CharlieC5Z06

Awesome Thanks.

CharlieC5Z06

Rob 02

Be careful cleaning the engine deck surface. Don't use any abrasive. I carefully scraped the gasket material off with a razor. Both the engine and cylinder head deck surfaces need to be perfectly flat like within less than .001". The exact speck is in the book. That doesn't leave much margin for error. If the Head shop has to deck the head more than .003" you may need a thicker gasket to maintain the same compression ratio so wait to order the gasket. With a supercharged engine too high of a compression ratio can cause pre-detonation problems (knock). Pre-detonation is the enemy. You may want a thicker gasket anyway with 243 heads as the LS6 has 10.7:1 compression ratio. 11:1 would be a little too much for FE unless you are planning on running E85, meth water injection etc...

If you want to be **** you could check your cylinder bores with a dial bore gauge to make sure they are not tapered or out of round. That's is up to you.

What do the heads look like?

CharlieC5Z06

Great thanks for the tip. Any idea what gasket I should get? Also after I vacuum all the coolant out of the cylinders is there anyway for me to tell if the pistons are bad?

Rob 02

Were all four low compression pistons on the same side?

Rob 02

Vertical grooves in the cylinder would indicate a broken ring (large enough to catch your finger nail). There may be some cross hatching but that is just the factory hone. If you can still see the cross hatching from the factory hone then you probably don't have substantial cylinder wear. These engines are really pretty hardy. Look for any chips or cracks on the edge of the piston (ring-lands). Get each one at top dead center where you can see them. You can only make an estimation at this point.

There is no good way to check ring seal with the head off or with leaky heads. When You put the rebuilt head on you can check compression.

Rob 02

By looking at the spark plugs in your other thread it appeared that the carbon build up was consistent with the carbon on the pistons with no burnt oily residue. The oil on your Plugs looked wet and fresh, probably from your compression test.

If all checks out I would have a fair amount of confidence that the ring seal is good.

Don't get any sand or trash near the cylinders or rings. I know that is near impossible but do you best.


If you are going to try to DYI polishing the heads then do it before you may want to do it before you take them to the machine shop. It may be better to let the shop do it.

CharlieC5Z06

OK cool, ill do my best at inspecting the cylinders tonight. Yeah I am going to just bring the heads to a machine shop for a cleaning. Should I buy all new valves and rockers and everything while I have them out? The springs are new from when I did the cam. Just wondering what else I should do while I have all this apart. I dont think I am going to get them ported. I would have to send them out and it costs almost as much as buying new heads for not much HP gain on the forced induction.

CharlieC5Z06

No 2 bad cylinders on each side. I gotta get the power steering pump off when I get home from work then ill be able to get the other head off.

Rob 02

It might be hard to get new sodium filled valves and perhaps unnecessary. The head shop will determine that. They will reface the valves and seats so they seat like new. Ask if they triple grind them. Most shops do. They grind at three angles for better flow and combustion efficiency.

I would consider refitting the stock rocker bearings with the bronze bushing type trunnions, especially with your performance cam. If you do a search you will see a lot of info on them. They should run quieter and be less prone to failure.

If you want better push rods and lifters now is the time. I used LS7 lifters and trays but there are always better choices depending on your budget and goals. I only have a LS6 cam so I didn't bother going high end on the valve train so I can't speak from personal experience on these items. I just did mild upgrades refreshing the engine internals.

CharlieC5Z06

Ok thanks. I just installed new comp cams pushrods so maybe ill get new lifters and rocker bearings. Will new rockers be worth it?

Rob 02

Were all four of the bad compression cylinders in the back of the engine or in the middle? Just curious.

CharlieC5Z06

middle

Rob 02

You could just install trunnions on the stock rockers.

Rob 02

That makes since as far as my theory goes. That is the area under the most stress from cylinder pressure.

You can clean the carbon off of the pistons with a soft brush and brake cleaner. Try to keep trash out of the ring area. The pistons stick out of the hole a few thousandths so you should be able to hold a rag around the edge. Carbon isn't as bad as getting sand in there but be careful.

CharlieC5Z06

Rob thanks for all the help man. Appreciate it. Im looking at those comp cams trunnions now. Gonna order a set of them.

Rob 02

Get stronger head bolts and research head gaskets recommended for supercharging. You don't know the thickness of the head gasket you will need yet until you know how much material the shop will be removing when surfacing the head. It is not 1 to 1. Remember that the combustion chamber is smaller than the cylinder bore. If the shop only removes .0035" from the deck then I wouldn't worry unless you want a lower compression ratio. If they have to remove .007" or more then you will want to consider a thicker gasket. Some people use LS9 gaskets but they have a slightly larger bore so there is some controversy about that in theory.

neutron82

I would advise against ordering comps trunnion kit... I made an old thread showing the abnormal wear they were having on my car and many others have had the same issue, if you search you can find that thread and there are lots of pics... in my opinion the straub trunnion kit is the best choice... a friend showed me a trick of how to get all the trash out of the rings... you don't want to use compressed air to blow it out because that can also get more trash lodged in the rings... get a can of wd40 and spray it in around the edges of each piston and turn the motor over and all the trash will collect in the wd40 and get pushed to the top of the wall and then you can use a cotton towel to wipe it up... just repeat that process until they are squeaky clean... also use mineral spirits to clean the dog crap out of the deck to make sure the new gaskets seal

CharlieC5Z06

ok great thanks. So the shop should tell me how much they had to take off then Ill go from there? Good idea about using wd40 on the rings.

Rob 02

Yep! Maybe someone will chime in on what brand of head gasket to use for a supercharged LS6 or you could ask in he FI section.