HOLY CRAP! They tuned your car with a 12.0 A/F? Or am I not seeing that correctly? Old eyes and all. lol If it is 12.0, WOW, there is the problem. Tuning is the cause. These motors DO NOT like 12.0 A/F even on a fully forged motor. For your application, the safe A/F should be 11.0 - 11.3.
That and fade off to 10 as you approach red line to keep those EGT's down a bit. Speaking of which I wonder how high your EGT's got during the "tuning" I would check your headers and exhaust system in general to make sure you didn't start burning through something.
At least something good came out of that deal...And please define M when speaking about it...His name is Marty, and the shop is KRC. Steer clear.
That A/F is way to lean. Proof of all your issues are in black n white in that dyno chart! Oh and boiling your coolant is far from normal.
I had my '70 Cutlass dynoed a few years back after 500 miles on built Olds 350. I didn't have a temp gauge and boiled the coolant. Ended up blowing the head gaskets on the dyno. Car was never the same.
Back in the day (3yrs ago LOL) We maneged to run our truck at 12.6 A/F in 3rd gear without trouble and zero knock retard. BUT, we were also spraying W/M, 2 375 nozzles wide open at 6psi. The truck ran high 12's at the time. (forged 392) Since then we went to larger injectors and are running it at 10.8 A/F. It really likes that. I'm just saying,,, I wouldn't recomend anyone to run one of these boosted motor above 11.5 A/F unless your monitoring everything. Sorry for your troubles OP
Damn Howard. I'm very sorry this has happened. I know I'm not saying anything new here, but it was the tune that took out the pistons. And Mike, come one dude, this type of information should be made public. And for you guys that rely on a AF reading to determine whats safe. Sorry, a motor likes what it likes. And the only way to properly tell is to monitor not only AF's, but EGT's as well. And anyone tuning this type of build should have paid more attention to EGT and knock sensor activity than most anything else. You can have what you feel is a safe AF, but the injector timing is so important in a situation like this. Determining that is a talent, so much of that needs to be based on of the cam profile. Also the injectors and fuel delivery. Hell, I could go on for hours. Good luck Howard.
Learned something here...the Viper engine is fine at 12.0 with FI....surprising the Hemi would be better at a full point fatter..
Sure wish you guys would stop advising what is a safe AF. Let me give you an example. This is as simple as I ca explain it. I'm hoping everyone has the basic theory behind a four stroke motor. Lets start on the compression stroke, the fuel charge has lit off and the piston comes down. After BTC, the exhaust valve begins to open and as the piston comes up, out goes the gas right. Now as the piston reaches TDC and starts down, the exhaust valve is still open and on it's way to closing. At this same time after TDC, the intake valve begins to open (this is called overlap), at that point, the injector fires. Some of this raw fuel is also evac'd straight out the exhaust and never makes it into the combustion process. Now at that point, the raw gas hits the cats and flashes off and low and behold, you get a AF value. But the fact is how much fuel is actually in the charge. The only way to determine when/where/how is to monitor EGT's. Something most every shop out there is unable to do. So, most tuners just continue to add fuel until power is increased and knock sensor activity is decreased. So what you think is a safe AF is nothing more than garbage based upon cam overlap, injector timing, pulse width, flow rating and pressure. Many of these variables can be tuned around if you truely understand what your looking at. OK, nuff said. Fact is, the tune cost Howard a motor. The piston damage tells all.
You mean because they're burnt? We need to talk more about the effect of overlap. I'm curious on the effect of overlap on EGT (wouldn't it have a cooling effect?). Maybe another thread? Maybe a Vendor Feature article? (hint, hint) You could get your name on the big page at the front door.
Howard, hope you get things straightened out, sorry to hear about your motor. Let us know if we can do anything to help.
Dave we can talk about that all you want some place else. And after I'm caught up on a few projects. I took tonight off to rest for a little RnR.
Wouldn't that just cause the oscillations seen in the AFR graph? I mean if you look at the mean of the AFR then you should be able to average out the overlap right? or am I thinking about this wrong?
You're thinking about it wrong (if you're thinking about little puffs of unburnt fuel going down stream). It happens between every exhaust/intake stroke at every cylinder. Each cylinder would produce an "afr pulse" every other revolution. and there's 8 of 'em. so 4 pulses every rpm, so 20,000 pulses every minute at 5,000 rpm so 333 pulses every second... You're not going to see those oscillations on that graph.
Well it would only be 4 cylinders but that still holds true. Ok so my next question would be would the amount of unburnt fuel being pushed out in the exhaust due to overlap be relatively the same on every cycle? In other words could you make a basic assumption that the AFR's would be off by XX amount?
Depends on RPM and throttle, etc. But for a given set of conditions, yes? We'll get another thread going and Cam can give us a tutorial after he's had his nap. (I'll move these posts over there). later today.
