3.9L LZ9 engine internal upgrade & performance?

[mrtohil]

I'm serious looking into forged rods of 5.9in for this motor (yes-yes, before I get it from all sides. I know the options. I've thought it through. I just can't don't like the welding crank option on this really nice crank. And this will help with the aftermarket performance options, or lack thereof, for this motor). So far I think I get them made with the same crank rod journal size but I'm changing the wrist pin size from .941(I can't remember the size off hand) to .927. Which is that same wrist pin size for an LS1.

[Nightingale]

Don't know its wierd like I said I had it measured by pauter rods and then I added up stroke and compression height and it all checks out on my engine. It might have been that on earliar engine they might have used a different length rod and piston. This wouldn't be the first instance of inconsistancy or lack of information from manufactuer.

[mrtohil]

Okay. I got two things accomplished today. I 1. installed my ARP main studs and found out my crankshaft main bore diameter specs and 2. sonic tested the block to find out how much I can bore this thing out. Which unfortunately is pretty much nothing.
I'm going to let you know that I initially checked my main bearing diameter spec with the stock bolts...
And what sonic testing revealed...

[mrtohil]

Sonic testing revealed that there isn't much metal left to play with. The following spec are in thousandths...Each cylinder was checked at 12 locations. If looking at a cylinder from the top, it would be at 12 (front of motor),3,6 & 9 o'clock. And then at the top, middle and bottom of the cylinder.
The highest value obtained was 320 @ cyl.5 9 o'clock middle.
The lowest value was 153 @ cyl.3 12 o'clock middle.
SO, this means I can only safely bore to about 30 over. SO no 4.0in bore unfortunately. But it's such a nice whole number. Oh well. Deal with it and move on...

[mrtohil]

Here are the specs that I found in my engine. The OEM spec is 2.840-2.841. Which is pretty anal of spec. I set up for a measurement of 2.8405.
Here's the measurement of the main caps, front to back(1 through 4) with two additional measurement per cap, front(F) & back(B). With the OEM bolts.
1. F:+.0019; B:+.0020
2. F:+.0024; B:+.0027
3. F:+.0024; B:+.0025
4. F:+.0013; B:+.0017
As you can see the main bearing bore is bigger than it should be.
Here are the measurements taken after installing ARP studs:
1. F:+.0011; B:+.0011
2. F:+.0013; B:+.0015
3. F:+.0009; B:+.0007
4. F:+.0007; B:+.0002

So as you can see the ARP studs DO make a difference! I didn't think it would make that much of a difference, but I was wrong.
So now I have to grind the main caps down and hone it to spec.
Oh, before I forget, the cylinder head passages and bolt pattern are pretty much the same as a 3.1L. I laid my head gasket on the block of a 3.1L that a classmate is doing and it all pretty much lined up. Only noticable difference was the cylinder bore. Which was massive compared to the 3.1L. Thought you'd like that bit of 411.

[IsaacHayes]

I wonder if a 3400 bored to a 3500 size would be enough for the heads... I wonder then if the valve train geometry would still work with the pushrods and such. I haven't looked into the #'s for bore sizes so don't shoot me if I'm asking a silly question.

[mrtohil]

I'm trying to understand the question you might be asking or posing. Please restate.

[IsaacHayes]

Take a 3400, bore it to 3.5L (or max it can be bored) and put on 3900 heads. That way you don't have to deal with cam phaser, it will fit and bolt in older cars, and no crank trigger or other stuff to mess with. Just bolt on the good 3900 top end, and run a 3500VVT UIM (since its not variable). That is if you can bore the 3400 out enough to fit the 3900 heads combustion chambers.

[mrtohil]

Well I measured by cylinder bores last night. What I found was that the bores were consistantly 3.8985-3.898in. Not the 3.9in stated for the spec for this engine. Once I find out what piston I'm going to use it'll probrably mean little if any boring and mostly honing to get it big enough for the pistons. The pistons I'm looking at are 3.905-3.908in.
I finished grinding the main caps to prep them for the line hone. Which should be tomorrow hopefully. After that I'll be decking the block and stating the deck height.

[IsaacHayes]

Hmm. From looking at the CR calc, that would be a .2" overbore on an LX9... LOL. So I'm assuming you can't really use the LZ9 heads on anything older than the gen4s... Darn.

[Monzsta]

I'm serious looking into forged rods of 5.9in for this motor (yes-yes, before I get it from all sides. I know the options. I've thought it through. I just can't don't like the welding crank option on this really nice crank. And this will help with the aftermarket performance options, or lack thereof, for this motor). So far I think I get them made with the same crank rod journal size but I'm changing the wrist pin size from .941(I can't remember the size off hand) to .927. Which is that same wrist pin size for an LS1.

Sorry I'm late to the thread.

With the huge 2.250 crank pins there would be no welding if you wanted to stroke the crank. You'd simply grind the crank to the desired offset and use Chevy SBC 2.000" rods.

This was discussed in length here.

http://60degreev6.com/forum/f96/3500-crank-t38267

[Joseph Upson]

Sorry I'm late to the thread.

With the huge 2.250 crank pins there would be no welding if you wanted to stroke the crank. You'd simply grind the crank to the desired offset and use Chevy SBC 2.000" rods.

This was discussed in length here.

http://60degreev6.com/forum/f96/3500-crank-t38267

That would be the best route to take if he's planning to take advantage of the LS1 piston options. Otherwise the closest chevy rod I've found to 5.9" is a 5.85" rod. The power output should be the ultimate decision maker because up to about 450 hp the stock rods should handle that and can be rebushed for the .927" pins down from .941. He could also have the crank offset ground and use the stock forged 5.7" rods with the correct piston compression height combo, to avoid modifying chevy rods.

If he plans to go all out then after market modified rods would be the way to go. There are a lot of options since the engine shares the same cylinder bore with a very popular motor.

[mrtohil]

Okay, is there any information as to what valvetrain can be used on this motor. I somewhat remember GM messing around with the intake and placing LS6/7 intake valves on this motor. Next semester is cylinder heads. Might as well start researching now.

[gectek]

LS valves are too long and alot bigger...wont work. dont know where you read that but they were smoking something

[Nightingale]

Wiseco has one of my stock pistons from which to engineer a forged piston. Once its done you can call them up with the job number and request modifications for it for your application. The one they are making up for me is 8.5:1 compression dish piston, extra valve clearence, zero deck, and a sbc wrist pin diameter.