If a 2.8 cologne engine has it's CR reduced from standard 9.2 to 8.,would the compression reading also be lowered? The cologne is reading 125psi with 8. CR,seems a bit low to me. The standard 9.2 CR from the cologne,is 167-181psi. Thanks
If a 2.8 cologne engine has it's CR reduced from standard 9.2 to 8.,would the compression reading also be lowered? The cologne is reading 125psi with 8. CR,seems a bit low to me. The standard 9.2 CR from the cologne,is 167-181psi. Thanks
psi and compression ratios dont directly compare, the pressure readings are effected by cranking speed (faster cranking higher reading) throttle position (wide open can give higher) plus cam duration has an effect, not to mention compression testers themselves vary, but i'd say the 125psi your seeing is about right, on a std 2.8 i'd expect so see in the region of 150-170 psi,
if you want to check engine condition a leakage test is better
ta Graham. I've just rebuilt the engine,and have had 4mmx65mm (13.27cc) dish cut out on the OE piston,as the chamber is reading 40cc,they've been skimmed I reckon. 41.55cc +/- is the original measurement.
hmmm...leakage test. Didn't know what it is,just checked and will try this.
if you have just rebuilt the engine why are you doing compresion tests? are you trying to check the engines condition or your maths/cr?
having just done a bit of maths and making a couple of assumptions for head gasket volume and the piston being a bit down the bore i'd say you do indeed have 8.1 cr
Last edited by Graham; 01-04-2012 at 09:54.
I'm doing the tests to understand why it's taking alot of aggro to get it started. The fuel seems to be drowning the spark,although I will say that I have put Capri bosch 019 injectors in,XR4i(my car) are 025,different bar rating.
This is my second attempt in renewing the headgaskets,well,the N/S bank had failed,O/S was ok. SO this is the reason for the test. I'm going up to my unit now,and will change the injectors back to 025,and check/adjust valve clearances
I've done the calculations aswell,my head is spinning just a bit
Just to add,brand new accummulator,replaced metering MFI unit. Inline fuel gauge showing 43psi
the lower compression will require quite a few more degrees initial ignition advance
right ok,thanks Graham. I tested all injectors. Some weren't performing fantastic,so I swopped them. Still,the spark is being drowned out by the fuel. I'll see if the shims on pressure relief valve might need dealing with.
I'm now evaluating whether the added dish in the piston is causing petrol to fill in it,causing the engine to flood
have you got the cold start attached??
You have probably done this loads of times but the dizzy could be out 180°
Does it sound like its catching??
sorry r2vdh I've not replied to your suggestion. I've always had the cold start injector disconnected due too much,but no change. Yes,I had checked the 180° out possibilty even though I was telling myself it is not,but tried it,and it wasn't. It does fire up eventually but requires high revs. As I had mentioned before about the pistons,I had them machined
because they are machined straight,I'd say the fuel is not dispersing and collecting in the dish. So I've angled out the edges and see from there.
i cannot imagine for one moment your problem is fuel collecting in the piston bowl due to the way its machined
Well,it's the only diagnosis can I think it'll be. I've checked the performance of the injectors
http://s909.photobucket.com/albums/a...ecterTest1.mp4
I've swopped out the bad ones for ones that are an improvement. And looking at how the crown is designed on YB pistons,the dish is concave
it is but x/flow pistons have a similar bowl as did numerous vw engines, leyland o series pistons had very similar bowl to your pic, fuel will not collect in a piston bowl unless you are hosing way way too much in.And looking at how the crown is designed on YB pistons,the dish is concave
interestingly it looked to me like those injectors squirted fuel in long after the engine stopped cranking, which could indicate a metering unit fault or a fault with the warm up regulator which adjusts the control pressure which in turn adjusts the main pressure, to check out k jet you need to measure both pressures
Oh right,that's interestingOriginally Posted by Graham
I thought the video is the last test,but is actually the first test with the original injectors before swopping them. I have a footage of the final test with improved injectors,but the footage isn't great. Although,you've pointed out that the injectors are deliveing fuel after the engine is switched off. I will add though,that I've installed a Audi 80 Warm up reg (my 4i has a turbo). But I had the same issue with the original WUR. Hopefully seafoam will clean the injectors out. Oh,and a brand new accumulator is on.
Up and running now Graham,thanks. What is baffling me is the Kjet air/fuel flow meter when turning the 3mm screw.lean is anti-clockwise and obviously clockwise is richer. As I had too much fuel going in,I naturally turned the screw to max lean till the screw stopped. I tried clockwise(richer) and it starts without a problem
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