Timing advance on a car with hotter cams

[Buddyworm]

So I've been diagnosing/tuning a friend's CA18 build with 272's and a biggish turbo (greddy TD05-18G). I've got it running butter smooth through most of the revband on vacuum and full boost up to 5500-6000rpm where the turbo starts to "bite" and ignition starts to break up; loss of power, backfiring, but no bucking. Initially I suspected detonation so I backed it off from ~21deg to 17deg in the affected region to no avail. His wastegate is set at 1bar and I just don't see how it can be pinging at 17deg advance so my question is this:

How should timing advance be changed in order to accomodate the longer duration cams? Could it be that the cams themselves need to be timed differently?

Thanks for any input you peeps can give,
Kenji

[TM_S13]

Usually to take the most out of upgraded cams you need to tune on the dyno and do small cam (intake and exhaust or just intake or just exhaust, depending on aplication) adjustments at each time and see the diferences in the power run. Off course it gets to the point when you're an experienced tuner you almost know what to do imediatly at each setup and then just fine tune it specifically for that car.
Anyway...
So you say you hear knock (pinging) ? Or you think there's knock ? Quite important the diference between knowing it is and thinking it is.

[Buddyworm]

To be honest I'm not even sure I could hear it if it was there, atmo wastegate, hks hipower exhaust and a gutted car does not a quiet interior make. All I can hear is the ignition breaking up, sometimes a telltale sign of light knock, yes?

I agree a dyno would be optimal, but I'm not actively pushing timing upwards, just trying to find a safe spot where combustion is solid and tune the fuel curves.

[TM_S13]

Just out of "curiosity", what sparkplugs is your friend using on the engine ?

[Buddyworm]

NGK coppers, heatrange 6. BCP6EY or something like that.

[TM_S13]

I replied to your PM a few minutes ago

As I said in that PM, you should change the spark plugs

Try some BCPR7ES

By the way, what other mods does the car have? diferent injectors and diferent AFM ?

[PL]

Sounds like it could be just IGN breaking down. FWIW when I've had engines with sus IGN systems they have tended to improve when IGN timing is advanced further. This is only covering up the problem but it's a good indicator of a borderline IGN system.

I'd fit a set of 7's and make sure they're gapped to 0.8mm for a start. Could be coils too...

And ditch the screamer pipe. I hate tuning cars with screamers on them!!!!

PL

[Buddyworm]

Will be trying the 7's when it stops raining. Cuz I'm not wild about that 18G hitting its sweet spot at highway speeds on a sopping wet road...

And I'm afraid I'm gonna have to disappoint you on the screamer pipe PL. I like a woman who's cool and reserved in mixed company, but a real screamer when you're really giving it to her. Nissans are no different.

[PL]

He he he - as long as I don't have to tune it.

Actually I did an SR with a Trust turbo the other day. T518Z. Not sure if they run the 18G comp wheel. I thought they did.

But man those suckers come on HARD! Full boost at 4000. Which I guess isn't too bad. But at 3900 it's making 80rwkw and at 4100 it's at 180rwkw - literally. It was sending the dyno into spasms trying to control the quick ramp up in torque. Amazing. It made similar power to a 2871R but just hit so hard. 277rwkw on 21psi was the final figure. Pretty healthy setup.

PL

[Buddyworm]

^That's why I'm a MHI fanboy. This'll be the 3rd MHI wheel I've tuned a CA for (14B, 17C, 18G) and every one comes on like a lightswitch. My theory is that they were originally designed for heavy equipment apps and thus only had to run efficiently in a very particular range.

[PL]

That sounds like a totally reasonable assumption to me.

I've also seen exceptional results from a TD06SL2-20G on an SR20. Well, it was actually an SR24 once it was all said and done. But the turbo delivered in spades.

PL