3.5L / 3.9L Connecting rod group buy

[NateD4]

I'm looking into a group buy for a few sets of 3.5L and 3.9L large journal connecting rods.

Is anyone interested in them?

These would be billet 4340 I beam US made rods with 250 KSI 3/8 or 7/16" bolts. good for at least 7500-8000 RPM and boost application.

Please respond with interest and your idea of a fair price for these. If the prices people are willing to pay are close to what I can get them for I'll arrange an order.

[caffeine]

Will these fit an LX9?

[NateD4]

Do you know the journal size for the LX engines?

Also rod length and desired compression ratio?

[Mars]

I would buy a set of 3900 ones IF :

They are compatible with off the shelf LSX pistons.

AND

If you provide a part # for an LSX piston that would require either no bore or very SLIGHT bore increase in a 3.9 block while retaining roughly the stock compression ratio, or slightly lower.

I'll take 6 rods if those 2 conditions are met.

[NateD4]

Well I'm not sure about LS X pistons per say. However I think I can meet those two objectives.

If you look at the other post I replied to on performance parts a discussion of pistons was present.

I did some research and found that the 3.9L pistons are 3.899" while the 5.7L LS pistons are 3.903 or 3.905 depending on vendor.

there aren't really too many options for off the shelf LS pistons as LS engines have a chamber size that is close to double the 3.9L (mine measured 33cc with stock valves and plugs).

There are 2-3 sets of pistons available off the shelf in a 'forged' alloy that will get very close to a 10:1 with a .040 to .050 piston to head clearance height (not sure without doing the math what the translates into for compression height). I should point out that these pistons are considered high output for LS engines but aren't quite beefy enough for high boost on a V6.

What compression are you looking for? 10:1 (stock I think was 9.8:1)? If you are going with a low compression piston and want billet rods I can only imagine you are looking at boost.

I didn't mention it in the first post but I think it would also make sense to figure out what people want for pistons and do a group buy on correct pistons for this application. Especially if your goal is to use boost. I'll keep looking for a boost rated piston in an LS series, but so far the only pistons I've found the manufacturer doesn't recommend more than 12-15 PSI (if that).

Anyone else interested?

[Mars]

It just gets confusing when you mix rod lenght, then compression height, ect. I don't have the means to measure any of this stuff correctly at the moment.

Are the LSX piston pins the same dia. as a 3900 ? I don't want to mess with bushing the rods, ect...

Just want something bolt on and go, besides the bore job for the slugs.

I was looking for 9.5:1

Boosted application, 20+ psi.

[NateD4]

It's actually not that confusing. However be aware that off the shelf pistons may not be perfect for your application.

The rods will have stock LS pin diameters.

Compression height isn't too confusing. Just understand that it has to be within a certain range to give you proper piston to head clearance and compression ratio.

If a group buy happens I'll make sure they fit the 3.9 or 3.5 with off the shelf pistons.

[caffeine]

Sorry if this is a stupid question but couldn't the rods be made shorter to lower compression?

[boomofdoom88]

If my logic is right, The rods can only be made with a larger stroke with a larger offset bore on either or each end. You can't make a hole smaller or move it with making a new rod, you can't modify a rod length.

EDIT: You could make a rod longer or shorter by using an offset bore. Heck you could even cut and weld the rod back together, but cost and strength would be an issue.

[young gun]

I might be interested on this depending on purchase timing and price.

[caffeine]

After checking out the specs for the LZ9 and the LX9 it appears that the rod specs are identical. I would probably be interested in a set provided I could get some cost-effective pistons to match.

[Mars]

Yeah I got cash in hand if they work with some type of relatively easy to get pistons that don't require custom specs.

[NateD4]

I'll get the right rod length and give a list of pistons. It'll take me a few more days (perhaps a week) to get pricing. So please be patient.

Additionally, if possible please list what compression ratio and application (boost/no boost) you are looking for this will help me with finalizing things.

[NateD4]

Since everyone seems concerned about pistons. What pistons are you looking for? My suggestion is a 10.2 to 10.5:1 setup for mild boost. Any thoughts on that?

[caffeine]

I'd like to run lots of boost. So maybe between 9:1 and 9.5:1