3.9L LZ9 engine internal upgrade & performance?

[ericjon262]

I know this is almost 7 years old, but what ever happened to the engine? ever run? dyno?

[ForcedFirebird]

I measured my stock gasket at .053" compressing it with the caliper.

Very scientific.

[ericjon262]

I think I measured my stock gasket at .053" compressing it with the caliper. However you can order shim gaskets to whatever thickness or buy a spare gasket and remove the rivets and re-stack them.

Check out diamond racing they may have a set of LS pistons that are 'semi-custom' thats what I did for my LZG build. You can use modified buick V6 rods on the stock 3.5/3.9L cranks. I think the buick rods need to be narrowed slightly. The bearing diamters are within .0002" of each other if you compare the tolerances from Clevite. The main problem with most buick rods I've found is that they aren't the right length.

the buick rods are a tad on the narrow side for a LX9, I would imagine the same is true for the LZ engines.

[NateD4]

I think I measured my stock gasket at .053" compressing it with the caliper. However you can order shim gaskets to whatever thickness or buy a spare gasket and remove the rivets and re-stack them.

Check out diamond racing they may have a set of LS pistons that are 'semi-custom' thats what I did for my LZG build. You can use modified buick V6 rods on the stock 3.5/3.9L cranks. I think the buick rods need to be narrowed slightly. The bearing diamters are within .0002" of each other if you compare the tolerances from Clevite. The main problem with most buick rods I've found is that they aren't the right length.

I am going to assume that everything is blueprinted to spec to do the math on these mahle pistons.

3.31 stroke /2 = 1.655

+ 5.9 rod

+1.34 CH of piston =

8.895

The deck height specs are listed as 8.818 which means these pistons would stick up out of the block .077

To get a 0 deck height you would need a CH of 1.263

Now the piston pin diameter for the mahle is .945 and factory piston pin diameter is .942-.943.

It might be possible to shave that .077 off the top of the piston, machine the piston pin down .001.

Of course now to factor in the CR you would have to use 4cc or less since the piston is shaved.

This would net you a zero deck height. If the gasket is .070 when compressed( I have never measured) then that would give a quench of .070

A quick online CR calc states roughly a 12.7:1 Compression ratio with these pistons

[Mars]

^ Yes, someone look at this.

what about these mahle pistons?

http://www.jegs.com/i/Mahle/644/LS1340898F04/10002/-1?parentProductId=757295#moreDetails

Mahle LS1340898F04

Forged 4032 High Silicone Low Expansion Aluminum Alloy
Bore: 3.898''
Pin Diameter: .945''
-4cc Dome Volume
Comp. Ratio @64cc: 10.4:1
Precision Ring Grooves for Included 1.5, 1.5, 3.0mm Rings

Compression Height: 1.340
Weight: 394g

From the specs posted by nated4, if those are correct then it appears this pin diameter is real close, as well as the compression height.

Can someone do the math to see if these are down in the bore too far or up too high with a factory head gasket?

[Mars]

pretty sure in a performance oriented setup you want the wide open 3.5 LZ4 plenum with none of the variable junk.... You can port the hell out of them for maximum top end... My 3900 camaro makes gobs of power.

[robertisaar]

from what i can tell, have been told, they're not actually variable length.... the variable portion of the intake is plenum volume. seems that the plenum can be divided into two equal portions, one for each bank of the engine, or combined into a single large plenum.

[Khipset]

The Variable Length runners on the 3900 - What state are the runners in with no power supplied?

[Fieroghini]

You'll have to adjust for the 1.7 rockers. This is for 1.5's.

[Mars]

My 3900 with cam and springs did a 13.3 with an automatic at 103mph. With the 4 speed manual it did 13.4 at 106mph. I'm switching to the F23 with the hopes of clearing up my shifting issues. I've been told that my cam leaves a lot on the table so you may do better. Good luck.

what were your cam specs?

That's pretty fast...

[Fieroghini]

My 3900 with cam and springs did a 13.3 with an automatic at 103mph. With the 4 speed manual it did 13.4 at 106mph. I'm switching to the F23 with the hopes of clearing up my shifting issues. I've been told that my cam leaves a lot on the table so you may do better. Good luck.

[Fireball]

Seems like enough work and research will need to be done yet.

I'm just half an hour from having mine installed into my Camaro. We shall see what a cam and spring only 3900 can do next summer.

The intake manifold ports on this engine are HUGE compared to a 3500. I hope it's as reliable / powerful as my 3500 was.

Deard lord you always have the most bad ass cars lol

[Mars]

Seems like enough work and research will need to be done yet.

I'm just half an hour from having mine installed into my Camaro. We shall see what a cam and spring only 3900 can do next summer.

The intake manifold ports on this engine are HUGE compared to a 3500. I hope it's as reliable / powerful as my 3500 was.