Aprilia 550 RXV - Knock limited?

[Thomas_UoA]

Hello guys,

we use a 550 RXV Aprilia engine. And right now I am tuning the ignition table. I mounted a microfon on the block, put that signal into an amplifier and connected that to a speaker. The idea was to hear knocks. I can definitly hear combustions..

I tried that @4000rpm partload (880mbar intake mainfold pressure).

Here the results:
Ignition angle:
36BTDC - Exhaust Temp: 780°C
47BTDC - exhaust Temp: 680°C

but still the noise was not different in the speakers.. stopped there, because i was afraid that my knock dection didn't work.

What are your results about the knock limition of that engine? Perhaps it's not knock limited? Did anyone make the same experience?

would appreciate help!

Thomas
Adelaide

[Thomas_UoA]

Hello guys,

we use a 550 RXV Aprilia engine. And right now I am tuning the ignition table. I mounted a microfon on the block, put that signal into an amplifier and connected that to a speaker. The idea was to hear knocks. I can definitly hear combustions..

I tried that @4000rpm partload (880mbar intake mainfold pressure).

Here the results:
Ignition angle:
36BTDC - Exhaust Temp: 780°C
47BTDC - exhaust Temp: 680°C

but still the noise was not different in the speakers.. stopped there, because i was afraid that my knock dection didn't work.

What are your results about the knock limition of that engine? Perhaps it's not knock limited? Did anyone make the same experience?

would appreciate help!

Thomas
Adelaide

[Damon Pipenberg]

A few things -

-I'd recommend using a knock sensor from a late-model car. You should be able to get one from any auto parts store. It should be rigidly mounted to the block and feed the signal into your amplifier.

-Filtering the signal to attenuate certain frequencies can help and is often done in dyno labs. I can't help with the design of the filter, this would require experimentation.

-If you can't get it to knock on the normal fuel, you can run lower-octane fuel. This can help you learn what knock sounds like. However, I probably wouldn't recommend this unless you have a very good dyno and are very comfortable with engine tuning. If you try this, I would start with the ignition map very retarded and slowing increase the advance until you hear knock occurring.

-If you suspect that it is knocking, it doesn't hurt to take the head off and check the pistons.

[rjwoods77]

Link to help use OEM sensors:

http://www.deviantmethods.com/...oose/pages/knock.htm (http://www.deviantmethods.com/bigmoose/pages/knock.htm)

[Drew Price]

Thomas,

Make readings:

The KnockBox (http://www.theknockbox.com.au/content/blogcategory/3/8/)

Best,
Drew

[ZAMR]

We run an RXV as well (2008 model). Last year we were running at a full 50 degree advance at one time with no noticeable knock. However this was at high RPM's, not 4000rpm.

Zach Moorhead
Sooner Racing
Engine & Body '09
Cooling & Lube '10

[PProb]

the amount of ignition timing you can run will be dependent on the efficiency of you intake and exhaust at that rpm and load point.

You have not specified if that timing is at full throttle or part throttle? (for part throttle it seems quite low).

In saying all that, since the temperature has dropped it may indicate that the engine likes more timing. (assuming the air/fuel ratio hasn't changed between running the different ignition timing values)

[JamesWolak]

Thomas,

I haven't dealt with an Aprilia 550 but i found on a FSAE car its pretty hard to hear knock with a microphone before it was too late. The background noise of the exhaust, chain, dyno, ignition, valves, etc is too overwhelming. And it's even worse when your engine isn't insulated in a separate room. Knockbox.com has some recordings of knock that you can DL so that you at least have the experience of hearing knock before.

I am sure you know this but another thing you should be looking at is your torque while you are doing this. If your torque is not increasing with your timing advance then you have reached (and probably passed) MBT.

But i am going to warn you. I have wasted weeks trying to dial spark to MBT/KSLA and end result was not worth the trouble. Just get it close, the additional 2 ft-lbs isn't worth it.

Also if i were to do it all over again i would have spent more time working on low manifold pressure areas. This drastically helped with tip in response. Drivers could immediately tell when i made changes to spark in low pressure areas but never knew if i pulled 15 degrees in areas above 100kpa.

But if you are going tune to MBT/KLSA I would invest in something like the knock box. They are expensive but so is the cost of melting a piston. I know if i was still involved with FSAE i would just buy one myself because its too stressful and frustrating to melt a piston. Or even better contact AVL about sponsoring you with some combustion equipment.

[Thor]

Interesting your issue with knock at low throttle openings and load. One area of the SXV/RXV engine that is fairly good is the charge turbulence of the chamber. I agree with the previous poster that a mic is not a good way to determine det. I would specifically look at a det counter if you really had to know. And tune for more advance in the low pressure as the other poster suggested.

Are you using the stock ECU? if so what map have you loaded. Some of the Maps that are available to load via the Axone or Navigator increase the map points for finer control of mixture.

Why does everyone use the RXV engine. Is it the camshafts? Has anyone here tried the Vanden Bosch cams? I have been building these engines for Supermotard racing for a couple years, but have not had to deal with the venturi that the FSAE guys have. Did you know that the 2008 throttle bodies flow 16% more than the 2007 throttle bodies. HMM? We have things like Ti rods and Ti nitrited rings, and make sure you remove the stator bolts and red locktite them, they back out. Good luck, pm me if you have questions.

Thor