A/F ratio and ignition timing - Page 2

kjewer1 · #16 09-08-2008, 07:56 PM

I've found that you can be running as much as 5 degrees too much without knocking. The only way to be sure is on a dyno. When you stop picking up significant HP with each degree, you've gone too far, and it has nothing to do with knock. Assuming there is nothing "wrong," knock comes in well after the point of diminishing return. On pump gas this conversation gets a little more complicated, but the principle is exactly the same.

I don't have the timing maps handy, but if you are reaching full boost below 3500-4000 rpm, you should probably be in single digits at this point. Of course with this being a 420A turboed (I think), boost may be lower, making 10-12 acceptable. Only way to be sure is on a dyno. Prefereably one that can load the motor and hold RPM while you tune.

SilvrEclipse · #17 09-08-2008, 08:26 PM

Wow single digits. I never thought I would have to set the timing that low.

The car blew out the exhaust manifold gasket again and one of the studs stripped. I got a gasket I can put on it but I need to have a helicoil installed also. Damn it is always something with this car.

There is something I dont really understand. When the turbo spools up it will hit 16-17psi around 4k or so. The wastegate opens and boost stays there only for a sec and then starts to drop as the rpms increase. By 6k Im only at 14psi or so. The thing I dont get is that the wastegate will stay open allowing the boost to continue dropping. I am running the wastegate off the intake mani so shouldn't the gate close as boost drops? I know I should check for boost leak and the BOV leaking but the wastegate should still be closing I would think.

kjewer1 · #18 09-08-2008, 08:36 PM

Boost dropping as RPM increases is generall a maxed out turbo. It seems like a 14b should be able to hold that boost to redline though, so something could be up. Boost leak, etc. It's possible that head just flows really well, but I don't see cams in the sig, so I'm not sure how likely that is... Turboed 420s are completely outside of my experience.

SilvrEclipse · #19 09-08-2008, 09:35 PM

The 14b cant be maxed out yet. The head should flow pretty well, it was ported pretty good along with the intake manifold and I upgraded to the 60mm TB. It just doesn't make sence that the wastegate doesn't close when the boost drops. I got a bad exhaust leak today before the turbo so maybe thats hurting it also. Here is a log I took earlier today, you can see the boost dropping off and also the intake temps shooting way the hell up there.

Is the cheap ebay FM why my temps raise so high so fast? Ambient was probably around 90F or so.

kjewer1 · #20 09-15-2008, 03:21 AM

That boost taper doesn't seem like enough to worry about. EVOs do it too, I've never been able to get rid of it completely on mine. Is MAT the temp? If so, it looks to be on par with a mediocre intercooler. A good IC will only allow a 10-20 degree temp rise on a quarter mile run.

SilvrEclipse · #21 09-15-2008, 09:12 AM

Hoping to install a small 16g in the next few weeks. So we will see if there is any change. The MAT is the manifold air temp, I guess a nicer intercooler would be a good bit more efficient. Then again the temps here are in the 90s. Once it starts to get cooler Im sure the temps will not rise as much. I should do a few runs in the evening and compare logs.

kjewer1 · #22 09-15-2008, 09:16 AM

Temp rise has little to do with starting temps, since the air cooling the core is the same temp throughout the pull. Efficiency will change, but the result is insignificant. Your numbers aren't terrible, fairly average. Only the very best of cores will provide the performance I mentioned above. In fact there are only two that I am aware of, the most popular being the garrett 24x13x4, which is more than most people are willing/able to run.

SilvrEclipse · #23 09-15-2008, 09:45 AM

Mine is a good bit smaller than that. I think its around 24x7x2.5. How much does the intake temp effect knock? Say between 100F and 140F. With a 40 degree increase in air temps is the chance of knock going to increase a good bit also or not enough to notice.

steviek · #24 09-15-2008, 11:45 AM

from what I understand and don't quote me on this. I think 10 degrees equals about 1 degree of timing. So 40 degree intake rise may require you to subtract about 4 degrees of timing.

SilvrEclipse · #25 09-15-2008, 02:42 PM

Quote:

Originally Posted by steviek

from what I understand and don't quote me on this. I think 10 degrees equals about 1 degree of timing. So 40 degree intake rise may require you to subtract about 4 degrees of timing.

Holy shit - thats not really what I was expecting. I guess that is why people make so much more power with meth injection systems.

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