Re: Old car, new engine. Spanking...

I never claimed otherwise. I did originally build and use braked dynos though and because of the use of load cells to measure torque (which have problems with hysteresis and temp stability) and analog digital conversion errors they are all but useless for reliable and repeatable backups giving the sort of errors you previously infered.

Plus in the real world the correct settings are set for dynamic conditions. At least on any race car and race bike when you open the throttle in any gear on any track it actually DOES accelerate.

Under aceleration things like fueling and ignition timing need to be a little different for optimum. A highly tuned two stroke or turbo bike for eg will always be safe with the correct advance while in an accelerating dynamic condition. With the revs held static you would possibly begin to get detonation and internal heat problems that do not occur on the track or the inertia dyno.

As an example, I really wouldnt have been able to run my own turbo/nitrous drag bike engine at certain rpms with full load for 1 minute! Or even for 5 secs. Because the fueling was correct for a rapidly accelerating engine. Holding the revs steady at say 7 thousand revs under load would allow it to develop full boost at this low figure where it wouldnt have had chance to spin up the big T4 that fast - the bike accelerates as fast as the olde worlde Rajay T04e did at least in low gears. In high gears it doesent matter because we are already up at the 10,000 rpm mark! Only time WOT can be used in low gears (1st, 2nd, partly third) is off boost due to huge lag. So the fueling allowed for this rather than being over rich on purpose for cooling and to allow 25lb boost. Run the correctly set up bike at say 7k under load at WOT and it will burn pistons as its too lean at that rpm for the amount of boost.

No they dont.

They time each and every drum revolution individually. They subtract one from the other and the result is the difference in time taken on that next revolution. Then they plot a point - They sample the engines RPM during the drums revolution and both the average engine rpm for that drums 360 degree cycle and the time taken for the drum revolution is sent as a data packet with a handshake (and checked) to the software. It can and does plot drum revolutions. In my software you can choose to display this every rpm or every whatever you choose rpm. But it grabs ALL the data and does so in real time. It can see the gear ratio changing as the run progresses. It can do accurate plots of twist and goes or automatics as some of my car dyno customers do daily.

Err crap! What can I say!!!

Yes and thats a GOOD thing at least for race vehicles!

Secondly an engine dyno has the annoying fact that they drive

Yes much the same as the car/bike itself does when you drive it. And that can also be useful in setting up fueling on a trailing throttle or when setting up fuel injection on various modern bikes to spit flames on overun only at high rpm consistently! :)

When the measured flywheel acceleration this

Its a big big problem. The ingines own internal and flywheel mass is massively too small for the result to mean anything! In the case of carbs all you can tell is that it gives a different "power" curve as you change the accelerator pump jet. Throw it away. Its a gimick for dummies.

but if they drive a steel drum , the energy in it is

Yes they are! The drums inertia is designed to match an average car or bike. What do you think happens in your car when you lift your foot off the throttle? Or isnt it designed to slow down with engine braking! My good where do you get all this crap?

Yes : better ones

In whose experience? Better ones use all kinds of emf devices and they dont wear and last indefinitely.

Well you are again wrong. Why am I not surprised!

1) Engine dynos can be and often are inertial dynos too. 2) An inertial engine dyno is just as simple as an inertial chassis dyno using the exact same technology...

Inertia dynos are cheaper no matter engine or chassis. They are the ONLY dyno system that is truly totally repeatable, even simple ones. They are because of this better for seeing really small changes like different coils or changing plug gaps. As I said you can clearly see the power output drop even turning on the lights during a run. Repeatably at will. I have never found any way to make braked dynos get close to this ideal.

Real reason is that tuners are as lazy as the rest of us. And a chassis dyno offers almost as much capability and gives the chance to evaluate gearbox/diff/oil/torque converter/gear change system like air shifters, etc as well as just testing an engine alone.

Leon Moss told me he couldnt see the difference testing engines on his chassis dyno or on the fancy engine dyno. He knew more about tuning than anyone else I ever met and I have met a lot of them!

The hand held thing is almost pointless. The braked dyno is the good old bocsh that the rep tests and calibrates using his reps car by turning a screw? Is that the one? Well trust me, buy a dynojet inertial dyno and prepare to be amazed. The bosch dynos are great for setting up basic fuelling, and ignition mapping etc because they let you read gasses and hold the rpm steady. For real race back to back testing and ABSOLUTE accuraccy between runs the cheapo dynojet dyno or one of mine if I was still interested in doing it would be much better.

The only reason they claim 500 is because they can actually do any amount! The only limit is traction. Again, another reason that bosch dynos are inconsistent is the rollers! Miles too small diameter and anything with a pair of rollers trapping the tyre has all sorts of grip problems. I couldnt even test my brothers 400bhp ish nitrous car on a bosch dyno because the thing just shook and wheelspins all the time! So much so all the dust and crap was falling from the headlining! And we had me, and two mechanics sat in the boot with a ratchet strap over the roof.

I have seen 1500 bhp cars tested without issue on single drum 48 inch diameter dynojet rollers.

I agree some do. In the same way that some "tuners" sell all kinds of expensive stuff that glitters and doesent work. Thats not the dynos fault - thats just because they get used because they are cheaper to buy.

That is not something feasable if

Well actually it is feasable. But would you want to be the one that tried to hold some seriously leant on turbo bike at steady rpm? Mine? Because when it detonated itself to death I would then be able to explain it was your fault!

Reply to
Burgerman
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I'm no metallurgist, but why a billet crank? Surely the strongest crankshaft is going to be a forged one? Or is that far stronger and far more expensive than needed?

Reply to
Doki

A billet crank is a crank cut out 1 billet, a cilindre of (special) steel out of which the crank is turned on a lathe.

It offres complete freedom, no distorsion, much stronger because the abscence of induced stresses, much more controlled as to dimensions and thus better balanced, better dimensionwise (so lighter), etc. Downside is the enormous "loss" of material and the work involved. There are around 10 companies worldwide who offre this service, all those I know are in the US.

For small badges of special engines however (once power > 100 HP/liter) it is the only option. Prices start around 7000 UKP (on known engine, known dimensions) to 12000 UKP (on prototypes).

CNC-cutting has however (for people like Prodrive etc) has reduced the workload on the lathe enormously and this means that on smaller badges (100-500) the cost per crankshaft descends enormously. Seems that all is as most on the times in numbers.

Tom De Moor

Reply to
Tom De Moor

I've often wondered about why billet cranks are supposed to be better when the grain flow will only be in one direction, I would assume along the axis of the crank, and a forged crank should have grain following the crank profile so should be stronger. Maybe this is down to the use of steel for the billet which has superior properties compared to a forging steel although my experience with BMC A series tells me that the factory made forged EN40B cranks and that is a material often used for billet cranks.

Machining will produce distortion, a common problem, especially with such large metal removal and it is very likely the billet crank goes through various heattreat stages to relieve induced stresses to ensure a stable crank. Any reason why a forged crank can't be as accurate dimensionally, it can be fully machined just as easily to the same tolerances.

I suspect the main reasons are going to be down to the original engine having an iron crank or inferior grade steel crank so billet is the option for greater strength and fatigue resistance.

Reply to
David Billington

I know what CNC machining is, and as far as I can see its main advantage is in short runs, rapid prototyping etc. which is why it's used so much in Aerospace development. What I don't understand is that 9 times out of 10 the lightest and strongest bike parts are forged...

Reply to
Doki

That's complete and utter s**te.

Also s**te.

More s**te.

And s**te again.

And the unidirectional grain of the steel, the heavier construction needed in consequence

And there are only two major manufacturers of forged crankshafts.

Indeed, it's the only option for very small production runs, that doesnt mean that it's the best.

Cost, time, ability to change dimensions on the fly. These are the reasons for choosing a billet crankshaft. Everything else is against it. Forged crankshafts are lighter, stronger, more durable and can be balanced and machined to the same tolerances as billet crankshafts.

Reply to
Steve Firth

Because the "grain" follows the shape giving better strength as in forged pistons. A billet crank does not have this advantage but to make small numbers of good cranks to your own design (maybe a stronger design shape) a billet is easier to work with.

Reply to
Burgerman

I guess it is indeed down to the quality of steel used. Maybe there is loss in strength after the heating cycles but that I do not know. My lessons metallurgie are to far in the past.

Your assumption might even be correct that forging in the same steel is better. Forging however is once again a very costly operation if done for very small production numbers.

Machining if done properly doesn't produce distortion. I don't know the exact wording in English but the large portions are taken away first in big steps (torque and power of the lathe are determing factors), in Dutch this is called "ruwen" -roughning translated. In this stage some distortion can take place but the part after "ruwen" is still 1-2 mm bigger than then final part. Controlling and escaping distortion is an integral part of the machinist job.

The final part is obtained by very small increments, often -in CNC always- with a special chisel and in steps of 0.1 to 0.4 mm.

The main reason for a billet crank is that the desired crank as such doesn't exist. It can be that a long course crank is wanted (for extra displacement) or lower course (so the engine can rev higher).

The engine in the cosworth of the Greek was stated as 1.9 l displacement, so it is possible that he traded some 100cc (or more) for revs. His revs com from smaller course and lighter (but maybe bigger) pistons (The pistons are displayed but diameter isn't mentioned).

Finally : there is a cheap mans version of the special crank with either longer or shorter course. The standard crank can be regrinded ex center. Most cranks take accept excentergrinding to 1 mm for the main bearings,

0.5mm for the bearing of the conrods. It means a variation on the course of -3 to +3 mm.

Big disadvantage is that the crank is weaker: bad news as the aim of the operation is more power and/or higher rpm

All this said: safety margins on any crank are huge, so the cheap man version is a tale of "it is not supposed to work but it works".

Tom De Moor

Reply to
Tom De Moor

Tom,

I had wondered if you were Dutch from some of your postings. I must make notes of that word "ruwen" as I am trying to study Dutch as I have friends in Holland who would appreciate me putting in the effort. They have been speaking to me for years in English but I know they would love it if I could do the Dutch, each year I understand more and can speak some but need to raise it a level.

Regarding the comments on cranks I think that sums it up, while forged might be better if available in a suitable material it's mostly not practical due to the cost of forging and forging dies in small quantities so billet is the practical option.

Small comment >>

Reply to
David Billington

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