I'm helping a friend get his '73 T-Top coupe back on the road. He has purchased a crate motor that has these heads:

SB-Chevy Aluminum Vortec Cylinder Head
 210cc Intake Ports
 62cc Combustion Chambers
 2.000'' Int/1.550'' Exh Valves

The engine is a 355 CI 9.8 CR with a extreme energy 477/480 Hyd cam.

Can anyone suggest a proper spark plug?

 

I'd suggest you ask Pasta!

 

Why, we already know what Pasta will say - Autolite

 

I run Champion with good success. With electronic ignition I try to get the Iridium plugs for all the modern technology and long life.
The Vortec Heads were Factory with Cast Iron and that is the only way I could catalog them for you.
Vortec Plugs
Iridium Part # 9404 Best Spark quality and Longest life
Double Platinum Part # 7940 very long life but need a high energy spark system
Copper Plus Part # 13 RS14YC6 Original OEM type plug Good plug but short life
All three are the same heat range and type. As you move up you get better life and spark quality. If you are running Standard ignition and not High Energy I would stay with either the Copper or Iridium both work better in the low voltage system than Double Platinum.
IF the Aluminum Vortec is modified and not the same as the Cast iron design all bets are off, call the manufacturer to get a plug type to run.
The Iridium and Platinum plugs use precious metals on both sides of the ground electrode, these don't wear as the plug sparks over time allowing you to run them 100.000 miles plus
Copper Plus Good low voltage plug but short life as all old plugs were, the electrodes wear with each spark, you can re gap them a few times in their life for better performance but you will use 5 sets of these to one of the double platinums and even more against the Iridiums. These are cheap though and do a good job for a short time. That could be years in one of these cars.

 

If he just installed it why does it need new plugs already? And since when do you have friends? Shudda put *TQ*

 

It`s probably a tapered seat style plug and a resistor AC plug in the proper heat range that would work the best is R45TS or R45T, set the plug at .035

 

Although AC built plugs at one time now they just package what others make for them.
That is why I go with the manufacturer not the repackager.

 

We have not installed it ....yet.

I do have some friends (though not many), I'd rather hang out with my dog than most people I know

What does *TQ* stand for?

 

Thanks Westlotorn and Ironcross, I appreciate the help.

The heads are GM units, I thought a few members here were running them.

GM has not been much help on this, maybe I'm not looking in the right places??

 

Bare head PN:
http://www.superchevyperformance.com...p/12497186.htm

See the tech specs tab for plug type.

Complete head PN:
http://www.summitracing.com/parts/NAL-12464298/

Here is an engine build spec sheet for someone using those heads:

Fast Burn 385 Technical Information
Horsepower 385 @ 5600 RPM
Torque 385 @ 4000 RPM
Max. Recommended RPM 5800
Compression Ratio 9.6:1
Partial Engine 12561723
Block 10105123 Four bolt main, cast iron
Crankshaft 12556307
Connecting Rods 10108688 PM rods
Pistons 10159436 High silicon aluminum with offset pins
Piston Rings 12528817
Camshaft 10185071 Hydraulic Roller
Lift .474/.510"
Duration @.050, 2.08/.221
Cylinder Heads 12464298 Includes valves and springs
Intake Valves 12555331 2.00"
Exhaust Valves 12551313 1.55"
Valve Springs 12551483
Rocker Arms 10089648 Steel 1.5
Intake Manifold 12366573 Aluminum dual plane, no EGR
12496820 Aluminum dual plane, w/EGR and dual carburetor pad
Valve Lash Zero
Spark Plugs MR 43LTS Gap @ .045
Fuel 92 Octane
Ignition Timing 32º total @ 4000 RPM with vacuum advance disconnected

 

Thanks Joe.

 

Post is edited..........more information added.

You probably made the same search and found the same thing..............or not.
It was not easy to find a single post showing specific spark plugs.
Except for the last, which shows MR43LTS. Dunno what they are, but of course you can find a cross reference chart and/or call AC spark tech support for further help.
I hope I helped you in some way.

 

Google forth and thou shalt find:

http://www.summitracing.com/parts/ACF-MR43LTS/

Obvious signs that Moses did indeed go to the Summit seeking knowledge. I'm still leery of the burning bush story, if you know what I mean

 

You a funny bastard.
I'm glad you're leery and not Leary

 

I don't think that Summit's picture is right - try this instead:


I think the M stands for marine usage; the R43LTS would work as well.

 

A tuner I know who consults for NASCAR and Formula I teams recommends Delco ignition components for any GM vehicle including plug wires, but NOT spark plugs.

Unless sponsorship gets in the way, his "go-to" plug manufacturer is NGK. I remember back in the late '60s and early '70s when ACs and Champions would only last 7,000 miles in my 327. NGK B6S plugs would go double that mileage. BTW same plug number also fits Harleys.

 

I have been using NGK XR4's in my 461 iron heads. I highly recommend this plug if you need standard reach (3/8"), non tapered seats, and have enough clearance for an extended tip.

The NGK B6S is the entry level replacement for the AC 45 plug, and does not have an extended tip.

It looks as if Mark's friend's heads take a long reach (3/4") rather than a standard 3/8".
AC R43LTS crosses to NGK BPR6EFS.
The NGK plug is widely preferred over the AC plug.

http://www.clubplug.net/files/ngk_cr...nce_tables.xls