spark plug question

what kind of plug should I use for a 355 with afr 210 heads and a 88mm turbo??

Wow that is a combination. I would recommend using some Autolite 103's. :)

The Autolite 103's are a taper seat plug like stock. But the AFR heads use a gasket seat plug. I believe a 3923 is the same heat range as the 103, but has a gasket seat. If you want colder, they make a 3922, which is the coldest they offer.

Mike

I'm running almost the same combo. Mine is a 383 with the AFR's and T88. I'm using TR6's.

Jose

I don't doubt that many, many people are using taper-seat plugs (like the TR6 and 103) in heads that are machined for gasket seat (like AFR).

But, it's not the correct plug. Look at your AFR instructions or go to their website, which recommends a 3910 (gasket seat plug) for their heads - even LT1/LT4.

Look at the way that the stock LT1 spark plug hole is machined, with a bevel for the tapered part of the plug to seat on, versus the AFR's, which have a flat surface around the plug hole for the gasket to seat on.

Mike

glad i saw this thread cause i too had the wrong type plugs in. just to let you know i talked with autolite and they also recommend the ar3923 but the ar3922 has been discontinued so if you need the next lower heat range it would be the ar3935.
hope this helps

Any ideas if there is a colder plug than ngk tr6 or what would be a good Ac plug

Ummmm. . . Except that the TR6 is a taper seat plug and your heads are machined for gasket set plugs???

I was to from afr that heads were made for 14mm with a 3/4 reach and a gasket plug

what kind of plugs are you engineermike useing and what kind of boost ??

I'm using Autolite 3923's with 14 psi non-intercooled boost.

Mike

Mike,
what gap do you run?
thanks

NGK makes a large range of plugs that will fit the LT1/4 AFR castings. Everything from a "5" heat range (stock) to a very cold "11", which is what I am using. If you want a pn, I could find it later. But just pick up their catalog, it's pretty self explanatory. The TR6, autolite 103 or 3922 may not be cold enough if you plan to plant your foot in it for more than a few seconds at a time. I would go more than one or two heat ranges colder. I have only had a plug fouling problem once with 6 ranges colder than stock. My ignition uses an MSD6AL box, Accel coil, stock wires. So it's nothing special. And that was when I had to run the car for a couple of minutes way out of tune in speed density mode. It was rich as hell and fuld the plugs. I changed the 4 "easy" ones, and it fired right up and cleaned the other 4 right off.

Rich Krause

Rich,
what gap would you reccomend?
thanks

So what is the problem with using a taper plug in a gasketed hole? Do they leak? I've been doing this for the last 2 years!!! I haven't noticed anything, but maybe I'll try out a new plug down the line sometime. The 103's have worked good for me.

Rich could you post the P/N when you find it? I know you have in the past, but I couldn't find it.


Bill

anyone know on the plug gap?
kinda need to know quick as i'm installing this evening
thanks

I used to use 3923's gapped to 0.035" with an MSD-6AL producing 14-psig boost. I will be making significantly more boost with my new setup (>20-psig). I am now using NGK's R5671A-7 (stock #4091) plug. It is two heat ranges colder than the FR-1LS, which I believe is two ranges colder than the 3923 (please correct if I am mistaken). I know Larry at ASSC Racing uses these plugs gapped to 0.032", which is what I've gapped mine to. He is making 26-psig boost (F1) on his L98 (runs 9's and he drives it daily). And if you feel these NGK's are not cold enough, the following is a list of even colder plugs w/stock numbers:

R5671A-8 (7173)
R5671A-9 (7405)
R5671A-10 (7942)

Originally posted by tubby
Rich,
what gap would you reccomend?
thanks

I have been using 0.035" for quite a while.

Rich Krause

rskrause what plug would you sudgest for a 355 with afr 210 F.A.S.T msd digital 6 about 20-25 psi form a 88mm turbo?

rskrause what plug would you sudgest for a 355 with afr 210 F.A.S.T msd digital 6 about 20-25 psi form a 88mm turbo?

I'm not Rich, but Larry's car I talked about above is a 355 with AFR's, MSD-6AL, FAST system with 72-lb injectors, running 26-psig with an F1. He uses the plugs I mentioned, gapped to 0.032".

Willie

i'm only seeing 8-9 lbs boost. would .040 gap be okay for the 3923's?

SMOKNZ, using the wrong plug style could cause two problems (that I can think of).

1. The gasket seat head doesn't have a tapered seat cut into it, so the sealing surface. I'm not saying that they all leak, but I could see how a leak would be more likely.

2. Since there is not a seating surface, the reach of the plug may be incorrect. The seating surface is what determines how far into the chamber the plug extends. So, mis-matched parts could lead to a problem with reach.

I'm not quite sure why I'm having to justify using the correct parts, though, since AFR's instructions clearly state what style plug to use.

Mike

Originally posted by engineermike
SMOKNZ, using the wrong plug style could cause two problems (that I can think of).

1. The gasket seat head doesn't have a tapered seat cut into it, so the sealing surface. I'm not saying that they all leak, but I could see how a leak would be more likely.

2. Since there is not a seating surface, the reach of the plug may be incorrect. The seating surface is what determines how far into the chamber the plug extends. So, mis-matched parts could lead to a problem with reach.

I'm not quite sure why I'm having to justify using the correct parts, though, since AFR's instructions clearly state what style plug to use.

Mike



Mike the plugs will work either way. tapered or gasket. They both also extend into the chambers the same and will not leak if tight . I think what some people are thinking is should they change their plugs if they are running the tapered style on the AFR heads. No need until you need new plugs for some reason because you not going to gain anything. Unless it will make you sleep easier..;)

Originally posted by Willie
rskrause what plug would you sudgest for a 355 with afr 210 F.A.S.T msd digital 6 about 20-25 psi form a 88mm turbo?

I'm not Rich, but Larry's car I talked about above is a 355 with AFR's, MSD-6AL, FAST system with 72-lb injectors, running 26-psig with an F1. He uses the plugs I mentioned, gapped to 0.032".

Willie
I am using a R5724-8, gapped @ .032 in my blown 2001 LS1. How does this plug compare to the R5671A-8?