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Discussion Starter #1
So at 68,000 miles my 2005 Colorado (crew cab 4x4 3.5L Z85) threw me a P0302 code. I've been waiting for it. Idle has been rough for a while, MPG down from 20 hwy to 17 hwy, so yeah, seen it coming. Haven't done a compression or leakdown test yet, but I am planning for the worst anyway.

But I'm not going to jump at a replacement. In fact, I'm pretty much going to run that motor into the ground. And when I put a new one in, I want it to be badass. In short, I will be building a sweet replacement from the block up while the current I5 stumbles and stutters along at 15mpg.

I have seen alot of opinions here about getting big HP from these motors and various ways to do it. I will be ordering a block to modify and swap in when the time is right, saving all components from the original engine excluding the head.

I'm not looking for you all to build this for me, but I want to know my best and most economical options.

So, on to the questions:

1: Can these motors be bored/decked/planed? If so, 3.5 or 3.7 the better option? (or any difference at all?).

2: How damn complicated and expensive is it to have a turbo made? (or is there a kit?).

I don't like turbochargers to be honest. IMHO they just add more moving parts that can break, so if either the 3.5 or 3.7 can be stroked, I would prefer that.

3: What sort of bottom end mods will I need to make, or will I even get that much HP from option A or B?

4: What kind of HP and Torque can the stock tranny/rear end handle, or will that even matter?

5: Am I going about this COMPLETELY the wrong way? If so let me know, and maybe point me in the right direction.

6: Legality is no issue as far as mods. In Fairbanks Alaska, there is neither safety inspection or emissions testing. Whatever I do to this truck no one would be the wiser.

I know I am going to have to replace at least the head, but I want to just replace the entire powerplant with something that people driving trucks twice the size wouldn't expect. The rest of the truck other than this problem is perfect. I've been saving some cash towards it for a few years now knowing that I would have to address the issue sooner or later... now I just need some advice on how to spend it, or basically, how to get the most HP for my dollar.

Thanks in advance for your time in replying!
-Glenn
 

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I'd say 3.7. Alittle more hp stock. You should be able to get the dealer to replace your head if its bad with only 68k on it because of the warranty on them. It's at least worth a shot.
 

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Discussion Starter #3
I'd say 3.7. Alittle more hp stock. You should be able to get the dealer to replace your head if its bad with only 68k on it because of the warranty on them. It's at least worth a shot.
Dealer said no. It's a full year out of warranty.

Honestly I'm not looking to more stock HP. I'm looking for A: which block will modify better, and B: which modifications = more HP for the money.
 

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That year shit is bullshit. 68k isn't anything. The head doesn't just go bad from sitting. They should put a mileage warranty on drivetrain and that's it. I'm not sure which would be best. I would say the 3.7 is designed alittle better than the 3.5. You wouldn't have to worry about a head issue if you picked up a full 3.7 motor. The 07s are the easiest to swap into a older truck. Kmac swapped an 08 but had problems and had to add some sensors if I think correctly.
 

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You're going at this the wrong way.

You ask for "best and most economical" method. That means 1) boost the I5 or 2) go V8.

The 3.7 is already at its displacement limits. The only way to get more power is by boosting or increasing engine speed. The problem with the latter, is that the engine is designed for a truck, meaning small cams and exhaust ports. You could get custom cams and a port job, but by then you're in a few thousand for a motor that *might* be approaching 300 hp at the flywheel.

I'd say rethink your turbo position. Check out lime-swap.com for some parts: turbo manifold, injectors, and tune.

Otherwise, your best option is a V8.
 

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You're going at this the wrong way.

You ask for "best and most economical" method. That means 1) boost the I5 or 2) go V8.

The 3.7 is already at its displacement limits. The only way to get more power is by boosting or increasing engine speed. The problem with the latter, is that the engine is designed for a truck, meaning small cams and exhaust ports. You could get custom cams and a port job, but by then you're in a few thousand for a motor that *might* be approaching 300 hp at the flywheel.

I'd say rethink your turbo position. Check out lime-swap.com for some parts: turbo manifold, injectors, and tune.

Otherwise, your best option is a V8.
100% agreed, unless boosting with turbo or custom s/c set-up your not going to get much more out of the I5 without dumping stupid money at it in custom parts.
 

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I don't have any answers, but man this sounds like a cool build. I'll have to stop by & see it whenever I'm in Fairbanks next!
 

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I see the V8 swap and the most cost effective and proven in the long run. There are just to many unknowns and alot of custom required parts would make the build no longer cost effective.

We all know a LS long block with a 100,000 would go another 100,00 with no worries. Building or rebuilding is pretty cheap and there is a huge after market for them. The used performance part market is ample too. So a budget build is very doable.

Research and planning will go a long ways
 

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ya save the money and do a v8 5.3s are cheap and you have a trans that just needs a rebuild and the rear will hold up to it but if you dont have a locker your going to want to swap no one likes one tire burn outs
 

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Discussion Starter #10
So it seems it's either turbo or V8 swap.

From those two (if effort and $$$ are not a concern), which offers the most potential for performance coupled with longevity? Sure I want power and am willing to pay for it, but not twice.

Thanks for all the prompt answers.
 

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V8 all the way. You can mod it later if you want and make way more power than you will with turboing our motor. You can always turbo the v8 too lol.
 

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The real question is how different do you want to be? Its most cost effective for you to just drop a built LSX in. Or be really crazy and drop one in with Twin turbos. But the reliability part, just stick with a stock LSX.
I have chosen to be completely different, and started saving for a fully forgedshort block I6, and it will be seeing 20+ lbs of boost, but only because I choose to be different. Building the atlas series engines is a huge investment, as only a few places make solid lower end parts, and you still have to buy them in sets of 5, or 10 because they're still considered "custom"(not mass produced). In the long run reliability stays with the V8, not in these atlas series engines.... Good luck with your build, look forward to seeing it done.
 

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Also depends on the ultimate power goals. Think you'll be happy with 350-400 Hp?
You can piece together a turbo system for pretty cheap that will do that.

Much more...go for the V8.
 

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Discussion Starter #14
Thank you all for your input, very helpful.

I think I have set my sights on a 3.7 swap with turbo. From here, I can take over the R&D. (Unless someone can make a case for why the 3.5 is better than the 3.7 when considering a turbo setup).

I love how when I pop the hood people still say first "Four banger, huh?" Nope. "Straight six then?". Try again. :) I like my 5 cyl., and 300-400 HP is plenty for me.

So last question (I swear): With turbo setup, 3.5 or 3.7? And yes I know it will be more work to swap in the 3.7 but consider that point moot.

Thanks again!
 

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Thank you all for your input, very helpful.

I think I have set my sights on a 3.7 swap with turbo. From here, I can take over the R&D. (Unless someone can make a case for why the 3.5 is better than the 3.7 when considering a turbo setup).

I love how when I pop the hood people still say first "Four banger, huh?" Nope. "Straight six then?". Try again. :) I like my 5 cyl., and 300-400 HP is plenty for me.

So last question (I swear): With turbo setup, 3.5 or 3.7? And yes I know it will be more work to swap in the 3.7 but consider that point moot.

Thanks again!
3.7. Not only do you get the displacement bump, but the valves, ports, and cams are bigger as well.
 
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