[Ozzmann]

So I was out cruising on the week-end with a club when we hit a long straight and I put the foot down and she pulled hard all the way to 120mph, no sign of any problem until I pulled up and was told it started blowing heaps of smoke out the pipes from when I went WOT, and it was still smoking all the way home.
I have had problems with excessive crank case pressure, but when I lifted the hood there was oil everywhere from my breathers, never been this bad before.
Anyway I did a compression check and found no compression in number 5!
and only 175 in #6 and #7, the rest were 200-210
This is a recent 488 build with top shelf everything, and only around 3000miles on it. Car starts and runs fine except for the smoke machine out back.
Whats my next step to determine the cause?

[ID67goat]

Do you notice any strange noises in top or bottom end? I would probably start with pulling the valve covers if you haven't already. Check for anything obvious with valvetrain/seals etc. If you have a borescope tool, check the cylinders through the spark plug hole. Next would be digging deeper with pulling the heads etc.

[PunchT37]

If you were running pump gas, I would suspect busted pistons.

[steve25]

Your cranking compression is / was high so I would suspect damage from knocking due to timing and or full throttle jetting.
It could a number of things but first off the top of my head would be that you now have broken rings due to lack of proper ting gap on one or both of the compression rings .

If the motor was built with hyperutic Pistons and the motor was knocking under full throttle then you could have a broken piston

Also note that if you have the broken ring syndrome that the ring are very likely scratching up the cylinder walls so you really do not want to run it any longer.

Anyway you look at it your resigned to pulling it out now to find out what's wrong and repair it

[shaker455]

Originally Posted by Ozzmann

So I was out cruising on the week-end with a club when we hit a long straight and I put the foot down and she pulled hard all the way to 120mph, no sign of any problem until I pulled up and was told it started blowing heaps of smoke out the pipes from when I went WOT, and it was still smoking all the way home.
I have had problems with excessive crank case pressure, but when I lifted the hood there was oil everywhere from my breathers, never been this bad before.
Anyway I did a compression check and found no compression in number 5!
and only 175 in #6 and #7, the rest were 200-210
This is a recent 488 build with top shelf everything, and only around 3000miles on it. Car starts and runs fine except for the smoke machine out back.
Whats my next step to determine the cause?

If your normal cyl pressure was 200-210 then you had excessive cylinder pressure that normal pump gas can not handle.
How hot did the motor run?
Time to pop the heads and see what damage you have.
You would be lucky if was just head gasket...is your coolant low?

[johnta1]

I'd pull the valve cover off and look at the vavle train for 5 & 7
Rotate engine by hand if nothing major sticks out on looking it over.
See if the valves move normally.

But with one completely dead cyl. not looking good without taking head off to see further what the problem is.

[Formulajones]

Originally Posted by shaker455

If your normal cyl pressure was 200-210 then you had excessive cylinder pressure that normal pump gas can not handle.
?

Ditto

That's fairly high cylinder pressure for even 94-95 octane. If forged pistons they may have survived. More than likely rings.

[gtofreek]

If it has KB Hypereutectic pistons in it, I suspect one broke.

[72projectbird]

Stick a bore scope in cylinder # 5 and see what's up.

[Tim Corcoran]

Can't believe your running that high of compression on pump gas a disaster waiting to happen

["QUICK-SILVER"]

http://forums.maxperformanceinc.com/...d.php?t=817113

400 XX Block, bored to 4.180’’.aligned and decked .0005’’ clearance
Fully Balanced and blueprinted
4 Bolt Mains
Canton road race oil pan
Cloyes billet timing set
Tomahawk push rod cover
4.5’’ Forged Eagle Crank
6.8’’ Forged I Beam Rods
D.S.S Premium Forged Pistons 6150X
Sandoval Stage 4 roller cam 246/252@.050’’ .400’’ lobe lift on a 112 LSA
Kauffman D-Port 310cm Alum heads
Comp Cams Roller lifters
Crower SS rockers 1.5.1 ratio
Ported Performer RPM Intake
SMI Quadzilla Q-jet 900CFM

10.9:1 CR, Had ping/det problems with first carb running lean.

Clay

[Schurkey]

ZERO compression? You just spent a lot of money.

"I" would do a leakdown test of (at least) the cylinders with low compression pressures. AFTER the leakdown test, I expect the engine comes out-and-apart for repair. (But sometimes a person gets lucky--which is why I'd do the leakdown test which will confirm whether the problem is piston/rings, or valves (or both).

[STEELCITYFIREBIRD]

Valve covers off back off rockers look for obvious valve stuck open sometimes those heads drop seats. All valves look good move next to removing plugs air up Problem cylinder see where the air goes.

[Will]

The cranking compression seems awfully high for the stated CR and cam...???

[Formulajones]

I was looking at that Will, but no mention of where the cam was installed. I'll assume with that high cranking compression he's close to sea level too.

The .050 duration doesn't seem all that big for 488 cubes. It would suck up another 10 degrees and still be streetable.

10.9 compression with an aluminum head is easily doable on pump gas...with the right camshaft.

[track73]

Originally Posted by gtofreek

If it has KB Hypereutectic pistons in it, I suspect one broke.

I burned a TRW forged piston doing the same thing. Probably going more than 120 but it caused the black death.

[MarkS57]

Originally Posted by STEELCITYFIREBIRD

Valve covers off back off rockers look for obvious valve stuck open sometimes those heads drop seats. All valves look good move next to removing plugs air up Problem cylinder see where the air goes.

Agree, pull the valve covers. A broken intake rocker arm stud on 5 could do that although it wouldn't explain the lower compression #'s on the other cylinders.

["QUICK-SILVER"]

Get your paper work back out and double check those cam specs.

Sandoval site doesn't show a cam with the info you posted in the other thread.
http://sandovalperformance.wix.com/e...-velocity-cams

Duration and lift you did post looks more like their Stage 5 cam that has 108° lobe seperation. That could help explain the high cranking compression and det/ping problem.

Clay

[694.1]

For Airfare to Australia, I would be very happy to take a look

[Ozzmann]

If your normal cyl pressure was 200-210 then you had excessive cylinder pressure that normal pump gas can not handle.
How hot did the motor run?
Time to pop the heads and see what damage you have.
You would be lucky if was just head gasket...is your coolant low?

Car normally ran at 180 deg and went to 190- 200 when pushed hard, once or twice maybe 210 for a minute, but I don't believe that's too hot?
Engine was very street able, idles nicely and never was a pig to drive, haven't looked at the coolant level as yet, however I did just notice last week that I had a small leak under pressure at the neck,
but I did top up the coolant that morning before I left.
Wouldn't the oil be milky if it was just a head gasket?

10.9:1 CR, Had ping/det problems with first carb running lean

I have had slight pinging issues, mainly on hotter days, but it wasn't always audible, and never seemed to be too bad, I did run octane booster every 5-6 tanks

I was looking at that Will, but no mention of where the cam was installed. I'll assume with that high cranking compression he's close to sea level too.

The .050 duration doesn't seem all that big for 488 cubes. It would suck up another 10 degrees and still be streetable.

10.9 compression with an aluminum head is easily doable on pump gas...with the right camshaft.

I am at sea level, and have mates running close to 12-1 engines without any issues on the same fuel.

A lot of you are saying the 200-210 was too high compression, where would you expect it to be?

I'm by no means an engine mechanic, have no problems doing bolt on jobs, so pulling this apart will be a first for me, so expect me on here asking plenty of questions men, I will pull the valve cover tonight and see if anything is visible.
I will also do a leak down test.