I'm curious, what are the coldest plugs that you guys have gotten away with on the street that would tolerate some normal, daily (DC Metro area) idling in traffic… without fouling all the time and just being generally unhappy? I've had OK luck with some NGK TR6's (about the same as AC 41's or autolite 103's) in my LT1 (uses the same plug as my formula L98, a 43 heat range AC). That was fairly happy most of the time except if you let it sit for a long time, then it would throw misfire codes and run rough until you took it and blew the gunk out a couple of times. I'm considering trying one step cooler then that in the L98 (it would be an AC heat range 40 or autolite 51… I'll have to look to see what plugs are actually available that cold, I don't think I've ever seen a 40 heat range AC… I'm pretty sure that there's an Accel non resistor race plug with the right reach and tapered seat in that heat range, but I've never seen anyone that stocks them). I suspect that I may have to go for some race plugs to actually get into that heat range, but I'm not opposed to running non resistor plugs anyway (especially if all I can find is autolites, the resistor autolites are complete junk).

For that matter, what are you blower/turbo guys running (lemme guess, ½ of you are running stock plugs or some autolite 104's or something)?

Autolite AR 51 is the coldest Ive run on the street..

How were they on the street? I take it that this was in your Track 1's?

I wonder what the tapered seat, 14mm, .460" reach version of the 51's is?

I run AC Delco R42LTS(gapped at either .030 or .032). Only complaint is they run rough on startup when the motors cold, for the first minute or two.

I'm just wondering, why are you looking to go with such a cold plug?

Steve

I could tell you but then I would have to…

Well, let's just say that things are coming together and I intend to figure out exactly how hard you can push a stock L98 before you carry it home in a bucket.

nice

Running AC 43's.... BW

yea, but that's in a 305 that had 45's stock. that's like me running 41's...

TTA850, what engine was that that you were running 42's in?

Those are in my Buick V6, with a compression ratio of just under 8:1 and boost levels of 18-19psi on pumpgas and 25-27psi on racegas(mostly 25psi but have been up to 27psi on a few occasions while tuning last year but was running out of fuel, hence the larger 83# injectors this year over the 55# injectors I ran last year).

HTH,
Steve

Thanks steve… so if I'm reading the cross-reference charts right (they're a little ambiguous with the 3.8 plugs), it looks like those are about 2 steps cooler, like running a 41 in my L98… Considering that you started turbocharged and just added more boost where I'm going from NA to boost… I'm not sure that that's that big a drop.

I use autolite 3923's for the street

Huh, what do those cross-reference to? Resistor/non resistor, tapered/washer seat, reach…?

They are for L98 style heads. 14mm, 3/4" reach 5/8ths wrench flat seat.

Here is a link to autolites performance listings

http://www.autolite.com/sports/index.html

Huh… they list those as the stock replacement for the aluminum L98 heads (well, one step warmer), and the straight 24's for the iron heads. Interesting that they're the same heat range… anyone know what the difference is between that plugs for the aluminum and iron heads? Maybe one is a washer seat or different reach? Wait, that's probably it, ¾" reach is almost 2x the reach that the iron head plugs use.

Huh, funny, but my L98, L05 (350 TBI truck), and LT1('97 WS6, aluminum heads) all use the same standard AC plug, but all have different plugs recommended by autolite… Hum, LT1 and 'vette heads use a different plug location? That's suprising, since the same manifolds were used on the 'vettes for both...

FYI,

stock plugs for L98 are AC-DELCO 45RTS.

I'm running 43's right now. They are working ok.

-- Joe

NGK range 6.

Phoenix AZ in a 385 motor, 64cc chamber.

They do just dandy for me.

I'm assuming you mean R45TS.

Stock plugs for an L98 are R43TS, like I originally said. The 45's are the stock plugs on the 305's. Look it up on AC's site, or on your hood sticker…

so you're running stock heat range plugs.



NGK 6's… yea, I'm running TR6's on my LT1 with spray. Funny, AC tends to have 2 steps for every one step that NGK has (6's are like 41's in ac plugs, the stock 43's cross to TR5's or TR55's), and autolite has 2.5-3 steps for every NGK step (reason for the debate over whether the 104 or 103 is "2 steps cooler" in the LT1 world).

Well I dont have a factory hood, but I do have a factory service manual from when my family owned a pontiac dealership.

My 1992 pontiac firebird service manual states the following for plug replacement, and GAP on page 0B-5:

3.1l (VIN T) AC Type * R43TSK 1.14mm (0.045")
5.0L (VIN E AND F) and 5.7L (VIN8) AC Type * R45TS .89mm (0.035")

I also checked autozone's website (www.autozone.com) and for a 5.7 in '89 (maf car to show spectrum of years) they list:

AC-DELCO R45TS $1.69



edit: I just checked AC-DELCO's site. For my car (1989 PONTIAC FIREBIRD FORMULA V8 5.7L 350cid GAS FI N Engine VIN = 8 ), it says R45TS.





No I'm running 1 degree colder than my head manufacture (world products) recommends, and 2 colder than stock.



-- Joe

Now actually read the footnote there… there is an error in AC's database (well, I guess that it's with GM's original info) and if you look at the footnote when you look up I think it's 90-92 (may happen earlier) it will tell you R45TS or CR45TS (depending on the year), with a footnote saying that it's the L03 number and lists the L03 gap… for example, looking up a '92 you get:

1992 PONTIAC FIREBIRD FORMULA V8 5.7L 350cid GAS FI N Engine VIN = 8
Qty
Req Qty
ACDelco Part# Description

IGNITION / SPARK PLUG

08 41-905
SPARK PLUG, PLATINUM PLUG
GAP .035 With RPO 5.0E(L03)


08 2
SPARK PLUG, RAPIDFIRE PLUG
GAP .045 With RPO 5.0E(L03)


08 CR45TS
SPARK PLUG, STANDARD PLUG
GAP .035 With RPO 5.0E(L03)


If you look up an earlier car, same engine you just get a R43TS. I'm pretty sure that if you check the supplement for the service manual (the latest service manual+supplement that I have that covers a TPI car is the '87 which is a complete piece of junk, riddled with errors) you'll see the same thing showing a 43 plug. Funny thing is that if you look it up backwards, see what an [C]R43TS is recommended for, it does come up…

So world products actually recommends a 44?

Here check out this cross reference i found.

http://www.nology.com/crossref.html

im running autolite 24's

You know, I saw that already and to be honest, I can't figure out what they're doing… it's not sorted by heat range or by plug reach/hex/thread, for example, they have some .460" reach AC plugs listed under their .7xx" reach plugs, and they have all sorts of heat ranges bunched together… They have one plug listed as replacing AC ranges 42-44, Champion 9-15, and NGK 4-7… that's just not possible…

As I said before I use the autolite 3923 on the street I was looking last night and it seems the FR5LS AC is a interchange. Any thoughts? Does anybody have a interchange between NGK/AC/Autolite ??

I am running TR55's, I had problems with TR6's fouling out on me.

on a LS-1 trans-am we put on Nology wires and iriduim plugs and made zero gains on our dyno. I guess you could look at the fact that throttle response isnt really measured on a dyno, maybe they improved there.

What motor combo?

10:1 vortec headed 350.

Mark, FWIW, I ran R42LTS and Autolite 103's in the TTA. Gapped at a tight 35 and never had a problem with either. The AC ones are the stock plug and the 103's are the Autolite equivilent.

Here is a site that has a cross reference to autolite plugs and gives the physical dimensions of the plug. Just enter the plug number.

http://www.autolitesparkplugs.com/

For aluminum l98 heads, autolite 3924 is stock, 3923 is one step colder.
Many people use 104's but not sure if it's a problem. The reach is different and it's a tappered seat instead of gasket.

For supercharged or turbo applications I read:

4 to 7 psi - one step colder
8 to 14 psi - two steps colder
15 to 20 psi - three steps colder

I run AC R42TS's in my TT Iroc. This is what my AC Delco dealer gave me when I asked for a one step older plug.

I had them gapped at .035", but I am not sure that is necessary with my MSD 6BTM. On a mild turbo boost, does the gap really need to be that narrow with a good ignition amplifier??