Stroker Pinging

[jules325i]

Just built a 2.8 stroker with a compression ratio of 10:1, 284/272 cam with an alpina c2 2.7 replica chip.
The timing is spot on so it's not that im one tooth out, (advanced)
I run the car on 98 octane fuel.
i am currently running the stock injectors until my 19lb show up.
is it possible that the lean mixture is causing cylinder tempretures to rise and cause pinging.
When driving the car at about 2k rpm light throttle pinging occurs to a point where you have to stop accelerating.
Has anyone experienced this before
I knew this was going to be an issue with a car without knock sensor, thats why i went with a modest 10:1.


My DD is also a stroker setup with 2.9 10:5.1 and i dont have this problem.

[digger]

Just built a 2.8 stroker with a compression ratio of 10:1, 284/272 cam with an alpina c2 2.7 replica chip.
The timing is spot on so it's not that im one tooth out, (advanced)
I run the car on 98 octane fuel.
i am currently running the stock injectors until my 19lb show up.
is it possible that the lean mixture is causing cylinder tempretures to rise and cause pinging.
When driving the car at about 2k rpm light throttle pinging occurs to a point where you have to stop accelerating.
Has anyone experienced this before
I knew this was going to be an issue with a car without knock sensor, thats why i went with a modest 10:1.


My DD is also a stroker setup with 2.9 10:5.1 and i dont have this problem.

what pistons?
what is the AFR?
bad fuel?
how is the cam timed? even if its not a whole tooth out it could be advanced a fair bit. do you have an adjustable cam gear?
can you test the 2.9L's computer to see if that suits

[jules325i]

what pistons?
what is the AFR?
bad fuel?
how is the cam timed? even if its not a whole tooth out it could be advanced a fair bit. do you have an adjustable cam gear?
can you test the 2.9L's computer to see if that suits

Ross Racing forged pistons 10:1
Im yet to put it on a gas analyser but ill be doing that shortly.
im running the stock cam gear.
Thought about the fuel so i topped up with 98 and an octane booster still no change.
Im running the miller psik and war and i cant really swap it over easily.
I forgot to mention i used a brand new AMC head (got it ported to get it flowing properly)
so it wasn't skimmed, also the block wasn't decked and i used a OEM head gasket.
So my thoughts are it should be a dead set 10:1 which i thought would be fine with premium fuel.

[travish325]

is it possible that the lean mixture is causing cylinder tempretures to rise and cause pinging.

....

[jules325i]

....

Could it be a Lean mixture causing cylinder temps to rise.
Happy

[digger]

the chip you have might be rubbish, try a stock chip to start with

if the mixture is off then yes it certainly wont help, you could test by fooling the engine into adding more fuel. if you are in closed loop mode the AFR will likely be stoich though

kind of pointing out the obvious but you really need to tune to suit the engine.

you can adjust cam timing with an adjustable cam gear to retard timing but not a great solution.

also what plugs you using? try a colder plug NGK BPR6ES

assuming an 885 AMC id be surprised if Ross pistons have the same sort of squish as the stock pistons, the squish helps with mixture turbulence in the chamber and reduces " end gas autoignition"/detonation

i have heard of similar problems in a B28/29 with that sort of CR and 284/272. a custom chip tune helped IIRC. Nando has a similar spec engine

[jules325i]

the chip you have might be rubbish, try a stock chip to start with

if the mixture is off then yes it certainly wont help, you could test by fooling the engine into adding more fuel. if you are in closed loop mode the AFR will likely be stoich though

kind of pointing out the obvious but you really need to tune to suit the engine.

you can adjust cam timing with an adjustable cam gear to retard timing but not a great solution.

also what plugs you using? try a colder plug NGK BPR6ES

assuming an 885 AMC id be surprised if Ross pistons have the same sort of squish as the stock pistons, the squish helps with mixture turbulence in the chamber and reduces " end gas autoignition"/detonation
i have heard of similar problems in a B28/29 with that sort of CR and 284/272. a custom chip tune helped IIRC

Forgot to mention i started with the stock chip and it was the same scenario.
Yes 885 AMC head, that very interesting what you say about squish, on my other stroker my engineer managed to find me a set of pistons with 4 deep valve reliefs and then cut in an additional yet very shallow relief for my intake valve, i always wondered if it would help with creating turbulence.
Cheers for your help ill try the colder plugs and look into a tune.

[travish325]

Colder plugs usaully dont help with pinging lower down, mostly you will get misses under a load from running too hot of a plug. Likely your injectors are to small, stock 14.5lb on a 10:1 cr 2.8? Throw some 19s or so in there and try that with a correct tune.

[Todd Black 88]

If you are running a miller maf, you should be running a chip for the maf, not one tuned for an AFM

[digger]

the miller is for the other car if i read correctly.

if you are talking light throttle at 2k then the ECU should be in closed loop with 14.7:1 AFR getting feedback from the O2 sensor.

even if you put bigger injectors after a bit of time the ECU will deliver the AFR will still be 14.7:1 because you have an O2 sensor.

when i had my chip custom tuned i did not use the O2 sensor so it ran in open loop mode. of course the chip needs to be custom for this to be a long term solution

being a little bit lean on that engine at very low load should not be causing bad pinging.

a 2.7L alpina used stock injectors.

im guessing you may need to adjust the ignition advance even when the fuelling is spot on....

[digger]

Forgot to mention i started with the stock chip and it was the same scenario.
Yes 885 AMC head, that very interesting what you say about squish, on my other stroker my engineer managed to find me a set of pistons with 4 deep valve reliefs and then cut in an additional yet very shallow relief for my intake valve, i always wondered if it would help with creating turbulence.
Cheers for your help ill try the colder plugs and look into a tune.

i assume your pistons are essentially flat top? those style are suited to the 731 and 200 head. the 885 has good swirl due to its basic layout but mixture motion is very important and a 0.040" squish clearance on the 885 angled squish band helps with that. valve reliefs are not good they create areas that dont burn and the sharpish edges can create hot spots so usually try and minimise as much as practical

a bigger cam also helps bleed off some pressure....lol

[SkiFree]

i assume your pistons are essentially flat top? those style are suited to the 731 and 200 head. the 885 has good swirl due to its basic layout but mixture motion is very important and a 0.040" squish clearance on the 885 angled squish band helps with that. valve reliefs are not good they create areas that dont burn and the sharpish edges can create hot spots so usually try and minimise as much as practical

a bigger cam also helps bleed off some pressure....lol

But I do highly doubt that this is the reason behind the pinging given the modest octane to compression. Maybe overall efficiency, but not pinging....

I would be very interested in seeing the tune.

[ForcedFirebird]

I am also curious. Where did you get this "Alpina Replica" chip?

I have given the m20 all kinds of ignition advance (we can go to 40* in Motronic) and never heard a ping, just showed loss of power on the dyno.

Seeing it's 2000-ish RPM and low part throttle is odd.

[digger]

But I do highly doubt that this is the reason behind the pinging given the modest octane to compression. Maybe overall efficiency, but not pinging....

I would be very interested in seeing the tune.

yes def not the root cause, but im not sure it helps, others have done it successfully so can be done.

the key is the tune. why get customs pistons etc and generic unknown chip, never gets the potential from the engine.

everyone always thinks because it is too lean it knocks but usually its excessive advance. the low load ignition advance is usually pretty high.

To the OP, does it knock at WOT at all?

[ForcedFirebird]

excessive advance. the low load ignition advance is usually pretty high.

To the OP, does it knock at WOT at all?

BMW loves to lean-cruise tunes...