Fast_vette89

Ok, I'm trying to compare the heat ranges on the L98 LT1 and LS1 motor. I want to know who has the hotest and coldest plug. AC Delco won't give that info out....bastards. Anyone know how the LT and LS plugs compare to the L98 alm head plugs as far as heat ranges?? L98 takes a Bosch 4202, LT1 takes a Bosch 4205. Those are the best comparative numbers I came up with.

HighHopes85

Well, compare apples to apples. Occasionally, when you go from a stock ACDelco plug to a crossreferenced plug (i.e. Bosch) the heat range can fluxuate up or down one.

Now for the problem. Delco uses a conventional numbering system for most of their earlier plugs...up until the LT era. Then they started going with a different style.

On an R45TS, the R = resistor, 4 = thread, 5 = heat range, TS = tapered seat design normal length.

One the newer plug numbers (don't know off the top of my head, but something like 601-XX or 61-XXX) the first set of digits represent an automotive application. I have searched a few times through Delco catalogs and have not been able to get enough info out of their newer naming convention (i.e. platinum tipped plugs) to cross it to a standard electrode plug.

BTW, when plat plugs are used, the heatrange is no longer 'conventional' thinking.

Fast_vette89

i know exactly what you're talking about. I've done a lot of research on all this spark plug tech stuff. For apple to apple purposes, i used NGK, not to mention every plug they has a heat range number, and they offer "conventional" plugs for every application IE LT1+ era so it makes everything easier to measure up. Heres the facts: the L98 cast or alum heads have a 4 heat range. LT1/Lt4/LS1 has a heat range of 5. (this is all for conventional NGK plugs). SO what i needed to get to the 6 heat range. Problem here though. FR4 is the alm factory NGK plug. SO....FR6 is what you need right?? yes, but they don't make it. they make s FR5. SO.... i did a search on NGK.com by characteristics like 14mm, 5/8" hex, 3/4" reach, 6 heat range, and JIS length. came up with about 5 V grooves. DIfferences are very minor. Heres the end verdict for us L98 alm guys:
NGK part # BCPR6E-11 NAPA stock number 5632 I spend hrs on this. Stock gap on the iron heads is .045", alm is .035". I'm running MSD6AL, MSD super conductor wires, MSD coil, Brass cap/rotor upgrade. other mods are full length headers, exhuast, 160thermo, custom chip, and more..... I called MSD myself. they said gap them at .040" to .045". I'm going to put them in tonight gapped at .045". We'll see how the car runs. I'll hook the scanner up to see how the Detonation counts do on a heavy load/high speed application. Heat range 4 is to damn hot for a performance motor. LT1 motors go 1 colder to the 6 range when you do NOS, or forced induction...so I'm sure i'll have good results going 2 colder to catch up to the 80's crapera engineering faults. hope this helps you guys. Oh, by the way... NGK has a good tech page, read it. NOW. Point of all of this: you want the coldest plug w/out fouling and really hard starting present. SO hot is bad, cold can only not start and foul. Happy tunning.
-Jason
89 L98/ 84 custom Turbo Supra 600HP

Nathan Plemons

All I know is that I finally found a cross reference that put my AC Delco 41-904 the same as a Delco R44LTS. I've been running them for several months now with no problems. I now know 3 LT1's running this plug. They don't detonate and they don't foul out. It's the perfect cheap plug as far as I'm concerned for stock and mildly modified LT1's. BTW, a friend of mine even put these in his LS1 and is having good results.

In my particular case I'm running an MSD coil, MSD 8.5 wires and MSD digital 6. I think I gap them at .45

HighHopes85

Jason-Sorry. I didn't mean to insult your intelligence any (if you took it that way or not, I am not sure). I just get really REALLY used to having to explain the differences to people day in and day out...and then once you consider AC Delco uses higher numbers for hotter and not all people do it that way...well, you get the picture ;)

Good to see that other people actually source out catalogs and stuff too! I get used to a lot of people saying "Uhm, we don't show that for this car..." and then I pull out their parts catalogs...

Fast_vette89

not a prob bud. I didn't take it like that...lol. info and tech is good. I believe in sharing info. :cheers: thanks for the reply man. I was posting topics as i was doing research on the net and at napa... i might of ranted on. :rant: sorry bout that. but i like to get every detail taken care of. to some it's a plug, to others its part of tunning. you wouldn't belive how well the car runs now with the BCPR6E-11 NGK V grooves in!!! it's great!!! anyone with Alm heads on a TPI motor DO IT!!!!!!! if your mainly stock do the FR5, make life easier. I think this is a great $18 mod. GREAT!!! I hooked up the Scanner and Detonation counts are WAY down. a 4 is way to hot for a mod'd or even stock sports car motor. (LOVE ThAT EMISSIONS man....NOT...) I guess GM figures if the temp is hotter it will burn leaner or at least help in burning up the carbon and passing emisions or along those lines... :cuss emissions.
SO, it's all over and done with. heres the facts.
Stock L98 Alm head plug- FR4
for a slightly mod'd or stock L98 Alm head use a FR5 (1 colder)
for a even more mod'd motor go with BCPR6E-11 (b/c a FR6 doesn't exist) Hope this helps us 80's era TPI/L98 guys. It's all in the tunning! Scan tool shows the proof.