.8bhp
TC - Cerbera 4.2 364bhp
Englishman - Sagaris 353.5bhp 300ft/lbs
WhyTwo - Cerbera 4.2 341bhp
Biper - Chimaera 500 302.3 332 ft/lbs

[PascalBuyens]

steviejasp said:

Extra 500cc helps i would have thought.

And probably the extra 2 cylinders as well...

[JR]

steviejasp said:

Extra 500cc helps i would have thought.

Except that there isn't an extra 500cc, as posted above.

[tejr]

Approaching 100bhp/litre isn't a bad figure, most cars making those figures make them high up in the rev range, and probably prefer a lighter piston/smaller displacement configuration rather than a big straight 6.. and at 4.0litre the Speed 6 is a quite a big 6 pot?

[JR]

In short the V8 was the result of a lifetime of experience in trying to get a powerful, torquey, lightweight compact engine and the S6 was the result of one man's romantic dream ignoring the technological drawbacks of a long engine.

[V8 GRF]

JR said:

In short the V8 was the result of a lifetime of experience in trying to get a powerful, torquey, lightweight compact engine and the S6 was the result of one man's romantic dream ignoring the technological drawbacks of a long engine.

Nicely put... mind if I use that line sometime?

[PipeNslippers]

V8 GRF said:

Nicely put... mind if I use that line sometime?

So BMW (and the Nissan Skyline's)have got it wrong all this time?

'In-line' or 'V' should not affect power output, or should it?

I thought V's were preferred for their packaging advantages..?

[steviejasp]

JR said:

Except that there isn't an extra 500cc, as posted above.

I don't understand. 4.5l Ajp and 4l speed 6, surely that is an extra 500cc isn't it?

[JR]

V8 GRF said:

JR said:

In short the V8 was the result of a lifetime of experience in trying to get a powerful, torquey, lightweight compact engine and the S6 was the result of one man's romantic dream ignoring the technological drawbacks of a long engine.

Nicely put... mind if I use that line sometime?

Ha ha, no problem.

[JR]

steviejasp said:

JR said:

Except that there isn't an extra 500cc, as posted above.

I don't understand. 4.5l Ajp and 4l speed 6, surely that is an extra 500cc isn't it?

4.5 AJP V8 vs 4.5 AJP6 (or S6 if you like) is the same cc.

[PipeNslippers]

steviejasp said:

I don't understand. 4.5l Ajp and 4l speed 6, surely that is an extra 500cc isn't it?

There's a 4.5 (Speed Six) Sagaris in the mix..

[steviejasp]

JR said:

4.5 AJP V8 vs 4.5 AJP6 (or S6 if you like) is the same cc.

s6 is 4.0l isn't it?.

Edited by steviejasp on Monday 14th November 15:38

[JR]

PipeNslippers said:

V8 GRF said:

Nicely put... mind if I use that line sometime?

So BMW (and the Nissan Skyline's)have got it wrong all this time?

Hmmm, I can see this thread going tits up.

Take BMW. If they didn't have all the tooling and experience of the S6 then I'm sure that they would have switched to a V layout earlier. When they finally could not ignor the inevitable they went to V8s and then V10s. For a road car the smoothness of the S6 is a nominal advantage but not a lot these days. In short you can't ignor the commercial aspect when looking at engine choice.

[steviejasp]

PipeNslippers said:

There's a 4.5 (Speed Six) Sagaris in the mix..

There was some dispute/upset on this at the time iirc.

[PipeNslippers]

steviejasp said:

s6 is 4.0l isn't it?.

Edited by steviejasp on Monday 14th November 15:38

I belive this is one of the TVR Power s6 4.5 upgrades...

[JR]

PipeNslippers said:

'In-line' or 'V' should not affect power output, or should it?
I thought V's were preferred for their packaging advantages..?

Yes it should and it does from having a shorter crank.
That's only one advantage.

[PipeNslippers]

JR said:

Yes it should and it does from having a shorter crank.
That's only one advantage.

How does a shorter crank improve power?

The increased weight of a crank may affect the rate of acceleration (as it is harder to increase it's speed of rotation), but why would it reduce power (as it is not a reciprocating component like pistons and rods)?