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.

[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 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).

[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)

[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!

[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

[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?

[68 Stepper]

Go Seahawks!

[Wizo]

[jjzepplin]

Subbed for plug info.

[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