3.9L LZ9 engine internal upgrade & performance? - Page 5

Monzsta · 10-24-2008, 08:38 AM

Quote:

Originally Posted by 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.

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 · 10-24-2008, 09:11 AM

Quote:

Originally Posted by Monzsta

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 · 11-13-2008, 10:10 PM

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 · 11-14-2008, 11:24 AM

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

Nightingale · 11-21-2008, 08:52 PM

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.

Superdave · 11-22-2008, 04:26 PM

Quote:

Originally Posted by 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.

iirc there were other changes in the block that made that head swap not work. Something about coolant ports not lining up...

Joseph Upson · 11-22-2008, 08:37 PM

Quote:

Originally Posted by Superdave

iirc there were other changes in the block that made that head swap not work. Something about coolant ports not lining up...

The heads are left and right and their deck surface coolant passages differ as you move from the front end of the head to the rear. They also have a larger surface and would overhang on the non VVT motors deck surface towards the sides. They are made very well and after looking at mine in consideration of some port work I lost motivation as the area around the valve guide in the bowl is pretty neat as well as the overall port, so aside from widening the passage beneath the valve there probably isn't much to gain.

IsaacHayes · 11-22-2008, 09:16 PM

^^ Cool, so you can get a 3900 and leave it alone and just slap a turbo on

Of course that means less potential if it's already close to optimal from the factory. I'm really curious to see the #s from a turbo 3900.

**SappySE107** · 11-23-2008, 07:04 AM

The heads are left and right? I don't recall that one and I have plenty of 3900 heads here. What is the casting number difference?

Joseph Upson · 11-23-2008, 10:53 AM

Quote:

Originally Posted by SappySE107

The heads are left and right? I don't recall that one and I have plenty of 3900 heads here. What is the casting number difference?

Having coolant flow outlets at one end makes them left and right and I distinctly remember the deck surface flow pattern varrying from one end to the other apparently to assist in proper cooling for the u-flow coolant design.

I'm not able to get numbers right now but GM does seem to show more than one part number for various parts in which case this may also explain why two different connecting rod lengths have been measured; 5.827" and 5.9".