Why’d it blow up .... twice

Im assuming you guys have broke some stuff...

Two passes in a row I disentegrated the heads at .25 off the brake.

New combination that had ignition issues but had run enough to see the plugs looked decent.

The first time it blew up I thought I had messed up the software, but I added fuel and took a little timing out for the next pass just in case. And it did it again. Comes off the 2 step, goes straight up to the converter nice and clean, and then BANG, molten aluminum everywhere.

In general if the heads are liquified is there any good indicators whether it was timing or fuel? If it was timing that took the heads out at .25 into the run, how many degrees less timing would you think it takes to make the 1/4 mile (I’m thinking at least 10-15 which just doesn’t make any sense to me)?

I know these are horibke questions with not much info, just looking for good questions at this point cuz I’m stumped. I’m tempted to think the timing number is somehow changing when it’s not supposed to, or is it possible to be kinda close and vaporize a head right off the brake?? I mean, it basically made a couple of half passes where the tune up looked ok, changed the method of reading the crank, and it turns into a hand grenade.

 

I usually like to go back to the last thing that I changed. If you changed the way the crank reads, what’s the possibility the timing is off? Did you verify it with a timing light?

 

What do you have controlling the timing?

 

Thanks guys.

Haltech VMS.

Software locked to 0 degrees and verified with a timing light while cranking. This setup wont light my timingnlight while running (have heard others have had this problem) so relying on software after the lock procedure. I need to check tonight but i think I used a Falling edge trigger setting. It’s a typical msd 4 magnet wheel now. I wonder if that was a bad idea? I was trying to get the cam and crank event farther away from each other is why I set it that way. They can’t “touch” and i was limited on crank trigger adjustment without re-fabricating something. 0 cam trigger adjustment.

Timing was at 14 and then 13 degrees respectively when it popped. I don’t really have a launch curve in it yet, more of an rpm curve and still soft enough (I.e. blower turned down) that it shouldn’t need a launch curve yet. Some guys say this combo needs to be at 10 degrees or less on the converter. others have gotten away with a lot more than that. I’ve had it on the converter multiple times before this at 10-15 degrees.

No flow sensor. Crew chief verified fuel shutoff open visually before the 2nd pass. I verified that if it looks open on the outside, it’s open on the inside before the race. Same with barrel valve. Will check these again on disassembly tonight. I’ll also jack the car up with the nose hanging to see if flex could cause the cable to move the shutoff. It worked fine for dozens of passes but then the last pass with the old engine combo it damaged the heads then too (in the lights though, not on brake release). Not much in common between the two combos besides shutoff, shutoff cable, barrel valve and distribution blocks. Completely different ignition and wiring after the ignition switch.

I did have the pump inlet hose off before this race. I remember checking the clamps on the inlet before the race but not after the first pass, will double check.

TDC mechanically verified upon assembly by someone else. I did a quick thumb and eyeball check while swapping heads. Felt like it was off about 0.5 to maybe 1 degree to me in the safe direction (I.e. it was pointed at 1 when I felt like it was at TDC)..

Also, calculated fuel system pressure is a Little low (~80 to 90 psi) because the blower is turned down and I didn’t want to change all he nozzles just for a couple test passes. Any chance ~35 psi boost and 80 psi (calculated not measured) at the pump is causing the ports to not flow? I think I ran similar numbers in my old combo on a couple checkout runs without any trouble. Also, it wouldn’t even come up on the 2 step if the ports weren’t flowing, right?

 

I'm probably wrong about this, but since i cannot get aluminum to liquify with a 300A tig welder in .25 seconds, my suspicion is you are gaining the excess temp before launch, possibly when staging, and the extra normal temp rise of going to full power is taking you over the edge.
I have had trouble with both the crank triggers and the connecting cord to the MSD being reversed in the plug --out of the box new--which will change your falling edge point a bunch.

I am curious about the timing light too..

I hope you figure it out, it sounds frustrating.

 

Put boost and detonation together in you will melt aluminium in less than.25 this happens when its to lean or timing is wrong which leads to the d word

 

You got a diagram of your ignition system ....????? ....Make sure your cam firing order is the same as the ignition firing order. Had a cam marked wrong from cam grinder and it makes an unhappy motor.

 

Haltech VMS running coil near plug coils with stock LS cam sensor. Was stock crank sensor but a bunch of people told me to go flying magnet instead. Plenty of people making more power than me with this general setup.

Ron, I absolutely never verified firing order and feel kinda dumb now that you say that. I figured it sounded pretty good on the warmup stand so must be right. Will check tonight.

With the current BV setting I’ve never measured over 130F with an IR gun on the head.

Mike, I can’t remember the last time I measured the port check. 8 years if ever. Pretty sure I inspected/stroked it this winter but that’s the first thing I’ll do tonight. I keep thinking about the 2nd pass now, after it blew up and nosed over I stuck my foot back in it just to make sure it was completely destroyed (hey I’d just thrashed until 3 am I wanted my money’s worth) and it actually pulled a little for like 5 feet before it nosed over again and spit more material out. Maybe it can only crack the port but not keep it open (i would be mortified but relieved if I could prove this). That would mean the previous passes were on blower nozzles only, at least until higher rpm (it really took off up high). Is it possible to be TOO lean to burn one up and not bang the blower?? I’ve done this before with nitrous but never considered it on alky.

 

Mike, I think it’s the same idea. I saw where Holley or maybe big stuff you can change the value of the timing lock function that allows you to check timing. Haltech only allows you to temporarily lock at 0 and it’s specifically for checking the reference while cranking. My timing reference is actualy at 340 which seems typical for Haltech and big stuff. Holley wants it around 60.

I didn’t know any of this crap six months ago and didn’t really want to. 8 years ago I swore I would never own a race car that required a laptop. So much for that idea

 

Double check your rotar phasing. If your checking it with a window drilled in the cap, make sure the hole is at where it's suppose to be. My son and I just fought an ignition problem for almost two races. Turned out someone had drilled the rotor cap phase window 24 crank degrees off......

 

Another odd and end to check is the barrel valve, If it isn't set up to flow enough fuel at your launch rpm that can beet your motor up before you even launch. The TAFC team I used to work removed the converter and went back to a clutch but did not change the BV. It kept hurting parts but it wouldn't hurt itself until half track so that may not be your issue but it's a thought. I know Newburry likes to mod them for screw blowers so they get more fuel sooner.

Hope that helps,
Trev

 

Ron, this is CNP. No rotor.

I’ve had this same BV on 3 or 4 different roots motors with 3 different 14s. All of those made more power than what this current combo can. I stared at for awhile, just don’t see how the Bv can be the culprit. I appreciate the question though and will keep thinking about it.

Jacked up at firewall, nothing moves, not even a hint so probably not chassis flex affecting the cable.

Port check cracks at 15 flows at 20. 35 psi + 20 = 55 which isn’t real far from system pressure at 8k. Assuming system pressure is 15% lower at 6700 where it popped.... this one is in my short list for sure. In hindsight, this scenario vaguely crossed my mind in the middle of the thrash. I briefly thought about changing out all the nozzles but didn’t think I had time when the idea gelled. I’ll put a sensor in the port line when I reassemble. It will be the first piece of instrumentation I’ve ever ran on a race car.

I still think fornthat explanation to work it had to be TOO lean to burn up on an earlier pass and I’m still not sure if that’s possible.

 

Thought sure I found the smoking gun. Figured out I could lock timing at 20 instead of 0 and if I put my inline coil tester on #1 it will fire the timing light while running.

Sweet.

Locked at 20, turns out it read a whole bunch more than 20.

Crap. Well, at least I found the problem right....




Add some pressure sensors, thrashed it back together, dropped the timing way down and threw a good amount of fuel at it just so it would definetely go down the track.


It left real lazy (figured it would, bunch of fuel and no timing), figured I’d click it at the top of low gear and look at plugs and data.

It went 1.8 seconds and BOOM. Knocked the blower clean off the intake.

Secondary check never opened. I sure wish now I had measured pump outlet but I didn’t, I only measured at the port distribution block. Port distro block pressure overlays the boost curve perfectly.

Even though RPMs were pretty low, This thing should have had like 150 psi plus with the port check closed, therefore the port check should have opened.

The only thing I just realized I never did is I never actually put pressure on the shutoff and made sure it didn’t bypass anything when opened. Other than that, I’m out of ideas.