Mr. Wonderful

I'm trying to tweak performance on my coupe. I've got some hesitation
at take-off, but lots of power afterwards. I'm wondering if the plugs can
make any difference.
I've read in some posts, that the plugs I need, R44 have been discontinued.
I want to narrow this down before going to the carb.

Ironcross

Yes, use R45. I know 44`s are no longer available and I was using the 43`s also but went to 45`s and the engine cleaned right up. The 43`s are TOO cold and will foul. :thumbs:

SWCDuke

The OE heat range for SBs was "4" (Heat range is the second number. The first "4" indicates a 14mm thread.), but this is too cold for normal driving, and heat range "5" works best. Heat range "3" is way too cold for the street. I used 43s when hot lapping tracks, with good results.

Fouling due to too cold plugs usually results in high rev ignition breakup. I won't guarantee that heat range "5" will solve your hesitation problem, but you should install 5s or equivalent before you do anything else.

OE plugs for midyears were non-resistor (no R prefix), but AC no longer offers non-resistor plugs. If you want to go with non-resistor plugs the NGK B4 and Denso W14-U are equivalent to the old non-resistor AC 45.

Duke

Mr. Wonderful

Duke... can always depend on you for great info. Thanks

Mr. Wonderful

I will switch plugs, as you and SWCDuke have recommended. Thanks

Allcoupedup

Here's what R43's look like in an engine that leaves R45's looking like this:

Brian

SWCDuke

Excellent photos, and real lesson in heat range selection!

The key is the condition of the ceramic insulator. Too cold a plug will not allow the insulator to get hot enough to burn off deposits. A clean insulator means the heat range is right - off white to tan, with no glazing, which could indicate too hot a plug that is melting previous desposits. Also, if you look at the insulator with a magnifying glass you will often see tiny reddish-brown specs - almost looks like little rust specs. It's normal and due to fuel additives.

Regardless of heat range you will always get some buildup on the metal shell depending on mixture and oil consumption, but this doesn't really affect plug performance. Insulator deposits will shunt ignition energy away and eventually lead to misfire.

Duke

Mr. Wonderful

"Here's what R43's look like in an engine that leaves R45's looking like this"
Thanks for the pics Allcoupedup :thumbs:
Anxious to see what mine look like when they are removed.

Subfixer

If there are any purists out there, I have a set of Non-resistor AC 45's that I'm not using. I picked them up a few weeks ago just in case someone wants them.

I also bought a set of R45's for use in my car.

EVERGREEN

Subfixer,
My 327/300 has R46S plugs and misses like crazy at 4200rpm, believe the plugs are resistor types and the combination of resistor wire and plugs is killing the spark, do you still have the plugs for sale?

EVERGREEN
ALASKAN CORVETTE

Subfixer

Although I'd love to take your money ;) , It sounds like your problem is not the plugs or wires, but either the coil or the timing is too far advanced. I'm pretty sure the plugs won't help your situation. I'm running resistor plugs (R45's) and resistor wires with no problems as far up as 5500rpm. Check out the rest of your ignition system and maybe try R45's vs the R46's.
Before my coil completely died, I too had a problem with break up at around 3500-4000rpm.

EVERGREEN

Subfixer,
Sorry it took so long to reply, I'm a busy guy! The coil is a brand new Pertronix added at the same time as the Pertronix 1182D ignition unit (dual points replacement). A check of the plug wires shows the worst one to be 13K ohms, or well within the 10K per foot range. Timing, well, it is a 1968 engine with the 1961 distributor and I really don't know for sure. Timing was set at 10degrees at idle (about 825-850rpm) so I have left it there but do question it! Any suggestions?

EVERGREEN
ALASKAN CORVETTE

Subfixer

Is your distributor a vacuum advance unit or just a centrifical advance unit?

magicv8

43 heat range is for higher rev performance - generally used for racing.

44 heat range was factory installed/specified in 1966

45 heat range will burn off the city traffic crud.

IMO Resistor plugs should only be used with metal core wires on an original coil. Use of both resistor plugs and resistor wires will overload the coil. I use a Pertronix coil to avoid the problem (if it fails, I can get another) - my original ACDelco coil is bagged.

66427-450

I always tried to run the coldest plug I could (ever wonder why the factory used colder plugs in the SHP engines?)....... I guess it all depends on your priorities.

SWCDuke

Chevrolet did not use colder plugs for SHP engines, either SB or BB. Plug heat range is based on the average load required for the driving conditons, not the state of tune of the engine. Normal road driving requires a fairly hot plug because the engine is normall only operating at a very small fraction of full load.

For road racing a relatively cold plug is required because the engine is operating at full load 90 percent of the time.

Duke

EVERGREEN

Subfixer,
It is the centrifugal model 1110891 that was obviously on the original 283/270 dual carb engine. Now the car has a 1968 327/300, Holley list 1850, Edelbrock aluminum manifold. Engine pulls good as long as I keep the rev's up until it reaches about 4000-4200 then it starts missing to the point it will pull no more. It has a hydralic cam but do not know if it is GM or aftermarket.

EVERGREEN
ALASKAN CORVETTE

Ironcross

:iagree: :D

66427-450

looks like you're right......again :) they all came with the same plug (std/SHP).

back in the old days we always used the colder pulgs in our hot rod chevys...... we considered the cold plugs better in our street racers (better hi RPM performance), like I said, we always tried to run the coldest plug we could. If they lasted all weekend without fouling out at 7000 revs they were considered about right .... lol.

my old parts manual says:
45 continuious city operation
44 town and country
43 HD operation

i always equate "colder plug" with HI RPM performance applications, and "hot plug" with low RPM, low maintenance applications. and for some reason thought for sure the factory fitted them that way...... you learn something every day
:seeya

SWCDuke

Yes, I remember that ill-informed advice from the sixties. I did know enough to install AC 43s when I took the SWC out to Kent for days of hot lapping in the summer, but I couldn't keep the OE 44s from fouling on the street, which was a combination of "town and country driving". Finally tried a set of 45s for normal driving, and as they say, the rest is history.

The 45s were just fine for the freeway as is only takes 30-60 RWHP to cruise at 60-80 MPH, and my occasional forays to 130+ were only long enough to get the plugs good and hot to clean them off.

Chevrolet's heat range recommendations were on the conservative side - about one heat range too cold for a Corvette.

Duke





[Modified by SWCDuke, 5:59 PM 11/12/2003]