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tl;dr: They do. It's just harder to tell how much. The longer answer is that they do and that effective compression is failing you as an approximation for actual effects. Think about detonation (AKA premature ignition of the fuel-air mixture). Normally we consider two causes: compression (the change in the space enclosed by the cylinder as the piston ...


4

One of the reasons that a turbo setup with the equivalent effective compression is more forgiving of low octane gas than than a static compression setup is that you're not at that compression ratio all the time. Take that honda, for example. At 9:1 static ratio, you can run 87 octane all day as long as you don't push any boost at it. When you do start ...


3

Wow! Textbook case of worn rings. The oil helps seal the ringland area. That's a large increase on cylinders 2, 3, and 4. Your fuel efficiency should be pretty poor with those compression numbers. Is it? If your fuel efficiency is miserable, it's time for a rebuild. Depending on the car it might be cheaper just to replace the engine with one from a engine ...


3

Measure each cylinder and buy over sized pistons / rings to accommodate the sizes.. this will be your cheapest option because installing new liners and buying stock pistons is very expensive / allot of machining work. If you don't have the time or money, keep driving it the way it is - if its not smoking bad you should get another 35k or more off of it.


3

Yes, a warped lower end can affect the compression test. A seriously warped head of block can lead to compression leakage through the small space between the head gasket and the head or block. But I don't think you have a bend block, I suspect you used your old head with a new head gasket? You need to have a specialized company 'flatten' the head. I don't ...


2

In addition to good answer by @Bob: There are some tricks that can be used to ease the problem: A knock sensor for detecting premature detonations (and adjusting boost pressure). E.g. Saab APC allows safe use of lower octane fuels. Injecting water to cool the combustion chambers (instead of excessive fuel) Per cylinder exthaust thermometers (and ...


2

To make sure I answer correctly let me make sure I understand the question. The engine was using 1.5 L of oil per 2000km, you did the following repairs to the engine: Valve job including replacing the exhaust valve. Bored the engine 0.5mm over New 0.5 mm over piston and rings Now that the repairs have been made it seems to be fixed. It's running well and ...


1

Oil on the spark plug is likely either because the piston rings are not sealing or the valve guides are leaking oil. Both could also be related to low compression. You could either have ring seal problems or a valve that is not seating properly. Valve seat problems could be due to physical damage or carbon build-up coming loose. Guess at what is most likely ...


1

There's a wide variation, but back in the '90's it was clustered in the 10-12psi range for a typical 4-cyl turbocharged performance model. Nowadays 16-18psi is not abnormal for high performance factory cars. Of course, you'll find some economy cars in the 5-6psi range, where they're using boost to let a little tiny fuel-efficient engine not be completely ...


1

This question doesn't provide enough information for us to answer it well as originally written. Some of the important factors determining what boost level is used include: Base compression rate of the engine (see this question for related discussion). Octane of the fuel to reduce the risk of detonation (see point 1). The temperature and humidity of the ...


1

If the bore has been honed and rings replaced then perhaps the issue is with the valve stems. I once had a CBX250 bike that blew a lot of smoke. It was a 4-stroke, like yours. In the end, it turned out the value stems were leaking oil into the cylinder. Does your bike produce a lot of smoke?



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