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Stock Compression PSI on a Boss

Seven

Dacia Sandero
Just wondering what stock compression numbers (in psi) are for a 12-13 Boss.

I got my car used with 3800 on it, and I sent logs to a tuner and based on the log it seems like the car is pulling timing - My g/f put costco gas in the car this weekend, which is likely the cause but now the tuner wants me to see what the compression numbers are as the timing was the worst in cyl #8.
Which I heard was common in GTs... IIRC?

Just wondering what I should see when I check the compression at a shop (whenever I have time/they have appointments) so I know whether to call the dealer (as the car was sold to me as "stock" for what might be some big warranty work - or the tuner to say its just the bad gas)

Thanks all
 
Seven said:
Just wondering what stock compression numbers (in psi) are for a 12-13 Boss.

I got my car used with 3800 on it, and I sent logs to a tuner and based on the log it seems like the car is pulling timing - My g/f put costco gas in the car this weekend, which is likely the cause but now the tuner wants me to see what the compression numbers are as the timing was the worst in cyl #8.
Which I heard was common in GTs... IIRC?

Just wondering what I should see when I check the compression at a shop (whenever I have time/they have appointments) so I know whether to call the dealer (as the car was sold to me as "stock" for what might be some big warranty work - or the tuner to say its just the bad gas)

Thanks all
It's 11.0:1. There have been numerous reported failures of the #8 piston on 5.0s with faulty tunes. Most of the big tuners have adjusted their tunes.

e.g. http://www.allfordmustangs.com/forums/2011-mustang-gt-tech/293943-aftermarket-tunes-causing-8-cylinder-take-dump.html
 

unrealford

Mustang owner since 84
521
0
Depending on dealer, they might refuse any warranty work if they look deep enough and realized you had a tuner on it.
 

Seven

Dacia Sandero
cloud9 said:
It's 11.0:1. There have been numerous reported failures of the #8 piston on 5.0s with faulty tunes. Most of the big tuners have adjusted their tunes.
Stock compression in psi - IE as if you used a compression tester for it. I noted that above I'm guessing you missed it, so I bolded it :)
*edit* - it actually says it in the title of the thread too 8)
unrealford said:
Depending on dealer, they might refuse any warranty work if they look deep enough and realized you had a tuner on it.

I haven't had a tuner on it. It was sold to me as a stock vehicle and I HAVE NOT modified the engine in any way shape or form. If it was modified or tuned it would have been from the previous owner, and I'm sure there's debate but if the previous owner loaded a tune and the car fails on ME... you can bet I'll go after the dealer that sold it to me as a "stock vehicle" - which is what I was told numerous times during the buying process.
 
Seven said:
Stock compression in psi - IE as if you used a compression tester for it. I noted that above I'm guessing you missed it, so I bolded it :)
*edit* - it actually says it in the title of the thread too 8)
I haven't had a tuner on it. It was sold to me as a stock vehicle and I HAVE NOT modified the engine in any way shape or form. If it was modified or tuned it would have been from the previous owner, and I'm sure there's debate but if the previous owner loaded a tune and the car fails on ME... you can bet I'll go after the dealer that sold it to me as a "stock vehicle" - which is what I was told numerous times during the buying process.
Sorry glossed over it. PM PeteInCT as I know he's compression tested his.
 

steveespo

Lord knows I'm a Voodoo Child
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160-180. You are looking for variation more than a specific number. If one or more cylinders are off by 7% or more there is an issue. Could be rings, valves or piston damage at the ring lands.
Hope you don't have a problem. Are you seeing smoke or hearing funny noises?
Steve
 

Seven

Dacia Sandero
ArizonaGT said:
Personally I would burn off all that bullshit gas, load up with a fresh tank, then datalog again. Could save you a lot of headache.

Not good enough for the tuner... the one YOU recommended.

Dropped it off at the dealer earlier tonight.
 

PeteInCT

#LS-378 - So many Porsche's, so little time....
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steveespo said:
160-180. You are looking for variation more than a specific number. If one or more cylinders are off by 7% or more there is an issue. Could be rings, valves or piston damage at the ring lands.
Hope you don't have a problem. Are you seeing smoke or hearing funny noises?
Steve

Steve beat me to it ! ;D I saw 166 on all clyinders +/- 1 psi. This was measured at an altitude of about 350 ft above sea level. It's calculated as 14.696 (air pressure at sea level) times 11 (11:1 compression ratio).

-Pete
 

Seven

Dacia Sandero
PeteInCT said:
Steve beat me to it ! ;D I saw 166 on all clyinders +/- 1 psi. This was measured at an altitude of about 350 ft above sea level. It's calculated as 14.696 (air pressure at sea level) times 11 (11:1 compression ratio).

-Pete

Thank you sir
 
Comperssion PSI and timing on 8? Compression PSI should be done engine hot, WOT, three hits or more then read should be within 15 pouns or so across all cylinders ( remeber we have variable cam timing and without running the motor between every cylinder reading makes the test bogus). Different timing on eight means one of two things. First you have a very advanced person testing your motor and he is trying to sell you snake oil, because only a bad reluctor ring would cause this ( simple dealer fix) and he knows this) or laptop lag on cycle reset to one. Compression is a very basic and crude test for bad things. Due to carbon and other variables small differences between cylinder is normal. Compression is a quick and easy test after an over rev or strange noise to find a gross problem. A properly done leak down test is the only true test for fine ballance between cylinders. Back to compession testing it will find a ( shortend bent rod, spun bearing, cracked wrist pin boss) problem sometimes.
 

captdistraction

GrumpyRacer
1,862
1,519
Phoenix, Az
ArizonaGT said:
Personally I would burn off all that bullshit gas, load up with a fresh tank, then datalog again. Could save you a lot of headache.

This is the most relevant answer.

Quality of Fuels can cause huge differences in timing in these cars. The boss cars aren't prone to #8 issues like the GT cars are. The piston material, head composition and valves are all different.

8 will also typically be the one cylinder with the most pulled timing on these cars as its the most hot. I can't speak to the boss factory strategy in regards to this however I'd be willing to bet the compression is fine and its just a matter of getting good fuel in the car.
 

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