As posted earlier I decided to push the limits of iron manifolds by changing to the Crower level 4 cam and had another set of heads made up with the TA large valves. The compression came up to 10.12 from 9.8. No other changes. Cam break in went well and tuning began. The idle vacuum was down to 12 inches and it wanted more initial timing. As expected with a bigger cam. Recurved the distributor limiting the total mechanical advance and ended up at about 20 initial and 36 total. Checking the carb by using my air/fuel meter, no jetting changes were required. Air screws were adjusted to attempt to smooth the idle and increase the vacuum. This level 4 cam has a pretty good lope to it. Initial seat of the pants (aka butt dyno) impression was low end power was down and the top felt about the same. The power brakes had enough vacuum and work fine. Fuel mileage if that matters did drop off some. At the track conditions were not good with very humid air. It was slow off the line with a best 60 foot time of 2.07. Was running low 14's @95 mph letting it shift itself at 5200. I decided to try shifting it manually at higher RPM. It did run faster and higher MPH and I ended up shifting at 5800 and ran 13.96 at 98. Still no where near its best ever with the old combo. My intake has a removable center divider so I tried opening the plenum thinking this cam may like it. It killed even more low end power slowing to 14.50. Back in with the divider. The open plenum trick has never helped with any of my 350 setups. After my last run I noticed it was missing badly and shut it down. Oil blowby was puffing into the air filter housing thru the valve cover breather. When I got it home and ran a compression check there was only 37lbs in the number 3 cylinder. Off with the head. Gasket looking good. Out with the engine and number 3 piston was found as shown. The rings held the broken chunk in and the cylinder was not damaged at all. Apparently hyper eutectic pistons don't like near 6000 RPM. I say 6000 because the sun was in my eyes that last run, I couldn't see the tach very well and I may have shifted it at more than 5800. I could not hear any detonation and found no other indications of it, so believe it was just too many RPMs for them. This is why I'm against using cheap cast pistons just to get enough compression to run bigger cams. Keep your revs under 5500. I think if you were to run this cam it would need a 2500-2800 RPM converter and then slicks to hook it up. I believe it would really like a single plane intake as well and headers. 3.73 gears would work nice also. Not quite what I can run for stock appearing/Pure Stock. So now I am thinking at this point it may be cheaper to build a 455 to replace it. What do you think? Do I jump ship?
Wow Steve, seems strange. My Z06 has hypers from factory, along with a lot of other new cars, shift it @6,500. The other eng. that I ran the Voodoo cam in had hypers, shifted that at @ 6,000 , (6 grand tach), Had 5,000 miles on that before it lost a lobe. Only my Speed Pro hypers didn't have the Shizamm monogram on the skirts, and weren't coated. TXGS (Phil) also is running hypers, as well as gsjohnny, I believe. o No: I hope you get it figured out........
It's not the rpm and it's not the piston material. I've taken cast pistons in other apps. to 7500 rpm. Your pics show a clear story. Looks like detonation. Could be some other things going on too, but that one's obvious. Your upper rod bearing is pounded on. That's a pretty good indicator right there. I see cracked skirts similar to that from way too much bore clearance/taper (.008-.015" instead of .003" or so), but only you would know the answer to that.
Poss rattled it as said, or ive seen pistons broken when installed on rod and missed during assy? Regardless that sucks. Sorry to see it happen
One pistons and one set of rings would cost less than a 455, but if you have to have a 455 give me a call I have a .020" block all machined ready to build and a virgin block that needs everything. I also have '70 heads converted to stage 1 valves I can give you a great deal on as well and a few other goodies, I could even deliver. LOL Derek
Don't really think it was detonation. Keep in mind those bearings have over 7000 miles on them. The cranking compression is only 180-185. Will need to pull the others to look for damage. Will also measure bore taper.
Not delving into details within the thread, but shiny upper bearing really points to detonation. Hard to tell if it's just the flash coating wiped off of the bearing, but whether or not they "fall out" of the rod would point to the severity of the det. Remember on a scale of 1-10, audible detonation isn't heard until maybe 9... way too late. Not sure if this was home built but shops don't normally press the piston pins upon assembly, they are heated and slipped in. Cranking compression doesn't rule out anything. Things like altitude or air conditions, exhaust valve seat width (contact pattern) and many other things will affect octane tolerance. Detonation COULD have easily knocked the ring lands out, leading to the skirts collapsing. The crack leads right to the weak slotted oil return area, same area that cracks when there's too much bore clearance and the skirts are being pushed while cocked in the bore. Press damage I've seen breaks the piston from somewhere near the pin area or the ring lands themselves near that area.
At WOT, I doubt whether you would actually hear detonation. I never run at the track without some race gas mixed in. It might slow you down a bit, but it's good insurance against detonation. Hyper pistons are more brittle and they are notorious for not liking detonation. It doesn't have to detonate a lot at WOT under high load to cause damage.
Wow Steve, I'm really sorry to read about your motor. I follow your posts because I value your advice and experience, I hope your build can be fixed within a reasonable budget.
Reading through your other results as well as this post, this throws up a red flag. Your IVC point would have to be way less for cranking pressure to be at these numbers, which means it has a serious advancement issue. Either that, or your calculated static compression is way, way more than 10.12:1... These compression numbers correspond to something closer to 11:1 or 11.5:1 static with a ~70* ish IVC point...so I'm going to have to agree with others with the detonation suggestion. Not to mention that with increased overlap, Effective Compression will go up as RPMs increase, exacerbating the issue even further. Give us your numbers for calculating compression and maybe we can sort it out...maybe an oversight? No one's perfect. I would love to help as much as I can, as I'm sure others here would as well. Something is definitely amiss. You're one of the go-to people for Buick 350 knowledge. I'd hate to see you abandon ship. The information you have/are providing is incredibly important. Gary
Larry, if you only add race gas at the track do you NEVER go WOT on a deserted country road? For testing purposes only of course. The engine would not know if it's at the track or not. I used to do this also but it messes with you carb settings when you don't have consistent fuel blending. Specs for calculating compression are; 53cc chamber. .045 gasket with 3.9 ID, -.015 deck, 15.5cc dish.3.84 bore. I came up with 10.12. I will check the bore for taper tomorrow. The bearing was tight in the rod, I still have not removed it. The coating is barely worn off. That's to be expected for 7000+ miles. You have to remember there are many times when it sits for a month or more without being started so most startups are dry from sitting. There were no signs on the rings or in the ring lands of damage. If this was done on assembly I don't think it would have made it this long before breaking. If anything I'm leaning toward the bore being rather loose. Though I would expect there would be more lower skirt wear if so.
So was the lower gear on the timing set put at the 2 degree retarded position and called it good or was the cam actually set at 2 degrees retarded using a degree wheel? Paul
The top ring groove looks like that piston was cracked(broken) for a while and just recently came all the way apart at the ends? Possibly the rings trying to keep it together for a while? That engine was I would say "limping" for quite a while with the way that crack looks and just finally gave up the ghost, look at the bottom of the top ring land where the color is darker than the 2 sides that are gray. Steve did you look at the detonation gauge in the link I posted? I didn't post it to be a smartass, I thought it could be a useful tool for you in the future when you get the car back on the road. I would recommend one of those to anyone that does the aggressive tuning that Steve does, if you can't hear it at least you'll be able to see it. The RPM didn't kill that piston, I think its is a defect, you do know that the Speed-Pro stuff is made in India now don't you? Most of todays car's engines use hypereutectic pistons with much higher RPM you ever thought of spinning the sbb 350. The difference is that the computer controlled FI of today have very sensitive knock sensors that will dictate that the timing be turned back when the knock is sensed. Take the obsolete sbc Vortec engines of 96-2002 they had a static compression of 9.4:1 with a 61.5* intake closing point which put dynamic at 7.91:1 according to the Wallace Racing dynamic calculator if I did the calculations correct and their recommended fuel to run from the General was 87 octane. Anyway my point being is that engine only had cast pistons! LOL And the timing swings to keep those in check under load had to be on the larger side depending on the load the truck was hauling and or pulling. I have to also say that I have never been a fan of the Speed-Pro stuff even though I have S/P hypereutectic sbc pistons in the sbc 383 in my '65 Impala. In that car when I shift manually I like to shift it at 6,000 RPM only because it won't rev any faster. LOL The heads have the flat tappet springs on them that I just never got around to changing with a .550" .546" 202*/212* @ .050" cam with a 113* LSA roller cam with 9.8:1 compression. Basically a bad ass truck engine to get that barge moving. If you take your pistons out I will be trying to make it out to Dave's shop this weekend and we can try magna fluxing them if that's even possible to do on aluminum? To see if any of the others are cracked if you have time this weekend? Then I'll sneak them in the jet washer for you if you want? Shhhhhhhhhhhhhh, don't tell Dave. Is this the piston you need?; http://www.summitracing.com/parts/uem-s1749h-040/overview/ I see they are only 1.835" compression distance, that would put them .043" in the hole with a "blueprinted" block! WTH?! Are those the right ones? What are your piston choices to stay within the rules of the "stock" racing class? There has to better choices than that! Or did the Chevy guys make the rules? I think you should just take the block down all the way apart and just do a repair on the engine, ball hone the one cylinder clean everything up have a new piston hung on the rod get one piston worth of rings and put her back together. As long as the rest of the pistons don't have any issues. Or get 8 and bring them to Dave's shop and we'll make him hang them while you wait.(maybe, let me know if you want my assistance, I would be happy to help) If you only do one piston that way it will only have to break in one set of rings on one piston. I don't think you'll notice the difference until the rings break in on that one piston. LOL Then you can start racing with 8 good pistons! And make those old numbers look like a punk! Derek
Steve, Around here, there really is no where I can go wide open throttle except for a few seconds. I had to get up really early on a Sunday to do my WOT 1-2 shift point check when there was very little traffic. At other times, it too crowded around here with people walking around. I had to put the drag radials on to boot because there is no flooring this engine at lower speeds without sticky tires. I had to wait until the track to check the 2-3 because there is no way I would take the chance doing 80+ with my commercial drivers licence, the cops are all over. There is a huge difference when you are at WOT momentarily on the street, and when you are wide open from dead stop for 11-14 seconds under high load. If it is going to detonate, that is when it will occur. One of our club members was tuning his carburetor at the track for pump gas. He was leaning it out because the trap speeds were going up as a result. He was running 93 pump gas. The car ended up going back in the trailer because it started pissing coolant from between the block and head. When he got it home, he changed the head gasket and then it started blowing the freeze plug out on that same side. He ended up changing the block. This was on a freshly rebuilt 550+ HP big block Buick. JW told me when my engine was delivered that he would like me to mix in some 110 at the track. Yes it affects the carburetor calibration. I would rather deal with that than detonation. If you want to race at the track with iron heads and 10:1 SCR, with pump gas, I'd have forged pistons next time. The Hypereutechtic pistons are more brittle due to the higher silicone content. They don't tolerate detonation very well at all.
Pulled all the pistons today. All others look fine. Checked the bores for taper and could not detect any measurable difference. Used snap gauge/micrometer. Was very surprised but I'm OK with it. But keep in mind these bores have less than 10,000 miles. There is no detectable ridge on top either. The piston could have been cracked for some time and finally just completely broke. I don't think there's anyway to determine that. You can see were the piece was rubbing on the piston but could that be from 5 minutes of run time or 2000 miles? The shiny spot on the bearing does not even go all the way to the edge of the bearing. All the bearings look that way, some better, some the same. The piston broke on the valley side of the driver bank. Is that the thrust side or not? Pistons are from 2006, I don't think they said made anywhere but US or I would probably not used them. Larry, guess I'm lucky to live semi rural area and only have to dodge stray deer from time to time. Also have a highway on ramp 1 mile away. I'll go thru the top of 2nd before letting off. Thanks to all for the help. Is no one going to try to talk me out of going 455 beside Gary? I have all the parts on the shelf waiting to be used.
A well blueprinted 455 will walk all over that 350 in your application. With tall gears an no converter there is no comparison. When the car is heavy , and the drivetrain is mild, the cubes rule!!!!!!!!! Now if you had a ton of converter and gear, id say try and test the limit of a 350 Good luck
Well it checks out at 10.115:1, so you're spot on with that. According to the wallaceracing dynamic compression calculator, having 180-185 psi dynamic cranking pressure equals around 11.5:1 with a 70* IVC point. Is there something I'm missing? I'm certainly not perfect. You used to run the Crower level 2 with this setup, if I recall. Perhaps there was some detonation with that 58* IVC cam before you changed to the level 3 and you never noticed? It would have ran fine for a while, even with some stress fractures until it finally gave up with the level 4, as Derek suggests. Running fine and holding together at lower RPMs, the pistons just couldn't hang on any longer after revving it to close to 6,000 RPM, and actually has nothing to do with cast piston durability at these RPMs, since 'stock' eutectic pistons at ~12% silicon and the hyper-eutectic pistons at ~16-18% are both capable of safe operation up to 6,200 RPM, so I've read. Others here say the hypers are good to even beyond that. Hypers will be stronger and lighter yes, but regular cast are still good for stock-moderate builds and aren't nearly as brittle as hypers. The Sealed Power '10:1' pistons are supposed to be pretty good, and can be set to closer clearances (vs OEM pistons) even though they're not 'hyper' saturated with silicon. Here's the link at Summit Racing: http://www.summitracing.com/parts/slp-340p40/overview/make/buick I'm not suggesting you use them, as you may need to bore the engine again and these only come in two sizes: .030 and .040. Just giving reference. Does someone make a detonation detector you can drill and tap into any block? Would be cool if you could do this and have like a red light with a buzzer or something that comes on to warn you when detonation occurs. Either way it sucks bigtime to have this happen, but I sure hope you don't give up on this project out of frustration. You are providing extremely valuable information to the Buick community with your sacrifice and time. I for one greatly appreciate all you've done. I'm sure others here do as well. Bottom line here (outside of the piston disaster) shows that the increase from level 3 to level 4 actually decreased power (and no doubt longevity and fuel economy), showing that bigger is not always better, particularly when other parts are not matched to it (head flow, headers, etc.). The increase in cam lift and duration did nothing to improve power on a head that flows optimally at lower lifts. This is the 'proof' we needed to back up mathematical calculations and claims. Thank you, Steve. Gary
Wise words here. Been there, done that. I can attest. You lose the charm of the 350 (sound, feel, mileage, etc.), and lose some RPM if the 455 is stock/mild. Handling would suffer some too. There's more to the entire package besides cubes and straight-line power. Something to consider. In hindsight, I would have kept my 350 instead of swapping over to the 455. The experience and knowledge was good, but I like the 350 better (even though it didn't have the torque the 455 did). Gary
