LZ4 3500 rod info and forged Pistons options.

[Shaun41178(2)]

So I took some more measurements. I went to the boneyard, and what I was told was a 3900 turned out to be a 3500.

I confirmed this by the part numbers on the rods, and on the front of the crank under the balancer.

Anyways, I measured the compression height of the piston. The same pistons is used in in both 3.5 and 3.9.

Compression height came in at 1.291. Now if you plug that number into my previous 3.5 numbers with the rod being 6.030 length, you get the piston sitting about .002 in the hole

Well I took a look at the piston of this jyard 3500, and low and behold the piston is damn near at the top. Without putting a measuring tool on it, eyeball says it's darn flush with the deck height.

On my 3900 it was visible with the naked eye that piston sat below the deck by a good amount, and I measured it to be about .036 below the deck.

So with this new lz4 data, this brings compression ratio to about 10.03:1, not the 9.8 gm claims.

Here is my maths

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[Shaun41178(2)]

So here is the pic of the 3900 engine, with the piston visibly sitting much lower in the hole.

20210508_191822_2.jpg (774.16 KiB) Viewed 1941 times

And here is the 3500 lz4 piston in relation to deck height. It's right at the top.

IMG_20230216_181206368_HDR~2.jpg (204.05 KiB) Viewed 1941 times

IMG_20230216_181242978_HDR.jpg (779.96 KiB) Viewed 1941 times

[neophile_17]

So I took some more measurements. I went to the boneyard, and what I was told was a 3900 turned out to be a 3500.

I confirmed this by the part numbers on the rods, and on the front of the crank under the balancer.

Anyways, I measured the compression height of the piston. The same pistons is used in in both 3.5 and 3.9.

Compression height came in at 1.291. Now if you plug that number into my previous 3.5 numbers with the rod being 6.030 length, you get the piston sitting about .002 in the hole

Well I took a look at the piston of this jyard 3500, and low and behold the piston is damn near at the top. Without putting a measuring tool on it, eyeball says it's darn flush with the deck height.

On my 3900 it was visible with the naked eye that piston sat below the deck by a good amount, and I measured it to be about .036 below the deck.

So with this new lz4 data, this brings compression ratio to about 10.03:1, not the 9.8 gm claims.

This matches with what I found on my LZ4. Not having an LZ9 I couldn't be sure it was an apples to apples comparison but this confirms it.

[Shaun41178(2)]

I put a set of my LZ cam bearing spacers and new bearings in this 3500 and I think I am going to give it a rip. See what a cammed lz4 will make power wise.

And hopefully make power all the way to 6500 vs falling around 5600 as before.

IMG_20230319_220239122_HDR.jpg (760.1 KiB) Viewed 1827 times

[eHoward]

You going to see what it does NA before applying boost? Or jumping right in?

I put a set of my LZ cam bearing spacers and new bearings in this 3500 and I think I am going to give it a rip. See what a cammed lz4 will make power wise.

And hopefully make power all the way to 6500 vs falling around 5600 as before.IMG_20230319_220239122_HDR.jpg

[Shaun41178(2)]

Jumping right in. Just gonna hook everything back up as before

[zok15]

Why go LZ4 over another LZ9? Any benefits for a boosted application? I was hoping to see what your built one would make once you got it dialed in before it dropped the valve seat.

[Shaun41178(2)]

Kinda curious what the lz4 rods can handle power wise. I checked some calcs and the 3.9 at 6500 rpm has a piston speed of 59.76 fps.

The 3.5 at 6500 has a piston speed of 54 fps or about 10% less.

I'd imagine the stresses on the 3.5 rod would be much less. However I imagine that since the lz4 rods is longer, it probably weighs more, so maybe the whole thing is a wash?

[The Dark Side of Will]

Shorter stroke and reduces rod stress in a linear relationship. RPM increases rod stress in a squared relationship.

[Shaun41178(2)]

I installed my old 1615 grind comp cam that I bought 15 years ago into this lz4. Since the piston comes up about .035 higher in the bore vs an lz9, I wanted to verify piston to valve clearance.

Here are the cam specs.
225/227.6 duration @.050", .565/.526" lift w/ 1.5 rockers, 111 ICL, 111 LSA

So with a 1.7 rocker as the LZ engines are claimed to have this puts lift at .640/.596

It appears that with this lift and duration, there doesn't appear to be issues with piston clearance on the lz4 which means the lz9 is even safer.. However, there isn't much clearance between the retainer and the valve guide seal. I don't know how much there is supposed to be there for safety margin. I didn't take a measurement but it prob less than .1. Hard to say.

Obviously a dual valve spring would be necessary which is available, that offers a max lift of .660 for LS engines.

IMG_20230328_215953794_HDR.jpg (804.58 KiB) Viewed 1780 times

[ericjon262]

I installed my old 1615 grind comp cam that I bought 15 years ago into this lz4. Since the piston comes up about .035 higher in the bore vs an lz9, I wanted to verify piston to valve clearance.

Here are the cam specs.
225/227.6 duration @.050", .565/.526" lift w/ 1.5 rockers, 111 ICL, 111 LSA

So with a 1.7 rocker as the LZ engines are claimed to have this puts lift at .640/.596

It appears that with this lift and duration, there doesn't appear to be issues with piston clearance on the lz4 which means the lz9 is even safer.. However, there isn't much clearance between the retainer and the valve guide seal. I don't know how much there is supposed to be there for safety margin. I didn't take a measurement but it prob less than .1. Hard to say.

Obviously a dual valve spring would be necessary which is available, that offers a max lift of .660 for LS engines.

IMG_20230328_215953794_HDR.jpg

I see I'm not the only idiot up late working on a crappy V6...

in all seriousness, thanks for posting the info, it's good to know that a big-ish cam fits ok. I would still like to get VVT working with a big cam, it would be neat to be able to adjust the centerline, on the fly, which I suspect could also make a pretty nice difference in turbo spool times.

[The Dark Side of Will]

Shaun has setup springs... Looking like a pro builder.

[SappySE107]

.

[The Dark Side of Will]

Thats a wot-tech regrind, not a comp cam. Your numbers aren't the same as mine. Id share but you call me a scammer so im not inclined.

Warned

[CaptainHindsight]

Thanks for digging into all of this on these engines. Our project is still back in storage but might come in handy since these engines are so readily available in bone yards now.