What caused this to happen - cracked exhaust manifold??

[Ant97GTR]

Hey Guys,

After the really hot track day at Phillip Island my car was sounding like it had a gasket leak on the exhaust side. Stripped her down this week only to find a cracked & severely warped exhaust manifold

There was a 2 inch split/crack in cyl 3's manifold pipe and the metal was tinted blue suggesting some major heat.

Anyone know if the heat was the major factor in this -or- is it more likely that the crack had been developing over time and the heat just made it worse??

[inark]

at a guess heat would have to play a bloody good part in it wouldnt it?

oh well... now u can get a nice shiney S/S one

[R31Nismoid]

unless the car was running dangerously lean, thats the only thing i could think of.

You've got everything else that would prevent it

ie. free flowing exhaust etc etc

[Ant97GTR]

hahaha.........I would have thought so Nark but its not the only thing that would cause it. Maybe if a lot of people had this happen it could be an inherent fault in the design or something......All I know is it was an absolute b@stard of a thing to pull off the block 'cause it had warped sooooo much (and warped the heat shield 2). As for the shiney S/S one, if I had more time before the next track day I would have hunted an aftermarket one down but unfortunately I had to have the car back together ready for winton. Anyway managed to get my hands on a ported std item so should flow pretty well anyway.

Ash....thanks for the suggestion but my car has an a'market ecu etc etc and only got dyno'd recently so I know shes not running lean. Do have the req'd free flowing exhaust which helps but I'm thinking maybe when my manifold was match ported they could've shaved too much off in that area which led it to crack.

[Roy]

Did it snap and studs?

Looking at the designm they will always want to warp as the heat form all 6 cylinders is focussed int he centre.

But one thing i have noticed at a few Voc track days, you boys hok straight into full throttl work once leaving pit lane. I always do a lap of light throttle / med revs stuff to get a bit of heat into not old tyres, brakes, gearbox, diff etc, but also because i have a stainless steel manifold and i dont want to hit it with a bucket load of heat straight away.

So maybe a slighlty slower out lap may help reduce the heat shock/distortion?!?!?!

[ferni]

Roy i never hook full throttle straight from pit lane, usually put around for the first 1/4-1/2 lap and only go full stick on 2nd lap

[Ant97GTR]

Troy.......Man it was a b@stard. Luckily it only snapped one bolt so not much drilling out to be done. B@stard part of it was that it was warped so that the studs were forced up against the edges of the holes in the manifold preventing it from being taken off the block. The diff was really apparent when I went to put the new one on....fitted straight up with the studs right in the centre of the holes.

You are right about the warping happening at the centre of the manifold as the crack was in the pipe off cyl 3 and once the manifold was off the block it had warped in a concave shape.

I usually do a slow lap outta the pits mainly putting heat into brakes etc - never thought about things like the exhaust manifold. Going against that is the fact that I'm running street rubber (more heat=less grip) so I tend to hit the gas straight after the out lap.

Will go easier for the first couple of laps at Winton and see how I go....

[R31Nismoid]

Where is the crack?

right neat the plate?And troy, en EX man will get most the heat-up done just idling before you hit the track man.

Yeah it'll rise somewhat more... but most if its already done.

Its the mechanical bits after the motor that need the warmup more-so

[Ant97GTR]

Ash.....Nah mate the crack was no where near the flange plates that connect to the block or the flange plate that connects to the turbo. The crack was close to where the pipe off cyl 3 mates into the common runner that lead to the turbo - but the crack actually ran along cyl3's exhuast pipe.

check the crappy attached pic......

[R31Nismoid]

i doubt match porting would ahve caused that then, dont they just do the edges and in a bit ?

[adznight]

I personally think it was some type of failure in the flux capacitor or possibly the Mr. Fusion......

Nah but really, could be simply a defect in manufacturing? What about timing and cams? Have you had diff cams put in? I'm not expert but you know how they play with timing (or is is exhaust cams) and it draws more heat away from the engine, perpahs it's caused the manifold to get super hot. Could be combination of both! If there was an impurity in the metal could be a probelm...

[INASNT]

Ant if u havent thrown the cracked manifold away do an NDT test on it then you can see if further cracks have started to form around the other cyclinders. That will give you a good indication as to where the heat was building up on the manifold