If TVR made a V12..
Discussion
Thats a bit surprising really, plenty of other cars have similar or more power and don't break dynos...
I'm going to start an internet rumour saying that TVR realised the power was going to be embarassingly less than what they hoped it would be, and so said the dyno broke to save face!
I'm going to start an internet rumour saying that TVR realised the power was going to be embarassingly less than what they hoped it would be, and so said the dyno broke to save face!
It's not really about bhp/litre though. I suspect the Speed-12 makes it's power owing to the "8-litre" statistic, which makes it "only" 100bhp/litre.
4-cylinder engines tend to make over 120bhp/litre in "tuned" form.
Contrast that with a 350bhp 5-litre RV8 which makes a mere 70bhp/litre.
An AJP8 can easily break the 100bhp/litre barrier and that's only a 2-valve-per-cylinder engine. If TVR designed a proper 4-valve-per-cylinder engine, even a large capacity V12 ought to make 110bhp/litre easily.
Some of the bike engine-derived V8s have interesting stats though. A 2.6-litre RST-V8 can make North of 350bhp. People complain they lack torque but given they rev far higher than a conventional V8, you can afford to "gear-down" with a higher ratio differential. That more than compensates for low torque at the flywheel.
So, my betting would be to copy some of the small capacity Ferrari V12 engines from the 60's. Make 'em rev..!!
4-cylinder engines tend to make over 120bhp/litre in "tuned" form.
Contrast that with a 350bhp 5-litre RV8 which makes a mere 70bhp/litre.
An AJP8 can easily break the 100bhp/litre barrier and that's only a 2-valve-per-cylinder engine. If TVR designed a proper 4-valve-per-cylinder engine, even a large capacity V12 ought to make 110bhp/litre easily.
Some of the bike engine-derived V8s have interesting stats though. A 2.6-litre RST-V8 can make North of 350bhp. People complain they lack torque but given they rev far higher than a conventional V8, you can afford to "gear-down" with a higher ratio differential. That more than compensates for low torque at the flywheel.
So, my betting would be to copy some of the small capacity Ferrari V12 engines from the 60's. Make 'em rev..!!
Mars said:
An AJP8 can easily break the 100bhp/litre barrier and that's only a 2-valve-per-cylinder engine.
Are you sure ? HarryW's Cerb is the only one I know of that makes 450bhp from 4.5 litres. Of course if you're talking of wild cams or turbo/supercharging then that's different.Edited by S5TVR on Monday 25th August 18:34
As far as I'm aware very few of them have had any *proper* headwork done. Yes I've heard all about the Red Rose variants but they are pretty limited in their scope. I'm convinced with a decent headjob and possibly slightly larger valves you could be knocking on 100bhp/litre with any of them.
Also, the Whirlwind induction could be supplimented by much longer secondary induction (from the airboxes to the filter box). There's more to be had with a bit of care and development. It might require slightly higher revs though.
Also, the Whirlwind induction could be supplimented by much longer secondary induction (from the airboxes to the filter box). There's more to be had with a bit of care and development. It might require slightly higher revs though.
... and (I forgot) of course we are talking "theoretics" here, so while te AJP8s may, in practice, rarely achieve 100bhp/litre, their basic design isn't preventing this.
So, we want to design a V12, therefore I propose some of the AJP8 design aspects are a good place to start. Perhaps better cams and genuine steel components (the 4.5 steel cranks are, I believe, somewhat mythical), but the basics of the AJP8 appear to work well.
However I must declare my ignorance regarding the dimensions of V12 cranks though. Are they 3D like the RV8 or flat plane like the AJP8? Anyone know?
So, we want to design a V12, therefore I propose some of the AJP8 design aspects are a good place to start. Perhaps better cams and genuine steel components (the 4.5 steel cranks are, I believe, somewhat mythical), but the basics of the AJP8 appear to work well.
However I must declare my ignorance regarding the dimensions of V12 cranks though. Are they 3D like the RV8 or flat plane like the AJP8? Anyone know?
JR said:
Mars said:
What's the same thing?
You mean either flat or in-plane.The AJP8 is the eight cylinder version of the AJP12, or Speed 12 if you prefer.
Yes the engines are all flat plane but my understanding was that the V12 was a dervative of two Speed6 engines rather than an extended AJP8?
V8 GRF said:
my understanding was that the V12 was a dervative of two Speed6 engines rather than an extended AJP8?
The (singular) engine was designed as a modular V12 from which various engines could be carved out: V8, V10, V6 etc. Only the V8 and S6 got built as cast engines. The S6 head is the head off the V12. The V12 in the Speed 12 cars has a fabricated block (as per some pre WW1 cars but with modern technology eg. stress relieving techniques)which was the subject of an IMechE paper by the other JR.V8 GRF said:
Ok I understand the first principle, but am I correct though in thinking the fabricated V12 block came from two Speed6 blocks or was it built someother way?
According to my TVR "postcard" on the Speed 12:-"In principle it is two Speed Sixes but in reality it shares little but the valves of its smaller sister..."
Bob
This is taken from the Cerbera FAQ on here
What on earth is a flat-plane crank?
Like most Ferraris, the Cerbera's AJP8 engine uses a flat-plane crank. "Flat-plane" means that the crank throws are all in a single plane - i.e. if you laid the crank on a desk it would be flat. Laying the crank of a conventional (twin-plane) V8 on a desk would result in a very three-dimensional wobbly thing sitting there. In both cases however, the desk will get very oily. With a twin plane you get eight evenly spaced firing intervals for every two complete engine revolutions, but the downside is that you can't take advantage of exhaust pulse extraction effects since the manifold design is prohibitive. The Cerbera's flat plane crank means that the engine (essentially) becomes two four cylinder engines operating on a common crankshaft, so the exhaust design is made like a traditional 4-2-1 set up to take advantage of pulse tuning effects.
Thus a flat-plane crank produces an engine that is more powerful but rougher in nature. It also means that the engine sounds like a pair of four cylinder engines together, rather than the classic "warble" of a V8 (e.g. the Rover engines used in Griffiths and Chimaeras). As a point of useless trivia, a four cylinder engine in a "boxer" configuration, as used by old Alfas, Beetles and of course the Subaru Impreza sounds like a classic V8.
The unusual exhaust sound is made even more weird by the "V" angle not being 90 degrees. Its 75 degree angle means the engine doesn't behave exactly like two four-cylinder engines since instead of the firing intervals being 90 + 90 degrees apart they are 75 + 105 degrees apart.
I bet you didn't really want all that gory detail, did you? And I bet you're now wanting to know what "pulse effects" are? Basically its a technique where exhaust gets actively sucked out of the cylinders by the exhaust system, due to standing waves being set up in the exhaust pipes. Better? I didn't think so....
Other variations in noise on similar designs are down to induction and obviously silencing design and type.
What on earth is a flat-plane crank?
Like most Ferraris, the Cerbera's AJP8 engine uses a flat-plane crank. "Flat-plane" means that the crank throws are all in a single plane - i.e. if you laid the crank on a desk it would be flat. Laying the crank of a conventional (twin-plane) V8 on a desk would result in a very three-dimensional wobbly thing sitting there. In both cases however, the desk will get very oily. With a twin plane you get eight evenly spaced firing intervals for every two complete engine revolutions, but the downside is that you can't take advantage of exhaust pulse extraction effects since the manifold design is prohibitive. The Cerbera's flat plane crank means that the engine (essentially) becomes two four cylinder engines operating on a common crankshaft, so the exhaust design is made like a traditional 4-2-1 set up to take advantage of pulse tuning effects.
Thus a flat-plane crank produces an engine that is more powerful but rougher in nature. It also means that the engine sounds like a pair of four cylinder engines together, rather than the classic "warble" of a V8 (e.g. the Rover engines used in Griffiths and Chimaeras). As a point of useless trivia, a four cylinder engine in a "boxer" configuration, as used by old Alfas, Beetles and of course the Subaru Impreza sounds like a classic V8.
The unusual exhaust sound is made even more weird by the "V" angle not being 90 degrees. Its 75 degree angle means the engine doesn't behave exactly like two four-cylinder engines since instead of the firing intervals being 90 + 90 degrees apart they are 75 + 105 degrees apart.
I bet you didn't really want all that gory detail, did you? And I bet you're now wanting to know what "pulse effects" are? Basically its a technique where exhaust gets actively sucked out of the cylinders by the exhaust system, due to standing waves being set up in the exhaust pipes. Better? I didn't think so....
Other variations in noise on similar designs are down to induction and obviously silencing design and type.
Edited by V8 GRF on Tuesday 26th August 14:57
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