What should my compression be?

[Momar]

I have a 6 bolt that I was told the bottom end was just rebuilt. I put the top end together myself so I know it is fresh. I did a compression test and got right around 140 across the board. Is that about right?

 

[agentorange313]

I think it should be more

my compression test was 156-158-150-153

Also it depends on the pistons used in the engine, if you have a 6 bolt that was rebuild it should have the 7.8:1 compression ratio. I also have stock internals

compression test should be greater with a high compression ratio

goodluck

 

[wdawson4]

The only compression test that I have done was 160's across all 4 cylinders from what I read about everyone else u def have low results do u have any clue what pistons where used when the bottom end was rebuilt....

 

[JayRolla]

I believe 140 is the service point but if they are all close and its running fine I wouldnt worry about it.

 

[Jrock11]

When I did a compression test on my 2g it was right around 152 with just a few cranks

 

[thomcasey]

I have a 6 bolt that I was told the bottom end was just rebuilt. I put the top end together myself so I know it is fresh. I did a compression test and got right around 140 across the board. Is that about right?

Since it is a fresh rebuild, they might be a little lower until the rings seat.

 

[tjbiker031]

did you test it cold or hot?

 

[Momar]

The motor has stock pistons. The car has only been drivin about 30 miles since it was done. I am hoping that if that is low that the rings just are not fully seated. That was tested hot. I thought I remembered reading that 121 was the service limit or something. I will try to search it again.

I found this:

1G (90-94) T/E/L 2.0L Turbo engine
Compression ratio 7.8:1
Standard compression 164 psi
Service limit 121 psi

So I guess it is definately lower than what you would assume it should be new but is above the service limit. I am going to check it again when I have some more miles on it. Like I said, I only have about 30 miles on it since I got it together. Also, when I first put the head on the compression was low enough that the car didint want to start. 60-80 on all cyls. I ended up putting a little oil in each cyl to give it enough compression to start, and it has started every time since, and the compression has come up to 140ish(up to 145 on one or 2 of the cyls). Maybe the rings will finish seating and it will be fine.

 

[JayRolla]

How are you breaking the motor in? How are you seating the rings? I know my engine builder has always have me run 10psi during break in and everyonce in awhile you go WOT to around 5000rpms at most just to help fully seat the rings and fight blow bye.

 

[Thomas91169]

1) was this compression check done with a warm motor or cold motor?
2) how many miles since rebuild?

 

[cookmeup272]

1) was this compression check done with a warm motor or cold motor?
2) how many miles since rebuild?

if you read it, it was done hot and 30 miles

 

[khomza]

as long as all 4 are within about 2-3 lbs of each other your ok.

 

[Momar]

as long as all 4 are within about 2-3 lbs of each other your ok.

They are all real close to each other, and it runs good. I will recheck the compression after I get some more mileage on the engine.

 

[my dreamt dsm]

It should be good. As long as the compression is within 4% of each other.

 

[Momar]

Cool hope so. Still going to test it again after I get some mileage on it just so I know if it changes.

 

[luckynumber5]

If it only has 30 miles on it and the numbers are close by I would just recheck it down the road. Best of luck

 

[rinmancustom]

Hey I'm going to school for auto mechanics and just had a class on compression tests. Okay this is what the shop manuel says. what ever your # is it has to be 75% within spec of that number. There is no magic number. it just has to be with in 75% of that #. Best thing I did learn always have a battery charger hooked up when doing a copression test.

 

[jrohner]

They might have used a thicker-than-stock head gasket, which would lower the compression too. I think both my 1G's were at 145psi.

 

[kawgomoo]

your rings are fully seated by the time your motor is completely assembled. this i guarantee.

if your compression is low, it either a by product of engine wear, poor rebuilding or low comp pistons.

thicker head gaskets ARE STUPID. they lower the compression by destroying the QUENCH AREA which is absolutely vital to having your motor not detonate.

that about covers it. as long as the cylinders are even i wouldnt sweat it.

also, did you make sure the throttle plate was held wide open while doing the comp test?

a little squirt of oil in the cylinders will tell you if its the rings not sealing...

 

[Momar]

I did not hold throttle open. The rings definitely were not seated by the time the engine was assembled. Compression was only 65-80 after i installed the head. After I got it started and ran it some it came up to this. Guess I will see if it comes up any more or not. Either way I think it will be fine.

Would holding the throttle body open make a difference?

 

[asrdave]

with a compression test you are supposed to hold the throttle open

 

[Hubbell91Tsi]

at 0 miles my engine cold cranked 150 across the board. 2700 miles later its at 205 across the board . If the car runs fine i wouldnt worry about it until its an issue. My junk isnt close to stock though.