tuning questiion - ZR-1 Net Registry Forums

LGAFF · 09-15-2012

Car is pulling 4-5 degrees timing over 4k blms at 128 and o2 at 920-940, thoughts or other things I need to check? False knock?

LGAFF · 09-15-2012

I think it goes to 128 BLM at WOT????

XfireZ51 · 09-15-2012

Lee,

You really need to put a scantool on it first of all. Secondly, BLMs lock at 128 when you go into PE mode. The O2 sensor reading at WOT is not accurate. Its rich, which it should be but the resolution of a narrow-band O2 isn't usable for determining AFR at WOT. You need to get a WB O2 like a Zeitronix or Innovate.
Frankly, the most expedient thing to do is get the car on a dyno and let's thrash it there. Everything else is just speculative. We don't know if the part throttle or WOT fueling and timing are causing the issue. And you won't unless its ON THE DYNO.

XfireZ51 · 09-15-2012

Lee,

Have you pulled plugs and checked for specks in the porcelain? That would confirm detonation.
You may want to try a colder plug.

LGAFF · 09-15-2012

I pulled a plug today, the strap looked fine, but the base looked pretty white, if our cars like slightly rich, I am guessing I am too lean...

XfireZ51 · 09-16-2012

Quote:

Originally Posted by LGAFF

I pulled a plug today, the strap looked fine, but the base looked pretty white, if our cars like slightly rich, I am guessing I am too lean...

Which plugs are u using? Heat range?

Hib Halverson · 09-16-2012

First, I'd not assume you have a problem with false knock until you conclusively rule-out detonation.

Second, unless you subject your LT5 to frequent engine starts without warm-up, you're using a plug that's too hot for an LT5 and running too hot a plug at WOT, make the engine more prone to detonation. Unless the engine sees a lot of starts without warm-ups, you need to run either an NGK 7, a Denso 22 or, if you're familiar with the old ACDelco numbering system, an AC 1 spark plug. FYI, the original LT5 plug was the FR41LS, but that was changed just before introduction for the 1990 model year to the FR2LS because of concerns about pre-delivery fouling.

Now, false knock...it is true that the LT5 can have problems with that and such problems can be aggravated with the installation of headers, but again, I'd not assume false knock until you determine the engine is not detonating.

It was suggested earlier that you acquire a scan tester which takes data. That's a wise purchase. If you see 5-deg KR near peak torque, in warm or even 75° weather, your coolant temp is in the 190s, and your running 91-oct gas, it's probably legitimate detonation.

One way to gain info on whether or not the engine is detonating is to increase your octane just a bit by adding a little 100-octane unleaded racing gas to get the octane of the fuel to 95-96. If you up the octane a bit and the KR either is significantly less or goes away, you had actual detonation and not false KR.

Do not run straight 100-octane unleaded as that often prevents the engine controls from passing the knock sensor test and when the engine can't do that, it sets a code.

You can find blending charts for 91, 92 and 93 octane at http://www.rockettbrand.com/techsupp...taneblend.html

Good luck!

Paul Workman · 09-16-2012

The AC/Delco site coughed up the 41-602 @. 35" (standard resistor, copper core plug), and FWIW, it is the plug Pete recommends and has good results with. I've got 8000 miles on a set of them, and have had no performance issues with them in that time. AND, @ under $2 a copy, anyone can afford to have a fresh set in their LT5 every season w/o coming close to wearing them out.

Y'all can spend more, but fresh plugs are tough to beat, and for the price the 41 602 should work, has been my experience.

P.

Pete · 09-16-2012

Quote:

Originally Posted by Paul Workman

The AC/Delco site coughed up the 61 402 @. 35" (standard resistor, copper core plug), and FWIW, it is the plug Pete recommends and has good results with. I've got 8000 miles on a set of them, and have had no performance issues with them in that time. AND, @ under $2 a copy, anyone can afford to have a fresh set in their LT5 every season w/o coming close to wearing them out.

Y'all can spend more, but fresh plugs are tough to beat, and for the price the 61 402s should work, has been my experience.

P.

All the 10 second FBI Z's run these,nuff said.

Pete

LGAFF · 09-16-2012

I usually run the cheap ones too, this was in the lot of LT-5 stuff I got at auction....

09-15-2012	#1
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,194	tuning questiion Car is pulling 4-5 degrees timing over 4k blms at 128 and o2 at 920-940, thoughts or other things I need to check? False knock? __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359

09-15-2012	#2
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,194	Re: tuning questiion I think it goes to 128 BLM at WOT???? __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359

09-15-2012	#3
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,709	Re: tuning questiion Lee, You really need to put a scantool on it first of all. Secondly, BLMs lock at 128 when you go into PE mode. The O2 sensor reading at WOT is not accurate. Its rich, which it should be but the resolution of a narrow-band O2 isn't usable for determining AFR at WOT. You need to get a WB O2 like a Zeitronix or Innovate. Frankly, the most expedient thing to do is get the car on a dyno and let's thrash it there. Everything else is just speculative. We don't know if the part throttle or WOT fueling and timing are causing the issue. And you won't unless its ON THE DYNO. __________________ [SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX

09-15-2012	#4
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,709	Re: tuning questiion Lee, Have you pulled plugs and checked for specks in the porcelain? That would confirm detonation. You may want to try a colder plug. __________________ [SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX Last edited by XfireZ51; 09-15-2012 at 11:26 PM.

09-15-2012	#5
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,194	Re: tuning questiion I pulled a plug today, the strap looked fine, but the base looked pretty white, if our cars like slightly rich, I am guessing I am too lean... __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359

09-16-2012	#7
Hib Halverson Join Date: Jun 2005 Location: CenCoast California Posts: 899	Re: tuning questiion First, I'd not assume you have a problem with false knock until you conclusively rule-out detonation. Second, unless you subject your LT5 to frequent engine starts without warm-up, you're using a plug that's too hot for an LT5 and running too hot a plug at WOT, make the engine more prone to detonation. Unless the engine sees a lot of starts without warm-ups, you need to run either an NGK 7, a Denso 22 or, if you're familiar with the old ACDelco numbering system, an AC 1 spark plug. FYI, the original LT5 plug was the FR41LS, but that was changed just before introduction for the 1990 model year to the FR2LS because of concerns about pre-delivery fouling. Now, false knock...it is true that the LT5 can have problems with that and such problems can be aggravated with the installation of headers, but again, I'd not assume false knock until you determine the engine is not detonating. It was suggested earlier that you acquire a scan tester which takes data. That's a wise purchase. If you see 5-deg KR near peak torque, in warm or even 75° weather, your coolant temp is in the 190s, and your running 91-oct gas, it's probably legitimate detonation. One way to gain info on whether or not the engine is detonating is to increase your octane just a bit by adding a little 100-octane unleaded racing gas to get the octane of the fuel to 95-96. If you up the octane a bit and the KR either is significantly less or goes away, you had actual detonation and not false KR. Do not run straight 100-octane unleaded as that often prevents the engine controls from passing the knock sensor test and when the engine can't do that, it sets a code. You can find blending charts for 91, 92 and 93 octane at http://www.rockettbrand.com/techsupp...taneblend.html Good luck! __________________ Hib Halverson Technical Writer former owner 95 VIN 0140 current owner 19 VIN 1878

09-16-2012	#8
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	Re: tuning questiion The AC/Delco site coughed up the 41-602 @. 35" (standard resistor, copper core plug), and FWIW, it is the plug Pete recommends and has good results with. I've got 8000 miles on a set of them, and have had no performance issues with them in that time. AND, @ under $2 a copy, anyone can afford to have a fresh set in their LT5 every season w/o coming close to wearing them out. Y'all can spend more, but fresh plugs are tough to beat, and for the price the 41 602 should work, has been my experience. P. __________________ Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry Last edited by Paul Workman; 09-19-2012 at 06:51 PM.

09-16-2012	#10
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,194	Re: tuning questiion I usually run the cheap ones too, this was in the lot of LT-5 stuff I got at auction.... __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359 Last edited by LGAFF; 09-16-2012 at 05:31 PM.