KR 428 Cobra Jet Spark plugs

[GT350AUS]

What spark plugs and gap should be used bearing in mind I can only get 98ron fuel in Australia.

[427heaven]

What ever is on sale.

[1967 eight barrel]

BF45 is the current Motorcraft offering. However, if you're not planning on concours judging I would suggest you run NGK WR5, STK#2438.  They run much better than BF45 and are better heat range wise. I am running them in my 67 GT500, The BF32 are prone to fouling.
                                                                                                    -Keith

[CSX 3183]

BF 32 is the installed and recommended plug, I put on over 80,000 miles on my KR, never fouled a plug, put on 10,000 miles on my 66 427 Cobra, never fouled a plug, put on over 10,000 miles on my 72 Pantera, never fouled a plug,  I say old wives tale!

[GT350AUS]

Good to know.

Thanks or the details.

I just want to make sure I don't have to pull them out any time soon since its not he easiest of jobs.

[shelbydoug]

BF 32 is the installed and recommended plug, I put on over 80,000 miles on my KR, never fouled a plug, put on 10,000 miles on my 66 427 Cobra, never fouled a plug, put on over 10,000 miles on my 72 Pantera, never fouled a plug,  I say old wives tale!

Fouling BF32's is often a sign of a weak ignition. 32's are what to use. 52's will melt the tops of the pistons. 42's are about the limit and would only be useful to about 5,000 rpm. Over that they may lean/misfire in a performance application. I've been running 32's since 1968 in Kindergarten. 

[GT350AUS]

Sounds like great advice.

so 32's it shall be.

[1967 eight barrel]

The issue with BF32's is they are a cold plug and the vehicles usually aren't driven enough. All dual quad cars run rich at idle.  I'll guarantee my ignition isn't weak with the igniter II and matching coil.  The NGK U groove is a much better plug than the BF32, and they are NOT available from the parts store.  Jay Brown and a couple other FE builders will also tell you to stay away from the BF32. If you're competing in Concours, then you might want to run them. Otherwise its plain stupid to waste 7-10 a plug on stock poor plugs.

[GT350AUS]

Ok so ill check what I've got in it and see how they've been burning.

If they're clean with no build up of carbon or excessive wear ill replace them with what's currently in there.

[GT350AUS]

The issue with BF32's is they are a cold plug and the vehicles usually aren't driven enough. All dual quad cars run rich at idle.  I'll guarantee my ignition isn't weak with the igniter II and matching coil.  The NGK U groove is a much better plug than the BF32, and they are NOT available from the parts store.  Jay Brown and a couple other FE builders will also tell you to stay away from the BF32. If you're competing in Concours, then you might want to run them. Otherwise its plain stupid to waste 7-10 a plug on stock poor plugs.

Mine doesnt run a dual quad as its a KR with the Holley 735.

My issue is it currently backfires underload but drives along ok until I accelerate hard then it goes off with backfiring. Carby has been rebuilt, timing set, new points and condenser, coil is fine so the only thing left is the plugs.

I just want to make sure i put the right ones in due to the difficulty in changing them. If it was my 66 GT350 it wouldn't be an issue as access is easy.

So just to be sure is BF 32 the right ones that won't give me issues??

[Bob Gaines]

The issue with BF32's is they are a cold plug and the vehicles usually aren't driven enough. All dual quad cars run rich at idle.  I'll guarantee my ignition isn't weak with the igniter II and matching coil.  The NGK U groove is a much better plug than the BF32, and they are NOT available from the parts store.  Jay Brown and a couple other FE builders will also tell you to stay away from the BF32. If you're competing in Concours, then you might want to run them. Otherwise its plain stupid to waste 7-10 a plug on stock poor plugs.

Mine doesnt run a dual quad as its a KR with the Holley 735.

My issue is it currently backfires underload but drives along ok until I accelerate hard then it goes off with backfiring. Carby has been rebuilt, timing set, new points and condenser, coil is fine so the only thing left is the plugs.

I just want to make sure i put the right ones in due to the difficulty in changing them. If it was my 66 GT350 it wouldn't be an issue as access is easy.

So just to be sure is BF 32 the right ones that won't give me issues??

If all those things have been rebuilt and set properly it does sound like you have one or more fouled plugs or even carbon build up on the pistons which is causing detonation. BF32 is what came in your car from the factory .They are a colder plug and need the be driven hard to stay clean. If a lot of slower city driving many of use go with the next hotter plug like the BF42.That is what we always did back in the day when we drove them everyday.  The BF 42 will not foul out as much. If you want the most horse power performance stick with the BF 32 or equivalent and just expect to change them or clean them often. If the highest horsepower is not your goal and you don't want to mess with changing the plugs often then go with the BF 42.

[GT350AUS]

Hi Bob,

Thanks for your prompt reply.

The car has origina 32,000 miles on it.

It doesnt get driven much at all. Lucky if I do 500 miles in a year and they would be highway miles.

I don't drive it hard so maximum horsepower isn't a priority.

Just the occasional squirt when I take it out and it warms up.

So BF42??

I have BRF42 CU Motorcraft but they are resistor type I think for al later model Australian ford.351 I think

Ross

[Bob Gaines]

Hi Bob,

Thanks for your prompt reply.

The car has origina 32,000 miles on it.

It doesnt get driven much at all. Lucky if I do 500 miles in a year and they would be highway miles.

I don't drive it hard so maximum horsepower isn't a priority.

Just the occasional squirt when I take it out and it warms up.

So BF42??

Ross

That is what I would run given the driving details. If that doesn't solve your symptoms it may be carbon build up on the pistons but the plug situation will be solved . Also make sure you have a high octane fuel or use a additive to raise the octane . The stock engine is not designed for todays fuels and you may have to retard your timing some so it doesn't detonate. Try the plugs first . If they haven't been changed in a while then a fouled plug is probably it.  Keep us posted.

[GT350AUS]

My plan is to get to it next week.....once I've summoned the courage to tackle the tight fit.

Bob I have BRF42 CU plugs here would they be ok although not concourse??

I can't get the concourse ones here so I may even try the NGK AP5FS as they seem to be a replacement alternative.

Your thoughts??

[GT350AUS]

Just pulled plug out of number 1 and found it to be a NGK AP6FS which on cross reference is a either a
Mototrcraft BF22 or BF32

Looks like its too cool for the driving I do.