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#7 Cylinder Prone To Failure?


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To Keep it short, I had a stock LQ9, with a vortech blower: completely destoyed #7 piston, chiped cylineder wall, bent rod.

 

I went through past post and seen many of you had pictures that looked like mine.

 

Has any body else destroyed this cylinder?

 

So I built a 408ci stroker as a replacement while I had it out.

 

I have 1000mi on my stroker and it threw a p0300 code yesterday and started running rough, and had an intermettint rattle kinda like valve train. I had it towed home, diaged it and found 5psi compression in cylinder 7, and 150 psi in the remaining cylinders

 

I have JE forged dished pistons, I have valve covers off, dont appear to be valve train, Waiting on a borescope to see what is really happening. ( will update on condition )

 

WTF, I did the motor myself and I Spent $6000 in parts! AKA: All the extra money I have aquired since last january. :fume:

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Here is a LOG from HPTUNERS about 75mi ago. Is there somthing I am missing to cause this? Any help would be greatly appreciated.

 

sorry guess I cant upload it..

Edited by Riddler
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yes this is a known problem i did this to my stock lq9 the problem is the stock truck intake. the air all flows to the back two cylinders first then the others get it. this is why alot of us have switched to a spider style intake. aka vic jr or gmpp intake. gus with maggies dont have this problem with their because the intake was set up correctly. these motors werent meant for boost so you have to do kind of alot of mods to have a strong running motor with boost.

i would suggest you lookin into this but in all honest it could be worse , check all your parts but at best it could be just one new piston. here is a pic of the intake you should look into imo.

 

DSC00536.jpg

DSC00542.jpg

DSC04170.jpg

 

btw what kind of boost is your vortech making on the 408? cam specs?? is it still the sq or stock vortech blower?

 

i have upgraded to a t trim and it makes a bit more efficeint boost but nothing crazy . just want an idea of what kind of boost i could expect on a larger cubed motor.

 

thanks and good luck

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Chase, Thanks for the insight, thought it was weired to do this twice?

 

I like the intake, especially haveing the MAF/IAT on the boosted side, who makes it? I have never seen one? where do I get one? Thank's

 

I have the stock blower S-Trim I beleive? w/ the 3.3 pully I lost alot of boost w/408 went from 8psi to 4psi, I have installed a 2.8 inch pully and got the 408 boosted too 9-10 psi

 

Cam spec is 550 lift intake and exhaust, and 204/218 duration int/exh. ( stock 02 Z06 cam )

also running Z06 CNC gm performance heads, kinda did the build based of the SA Designs book how to Hot Rod gen 3 chevy.

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well another thing in question is your tune. what is your afr during boost? when changing pullies a new tune is mandatory.

 

as for the maf/iat on the boosted side my maf is pre blower but i have installed an iat sensor before the tb on the boosted side.

 

btw that psi is high for a 408 , i was seeing 11-12 psi with a 3.1 on my stock 6.0 i just hope i can get 15 psi with a 2.7 on my new 370.

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well another thing in question is your tune. what is your afr during boost? when changing pullies a new tune is mandatory.

 

as for the maf/iat on the boosted side my maf is pre blower but i have installed an iat sensor before the tb on the boosted side.

 

btw that psi is high for a 408 , i was seeing 11-12 psi with a 3.1 on my stock 6.0 i just hope i can get 15 psi with a 2.7 on my new 370.

 

I only have the standered version of HPT,so I dont know how to get afr, w/o wide band, is it possible?

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if your piston failure was a lean condition it could a couple things, your an 03 so your fuel system is stronger than an 04 but with a 408 and boost you have alot of air to supply .

 

what kind of injectors are you using?what fuel pump? what is your idc(injector duty cycle) when wot at full boost?

 

send a log to [email protected]

 

my guess is you do probably need more fuel and there are a few options out there. along with a better intake couldnt hurt but not 100% necessary. the fuel system however is.

 

this is partially the reason i ruined my 2nd motor.

 

for your setup id be using dual walbro pumps, the stock fuel lines are ok but youll need to delete the stock fpr with a boost referenced one. so your fuel press will rise when it see's boost.

 

to get your truck back and running safely your going to have to spend some lute. not to mention getting a intercooler on that huffer.

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His FPR should be fine, but I'd definitely suspect inadequate fueling.

 

If your injectors are big enough (svo 42s at the bare minimum), I'd have them flow tested while the motor is apart. Install them in the following order, with the highest flowing injectors being installed first... #7, #5, #8, #6, #3, #4, #1, #2 making sure that there is no more than 5% variance between any two injectors... This will ensure that the rear cylinders which tend to get more air will also tend to get more fuel.

 

Justin

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I have 42lbs injectors, thanks for the help, who can test them? also I have an extra set of 8 brand new injectors 42lbs, maybe I should check those too?

 

Thank You, Dan

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I have 42lbs injectors, thanks for the help, who can test them? also I have an extra set of 8 brand new injectors 42lbs, maybe I should check those too?

 

Thank You, Dan

 

Dan,

 

You're going to need a lot more fuel than just the multec 42s. The SVO 42s are 50# injectors at GM pressure and would likely be overtasked with your setup.

 

You really should step up to some mototron 60# injectors... they'll flow 72.3# at GM's 58psi of fuel pressure...

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i ran svo 42s N/A and they were at 75% duty cycle

 

for boost and 408i would look into some 96# injectors and as for that intake plenty of setups over on tech running the ls2/ls6 intake producing 1xxx rwhp. and in some result the carb'd intake produced less power then the LS2/LS6 intake

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UPDATE:

 

Just checked on the cylinder w/ bore scope, I could only see bout 70% of the piston and it looked good,(Hell I was excited to see it was still there)

 

So I added 5w40 inot the cylinder and the comp. rised from about 5psi dry, to 108 psi wet. Telling me that my rings are shot? Still wondering what that erratic rattle might be? Ring chunks? not sure? all the other cylinders are 150psi dry.

 

anybody change that piston while it was still in the truck? Maybe I will have to yard the head off tommorow. SUCKS, (also spark plug wasn't beat up like last time I blew up.

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By my calculations here...

 

On those 42# injectors, assuming a target AFR of 11.5:1 and a 95% VE at 6000rpms, you were maxing your injectors (100% IDC) at 3.5psi of boost. Crank it on up to 8-9psi and you're at 134% IDC... your 11.5 target AFR has become at best, 15.4:1... Your fuel injectors went static at 4400rpms... I'm surprised you only lost one piston.

 

To fuel your setup (again, assuming an optimistic 95% VE) to a 6000rpm shift point and maintaining 80% IDC, you'll need the mototron 60s (putting you at 81% at 9psi). Raise your shift points and your requirements change. To turn it up to 6400rpms, you can get away with the 60s, but ideally would want at least 80#/hr. 6800 rpms requires around 84#/hr to maintain an 80%IDC.

 

The 96#ers that Quik suggested would require low impedence injector drivers, but would leave you with plenty of fuel... At GM's 58psi of fuel pressure, they flow right at 110#/hr, giving you ample fueling to run 235kPa of boost at 6400rpms... right at 20psi.

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i ran svo 42s N/A and they were at 75% duty cycle

 

for boost and 408i would look into some 96# injectors and as for that intake plenty of setups over on tech running the ls2/ls6 intake producing 1xxx rwhp. and in some result the carb'd intake produced less power then the LS2/LS6 intake

 

 

Looking at my Log, ( INJ. Duty cylce is @ 98% , TPS 100%, 5854 peak RPM. ) :freak:

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Looking at my Log, ( INJ. Duty cylce is @ 98% , TPS 100%, 5854 peak RPM. ) :freak:

 

 

yeah that seems a little weird to me too. not to mention your getting some kr up there but nothing crazy max i saw was 3 degrees but still its something that should be addressed , but i saw the kr with only 9.5 degree advance.

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