been using accel u groove 416s on my 383 for the first 3000miles. unfortunatly the ceramic part of the plugs has hair cracks all over them. so im replacing them... ive decided to get away from accel ( had there plugs/wires/control module and i didnt like any of them) so im going with NGKs which i used on my stock 350TPI and loved them.

heres the accels im using now, car runs fine.
http://www.summitracing.com/parts/ACC-8189/
problem is that the manufacture heat range is at 6... and the NGKs i got are at heat range 4.
http://www.summitracing.com/parts/NGK-5155/

the car gets beat on and sees some track duty, ignition upgrades are MSD blaster coil, kinda new mallory wires (making new MSD wires when i go the NGKs plugs), DUI performance control module, DUI cap and rotor. and ive open the plug gaps from stock .035 to .045". engine is a aluminum head 383 with 9.8:1 compression and will see a peak RPM of 5500-6000 at the track.

just trying to figure out why the accels are heat ranged at 6 and the NGKs are set at 4. i kno how they make the plugs a different heat range but idk what the actual NUMBER means and how it relates to the type of engine.

 

You can't directly compare heat ranges between different makers ; only within the same brand
Some go 1 - 10 cold to hot;
Some go 1 -10 hot to cold
For example
NGK use high # = cold whereas Champion use high # = hot
A 5 NGK ( hot plug ) is equal to a 11 Champion

Could be your two plugs are exactly the same heat range
Only way to compare is a spark plug cross reference chart

 

on the box of accels there was a cross reference chart... on them was the NGK's that i bought. or are you talking about a different cross reference chart?

does any one know what the stock heat range is for the plugs used in stock 305/350 TPI's? i dnt need a hot/cold plug... i was just wondering what the numbers actually meant and how they relate to a specific setup. like NOS/forced induction cars need colder plugs bc of hotter combustion temps... so they pick colder than stock (but wats stock for our cars?) but how do they judge how much colder to go than stock? and how would they judge how much hotter to go than stock? and wat kind of engine would need a hotter plug?

 

the way to tell if you need a hotter or colder plug is to read them. If their is excessive build up on the plug you need a hotter plug to help burn off the buildup. too hot of a plug and you can melt the tips. hope this helps and yeah accel plugs are known to be crap bosh and NGK have always done me right love them.

 

This is Joe Sherman's take on plugs.
http://speedtalk.com/forum/viewtopic.php?f=1&t=11739

This cross reference list
http://www.accel-ignition.com/pdf/Sp...sReference.pdf

lists 416 as equivalent to the FR4, another chart lists FR5 as the equivalent.

 

sry guys my car was stolen fri night so im not gona waste your time on plugs. but i will read the links and see what i can learn.