8 bar of pressure on 3 cylinders

Jorge_EETC

Jorge_EETC

Hi guys, just did a compression test on my cg13 as it seem to have low power. It's enough to go up to 160 170ish km/h but seemed weak


Compression test results:
-Cyl 1: 8 bar
-Cyl 2: 6 ish bar
-Cyl 3: 8 bar
-Cyl 4: 8 bar

Bare in mind that it has a 1mm head skim, should be over 13 bar for sure!?

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the 1mm skim will make the inlet valves close slightly later if not corrected
and throttle needs to be fully open
and compression will be lower on a 20yr old engine
 
UPDATE

did the test again but with the tb fully open, and the pressure slightly raised and now all cylinders have the same pressure.

Cyl 1: 8.5 bar
Cyl 2: 8.5 bar
Cyl 3: 8.5 bar
Cyl 4: 8.5 bar

With oil the pressure slightly raised do almost 9 bar.

Any ideas?

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the inlets should close at about 42 deg abdc
worn chains will retard that by 5 or 10 deg, and the skim will retard the closing by about 5 deg too
you need to check the piston height at that valve closing point ideally, i used to do it by rotating the bucket when free from the lobe
if the valve closed at bdc then in theory the compression should be 9.5 x 1 bar (or 10.5 in your case)
 
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So if my back of napkin maths is correct it's 60 degrees ABDC that the valve is closing or 1/3 of the stroke in terms of angle, but that's not the same as the piston, so I figure the piston is 1/4 The way up the bore as the valves close.
0.75 x 10.5 = 7.875 so 8 bar is pretty close.
 
But with that logic, Standart pressure should be 9.5 bar, but heynes manual states 13.2 bar (standart)

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And how the hell skiming 1mm reduces compression ratio?

*Edit
Only now I realised we are measuring dinâmica pressure (that takes into account camshaft timing), and according to this calculator it should be 8.95 bar with 1mm skim and 8.14 bar standart....

But what about the heynes manual?????? It states 13.2 bar standart

Calculator -> https://www.gofastmath.com/Compress...atic-And-Dynamic-Compression-Ratio-Calculator

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you should get some extra heated air pressure, and cram some more pressure into the gauge by continually spinning on the starter
but the VE will be nowhere near 100% tho
if you run the 1.0 valve closing timing of 18 deg abdc (advance the cam) then you might get near that haynes spec
 
How many times do you turn it over, usually the readings will jump up on each turn, needs about 5 or 6 to get it stable.

I've always wondered if the first one is closer to the real value since you get more heating effect as you go on turning it over.
 
Jorge_EETC said:
Each teeth on the sprocket will change the timing by how much degrees?

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Click to expand...

31 deg maybe ?

Adjustable Cam Sprockets

Been randomly looking around at cam sprockets and the ability to advance / retard the cams. Just been looking at Mulhollands and Aspect Racing's adjustables... Mulhollands http://www.mulholland-rp.com/etc/sproket.jpg Aspects http://aspectk11.web.fc2.com/CA5DEE9O1.jpg Now Mulholland dont...
www.micra.org.uk www.micra.org.uk
 
But with no skim and standard camshaft timing, should it do those 13 bar of heynes manual?

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