Compression numbers

[David Martin]

Anyone have compression numbers on a 1.8 engine..............I just found a second reference in my service manual specking 110.9 PSI.......my gauge is a good quality(almost new), BUT it has to be Furber'd up if I'm getting 190 to 200PSI.

 

[zipper]

130-135 Factory Compression Edit: low value. Should be 170+


On a NA engine I use this to get in the ballpark. 14.7 psi average air pressure at sea level. It can go as high as 15.1psi . I use 15 psi, times the compression ratio of 8.5 which equals 127.5 psi. Consistency between cylinders is important. That air pulled into the cylinders is likely under some small amount of added pressure <1 psi and not ambient, raising the compression reading more. Just my $.02.

 

[Neutron]

Anyone have compression numbers on a 1.8 engine..............I just found a second reference in my service manual specking 110.9 PSI.......my gauge is a good quality(almost new), BUT it has to be Furber'd up if I'm getting 190 to 200PSI.

That is good readings, nothing fubared at all.
110 to 150 is good for a 2 stroke

 

[FSH 210 Sport]

Something equally important is if the numbers are close to each other.

 

[David Martin]

Thanks guys the 130-135 for the SVHO sounds about right for a 11:0:1 high octane and 110.9 in my manual should be in the ball park an HO at 8:5:1 on regular gas.

Thanks again now I'll see if my gages can be recalibrated 195 to 200 on a HO 1.8 4cyl is not accurate.

 

[Neutron]

Thanks guys the 130-135 for the SVHO sounds about right for a 11:0:1 high octane and 110.9 in my manual should be in the ball park an HO at 8:5:1 on regular gas.

Thanks again now I'll see if my gages can be recalibrated 195 to 200 on a HO 1.8 4cyl is not accurate.

195 to 200 is accurate trust me i work on these things for a living. All good 4 strokes are 185 to 200 psi. That goes for a svho or ho. That is a different reading than the compression ratio. I have 3 different compression gauges they all read very close.
I think you have those compression ratios backwards, a SC engine uses lower compression pistons because of the boost.

I looked in my manuals and my boat shows 110psi for a minimum reading. And my ex ski is 128 psi minimum, and my svho ski is 71 psi minimum.
These are the very minimum to make it run. But i will tell you from experience if you are close to the minimum on any of those engines, you will need engine work soon.

Your readings are correct, or damn close to correct, trust me. You have a strong engine

Tomorrow i will be doing a compression test on an 08 yamaha sho 1.8l. I just need to replace the starter solenoid first

 

[zipper]

195 to 200 is accurate trust me i work on these things for a living. All good 4 strokes are 185 to 200 psi. That goes for a svho or ho. That is a different reading than the compression ratio. I have 3 different compression gauges they all read very close.
I think you have those compression ratios backwards, a SC engine uses lower compression pistons because of the boost.

I looked in my manuals and my boat shows 110psi for a minimum reading. And my ex ski is 128 psi minimum, and my svho ski is 71 psi minimum.
These are the very minimum to make it run. But i will tell you from experience if you are close to the minimum on any of those engines, you will need engine work soon.

Your readings are correct, or damn close to correct, trust me. You have a strong engine

Tomorrow i will be doing a compression test on an 08 yamaha sho 1.8l. I just need to replace the starter solenoid first

The compression ratios came from here, Yamaha HO and SVHO Engine Specs and Review [Chart] - jetdrift.com

Edit: Compression ratios are reversed on the two motors.

 

[Neutron]

The compression ratios came from here, Yamaha HO and SVHO Engine Specs and Review [Chart] - jetdrift.com

I saw that but its backwards. Whenever you add a turbocharger or supercharger you need to lower the compression ratio. Just ask any engine builder. That is engine building 101

 

[zipper]

I saw that but its backwards. Whenever you add a turbocharger or supercharger you need to lower the compression ratio. Just ask any engine builder. That is engine building 101

I agree. That is why I never put a turbo on my 83 Rabbit GTI after putting 10:1 cr .030 over pistons and decking the block for 10.5:1 final, cam, valves...I questioned the statement, but posted that info.

 

[zipper]

That site is wrong. SVHO compression ratio is 8.5 and it makes sence for the OP getting the higher readings than 130 at 11.

 

[Neutron]

Did a compression reading on this 08 yamaha fx sho and all 4 were around 120psi on all three of my gauges. I would have thought it would be a little higher but the ski is a litt beat up and someone put a new head on it, dont know why. Only could speculate it was a timing chain issue.
Also did my wifes EX with a tr1 and all 3 cylinders were about 195/200