View Full Version : How much power from a 16V ?
Hi
Most of the logic here comes from excellent site:
www.pumaracing.co.uk
Considering VW 16V (1.8 or 2.0L), the overall power output is governed by the induction tract flow. If fitted with TB's etc, its likely that the limit on this flow will be the valve.
Stock valves are 32mm inlet, 28mm exhaust, both with 7mm stems.
For stock valves:
Total inlet valve area = 6434 mm2
Adjustment calc for 16V design (increase by 10%) = 7078
Divide by 30 = 235 bhp (this is maximum race tune, TB's, hot cams etc)
Fast road is 75% of this = 176bhp
Rally tune = 85-90% = 199-211bhp
These figures from generalizations hold up pretty well I'd say.
Now, this engine will take 34mm inlets:
Total valve area = 7264 mm2
Race tune = 266 bhp
Road tune = 199 bhp
Rally tune = 226-239 bhp.
Note that capacity of the engine has not entered into this. A smaller engine will just have to burn more air per unit time to make same power as a larger engine, i.e rev more.
Now then.....
A stock 1800 has 86.4mm stroke and 81mm bore. This can be bored to 83.5mm for sure and perhaps 84mm. At 83.5mm, capacity = 1892cc. Old BRM literature has this configuration listed that made 170 bhp @ 7K with head/cams and std induction.
A longer stroke engine, a-la-9A, has a 92.8mm stroke with same choice of pistons. When fited with a std 81mm piston, you get 1984cc and my engine in this configuration pre-TB's made 180bhp (and the BRM literature agrees with this).
So....I was always under the impression that a race engine was better with a bigger bore / shorter stroke and the bored 1800 is more along these lines and thus, much more likely to want to rev for some serious powermore than the 9A, perhaps this will get closer to the theoretical figs that the head could flow above.
Thoughts or comments ?
Cheeers
Rob
How did Lehmann get 260bhp from a 'similar' engine? ie there isn't much more to remove from the head.
that said - it did rev to 9k.
how would that work?
Mark
Originally posted by m0rk
How did Lehmann get 260bhp from a 'similar' engine? ie there isn't much more to remove from the head.
that said - it did rev to 9k.
how would that work?
Mark
The multiplier for total valve area for custom designed money no issue race engines is 25%
Thus, stock valves = 8042 mm2 = 268 bhp race tune
Big valves = 9080 mm2 = 302 bhp in race tune
About right.
Cheers
Rob
Originally posted by RobT
The multiplier for total valve area for custom designed money no issue race engines is 25%
Thus, stock valves = 8042 mm2 = 268 bhp race tune
Big valves = 9080 mm2 = 302 bhp in race tune
About right.#
The fact that it revved to 9K is irrelevant - these power estimations are based on the fact that the engine would have to rev as much as would be needed to max out on the inlet flow - whether this would be possible is another question, the engine may not be able to rev that much without falling apart - hence my point about using a shorter throw crank.
Cheers
Rob
bloody well it is as well
TOCA no limits ish engines of a couple of years back made circa 300
sounds like an amazing freak of maths, or it's a damned close approximation.
The other interesting thing is that the common belief with this engine is that the exhaust ports are limiting to flow - there have been some cracking photo's on Vortex where a chap has taken a 16V head and sliced it up with a big bandsaw to show the port shapes - admittedly the exhaust ports are tighter than the inlets but they dont look so bad to me
Flow figs I have for my BRM head (stock valve sizes) are 106 cuft/min (inlet) and 92 cuft/min exhaust (both at 10 in WG). Not so different.
(stock are 87 inlet and 66 exhaust)
Personally, I'm not so sure the exhaust side is limiting to power.
Cheers
Rob
so what is the limiting factor then? :)
sean martin
19-02-2004, 09:43
aaaaaaarrrrrrrggggggghhhhhh! 16v just cost too much to tune. I could have a 1.8t transpant and had some change left over. f**k!!!!
max_torque
19-02-2004, 10:22
Originally posted by Saul
so what is the limiting factor then? :)
the size your wallet!:D
For an Normally aspirated engine, torque = Vol eff (cylinder filling) and power = revs.
even with the best intake system availible you can only ever get so much fresh charge into the cylinder (say 105 to 110% manifold Vol Eff), but if you can do this at 9000rpm you can make proper big power!
for a road car based engine (ie not started as a race engine design) typically 7000rpm is good for approx 100/bhp per litre, 8500rpm takes this to 120bhp per litre, and 9000rpm and upwards takes you to 150bhp per litre (the exception being the super tourers that made 150bhp per litre down at 8500rpm thanks to million of ££'s turning a road engine into a race engine!)
What you need to do is to work out how much you have to spend, build a bottom end to take the neccessary rpm then spend the rest on the head!. The basic difference between a pucka race engine builder ie the Ilmor's and Cosworhts of this world and you common or garden builder is the extent to which they optimise the basic parameters of an engine layout, ie bore stroke CR valve size / squish / port flow / tumble / injector location and spray / timing, and importantly FRICTION.
As friction increase as almost the square of engine speed, at say 7000rpm it's not too big a problem, at 8500 it's a big deal!
This is why peak torque is always lower rpm that peak power, because if say a cylinder has the same charge / heat release at 4000rpm as at 6000rpm, there will be the same force on the piston but the higher friction at the 6000rpm speed will result in less torque, but more power as the rpm is higher.
max_torque
19-02-2004, 10:28
Any idea how long the std 16v inlet valve is?
i have fitted pug 306 Gti-6 inlets into my renault engine, they are 34mm dia but have a 6mm stem, (require an easy change of valve guide to suit), in my case the std Renault and std Pug valve are within 0.24mm of each other in length, easily sorted when you come to shim you cam up.
(PS the pug valves are only£5 each from a decent engine recon place etc.)
Originally posted by sean martin
aaaaaaarrrrrrrggggggghhhhhh! 16v just cost too much to tune. I could have a 1.8t transpant and had some change left over. f**k!!!!
I would say for a road car the turbo route is a better option but for racing, the class capacity limits you.
For a turbo engine, now multiply capacity by 1.7 (latest blue book), so a 1.8T would have a NA equivalent of 3060cc - i.e over 2L and you would find yourself up against TVR's and the like which are seriously fast when prepared for racing.
There's something about a tuned 16V on full throttle though......personally I love them.
My next one will howl believe me.
Cheers
Rob
Originally posted by max_torque
for a road car based engine (ie not started as a race engine design) typically 7000rpm is good for approx 100/bhp per litre, 8500rpm takes this to 120bhp per litre, and 9000rpm and upwards takes you to 150bhp per litre (the exception being the super tourers that made 150bhp per litre down at 8500rpm thanks to million of ££'s turning a road engine into a race engine!)
What I am chewing over right now is stay with 1984cc (class limit 2L) and use a long stroke engine or drop to 1892cc and use the short stroke engine. As I am after 240 bhp this time, this will only come with 8.5 - 9K rpm and I think this will be much more do-able with the short stroke than the long. But the long will still rev so perhaps I am being over cautious.
Other point is that its getting hard to get 9A (2L)motors but KR's (1.8)are very easy to get hold of for a starter engine. I dont want to go ABF route since the engine is taller (likely heavier, less under bonnet clearance - which is tight with DTH TB's, tubular manifold will have to be modded to fit).
Max (or anyone else) - what are your thoughts on short vs long stroke ?
Cheers
Rob
max_torque
19-02-2004, 13:42
Biggest bore, shortest stroke everytime!
also if the class capacity limit is 2.0 litres, make very sure your engine is at least 1999cc, because at 120bhp per litre, every cc is 0.12 bhp, so a 1984cc engine looses 2bhp straightaway!
what is the std bore / stroke of the 2.0l?
of course big bore / short stroke means £££, not really on the piston / bore side of things but due to the custom crank required
(approx £1200 to £1800 from Doug Kiddie etc.)
(although you might find something left over from the VW F2 rally car days, either Ibiza or Golf 3 /4?)
Whats the 1.8 bore stroke? (can you get 2.0 with a 1.8 crank and big bore?
for over 34mm intake valves you needs a bore upwards of 85mm to get the reasonably unshrouded.
Originally posted by max_torque
Biggest bore, shortest stroke everytime!
also if the class capacity limit is 2.0 litres, make very sure your engine is at least 1999cc, because at 120bhp per litre, every cc is 0.12 bhp, so a 1984cc engine looses 2bhp straightaway!
what is the std bore / stroke of the 2.0l?
of course big bore / short stroke means £££, not really on the piston / bore side of things but due to the custom crank required
(approx £1200 to £1800 from Doug Kiddie etc.)
(although you might find something left over from the VW F2 rally car days, either Ibiza or Golf 3 /4?)
Whats the 1.8 bore stroke? (can you get 2.0 with a 1.8 crank and big bore?
for over 34mm intake valves you needs a bore upwards of 85mm to get the reasonably unshrouded.
Std 1.8 crank is 86.4mm and pistons certainly go to 83.5mm = 1892.7 cc. I have heard that 84mm pistons are available but do not yet have confirmation = 1915.5cc. I believe thats it as far as boring a std block. 84mm piston is getting big enough to get those 34mm valves working though !
Std 2L crank is 92.8mm and std pistons are 82.5mm = 1984.5cc. 83mm gives you 2008.7cc i.e. too far for class limit.
I cannot afford to get a custom crank made but intend to make use of std forged item.
Cheers
Rob
Originally posted by max_torque
Any idea how long the std 16v inlet valve is?
(PS the pug valves are only£5 each from a decent engine recon place etc.)
you know my dad then :p
if it needs a specific he'll find it or adapt it
be warned his favourite list is Ford ;) theres a lovely 1930's bugatti running round ere winning awards and comment of how smooth it runs - little do they know there's half a pinto inside that old crankcase
max_torque
19-02-2004, 20:06
Pistons should not be a problem, for example see Accralite's web site, ( www.accralite.com ) which has a convient piston chart finder thingy, just type in the bore you want and it looks up all the availible sizes.
However as they have a range of forged blanks it is no probs to tailor the piston and ring pack to you needs for no extra cash. (budget approx £180 per piston typically)
Accralite do a piston for the renault 2.0 16v, which has a 82.7mm bore and 93mm stroke for 1999 cc, so on the vw's 92.8 mm stroke this would be about just about ideal.
However the Grp A rally engines used a large bore / short stroke to enable them to get over 260bhp, because with a 93mm stroke your pistons are approaching a mean of 25m/s at 8000rpm which is limiting, both in accel (3890 G peak!) and speed (friction!)
The Pug gti-6 engine is square at 86/86 and has a good unshrouded inlet valve and room for reasonable squish band around the chamber edges, even then the Grp A engine is taken to an 89mm bore to maximise the advantage.
For a long stroke also take care to package the longest rod you can to minimise thrust loads, use a short compression height piston with a shallow top land, and add back the height with the rod. Also consider reducing your crank big end journal diameter to reduce reciprocating mass and oil drag. (typically this will be over sized to cope with production car mileages and poor oils / poor driving, ie WOT at 1000rpm etc)