Dominic Sorresso

I mentioned in the Byron thread that I hadn't noticed any real improvement in trap speed from my first time out with stock motor/B+B exhaust and this last trip to Byron after having installed Watson headers.
I decided to check injectors and those ohmed out fine. Nice day today so I threw on the scan tool and went for a ride just to see if headers had "leaned" things out. BLMs were in fine range of 131L/128R, typical split BLM. I made a couple of WOT bursts curious to look at NBO2 just for grins.(I know you can't really tell. I have ZT-2 to install maybe tomorrow).
But what I did see on scan was Total SA was 23d at full tilt. Looking at the bin file, I should be getting 29d at 6000rpm/95-100kPa. There was about 4d KR but I'm also seeing a 1.8d SA relative to ref at 850rpm! SA table shows I should have 20d. While the scantool is showing KR, my knock counts stayed at 7 before and after. Maybe I have some of the terminology wrong but even accounting for an additional 5.9d as Initial SA, the numbers don't add up. Any help is appreciated.

lgaff

Haibeck notes on his site that the ignition timing sensor is offset by 6 degrees on the LT5, so you need to add 6 degrees of timing to your #s if you have Diacom, Tech1 automatically adds it in

http://www.zr1specialist.com/HAT%20W...es/knock2a.jpg

LGAFF

Axelrod

It's the driver

Dominic Sorresso

Lee,

I'm using EASE scantool. Not sure if it includes 5.9d of Initial SA or not.
I'm getting KR even though the Knock Counts don't change. I may change the bin to reduce or eliminate KR depending on what I see from the Wide Band O2. We should do yours and see if we get similar results from the scan.

tpepmeie

The knock counter is a double byte value. I have noticed some scan tools will only display the MSB, and truncate the rest. That will give the appearance of knock counter not increasing, yet spark retard is present.

From what I recall, EASE does not include the 6* offset.

Todd

ccmano

Hans

Aurora40

If you are getting knock retard, try driving the hell out of the car for a bit. That usually clears it up for me. They seem to build up carbon pretty easily.

So what were your trap speeds?

Dominic Sorresso

Todd,

Thanks. But there doesn't seem to be enough of the LSB bytes to increment the main knock counts. Looks to me like the cal is very sensitive. My experience has been with an 84 Xfire so not sure if the
LT5 required that level of protection. Given that the car ran very similar trap speeds with and without headers, I might conclude that the headers are what's causing the KR. With the 84, I actually ran with the KR at 0 in the cal. The point being that the tune should be such as to not bring in knock. Here the KS may be reporting a false knock. Looking at the scan, the prevalent area for KR seems to be coming from the 4000rpm range. Typically its pulling 3-4d and in one case 10d.

Aurora40

I believe the car is most likely to have real knock where the torque curve is the highest. This is where the engine is most efficient, and therefore cylinder pressures are the highest. So it sounds like legitimate knock.

I think if you tuned out all the knock on a car, you'd leave a lot of horsepower on the table. Depending on the air, fuel quality, and how the car has been driven previously, knock seems to happen or not. To tune it out would be to basically set the timing such that it was already retarded, but all the time. Or is there some other way to tune it out?

How many runs down the 1/4 did you do? Did you have the same amount of KR on the first run as on the last one? These cars really seem prone to buildup which causes knock. But some hard beating (more than just one or two WOT passes, it seems) on it and the KR will go away as the buildup is burned off.

Dominic Sorresso

Aurora,

Trap with stock exhaust was 111.1. Trap with headers and no cats was 111.6. One other issue is also that the clocks at Byron seem to be having a problem. But Lgaff ran pretty consistently 3mph higher with a similar setup. He has the same headers I do but with 4.09gears and an Xpipe. Thing to do is hook up the WB O2 and make sure its not going lean. But the KR is coming in at mid-range(4000rpm) and not really at the top.
One other thing I noticed is that my highest rpms on scantool were in the 6300rpm range but I thought I was shifting at 7000. Wonder if the scantool doesn't register that high or the tach is off.

tpepmeie

Very unlikely you are going lean, unless there is a mechanical problem, i.e., injectors or secondary fuel pump. The stock fueling and most off the shelf cals are just right for a car w/ headers.

4000 RPM is almost certainly real knock. That is where the LT5 seems most prone to knock. GM must have known that, too -- Look at the stock timing curve...there is an obvious dip at 4000 to combat the tendency, at least on the early cals.

I have found that it is really difficult to get an LT5 to knock above 6000 or so, even with a lot of spark advance. Power will decline w/ too much advance before it will knock, in my experience.

You won't pick up more than 6375 RPM through the ALDL stream, because the RPM byte in the stream is RPM/25.

Todd

Aurora40

TTS Datamaster has some additional value called "RPM16" that I believe they interpolate based on speed and rpm data. You could do the same manually to try to figure out about where the shift is happening.

Axelrod

You are totally comparing apples to oranges. Gears? Yes, expect a higher trap speed.

Dominic Sorresso

I expect a higher trap speed with headers than with stock exhaust? Yeah I do. I was using Lee's car to make the point that his car was trapping higher and so the issue of the clocks being off wasn't the major factor.

Todd,

I agree I am probably not running lean. A precautionary step mostly.The rpms looked artificial so I suspected it was a limitation. I should be able to see true rpm with the ZT-2 logging tool.
Looking at the my current cal and compared to stock bin, there is an additional 2-7d in from 2500 through 5000rpm/ and from 70-95kPa.
Looks aggressive and most of it is coming back out due to the KR.
This is a fairly old Marc Randolph calibration.
I could drop some timing and see where it stops tickling the KS.

lgaff

May be the resonator, mine was 112.25 at the last run picked up to 115.06 with X-Pipe.


LGAFF

Dominic Sorresso

Lee,

Don't forget you had bad injectors as well.

Goldcylon

How much fuel were you carrying? X pipe next? Was the temperature or track conditions an issue between the runs? Maybe time for some RC injectors?

Dominic Sorresso

Daryll,

I did have a full tank with spare tire. Looking to replicate the conditions I had first time out. I went to the scales for grins and had the car weighed with me in it. 3760lbs! My old 84 weighed in at 3240 with no fuel and no driver.
As ccmano said "Its the driver!"
Looking at the calibration, the Spark Advance tables show that there's addtional timing(up to 7d) added to the stock bin pretty much in the same areas I am experiencing knock now. So my next step is to drop that additional timing by half and see what happens. I'm going to try and work a trip to the track and play with the calibration while there using my Ostrich emulator. Then we can get back to back results. Could do that on a dyno day too.

GTB/ZR-1

Absolutely...

My ZR went up 3ish mph as well w/ headers & Flowmaster over the stock setup in similar air conditions.

Gears will have no real affect on trap, although it will on ET.

Saying it's the driver (the same one @ that), as mentioned before, is, well.....

Dominic Sorresso

Thank you, GTB.