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?

Re: tuning questiion
 

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

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.

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.

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...

Re: tuning questiion
 

Which plugs are u using? Heat range?

Re: tuning questiion
 

NGK BKR5EIX-11

Heat range is a 5/6; gap is .044

http://i134.photobucket.com/albums/q...f/DSCN4822.jpg

Re: tuning questiion
 

These plugs have 3K miles on them

http://i134.photobucket.com/albums/q...f/DSCN4823.jpg

Re: tuning questiion
 

Get a set of BKR7. Just buy the standard plug and gap to .035". I use 6s in mine. I can see black specks on the ceramic w your pics, so it's detonating and the straps look like heat range is a bit too hot. One other thing is to do plug cuts. Cut the threaded portion of the plug off and let's see what bottom of ceramic looks like. That tells the story of WOT.

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!

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.

Re: tuning questiion
 

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

Pete

Re: tuning questiion
 

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

Re: tuning questiion
 

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.

Re: tuning questiion
 

Nice catch, Dom! Thanks for that!

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

P.

Re: tuning questiion
 

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.

Re: tuning questiion
 

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.

Re: tuning questiion
 

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?

Re: tuning questiion
 

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.

Re: tuning questiion
 

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.

Re: tuning questiion
 

Read this article on selecting the right heat range.

http://www.moparmusclemagazine.com/t...s/viewall.html

You start from there then move on to gap and timing.

Re: tuning questiion
 

That story doesn't say much at all about how to select a heat range but what's there, if anything, confirms what I said earlier about plugs.

But...if the plug originally developed for the engine was an AC 1 heat range, unless the engine is in a trailer queen...why is everyone running such hot plugs?

Do they know more than the engineers who spent years testing plugs?

I'll stick with my Denso 22 heat range.

But I will grant you, for engines which see a lot of starts without warm-ups, are running too rich at idle and part throttle or are using oil, the cold plug is a mistake.

Re: tuning questiion
 

Great post. Thanks !

Re: tuning questiion
 

Click in the pics of the various plugs. The one w high miles
but in good condition. Read the material there. It describes how to choose plug heat range using the coloring of the ground strap. This is really well known in performance circles. Nothing new actually. You don't pick heat range based on the color of the ceramic.

Re: tuning questiion
 

Well I haven't heard that much about using the color of the ground strap to select heat range.

But, heck, maybe I've not been in "performance circles".

Re: tuning questiion
 

I have never deviated more than one heat range from 'stock' (if known) for any particular engine incl mild street supercharged applications.

The one time I got some free plugs that were 3 or 4 heat ranges colder that I threw into a tpi 305 camaro, it immediately failed to meet the max allowed hydrocarbons on the two speed idle emissions test that we used to use here. (I worked at a shop and we had the 4-gas bar-90 machine). It idled fine, ran fine, ...just ran dirty at idle loads.

if you don't run catalysts, I suppose it doesn't much matter.