How To: Increase Compression Chamber Pressure

[TheIVJackal]

I have a feeling my compression may be a little low on my car from wear put on by previous owner, with that said, what are some proven ways to increase combustion pressure? How well do products like Restore or other engine oil additives work in increasing the pressure permanently?
Second, if the problem is instead carbon on the top of valves, what are some proven ways to remove the carbon? I've heard of spraying water into the intake but how much and at what rate? Videos would really help in this process!
Thanks.
- Aaron

[Cobb]

When I use to screw around with lawn mower engines as a kid we used glumps of wheel bearing grease to take up displacement in the head to bump the compression. I dont know if it worked, but it seems like a good idea.

Basically you need to make the room smaller or pack mo air in it. You can mill the head, deck the block or used force induction.

[razor02097]

Rent, borrow, beg or buy a diagnostic vacuum gauge. Hook the gauge to a manifold port directly on the intake manifold and start the engine. Allow the engine to warm up and stabilize. The reading should be over 20" at a warm idle. If the needle isn't steady or the reading is low it could indicate a problem.

Here is a resource for you about reading a vacuum gauge.
Tips on Reading Gauges: Vacuum Gauges


If the vacuum gauge indicates a problem or you wish to further check the health of the engine the next step is to acquire a compression gauge and get an actual reading on all of the cylinders.

Hook up the gauge by removing all of your spark plugs . Install the gauge to each cylinder and hold the throttle wide open while cranking the engine over. You should be able to listen for a lumping as the cylinder with the gauge pushes air in to the gauge. Wait for 5 of those audio indications then stop cranking and check the gauge.

Write down the compression number for each cylinder and get a calculator out. Each cylinder should not be more than 10% away from the highest number. Low numbers for all cylinders typically indicate a worn out engine or incorrectly timed camshaft. If you have low numbers repeat the test on all cylinders but add a tablespoon of oil in each cylinder before installing the gauge. If the numbers rise a lot you most likely have worn out piston rings. If there isn't a significant rise in compression your issue is likely valve train related or blown head gasket.


Evaluating the health of an engine using tools you can use at home isn't very expensive but it will take research to understand what the numbers mean. The rule of thumb is even if the compression is lower... if the compression readings are within 10% of each other and the engine runs okay it means the engine is just tired and the only option is rebuild or replace.



As far as raising compression. Take this how you will. Surfacing the head will reduce the size of the combustion chamber which will increase the compression ratio. Using pistons with a different profile can also increase compression. Neither way is a fix for worn out piston rings. Once an engine is torn down to the point the piston leaves the cylinder the minimum is piston ring replacement and honing the cylinder. Expect the new rings to not last though. Cylinders over time will wear out and require them to be bored and honed. Though not by much boring a cylinder doesn't necessarily mean you are going for increased power it is to square up the cylinder again to make a good surface for the piston to travel in.

[nbleak21]

Razor gave you a lot of great advice, I just wanted to mention in addition to removing all of the plugs when doing the compression test, be sure to disable the EFI (pull the fuse) as a safety measure... It is also good practice to disconnect the ignition coil(s), as on some models, they can easily burn out.

[TheIVJackal]

I know how to check vacuum and use a compression tester. My question is for a simpler fix for these problems such as using Restore or other products that claim to fix compression problems. Also, how to remove carbon from the back of i/e valves by either putting something in the gas tank or spraying something directly into the throttle body. Thanks.

[razor02097]

Great


Are there any products work to restore compression? Simple answer is no.

How do you remove carbon from the combustion chamber? There are many ways including the water trick you mentioned. Here is an example of it being done.

www.youtube.com/watch?v=UXetbuEFLvM

Many many many people use a product called seafoam. The instructions for use are on the can you just allow the engine to suck it through one of the vacuum lines.

I use a kit from 3M called the fuel system "tune-up" kit...

www.youtube.com/watch?v=RX5J5kZLTw4

[Daox]

If you have low compression and free up any carbon build up, you're only going to make your low compression worse. Chances are that carbon is helping keep compression up.

[TheIVJackal]

He poured a crap ton of water into that car! Wasn't expecting it to be that much. Thanks for the tips, if I end up doing any of this ill try to post any results.

[D.O.G.]

A relevant post from a thread about catch cans early last year.

Originally Posted by D.O.G.

When I was driving "BoB" as my daily, I fitted a catch can (home made) because of the amount of oil coming through the PCV.
I later fitted a basic water injection system (also home made) to clean carbon from the combustion chamber and rings.
It restored some of the power and fuel economy the engine had lost over the years (over a few weeks), it also stopped the engine dumping so much oil out the PCV.
I'd been draining 15 to 20 CCs from the catch can every couple of weeks. After the rings had freed up (I guess), I only got a few drops out of the catch can.

Cleaning out carbon (that may be causing your rings to stick) won't restore compression in every case, but it's cheap, it's easy and it worked for "BoB" (now retired).

[3-Wheeler]

Originally Posted by Daox

If you have low compression and free up any carbon build up, you're only going to make your low compression worse. Chances are that carbon is helping keep compression up.

It's still a good idea to get rid of excess carbon, as it can glow at high throttle settings and pre-ignite the combustion gases before the spark has a chance to.

Jim