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Discussion Starter #1 (Edited)
Hey folks,

Haven't been active in a while, but I'm back and have been researching some options for my goat.

Had some bad luck last year. My engine blew on the DD '05 and then my '06 BOM got totalled while parked. School has been crazy, but I'm hoping to get some real work done on the '05 I have left this summer.

I'm a little conflicted over whether or not to build and upgrade another LS2, or if I should spend the extra to put an LS3 in it. Any opinions and experience?

I was thinking I would get a new short block either way, and build it from there. My LS2 in the '05 had about 115k when it went, and it is an M6. I'm not sure what went, because I haven't pulled it yet. I think it was the bottom end. The engine started screaming at me on the way to work, it sounded like the grinding from a lifter, but when it came off the tow it had dumped all of the oil, which makes me think something failed in the bottom end. The block may be salvageable, and I may just pull it and have it gone over by a local builder if so, but I'm not quite sure if that is worth doing at this time.

It was largely stock, so I'm not sure I'll be using much from it either way, but I've read the LS3s don't like to take a tune in our cars (and cost over 2x as much).

So, what do y'all think; is it worth trying to fight with an LS3 or should I just build a new LS2 with a more aggressive cam and better heads and call it good?

Thanks,
Jim
 

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If all of the oil's gone out of it I rather doubt your existing block can be saved. If going with a new shortblock though I'd say go with the LS3, especially if building it yourself. One point of concern though is the reluctor wheel on the LS3 being a 58x while the stock LS2s in our cars are 24x. At the end of the day its your decision and your $$ though.
 

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Discussion Starter #4 (Edited)
If all of the oil's gone out of it I rather doubt your existing block can be saved. If going with a new shortblock though I'd say go with the LS3, especially if building it yourself. One point of concern though is the reluctor wheel on the LS3 being a 58x while the stock LS2s in our cars are 24x. At the end of the day its your decision and your $$ though.
That was my initial thought too, RE: the block. I won't know for sure until I pull it, but I am not expecting much.

smurf, I forgot about that reluctor wheel. I'm not sure I feel comfortable trying to change that myself in a garage. Is that something I could have a reliable builder do shortly after I get the block? If so, it's an extra expense I'll have to factor in, but if I can just put the 24x on the LS3 without issue then it may not be a huge deal.

ETA: actually, that may not matter that much for labor cost. I think I may have a builder do the bottom end work anyway, just to be sure about it.

How does an LS3 not "take a tune?"
I'm not a tuner, so I'm not sure what the problem is exactly. I was reading some threads on here that had a handful of professional tuners that were trying to figure out why they wouldn't idle right in the GTO. Something to do with the existing computers and the airflow values needed.

I think it was finally resolved, and it involved replacing the intake(?) and associated sensors to the LS2 versions before it would run right.

I'm not sure 100%, and I don't know if there is a reliable tuner that can figure all that out near me.
 

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You will still need to keep all the GTO computers/parts in place so it doesn't matter what block you use. Another little known fact regarding GTO's, is that a 800 RPM idle is hardwired into the ECM and you can't change it no-matter what HPTuners tells you; it's an Australian thing only and why Holden choose to do it is unknown. Many people/tuners will dispute what I just said, but any other idle speed is going to cause other problems within the tune. I would build a LS3 with a billet 24 tooth reluctor, and bolt all the GTO LS2 sensors onto it. Good luck.
 

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You will still need to keep all the GTO computers/parts in place so it doesn't matter what block you use. Another little known fact regarding GTO's, is that a 800 RPM idle is hardwired into the ECM and you can't change it no-matter what HPTuners tells you; it's an Australian thing only and why Holden choose to do it is unknown. Many people/tuners will dispute what I just said, but any other idle speed is going to cause other problems within the tune. I would build a LS3 with a billet 24 tooth reluctor, and bolt all the GTO LS2 sensors onto it. Good luck.
What specifically are these other tuning problems you create by changing the 800 rpm idle?

How do you explain cars that idle right at commanded idle speeds other than 800 rpm and what about cold idle at 1100?

eta: If I command a 900 rpm idle what keeps the over/under speed spark and idle proportional airflow from trying to drive the rpm to 800 if that is the hard coded speed? I know there are some hard coded limits on the ls1 like the maf for example, but never had any issues changing idle speed.
 

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Another little known fact regarding GTO's, is that a 800 RPM idle is hardwired into the ECM and you can't change it no-matter what HPTuners tells you; it's an Australian thing only and why Holden choose to do it is unknown.
i've never had issues?

maybe you're thinking of the idle air effective area table.

I would build a LS3 with a billet 24 tooth reluctor, and bolt all the GTO LS2 sensors onto it. Good luck.
that's really the best way. if you want to use a crate engine, there are folks that have had success with the ligenfelter 24x-58x converter.
 

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Discussion Starter #8
So I'm looking right now at getting a new bare block, and then going from there.

Is there any reason I can't get an LS2 and have it bored out to match the displacement for the LS3?

I guess I'm just not 100% clear on what other differences there are between the blocks.

If it helps, I'm strongly considering having it stroked out either way. The bare block is $1500 cheaper, so if there isn't a difference in buying the LS2 and having it machined, then I may consider that, if it proves cheaper to do.
 

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You'd have to get the LS2 resleeved, and you might as well build a 427 at that point.

The great thing about the LS3 is the heads, the bore size just helps with flow around the larger intake valve.
 

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BS on you can’t change the idle speed. I can, at will, on my 04 and 05 with HP Tuners. Can verify it via the hidden menu, a handheld actron scanner, and data logging with HP Tuners. No issue whatsoever with my tune either.
 

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BS on you can’t change the idle speed. I can, at will, on my 04 and 05 with HP Tuners. Can verify it via the hidden menu, a handheld actron scanner, and data logging with HP Tuners. No issue whatsoever with my tune either.
I never said that you can't change the idle with HP Tuners... I said that changing it from the hardwired factory settings in engine idle "base setpoints" and "minimum setpoints" will cause anomalies within the tune elsewhere. Holden hardwired those settings into the ECM on 2005-06 GTO; believe it or not.
 

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The Ls2 has thicker sleeves than the ls3. Smaller bores leave more sealing area for head gaskets. Since I’m boosted I’ll be going with an ls2 block when the time comes for a forged motor. Naturally aspirated those minor things will not matter so go with the most cubic inches and best heads you can afford.
 

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You will still need to keep all the GTO computers/parts in place so it doesn't matter what block you use. Another little known fact regarding GTO's, is that a 800 RPM idle is hardwired into the ECM and you can't change it no-matter what HPTuners tells you; it's an Australian thing only and why Holden choose to do it is unknown. Many people/tuners will dispute what I just said, but any other idle speed is going to cause other problems within the tune. I would build a LS3 with a billet 24 tooth reluctor, and bolt all the GTO LS2 sensors onto it. Good luck.
I never said that you can't change the idle with HP Tuners... I said that changing it from the hardwired factory settings in engine idle "base setpoints" and "minimum setpoints" will cause anomalies within the tune elsewhere. Holden hardwired those settings into the ECM on 2005-06 GTO; believe it or not.
Sure seems like you said you can't change it via HP tuners in your first post.

That said, I do not have my idle set below 800rpm. My 04 is set at 800 and my 05 (cammed) at 850.

Oh and this is a fun tidbit of info in that other thread that I experimented with last summer:

Just change the idle timing to get the sound you like. I can make a 224 lope like a big cam and my 240ish cam idle like a stocker just changing the idle timing.
I don't know if your Predator will let you adjust idle timing, but HPt will, and if you use the scanner/realtime editor you can run the timing up and down until it sounds the way you like, then go over to the editor and change it to the value you found.
My 04 with a stock cam has a much rougher idle now by playing around with the idle timing cells.
 

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L96 from junkyard $1200
Freshin it up with new bearings and cam $1500
Forged rod and piston $1500
Flow heads $1200
Turbo kit or LSA blower $3000

Forged and boosted 6.0L iron block that will make 700+ to the tires for less than a LS3...

PRICELESS
 

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Discussion Starter #19
L96 from junkyard $1200
Freshin it up with new bearings and cam $1500
Forged rod and piston $1500
Flow heads $1200
Turbo kit or LSA blower $3000

Forged and boosted 6.0L iron block that will make 700+ to the tires for less than a LS3...

PRICELESS
I looked at that too, but I don't think I'm going to boost the goat, so I'm not sure I want the extra weight.
 

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Discussion Starter #20 (Edited)
You'd have to get the LS2 resleeved, and you might as well build a 427 at that point.

The great thing about the LS3 is the heads, the bore size just helps with flow around the larger intake valve.
I'm actually considering that. I may reach out to a local engine builder this week and get an estimate on what the machine work and bottom end labor cost would be, and then I guess I'll go from there.

I suppose I'll make the decision on what is best once I get a better handle on the cost of everything.
 
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