As some of you may have read in my other thread, I had an issue Friday night at the drag strip.

During my 8th pass of the night, the car sputtered a bit, and then started ticking. I immediately put it on the trailer and hauled it home. Saturday morning when I unloaded, it was still ticking, but got quieter after a minute or so. I put it in the shop and started pulling things apart on Sunday.

Well....I got the driver's side head off today, and it looks like I broke a piston. There's a chunk missing of the top left side. It looks like it didn't damage the head or valves, and it still had oil pressure, etc. The cylinder walls even still look fine. The engine had 155,000 miles, so I can't say this is a huge surprise.

So, what's the most cost-effective way of going about this? I do run a supercharger, so I'm sure I need to go forged bottom end, but should I pull this motor and rebuild, or is the cost a wash to just buy a forged short block?

I'll have lots of questions going forward, so thank you for your input in advance!

Stacey

 

Other thread said you could spin the rod by hand. That's independent of the piston problem right? We're there 2 issues then? Sorry just questions no answers

 

Yes, could spin pushrod by hand on what I think would be the #7 cyl intake valve. When I pulled the head, hoping to just replace some lifters, I found the broken piston on #3 cylinder.

Decent size chunk is gone, but it's nowhere to be found. Head and valves look undamaged.

 

You can replace just the piston with the engine in the car if you don't have funds for a new engine. Pretty cheap if you do the work yourself and you might find the chunk in the oil pan or pickup screen. My friend did that and ran the car for a long time, eventually he put in a stroker kit to ease his mind. Pretty decent shot you cracked the cylinder though, you'll want to do a leak down test after you replace the piston even if the cylinder and head look good.

Obviously if you can afford it you would be much better off with an new forged engine, particularly since you can't find the broken chunk (maybe it shot out the exhaust or is in the intake, look there while you have it apart, HOXXOH filled his intake with chunks).

 

I've been in this position before with my 85, if you get it back together after only installing the piston, and there is still some other problem, then your time is wasted, so its a gamble you need to weigh.

I would pull it, inspect everything and then you can minimize the cash outlay, but I would certainly want to look at the mains and rod bearings, and I would replace them just because if it were me.

 

I would just use this as an excuse to go with either a forged stock stroke or 416 if you have the funds. Otherwise find those missing chunks and install another piston, but that wont be the choice for a lot of people.

 

I had pretty much the same thing happen and was able to replace the one broken piston on a Friday and went racing with it Saturday. Also, even though it's a challenging job it's very doable to do the replacement without having to pull the engine.

 

Christopher your wrenching skills in your 2 car garage are legendary...not many folks would swap transmissions and motors like you do in the garage. OP should realize that your skills are not normal when he makes his decision!

BTW I forgot to post earlier, I'd suggest increasing fueling as well on the tune, the notorious #7 ring land bites yet another Vette fan.

Christopher have you gone to a slightly larger injector on 7? I have heard of guys doing that or flow testing and putting the fattest one on 7.

 

I tried LS9 injectors a few times but for whatever reason the car seems to run better with the stock LS7 injectors. My injector duty cycle is pretty high but I scan every single pass to keep an eye on KR and also use an awesome full additive which raises my octane by about 9 points. Even though the stuff costs $80/quart, each bottle actually saves me around $400 since I no longer have to buy race gas at over $8 a gallon.

 

Sorry for the hijack OP...

What additive? I add 1 gallon of $12 race fuel to my ¼ tank or so and it kills knock right now, when I'm getting knock which isn't all that often given my 12.5 AFR.

Do you find it working as well as race fuel and what's your math on how much to add?

 

It's called Aces IV and I believe it's main purpose if for increased upper cylinder lubrication. I'm not sure if the octane boost is a desired or accidental side effect but regardless of that, the stuff absolutely works.

Dave Myers from Yank originally told me about it and I was initially skeptical given all the other ones out there that don't seem to deliver on their promises.

How I ended up testing it was running a half tank of 91 octane with the additive mixed in and then heading to the drag strip. To be safe I pulled 10 degrees of timing out across the board and then starting making passes, adding in two additional degrees back after each one providing I wasn't seeing any knock.

Not only was I able to get back to running the same amount of timing as I did while running 95.5 octane (50/50 blend of 91 and 100 octane), I was able to actually add a few degrees beyond that. I probably could have kept going as I still wasn't seeing any knock when I stopped.

The recommended mixture is 1 ounce to 6 gallons if you're running 11 to 1 compression or less. Since I'm at 11.6 to 1, Brian (the owner of the company) recommended going with 1 ounce for every 5 gallons. Late last year I started getting some KR out of the blue and according to Brian it was due to the stupid winter blend we have out here in California. He suggested going with 1 ounce to every 4 gallons and voila, problem solved. Even though I could probably switch back to a 1-5 mix, I stuck with 1-4 as a safety precaution.

 

^^^ Wow learned something new. Glad I asked and thanks for posting.

Does it turn your plugs orange like Torco (not that it matters). Saw I can buy it on line.

The math works well - ¼ tank is about 4 gallons give or take, the additive is $2.50/ounce so rather than spending $12 for a gallon of race fuel to treat the 4 gallons, spend $2.50 for the ounce of additive.

Seems crazy that 1 ounce of anything would make much of a difference, but only a fool would argue with your testing, you're one of the most meticulous guys on this board. Might have to pick some up.

 

If you end up not liking it, I'll be more than happy to buy whatever you don't use.

One other benefit I forgot to mention is that it stabilizes the octane content in your fuel. Untreated fuel will start to lose octane after about three weeks but once it's been treated with the additive it'll stay that way for around three months. I can't testify one way or the other as to this claim as I never have fuel around long enough, but it seems to make sense based on having talked to him personally and how he explained it.

 

^^^ sounds great, and actually, we didn't really hijack this thread as I think about it, you posted up a proven solution on how to eliminate knock and hopefully avoid breaking another #7 piston land!

 

Wow, didn't know there was any way to replace a piston without pulling the engine.

When I say cost-effective, what I mean is, I see no need to spend $6k++ on a new forged short block if I could buy a rotating assy, cam, lifters, etc. and have the block cleaned up and checked for say $3K. I'm making numbers up. Now, if it's $6K for new and $5700 for a rebuild with me doing the assy work, then it's a no-brainer. Buy the new short block and put it in!

I'm not after crazy HP numbers, but I do want the rebuild to be durable at my power level. If I rebuild, I might do a mild blower cam or something, but nothing crazy.

When I pulled the plugs, I did notice that #3 cyl looked different from the others on that side. When I pulled the head, the valves definitely look different on the cylinder v/s the others. I do not know if that injector shut down and it leaned out, or if this is just a consequence of having a 155K mile motor, supercharged, and driving the out of it on a weekly basis.

BTW, I do have 60# injectors and a KB BAP.

Thanks for all the input so far!
Stacey

 

I was hoping you wouldn't divulge all my speed secrets.

Missing a chunk off the top of a piston without snapping off a valve head is really strange. But then again, it gets really weird when you find exhaust valves in the intake manifold and piston ring pieces in the cats.

 

Lol Tom sorry about that!

Stacy I missed the fact that your engine has 155k miles. I would say that mill owes you nothing and it should be retired. 155k hard miles mean it's done IMHO and not worth sinking money into.

If you have funds if buy a new stroker motor...if funds are tight, a junkyard low mileage ls2 and get another 155k out of it.

 

HOXXOH - When I put this engine back together, I'll just throw all my old used pieces in the mouth of the intake if that will make it faster!

Joe_G - No, it's served it's time. It didn't last a long time with the blower, but since last August, probably 90% of the miles put on it were at the dragstrip. The only thing that I had started to notice was that after making several passes and the car was hot, my oil pressure was slightly lower than what I remembered it being. It was still 28-30 psi at idle, however. 40 psi cold at idle. It still shot up like a rocket when accelerating.

So...where do I start with putting this thing back together? Is the block salvageable? Have the machine shop clean up everything and then put it back together with forged internals, or just buy a short block? Where is the best package deal on forged short blocks? If the block is still good, can I just buy a forged rotating assy from one vendor as a package? I really don't have the time or desire to sit down and try to figure out every part I need from 12 different vendors. I'd rather just buy the whole thing as one piece if possible!

Thanks for all your help!

Stacey

 

I would personally retire that long block and get a new one.

If you have funds, I'd look at vendors such as Scoggins Dickey for long block options, I have no experience with them but have seen their ads quite a bit and they have a wide assortment. There are other shops that come to mind.

And you are very wise to source your long block from one vendor, so there are no fingers pointed if warranty claims arise. To the extent you can get a warranty on a blown engine.

You might want to put up a new thread asking for experience with engine builders and get some comments from folks with experience.

If funds are a big issue, a junkyard engine is an option, fraught with the perils that come with such. Not the best plan if you think you will put the blower back on, but you could buy 2 or 3 used motors for one built forged long block.

I would think about enhancing your fueling system with a new pump if I was you. My internet observations (no personal experience) lead me to draw a conclusion that a higher output pump is a great idea in boosted situations.

 

Thanks for the input Joe_G.

I do have a KB BAP and 60# injectors. I did use the Racetronix harness for the BAP, and oddly enough, I check the inline fuse under the hood before every trip to the drag strip. I know that if the BAP stops, I'm lean, and bye-bye pistons. I checked it again after I found the broken piston, and it was still good.

Are you suggesting I eliminate the BAP and go with the ZO6 fuel pump?