What spark plugs to use?

[Wizo]

THis is a question for all you guys that built small block 400"s
I'm wondering what spark plugs you guys use? What brand name? What part number? What heat range? I have been using NGK YR5 not even sure if those are the correct ones.
Heres what I built: .030 over 400, 9.01:1 pistons 268XE cam, 2.02 heads, triple spring stainless valves, duel plane intake, holly 3310 750cfm
what works good for you guys. thanks in advance.

[Fitz]

AC Delco R45XLS / GM 5613878

· R = Resistor
· 4 = 14 mm Thread
· 3 = Heat Range (range 1-5 start with a 5) and maybe drop to a 3 but that is probably too cold for around town
· XL = Extra Long Reach, 3/4" fully threaded
· S = Extended Tip

[Wizo]

Interesting because i was considering the R44TX. Is the R45XLS a hotter heat range?

[Wizo]

Fitz: I'm guessing by your response (Thank you) that your running a 400. If so what comp ratio are you running? mines a 9.02:1. my concern is that the XLR will be to close to or even hit the piston.

[davepl]

Get the correct plug for those heads. If they are an aftermarket head, ask the head vendor.

The plug needs to be matched to the head and verified for piston clearance, but it sounds a little late for that now.

No nitrous, not a lot of compression, no need to get fancy. Err on the side of shorter if you have to guess, and stick with the stock heat range unless and until you see excessive fouling. You ideally want the coldest plug that works perfectly for your setup.

[skokie]

Not trying to hijack the thread here but what is a good plug for a stock 350 or 260 hp crate?

Thanks!

[Fitz]

Originally Posted by Wizo

Interesting because i was considering the R44TX. Is the R45XLS a hotter heat range?

Yes. Range goes from 1 (coldest) to 5 (hottest)

[Fitz]

Originally Posted by Wizo

Fitz: I'm guessing by your response (Thank you) that your running a 400. If so what comp ratio are you running? mines a 9.02:1. my concern is that the XLR will be to close to or even hit the piston.

ZZ572, not 400. 9.7:1 compression. Every big block after the 409 (396, 400, 427, 454) used that plug.

[davepl]

Originally Posted by skokie

Not trying to hijack the thread here but what is a good plug for a stock 350 or 260 hp crate?

Thanks!

Accel #0574-4

See: http://www.jegs.com/i/Chevrolet-Perf...67353/10002/-1

[davepl]

Originally Posted by Fitz

ZZ572, not 400. 9.7:1 compression. Every big block after the 409 (396, 400, 427, 454) used that plug.

Not doubting you, but I've had a lot of big blocks over the years and some had flat (washer style) plugs and others had tapered plugs. I've also had closed chamber and open chamber and round, roval, and square ports. Maybe they vary with some combinations of chamber and port?

I've sure never owned anything fancy like a 409 or 572, so I've run into at least two different styles along the way.

GM 454HO requires AC Delco MR43T
GM L72HP requires AC Delco R46N

I -think- most of the older ones are washer style but I can find heat ranges from AC43 to AC45 (and 46 above) so it must vary with compression ratio or something, that's my only guess (colder plug to avoid detonation).

My owner's manual has a 1972 Delco plug box top stapled to the maintenance page, done at the dealer, but there's no guarantee they used the right plugs, so I won't even cite it. Clearly they worked for a long time after that, though.

Sometimes worth it to index the plugs, but probably not for low compression street use. Unless you're really tight on the plug to piston clearance, but I'm not sure how to measure that accurately without the head off. There's probably a tool or trick for that though. Piston stop? No idea.

We could debate for weeks, but the shop manual tells all (except for changes in gasoline or aftermarket mods).

[Wizo]

Tks Davepl; my heads were stock(1984 car or truck 194)
I did a heck of a lot of reading and did my homework and turned them into 2.02's with stainless valves and triple springs. I build the engine with upgrade possibilities. NOS and or a blower. I'm thinking for now that an ACDELCO R44tx should do the trick. Your thoughts?

[Fitz]

Originally Posted by davepl

GM 454HO requires AC Delco MR43T
GM L72HP requires AC Delco R46N

dave:
GM 454HO requires AC Delco MR43T Resistor plug, 14 mm thread, heat range 3, Tapered seat
GM L72HP requires AC Delco R46N: Resistor plug, 14mm thread, long reach

In essence you're arguing about heat range, not thread size or resistor, or non resistor plugs.
The following matix of spark plugs used are for AC Delco as installed by General Motors on the assembly line. Some of these may no longer be readily available or have been superceded by GM and can be used to crossreference to another brand such as Autolite, Bosch, NGK, Champion, etc.

Year Engine AC Delco Spark Plug
1964 194/230 46N
283/327 44/45
1965 194/230 46N
283/327 44/45
396 43N
1966 194/230 46N
283/327 44/45
396 43N
1967 194/230 46N
283/327 44/45
396 43N
1968 194/230 R46N
307 R45S
327 44
396 43N/44N
1969 230/250 R46N
307 R45S
350 R44
396 R43N *
1970 250 R46T
307 R45
350 R44
396/402 R44T *
454 R43T
1971 250 R46TS
307/350 (L65) R45TS
350 (L48)/402 R44TS
454 (LS5) R43TS
1972 250 R46T
All V8 R44T

* Early in 1970 the 3964290 cylinder head was recast to use the R44T tapered seat plugs so early castings may still use the R43N 'standard' plugs.

[Wizo]

Wow, Wow and just Wow. Once again I'm reminded why I'm a member of this forum. Awesome discussion here and a great amount of very useful information here. And all I wanted to know if I was using the correct spark plug. Thanks fellas. Have a great Sunday. Go Seahawks #12

[68 Stepper]

Go Seahawks!

[jjzepplin]

Subbed for plug info.

[Wizo]

[67ctener]

I ran some good old ac delcos. Nice looking dmax wizo.

[Wizo]

thanks, I'm thinking I'm going to also, R44T. I can get them for a pretty good price at the NAPA warehouse in Kent.

[67 chevelle]

find the casting number on your heads , determine what they came on originally , use the plug recommended for that application

[davepl]

Originally Posted by Fitz

dave:
GM 454HO requires AC Delco MR43T Resistor plug, 14 mm thread, heat range 3, Tapered seat
GM L72HP requires AC Delco R46N: Resistor plug, 14mm thread, long reach

Not worth an in-depth argument but a couple of points
- I think the MR43T has a tapered seat, the R46N may not
- The R46N is long reach, the MR43T is not, could cause interference maybe?
- I have no idea what the M is

Your chart's a keeper, thanks!

Why did trucks without radios come with resistance wires and plugs I wonder? That's the only reason, to my knowledge, they exist. On Corvettes where they needed extra shielding (no metal body) they only did it on radio equipped cars, so it wouldn't have been unheard of, and a lot of these trucks didn't have a radio.