Can anyone help me with the correct plug I should be using to suit the changes made during the last engine rebuilt, since the standard R44TX just aren't working anymore. Stock engine is a 75, 350 L48 .060 gap 8.5 compression changed to 10 with a 350 horse cam. Stock was 165hp and the dyno states it's now 285. There were other changes but I don't think it's relevant to the plug change. Any advise would really be appreciated.
Thanks.

 

It would help if you told us what you mean by "not working anymore".

Generally when you increase compression you need a colder plug. For AC delco lower numbers are colder so maybe a R43TX.

But again, if you could detail what exacty isn't working you might get better advice.

You also want about a 0.045" or so gap.

 

What I should have said was it's running too hot, the isolator is blistering and the electrode is wearing far to fast. Coolant temperature is running at around 190 deg. I also can't seem to get the engine to idle smooth, and I know that the word " smooth " can be left up to interpretation.

Thanks zwede

 

When you have a plug that is let's say R43T or S or X. I believe "R" stands for resistor, is the 43 the heat range, and what does the T, S, & X stand for?

 

Prefix -- R = Resistor
4 = 14 mm Thread
5 = Heat Range
T = Taper Seat
S = Extended Tip

Prefix --
B - Series Gap
C - Commercial
CS - Chain Saw
F - Fine Line 14 mm 5/8" Hex
M - Marine
LM - Lawn mower type
R - Resistor
S - Shielded (5/8-24 thread)
V - Surface Gap

Numbering
1st number denotes THREAD SIZE
2nd number denotes HEAT RANGE

Suffix
A - Clip Gap
C - Copper Core Center Electrode
C - Colder Version of M44 Plug
E - Special Design Electrode Extended Tip
F - 1/2" (12.7 mm) reach
FF - 1/2" (12.7 mm) reach, fully threaded
G - Pin Gap (cold -running)
I - Iridium Center Electrode
J - Boot Release Agent, Anti-Seize Compound
K - Special Design
L - Long Reach
--- 7/16" (11.1mm) reach, (14mm) thread
--- 3/4" (19mm) reach, (18mm) thread
--- 3/4" (19mm) reach, (14mm) thread (fineline)
LT - Long reach, .715" (18.16 mm), Tapered Seat
M - Special Design Electrode
N - 3/4" (19 mm) reach, 3/8" (9.5 mm) thread length
R - Resistor (Sport Vehicle Plugs)
S - Extended Tip
S - 7/8" (22.3mm) Moderate Long reach 23/32" (18.25mm)
T - Tapered Seat Shell Design
TS - Tapered seat with extended tip
X - Wide Gap (H.E.I.) (high energy ignition)
XL - Extra Long reach, 3/4" (19 mm) fully threaded
Y - 3 prong cloverleaf electrode
Z - Special gap (usually denotes wide gap)
5 - .050" (1.3 mm) gap
6 - .060" (1.5 mm) gap
8 - .080" (2 mm) gap
100 - Iridium
600 - Resistor Type
800 - Platinum Type
900 - Double Platinum Type

 

Thanks alot BSeery, that's great, now I just need to find the right plug and so far it may be R43TX.