Compression test results

[bigwheel]

I just did the first compression test on my 2000 7.3l. and looking for you guys to help and give me some feed back on the numbers I got. For this first test the motor was cold around 55 degrees and hasn't ran in a couple of days. Also I live right at 8000 ft so elevation which will play a little part.

Cold test #1
1-282
2-270
3-280
4-285
5-290
6-265
7-280
8-283

These numbers seem pretty low to me, but what I was suprised about was they are all right around the same area no big changes on one. Right now I have the truck pluged in trying to heat it up for a couple of hours. I will do test number 2 with it some what warm. What do you guys think about these numbers?
Thanks for the help

 

[CSIPSD]

Even at 8000k that is very low. At 3500k mine was at 320-330... And I was told that was bad... 35,000 miles later its still going!

 

[bigwheel]

Ya for sure, I was thinking anything at this elevation 310 and up is ok but I might be wrong.
Couple of things I left out was the truck has 146,000 miles I am the orig. owner. The truck has been stock untill about 6 months ago when I did 160/80 and 38R. Let me know if any details I am leaving out.

 

[Magnum PD]

What air filter did you use? Please don't say drop in K&N.

 

[bigwheel]

haha, No I didn't use a drop in k&n. It was stock paper style for the first 3 years and then I went to a AFE stage 1 ever since.

So I let the truck sit with the block heater pluged in for 3hr and did the same test with different results.

Test 2 block heater 3hr
1-300
2-280
3-330
4-300
5-302
6-275
7-300
8-298

So they all came up a little but still not great. The gauge I am using is the Ford Rotunda.
All glow plugs are out while doing this. I do notice a white hase coming off the gp ports when the truck is cranking. I put my hand over the port and has a strong diesel smell. Thanks

 

[Tom S]

I decided to do a compression test today while I was installing my injectors. I borrowed a gauge from Shoebear (thank you very much). I live at about 5800ft so the numbers are a little lower than normal.



1-350

3-350

5-340

7-350



2-335

4-340

6-340

8-340



The one glitch I got was on cylinder number 7. The intial couple of times I tried that cylinder I could only get about 220psi. I was about ready to be very ticked cause I know that is a major problem. I was wondering about the copper washer falling off, a cracked piston, bent push rods and all that kind of stuff. I was pretty darn sure I had the gauge sealing good. I finally hooked it up to blow air into that cylinder to see if I could hear where it was coming out. I could hear and feel it comming out the exhaust even though I thought it was in a position where the vavles were closed. I messed around a little more and tried the test again. This time she went to 350 and I felt a ton better. Any thoughts on what was going on here? The only one I can think of is a little piece of carbon from a glow plug or something holding the valve open just a hair. I sure am glad it was OK though.



Tom

Found this on the web

[ QUOTE ]



There are some variables that affect the readings obtained from compression testing. They are cranking speed, altitude, temperature, worn camshaft lobes and high-performance, long-duration profile camshafts. The cranking speed needs to be maintained the same for each cylinder. This may mean jumping your battery to maintain the speed. There are factors to compensate for the different altitudes and the corresponding temperature differences. These are as follows: 1,000 feet = .9711, 2,000 feet = .9428, 3,000 feet = .9151, 4,000 feet = .8881, 5,000 feet = .8617, 6,000 feet = .8359, 7,000 feet = .8106, 8,000 feet = .7860. The equivalent compression reading for a cylinder that should be 135 psi by the data at 5,000 feet would be 135 x .8617 = 116.33.



[/ QUOTE ]



420psi X .84 = 353psi

400psi X .84 = 335psi



So maybe mine is pretty close?

I see you found the information. I went through this many year ago trying to calculate the correct compression reading on a porsche I modified. The correction factor for altitude is basically the ratio of the atmospheric pressure at whatever altitude you happen to be at to sea level atmospheric pressure. At 5000 ft. the pressure is about 12.5 PSI, can't remember the exact number, and sea level is 14.7 PSI.



As a side note: Now, if you put a modified cam in things get a little more complex. You need to know where the intake valve closes after BDC and calculate from actual displacement ratio rather than specified compression ratio. I've seen worn cams show anomalously high cranking pressure.



Your truck's compression looks prety good.

Somehow google found this for me Kevin. That was at my house 5700 ft on a cold motor.

 

[golfer]

nice find Tom.

 

[Tom S]

nice find Tom.

I was hoping you would look at this. Any thought of Kevins results? I thought it was interesting on how much his came up with it plugged in for a while.

 

[Blowby]

All the cylinders are pretty close. I'm not sure what problems you're having with lower than normal compression but you can tune for it. Post the issues from your other posts so we can see where you stand at this point in time.

 

[Tom S]

He has a bit of a hazy idle for one and this was the truck that does not want to make more then 2000psi if you stab the throttle was the main part I recall. Mike have you ever done a compression test at our altitude?

 

[Blowby]

Yes. With my normal compression ratio engine I was about 340-345 warmed up.
Haven't checked my current build but after the rings seat I will. I'll guess I'm at 290-300 warmed up but the stage II cam might alter that.

 

[bigwheel]

Awesome thanks guys,
I installed some 160/80 stage 2 injectors about 6 months ago and this is when I started noticing a good amount of white to blue smoke at start up. It has a strong fuel smell at idle doesn't matter the temp. Like as Tom said right now the truck will only make 2200 psi if I stab it, and close to 3000 if I slowly roll in to it. Right now I am doing new injector o-rings and will put it all back together and see how it runs after. Any thought on what else I should look at? Thanks

 

[Blowby]

I'm visualizing the maps in my head and the fix is in the tuning. Think about the "stabing the throttle" and what's going on with the the ICP, Boost, PW and MFD per RPM rate of increase. Talk to your tuner so he can resolve this as well as fuel quality at idle.

 

[stroker2]

For reference, my truck tested out at 310-340 across the board at almost 7k ft of altitude and it fires right up when cold or warm, doesnt haze at idle unless its cold, and runs great

 

[bigwheel]

So I installed the new injector o-rings 2 weeks ago and got some seat time over the weekend. About 400 miles. Seems like the truck might be the same with a lot of white smoke at first start. It will burn your eyes if walk into it. So a lot of fuel. Temps might be a little less by 50 and at the stab of the throttle the truck still falls on it face. Any thoughts? I am going to install a different IPR this week and see where we stand.