# Spark plugs in a 30 over 400



## Hallett Dave (Apr 29, 2016)

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
home 661-723-6880


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## rickm (Feb 8, 2012)

the stock a/c plugs for your engine gapped correctly.


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## PontiacJim (Dec 29, 2012)

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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## Hallett Dave (Apr 29, 2016)

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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## geeteeohguy (Feb 2, 2008)

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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## PontiacJim (Dec 29, 2012)

geeteeohguy said:


> 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. :thumbsup:


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## Bensjammin66 (May 12, 2009)

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


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## Bensjammin66 (May 12, 2009)

Hallett Dave said:


> 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!


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## Lemans guy (Oct 14, 2014)

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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## Hallett Dave (Apr 29, 2016)

Bensjammin66 said:


> 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. :smile3:
Dave


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## Hallett Dave (Apr 29, 2016)

Lemans guy said:


> 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...


This makes a lot of sense to me, as I cruise my Hallett jet boat with a locked out Mallory at 5,000 to 6,000 RPM all day long with no problems. 
The Scott Foxwell built/Chris Straub cammed engine in the boat was purposely built for these conditions. Not a race boat just a fast river cruiser.
Wow, what an eye opener. 
Thank you so much.
Dave


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## Lemans guy (Oct 14, 2014)

Right Dave, speed boat operated like that only needs mechanical advance. If nothing else is wrong with your engine than from what you describe a stock or HEI distributor with the proper advance curve and Vacumn advance tuned in would run fabulous.....

I just curved a 65 corvette my friend has 365 hp, 30-30 cam....we put in a steep advance curve and real quick Vacumn can which that car had and needs and was not in there,...it completely changes the ride if done right...I hope that is what you need Dave..

Good luck and let us know how it turns our

We are pulling for you!


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## Hallett Dave (Apr 29, 2016)

Lemans guy said:


> Right Dave, speed boat operated like that only needs mechanical advance. If nothing else is wrong with your engine than from what you describe a stock or HEI distributor with the proper advance curve and Vacumn advance tuned in would run fabulous.....
> 
> I just curved a 65 corvette my friend has 365 hp, 30-30 cam....we put in a steep advance curve and real quick Vacumn can which that car had and needs and was not in there,...it completely changes the ride if done right...I hope that is what you need Dave..
> 
> ...


Thank you so much for sharing all of your insight and knowledge.

I have printed all of the dialogue from this thread to take to the shop tomorrow. 
Even though JMS says I have a one year warranty on everything they did on the GOAT, I'm thinking I'm screwed. 

I am pissed off but I do somewhat have respect for Mike the owner of JMS as he has built and driven a lot of GN Race boats that were winners. 
A blown GN boat is nothing like a daily driver, why the locked out distributor in my GTO? How did I miss that?

Thank you Lemans Guy

JMS did not build this engine but they did not deliver a final product that we agreed on.

I will address my issues with JMS after I get the diagnosis from my shop and go from there. 

I'm 66 years old and soon to retire in 10 months. 
I have waited for 49 years for this GOAT. 
I hope I can get things worked out.
Thanks Lemans Guy and everyone else for your input. 
Is your GTO Montreuax blue? Mine is.
Thank you everyone.
Dave


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## Lemans guy (Oct 14, 2014)

Dave..mine is blue..maybe it is Fontaine Blue Metallic?.....Montreax blue...too cool for school.....

.ps solid advice from all, I saw another post from Benjamin on another topic, he knows his timing and compression stuff, ...each car is a little different, .......and timing has to be the optimum setup without detonation.

Also you can use a Petronix igniter in the distributor with the right Vacumn can, had one in that corvette I mentioned, but your Centrifigal and base must be right as well. 

You will get it, if that is it it should be easy fix..let's hope so!....could be another miss as well, they will find it........


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## geeteeohguy (Feb 2, 2008)

Ok....we now know the issue. Sealed Power pistons (which I am running in both of my GTO's) are forged flat topped pistons. I was unable to run my '67 GTO back in the '80's on pump gas with water injection and the timing set 6 degrees retarded...it pounded like a sledgehammer. Still pinged on 94 octane with the 670 heads in the dry CA heat. And I was running an 068 cam. Too much compression. With your XE cam and your stock heads with Sealed Power flat tops, you will need to run 100 octane or probably higher and tune the engine accordingly, if you haven't already broken a piston ring or blown a head gasket. Very easy to damage these engines by detonation. I broke 4-5 pistons in a 428 years ago and never heard it ping. Ruined the engine. What I finally did with my '67 GTO was install a set of later heads with 87cc chambers to bring the CR down to 9.3:1, which still pings a bit on 91 on hot days. And my engine has an 068 cam, which does not build up anywhere NEAR the cylinder pressure of your Comp cam. Comp cam's such as yours are excellent, and are meant to use in low compression engines..8:1 or so. In a 10.5-11;1 engine, a GUARANTEED disaster. Your options: Change the cam, retard the timing, and run pump gas and have a sluggish engine; Change the heads and cam and run pump gas, or leave it alone and run $9 per gallon race gas as long as you own the car. Just hearing that your 'mechanic' locked out your distributor made me cringe.....I've been tuning cars for over 35 years for a living, and that is just plain ignorant.


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## Lemans guy (Oct 14, 2014)

solid assessment Geetee....dave has to get it looked at and re-evaluate the build and his options


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## Hallett Dave (Apr 29, 2016)

Lemans guy said:


> solid assessment Geetee....dave has to get it looked at and re-evaluate the build and his options


I'm hearing some rather disheartening replies, but that is OK.
I took the GTO to a shop that I trust this morning. I'm sure they will diagnose the problem or problems with this engine.
If it turns out there is a major problem I will take care of it.
I plan on retiring in 10 months so I guess I'd rather hear any bad news now while I'm still making full salary.

I left a message for my friends Chris Straub and Scott Foxwell at Straub Tech to see what they have available for the Poncho if it needs to be rebuilt. (Straub cam, Morrel roller lifters and KB forged Icon pistons)

I've got some good parts in my 40 over 10.5-1 BBC 492 stroker with 990 heads in the boat which makes 750 HP on 91 octane so if a rebuild is in order I will feed the Poncho with good parts. 

The verdict isn't in on my 400 yet but I am planning ahead just in case.

Thank you everyone for your feed back and concerns.:smile3::|
Stay tuned.

Feel free to call me if you have the time.
Dave
home 661-723-6880


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## Lemans guy (Oct 14, 2014)

Hang in there Dave ,..you have the right outlook. We can all offer some thoughts, but it is going to take the hands on work and info from the builder to get it set the way you want it.

Kudos to you for staying with it,...keep an open outlook and they may offer some different ways to go!


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## Bensjammin66 (May 12, 2009)

CORN FED!!! I dont have any personal E85 experience but it is worth a look if no damage is done to the motor yet. Its actually cheaper than pump gas yet E85 is 100-102 octane on average. It is an 85% ethanol / 15% 87 octane gas blend but you need to tune the carb and timing to run it. I think maybe different floats and jets? Custom temp plugs too? Fuel pump? Google is your friend if no one can chime in with E85 experience but your builder should know all about it and offer it as an option. It allows for higher compression or lots of MAP pressure from power adders without ping and best of all without buying $9/gallon race fuel as geeteeohguy said. A friend has a 650hp+ turbo 9.5:1 LS with 12 psi worth the boost and he runs E85 just fine. Regular 92 octane would have beat that motor to death like i suspect is happening to yours. The only downsides are that it is about 60-70% as efficient as gasoline so your fuel mileage is cut by an EASY 30% or more and not every gas station sells it either. Just another option that may not require engine disassembly. First get that motor leak and compression tested and you will have your answers.


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## Hallett Dave (Apr 29, 2016)

Bensjammin66 said:


> CORN FED!!! I dont have any personal E85 experience but it is worth a look if no damage is done to the motor yet. Its actually cheaper than pump gas yet E85 is 100-102 octane on average. It is an 85% ethanol / 15% 87 octane gas blend but you need to tune the carb and timing to run it. I think maybe different floats and jets? Custom temp plugs too? Fuel pump? Google is your friend if no one can chime in with E85 experience but your builder should know all about it and offer it as an option. It allows for higher compression or lots of MAP pressure from power adders without ping and best of all without buying $9/gallon race fuel as geeteeohguy said. A friend has a 650hp+ turbo 9.5:1 LS with 12 psi worth the boost and he runs E85 just fine. Regular 92 octane would have beat that motor to death like i suspect is happening to yours. The only downsides are that it is about 60-70% as efficient as gasoline so your fuel mileage is cut by an EASY 30% or more and not every gas station sells it either. Just another option that may not require engine disassembly. First get that motor leak and compression tested and you will have your answers.


Thanks for the suggestion of E-85.
I know a lot of guys running E-85 on their boosted jet boats, however, they are in the Midwest for the most part.
As far as I know E-85 in California is unattainable where I live.
I don't see E-85 anywhere in Mohave Valley Az. where my Colorado River retirement house is.
I am sure I will get it figured out.
With help and good advise I will get this figured out.
Hallett Dave


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## Hallett Dave (Apr 29, 2016)

Still no verdict from the local shop where I took car to on Wed. May 25.

Here is a reply to my latest email to Joe at JMS Racing in So Cal.
I would like some feed back from you all concerning his explanation.

From Joe

"Thanks Dave. Appreciate the comment on my son. 

We did rebuild that engine. It is under warranty. But, we do not pay other people to do our warranty work. Bring it back, and we will take care of it. 

The vacuum advance is capped for a reason. We run 34* total advance in a build like yours, with roughly 16-20 degrees mechanical advance. There is no reason to run vacuum advance. 

Now if you want better milage and less power, then you could hook up the vacuum advance. Set the initial timing to about 10*, and don't worry about the total. 

It will probably ping on regular like this, so you can adjust the vacuum advance if it does. Premium may take care of the ping, but then you eliminate your fuel cost savings. 

Also, you could rejet the carb to compensate as well. So make sure to have someone play with the tuning that has a Lot of experience in such things. 

There are a lot of factors involved, and if not done right, you can easily destroy a good engine. We will not warrant anything damaged from improper tuning. 

Just in case we didn't tell you before, that engine was set up to run on regular. The way I tuned it, it will not run better on premium fuel. The extra octaine will slow down the burn, and result in a lack of power. I suggest you use Chevron or Mobil at all times and add fuel stabilizer at each fill up. 

Due to the ten percent alcohol factor in all fuels these days, it will go bad in about three months. Make sure you do the same in your boat. Bad gas will destroy an engine."
-Joe 

By the way I have been using 91 octane since I took delivery of the GTO.
HD


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## Lemans guy (Oct 14, 2014)

Vacuum Advance- how is it supposed to work? - ChevyTalk - FREE Restoration and Repair Help for your Chevrolet

Dave,I think the builder can work with you on it. Above is Lars comments on timing, he also has other papers on the web about timing and vac advance, he is in Colorado and runs a speed shop. Look over his stuff, I think he is the best at it, anywhere. Dave Williams has written with him as well and seems extremely knowlegable.

I don't know them, I just read what they write and use it. It is spot on in my view. The builder said he could work with you on the timing and vacumn advance..

good luck you will get it!


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## Hallett Dave (Apr 29, 2016)

Lemans guy said:


> Vacuum Advance- how is it supposed to work? - ChevyTalk - FREE Restoration and Repair Help for your Chevrolet
> 
> Dave,I think the builder can work with you on it. Above is Lars comments on timing, he also has other papers on the web about timing and vac advance, he is in Colorado and runs a speed shop. Look over his stuff, I think he is the best at it, anywhere. Dave Williams has written with him as well and seems extremely knowlegable.
> 
> ...


JMS Racing is 82 miles from me and I'm not taking the chance of driving it that distance.

Thanks for your encouraging words

I'm washing my hands, I'm done with JMS.
HD


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