motogib1

Hey gang, I have my 02 C5 at a shop in Longwood, Fla, Next level performance. The car has had oil in the cleanside airline and recently threw a flashing cell p0300 code. A compression chechek showed low compression in #7. They are removing the head to check for damage. My question is, what are my best options. If I rebuild, should I put in a new shortblock with forged pistons? I think this issue may be related to the cast pistons and lack of strength. I have had the car a long time and it has heads/cam Fast) Nick Williams throttle body and the supporting parts. I will update once they check get the head off.

Thanks,

Moto

aaronc7

I cracked #7 on the road course due to heat I believe... no knock, etc. In the process it also cracked the block/cylinder liner of that cylinder. Have them check everything out to confirm the block is still useable or not.

I figured it made sense to at least do a mild upgrade on the rebuild since labor $$$ is fixed and going to be a huge chunk of the bill either way. I did basic forged pistons and I beam connecting rods w/ ARP rod bolts. Those are the biggest weak points, I figured I might as well address them now. My builder used Wiseco pistons and scat rods.... lots of good options out there.

Ultimately what you end up doing probably depends a lot on your goals and usage down the line. I ended up supercharging mine, but that wasn't the plan at the time.

motogib1

Thanks, could you divulge the $$ involved in the rebuild?

aaronc7

Apparently I didn't save a copy of the invoice.... but I want to say the short block was around $4k with above mentioned parts, new crank, oil pump, teflon coated bearings as 'extras'. Keep in mind that was an all new shortblock... if your block is good and you can resuse that and crank etc, that will save a good bit. Only thing I was really able to sell off my original engine was the oil pump, crank and some small misc stuff.

Labor was about the same. I do a lot of my own work, but I wasn't nearly motivated at the time, so that was them pulling the engine, putting together the new longblock (moving stuff over from blown to new engine), and reinstall etc.

jim993

Cracked liners and broken piston ring lands are frequently caused by too little ring gap for the heat being generated in the cylinder. A ring that is too hot closes the gap, sticking the ring in the cylinder pulling the piston land off, breaking the piston and or cracking the liner.

Check the following:

https://www.enginelabs.com/engine-te...-ring-end-gap/

Hot Rod magazine once took a junkyard 4.3 LS, disassembled and reassembled it with the same junkyard parts but with one modification- they increased ring gap to 0.028. They then proceeded to add boost and ran it up to 1,000 HP during the last several of nearly 100 dyno pulls. It held together fine.

JHrinsin

The PO (a good friend of mine) also had #7 let go on the warmed over stock short block LS1 engine during a road course event back in 2015. Seems that #7 is the one that is most likely to fail. It doesn't help with the typical elimination of the rear coolant cross over / steam tube when you install the LS6 or aftermarket intake manifolds. Also the PO had been running a Melling #10296 high volume oil pump, no oil cooler, 5w-30 oil (with an extra quart added) and the early 1-pcs bat wing oil pan and a stock radiator with a 160 F thermostat. He was seeing oil temps as high as 300 F during track event secessions before the engine went south. No idea on what oil pressure reading he may have been seeing.

The PO had Mike Norris Motorsport in Indianapolis replace the engine with a 5.7L TMS stage #2 short block using a stock GM crank in a later 12561168 block, a set of forged Scat Pro Comp I-beam 4340 rods with ARP 8740 cap screws, and Diamond forged pistons with -2cc valve reliefs (due to high lift camshaft) with their 1.5mm x 1.5mm x 3.0mm ring package and 8620 alloy wrist pins, all blue printed and balanced. Mike installed a Melling 10295 high pressure oil pump and due to the bearing clearances he recommended at least 40 weight oil. He transferred the Comp Cams camshaft from the old engine and also installed a new LS2 timing chain, new LS7 lifters in new LS2 trays. Mike then topped it off the short block with a pair of reconditioned 243 heads and transferred all the Comp Cams valve train pieces / parts from the old 799 heads. He installed new Manley push rods and new GM gaskets throughout including the stock 0.053" MLS head gaskets (I wished he would have used Cometic 0.040" MLS head gaskets to gain back the cc's lost to those valve reliefs in the pistons - oh well). The PO also had him upgraded to FAST 36# injectors at the time as well. Total out the door cost with parts, labor, tax and a full dyno, idle and drive-ability tune was just under of $9.3K. As always YMMV.

The car has not seen track duty since the new engine was installed. Before I take her back out on the track though, I will re-install the 4-corner type coolant cross over / steam tube setup (removed when the PO installed the LS6 intake manifold) to help eliminate any hot spots in the back of these cylinder heads. I will also install a HD 2-row fabricated aluminum radiator as well as a thermostatically controlled oil cooler kit to maximize the cooling capacity and keep the fluid temps properly managed. For better oil control, I will install the Improved Racing trap door baffles in a later 2-pcs bat wing oil pan, as well as the update the valley cover and PVC system to the '04-05 LS6 setup and install an Elite Engineering catch can setup. All this to give me hopefully a more bullet proof setup (short of an Accusump or a dry sump conversion) and better peace on mind while out on the track, as well as to help protect the PO's investment in the new engine.

ASRoff

the number 7 on LS1-6 are notorious for letting go... the LS6 had the rear vent tube crossover removed from the factory. because of this I personally run evans coolant with a 4 corner steam kit . and ring end gaps opened up .005 ... I would do more if I ran nitrous or Force induction.

JHirnsin .... the slight gain in compression bump from .054 to .040 is not really the reason why someone should go with a thinner head gasket. Thinner gaskets are used to increase quench ..... which also helps with detonation...... here is a pretty good read on that if you are interested.... https://ls1tech.com/forums/generatio...tom-ls1-2.html

motogib1

Thanks, sounds like some rebuilds with all the good stuff. Personally I would like to do a budget friendly build with all the stock stuff if possible with the exception of forged pistons to avoid a repeat in the future. I wonder if there are some vendors on here with some shortblock options in case my block is damaged. It seems you cannot get ls1 blocks anymore.

aaronc7

Correct, actual LS blocks are rare, but there are plenty of alum 5.3 motors, and you just bore it out and it's more or less the same thing. That's what I did, and the only extra thing the shop had to do was a little clearancing the block around the motor mounts... I don't know exact details but it was very minor.

Here's a few places that I looked into for short blocks. I got mine from schwanke.

http://www.thompsonmotorsports.net/i..._31_653_35_364

https://www.schwankeengines.com/collections/ls1-ls2

Texas speed of course as well

tblu92

It all depends on your car's expected use----If it is a D/D type car I would just fix it as stock and keep an eye on coolant temps and overheating--Put in a lower thermostat and lower the fan settings--be sure your radiator is not clogged or full of bugs and debris is the front
If you plan on road racing or drag racings alot--it then may be wise to go to forged stuff--
PS make sure you have plenty of oil pressure

motogib1

Thanks, I really like some of the options there.

redzg

From the many stories here and on other LS forums, it seems as though ring gap and cylinder cooling are the biggest factors. Forged pistons may certainly be stronger, but if the ring ends butt even a strong piston is going to fail.
If the motor is pretty well cooked, i.e. crank is beyond hope, etc., why not think big? I'd be thinking used 6.0 with a fresh set of rings (properly gapped) and bearings, cam of your choice (maybe even the one in your current motor) and the current top end. Might be fun for not too much money. Personally, I think I would tend to a 24x reluctor.

motogib1

I like the idea of a 6.0 or even possible a 383 so long as I can use my current heads heads and cam as I put in heads/cam FAST and Nick Williams throttle body many yrs ago and I do not want to replace them if I don't need to. I will discuss this with the shop. It's kind of fun looking at the possibilities.

JHrinsin

Keep in mind that those stock 243 heads are fine to about 400-425 rwhp, but much more than that and you are looking at ported versions or aftermarket heads to get the most out of a higher horse power and/or bigger cubic inch package. Same goes for your camshaft. If you really wanted more cubic inches, then go with a LS2 block, just make sure that the crank and knock sensors are set up for your Gen III engine controls. The 4.00" stroker crank is popular, but there are other issues to consider - talk to you engine builder about the piston BDC position and how much piston side skirt is exposed as well as clearances and windage concerns. Keep in mind that the LS7 block was the only regular production LS block that was truly design for the 4" stroke. As always, YMMV.

motogib1

I have PRC stage 2.5 CNC ported 5.3 litre heads. Don't know how much power they can support.

motogib1

The shop is supposed to call me tomorrow about what they see once they get the head off. I will keep this thread going till so finish the project. Maybe h lpnl he next person who has this happen. So many times I run across threads on here with no resolution.

redzg

And it just bites. Particularly when it's a subject immediately at hand, and if the OP found the answer it would save time and money. Do keep the rest of us posted, and thanks!

motogib1

Ok, talked to the shop today, they got the head off and looked at the piston. They say the piston looks intact and may be an issue with the rings. I do know I never heard any noises coming from the engine but I did have some oil in the clean side air line which was probably caused by blowby given the low compression in the cylinder. So is the question is what to do next

JHrinsin

What about the cylinder wall, has it been scored or cracked? Are they 100% sure about the piston ring lands not being damaged. Hyperutechtic pistons can deform a very small amount before they fracture. If the cylinder wall was damaged then the block has to come out. The LS2 6.0L block and/or as you noted the stroker crank option is then available depending on your budget. Those ported heads will keep up with the added cubic inches. As noted above, if you decide on a swap, just make sure you stick with the 24X trigger wheel on the crank so that you don't add yet another layer of complication to a swap. GL with the rebuild and keep us posted..

aaronc7

I looked into the the gen4 engine options and yeah, any sort of trigger wheel conversion etc is definitely possible but it adds cost and complexity to the build. If you wanted to upgrade while you're there without spending a ton or making it overly complicated, 383 stroker is probably the best value, IMO. Looking back I kinda wish I had done that now.... would have only been about $1k more.