Plug reading and compression test

[Paul G]

Pulled the plugs to see how they look and did a compression test while they were out. Compression was a low of 160 to a high of 175.

1. 160    2. 170
3. 170    4. 165
5. 165    6. 175
7. 165    8. 160

Plugs are all about the same. The porcelin is bright white, the ground strap is a gray to brown. Do they look OK? Too hot, too cold? Timing OK. Plug reading is like voodoo magic to me?

I had the car out yesterday on a 70 mile road trip. On the way home did a full throttle run to 6000 RPM, that was about 15 minutes from home. Normal driving the rest of the way home. This morning I warmed the engine for a few minutes before doing the compression test. I dont know what effect that will have on the plug readings.

I would really like to know what cam I have and what compression ratio. I dont have the cam card. The engine is a 12 year old build, 360, ported iron heads. Dont know if there are cams available today with better performance than what ever is there right now?  The engine will pull to 6000 RPM in third gear, tops out about 130 MPH on a desert highway, 3.91 gears, 2500 stahl converter. I really need to take it to the track and see what it will do in the quarter mile.  

[Paul G]

Oh, and there gapped at .045, I am using an MSD 6a box.

[Chryco Psycho]

depending on the gas used they look lean to me , youy should gain power & milage running slightly richer

[elacruze]

Not much info to go on, but your compression is ok for pump gas if your timing is correct, and the plugs look generally good but could probably go up a size or 3 on the main jetting.

Plugs are pretty clean for 15 minutes of mixed driving plus a cold choke start-how does it run on the choke? Cold bloodedness might be improved by keeping the choke on a little more and a little longer. If you have a choke, that is.

[Paul G]

depending on the gas used they look lean to me , youy should gain power & milage running slightly richer

Richer meaning up size the primary jets? It is a Holley 750 I am running. I use 91 octane gas. No pinging. 

Not much info to go on, but your compression is ok for pump gas if your timing is correct, and the plugs look generally good but could probably go up a size or 3 on the main jetting.

Plugs are pretty clean for 15 minutes of mixed driving plus a cold choke start-how does it run on the choke? Cold bloodedness might be improved by keeping the choke on a little more and a little longer. If you have a choke, that is.

Not using a choke. The holley has a manual choke thats fixed in the open position. Cold start warm up's are all me feathering the throttle open for a minute. It never really gets cold enough to need a choke here.   

It is a Holley 750 I am running. I think I put the stock 72 primary jets in the carb when I rebuilt it. I have a set of 74's and 76's laying around. Try the 74's or go straight to the 76's?

[elacruze]

depending on the gas used they look lean to me , youy should gain power & milage running slightly richer

Richer meaning up size the primary jets? It is a Holley 750 I am running. I use 91 octane gas. No pinging. 

Not much info to go on, but your compression is ok for pump gas if your timing is correct, and the plugs look generally good but could probably go up a size or 3 on the main jetting.

Plugs are pretty clean for 15 minutes of mixed driving plus a cold choke start-how does it run on the choke? Cold bloodedness might be improved by keeping the choke on a little more and a little longer. If you have a choke, that is.

Not using a choke. The holley has a manual choke thats fixed in the open position. Cold start warm up's are all me feathering the throttle open for a minute. It never really gets cold enough to need a choke here.   

It is a Holley 750 I am running. I think I put the stock 72 primary jets in the carb when I rebuilt it. I have a set of 74's and 76's laying around. Try the 74's or go straight to the 76's?

Feh. For me, I'd go to the 76s and test.

[Chryco Psycho]

is there an ethanol mix in the fuel ?
AN O2 sensor would be a better way to judge

[Paul G]

is there an ethanol mix in the fuel ?
AN O2 sensor would be a better way to judge

Our pumps do have ethanol blends. Cant find any nearby without it. Only 91 octane as well. Used to have 93 back in the midwest.

What can I gain from an 02 sensor?

[BSB67]

The plugs look fine.  You cannot make any jetting changes based on the history of those plugs.  I would not change a thing. Determine your best driving and cruise jetting with an O2 meter, and best performance jetting at the track.

[flyinlow]

First off ,  damn you for never needing a choke ,20* this morning here, I would wear out my accelerator pump wihtout a choke.

The plugs look fine to me. Most of what you are reading is from the 15 minute cruise home and your warm up for the compression check. If you wanted a WOT reading you would have to make a WOT run then shut the engine off as soon as possible and pull the plugs. After 70 miles I would expect white insulators in a healthy street engine. The tan and gray is normal ash deposits from burning fuel.

Is the engine running well? If I remember you had some detonation issues in an other post. If it is running well, I would put the plugs back in and drive it.

A wide band O2 gauge will tell me my carb is running 12:1 at WOT without burning my fingers on headers . It tells me the 750 Holley cruises about 14:1 while the TQ can run as lean as 16:1 and not surge or ping. It reminds me to turn off the choke {why am I cruising at 13:1?} It is a cool  tuning tool.

[Chryco Psycho]

bump up the jetting to 74 , if it likes it you will feel the difference , it will be more responsive

[elacruze]

First off ,  damn you for never needing a choke ,20* this morning here, I would wear out my accelerator pump wihtout a choke.

The plugs look fine to me. Most of what you are reading is from the 15 minute cruise home and your warm up for the compression check. If you wanted a WOT reading you would have to make a WOT run then shut the engine off as soon as possible and pull the plugs. After 70 miles I would expect white insulators in a healthy street engine. The tan and gray is normal ash deposits from burning fuel.

Is the engine running well? If I remember you had some detonation issues in an other post. If it is running well, I would put the plugs back in and drive it.

A wide band O2 gauge will tell me my carb is running 12:1 at WOT without burning my fingers on headers . It tells me the 750 Holley cruises about 14:1 while the TQ can run as lean as 16:1 and not surge or ping. It reminds me to turn off the choke {why am I cruising at 13:1?} It is a cool  tuning tool.

Agreed, but to make the point you need a WIDE BAND O2 sensor and appropriate mixture gauge.

[flyinlow]

]

Agreed, but to make the point you need a WIDE BAND O2 sensor and appropriate mixture gauge.

Sorry, I used the wrong term. I have a a wide range Air/ Fuel ratio gauge mounted permanently in the car. It is an AEM gauge with a needle indicator from 8-18 A/F ratio. Reads the left bank just behind the header. Takes about 5 seconds to heat up after start up before it starts moving. It has about a .5 second delay at small throttle openings when the exhaust is moving slowly. almost instantaneously at WOT. You can hook a laptop to it and record the info. I have not done this. You can see it jump rich for a second when the accelerator pump discharges and then burns off returning to a leaner indication during part throttle acceleration. The carb is richest during closed throttle deceleration, about 11:1.  

[firefighter3931]

The plugs look fine.  You cannot make any jetting changes based on the history of those plugs.  I would not change a thing. Determine your best driving and cruise jetting with an O2 meter, and best performance jetting at the track.

The heat range & jetting both look fine to me 


Ron

[maxwellwedge]

This unleaded crap gas doesn't color plugs properly...and you have to cut the engine clean to read them properly even with real gas. So, if you are happy with the way it runs - enjoy.

If you want to play with the jetting and test - go ahead...have some fun.

[elacruze]

]

Agreed, but to make the point you need a WIDE BAND O2 sensor and appropriate mixture gauge.

Sorry, I used the wrong term. I have a a wide range Air/ Fuel ratio gauge mounted permanently in the car. It is an AEM gauge with a needle indicator from 8-18 A/F ratio. Reads the left bank just behind the header. Takes about 5 seconds to heat up after start up before it starts moving. It has about a .5 second delay at small throttle openings when the exhaust is moving slowly. almost instantaneously at WOT. You can hook a laptop to it and record the info. I have not done this. You can see it jump rich for a second when the accelerator pump discharges and then burns off returning to a leaner indication during part throttle acceleration. The carb is richest during closed throttle deceleration, about 11:1.  

I don't have a WB sensor on mine yet, because I'm a cheapskate and also because I wanted to get the seat-of-the-pants drivability dialed first, so I could see what the ratios felt like rather than dial what I thought it should be first. I'd be interested in knowing your cruising throttle ratio, say 55-75mph as well as your idle ratio.

[flyinlow]

[I don't have a WB sensor on mine yet, because I'm a cheapskate and also because I wanted to get the seat-of-the-pants drivability dialed first, so I could see what the ratios felt like rather than dial what I thought it should be first. I'd be interested in knowing your cruising throttle ratio, say 55-75mph as well as your idle ratio.

70 MPH ,2000 rpm OD about 15.5 :1 with the TQ.  About 13.5 : 1 at idle for a good idle. The Holley 750 and Eddy 800 EPS run about 14:1 at cruise.