Advice on knock sensor for tuning newb

[edfiero1]

This winter I'm going to be building a Pontiac Super Duty 4 engine. (Block is based on the Iron Duke, but much stronger)
I'm targeting compression to be around 10:1. I'd like to put a knock sensor on this engine (it did not originally have one).

Can someone recommend the sensor and associated module that would work best with this noisy four banger?

I plan to use something like Megasquirt or Dynamic EFI for computer.

Thanks

[Scorp1us]

Why would you ask this in the GM thread?

See whatever knock sensors the MegaSquirt or DEFI recommend.

The GM sensors are basically all the same, though there seems to be a difference between auto and manual transmissions. The auto is more expensive for some reason.

[edfiero1]

Why would I ask the question in the GM thread??? Uh, because its a GM engine, and a GM ECU. Call me crazy, but this seemed like a good place.
From whaI have read, all sensors are NOT the same. There are ~4K ones and ~100K ones , and perhaps others.
Megasquirt isn't going to require a specific sensor, the question is about what sensor is going to work best with this engine, give accurate results/less false knock and be easier to tune.
Hopefully that cleared up the question a bit.

[sturgillbd]

The knock sensors are also tuned for bore size. The size of the bore determines the knock frequencies. Edfiero1, what is the bore size of the engine you are putting together? Yoiu may be able to use a knock sensor from a comparable 4cyl like a grand-am etc. If the engine is noisy, there have been good results in using a 90 degree elbow or a straight fitting to space the sensor out from the block to transfer less noise to the sensor. It would be a trial and error kind of endeavor.
HTH
Brian

[Scorp1us]

Sorry, I thought a megasquirt was a computer, leaving you with just a GM engine block.
Not knowing much about what MS expects, you need to have something that is level-compatible with it, and something that won't register false knock.

Brian, any idea why the GM sensor varies based on manual vs auto?
auto - http://www.autozone.com/external-engine/knock-sensor/duralast-knock-sensor/31574_0_0_1277/
man - http://www.autozone.com/external-engine/knock-sensor/duralast-knock-sensor/45338_0_0/

[brian617]

On the trucks (assuming same for cars) PCMs were used for controlling E type transmissions, and ECMs remained for manual transmissions and non electric autos. The different computers required different knock sensors. The PCMs have an internal knock board on the Memcal, while the older ECMs had external knock filter.

[steveo]

how about an LN8 from an S10? i had one in a junk pile one time; pretty sure they had a factory knock sensor, and that's probably the closest you'll get. but those are chain drive. if this is a gear driven iron duke i'd really avoid a knock sensor, i think you'll constantly be fighting false knock. not many people have gotten knock sensors to work reliably with gear drive cam setups..

[edfiero1]

Thanks Guys.
Yes, this engine will be very similar to the Iron Duke, with a 4 inch bore, and gear drive. Plus solid roller lifters. So it will be noisey.
Do you think the elbow approach will be sufficient to keep the noise down, or it will just be futile using the knock sensor?

If the knock sensor is a no go, appreciate other tips to avoid detenation. Is all about keeping the timing pulled back a bit?

[steveo]

Thanks Guys.
Yes, this engine will be very similar to the Iron Duke, with a 4 inch bore, and gear drive. Plus solid roller lifters. So it will be noisey.
Do you think the elbow approach will be sufficient to keep the noise down, or it will just be futile using the knock sensor?

no, i dont. that's just too much noise. i wouldn't bother, you'll just be fighting it


If the knock sensor is a no go, appreciate other tips to avoid detenation. Is all about keeping the timing pulled back a bit?

kinda, yeah. a couple of degrees under 'to the limit' timing generally doesn't cost any power in the real world.

but things do change..

with a good air fuel ratio under heavy load, and consistently using higher octane fuel, the chances of suddenly getting knock is slim.

but there are lots of factors that can make a spark map that was perfectly fine just 'start knocking'. intake air temperature... buildup in coolant passages in the heads.. carbon buildup on piston crowns... errors in timing reference from distributor..

you need to make sure you test in as many conditions as possible. i'd say if you build your spark map on a warm day with 91 octane, then run 93 octane, you should be alright.

a VERY TINY bit of light knock will not destroy a really well built engine, there is no need to be completely paranoid about it.

there are other ways to determine correct timing without a knock sensor. in driving ranges, raise timing at each point and watch vacuum increase, the second it stops increasing, leave it alone. the point of knock is usually a couple degrees ahead of that point.

at WOT, you can just raise it gently until you start hearing the first evidence of knock then back it off a couple degrees.

after that i'd be reading plugs after some WOT pulls.