No worries..lol

Thank you.

I do predict some driveline issues that will cause it to be on jackstands...lol

 

I share the good and bad.

Well...I backed timing down to 25* and slowly started romping (quick bursts in 3rd gear) on it...felt AWESOME...AFR was low 11's and I corrected the too lean cruise (larger IFR and primary main jet,...now 14-15 AFR at light loads).

I then romped on it from 2nd to 4th....about halfway through 4th it backfired and started running like shit. Pulled plugs....#4 was wet....compression test...30 lbs in #4...160 lbs in #2..FUCK.

Not sure what caused it (given 25* and low 11 AFR)...I found my pressure signal line off to my pressure distribution block...but Im not sure if I removed it or it popped off...if it had popped of that is the obvious culprit due to potiential over boost and fuel pressure drop.

SO...I pulled the engine (needed pulled for rear main seal replacement anyway)....havent pulled the heads off....I ordered gaskets/seal and am working on trying to get a single piston (JE PN 257964) although I havent verified that is the cause yet...but strong money is on it.

Path forward will be to repair the engine and clean things up a bit...back timing off further...and remove the wastegate springs....and put a fucking zip tie on all the pressure signal connections.

 

Shit. Sorry, man. That's a bastard. I hope it's only as bad as you think it is. Fingers crossed for ya.

 

thanks

Years ago I told my buddies that I would mess up the engine I have money in because I have had such good luck with my junk stuff and tuning their junk stuff....damn murphy...lol

 

Doesn't that just figure? That Murphy guy can be a real cock sometimes.

 

Yep. By the way if you see him tell him I'll buy beer don't mention I'm gonna kick him in the weener.


Ss496 hope you get this figured out. On a bright note at least you have more than one turbo car so you can rip on the other and work on the other.

 

excited you got it out and by end of read broken :-( hopefully nothing serious. Post up findings

 

Glad you at least got a chance to brake it. Hope you get it fixed soon

 

Head gasket blew....eroded head. I got the head welded up yesterday and dropped it (both heads) off at the machine shop to be surfaced....hoping it will be done by friday

I ordered another piston since I found #7 and #8 had fine cracks.

I stepped up to a cometic headgasket as well.....the damage to the head really bummed me out since they are the most expensive pieces in the build.

Im banking that the pressure signal line came off the hat...it sends pressure to a distribution block for the fuel reg and wastegates. When it is running again I will further back the timing off (20*) and remove the wastegate springs.


I also found the rear main leaked because some idiot (me) installed one of the seal halfs backwards...lol

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I do not like the design of the piston valve reliefs. I allows a hot spot to form as well as a stress concentration. However, given the valve vs. piston geometry is fixed on a BBC (for the normal mans budget anyway) and I dont want to run a weenie cam....Im dont know of another option.

I toyed with running a pure flat top way in the hole...but that would kill quench.

 

Maybe smooth out the sharp edges? This should reduce stress risers and hot spots.

 

I had a set of custom JE pistons crack like that in the intake valve relief. They cracked into the ring land. Got 3 the first time and all 8 the second time.

 

the largest stress riser and hot spot is where the intake valve relief meets the outer circumference of the the piston....the blending or radiusing reduces the stress concentration marginally and doesnt help the reduced ringland thickness....but every little bit helps says the old woman as she pisses in the sea...lol......however, it certainly cannot hurt.

Obviously I had issues due to the engine running lean after some load was on it for awhile and was fine for quick bursts....so it is indirectly tune up based (from possible needle and seat size, or the pressure line)....Im not concerned for lower boost levels...but it does concern me when if I want to start tuning up the wick.


434chevelle...did you try different pistons with success?...What was the engine this occurred on?

 

stuff was happening fast enough I didnt get to glance at the wideband when the "pop" happened in forth gear....at the time I was comfortable enough with the quick bursts in 3rd and 4th seperately....so the sequential 2-3-4 romp got me....shame on me for being too excited....i know better than that and that is why this is so frustrating.

 

I went to an lq4. The pistons were in a 427 Rodeck tall deck sbc. Who knows for sure why. It was blow through and shit happens so fast that you can't watch gauges. ( no data logging). I went to Holley Dominator EFI on the lq4. The pistons were super thin in the ring land though.

 

Engine is back together...painted pretty.

I need to drill a hole in my new valve covers (of course I didnt have the correct size hole saw) and mount the exhaust manifolds/turbos....then it is ready to drop in the car.

 

good job getting it right back together
good luck

 

I have SRP pistons in my 496, probably have the same part number. I have not had an issue with my mine while it was running, but I recently pulled it to freshen so I'm curious to see how they held up. Probably going to hone the block another .010" and put new pistons in.

 

Let me know what they look like!!

 

Engine is back in the car and I put a couple hundred miles on it over the weekend. Ive done the following in addition to repairing the pistons/gaskets.

-Removed wastegate springs
-Replaced felpro head gaskets with Cometics
-set total timing at 25* (and has vacuum advance so it isnt a slobbery pig at part throttle, the centrifugal comes in really fast..by 2000 RPM)
-installed and degreed an adjustable timing pointer during engine assembly so I know it is spot on.
-installed 0.150" N/S assemblies in the carb....thought I already installed these long ago...but that was a different project..they all melt together...lol
-zip tied every pressure signal line
-put on new valve covers
-welded oil return bungs in the oil pan and routed new oil return lines instead of returning both to the fuel pump block off plate....I didnt have oil drain issues but since the pan was on the shop floor anyway I decided to do it right.

Rocking a huge 1.5 PSI of boost at 5500 RPM..lol. Also, got the part throttle stuff 95% there...still has a stumble at barely cracking the throttle below 1400 RPM....wouldnt go away not matter what I did with the IFR for AFR...I think it is simply a function of my cam timing and a single plane intake....if it was an automatic I would never notice it since the engine would buzz up past this point quickly....manual trans really exacerbates this.

I did notice my WOT AFR varied from 10.5 to 11.5 at the same RPM just on different blasts....also heard my fuel pump noise while changing pitch while driving...makes me nervous....needless to say the springs will not be going in the wastegates until this issue is figured out.....would be nice to have a datalogger to monitor pump voltage while driving to see if it is a pump or wiring issue...

The pump is an old "paxton" version of the Aeromotive A1000.