New built motor issues - compression test numbers inside

[sunshine-ga]

Just had a local reputable shop do a forged motor on my 98 cobra. Manley pistons and rods, Mach 1 chain guides, new main studs. Car has a on3 kit with a 70mm turbo. It’s a 9:1 compression build.

The car has about 250 miles on it with the new motor. Have done a lot of spirited driving to set the rings.

The issue is the car has major blow by. I have pcv vented with filter to atmosphere and if you pop the hood there a clearly smoke coming out of the passenger breather along with oil on the head from it dripping out the filter. Also after a pull it will puff a nice little cloud of blue smoke out the exhaust for 10 seconds or so.

Did a compression test and here are the numbers

cylinder #
1 - 142
2 - 160
3 - 160
4 - 155
5 - 150
6 - 155
7 - 145
8 - 143

Yes, the numbers are all with 10% but on a brand new motor? The builder said valve seals and guides all looked perfect and they didn’t see anything else that needed to be addressed. (Old motor had a hole burned up in #5 thanks to 15 psi)

The car doesn’t feel very fast either (8 psi). And at over 6k rpm it feels like it doesn’t pull as hard. AFR numbers are solid mid 11’s everywhere. This is the exact same build as before, nothing has changed.


Just wondering some opinions on this and what my best course of action should be.

 

[98 svt]

Is 250 too soon?
I have about 200 on my new engine/setup (built engine and 67mm turbo). My builder told me its not really broken in until 1000 miles or so and not to take it over 4000 too often until then. Maybe he was just be extra safe because he knows I wanted to beat on it.

 

[96dreamer]

Those numbers seem a little low even for a 9:1 motor. He said the guides and seals looked perfect. As in they did not replace them? Bad seals might cause some smoke on decel but shouldn't cause the compression and blow by problems.

Any idea what the rings were gapped at? What oil has been used since first start? As 98svt said it might not be fully broken in but most of the ring seating happens on the first few drives/ heat cycles so I wouldn't expect to see any appreciable difference in the coming miles. I am a full believer in not fully beating on a car but varying the rpms with lots of engine braking to pull a vaccum on the rings and if boosted getting into boost to also seat the rings.

 

[SVT GI]

Blow by is your rings, more than likely ring gaps. Personally, I feel the ring manufactures gap specs are on the loose side, I start with their specs and drop down a couple thousands. Put a vented catch can in.

compression tests look normal. There’s too many variables that affect tests. Cams, timing, test done cold or warm, wet or dry. Those numbers aren’t going to make your feel low on power. Neither will the valve guides or seals. It’s either in the tune or combination or parts used ie, cams, intake, hot side size, down pipe size, intake temps, etc.

smoke out the exhaust could be valve seals or guides. But if the shop feels confident it isn’t, it could also be over oil pressure to turbo. Rpms go up, so does oil pressure. Might need to put in an oil feed restrictor, or a smaller one if already have one. Different turbo brands seem to like different oil pressure without blowing through the seal.

 

[CobraBob]

Bear in mind that it's pretty common that if you suspect there might be some sort of engine issue, your "head" is going to starting thinking things like "maybe it's losing power at higher RPMs", or "it doesn't seem to feel as quick as I expected", and on and on. Been there. Done that!

 

[01yellercobra]

What kind of rings are in it?

 

[coposrv]

With a proper hone moly rings should seat in no time even that said I’m a big fan of not being a pussy on engine break in. Give it some cylinder pressure to really seat the rings. Driving around like a grandma will just buff the cylinder walls.

Are you running stock cams?


Sent from my iPhone using svtperformance.com

 

[01yellercobra]

With a proper hone moly rings should seat in no time even that said I’m a big fan of not being a pussy on engine break in. Give it some cylinder pressure to really seat the rings. Driving around like a grandma will just buff the cylinder walls.

Are you running stock cams?


Sent from my iPhone using svtperformance.com

That's why I was asking. I ran stainless rings in my last set up and they need to be beat on to seat. Plus they were gapless which I learned the 4.6's don't like for some reason. My next go round will have moly rings in it.

FWIW, when I built my engine I had it running in the driveway long enough to get some heat and make sure it wasn't leaking. I took it about a half mile down the road and it saw full boost. It turned 100 miles on the dyno. The rings in that engine worked so well they would pull oil through the guides on decel.

 

[Weather Man]

Pressurize the cylinders and make sure the valves aren't leaking.