S14 KA-T tuneing question

[Trippen]

Hello All,
Been working with my S14 Nistune board and i have a few questions. Got a basic tune done running 15psi feels good no knocks and decent times at the drag track but got to this in a weird way. I had a JWT ecu tuned for MSD 50lb injectors, Z32 MAF and a 50 trim stage 2 wheel.
I have added 248 deg cams with the Intake being retarded by 3 teeth to adjust for cam overlapping

1. K value is 330 for the car not to knock etc should be around 188 but i do that and it dies in idle and wont even start unless i set it to 280 or higher
2. My Injector Latency for those injectors at 14v is 490us but it knocked so when i took it to 650us all was good. with K being at 330.

Car pulls strong and track times says the tune is better in power. full boost AFR's are 10's cruise 14.8-14.5

So my main questions....Should i be stressed that i had to fudge numbers so bad to get it to run etc?


Also separate issue I cant get my LC-1 to connect. I have tried 2 serial cables...Well to say i can get it connected once then it dumps the gauge and the Nistune program has a connection error. once i start the car. Anything i should be looking at?

Matt Ill attach a debug log for this and Ill attach my Bin for my tune once i get back to the house this after noon.


Thanks for all the help in advance,
Rick
http://texasnissans.com/tx/forums/showt ... hp?t=12583 Link to my car thread and videos of the car at the track etc

[PL]

Hey Rick,

Retarding cam be 3 teeth seems a lot. That's 60 crankshaft degrees!

Regarding your tune - if you need to adjust your K constant a long way *from where you know it should be* then it usually indicates a problem. Usually fuel pressure.

The question then is - is 188 a known correct K Constant for your setup or is it just what NIStune came up with after inj/MAF changes? I have a few known good K constants for SR20 tunes (sorry we don't get KA's here) which I use all the time. So I know (when I start a tune on an engine with the same setup) if I need to adjust the K constant by more than a 2 or 3% then there's something wrong. Nearly always fuel pressure related.

But if it's just a basic calculation for K constant that NIStune has come up with then don't be too stressed about changing it. Just make sure your fuel pressure is correct so you're not trying to tune around a problem.

In the end, you gotta give the engine what it wants. You shouldn't be adjusting K constant to remove detonation - use K Constant to get you AFR's correct and then adjust IGN maps to control detonation. Setting K Constant can be an iterative process - have a read of the Tuning Basics document. Basically you gotta balance K Constant, Fuel map values and latency to get suitable AFR's at both full load and idle (and everything in between).

You'll probably be wanting around 11.5:1 for a DE+T job.

PL

[Trippen]

Thanks PL for the info.

Its common to do the cam retard when your running these cams from the original cams its only 2 teeth had to get my notes again..

I am running a little rich in the tune because i wasn't sure on the K constant. The number 188 or 230(?) was the nistune value. How much does over bore .020 and low compression pistons effect this value?

Fuel pressure is 43.5psi adjusted prior to any tuning with aeromotive FPR.


here is my bin only complaint i have is around 3200-3500 cruise think its a little off in timing..let me know if anyone sees anything weird.

the tune file was miss labeled its 360 K and 600us latency

[PL]

Those things won't affect K.

If your K value is just what NIStune came up with then don't be too concerned about changing it - the K value calculations in NIStune are just a rough starting point...

PL

[Trippen]

Great thanks again.