ooopps pressed wrong button
Orion CRF OS TZ Sirio Evo 2
Induction 255º 206º 213º
Transfer 107º 114º 114º
Exhaust 163º 155º 159º


AFM

Thanks AFM! I'll start working on the chart.

Understood. Thank you. :)

Hmmmm....

I have a partial chart, but I'm not sure how much value this has, if any. :sweat: Is this helpful at all? How could someone make an informed decision from something like this?

http://www.nitrokb.com/engines/chart1.jpg

Selection wise, I think most engines fall into this type of matrix, with usable powerband being an important metric.

http://www.nitrokb.com/engines/quadrant1.jpg

It would seem to me, that engine selection would be based on track (small, medium, large - technical vs sweeping) and driving style (degree of fine throttle control). Either an engine has good bottom-end to mid-range -or- mid-range to top-end. Is there an engine that has good bottom-end through top-end? A "one-size fits all" engine.

I realize that pipe, clutch setting and gearing can be adjusted to compensate for deficiencies in certain areas (i.e. torque vs speed), but what makes more sense? Going with the "one-size fits all" engine and tuning it for the track or choosing an engine based on the specific track? I know that some people are running the wrong engine for the types of tracks they run on and continuously struggle to find the performance they are looking. That must be extremely frustrating!

Tuneablity, reliablity and predictability are all important considerations of course. You just can't go by the numbers. :D Plus, if you're a team driver, you may have limited choices.

Comments? Corrections? Other opinions? All appreciated. :)

Corrections:

1.-You need to invert numbers on bore and stroke for the Sirio and Ninja engines, and correct the ratios.

2.-Orion engine has 13.75 stroke.

3.- Those HP figures are declared manufacturer values which are not standard
between manufacturers....pretty much unusable...what nitro % ??, what pipe?? what weather conditions???
Better get numbers from Nytrodyne Systems data base, which are corrected SAE values and standardized.....also add a torque column. Also you'll find that those numbers are all with 30% nitro and a certain pipe.

4.- Need to get timing info on all engines, because that is a major important info. that will really matter upon choosing an engine for specific applications

5. You need to add reference info. related to ratio numbers of rod, stroke and rod lenght
Stroke/Rod ratio 1.75 : 1 = wide power band. 2.00 : 1 = narrow power band
Stroke/bore ratio = ideal is between 1.0 : 1.0 to 1.2 : 1

AFM

Forgot to tell you Mega engines are 13.80 stroke 14.00 bore

AFM

Made some changes. Getting some of this info is going to be difficult. :nod:

BTW - Micromotori and K-America post that STI is Stroke: 13.70mm , Bore: 14mm. Both wrong! :sneaky:

http://www.nitrokb.com/engines/chart1a.jpg

[QUOTE=rmdhawaii]Made some changes. Getting some of this info is going to be difficult. :nod:

BTW - Micromotori and K-America post that STI is Stroke: 13.70mm , Bore: 14mm. Both wrong! :sneaky:

QUOTE]

Has to be a misprint, because I've phisically measured a Sirio and i'ts like I say.....unless someone proves me wrong or they made some later changes....anybody with a Sirio STI than can confirm this????

BTW can you e-mail me your Excel Sheet, so I can help you inputing info on it?? [email protected]

AFM

Hey rmd,

One thing I think you're assuming when you're comparing the engines is that you will be running identical gearing with every engine. The truth is, you have to gear accordingly to the engine's powerband, track size etc. Just thought I'd point that out.

Dave

I'm sorry if I gave you that impression, but I'm not really making that assumption. I know that the gearing needs to be changed, but you can only change the gearing so much.

In the WASP Rev thread, some people were saying that they couldn't gear their car any lower, because the manufacturer just didn't make the parts to go any lower. This is an example of someone running the wrong engine for the track they were running on. In the case that I'm aware of, the person just decided to use a different engine and things worked out just fine.

My take on it is, gearing up or down, the engine will only allow you to go so far, before you have to just to change the engine. What do you think?

Yes, but to know how to gear your engine you need to know how much torque it has and at what rpm's, and for how long.....if you have an engine with lots of HP but no torque it will never pull....take as an example the OS TZ...has lots of torque and keeps i'ts torque flat along the power curve, then for top speed you just have to gear it long on second speed...and the OS is one of the strogest engines on short tracks......on the other extreme you have the Orion with lots of HP, good torque but for short period...and both at such high rpm's that you have to gear it very short to have it revving all the time, plus the clutch also very tight so it slips all the time to keep engine on a very narrow powerband....

Resuming, the most important numbers for selecting an engine for any application are the timimg numbers and the HP and torque numbers along with the rpm's at which they are delivered.

AFM

AFM updated chart:

http://www.nitrokb.com/engines/chart2.jpg

I'm staring at the chart and still trying to find some value in it. It's interesting to note how the rod/stroke ratio corresponds to HP, with the exception of the STS Racing engine - which could possibly be an anomoly.

I think the chart raises more questons than provides answers. Too bad we don't have all the figures.

The fully modified JP engines absolutely rule on our techincal track. Could this imply that a wider power band and lower HP/torque engine does better on technical/shorter tracks, because a wider range of throtte control and consistent power is required? A lot of people acknowledge that the stock OS TZ does well on technical/shorter tracks as well.

Conversely, the JPs did extremely well at the U.S. Nats, which is by no means a technical track. It was stated in the Worlds thread, that Tosolini had a "milder motor" for the U.S. Nats, compared to Paolo and Scotty, but primarily for fuel mileage.

Is it possible, that there is an ideal performance metric for nitro engines and that anything that falls outside of the bell curve doesn't do well?

Maybe this is just way too academic, with no real benefit. ;) :lol:

Subjective driver analysis may still be the best way to choose an engine. :D Right guys? :nod:

Rainer

From my experience it's a question of tuning and setting.

If you really know how to properly tune your engine, match the right pipe, set your clutch accordingly and choose the proper gearing, you can take advantage of the power and torque of any engine.

Then there's the issue of beeing able to put the power on the track...if you have traction problems, you are better off with a milder wide power band engine, than a peaky high revving engine or a super torquier engine.

When you have lots of traction you can get away with lots of power and torque. With low traction, you're spinning tires all the time (which wears them fast) and getting low run time, and not able to put all the power on the track (I.E: ORION CRF)

With respect to track layout and size, you are allways going to be faster on a small tight track with a torquier engine with wide power band, because you are on the brakes a lot and have to pull up from very low rpm's on every turn....on the other hand, on a large open flowing track, in which you are on the gas all the time, you'll be best on a high revving engine with narrow powerband and lots of hp.

Now there are engines which have a well balanced power band, that when properly geared and tuned, as I said before, will perform well on any track.

So yes it is possibble on paper to more or less predict what an engine is capable of doing or not....then it's each one's abilities to tune it and set it properly.

90% of the time I've found that people don't know how to properly set their cars, more than a question of who has the most power out there, except for the pro's of course, because when you see them at a race they are so close on performace (we are talking 10th's of a second), and are using differnt cars, engines etc. etc....that one concludes that most of the top brand engines are quite even in performance.

Just my 2 cents

AFM

Hi Reiner.
Can I add something to your chart?
I would suggest for total induction timing add when it is open and when it is close.