Compression after rebuild.

[rruser]

What kind of warm compression numbers are you guys seeing on fresh OEM top ends? I did a hone/re-ring on a really nice used 2003 top end. STD sized Yamaha piston with new Yamaha rings. I'm showing 155psi warm with about 5-10 mins of break-in time total. The head was not decked per-say.. but was slightly resurfaced. Around .006-.010 taken off the head due to the previous owner's screw driver usage.:argh:


Should I just take it as a free high-comp upgrade and run 93 fuel? or throw a second base gasket in there? Also, i'm not sure if its the break-in or the use of 87 fuel, but the header gets pretty warm. It's a budget rebuild for a friend so I want it to be a good runner. :atv:

Thanks

 

[rruser]

I thought I would answer my own questions.. maybe it will help someone else out. :nanner:



1) The compression... either my compression gauge is messed up or the values stated in most of the manuals are wrong? My 100% stock and well cared for 2003 warrior shows 170PSI with the throttle wide open. Around 120 with it closed. I'm 99% sure this brand new Snap-On gauge is wrong.

2) The header heat. I ran the same tests on my 2003 as I did on the refreshed motor. When running on choke with high idle the header will slightly glow orange in the dark. It will also get a hint of orange if the throttle is held open a bit. Take a look at the picture below. From the motor to the red dot will almost always be above 600F. This happens even within 30-60 seconds of startup.

 

[rruser]

Does anyone have any of their own compression numbers from stock warriors? I know what the book says, but I'm looking for real values people have seen

 

[Gen1Pat]

Compression readings on a comp gauge is not your compression ratio. The compression ratio is the amount of air/fuel that is compressed into such a small space. The higher the comp, the need for higher octane fuel, because higher heat numbers are being produced. Idk what my comp reading is on my stroker after I completed it in March. No need to test it, obviously has idel comp, doesn't smoke, great power...

 

[rruser]

Right, that's why I was asking for a real world number of the PSI. Not what it should be, not what the book says, but what someone with a well running stock motor gets on a good battery with WOT. I'm not worried about the ratio now since I get the same value on a known stock motor. While there might not be direct math between the PSI and comp ratio, I do know the only way my PSI reading could be high is from a change in the cam, high comp piston, decked head, or high carbon. None of that is happening here.

 

[pwgsx]

Shouldn't it be around 123 or something?

 

[Gen1Pat]

No. It should be much higher. The usual minimum "good" comp reading shoud be no less then 120psi. Usually the 150 and up is what you'll find on most engines.

 

[rruser]

Thanks for all the feedback. Still hoping a builder will chime in and share some of the true values they get from a fresh motor.

 

[lbjamm]

He just did.

 

[rruser]

Oh, sorry about that. I guess when I saw "most engines" I took it as being a general statement. So no one has ever seen a 100% stock 350 motor in the 160-175 range?