Fastest928

Louis has set the mark...his 6.4L is belting out a reliable, drive it till you die 595 rwhp at 6.4L of displacement using "normal" stroker parts!

An amazing 93rwhp/L!

Mike Simards equally impressive 640 rwhp at 7L or 91 rwhp/L is an amazing engine in its own right.

With these two engines, a new bar has been set!!

Will there be a 700 rwhp at 7L or a 640 rwhp at 6.4L?

I don't know, what I do know is it is time to go back to the drawing boards!!

Best,
Marc

zoltan944

I thought that was calculated at crank? for instance the Euro E36 M3 was 333hp crank at 3.3 liters or something?
595hp is over 640 crank albeit there are still some high goals to be set to match some of these guys!

Lizard928

at 91 or 93 RWHP that is well over 100HP/litre!

It is showing very nice efficency with no real restrictions in the heads of these cars. You just need cams, ITBs, and proper exhaust!

IcemanG17

true......but the new GT3 is 114.5HP/L on the crank...so if Louie is 595rwhp thats 700HP crank at 15% loss or 109.375HP/L....Mike is 752hp or 107.43HP/L...so clearly the ITB's are the way to go...& remember both of these engines are designed for STREET GAS...Mikes is only 10.5CR & Louies is 11.3.....

As a comparison my M3 V8 makes peak HP at over 8,000rpm but is rated at "only" 103.5HP/L and it also has ITB intakes BUT 12.0CR....vs Louie and Mike making that power FAR lower in the RPM's

Of course Todd's 30psi monster makes 675whp or 843HP @ 20% on 5.0L or 168.6HP/L, but boost helps a bunch

danglerb

Can somebody explain to me why percent of HP is used for drive train loss?

I can't imagine how it would be related to anything but RPM, with the same loss in HP for a 220 HP OB or a 700 hp monster.

ptuomov

John Kuhn is I think over 600 rwhp at this point from a 5.0 liter turbo with an all-stock long block and intake manifold.

Of course, turbos would dominate any comparison like this so perhaps they should have their own category. I think that already in the 1980's one could get about 1200hp from a 1.5 liter turbo for a qualifying lap.

Lizard928

Brian, up the CR to 13:1 and get the cams maxed out and I think that Louie could br on par with the GT3s.

Boosted cars are in a whole nother league.

ptuomov

For the aspiring normally aspirated ones, here's a good link on engine technology:

http://www.epi-eng.com/piston_engine..._cup_to_f1.htm

At the time of writing, Nascar engines were at 140 hp/l with two-valve pushrod, helical springs and F1 engines were at 300+ hp/l with four-valve doch, pneumatic springs.

Mike Frye

I couldn't come up with a reasonable explanation so I did a little checking and found some stuff from Motor Trend that explains it.

Check here for a thread that explains it a bit (just the first two posts in this thread actually) Several of the links in the thread are dead, but here's one that explains it somewhat.

As I understand it, driveline loss can be calculated using an inertial dyno and some use different calculations than others, but basically at the end of the run the dyno operator has to put the car in neutral and the system can determine driveline loss by figuring out how fast the car decelerates on its own.

The amount of HP required to push a car from 150 mph to 200 mph is not linear and apparently neither is driveline loss due to friction.

slate blue

Tuomo that is great article, I lost that issue of RET and have been looking for that article ever since Thanks! I think that if the Cup engine was to run fi then it would equal the F1 engine, the F1 engine in reality is up against it as they have massive friction losses to contend with. Also the cup engine is a little down on capacity, only 5.9 litres, not 6.0 litres. An interesting fact and I'm sure a slight disadvantage to the F1 engine is that the pistons on the outer cylinders (In the V10) are cut to a different cam shape due to flexing of the block. The main disadvantage to the cup engine will be the flat tappet cam, a roller cam may allow faster acceleration of the valve but would the roller setup be too heavy for an endurance engine?

As to the 928 engines power outputs, what has been achieved is impressive indeed, I think they are pretty much optimized for the engine revs they are seeing. An engine is a symphony of parts and for revs to rise which is needed to raise the power per liter. A complete redesign is needed. An engine can only make a certain amount of power at set rpm levels. While I don't want to quote specific formulas, what engineers look at is volumetric efficiency at specific rpms. That is 105% at say 7000 rpm.

However if the volumetric efficiency drops to say 90% at 8000 rpm you will make less power. There is a few reasons why volumetric efficiencies drop. There is a very cheap and well regarded program that explains this well, it is called Pipemax, many top engine builders use it. What it details is the demand for air at specific crank angle. It has many other features too.

You plug in the figures to Pipemax for your head flow and cam figures. Basically what you supply is the amount of air that the heads can supply and the program tells you what the engine is demanding. So is the top end of your engine supplying the air the engine wants as the revs increase? If not volumetric efficiency drops away. However it is not that simple, if the port size is too small then airspeed will increase to a level that is generally regarded as leading to pumping losses. These losses are very large and overwhelm the gains from burning a greater amount of air and fuel.

The speed of the air that is relevant is around 700 fps and this is in the actual engine, it would be 310 fps if on a flowbench at a depression of 28" this critcial speed is about 0.60 mach. So despite the flow numbers on the bench being good you will lose power as this critical air speed kicks in in the real world. These are pumping losses.
http://www.slowgt.com/Calc2.htm#MinCross

Volumetric efficiency is about 110% at peak power for a Pro Stock engine (from memory) I have heard it is up to 145% for a Cosworth F1 engine. some of that extra power is lost due to friction otherwise the F1 engine would win easily.

You also don't want the port too big, if it is too big you will not achieve high volumetric numbers, now obviously these are not all the important issues, there is the helmholtz pulses that make a big contributions too, although Louie has commented that his experiments do not indicate a dramatic change on the intake side. The exhaust side is more powerful, these pulses can also work against you so again careful investigation needs to be carried out. We also have quite a lot of packaging issues on the 928.

So for power to rise in a meaningful way, the revs have to go up, this means reducing the stroke, to get the peak piston speeds down. A good calculator is below.

http://www.slowgt.com/Calc2.htm#PistSpeed If you want to compare to a Nascar engine which has very very high speeds for an endurance engine plug in a 3.25 stroke 10,000 rpm and a rod length of between 6 to 6.2 inches. (In fact in Nascar they reduce the crown thickness to run a slightly longer rod in the plate motors to reduce piston skirt loadings and piston rock. This is both a power and longevity issue.) They are able to reduce the crown thickness due to the lesser power outputs of the plate engine.

Then compare it to 3.75" stroke and a rod length of 5.85" you will see that the speed of the piston gets really fast is a long stroke engine, too fast in my opinion, this will have many effects, piston life will be short and it may fail around the pin bores.

Mike S has some great cams, I believe they are best made to date, cam lifts these days are in the 12.7 mm or 0.500" range, this is essential for the higher revs, remember the Cup engine has lots of lift around 0.800"+ You need some very nice springs, PSI probably make the best, some are polished to a mirror finish to remove stress risers.

Most cams in the new HiPo european engines use the radiused INA lifter, this is sort of like a roller for a cam over bucket arrangement, more valve speed and this means quicker openings in particular and the lesser duration for given airflow events, i.e more air able to flow in a smaller duration means the engine is able to build cylinder pressure earlier which directly influences the BMEP.

These are the issues that need to be addressed to increase the power, IMHO the headers and intakes that have been put to use to date are up to the task, the issues will arise are going to be in relation to mass forces, mass forces mass forces. Dry sump will mandatory for these high rpm engines along with proper vibration control, that may include balanced cams etc.

A word on dynos, different dynos will give dramatically different figures, the dyno jet generally from what i have seen gives the highest hp figures, I think a correction figure/factor should be around 10% for a manual 928 on this type of dyno. Nascar (again from memory) use a factor of 5% certainly no higher than 8% but the Nascar transmission has lower friction most likely than ours. It is specially produced for lightweight and low friction. Also other dyno tests with new cars indicate around 10% being a fair number on that dyno.

I think if we worked backwards from the engine revs where peak power is produced we could then work out the current volumetric efficiency. My guess is that Mike's engine is at 700 hp at the crank or 100 bhp per litre and depending what the revs were this would indicate a very high volumetric efficiency. Numbers aren't really my thing and I am on holidays at present. So I will leave that to someone else to workout.

Cheers Greg

FBIII

This 100 hp per liter isn't really a new concept. Years ago when Porsche was making much smaller engines they were nearly achieving this. My first Porsche a 70 911S was 2.2 liters and made 200hp din. 9.8 compression, individual throttle body mechanical injection, two valver with some healthy cams and a nicely tuned stock exhaust system. But as someone mentioned earlier less friction in a smaller engine and they are easier to buzz higher. This little engine redlined at a conservative 7300. The RSR's of the same era using the same cams but larger displacement and longer stroke redlined at 7800. But having to comply with todays emissions and lower octane unleaded gasolines probably evens the playing field with the lower tech engines of almost 40 years ago.

danglerb

I do understand the Dynojet drive line inertia trick, and I understand frictional losses increase related to speed, but speed isn't HP its rpm, which is what I was saying. An OB and a 700 hp monster accepting maybe some differences at the highest speeds, all of the speeds in the dyno test common to both will have exactly the same amount of HP loss, and widely different percentages of loss.

Maybe I shouldn't complain, without DynoJet if everybody had to use a drag strip for testing the whole aftermarket parts industry might not exist.

Fastest928

As far as I know, there are very few normally aspirated street able vehicles that produce 100 RWHP/L that have usable torque across a reasonable rpm band.

The S2000 is a great engine, but is really terrible to drive daily...having to spin the engine to 8K is not so much fun as it sounds.

FBIII

Having grown up in the late 60's, an era of cammy polluters, I still like engines that have less than flat torque curves. The 911S was a complete dog under 4500 but just howled when it came on the cam. A friends 69 Z28 behaved exactly the same way. A bit of a pain in the *** in stop and go traffic, but a pure delight when driven hard.

dprantl

If we could make a 928 engine that could reliably rev to 8,500RPM, it would be very easy to achieve a good deal over 100rwhp/liter NA.

Dan
'91 928GT S/C 475hp/460lb.ft