last year detonation ate #8 piston when the bt carb leaned out. at least that's what i thought at the time. car was on the dyno and was at 650 rwhp 15 psi boost at the time when it all went bad. when i removed heads to inspect the damage i noticed the cometic head gaskets were mashed. initially thought this was the heads lifting from detonation. the gasket in #8 pot was also blown into the valley.
read somewhere recently that this is what happens when the crossover pipe is sized too small. my x over pipe is 2.25".
combo is a 410 sbm, S475 t6 1.32ar. 4" down pipe, 2.25" crossover pipe, 60mm Tial wastegate.

#ad

 

I'm no pro but IMO it looks like classic lifted ringland. Usually thought to be caused by too much fuel and/or wrong ring gap too. Gas seeps past, and sits between the rings both detonating with the oil and washing the wall of your cylinder down. The rings and edge of the piston heat up and the soft swollen piston starts peeling off the top edge on the downstroke leaving those nifty little curled areas where you have a chunk missing. It doesnt look to me like you have any big detonation marks in the dish, what do the other pistons look like?

I think there are a few guys running 2" on some 800+ builds around here, and 1200+ on 2.5.

 

NOT the x over....

 

fuel problem or ring but is my vote

 

the deck was scorched where the gasket blew out. the bore was still like new, no damage at all.

 

I say detonation, which could be caused by many things, including a small crossover, but i'm betting its something else.

 

I've seen on here where they've made 800 HP with a 2 in crossover. Not saying anyones wrong, just trying to learn this stuff.

 

i am fairly new to the turbo seen and was told the smaller 2.25" pipe would keep exhaust gas velocity up which in turn helps with spool.
the melted piston was detonation. the full story was a electrical fault caused the water/meth to fail when we were doing a power pull. the operator did not see the fail light and a argument erupted. couple of weeks later found out through the grape vine that his knock block was f#%ked. sent him a bill for pistons and labor, still waiting. all care no responsibility apparently. one of lifes costly lessons.
the car has evolved from NA to pwerdyne bd11a which sucked, to vortech v2 which was not bad except for belt slip, to s475 turbo which scared the crap outa me. OMG the turbo is so impressive.

 

Not the crossover IMO. I've seen 1400 crank on 2.25" without a problem.

Clearly looks like you got the piston too hot for the ring gap… (most likely due to detonation) then the top ring butted… and pulled the top of the ring land off.

I'm currently running 2” hot side at 1000ish crank HP (going by weight and trap speed) on a 370” engine. No detonation issues.

 

Sharp edges on those valve reliefs could cause hot spots in a lean condition .

 

Were you monitoring AFR? I am wondering if the gasket blew, which pulled in extra air causing it to lean out. What piston is that? They look like the SRP's I have in my engine with tool steel top rings.

It seems like it would be pretty hard to blow a metal head gasket like that unless something was really wrong.

My old crossover was 2" tubing. My new one is 2" schedule 10 304 Stainless Steel Pipe, which measures a little over 2 1/8" ID.

 

not the X over ...

but on anything over 800 hp I like to use a 2.5" x over ... a lot depends on the header design that the Xover feeds into

 

Based on what?

 

#ad


#ad

 

about 20 dyno pulls ... the 2.5" X over on my kit made a substantial difference at that power level

 

Wayfarer, That is NICE packaging! Well Done Sir!

Turbotime, You're going to get called out on this at some point anyway so I may as well ask while I'm here...Can you define: "substantial difference"? You changed nothing else but the crossover to gain this: "substantial difference"? What size was the other crossover you are comparing to? Any noticeable difference in spool RPM between them? Thank You, Lorne

 

It would be interesting to see some dyno numbers on 2" vs 2.25" vs 2.5". Quite a few have made upwards of 1k hp thru a single 2.5" log on 300-350 cid. Turbotime, what is substantial? Any pics of the setup, and info on the combo?

 

Lorne .. im not here to play the call out game .. too old and too tired of the internet BS .. it was mid 90's when I was doing R&D on the fox body kits all the way upto the late 90's early 2000's when I released my own kit.

and that is correct .. I drove the car onto the dyno with 1 setup ... dyno'd .. got a baseline on a few different boost levels
swapped out the X over .. was a 2" .. went to a 2.5 " setup ... now your asking for exact numbers of what I did almost 20 years ago ..
it was enough to warrant me making the 2.5" standard on the kits ( I initially used 2" to clear the front hump of the oil pan .. the 2.5" needed spacers to clear so I had to refab the jigs of the initial 2" setup to go this route it also made the xover shorter) .. If I recall correctly it was something to the tune of 50lbft and ~20rwhp this was on a setup that was making 500rwhp .. the more power applied the more apparent the difference . There wasn't any perceivable difference in spoolup.
I also recall replacing a xover on a SN95 from a 2" to 2.5" with more pronounced results but that car was over 800hp at that time.

There were also differences in EGT's I also made some comparisons between Mild steel and stainless ... again there was a power difference just in the material change.

I will stress again .. it will depend on header design... and what the Xover path is to the turbine housing as well as power level.

I did the same thing to the Buick Turbo V6 at ~400 hp .. went to a 2.5" xover and gained nothing .. but on the SBF when making 800 .. it was a substantial gain . Which is why I posted

 

Sure ... I have witnessed 2500hp through a single log header ... but when that was changed to a equal length header without ANY OTHER change .. that power level went to 2800+
and longevity / reliability / consistency was dramatically increased.

To some 10% is nothing to even consider .. to me 10% is substantial ..

 

Sorry, my mention of a log wasn't to compare manifold styles, (that's a different discussion) but rather to say that the area of a 2.5" is enough to process all 300-350 cid (most with a decent aftermarket head), and to reliably support near or at 1k hp, and a 2" is only about 35% smaller in area than the 2.5"