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I finally started disassembly of my factory stock long block turbocharged 350 that broke in the last auto cross session at 6,500 rpms @15psi of boost. Engine is Commander 950 managed with Holley HSR and Venom 60#'s injectors. Engine was tuned at dyno before the event with 470rwhp and 500#/lbs.
Here is what I found; #7 piston damge and some damage on #5. Aluminum piston flashing was also found in #7 chamber.
Before disassembly I always thought that the engine broke due to detonation, I have another theory now, what is your opinion?
Preignition, how do the electrodes on spark plug #7 look?
RBob.
Something had hit plug #5, probabbly a piece of ring. I have to go back and check on #7.
Could that damage be done by a lean condition? All other 6 cylinders are perfect, I am having second thoughts on the detonation theory because of that. Could it be a faulty injector in #7.
Something had hit plug #5, probabbly a piece of ring. I have to go back and check on #7.
If you can post a picture of the #7 plug electrode end that would help.
Could that damage be done by a lean condition? All other 6 cylinders are perfect, I am having second thoughts on the detonation theory because of that. Could it be a faulty injector in #7.
Yes to possibly lean, and yes to possibly an injector issue. It may be debris in the injector basket reducing fuel flow, bad connector on that injector will also do it.
Why do you think its not detonation? There is melted aluminum everywhere.
(edit) A pal said it looks just like when an injector fails. then it goes lean, then, detonation.
What are your plans?
I am going to get the block out to a machine shop, get a new sleeve for #7, bore it to .030, add eagle splayed main caps, GM performance forged crank, forged dish pistons with H-beams, a new solid roller turbo cam, aluminum heads with roller rockers, might be shaft mount style. The plan is to build a bullet proof four digit hp capable long block and run it only at 40-50% capacity. For road racing/time attack 500rwhp and 2,800pounds is more than enough and a VERY quick car.
But I want to make sure that my injector are ok, I will get them checked or replace them.
the problem here is hypereutectic pistons holding too much heat in the crown, add some detonation and the already overheated top land will let go. Does not even have to be injector flow, can also be distribution with 7 running leaner (8 would run leaner also then, check that one). You simply found the limits of your stock bottom end
the problem here is hypereutectic pistons holding too much heat in the crown, add some detonation and the already overheated top land will let go. Does not even have to be injector flow, can also be distribution with 7 running leaner (8 would run leaner also then, check that one). You simply found the limits of your stock bottom end
X2.
Road racing with stock/hypers is a much tougher application than dyno or drag racing. This could be caused due to #7 cylinder doesn't cool as efficiently as the rest. Or it could be the weakest/poorest casting of the 8 cylinders. Personally, it constitutes a who knows for sure, but I'd get the injectors checked for sure and build the stoutest bottom end I could afford.
I think your plan of overbuilding is the correct way to go if you want a motor to stick together for extended periods.
Good luck - Jim
p.s. - chuck this block out. Go aftermarket or find a fresh one.
Yes, injectors are definitely going to get inspected👍
As for a new or aftermarket stouter block, that's a bit uphill.
I would love to get my hands on a Dart block, but they are too damn expensive plus I would need to buy a special $$$ flywheel in order to use my T56. I would also need a new crank
That alone is around $3000.00 without machining, rods, pistons and heads and a block like that deserves and requires(to protect the investment) the very best.
In my case it would make sense if I was going to race the car at high hp numbers, but at 500~hp theres no doubt in my mind that the factory block can handle it and keep everything together.
I am begining to suspect and doubt my tuner's knowledge...
Last time the GTA went to the dyno it went because of poor timing issue after a clutch removal. After I re-installed the distributor it did not ran as before so I went in for a dyno session. I filled up the tank with PUMA 93 octane gas and head for the dyno. Car made 470 and 500 # torque @15psi but I guess he went too far in timming.
Another friend of mine went in for a dyno session, same dyno same tuner, in his road racing Ford Probe..,#@%&, oh... Sorry, I almost puke inside my mouth just there. Anyways he overheated his engine and damaged a head gasket the same day I broke the engine.
My GTA had never pre detonated before, not even with 87 octane gas and 420hp at the wheels in a dyno session several years ago and same timming as before the last dyno session. One thing is almost certain, the tuner either add too much timing or leaned the fuel map too much, and I am beginning to suspect the latter; lean condition. Most probabbly the injectors are in good condition and #7 is the least flowing, sum that with a low fuel map and poof...
Yes, injectors are definitely going to get inspected👍
As for a new or aftermarket stouter block, that's a bit uphill.
I would love to get my hands on a Dart block, but they are too damn expensive plus I would need to buy a special $$$ flywheel in order to use my T56. I would also need a new crank
That alone is around $3000.00 without machining, rods, pistons and heads and a block like that deserves and requires(to protect the investment) the very best.
In my case it would make sense if I was going to race the car at high hp numbers, but at 500~hp theres no doubt in my mind that the factory block can handle it and keep everything together.
.
Why would you need a special crank and flywheel to run an shp block?
Besides, you said you were buying an all new rorating assembly, right?
How much do you think sleeving the block will cost?
Why limit yourself to 500hp on a built motor?
Why do you think its not detonation? There is melted aluminum everywhere.
(edit) A pal said it looks just like when an injector fails. then it goes lean, then, detonation.
What are your plans?
It could have started as detonation, but the end result was pre-ignition. Detonation hammers and breaks parts, pre-ignition melts and destroys parts. And rather quickly at that. This is one reason I wanted to see the #7 spark plug.
If the porcelain is broken, that is either detonation or from pieces of the piston hitting it.
If the electrodes are melted, even slightly, that is pre-ignition.
It would actually be best to look at all 8 plugs, that can tell a lot about what was going on inside of that engine.
When it was tuned on dyno did you add fuel after it left for the street/track setup?
Any turbo car on a chassis dyno should expect to see near half point difference in air fuel from dyno to the track. Loading is way different.
That combo appeared to run too hot in cyl 7. Tuneup needs to be fatter for road race use and possibly do the coolant crossover in the rear as well. Also how are intake air temps thru a race?
No, no fuel was added after it left the last dyno session...:/
I did not even got a chance to check on temps, pressures, etc,. either, everything happened to fast.
I took two laps to warm up the tires with some sprints at 7 psi, then while taking the carrousel turn just before the straight in 2nd gear, turned the high boost switch to "on", I finished taking the turn, gently squeezed the gas pedal while exiting the turn, shift to 3rd and just when I was about to shift to 4th, a hellish rattling like sound notified me that something went wrong. Car managed to finish the lap cruising and while I was getting closer to the pit lane exit the car turned itself into BBQ mode.
Diggler, My understading is that 2pc rear seal crankshafts need a special flywheel to mate with T56's trannys.
I already have a new 1pc GM crank, a set of forged TRW's pistons, main splayed caps and LT1 style flywheel for 1pc rear seal. If I go the Dart route means buying everything new and top quality in order not to sacrifice the Dart block.
I already got a quote from a very competitive machine shop for $1090 that includes block machining(splayed caps, boring to .030", align, re-sleeving and full balancing).
That leaves me just to get a good set of H beams a rebuild kit from Summit and I am on the track again, theorically.
I bet you just were to lean and melted it down. Dyno tune likely ended up leaning out due to load increase. Seen it happen on every turbo setup on dynojets and similar nonload bearing dynos. Even some of the mustang types
I bet you just were to lean and melted it down. Dyno tune likely ended up leaning out due to load increase. Seen it happen on every turbo setup on dynojets and similar nonload bearing dynos. Even some of the mustang types
If you were to increase the fuel map area in the acceleration zone after it was tuned on the dyno, what percentage increase you might recommend in a map made in a Dynojet dyno, and how much in a map made in a Mustang dyno?
Whatever gives about a half point afr more fuel. As a start
My race car seems to see 8% increase in fuel from the enrichment adder to keep same airfuel on street or track vs dyno. Surprisingly significant amount. Other setups may not see as much
My 305 hasnt been to dyno yet but i know from playing around that a change in ve of 2 is about a 1 point afr change. Ve of 85 to 87 is like going from 12:1 to 11:1, roughly
You could also dyno for max power and note airfuel, add 3-5% do another pull and richen it up half point or so and then do some test hits on street to see if air fuel is same
I also usually pull a deg or 2 from dyno as extra safety
I remember telling the guy that the engine was old as fu%# and it needed to pull degrees until a noticeable decrease in horsepower was shown, and so he did. Either was not enough or the "shaping" of the fuel map he did was the culprit.
It has to be the fuel map. When I dynoed the GTA about 5-6 years ago at another Dynojet the guy was extra careful and tuned the granpa engine from rich to lean instead lean to rich like this guy did. Meaning it was super rich and he pulled numbers from the map until it was running good and safe considering the old condition of the engine. He managed to get 420 to the wheels and with 87 octane gas!!!! I do have to say, it was a gas hog.
I remember telling the guy that the engine was old as fu%# and it needed to pull degrees until a noticeable decrease in horsepower was shown, and so he did. Either was not enough or the "shaping" of the fuel map he did was the culprit.
Personally, I'd guess that 'old as fu%#' stock engine with 15 psi gave up the ghost. It was a matter of time, IMO. I wouldn't throw the dyno tuner under the bus based on this. If you were running a safer boost level, then maybe, but at 15 psi.....
I'd be curious as to how the rod bearings and ring lands look.
Personally, I'd guess that 'old as fu%#' stock engine with 15 psi gave up the ghost. It was a matter of time, IMO. I wouldn't throw the dyno tuner under the bus based on this. If you were running a safer boost level, then maybe, but at 15 psi.....
I'd be curious as to how the rod bearings and ring lands look.
Its one thing if it threw a rod or spun bearings but the damage looks tune related from high chamber heat. Could have been lean, maybe not. Maybe alittle too much timing. But it looks like heat from lack of fuel to me. It likely could have failed over time even if tune was spot on due to age and parts limitations but i wouldnt expect the piston to come apart like that.
Would also like to see the bearings and ring lands
It likely could have failed over time even if tune was spot on due to age and parts limitations
That was what I was implying. Probably this has been coming for a while. Was it the tune or was this the straw that broke the camels back?
Realistically, it was probably some of both the age and the current tune(s). Trying to live on the edge of a little rich and maximum power is difficult, especially with pump gas.
