tuning questiion

[Paul Workman]

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]

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]

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

[XfireZ51]

Paul,

Its 41-602. BTW, here's a really cool site for plug x-reference.

http://www.sparkplug-crossreference.com/ Converts the numbers for you.

The 41-602 crosses to an NGK 6 or 7. I tried the 7 and found them a bit too cold for my motor. The 6 works very well. Another alternative is the Autolite 3923. I use the NGKs because of their heat range bracketing. I MAY get some KR at torque peak (4500-5000rpm)but it usually lasts for 1-2 frames(17frames/sec) of the datalog. I had WOT timing up around 34d at 7000rpm on the dyno and got no detonation w them. In any case I would rather foul a plug than hole a piston. Give those shot.

[Paul Workman]

Originally Posted by XfireZ51

Paul,

Its 41-602.

Nice catch, Dom! Thanks for that!

(41-602 IS what I meant (and in my notes too). Memory is a terrible trixter, sometimes....)

P.

[Marc Haibeck]

Lee,

It is normal for the LT5 to detonate lightly during a WOT run after the engine has been driven in traffic for a while. Oil and carbon normally accumulate.

I recommend at least one, preferably three WOT runs to 90 mph to clean out the combustion chambers. Then record detonation on a fourth run. A normal engine might get a tip-in knock at -4 degrees and then a similar knock on a fast gear shift. That is normal. Other knocks should be less than -3 degrees and less than two knock events per run through a gear.

The bottom line for WOT AFR is a wide band oxygen sensor reading. WOT AFR tuning can be done on the street if you have a place where it is safe to make WOT runs in second or third gear depending on your axle ratio.

[LGAFF]

Thanks Marc....I plan on a dyno tune at some point, but appears I need to sort the trans issue first. I drove my 92 today, amazing difference in shifting vs the 90.....also my the 92 ZR-1 seems slow in comparison(and the 92 runs 12.42 @ 117.5) Whatever the trans issue is it is certainly hurting the cars speed on the track. Might have to wait until next year to sort, I have the Callaway TT on the lift right now....may need a new trans or a rebuild as it does have 140K miles on it.

[Hib Halverson]

Originally Posted by XfireZ51

Paul,

Its 41-602. BTW, here's a really cool site for plug x-reference.

http://www.sparkplug-crossreference.com/ Converts the numbers for you.

The 41-602 crosses to an NGK 6 or 7. I tried the 7 and found them a bit too cold for my motor. The 6 works very well. Another alternative is the Autolite 3923. I use the NGKs because of their heat range bracketing. I MAY get some KR at torque peak (4500-5000rpm)but it usually lasts for 1-2 frames(17frames/sec) of the datalog. I had WOT timing up around 34d at 7000rpm on the dyno and got no detonation w them. In any case I would rather foul a plug than hole a piston. Give those shot.

Oh, wow...now you guys have me worried. In the past I've run the NGK 7 heat range or equivalent plugs from Denso ACRapid Fire or ACDelco on the street a lot.

How did you decide that AC 41 or 42 or NGK 7 or 6 plugs are too cold for an LT5?

[XfireZ51]

I can only answer for my motor, but I was originally running the 5s and was chasing KR. I decided to check plugs for specks to confirm. I also examined the ground strap. It was a light gray color down to the plug thread which is indicative of a too hot plug. I went 2 steps colder w 7s and the strap was now dark to the end if the strap. The 6s produced coloring of the strap which transitioned from light to dark at the radius of the strap. That's the indication of a proper heat range. Also did plug cuts.

[Hib Halverson]

Originally Posted by XfireZ51

I can only answer for my motor, but I was originally running the 5s and was chasing KR. I decided to check plugs for specks to confirm. I also examined the ground strap. It was a light gray color down to the plug thread which is indicative of a too hot plug. I went 2 steps colder w 7s and the strap was now dark to the end if the strap. The 6s produced coloring of the strap which transitioned from light to dark at the radius of the strap. That's the indication of a proper heat range. Also did plug cuts.

Typically, spark plug coloring is used as a measure of air/fuel ratio not plug heat range but, with today's fuels having a lot of "exotic" components, the plug coloring you get with modern pump gas is really not even good for that. Today, the real measure of AFR is what you see on a wide-band O2 sensor.

As for how to select a heat range, my rule has been, given an engine which has its AFR at WOT pretty close and is not using ecessive amounts of oil, I go as cold as possible as long as the plugs do not foul during warm-up, idle or light throttle. That's led me to something along the lines of the AC 1, NGK 7 or Denso 22 heat ranges. I'll add that, if detonation is an issue and one things the spark plugs might be a contributing factor in causing it, then you want the coldest plug you can get. My rule has always been to try and take the plug out of the detonation equation but doing just that.

interestingly, during development and validation of the LT5 and its release for production, the plug GM specified for the LT5 was the FR1LS. The AC 1 heat range is about the same as the NGK 7. Just before the car went on sale, to mitigate fears of some inside GM about pre-delivery spark plug fouling on dealer lots, GM changed its mind and went with the FR2LS.

The majority of street-driven LT5s do not see duty like what would cause "pre-delivery fouling" and LT5s which are raced or driven aggressively on the street will never see it.

I've owned my LT5 for 18 years and on the street I've run either NGK 7s or, for the last decade, Denso IT-22s. When I go to the track or the chassis dyno, i put Denso IT-24s in the engine.