Low Compressions?

[MrStabby]

Did you do the test with the engine at normal operating temperature?

Does anyone know how much difference there can be hot/cold?

[Rolls]

I'd try a different gauge (decent one) and a leak down test.

But, those figures are shit, engine is about to blow son.

I had an rb20 that made 160kw stock and read 110 across the board, still going today without issue. Puffed a bit of smoke when cold but still made power and ran fine.

Moar boost to compensate

Do this and run a thicker oil.

what about if the car has some aftermarket cams? wouldnt that make the compression drop , my first car had the cam reground and the compression fell from 150psi to 110psi,

It will reduce dynamic compression.

Edited January 6, 2012 by Rolls

[JonnoHR31]

aswell as static compression

[Slattery Gts-t]

Engine is out (alot easier than i thought), looking down the spark plug holes i can see a few things on the pistons like 0.10 and "std" and what looks like a part number would this indicate it has been rebuilt previously ? also the block is painted blue.

Could the valve damage be caused by valve float at high rpm enough to hit a piston and force the cam to jump back a tooth? just a stab in the dark as it was %100 spot on before hand and definatly only jumped one tooth

[Rolls]

You will never get valve float bad enough to smash a valve especially multiple valves.

aswell as static compression

How? The cyclinder shape is the same hence so is the volume of the cylinder as you haven't changed the stroke. Sure it will fill better, but the static compression has not changed.

Edited January 6, 2012 by Rolls

[Slattery Gts-t]

It used oil when i was running a 5-40 oil but then i changed to 10-40 and all was good,

When it $hit itself I was running my highflow at 15-16 psi at an AFR of about 12.0:1 at WOT ( was asking alot from that ceramic exhaust wheel lol ) as soon as it happened my first thought was my turbos ended up in my exhaust or its pingged to death possibly because i switched to vortex 98 from ultimate 98, i never even suspected this sort of thing happening

[Slattery Gts-t]

Well valve float is out of the question then

[JustinP]

Painted blue block, it's been out before. I would be questioning those relatively low kilometers!

Engine is out (alot easier than i thought), looking down the spark plug holes i can see a few things on the pistons like 0.10 and "std" and what looks like a part number would this indicate it has been rebuilt previously ? also the block is painted blue.

Could the valve damage be caused by valve float at high rpm enough to hit a piston and force the cam to jump back a tooth? just a stab in the dark as it was %100 spot on before hand and definatly only jumped one tooth

[JonnoHR31]

Engine is out (alot easier than i thought), looking down the spark plug holes i can see a few things on the pistons like 0.10 and "std" and what looks like a part number would this indicate it has been rebuilt previously ? also the block is painted blue.

they're standard size pistons and probably original. blue block means its been out of the car before (assuming its painted everywhere?) though.

How? The cyclinder shape is the same hence so is the volume of the cylinder as you haven't changed the stroke. Sure it will fill better, but the static compression has not changed.

cam timing changes staitic compression too as the valves shut at different points and therefore there'll be different amounts of air in the cylinder when it shuts.

[Rolls]

cam timing changes staitic compression too as the valves shut at different points and therefore there'll be different amounts of air in the cylinder when it shuts.

Different amounts of air yes, but the compression RATIO is still the same. It doesn't matter if you double the amount of air in the cylinder, it still compresses the same ratio.

What you are talking about is dynamic compression.

Edited January 6, 2012 by Rolls

[Slattery Gts-t]

Yeah the whole block is painted blue

[AngryRB]

is there anyway to tell if you have aftermarket cams? would it be obvious?

[JonnoHR31]

Different amounts of air yes, but the compression RATIO is still the same. It doesn't matter if you double the amount of air in the cylinder, it still compresses the same ratio.

What you are talking about is dynamic compression.

maybe we're not on the same page, im talking about static compression figures as in what you'd get with a compression tester. when it comes to the actual compression ratio your right, static remains the same, sorry.

[Rolls]

maybe we're not on the same page, im talking about static compression figures as in what you'd get with a compression tester. when it comes to the actual compression ratio your right, static remains the same, sorry.

Yeah I get you, a compression tester is testing dynamic compression though as the engine is turning over and breathing. Static compression is simply maths, you can't really test it.

[Slattery Gts-t]

Turns out i need a new clutch i wouldnt be comfortable putting this one back in the friction plate is pretty worn and a little torn up, i thought it might be it slipped really bad on me while dropping it in 2nd around a tight corner on a hill didnt grab till it hit about 6000rpm and smelt horrible! its an NPC clutch with an exedy friction plate

[Slattery Gts-t]

Okay well got the head off today and its slightly more damaged than i thought

Turns out cylinder 4 piston is no longer connected to the crank! im guessing the bottom of the rod has come undone / fallen off and at the piston has tried to exit the engine via the head bending 3 of the 4 valves on that cylinder and forcing the cam back a tooth on the belt

The bore is still good can still see the hone marks pretty well and no scratches so thats why im guessing its the bottom of the rod that has let go

[Slattery Gts-t]

The block is rooted so is the crank and head

The rod is in 4 bits, the piston skirts are non existent, the gudgeon pin is cracked in half, the bore and crank have large gouges in them, the bottom of the bore has a chunk broken off it, the oil squirter is snapped off and the rod bearings are twisted and mangled

Cause of failure: Rod bolts snapped

Edited January 8, 2012 by Slattery Gts-t

[Rolls]

What caused it to snap? if it was recently built probably a poor build. You never see this happen with a factory motor.

[JustinP]

Ouch, sorry to hear it. On the upside you can now build it (or get it built) the right way and enjoy some reliable motoring.

The block is rooted so is the crank and head

The rod is in 4 bits, the piston skirts are non existent, the gudgeon pin is cracked in half, the bore and crank have large gouges in them, the bottom of the bore has a chunk broken off it, the oil squirter is snapped off and the rod bearings are twisted and mangled

Cause of failure: Rod bolts snapped

[JustinP]

Chuck Norris can.

Yeah I get you, a compression tester is testing dynamic compression though as the engine is turning over and breathing. Static compression is simply maths, you can't really test it.