Questions about my compression test results

[JD Cross]

First question - yes. Second question - most people don't get too upset about being a little higher than normal. Some carbon build up can raise the test results. If they were uniformly high, the compression tester could be a little bit out of calibration. If the compression tester is a bourdon style gauge which is calibrated at sea level, it will also tend to read high at Edmonton's altitude. Finally, altitude affects compression test results (beyond the effect on the compression testing gauge). I can't remember whether Honda specifies sea level or some other altitude in the shop manual. However, I expect that is not at play here unless Honda specified the compression at the top of Mount Fuji! The important thing is that the variation between the cylinders is within the limits. If the average of the numbers is closer to the 'normal' value rather than the 'minimum' value, that would also give me more warm and fuzzy feelings!

I didn't phrase my last point well.

What I meant to say is are the readings over the maximum variance allowed?

So does this mean the correct procedure is to take the readings for all six cylinders
Then if no one cylinder is below 142 psi you have passed condition #1?

Then you average the six readings and see if the variance between the average reading and each cylinder is within 28 psi plus/minus?

In QPDO's case no readings are below 142 so the first condition is met.

So now on to the averages.

In QPDO's case the average of the six cylinders is 178 psi.
The variance between the average of 178 and the high cylinder of 215 is 37 psi.
The variance of the two low cylinders and the average is 31 and 33 respectively
Does this mean in this test three cylinders don't meet the factory standard?

Sorry for all the questions but this is new info for me and I'd like to learn

 

[Old Guy]

I didn't phrase my last point well.

What I meant to say is are the readings over the maximum variance allowed?

So does this mean the correct procedure is to take the readings for all six cylinders
Then if no one cylinder is below 142 psi you have passed condition #1?

Then you average the six readings and see if the variance between the average reading and each cylinder is within 28 psi plus/minus?

In QPDO's case no readings are below 142 so the first condition is met.

So now on to the averages.

In QPDO's case the average of the six cylinders is 178 psi.
The variance between the average of 178 and the high cylinder of 215 is 37 psi.
The variance of the two low cylinders and the average is 31 and 33 respectively
Does this mean in this test three cylinders don't meet the factory standard?

Sorry for all the questions but this is new info for me and I'd like to learn

I also phrased my response poorly. You need to pass condition #1 as you described (all cylinders above 142 psi). The variation should be evaluated on the basis of the difference between the highest cylinder and the lowest cylinder. So 5 cylinders at 142 psi and one at 170 psi would technically fall within Honda's acceptable limit. My comment about average related to the fact that when you have 6 individual compression values, you would feel better if the average of the 6 is closer to the normal value (with the provision that the min and max values are within 28 psi). Average is not used when making an assessment of the condition of the engine. You need all 6 numbers and the lowest has to be above 142 psi and the range from highest to lowest has to be 28 psi or less to meet Honda's minimum acceptable limit.

 

[JD Cross]

I also phrased my response poorly. You need to pass condition #1 as you described (all cylinders above 142 psi). The variation should be evaluated on the basis of the difference between the highest cylinder and the lowest cylinder. So 5 cylinders at 142 psi and one at 170 psi would technically fall within Honda's acceptable limit. My comment about average related to the fact that when you have 6 individual compression values, you would feel better if the average of the 6 is closer to the normal value (with the provision that the min and max values are within 28 psi). Average is not used when making an assessment of the condition of the engine. You need all 6 numbers and the lowest has to be above 142 psi and the range from highest to lowest has to be 28 psi or less to meet Honda's minimum acceptable limit.

I now understand how a compression test works
Thank you

 

[goldtop]

I also phrased my response poorly. You need to pass condition #1 as you described (all cylinders above 142 psi). The variation should be evaluated on the basis of the difference between the highest cylinder and the lowest cylinder. So 5 cylinders at 142 psi and one at 170 psi would technically fall within Honda's acceptable limit. My comment about average related to the fact that when you have 6 individual compression values, you would feel better if the average of the 6 is closer to the normal value (with the provision that the min and max values are within 28 psi). Average is not used when making an assessment of the condition of the engine. You need all 6 numbers and the lowest has to be above 142 psi and the range from highest to lowest has to be 28 psi or less to meet Honda's minimum acceptable limit.

Another newbie appreciating the explanation. Plan to get my '93 car's 118000m engine checked thoroughly soon. Thanks

 

[QPDO]

Apparently my timing is fine, so now we delve deeper... time for a leak down test.

 

[Daedalus]

I would like to know how they checked. Did they really remove and replace the valve covers for free? Is there any other way to check valve timing besides verifying marks on the belt against the marks on the cam sprockets?

 

[QPDO]

The dealership has been doing a lot of work and diagnostics for free... guess dumping $4,500 on service last summer hasn't been forgotten. With that said, they have completed the leak down test with the rear cylinders having a 55/65/65% loss from the intake valves which had a 155/147/145psi compression. The front bank that had 215/205/200psi compression had ~5% across the board. Time to rebuild a head... balls.

 

[tof]

Well at least you confirmed an old adage. The fact that you didn't really notice a performance loss just proves once again that two heads are better than one. *groan*

 

[QPDO]

Now the question at hand is:

Do I rebuild the rear cylinder head with new OEM parts and leave the almost perfect front cylinder head alone?
Do I remove and rebuild both cylinder heads with SOS bits even though the front bank is near perfect?

 

[Nero Tenebre]

Just rebuild both so you have more protection if the labor is not that much more. I would imagine most of the cost is already built into having to pull the motor and not so much the work done once out.

 

[BATMANs]

Just rebuild both so you have more protection if the labor is not that much more. I would imagine most of the cost is already built into having to pull the motor and not so much the work done once out.

This.

And since u have the heads off why not do some upgrades and slight mods:

Port smoothing/clean up
Upgrading the valves to Ferrea undercut forged
Upgrading to cometic head gaskets

 

[QPDO]

Looking into the service manual, I don't believe they need to pull the engine. Can anyone confirm this? If my front bank is still perfectly sound, what 'protection' will I gain by rebuilding it to the same factory specs it's currently at? I'm not adamantly opposed to rebuilding both if the cost/benefit makes sense.

And BATMAN, would forged valves and port/polishing the heads be worth the extra cost if I have no future plans of power upgrades? Upgrading both head gaskets would be nice piece of mind though.

 

[BATMANs]

The cheapest price valves that I got was on Ebay.

For me the additional cost of the Ferrea valve outweighed the potential grief if I mis-shifted or if the valves just busted on their own demise, bounce around in the combustion chamber or worse, punch a hole through the block if the RPMs where high enough.

https://www.google.com/search?q=bro...&biw=1920&bih=1019&sei=gvDvUfq7J42TiAfJuoDQBQ

So it's really just preventative costs.

The other way of looking at it is that since it's lighter there are less parasitic power loss. That not only means more available or free power, but also should translate to better MPGs, which no one will ever complain about.

You taste in power upgrades may change down the road. That being said, why not have ur heads ready to support additional power.

By doing a 3 angle valve job I've been told that it's around a 12% improvement on flow across your entire RPM range. To me this translate not only to more power, but also more power down low - where the NSX needs it most IMHO.

No need to polish the heads. I just do a port clean up, sharpen the vanes that divided into each of the separate valve ports. More often than not when the valve seats are cast into the aluminum heads they are not flushed. This creates flow issues like vortexes, turbulence and poor distribution of the A/F mixture to the combustion chamber.

By doing the port cleanup and cleaning up the cast to match the valve seats there should be greater port velocities since less interruption in flow. All of this translates to greater efficiency and more power.

In the production of our "one piece forging valve," the head of the valve is forged under a slow two-step process to avoid damage to the material structure. The forging piece is then machined entirely to eliminate any imperfection from the forging operation. Next is triple heat treatment, the stress-relief process, the grinding, and then the coating. Finally the valve stem is rolled to remove the rough scale and any gross imperfection on the surface. Ultrasonic tests and x-rays are then performed piece-by-piece to give each part a certified quality....

Ferrea came out with Hollow Stem Lightweight Valves years ago revolutionizing the stainless steel valve market with a 22% lighter than your conventional stainless steel alloy valve. Made from exclusive Super Alloy materials, which they resist heat much better then conventional Inconel materials. Ferrea Hollow Stem Lightweight Valves are available in 7mm, 5/16, 11/32 and 3/8 stem diameters as well as semi finished blanks that we can machine for you application. Get the best in Valve technology today for your Race Engine!!!

 

[Nero Tenebre]

Great post Batmans.

 

[BATMANs]

Thanks honey.

BTW, to the OP:

I selected the strongest solid stem undercut valves for the job. I needed strength and longevity.

It's still lighter and MUCH stronger than the OEM valves - and being undercut they flow better.

What makes the Ferrera undercut valves better than the other brands is that the undercut is actually forged squeezed, not cut to size.

This preserves the metal grain and since there is no loss of metal material (since nothing is being trimmed away) it's strong as hell.

It seems to be a popular valve for some of these 1200HP MKIV Supra folks.

 

[QPDO]

Thanks BATMANs!

 

[BATMANs]

Anytime.

Just be prepared to do piston replacement if the valves and pistons "made love" :biggrin:

 

[QPDO]

BATMAN, when you rebuilt your heads, did you replace the valve springs, LMAs, and all those tidbits as well? Approximately how much did it all cost you?

 

[latzke]

This is not about your current symptoms, but given that you over-revved you may have compromised the integrity of your oil pump gear set. Look into replacing the oil pump gears with new OEM or aftermarket billet (like from SOS).

I would hate to see you get past/correct this current issue...only to have your oil pump gears shatter and take out the whole engine.

 

[BATMANs]

BATMAN, when you rebuilt your heads, did you replace the valve springs, LMAs, and all those tidbits as well? Approximately how much did it all cost you?

I kept the OEM valve springs since they were inspected and all measured at around 90lbs of spring pressure, which is pretty low (the lower the less parasitic drag on your power). The springs are double springs (which I wasn't expecting in a car from the '90's).

I forgot, but I'm 99% confident that I had the LMA installed since it's cheap. The rest of it I re-used the parts.

- - - Updated - - -

This is not about your current symptoms, but given that you over-revved you may have compromised the integrity of your oil pump gear set. Look into replacing the oil pump gears with new OEM or aftermarket billet (like from SOS).

I would hate to see you get past/correct this current issue...only to have your oil pump gears shatter and take out the whole engine.

You are correct. I forgot about this and looking back on my engine build, I should have just replaced this.