C409

..... Holley EFI on E85 ... the injectors were new 60# Siemens Deka's (less than 12 passes) and were sent out the day after the heads came off ... F.I.C. flowed them and they were all on target ... the last 10 runs had datalog's showing a split in AFR's 'tween left and right banks with left about a half point richer ... this piston was #7 cylinder ... water pump is belt driven and the engine didn't get hot ... I didn't shut it off until it was on the trailer after the meltdown pass ... funny that it melted on the intake side and not the exhaust side .....

bjankuski

Is your WB set up to read gasoline afr numbers or e85 numbers? In either case it is too lean. If the wb was set for gas you should see around 11.8 at wot for best power, but I would think 12.5 would not cause any issues. What is your compression ratio? If you have winter grade e70 not e85 it may have detonated due to high compression ratio from the e70 vs summer blend e85? E85 is good to around 13.5 compression where e70 is around 12 to one.

C409

..... Holley ECU reads out gas AFR numbers but does all its calculations using percentage of stoich . There is a dropdown where the readout can be switched to E85 but the average person (me) is far more familiar with gasoline AFR's ... This combo has been run at 13.0 @ WOT without any piston melting issues ... static compression is 13.4:1 ... I'm in Florida (we don't have a winter blend) and test every pump purchase before it goes into a can and have never found our pump E85 at less than E80 ... its usually 85 or better .....

bjankuski

OK, it just seems very strange that it burned down. How much timing were you running and what heads?

Were the rings end gaps too tight and they butted together and ripped out a piece of the piston top that then burned on the edges?

C409

..... Timing was set @ 30 degrees from 3000 RPM - up ... I had run up to 34 before with no issues ... The tune was set for safe operation (well that didn't work) so I could sneak up on the magic formula ... I just needed a nice batch of consistent runs before any adjustments could be empirically applied .....
..... Heads are Brodix KC227 T1's ... ring ends were set to N2O specs even though I never spray (again for safety) and show no evidence of butting .....
..... The consensus here is that it was detonating when on the 2-step ... (never had an issue while I foot braked only) ... and would eat itself up down track ... it may have been wounded on the prior run also ... Timing @ the 2-step RPM (2800) was set at 28 degrees ... coming off the line @ idle , I would run past that in a heartbeat with a 5000 stall converter ... But on the 2-step , its there for a few seconds ... 2-step was set on Spark , high only in the software .....

C409

..... Pics of #5 piston ... right next door ... This is the beginning of what happened to cylinder 7 piston ... note how the ring land was pushed up and eventually contacted the cyl head at the peak .....

383vett

Obviously either too lean or too much timing. Are you running a knock sensor. I don't on my motor because if the computer retards the timing a few degrees, I've lost the race. I'm running what I consider a conservative tune.

JrRifleCoach

C409

..... Per the datalog , the right bank was a half point leaner at 12.9 AFR with no damage ... I do not have a knock sensor ... same reason as you plus solid roller cam , shaft rockers , and solid motor mounts ... I'm not sure one would work at all if it was desensitized to all of the above . I thought my tune was pretty conservative too ! .....
..... I ran this combo for 2 years at 13.0 AFR and 34 degrees timing with no issues ... that's why I'm looking at the 2-step tune to see if it was too hot timing-wise ... Still curious as to why it burned the intake side and not the exhaust valve side .....

cardo0

Man that hurts to look at. My sympathies. Carnage is easy to look at when it's not your own but we all know how much work goes into rebuilding and getting the car running again.

Well #7 blew out downward while #5 started to move up. I don't think it was a ring/ring land problem. Maybe try some gas ports in the piston crown to help seat the rings just in case. Might be a localized hot spot in the block causing detonation between #5 and #7 take a look in the cooling jacket with a USB camera.

Just my 2 cents as I truly don't know the answer. Good luck.

jetskibruce

Your system sounds like it is in top shape, but what about low fuel pressure for any reason, tank level, voltage, weird pump issue. I've heard of people saying that the AFR sensor does not always react quick enough during full load. At full song it doesn't need to be lean for very long. Are you testing at Sunshine?

C409

..... Fuel pressure was datalogged as a flat line graph @ 40psi , the AFPR setting ... I haven't been to Sunshine in almost a year ... slip'n'slide ... I hear they have a new track mgr and that prep has been better and the contractor working on the Roosevelt extension has planted grass on the berms ... that should keep most of the sand from blowing around on the big end ... last time I went , there was a car in the middle of the track on fire just past the finish line ... its a shame because I'm less than 3 miles from the track .....

jetskibruce

So not knowing what happened is troublesome. Where was the fuel from? From what I am seeing the 15% from everyday pump gas can be what they call refinery drippings (almost anything ) Are you planning the new pistons to be at the same compression? If you do come to any theories to what happen... post them. Otherwise, the only idea I have is to really fatten it up to start and see if it slows or goes faster. Did the plugs tell you anything? the pistons look clean except for the damage.
And you running at Bradenton then? I've been a few times, different vehicles, just to get a real number of what I driving.

ghoastrider1

man you got lucky that your bores cleaned up.

C409

..... The engine shop ordered the new pistons yesterday ... JE custom ... 4.157 bore ... 0.990 compression height ... small ring pkg , 1mm , 1mm , 2mm ... Flat tops with deep valve pockets ... should be 11.8 - 12.0 static compression ... 2-3 weeks , maybe .....

Churchkey

Have puked quite a few small blocks your damage is new to me. Ran 13.5 to 1 with Brodex 12's for hundreds of laps at a time without piston heat issues, always used race fuel.

Just a guess, bore size indicates a 400 block if so are the heads drilled for the block steam ports? If not that could be the problem area since # 5 & # 7 intakes are next to each other + the back of the block will run hotter than the front. Brodex 12's have a water port mid way on the intake side if your heads have that feature connect it. Another option is to drill the intake for pipe fittings @ the rear water port in the head, connect with a thermostat riser block. Lefthanderchassis.com has riser blocks for about 30 bux.

Water flow: If using a stock paddle wheel water pump + driving it with stock pulleys @ high rpm the coolant will have cavitation = no coolant flow. Suggest a water pump with a cast radius vane impeller + reduce the water pump RPM by 30% with different size pulleys.

Luck with the rebuild.

BTW If using a thermostat circle file it & use a thermostat washer. A 3/4" opening is good for starters then reduce the opening size for more temp as you see fit.

Churchkey

Additional info: The steam ports for the heads need to be drilled @ an angle to get into the water jacket in the head. Mine were drilled on a Bridgeport mill with a quill but do not recall the angle required. Suggest a call to Brodex for tech info.

C409

..... Dart Little M Block ... no steam holes .....

cardo0

So I thought the steam hole angle would be easy to look up but there's more to it than that.

C409 is using a Dart Little M he reports no steam holes in the block. My Chevy Power Catalog (5th edition) says just use the stock 400 gasket as template. While my 7th edition Power Manual says the smaller 3/16" holes need to be at 10 degrees. But both my catalogs say it is not needed for race only motors driven above 3500rpm. Since C409 really has different 400 block I doubt he wants to go there.

Now to really confuse things the 7th edition catalog has a sidebar on Hendrick Motorsports conversions of any small block for NASCAR racing in that period. And of course they (Hendrick's) drill 0.090 holes on the sides of the block, 0.75" below deck surface, between siamesed cylinders - 3 on each side. The holes are connected by some kinda manifold I can't really see in the picture to the water pump to prevent air pockets under the block deck. Then plug the water pump bypass hole. Hendrick's also add holes to heads near the head bolts but I really don't know how they do it so I won't even try to explain it.

Man the details never end.

cardo0

Yes, many times this is overlooked but the cooling system needs some backpressure to work. Backpressure at the t-stat keeps the system in the heads and block under higher pressure to prevent air pockets/steam holes.