Compression? What Does This Mean?

[SlowWhite]

Ok a few months ago (probably 6 or 7 by now) Josh, Mike, John, Ryan I believe all have seen that my car's compression was around 155 on all 4(after 5 turns of the motor)

Now I can't remember if I had the 99 head swap done then or not.

We ran into some issues on the dyno and apon doing a compression test:

Tried 2 different compression Testers: (8-15 turns of the motor)
1st one)
-192 across all 4

2nd one)
-189-192 across all 4


Stock Max compression on a 2G is supposed to be what around 172ish?

Does this mean that my motor might be seizing up? (hopefully not crankwalking!)

Both on the dyno and on the Street I am not able to tune for a good power A/F. Due to the Car Knocking apon trying to lean it out?

I'm hoping to hit the dyno next week with Race Gas. To see if the knock sensor is bad. (I'll also be bringing my spare knock Sensor just in case)

Is the high compression part of the knock issues?

I ran the car almost completly out of gas and then filled up with 93 oct yesterday and did some more logs. With little improvement.

Basically if I Lean out the car anymore then 10.5:1 A/R the car knocks to where I have to back off the gas.

-brian

[LightningGSX]

If you swapped heads, it wouldn't be suprising to see a increase in compression.Especially if you had deck work done.

[SlowWhite]

It was a completely stock 2G head that came off Andy Nash's 2G. except for the HKS cams

No work was done to the motor or the head.


-brian

[1ViciousGSX]

If I remember correctly, that's in the same range as my 2g when I checked about a year ago. I'll look it up and post what's specified by Mitsu shortly.

It definately does not indicate that your engine is locking up, just good compression.

What problem were you experiencing on the dyno anyway?
If it was knock coming in I would check the base timing.

[SlowWhite]

Shane checked the timing marks and everything looked Ok, he swapped out several of my sensors, spark plugs, etc

The only thing we didn't do was the knock sensor itself. (maybe next time, as I have a spare)

Coming in with everything Zero'd at 20psi. 266whp@20psi with some rediculiously rich A/R (like 9:1) to rich to gas fumes were burning my eyes :headache:

After Next run Shane got it to around 290whp.

All in all I think we did 4 runs at 20psi. Top number was like 303whp but knocked to much so we had to shut it down early with out finishing the run.

After that was when we lowered the boost. and started swapping parts, etc.

Funny thing was when we lowered the boost we made just about the same HP as 20psi. But were still knocking (only now at 3 counts instead of like 5+)

In the end we gave up at like 1am, with a 10.5:1 A/R (at it's best A/R) 17psi and almost no knock (.04) making 280ish whp. (as you can see we didn't even start to get into a normal tuned A/R range)

We hopefully narrowed my problems down to 2 things:
-Bad Gas
-Bad knock sensor

I'm trying to schedual a time to get back on the dyno but this time with C-16 that way I know it's not the gas. and I'll bring my spare knock sensor. Plus another 02 sensor to replace the one that shane gave me.

Mine broke while trying to set the LTFT's. (wire broke right at the plug some how so there's no chance of fixing)

All and all it was a very long night. And I have to thank Shane, Moe, Tyler for helping me work on my car for so long that night. Plus the other 4 nights of running around getting parts to install my GTR FMIC and what not.

Sorry for the hastle Guys I really appreciate all the help and late nights you stayed and allowed me to work on my car.

[npaulseth]

I just read on FAQ yesterday that the compression is supose to be no higher than 178, and no lower than 133 for an engine with 8.5:1. It also says that is should be no higher than 164, then all the way down to 121 for the low for the 7.8:1.

[SlowWhite]

That's what Shane said also.

We even checked with moe and that's what he said.

We have no idea why it's so damn high. I'm stumped.

I thought I heard that higher compression is possible if the rings or motor is about to seize up? is that true?


I really don't know what's going on. Everything when it comes to the car seems to be in place and acting properly.

I spent alot of money this year revamping my set up and the car. To get it back up to par.

Mods done with in the last 1500 miles of driving:
-ACT 2600
-Tranny
-Xfer Case
-99 Head
-Head gasket
-ARP head studs
-Belts
-Tensioners
-Magnus SMI
-1G TB
-2.5" I/C piping
-GTR FMIC
-FIC 850 INJ
-Re-wired Fuel Pump
-Tranny Fluid
-Oil
-Thermostat
-Exhaust manifold Gasket
-Intake Manifold Gasket
-TB Gaskets
-Removed A/C system
-Working on new Suspension System
-DSMLINK V2
-Optima type 51 Battery
-Alternator -replaced at time of tranny swap
-Cam Angle sensor
-Crank Angle Sensor
-02 sensor
-TPS Sensor


probably a few other things I'm forgetting (sensors wern't new, but at least known to be working)

[npaulseth]

Good lord..... I used to go to highschool with your G/F. I've seen your car at elite about two-three years back when you had the GS-T. She was telling me how you have gone through like four or five trannys in a few months. I also saw you at rock falls, totally stripped out. The only run I saw you do was like a 13.8 I think? Like your car, well, your old one. Good luck to you on your problem. Noah

[SlowWhite]

If I ran a 13.8 at Rock Falls. Then that was either the day I ran 13.6

or the day I ran the 13.1 every other time I was in the 14's or 15's.

And yep 14's and 15's because I'm a chicken Sh_T and didn't want to break another Damn FWD Tranny.


Now onto the AWD's and I have to say just from a tranny aspect. I couldn't be happier with the swap.

Now if I can just get a tune down. I'm good to go.


Another ? - could the turbo be causing my Knock? it's the HRC S20G with about 50K miles on it.

Zero shaft play - (well besides the normal play that comes from HRC) - with a few slightly nicked up fins.

could the nicked up fines cause it to be out of balance and possibly cause a vibration which in turn causing knock?

-brian

[1ViciousGSX]

Normal compression psi for a 2g is 176psi. This is not a max or exact requirement. Compression can go up or down based on head gasket thickness, machining of the block deck, machining the head surface, camshaft profiles and cam timing, so I doubt you have a mechanical problem to wory about.

[Shane@DBPerformance]

It just doesn't make sense. I don't know why the compression is so high, we tried 2 testers and both were higher than factory spec. I am sure his rings have some wear and the aftermarket cams should lower the compression a tad also. His ARPs aren't cranked down crazy high either. When we do a boost leak test there is a fair amount of air coming out his breather hole like boost is getting past the rings. We also had a lot of oil blowby in his catch can after dynoing. So I am not sure how with those signs pointing to wore rings we also have 185+ compression.

We pulled the valve cover off to make sure the rockers, cams and lifters looked ok, we didn't see anything out of the ordinary. A lifter could still be failing us at higher rpms though.

We tried every combination of stock timing, more timing, less timing, very rich, somewhat rich, and normal A/Fs. We could only keep the knock down by either running a somewhat rich A/F of around 11.0:1 and pulling a lot of timing out of the stock maps or by running stockish timing but with an extremely rich A/F on the edge of misfiring. It's not like we are trying to run some crazy amount of boost with a poor setup. He has a decent sized turbo, with a good FMIC, big i/c piping, sheetmetal intake, big injectors, etc and we are only try to run 17psi creeping to almost 19psi. I don't think we can blame the knock sensor, unless its just way too tight or something. We can make it knock less by tuning, so it isn't just picking up random noise, but the A/Fs and timing we need to run to make it not knock are nowhere near normal. There were some old logs from around October that John Lacroix had done and he was able to get away with adding a fair amount of timing and running higher boost with very little knock. If we tried to run those setting now, the motor would probably blow up. Maybe it's just bad gas or the gas tank is full of crap.

[1ViciousGSX]

I'll take a look at my compression readings from my 2g with the HKS 264/264 cams tomorrow (Saturday) when I'm back at the house and post them up. I think they were in the same range as yours or at least higher than stock

[SlowWhite]

The car sat with out being run for almost 3 months in my parents garage.

Up until basically the day before bringing it to Elite. The car was near empty of fuel.

I filled it 3/4 of the way full of 92 oct right before driving it up there.


By the time we called it quits for the night there was less then a 1/8th of a tank of gas left?


Anypossibilities it was condesation in the tank or what ever happens when left almost empty in cold weather?

If so how do I fix?


-brian
ps: Shane anytime you can get me back on the dyno with some weather it's pump gas or Race Gas. Just let me know. Ready anytime

[MustGoFaster]

Carbon buildup?

[1ViciousGSX]

I didn't notice a fuel pump in your mod list?

[SlowWhite]

That's the other thing we were thinking it might be?

Like I said we're trying to figure out the knock and I'm trying to rule out the high compression as being the cause.

-brian

[SlowWhite]

Walboro 255 Re-wired.

It's a complete build up. (besides internals)


Ported 2G mani
HRC TD06 S20G with 10cm exh housing
2.5" 02
3" N1 downpipe/exhaust
99 Style head
HKS 264/272 cams
2.5" short route I/C piping (thermal wrapped)
Apexi GTR FMIC
FIC 850 inj
1G TB
2G Magnus SMI
ARP's
Walbor 255 Re-wired
Optima Type 51 Battery
DSMLINK V2
ACT2600 (for some reason the engagement point is near the top, usually near the bottom or middle)

[JET]

What head gasket did you use? You can get a cometic that is thinner than stock. Maybe you got that?

[npaulseth]

Head gasket shouldn't raise it much more? Also, didn't he do a test after the head was installed and got 155? Maybe I'm wrong or misread something. That's really weird though.

[Raptor]

I would agree with Ryan that carbon buildup is possbily the problem. It can effect static compression a lot more than you might expect. Also it could be responsible for the excessive knock as it creates hot spots and in many cases pre-ignition.

That and maybe try a third compression tester or verify the ones you have on another motor.