3rd gear knock... I need expert advice PLEASE

[Onefast99gsx]

Ok guys, i really need help here. I've had it. I cannot figure out why i get so much knock in 3rd gear, upto 3-4 degrees pulled. In 2nd gear at the same RPMS and same airflow, a/f ratio, etc.. i don't get the knock. What is so different about 3rd gear? I'm running 93 octane, 75/25% Alky/water injection and about 22-23psi. I've tried richening it, leaning it and still can't figure it out. I also went back to zero on the timing sliders. Sometimes i get more knock in 3rd gear than other times.

I don't have boost leaks, no exhaust leaks, my wires are brand new and so are the spark plugs. The head was all polished when it was out in the spring. The tops of the pistons were cleaned down to the aluminum as well. I don't suspect any carbon buildup.

ANY help would be greatly appreciated!

[Shane@DBPerformance]

There is more load on the engine in higher gears from rolling resistance and wind resistance. You also spend longer amounts of in each higher gear, so there is more time for heat buildup. You need to tune in 3rd and 4th gear and accept that it might be extra conservative in 1st and 2nd gear.

Have you tried less boost? Are you using methanol or just denatured alcohol? Have you tried going negative on the timing sliders? How are you reading A/F? The A/F ratio in DSMLink is a just a mathmatical guess and stock O2 volts often do not stay linear. Any chance the headwork did more harm than good?

[JET]

I'll let shane handle the tuning part, but hopefully the intake side of the head wasn't polished. That is a no-no!! It will create fuel puddling. That can lead to all kinds of issues.

[Onefast99gsx]

Hi Shane- First, thanks for the response. To answer your questions.... Makes sense that with each increase in gear, you're in it longer than the previous gear. Heat would be a very likely culprit. I thought for sure that Alky injection would lick the problem. Actually it has done a great deal for me I should say. I couldn't even hardly go over 16psi before on shitty 93 octane without knocking. Now i can go up about 5 more psi from that with pretty good results.

While the weather is cooler out today, i'm gonna back it down to 19-20psi and see what results i get. I using methanol(the stuff the drag and stock car racers use). I have not went negative on the sliders with timing. The only reason is because I hear so many people that can run 19-20psi on 93 octane with no problems. I have my W.I. coming on at about 16psi.

Is going negative on timing sliders necessary a bad thing??? I always thought the more you could advance it the better off you were. I always tried to get as close to 20 degrees as possible. Seems like at about the top of 3rd gear, i'm only getting 13-14* because of the knock. That's gotta provide a power loss. Unfortunately, i'm only reading A/F with dsmlink. I've always strived for 10.8 to 11.3 A/F Ratio. Who knows, maybe my car would like low 10's, something i'll have to try. I don't think the headwork did anything negative. No material was hogged out. The shape and flow characteristics are the same. The rough cast was just cleaned up and polished. The Griffin FMIC could be a possible culprit too. It's 20x10x2.75(core). I'm not sure how efficient they are with a 50 trim and over 20psi of boost.

Thanks.

[Onefast99gsx]

I'll let shane handle the tuning part, but hopefully the intake side of the head wasn't polished. That is a no-no!! It will create fuel puddling. That can lead to all kinds of issues.


Hmmmm. It was "cleaned" but with a much rougher wheel than the exhaust side. I think it was a 60 or 80 grit. Is that what they call 'tear-dropping' of the fuel, thus not breaking the fuel up into fine particles?


Slowwhite(Brian)- you still got that head available?? Gosh i hope i don't need a different head.

[Onefast99gsx]

I'm gonna post what Dave Mertz said from the DSMLink forum.... Basically is exactly what Shane said about heat building up. About the only thing i can try is to keep the setting exactly the way they are and get up on a cold or cooler morning and do a few pulls and see. If heat is the culprit, then the knock should go down from the cooler air. Thankfully it has cooled down some and I can take it out again.

BTW- I plan taking this to Rock Falls this Saturday on the $69 test/tune day. That's why i'm trying to weed out bugs NOW so i don't have to waste all day Saturday figuring it out.

**** Quoted from the DSMlink forum ****

By the time you reach third gear, the engine has built up enough heat that knock is more likely. On pump gas, I probably wouldn't worry about the 2 degrees of knock retard. The knock sensor system is doing exactly what it is designed to do.

In fact, besides a different global fuel setting for your larger injectors, for pump gas your settings are nearly identical to what I've run on my Talon for years, producing similar results.

Dave

[Onefast99gsx]

Wow! What an interesting lunch hour. Thankfully my lunches are 1hour. I decided to do about 2 pulls during lunch because it's less humid out. 1st pull..Shit! same thing knock! Starts at about 5700 in 3rd gear pulling about 2.5* of timing. Was also signs of .7* knock at the top of 2nd gear. So next and final pull i decide to richen it and basically go back to zero's on the dsmlink sliders. So i took off from a dead stop this time. Felt pretty good, 0-60mph felt great, get to about about the middle of 3rd gear and POOOOOOOF!! Car quit instantly. Not Good! I'm 3 miles from home, no phone with me. I get out look under the hood and it looks fine, no dripping of oil, Whew! In my past experience, that's from a hose blowing off. I couldn't find which one though. Must be behind the bumper cover. So again with experience i bury the fuel sliders to -40 and was able to limp it home at about 15mph, put..put..put. I found the hose that blew off. Had to be a bitch of a one to get at too. Dam, and i even have t-bolts on the dam thing. Not sure if this was on tight till the last moment and then she blew off or whether it was ongoing. Question: Can boost leaks cause bad knocking? I thought knocking was only from internal combustion, detonation, high pitch frequencies, etc..

Thanks guys.

[Shane@DBPerformance]

Boost leaks make the turbo work harder and put out hotter air. Hot air causes knock, which is why we get big FMICs and big turbos that put out cooler air.

[Onefast99gsx]

Thanks Shane. I'll remove the pipe tonight and weld some more nubs at the tip and put it back on and try it. Hopefully it was an ongoing thing that it was leaking and that's the cause of my problems. Should know by late tonight.

Thank you.