Need a spark plug gap for my engine

[BigDuke6 17]

mechanic was working on a steering issue and replaced the plugs as a favor to me.  Car went from instantly starting up to being difficult.  I asked if he gapped the plugs.  No.  So I need a good starting point.

351W

Edelbrock 60259 Alum heads (ported)

Hydraulic roller cam

Champion RC12YC plugs

11:1 CR

MSD 6AL ignition and HEI dizzy

Engine is about 450 hp

 

[Midlife 814]

Step 1: Find another mechanic.

[Print Dad 58]

Hello Big Duke6

I have been running fords since the mid 60's and NEVER had much luck with CHampion plugs in a Ford.

I think a good starting point  for the gap is 35 and then you can adjust after running the motor and reading the plugs.

There are a lot of charts that will show the color of the porcelain after running.

I think 35 is a good starting gap - make sure the plug wires are run to the correct plug. You would be surprised how well

the motor may seem to run with 2 wires crossed

 

Best of LUck - Sam

[barnett468 418]

yeah, .028" -,035", plus, you should be running 1 step colder than stock unless you have a huge cam to bleed off some compression.

 

[BigDuke6 17]

4 hours ago, barnett468 said:

yeah, .028" -,035", plus, you should be running 1 step colder than stock unless you have a huge cam to bleed off some compression.

 

I don’t know if you would call it a huge cam

hydraulic roller cam 

108 LSA

- LIFT: INT 560 , EXH 540

- DURATION AT .50 DEG: INT 236 , EXH 240

thanks everyone for your input so far

[1969_Mach1 333]

I run the MSD 6ALN on my 351W and gap my spark plugs at 0.040".  My static compression is slightly lower than yours at 10.7:1.  I use either the basic old school copper core resistor type Autolite or NGK spark plugs.  From everything I have read copper core plugs are better with an MSD type of ignition system.  The plug life is shorter, but they work better.

Yes, your cam is fairly aggressive for a 351W in a street car.  If you have vacuum assist power brakes, they likely will not work.

Honestly, I don't know if spark plugs are why it is more difficult to start.  Sometimes it's a matter of taking more time to get a fuel charge into the cylinders while cranking.  What carb does it have?  Is it correct for something with 11:1 CR and that aggressive of a cam?  Don't forget, as cam profiles get more aggressive, the signal to the carb gets weaker.  For example, you can simply do only a cam change and suddenly the motor runs much too rich or much too lean depending on if you went less or more aggressive with the cam.

[barnett468 418]

19 hours ago, BigDuke6 said:

I don’t know if you would call it a huge cam

hydraulic roller cam 

108 LSA

- LIFT: INT 560 , EXH 540

- DURATION AT .50 DEG: INT 236 , EXH 240

thanks everyone for your input so far

what is the advertised duration?

who made that cam?

.

[fvike 173]

BigDuke6; I have a 351W with the Edelbrock RPM package (same 60259 heads), 10.8 comp and a Crane HI-6 igintion system. I remember going to a colder plug, I think it was from NGK FR5 to a NGK BKR6E. I have them gapped at 0.050" or 1.3 mm. I remember that helped the engine alot. I run 98 RON gasoline (Shell V-Power) that is perhaps the same you get in Germany, or do you use 100 RON ?

[BigDuke6 17]

On 3/22/2019 at 1:31 PM, fvike said:

BigDuke6; I have a 351W with the Edelbrock RPM package (same 60259 heads), 10.8 comp and a Crane HI-6 igintion system. I remember going to a colder plug, I think it was from NGK FR5 to a NGK BKR6E. I have them gapped at 0.050" or 1.3 mm. I remember that helped the engine alot. I run 98 RON gasoline (Shell V-Power) that is perhaps the same you get in Germany, or do you use 100 RON ?

100 RON?  Hah.  Running 102 RON.

Good that our cars are mostly twins. I can use the benefit of your experience.  Does your brother still have his Challenger?

[BigDuke6 17]

On 3/22/2019 at 2:20 AM, barnett468 said:

what is the advertised duration?

who made that cam?

.

FPS in anaheim.  Ain't for sure about the AdDur

[BigDuke6 17]

On 3/21/2019 at 6:34 PM, 1969_Mach1 said:

I run the MSD 6ALN on my 351W and gap my spark plugs at 0.040".  My static compression is slightly lower than yours at 10.7:1.  I use either the basic old school copper core resistor type Autolite or NGK spark plugs.  From everything I have read copper core plugs are better with an MSD type of ignition system.  The plug life is shorter, but they work better.

Yes, your cam is fairly aggressive for a 351W in a street car.  If you have vacuum assist power brakes, they likely will not work.

Honestly, I don't know if spark plugs are why it is more difficult to start.  Sometimes it's a matter of taking more time to get a fuel charge into the cylinders while cranking.  What carb does it have?  Is it correct for something with 11:1 CR and that aggressive of a cam?  Don't forget, as cam profiles get more aggressive, the signal to the carb gets weaker.  For example, you can simply do only a cam change and suddenly the motor runs much too rich or much too lean depending on if you went less or more aggressive with the cam.

the car went from awesome cold starts after weeks of hibernation to having trouble turning over from one day to the next and the only change was the plugs.  

[fvike 173]

8 hours ago, BigDuke6 said:

100 RON?  Hah.  Running 102 RON.

Good that our cars are mostly twins. I can use the benefit of your experience.  Does your brother still have his Challenger?

102?!? D-D-D-Damn! 

Yeah, he still has it - It's a Plymouth Barracuda. Last month or so we have been installing a Edelbrock Pro-Flo4 EFI system on it, along with new long tube headers, Magnaflow Exhaust, new fuel tank and fuel lines. Big-ass job!

[BigDuke6 17]

On 3/31/2019 at 8:34 PM, fvike said:

102?!? D-D-D-Damn! 

Yeah, he still has it - It's a Plymouth Barracuda. Last month or so we have been installing a Edelbrock Pro-Flo4 EFI system on it, along with new long tube headers, Magnaflow Exhaust, new fuel tank and fuel lines. Big-ass job!

Aral to the rescue.  can bump the timing up just a bit with this stuff.

https://www.aral.de/de/retail/kraftstoffe-und-preise/unsere-kraftstoffe/aral-ultimate/aral-ultimate-102.html

What size wheels are you running?  I got 16" wheels back then only now, nobody makes tires for them anymore. I was going to wait til Spring to get some Toyo Proxes R888 in 255/50 r16 in the back and 225s up front except Toyo stopped that tire at the end of 2018 and the replacement only has 245/45R16s and they do not fill out the wheel well.  No more choices for 16" tires in Europe

[MikeStang 247]

You can probable locate some of those tires on Ebay brand new believe it or not, lots of places have stock left of discontinued tires.

I found a 275/45/18 which almost everyone has stopped making and those that do still make them want as much or more than what I could get Mickey Thompsons for.

Granted they may be a year old but I don't really care about them being on the shelf in a warehouse for a year or more b4 I get them, long as they are not dry rotting or showing signs of age I'm all good.

[BigDuke6 17]

On 4/2/2019 at 10:18 PM, MikeStang said:

You can probable locate some of those tires on Ebay brand new believe it or not, lots of places have stock left of discontinued tires.

I found a 275/45/18 which almost everyone has stopped making and those that do still make them want as much or more than what I could get Mickey Thompsons for.

Granted they may be a year old but I don't really care about them being on the shelf in a warehouse for a year or more b4 I get them, long as they are not dry rotting or showing signs of age I'm all good.

The problem is shipping to Germany. There are still plenty of 16x8 options CONUS but it is over $150 per tire in shipping and duty/VAT so a $135 tire costs me nearly $300 at the end of day

 

i have scoured every possible local possibility 

[fvike 173]

On 4/2/2019 at 10:45 AM, BigDuke6 said:

Aral to the rescue.  can bump the timing up just a bit with this stuff.

https://www.aral.de/de/retail/kraftstoffe-und-preise/unsere-kraftstoffe/aral-ultimate/aral-ultimate-102.html

What size wheels are you running?  I got 16" wheels back then only now, nobody makes tires for them anymore. I was going to wait til Spring to get some Toyo Proxes R888 in 255/50 r16 in the back and 225s up front except Toyo stopped that tire at the end of 2018 and the replacement only has 245/45R16s and they do not fill out the wheel well.  No more choices for 16" tires in Europe

I was running 245/45-17. I've sold those wheels, and haven't bought new ones yet. There should be room for 315s at the rear with the correct backspacing.

[BigDuke6 17]

found the problem and there were several. 

The plug gaps were all over the place, from 0.031 to 0.05.  This was from installing them straight out of the box.. 

Next, the 8th cyl. spark plug terminal connection was partially broken inside the boot.. 

Gapped everything at 0.040 and put a new wire on and the car fired up instantly.

Have to make new wires though, as the ones that were in there are black and the new one is red.  Can't have that.