turbo 6liter woes :\

6literEat'r

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been having a problem I have been fighting for a sometime now, my 99 trans am, iron lq4, turbo...will occasionally close the sparkplug gap on cyl 7, and it happened once on cyl 2. im running ngkbr7-ef plugs

ONCE it chipped a ring land right of cyl 7, and it smoked out the valvecover breather and you can tell the engine was hurt, as it would also misfire at idle only. so I removed/replaced cyl 7 piston and rings and all was good.. well this happened again today, I got on it hard, rowing through gears, full boost, brand new plugs and wires, and cyl 7 closes the gap again and I had to dogleg it home. im gonna run a borescope down the sparkplug hole and check out the piston, but I am doubting its hurt, as I have no driveability issues after I replace the plug.

car was tuned properly by Brandon, just trying to get an idea of what could be going wrong here, possibly a weak coilpack? or a bad map sensor (3bar sd tune) and its detonating closing the plug gap? HELP!

If I cant resolve this issue, im unfortunately gonna havta withdraw from the half mile event.
 

utryd2

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I was curious so I did a quick google search and the general consensus is detonation. Only other way I saw was piston to valve clearance was off and hitting the plug.
 

6literEat'r

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I was curious so I did a quick google search and the general consensus is detonation. Only other way I saw was piston to valve clearance was off and hitting the plug.
I was figuring as to that much too, I did a google search as well...
but what would cause it to detonate like that only on what it seems
like to be only cyl. 7?

not sure if I could have a weak coil possibly? a bad 3bar map, :dunno:
is it getting too hot back there and I need to think about getting a meth
kit installed? but guys with way more hp than me don't need it and don't
have this problem.
 

utryd2

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Id say its not an issue where you need meth since its only one cylinder. Id switch coil packs, throw new wires on it for starters.
 

1quick

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whats the plug look like on #7 color wise does it look like its running lean
 

utryd2

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Found this....copied the important stuff

So how do you get rid of detonation?

The two most common tricks (and easiest options) used by supercharger manufacturers and engine tuners looking to obtain maximum performance without detonation is 1. use higher octane fuel, and 2. retard the ignition timing.

Higher octane fuel burns more controllably and is not as likely to combust before the flame front. This is why racing engines use 100+ octane fuel. The ONLY benefit of racing fuel is that it moves you away from the detonation threshold, which allows you to be more aggressive with power producing factors - i.e. raise compression, advance timing, etc. So simply putting 100 octane fuel in a standard production car will not produce a racing car as it is just not tuned correctly to take advantage of the Octane rating.

Retarding the ignition timing will delay the timing of the spark, which also moves you away from your detonation threshold. Most popular "power programmers" or "chips" increase engine power by advancing the ignition timing, and requiring you to run a higher octane fuel to avoid detonation. These work great, except the advanced ignition timing is NOT compatible with most superchargers, unless you're happy to run 100 octane fuel. In fact, many supercharger systems include an "ignition boost retard" that retards the ignition timing when it senses boost from the supercharger.

Another way to avoid detonation is to cool the incoming air charge to lower the temperature inside the combustion chamber. On a supercharged application, this task can be handled by an intercooler/Charge cooler or by a water injection system (less common). The intercooler takes the incoming air charge and passes it over a series of air-cooled or water-cooled fins and ducts, thus cooling the air in the same way that a radiator cools your engine's coolant. Intercoolers are thus very popular in higher output supercharger systems, where detonation becomes more of a problem. A suitable intercooler allows you to run more boost and also allows you to eliminate the ignition boost retard, meaning you'll notice increased performance, and still experience no detonation.

Another way to lower the temperature of the combusting air and fuel is to run cooler heat range spark plugs. Many supercharger manufacturers will recommend cooler plugs for your supercharged engine.

Because a lean condition (fuel starvation) also contributes to detonation, it is important to make sure that the fuel system (pump, injectors, etc.) is capable of delivering the increased fuel requirements of the supercharged engine. Often, an otherwise perfectly tuned engine will experience detonation just because the fuelling system can't deliver enough fuel to the engine. Upgrading certain fuel components is sometimes necessary when supercharging an engine. More commonly the ECU that controls the Fuelling MAP needs to be upgraded. If you are installing a supercharger on an engine with other modifications, you need to make sure you consider the additional fuel requirements and compensate with larger injectors and / or a bigger fuel pump if required.
 

wolfe

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Are you getting enough fuel? What do you have for injectors and pump? Do you have a wideband? I would maybe think about a new tune.
 

6literEat'r

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Are you getting enough fuel? What do you have for injectors and pump? Do you have a wideband? I would maybe think about a new tune.
ive got 80# injectors...and im running dual walboro 255's
 

6literEat'r

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should I possibly step it up to br8ef plugs? and figure out where to get higher octane fuel...
 

Turbocharged400sbc

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id bet that something is up with cyl 7 inj spray pattern if oils not getting past the rings. leave it upright for teardown to prevent a false positive and when you pull 7 look for oil behind the top and second ring
 

6literEat'r

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id bet that something is up with cyl 7 inj spray pattern if oils not getting past the rings. leave it upright for teardown to prevent a false positive and when you pull 7 look for oil behind the top and second ring
im gonna bring home my borescope from work and
try taking a look through the sparkplug hole to see
whats goin on mechanically if anything, god I hope
not though. we shall see...

in the meantime if nothing seems to look obvious in
the cylinder, im gonna step it to a colder plug, and
possibly get a new coil
 

willizm

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I'd think at your boost levels your br7's would be a-ok. Do you know how much timing you are running? Did you vent the rear of the heads or just the fronts like what comes stock?This is one of the reasons I go out of my way to run e85. It burns cooler, has higher octane, and is just a cleaner fuel. They did put e85 at a shell on 59 toward Naperville FYI. Also fwiw, straightline performance tune from now on :)
 

OffshoreDrilling

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#7 is a pretty common cylinder to run lean. I'd bet detonation is your problem as others have said. Any sign of aluminum on the plug ground strap? If you had piston to valve contact your problem wouldn't be going away by tossing a fresh plug in it every time. Adding some more fuel to that cylinder wouldn't hurt it either if you can confirm you are getting detonation. You're tuning based on an average of the AFR of a bank of cylinders or the whole engine.
 

79vette

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colder plug isnt going to help, your detonating...... find out why. adjust accordingly. lower boost on pump gas, pull some timing, or keep boost up and add higher octane fuel.
 

79vette

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reading plugs only works after a hard pull and you shut down immediatly after, otherwise the plug reading is ruined by idling and normal driving. this is why drag cars shut down and get towed back to the pits after a run. so they can read plugs.
 

02BlueGT

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Just an idea,

Switch around your injector from 7 with another cylinder, if the problem follows, you can have a weak one. Even with flow matched injectors, problems can arise. Even with a good filter,it is possible for debris (even can even be filter material) to get logged in an injector and cause a weaker spray. Without individual cylinder o2 sensors, you would only know if an issue once it is bad enough to cause problems like this.
 

79vette

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I doubt it is an injector issue, though it is possible. I would more look at all four corners of your heads, if they have coolant crossover tubes. an air pocket can cause a overly hot cylinder and can cause detonation. you can try the injector switch too since it is simple enough.
 

Donnie

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Which Cyl typically runs hottest on those? My first move would be to test that Injector though.

Edit: Sorry, didn't see that was suggested already.
 

Turbocharged400sbc

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even with the reverse flow cooling system the rear cylinders run hotter, cyl 7 got butched twice and if the same inj is on that hole id say to replace it or at least flip the rails over and look at the spray pattern at cranking.
i dont see the coil doing anything...at most the mixture wouldnt light off and it would load up but i doubt it would lead to a piston chunk kicking the gap closed.

cyl 7 also isnt prone to oil slinging onto the cylinder walls excessivly from the crank at that would be cyl 8

i do know that 7 and 8 were always headaches on the old sbc's
 

SleeperLS

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This isnt going to solve your problem, but do you have any way to scan your car while you are driving? Scan gauges or something? Might help you save the motor if you can let off right when you see knock. I would pretty much never drive a performance boosted application without some type of scan tool.... You would be amazed at the strange shit that can happen when boost is involved.
 

6literEat'r

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I'd think at your boost levels your br7's would be a-ok. Do you know how much timing you are running? Did you vent the rear of the heads or just the fronts like what comes stock?This is one of the reasons I go out of my way to run e85. It burns cooler, has higher octane, and is just a cleaner fuel. They did put e85 at a shell on 59 toward Naperville FYI. Also fwiw, straightline performance tune from now on :)
when it was tuned, I was told its at 14 degrees timing, so very conservative there...I swapped over the 4port steam pipe setup from my old ls1 too, so yes the rear heads are venting coolant.
I may start looking into the e85 option as well.



#7 is a pretty common cylinder to run lean. I'd bet detonation is your problem as others have said. Any sign of aluminum on the plug ground strap? If you had piston to valve contact your problem wouldn't be going away by tossing a fresh plug in it every time. Adding some more fuel to that cylinder wouldn't hurt it either if you can confirm you are getting detonation. You're tuning based on an average of the AFR of a bank of cylinders or the whole engine.
yes, im still running stock rails, I was told they'd be ok at the power level im at :dunno: I haven't really noticed any aluminum on the plug, but when it happen, I dogleg it home potentially wiping clean of all the evidence off the plug.
 

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