Help with Compression #s please

[sja177]

Long story short, my brother bought an 03 cobra that had some basic boltons from a used car dealer. It appears there had been extenseive mods, as there is an upgarded fuel line.
Anyways,

There is a lot of smoke coming out of the exhaust, and a lot of blow by, coming out of the breather on the p/s of the block. Its covered the engine with oil.
Another concern was the compression, so I tested the #s:

Engine warm: (dry)

---firewall---
8= 165 7= 153
6= 177 5= 135
4= 168 3= 155
2= 170 1= 148

---radiator---

Engine warm: (wet)

---firewall---
8= 180 7= 170
6= 180 5= 160
4= 176 3= 173
2= 177 1= 161

At first glance the p/s bank was all lower that the d/s bank. It appeared cylinder 5 was gone on the initial compression test, but now im not sure, as the entire bank went up big time with oil added. I am going to buy a leakdown tester online today. I looked at the coolant (no signs of oil)
I started the car up and looked for bubbles in the coolant resevoir and did not see any. Any ideas would be appreciated, thanks guys!!

 

[1QUICK10TH]

Even though they went up when you did a went test doesn't mean its ok. Your smoke is more than likely coming from worn out rings in cylinder number 5

 

[RichM1983]

I had this same question before with similar numbers. I was told that if all the numbers on one bank were within range of each other but lower on the other bank then the cam may just be off enough to account for the lower compression. Although I guess cylinder 5 may be a little low. I was told that other people have ran these cars with numbers lower than what you have with high boost and no problems for several miles. All of this was obtained on this site.

 

[sja177]

ok thanks for the info, I think I will try and have my bro adjust the cam timing and see what kind of numbers we get

 

[MalcolmV8]

You have the cylinders numbered wrong. At least according to your diagram.

If it's like this

--- firewall ---
<engine>
--- radiator ---

Which I think is how you were trying to display it then cylinders go like this

--- firewall ---
4 8
3 7
2 6
1 5
--- radiator ---

So the cylinder you have low is actually number 7. Incidently I just compression tested a buddies 04 Cobra a few days ago and here's what his numbers looked like (not drawn in the layout like you had)

#1 - 165 psi #5 - 160 psi
#2 - 160 psi #6 - 160 psi
#3 - 170 psi #7 - 140 psi
#4 - 155 psi #8 - 165 psi

Notice his number 7 was also low. I then did a leak down test and found this

#1 - 10% #5 - 10%
#2 - 5% #6 - 6%
#3 - 10% #7 - 20%
#4 - 10% #8 - 10%

His number 7 was leaking by the rings as I suspect yours is too. I wonder if it's due to lack of head cooling mod that they both have # 7 with worn rings?

 

[sja177]

Yea I just did a bunch of reading, and realized it is #7 thats low just like your buddies car. The oil and coolant are full, so i'm guessing its worn rings in #7.
Is your buddy going to rebuild, or keep driving it?

You have the cylinders numbered wrong. At least according to your diagram.

If it's like this

--- firewall ---
<engine>
--- radiator ---

Which I think is how you were trying to display it then cylinders go like this

--- firewall ---
4 8
3 7
2 6
1 5
--- radiator ---

So the cylinder you have low is actually number 7. Incidently I just compression tested a buddies 04 Cobra a few days ago and here's what his numbers looked like (not drawn in the layout like you had)

#1 - 165 psi #5 - 160 psi
#2 - 160 psi #6 - 160 psi
#3 - 170 psi #7 - 140 psi
#4 - 155 psi #8 - 165 psi

Notice his number 7 was also low. I then did a leak down test and found this

#1 - 10% #5 - 10%
#2 - 5% #6 - 6%
#3 - 10% #7 - 20%
#4 - 10% #8 - 10%

His number 7 was leaking by the rings as I suspect yours is too. I wonder if it's due to lack of head cooling mod that they both have # 7 with worn rings?

 

[MalcolmV8]

Yea I just did a bunch of reading, and realized it is #7 thats low just like your buddies car. The oil and coolant are full, so i'm guessing its worn rings in #7.
Is your buddy going to rebuild, or keep driving it?

Keep on driving although his doesn't blow smoke or anything.

 

[RichM1983]

ok thanks for the info, I think I will try and have my bro adjust the cam timing and see what kind of numbers we get

I don't think it is necessary considering it was done that way from the factory.......I think it would be pointless....and a TON of work.

 

[sja177]

Got to thinking last night.
I still don't understand why the d/s bank is so much lower than the p/s bank. It appears there is an average of about 20psi higher on the p/s bank.
Is this simply because of the "head cooling mod" and if so then, wouldn't this just result in a warped head and/or headgasket causing the pressure loss. Perhaps a combination of piston rings and a slightly warped head?

Also, I dont understand how a lack of cooling on the head would cause all of the rings to lose compression on the entire bank. Heat rises right?

I would like to know why the compression is ok the passenger side, and not the drivers side.

MalcolmV8: When you did your leakdown did you hear where the leaks were? Possibly more than one? Thanks!

 

[MalcolmV8]

MalcolmV8: When you did your leakdown did you hear where the leaks were? Possibly more than one? Thanks!

Yes I used an automotive stethoscope to verify it was just the rings. Air was coming out the valve covers and dipstick tube only. Nothing in the cooling system, intake or exhaust.

I see you're new on the site and I assume new to 03 Cobras. If you do some searching you'll see these cars are notorious for over heating and damaging cylinders 7 & 8. The theory is that they get to hot because the coolant has no exit on the back of the driver's head. Search for head cooling mods, there's a few. Anyhow I've seen pics of melted pistons, damaged rings etc. that guys have posted up here from cylinder 7 & 8.

 

[suaveflooder]

My seven is low as well. I think I'm at 145 where all the surrounding are 165+. I've got a buddies who's 7 & 8 are going. He is around 125-135 in his. He's been beating on his for 3 years with that knowledge. When I say beating....I'm mean the car is BEATEN!! He loves his car and plans on an aluminator when he finally blows the motor.

 

[RichM1983]

Got to thinking last night.
I still don't understand why the d/s bank is so much lower than the p/s bank. It appears there is an average of about 20psi higher on the p/s bank.
Is this simply because of the "head cooling mod" and if so then, wouldn't this just result in a warped head and/or headgasket causing the pressure loss. Perhaps a combination of piston rings and a slightly warped head?

Also, I dont understand how a lack of cooling on the head would cause all of the rings to lose compression on the entire bank. Heat rises right?

I would like to know why the compression is ok the passenger side, and not the drivers side.

MalcolmV8: When you did your leakdown did you hear where the leaks were? Possibly more than one? Thanks!

Read what I posted earlier for an explanation of a possible reason one bank can read lower than another. Remember...POSSIBLE reason.

 

[Rambro]

Low#7 here too, still giving it hell.

 

[sja177]

Thanks for the reply guys! I checked out the head cooling mod on lethal performance, This will be the next mod, along with a tune, among other things

 

[gabe1530]

check out the LDC head cooling mod - ill be putting mine on in a couple weeks when i change out the clutch.
Ford 99-04 Mustang DOHC Cooling Mod [LCM] - $229.00 : Performance Parts - Ford Mustang - Cobra - Dodge Viper - Chevy Corvette - C6 - LS1

 

[MalcolmV8]

check out the LDC head cooling mod - ill be putting mine on in a couple weeks when i change out the clutch.
Ford 99-04 Mustang DOHC Cooling Mod [LCM] - $229.00 : Performance Parts - Ford Mustang - Cobra - Dodge Viper - Chevy Corvette - C6 - LS1

That's the one I have. Makes for a really clean install with nothing visible in the engine bay.

 

[suaveflooder]

Low#7 here too, still giving it hell.

I love seeing this! Any smoke on your end? I don't have any and either does my friend. I just figure when it goes, it goes. Until then...she gets punished :rockon: :burnout:

 

[Rambro]

I love seeing this! Any smoke on your end? I don't have any and either does my friend. I just figure when it goes, it goes. Until then...she gets punished :rockon: :burnout:

A little smoke on startup, nothing crazy though. It does make knocking noise until it gets up to normal temp but after that u can barely hear it. I'm going to do a port after I get my trans fixed then abuse it as usual.