Predator

I know this has been covered even though I can't find it searching, but why do our engines need knock sensors? Older engines back in the carb days never needed them, why do LSxs?

Predator

No one knows?? What is it about the modern engines that require timing to be retarded if you sneeze too loud? Is it all about the warranty?

horist

Technology is a wonderful thing... older motors back in the day would also start pinging if it got really hot out or if they got a bad tank of gas or used to low octane etc... now I don't know a whole lot about older cars... but I do know they didn't have computers in them... so it would have been kind of hard to use a knock sensor ... if there was a cheap and easy way to incorporate a Knock Sensor I'm sure they would have used them in older cars as well....


It's a safety feature... The knock sensors are there to try to prevent the engine from wearing prematurely and basically blowing up...

So it's not a matter of our motors needing them... people turn off the knock sensors all the time (though it's not reccommended) ... but it's just a little insurance that if something does go wrong... the motor's not going to grenade itself as easily ...

jimmyblue

iTrader: (11)

It's immediate protection plus the ability to learn max
timing. If you don't have this then you have to run
more conservative timing for bad gas and bad weather,
meaning less power in good conditions. In pursuit of
HP and economy you prefer to tune it up tight and
use a feedback loop to back it off only if necessary.

Predator

Thanks for the explanation Mike. I'm not an expert on older cars, but can I assume then that lots of the older motors were blowing up without knock sensors (sort-of-tongue-in-cheek, sorry)? I imagine since there were no knock sensors back in the day enthusiasts didn't talk about knock retard and knock sensors they just tuned their cars the best they could and that was it.

It just seems that KR is so wide-spread, even on factory vehicles, and it seems to be one of the major factors that kills performance. I just think knock sensors are way overrated as far as being necessary. I mean if you zero out the knock retard tables it's considered very risky, at the least, and just plain stupid, but in the pre-computer days it used to be the norm to tune without them.

But I think I understand, it's just that we have computers now and they can do stuff like knock sensors so they do it, and it's probably prevented a lot of warranty claims, seems logical.

Anyway, thanks again man.

foff667

iTrader: (2)

rule of thumb for most of those engines were turn up the timing till you hear pinging and then turn it back a couple of * to be safe. Like mike & jimmy explained technology is a great thing.

Predator

Thanks Jimmy, but I still can't get over the fact of all the years of driving and hotrodding without knock sensors, and now they're so essential. And I read your well-reasoned response, but it seems to me more theoretical than actual. It wasn't until I stopped worrying about all the scenarios of the things that could go wrong did I finally get my car really running.

2xLS1

iTrader: (25)

We also run cars way leaner now days for emissions than back in the olden days which makes them more susceptible to knock. I don't know for sure what year they first made their appearance, but I have an 85 Chev van with a carbed 305 that has a knock sensor, so they have been around for a while.

foff667

iTrader: (2)

also consider when they switched from leaded to unleaded fuel...leaded fuel has a much higher octane rating generally and helped reduce ping...with production of leaded fuel nearly non existant and much higher compression engines coming to production there has to be some sort of protection...there are guys with ls1's that dont want to run 93 octane & in some states they only offer 89 or 91 octane so there has to be more leway covered by the makers now to make sure they dont blow up these motors...especially with the 7 + 10 year powertrain warranties some of them offer now.

Predator

I see your point foff667, but that would only apply if the knock was indeed real knock. It's pretty hard to exactly pinpoint what is real or what is imagined knock.

Predator

Good point about octane, especially in a large market like California.

I forgot about leaded fuel too.

Predator

Jimmy, I thought of something you said, and yes, absolutely, you'd have to have a different tune for hot weather, without knock sensors.

speedracerz

iTrader: (8)

only reason not to run knock sensors is if you change to a solid roller setup. the noise created by solid rollers will retard the timing bad and will loose power over any previous setup you had.