Spark plugs in a 30 over 400 - Pontiac GTO Forum
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post #1 of 23 (permalink) Old 05-21-2016, 09:31 PM Thread Starter
 
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Spark plugs in a 30 over 400

I drove my 67 GTO this morning and the engine is definitely missing. The car sat for a week prior to this morning and ran tits the last time I had it out. It sounds like it is running on 7 cylinders.

I puled #8 & #6 spark plugs. They were both real wet and dark.
This is a 30 over original 400 engine, Comp Cams P8 XE256H-10 cam shaft.
The spark plugs that Mike Johnson @ JMS Racing installed in the engine after a supposedly freshen up are, NGK XR5 V- Power spark plugs. I don't thank these plugs are appropriate for this engine?

Thoughts and recommendations PLEASE!!!!!

Phone calls are welcome if you have the time.
Thanks
HD
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post #2 of 23 (permalink) Old 05-22-2016, 07:29 AM
 
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the stock a/c plugs for your engine gapped correctly.
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post #3 of 23 (permalink) Old 05-22-2016, 10:47 AM
 
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X2 on the AC spark plugs. You don't need anything fancy or high dollar. Make sure the gap is correct for your year and not the wider gap used on the later engines with HEI. Too wide a gap can cause problems.

Swap a known good plug with the #6 & #8 cylinders and check.

Also make sure your wires are firing the plug - could have a wire with high resistance or broken. I might simply swap a wire with a good known cylinder just to make a quick test. Another thought is the distributor cap & rotor.

Last thought is a carb problem - leaking or flooding.
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post #4 of 23 (permalink) Old 05-22-2016, 09:54 PM Thread Starter
 
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I'll pull the distributor cap and see what is going on.
The carb doesn't smell rich. The spark plugs that Mike @ JMS Racing installed are NGKR XR5 V Power.
I think the heat range of the plugs are too cold but I honestly don't thank that is the problem.
The distributor that Mike installed is a Pertronix Flame Thrower. The vacuum pod is plugged off.
The distributor must be locked out which is OK with me as I run the Mallory in my jet boat locked out with 36 degrees timing.
The 492 stroker engine in the boat likes it.
The Goat still has the original spark plug wire tubes. JMS had to make up the Accell wires so there may be a bad crimp somewhere.
All the spark plugs look wet which also makes me think it just might be a piston ring issue.
The engine idles rough and runs rough as RPMs increase.
I'll take the old girl into a shop that I trust this week and see what they discover.

I'll keep you all advised.

Thanks for your concern.

Dave
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post #5 of 23 (permalink) Old 05-23-2016, 05:48 PM
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If you are running stock '67 GTO heads and flat top pistons, with that cam, you will have waaaay too much cylinder pressure. That in turn can cause detonation that you may or may not be able to hear, which can lead to a blown head gasket. I use AC R44 plugs in my GTO's, and have for decades with good results. Check the obvious, as Jim said: plug wires, carbon tracked dist cap, and check for crossed wires. Next step is to do a compression check and/or connect a vacuum gauge to determine if the engine has even compression all the way around. I HOPE you installed dished pistons with this build if you are using the 670 heads. If not, you will need 100 octane fuel to run this beast.
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post #6 of 23 (permalink) Old 05-23-2016, 09:12 PM
 
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Originally Posted by geeteeohguy View Post
If you are running stock '67 GTO heads and flat top pistons, with that cam, you will have waaaay too much cylinder pressure. That in turn can cause detonation that you may or may not be able to hear, which can lead to a blown head gasket. I use AC R44 plugs in my GTO's, and have for decades with good results. Check the obvious, as Jim said: plug wires, carbon tracked dist cap, and check for crossed wires. Next step is to do a compression check and/or connect a vacuum gauge to determine if the engine has even compression all the way around. I HOPE you installed dished pistons with this build if you are using the 670 heads. If not, you will need 100 octane fuel to run this beast.
Geeteeohguy makes a great point on having too much dynamic compression IF you still have the engines stock compression. The Wallace calculator (Wallace Racing: Dynamic Compression Ratio Calculator) puts your dynamic compression at 8.98 to 1 looking at the cam's spec with its intake closing at 54 degrees after bottom dead center (ABDC). In selecting a cam for a street engine, a better target dynamic compression would be between 7-8 to 1 with 8 being about all you want on a street engine. As geeteeohguy stated, you can certainly run a higher dynamic compression, but you will most certainly need higher octane quality race gas (which you may be already using) to prevent detonation.

However, not sure if this is or is not a contributing factor at this point, but it could be a factory in "idling rough and running rough as RPM's increase." The wet plugs are still suspect and if it were me I would be looking at the ignition system to ensure all plugs are firing and then look at the carb for a possible over rich fuel issue.
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post #7 of 23 (permalink) Old 05-24-2016, 11:57 AM
 
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Those NGK V-power plugs are decades of technology ahead of the same old $1 AC's thats why your builder used them. Nothing wrong with ACs if you prefer them but to knock NGKs? V-powers are not just "fancy" or a gimic they work really well. I know I know good old AC plugs worked for decades on millions of cars.. Well so did carburetors yet we dont see any on brand new cars worldwide. V-powers are good enough for pro stocks but not a 1967 400 Pontiac motor? Come on... Anyway...

Looking at your part number you are running #5 heat range plugs. With NGK the lower the number the hotter the plug. I think Geeteeohguy is right on point. Your 400 (if it has original heads) has a small chamber 670 head and most likely will not tolerate pump gas. That hot of a plug is a bad combo if you have been putting pump gas in that motor. Real bad. As stated cylinder pressure is probably through the roof and you may have serious detonation going on if you're not running a race fuel/92 blend and mild timing. Did the builder tell you your compression ratio? #5 NGK plugs are plenty hot to burn off average or even slightly excessive oil blow by so if they are that wet my guess is your issue is either a cracked cap or bad wires to those cylinders if you are lucky. If you are really unlucky the detonation caused by pump gas and the hot plugs has broken rings and or a piston or two. Start with a simple leak down test on those cylinders. If they hold air like the rest of them try a new cap rotor and wires. If they leak more than the other cylinders you may have some breakage there. Just my .02

You outta see her on a road course, or a quarter mile
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post #8 of 23 (permalink) Old 05-24-2016, 12:02 PM
 
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Originally Posted by Hallett Dave View Post
The spark plugs that Mike @ JMS Racing installed are NGKR XR5 V Power.
I think the heat range of the plugs are too cold but I honestly don't thank that is the problem.
Dave
Surely being too cold is NOT the issue. Unlike other brands the lower the number the hotter the plug with NGK. #5s are as hot as they get. My KRE headed 455 uses #7s . 11s fouled in 30 minutes. 9s were gettng there. 8s were a tad too brown. 7s hit the mark perfectly. Just trial and error got me to that point. The plugs are not too cold. You lost spark or detonation finally cooked rings or a piston or two. Hopefully its a $25 cap and $50 wires. Fingers crossed for you my friend post your findings after a leak down and tune up!

You outta see her on a road course, or a quarter mile

Last edited by Bensjammin66; 05-24-2016 at 02:20 PM.
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post #9 of 23 (permalink) Old 05-24-2016, 08:52 PM
 
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A race car with locked out timing is one thing, a car driven on the street without a Vacumn advance or other digital load sensing timing advance will not reliably fire the mixture in any light throttle or cruise condition.

Just something to consider in your investigation. When you need more spark to burn the leaner mixture, at cruise, it won't,..it won't fire all the time, it is retired to much, an incomplete burn.....race car is pedal to the metal, does not need load sensing ( Vacumn Advance) for timing....so one thing to consider is set up the dizzy with a Vacumn can pulling in 8 degrees distributor...16 degrees at crank...that has it all in at least 2 hg below idle Vacumn.....your 36 is correct...and Vacumn will not effect open throttle as it drops out then.

New plugs, and the right Vacumn advance and agree with the recommendations of the gang as well for things to check. But if you are driving a street car set up for racing your timing is wrong most of the time to optimize your burn...
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post #10 of 23 (permalink) Old 05-24-2016, 10:08 PM Thread Starter
 
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Originally Posted by Bensjammin66 View Post
Surely being too cold is NOT the issue. Unlike other brands the lower the number the hotter the plug with NGK. #5s are as hot as they get. My KRE headed 455 uses #7s . 11s fouled in 30 minutes. 9s were gettng there. 8s were a tad too brown. 7s hit the mark perfectly. Just trial and error got me to that point. The plugs are not too cold. You lost spark or detonation finally cooked rings or a piston or two. Hopefully its a $25 cap and $50 wires. Fingers crossed for you my friend post your findings after a leak down and tune up!
Well I just got off the phone with Jay the second owner in Tucson who had the engine rebuilt in 2012.
He had stock style pistons installed, Shield Power. He told me he had the engine built to stock specs except for the cam. The engine should be 10.5 to 1 or less.
Mike at JMS supposedly replaced all the bearings and had the crank polished
.
The Pertronics distributor must be locked out since the vacuum module is capped off.
The spark plug wires are Accel Hi temp Super stock radio suppression, running through the factory tubes.
The carb that JMS installed is a Holley vac secondary 80783- list#.
Jay in Tucson put probably less than 1,000 miles on the engine when I purchased it and maybe 500 miles were put on it at JMS before I had it delivered to my house by AAA. I have put 150 miles on it since I brought it home.

All of my diagnostic shit is at the Colorado River house in Arizona with the Hallett Mini Cruiser, 4 hours away from me.

I'm taking the GOAT in tomorrow to a shop I trust so we will see what they discover.
I will post the results.

Thank you everyone for your advice and concerns.
Dave
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