foreveraudio

i have a 88 c4 - med cam - just now putting afr 180 heads on -
what spark plugs does everyone recommend -

i had ngk fr5p's on but there not made now -

thanks all

65Z01

For my mostly stock '88 I run OEM plugs with cut-back ground electrodes; TPIS shows ~5-8 chp gain over stock.

caddyboy84

Champion race plug c59yc.It'a medium plug.

mtnmanut

e-3

foreveraudio

so no one agrees one one ? lol,

65Z01

Welcome to C4 Tech...

foreveraudio

another question im getting mixed messages about is when i put these new afr heads on , do i need to measure length or can i put stock sized ones back in -

afr 180 heads , fel pro gasket set - standard rocker arms

Dexter McCay

Denso Platinum TT... Have them in my 1992 Corvette Built 383... I had NGK Iridium ix and had nothing but problems... Miss at Idle, strange power curve and more... Put Denso Platinum TT's in and WoW, smooth idle, never ran like this... The best thing the were only $2.99ea at NAPA auto parts...

ddahlgren

That is very hard to believe on a stock engine. Thats a 3% gain, let me guess they sell specially cut back plugs..
Dave

Black89Z51

I would use a heat range 6 in NGK terms.

I'm running NGK BKR6E (6962) with a 0.040" gap.

The local advance auto has them in stock.

foreveraudio

well i bought ngk stock #7373 gap at 35 - hope i didnt make a bad choice

caddyboy84

NGK is a good plug.

65Z01

Perhaps so, but I prefer to cut-back my own plugs.

Actually TPIS gives that suggstion as an old racer's trick to gain a little more "free" HP from more complete combustion due to a better flame front.

GREGGPENN

Talked to alot of people about this for my AFR setup. The consensus was not to run anything hotter than the plug listed on AFR's website. Even my local O'Reilly's said they recommend the same strength plug as AFR -- which I believe is 1 step down from OEM. (Has to do with Corvette cooling challenges IIRC.)

Also, many people caution against running a platinum plug.

AFR's are about the best chamber design...so with good quench, you don't need much to fire off the charge.

foreveraudio

forgive me for sounding dumb - but cutting back plugs ---- explain

ddahlgren

I used that old racers trick when I was limited to a dual point distributor and a black Mallory coil mounted to the firewall. Those days are long gone. Trust me there is no power to be had cutting .080 off the end of a ground electrode if youhave anything close to a high energy ignition system. BTW Iam an old racer and still a current one at least on the engineering and manufacturing level.
Dave

ddahlgren

AFR sells race heads as in used for racing and does not want to be liable for your melted piston in any way. While i do not work for them suspect that is the reason as they have no idea what you plan on using them for no matter what you say you will. They will certainly spec plug threat reach and if a 5/8 hex for the socket is needed along with a conservative heat range. There are no 'stronger' or 'weaker' plugs they all spark the same more or less given the material used but there are heat ranges determined by average operating conditions. 99% of all C4 Corvettes are driven on the street spending 95% of their time at 10% to 20% engine power available so lightly loaded. Changing to better heads and cam might add 20% at best more power available but does not change power required so cylinder pressure and temperature does not change. If getting a bit silly at least where I live in the northeaqst it is hard to drive at anything close to the limits for more than 30 seconds to a minute. There is either a corner or a speed trap so everything cools back down during that time.If drag racing max cylinder pressure is only in high gear and generally for a few seconds.

Plug style has a lot to do with things as well a Y gap in Champion which is an extended reach is always a good compromise for a street car as they run hotter at low speeds and cooler at high speeds than the equivilent standard gap plug. An example would be a R12YC vs. a R12C it is more like a R10C at high speed and a R14C at low speed. In the end it is all about how much insulator is exposed to combustion temperatures along with how much scavanging air is available during overlap so yes even cam lobe centerline choice changes plug requirements. The real key is to keep the tip temperature high enough to stay clean and cool enough to prevent pre ignition. I used Champion examples only because I am familiar with their numbering system in bigger number warmer plug along with gap style differences. Every manufacturer has various designs available so pick your own poison there. 99.999% of the plugs with exotic metals are for extended time between changes 99.999% of the C4's will never reach them with the same owner other than the few DD cars vs. the Sunday cruise cars.

Oh and if you have close to stock compression and get colder than a marine plug you have gone too cold as they run 75% WOT for extended time. Out of the harbor and throttle up until you get to the harbor you wanted to get to.

Dave

GREGGPENN

Those "Y" plugs sound like a great recommendation for street use.

I always thought heat range was related to spark intensity. Could u elaborate on heat range? (and, how would u alter range with more cam overlap?)

FWIW: Champion phone reps were the most relevant source recommending cooler plugs in a C4.

ddahlgren

Y plugs in Champion and yes everyone makes them though with numbers I do not know. They are extended gap so more insulator hanging out to get hot. This means during light load they run hotter than a standard gap with the porcelin close to the head. A spark plugs heat range is all about the temperature it runs at. Hot enough to not carbon uo and cool enough to not glow and cause pre-ignition. The temperature is related to load how you drive the car is the most important factor. In CT after a few seconds i am over the speed limit I can not speak forthe whole state but we have law enforcement all over the place and I am for it in the end. But a few seconds here and there is about all there is it would be fun to l;ive out west and the stories I have heard where you can run WOT for miles on end. So how you use the car determines the plug temp and that determines the correct heat range. If you live in the desert and can go as fast as you want for as long as you want ( yes wildly jealous) maybe a C59YC is for you but if you live in a congested area a R12YC might be a better choice and these are wildly ends of the spectrum of heat ranges.

Cam overlap is a simple easy thing to understand. It is air blown across the chamber to clear it of exhaust gases and pull in the intake charge. It will quickly cool the plug so a hotter one needed to keep the temp up above fouling. The number 1100F sticks in my mind as ideal though not sure if that is right or not a google search might be in order there. At the end of the day it takes less than 50 HP to drive at freeway speeds as a VW bug that has 40 can go 65 and would like to think a C4 is as aero friendly as the bug so at the end of the day less than 20% of available power. You can add every power adder you like but the heat range is subject to power required by the way you drive the majority of the time.
Dave

cv67

Did you call AFR?

Autolite 3924 always works well.
Used the fancy expensive plugs never noticed any difference at all.