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4.6L General Discussion This section is for non-tech specific information pertaining to 4.6L (Modular) Mustangs built from 1996 to 2004.

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Old 10-07-2013, 11:10 PM   #1
mrz2207
 
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Default Compression test results

hi guys i have these compression results and are replacing the heads soon and want to make sure i don't need to rebuild the engine so what do you guys think.

Cylinder# dry/wet cylinders 1&3 didn't get WOT so im assuming that it
would be somewhere around 185/200
1- 170/175
2- 150/175
3- 175/195
4- 185/205
5- 185/205
6- 185/210
7- 185/200
8- 185/200
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Old 10-08-2013, 06:17 PM   #2
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personally id be worried about number 2. id check it again make sure you got the right readings? your right on the edge of 10 percent difference between highest and lowest. i was 160-165 across the motor. so good solid numbers there, this a pi swapped motor?
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previous stuff=
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Best trap 105.49

New stuff=Si trim, fmic, 3.33 pullie. Fueling issue prevent good numbers 350.1 rwhp 332rwtq rev limiter set at 5900 running out of fuel at 5400. 8psi
Best quarter mile time 12.40@115.36, stock 17s with toyo tqs.
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Old 10-08-2013, 07:10 PM   #3
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no its not, im doing a i swap soon. I really don't wanna rebuild the motor so i would hate for that to be a problem. but the wet test didn't seal like the others so i think it might be a leaking valve or maybe even a head gasket problem. Also the main reason im doing a pi swap is to fix the valve seal leakage.
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Old 10-08-2013, 08:35 PM   #4
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ok i re ran the test and i was right about cylinders 1&3. They are both at 185 and i re-ran #2 and got 185 dry 195 wet. so i guess there all fine. thanks for the input bman2000
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Old 10-08-2013, 09:47 PM   #5
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that sounds much better. and honestly for the future, the wet test is really only necessary if you have lower compression on one of the cylinders. the idea behind it would be if you were 50 psi low and you wet test that one and it comes up to match then your rings are toast. if it doesn't come up then it means you need to do a leak down test because you may have a valve issue or head gasket and what not. But sounds good id say the bottom end sounds healthy. Although 180-185 seems high, so my only question would be how much is that going to go up when you pi swap, just because there is a point where the quality of fuel is just going to need to be higher to prevent issues? but maybe that's normal for non pi motor? youd have to ask someone else who knows more about normal cylinder pressures for our motors.

edit: by ok i just mean the numbers are much closer and by the rule of thumb your safe on the compression front, at least for now. im not sure why you had such a drastic increase on most of the wet tests but not all...but meh. maybe someone else will chime in.
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previous stuff=
mustang dyno 225hp 275tq
Best E.T. 13.39
Best trap 105.49

New stuff=Si trim, fmic, 3.33 pullie. Fueling issue prevent good numbers 350.1 rwhp 332rwtq rev limiter set at 5900 running out of fuel at 5400. 8psi
Best quarter mile time 12.40@115.36, stock 17s with toyo tqs.

Last edited by Bman2000; 10-08-2013 at 09:49 PM.
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Old 10-08-2013, 10:02 PM   #6
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The reason i did the wet test was to make sure i wasn't burning oil from the rings(because i am burning oil). i have symptoms of bad valve seals. Also my intake is leaking coolant like their known to do, so a pi swap would be best now. The compression tester could be off on the psi scale because its a cheap 40 dollar one from auto zone. Anyway thanks again for the input and help.

Last edited by mrz2207; 10-08-2013 at 11:02 PM.
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Old 10-09-2013, 08:36 PM   #7
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Those numbers on a cold or warm engine
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Old 10-09-2013, 11:05 PM   #8
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Quote:
Originally Posted by uberstang1 View Post
Those numbers on a cold or warm engine
it was warm
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Old 10-12-2013, 12:01 PM   #9
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Quote:
Originally Posted by mrz2207 View Post
it was warm
Gotcha, was gonna say those are nice numbers cold. I just recently comp checked mine cold cause and put down 160 exact on all 8.
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Old 10-14-2013, 10:06 PM   #10
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thats what i had, haha didnt think about warm vs cold, good catch.
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previous stuff=
mustang dyno 225hp 275tq
Best E.T. 13.39
Best trap 105.49

New stuff=Si trim, fmic, 3.33 pullie. Fueling issue prevent good numbers 350.1 rwhp 332rwtq rev limiter set at 5900 running out of fuel at 5400. 8psi
Best quarter mile time 12.40@115.36, stock 17s with toyo tqs.
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Old 10-14-2013, 10:06 PM
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