This dieselly sound I get with lots of throttle on advanced timing...

[FyreDaug]

Ive got the dizzy turned all the way advanced right now, and under a decent amount of acceleration in the lower (<3000rpm) revs, its got a bit of a dieselly sound. And as always, with this advancement I get good low end power, and it seems better for climbing these BC hills and kickin around town, so thats why I keep it here.

Now as for the sound, is that like detonation or something? It doesnt happen all the time, but a good example is going slow in 3rd gear at 1000rpm and giving it lots of throttle to accelerate, it may even sound a little pingy.

mods: pacesetter header, 2.5" straight through exhaust, flipped lid, vac line removal, dual ignition coil, high gap plugs.

I need to brush up on my mechanical sounds, but is it detonating? I dont lose power or anything:thumbdn:

[thegreatdane]

it's not detonation, it's knock and it's bad for your engine. You're igniting the gas mixture too early. set the igntion at ~16 degrees BTDC at idle, that is going to work best.

[AccordEpicenter]

do do stuff halfass like that or youre gonna be blowing motors, too much advance is hard on parts and kills performance, you need to put a timing light on it and see where youre at

[lostforawhile]

why are you at 1000 rpm in third gear? sounds like you are bogging the motor.

[FyreDaug]

That was just an example on how to get it, so its knocking, gotcha. Im gonna be turning it down, but it doesnt do it all the time, just up hills and stuff... its not actually killing performance, which is why I wasnt paying too much attention, but since I got in bc where everything isnt flat it seems to take a little more outta the 90hp motor.... I dont have a timing light, is in between full advance and full retard about right? Or slightly towards the advance side? Keep in mind its mostly city, so I like a little more low end power...

If its igniting it too early then the actual "knock" im hearing is it restricting the movement of the piston? Then why does it continue to run? If its slowing the piston down and using force against it, shouldnt the motor be bogging down? It has more power and accelerates quicker like this, thats why it doesnt QUITE make sence... Assuming all dizzy adjustments are about the same, how many *BTDC would I be at? 25? more?

[Strugglebucket]

you can't tell where the timing is by looking at the distributor because it can vary depending on the condition of the distributor. you need to use a timing light.

if you get "knocking" or "pinging", what you are hearing is detonation. low engine speed combined with a high load on the engine and too much ignition advance is a perfect recipe for detonation. and no, it won't hurt performance but it can damage your engine over a long period of time.

if you want to understand it better, read this:http://www.streetrodstuff.com/Articles/Engine/Detonation/index.php

[NXRacer]

correction: it can damage our engine in a SHORT amount of time. better retard that timing soon or say bye-bye to your motor y0.

[Soundy]

Yeah, pay attention the Page 8 in particular:


There is a situation called detonation induced pre-ignition. I don't want to sound like double speak here but it does happen. Imagine an engine under heavy load starting to detonate. Detonation continues for a long period of time. The plug heats up because the pressure spikes break down the protective boundary layer of gas surrounding the electrodes. The plug temperature suddenly starts to elevate unnaturally, to the point when it becomes a glow plug and induces pre-ignition. When the engine fails, I categon'ze that result as "detonation induced pre-ignition." There would not have been any danger of pre-ignition if the detonation had not occurred. Damage attributed to both detonation and pre-ignition would be evident.

Typically, that is what we see in passenger car engines. The engines will typically live for long periods of time under detonation. In fact, we actually run a lot of piston tests where we run the engine at the torque peak, induce moderate levels of detonation deliberately. Based on our resulting production design, the piston should pass those tests without any problem; the pistons should be robust enough to survive. If, however, under circumstances due to overheating or poor fuel, the spark plug tip overheats and induces pre-ignition, it's obviously not going to survive. If we see a failure, it probably is a detonation induced pre-ignition situation.

This is a picture of typical detonation damage to a piston:
http://www-cms.llnl.gov/s-t/hydro_ignition_images/westbrook-fig-01.jpg

Some other scary pictures and detonation info:
http://www.hastingsmfg.com/Service%20Tips/detonation_and_preignition.htm