3900 headgasket on 3400 head and other lz9 info

[Shaun41178(2)]

these pistons are different than my 3900. I have valve reliefs and this link does not.

http://www.ebay.com/itm/CHEVROLET-GM-20 ... aa&vxp=mtr

[The Dark Side of Will]

these pistons are different than my 3900. I have valve reliefs and this link does not.

http://www.ebay.com/itm/CHEVROLET-GM-20 ... aa&vxp=mtr

Old boy says LX9, LZ4, LZE... he's wrong about at least one...

Fudge... you gonna make me link the 60 degree V6 thread about 3900 swaps? I was pretty sure the LZ9 & LZ4 use the same Pistons and different rods. I think I remember that because it's backwards from what I was expecting. I don't know about year over year changes, but for the year I looked, P/N's were the same.

[Shaun41178(2)]

its prob an lx9 piston. I tried running the part number he lists and got nothing.

rod number came up with this link.
http://www.enginebuildermag.com/2011/10 ... -engine-2/ which I think I have posted up here before

Pretty sure based on my math the 3.5 has the 5.9 rod and the 3.9 has the 5.8 rod

Pauter rods make a set for the 3.9 They show the length at 5.827. I measured 5.835 on my rods so I was .008 off. close enough.

http://pauter.com/shop/rods/gm/chevrolet-3-9l-lz9-rods/

[Shaun41178(2)]

measured the cam. Ill do duration specs later to confirm other reports later I just wanted to get lift for now.

.287 intake
.282 exhaust.

I used a dial indicator off the lifter body, not the plunger. I tested each about 4 times to make sure the results were accurate. Its close enough I think. gm specs stated .272 for both intake and exhaust.

Ill measure lift at the valve next to confirm rocker arm ratio.

[Shaun41178(2)]

the first cam measurement for lift came from a 2006 cam. I never did get duration numbers for it however. These second numbers are going to be from a 2009 lgd 3.9. This differs from an lz9 as it was designed for flex fuel if wanted. This might make a difference in cam specs but not sure.

Measurements were made on the lifter body not the plunger.
Duration at .050.
Int 194
Exh 195

Lift
Int .272
Exh .286

Cam events @ .050
Int opens 12 ATDC
Int closes 26 ABDC

Exh opens 38 BBDC
Exh closes 23 BTDC

A genius it does not take to see this is a peanut for a cam.

[Shaun41178(2)]

Pretty sure based on my math the 3.5 has the 5.9 rod and the 3.9 has the 5.8 rod

Pauter rods make a set for the 3.9 They show the length at 5.827. I measured 5.835 on my rods so I was .008 off. close enough.

http://pauter.com/shop/rods/gm/chevrolet-3-9l-lz9-rods/

I did some more thinking on this today and remembered seeing that Silv-o-lite makes pistons for the lz4 and lz9 now, so I looked up their catalog. https://www.uempistons.com/catalogs/sil ... atalog.pdf

Piston 3531HC is for the 3.9 but the specs for 3.5 from silvolite are the same. Silvolite lists a CH of 1.295 Doing simple math shows that the 3.5 gets screwed unless it has a much longer rod than 5.9 or GMs listed CR for both these engines are way off.

GM says deck height is still 8.818 stroke for the 3.5 is 2.99. stroke for the 3.9 is 3.31 GM states the rod for both is 5.9. I measured 5.835 on my 3.9 rods

[The Dark Side of Will]

2006:

http://www.wholesalegmpartsonline.com/s ... evel=25580
LZ4:
Rod:
12609562
Piston:
89018065

http://www.wholesalegmpartsonline.com/s ... evel=25580
LZ9:
Rod:
12609561
Piston:
89018065

Both engines used the same pistons, but used two different rods. Slight differences from spec length resulted in the piston in the hole a bit on the LZ9, but at the deck on the LZ4 in order to keep compression what it should be for both engines.
Also, the consecutive part numbers of the rods means that they were part of the same design package when it was submitted to have part numbers assigned.

[Shaun41178(2)]

both engines were said to have the same compression ratio. the piston can not sit deeper in the hole with the lz9 and still have the same compression ratio as the lz4. So either the CR is not the same, or the lz4 rod can't be 5.9 inches.

I think the lz4 rod has to be closer to 5.99 instead of 5.9

lz4 = 1/2 stroke which is 1.495 + 5.9 = 7.395. Ch of block gm states is 8.818 - 7.395 = 1.423 CH on the piston to get 0 deck. With a 5.99 inch rod, then the CH of the piston is at 1.333

lz9 = 1/2 stroke which is 1.655 + 5.9 = 7.555. That equals a piston with 1.263 CH. Now I measured 5.83 length rod, and I can't remember off hand what a rough measurement of the CH of the pistons were. 1.655 + 5.83 = 7.485 thats a ch now needed of 1.333

I don't have an lz4 rod to measure though but either way, it can't be 5.9 inches and still use the same piston as the lz9 and have a 9.8:1 compression ratio.

The silvolite pistons in the link above lists the CH of both the lz4 and lz9 at 1.295 Add that number to a 5.9 inch rod and a lz4 crank, and your piston will be at 8.69 in the bore, which is .128 down in the bore and thats if the block is at a true 8.818 inch deck height. With a 5.83 rod and the 3.9 crank, you get 8.78 inches.

lz4 rod can't be 5.9 and use same pistons

[The Dark Side of Will]

the piston can not sit deeper in the hole with the lz9 and still have the same compression ratio as the lz4.

Why not? They use the same heads/chambers and the LZ9 has more displacement. The ONLY way they can have the same compression ratio is for the piston to be further in the hole in the LZ9.
The piston needs to be down in the hole to leave a clearance volume which results in a similar compression ratio with the larger cylinder volume.

[Shaun41178(2)]

I understand what you are saying, the problem is is that by the math, the lz4 piston sits deeper in the hole with a 5.9 inch rod like gm claims, then the lz9 not the other way around like you are saying.

[The Dark Side of Will]

Sooo....? I think it's obvious that the 5.9" rod number is not exactly correct. Why are you hung up on that number?

Both engines have 99mm bores. The LZ4 has 76mm stroke and the LZ9 has 84mm stroke.
The LZ4 has 585 cc cylinders.
The LZ9 has 646.6 cc cylinders.

If they both have 9.8:1 compression, then the LZ4 has 66.48 cc's of clearance volume and the LZ9 has 73.48 cc's of clearance volume. The difference is 6.997 cc's, which is a difference in piston deck height--and thus rod length--of 0.909mm or 0.036". The LZ9 rod is that much shorter than the LZ4 rod.

[Shaun41178(2)]

so exactly, thats my whole point, the rod can't be that length. when rebuilding an engine, one has to know the length of a rod, to get the right piston CH. Its that simple.

They both don't have 9.8:1 compression if the rod is 5.9 inches. I did the math. Not that I plan to find an lz4 and measure, but I am putting the info out there.'

according to your math, if the lz9 rod is .036 shorter, then that means that the lz4 rod is 5.871(based off my measurement of 5.835). Still not 5.9 which means comp ratio is not what its stated.

I plan to build a high CR e85 engine so I need to know this stuff. I am simply documenting for reference later. you can care or not care

[The Dark Side of Will]

I really don't get this bit about 5.9. When it comes out as 5.9 and not 5.900, it's obviously not the actual number. It was almost certainly rounded by some marketing douchebag who couldn't be bothered to list different rod lengths for the different engines (and probably had to look up how to round a decimal). That number was obvious bullshit from the second it was released. Let it go.

You have the numbers you need to build the engine you want. Thanks for sharing with us.

If you're interested in bumping the compression up a bit, but not too much, for a turbo E85 build, you might look into using LZ4 rods in your LZ9, as they'd bump the pistons 0.036 up in the bore and raise compression by 11%. Or maybe not, but the calc'd length can't be verified until someone measures one.

It occurs to me that GM could have used exactly the same powdered metal forging (not sure if it's actually a forging, but I don't have a better word) for both rods, and just drilled the small end hole 0.036" different for some of them.

[Shaun41178(2)]

I really don't get this bit about 5.9. When it comes out as 5.9 and not 5.900, it's obviously not the actual number. It was almost certainly rounded by some marketing douchebag who couldn't be bothered to list different rod lengths for the different engines (and probably had to look up how to round a decimal). That number was obvious bullshit from the second it was released. Let it go.

If you're interested in bumping the compression up a bit, but not too much, for a turbo E85 build, you might look into using LZ4 rods in your LZ9, as they'd bump the pistons 0.036 up in the bore and raise compression by 11%. Or maybe not, but the calc'd length can't be verified until someone measures one.

It occurs to me that GM could have used exactly the same powdered metal forging (not sure if it's actually a forging, but I don't have a better word) for both rods, and just drilled the small end hole 0.036" different for some of them.

if some douchebag rounded off the rod, he prob rounded off the compression ratio too. Which means the rod prob isn't .036 longer like your math suggests. I wouldn't be surprised. it is let go, once I did the math, I was done with it. I was posting the info so others won't be so surprised upon a tear down.

prob wont go turbo on this. just stay n/a. I want to use an off the shelf piston but will prob have to go custom. it will depend on how the deck height specs out.

[The Dark Side of Will]

What's said bag going to round it from? 9.78 to 9.8? That's well within the margin for error based on as cast combustion chamber size.

I agree, it's likely not exactly 0.036, so don't order your cometics until you measure the piston deck clearance.

You can get almost any deck height you want with LS pistons.

[Shaun41178(2)]

I will take a screenshot when I get home and post it but I ran the numbers last night and the silvolite pistons have a compression ratio of about 11:1 if not more

[Shaun41178(2)]

my piston dish measurement was wrong. Dish on the dilvolite is 17ccs that puts the CR at 10:1. Please calm down, nothing to see here.

[Shaun41178(2)]

My machinist measured the compression height of the 3.9 piston at 1.312

I'll start a thread of a 3.9 buildup once all is back from the machine shop.

[The Dark Side of Will]

Does that put you at 0.017" out of the hole? How's that 11:1?

[Shaun41178(2)]

The piston is still down in the hole but I don't remember how much.