knock at 5psi in new build

[tttype]

Got rebuild done & now getting knock at low boost , 5psi.

Only thing changed on new build is ;
- compression up to 9.1 from about 8.2.
- entire new fuel system, from 255l pump & stock lines upgraded to 400 lph pump & -8 lines.

Knock starts rapidly at 5psi , whether at WOT or 1/4 throttle & slowly approaching 5psi in second gear.

Using 91 octane. engine runs well under normal driving. Before rebuild could run 25psi w. alc.

Tune timing is about 27* when KR starts, dropped it down to 17* & still get KR .

XFI Log show no outstanding values.
Actual afr is close to requested 12: 1
EGT looks ok.

wandering if its something mechanical ?

Any ideas ???t

 

[haywire4130]

Maybe the knock sensor was overtorqued on install? I dont recall the spec but its not very tight. I would try a new sensor and search the correct torque spec. Cheap part and it will rule that out

 

[tttype]

Maybe the knock sensor was overtorqued on install? I dont recall the spec but its not very tight. I would try a new sensor and search the correct torque spec. Cheap part and it will rule that out

Unfortunately you can hear the knock, so I think the sensor is doing its job. By memory the sensor was torqued to 12 or 14 #.

Thanks

 

[Chuck Leeper]

Balancer loose/cracked?
Flex plate cracked, converter bolts loose?
DP hitting the frame?

 

[No disintegrations]

Contaminated fuel? Try to drain and refill the tank. (Use a different gas station.) Could have some diesel mixed in from the gas station. It has happened once in a while. Or possible sabotage.

 

[Pronto]

Get some fresh high octane fuel and see if it quells it.

 

[michael evans]

I think it is to much timing. Retard the timing 5 degrees and try to run again.

You said you only changed the compression some but did not say how.

How was it checked before and after ?

Was the cam shaft degreed in ?

 

[ITSAV6]

So you dropped timing 10 deg and still seeing knock? Can you hear it? Could the sensor be bad? I have had new one be bad out of the box. Did you change the wot timing only?

 

[Pronto]

I had a brand new one that spun around in the crimp. That was disappointing.

 

[earlbrown]

Your issue is paralleling exactly what my car is doing. I pulled my 4.1 down to replace the hypers with a set of my forged pistons. Now I have knock you can audibly hear in the next county that barely registers on a powermaster log.

I got some beers in me, pulled the extra fuel down to base and got the powermaster logs to really show knock. That's the extent of my testing. The car's got about 1/2" of dust on it now.

 

[Reggie West]

You need to add more fuel in the lower rpm ranges.

Look at the cells especially where you are starting to see low boost. 0 to 10 psi.

The 9 to 1 CR needs more fuel plain and simple.

 

[bison]

Maybe your timing is too aggressive for the garbage fuel. Did you verify baseline timing?


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[No disintegrations]

Maybe your timing is too aggressive for the garbage fuel. Did you verify baseline timing?


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No one ever answers this question. I guess that means no.

 

[earlbrown]

Finally made some pulls and logs with my car that's exhibiting the same assumptions as yours. first I disconnected my wastegate so it only makes 2PSI at the top of second.

My Extender chip has a BLM adjust that I maxed out. That helped. Then I removed +2 degrees extra advance on 1st and 2nd as default. That helped.

Then I maxed out the LoGear Fuel... 1st pass was SOGGY as hell at cruise and when I floored it.

Backed that pass up and it was better but still soggy.


Everything is looking like too much timing on my end but I have no way to lower total timing on my chip, short of modifying my crank trigger bracket (which I might do).

My build is high compression like yours but in a 4.2L form. I have a big ass roller to bleed off some dynamic compression and max ported stock heads with O/S valves. I spend a lot of time with my piston engineer trying to make the inverted dome as efficient as possible. He said that on certain situations in his experience his pistons can require as much as 4 degrees less advance. In my case, I think I shot myself in the foot and my burn rate is just too fast for my base timing.


If you haven't verified your base timing, you're basing your settings on an unverified foundation. If you have the ability, pull even more than the 17 degrees and see if that changes anything. (just be careful, if you go two far retarded, it can put a LOT of heat into the exhaust)

 

[tttype]

Been under the weather for last few days, worked on car today.

Fuels been changed to a different brand, no noticeable change in KR.

Checked timing w. light, it indicated within a few degrees of ECM.

Flexplate & balancer are good & tight.

 

[Chuck Leeper]

Checked timing w. light, it indicated within a few degrees of ECM.

Not accurate enough.

 

[No disintegrations]

only so many things are the root cause of knock. Octane too low, timing too high or air charge very hot. Changing one or all should help in some way. (Other than mech problem heard by sensor) You prob know this already, just a reminder.

 

[tttype]

Not accurate enough.

Can you explain more ?

The RX7 build is difficult to check timing on, the AC delete bracket is where the timing light needs to be.
I can see the 0 * mark , so use a timing light with a degree dial on it & dial down till balancer mark hits zero & read dial on light. Dont know accuracy of this dial label or the light.

For this check I'm thinking in trends.
ECM says 30 , timing light reads 33 , that 3 * will get adjusted for in tuning.

BUT if ECM says 30 & light indicates 50, something is mechanically out.

Please explain if this thinking is not correct.


Also how steady should the balancer timing mark be during testing ? Zero movement , couple degrees, 1/4" ?

 

[haywire4130]

It can be a little jumpy at idle, if you have an assistant hold it at like 1400 rpm or so it smooths out to within half a degree. Hindsight being 20/20 it would have been really easy to verify your indicator was accurate during assembly with a degree wheel and dial indicator. Its not impossible now but a little harder

 

[Chuck Leeper]

Dial back and waste spark can make for inaccurate readings....