Ok, let me first start off by saying, I'm a huge fan of the inline 6 motors. I've got a bmw 135i with a TT 3.0l I6. Its a great engine etc.

Totally unrelated, I am looking to build a bigger displacement (preferrably american) inline 6 motor with reasonable hp goals.

I am shooting for ~500hp. My idea so far has been the GM Atlas ll8 like the other gentleman here... however seems like to make decent hp.. I am goign to have to rework some internals (which is actually more than fine, just dont know where to begin).

I've got a master fabricator who builds rockets and military aircraft parts etc, so I am 100% confident pretty much anything is possible (and for cheap too!)

Is this motor worth my time and money? The motor itself can be had for real cheap, and I'd already planned on goign with the megasquirt solution as well. My questions were

1) Am I going to need to resleeve, port heads etc, and if so, am I underestimating the work?

2)I've heard people say that recent motors with appropriate electronics should be capable of close to stock compression. Is this true, or can I count on reducing compression to handle extra boost?

I'm very mechanically inclined (tho admittedly never had any custom decisions, like boring cylinders, or sleeving, or custom cam grinds etc), And I've tuned ecus before.

This would REALLY be the direction I'd like to go, but afraid I dont know enough about what I'd need for the boost.

What exactly is the GM Atlas engine you are describing. Also is it modern or vintage era,etc...,

Sorry, its the GM 4.2l fuel injected i6 in the new trailblazer, envoy, rainier etc.

I believe efi-diy has done this exact setup.

I can answer #2.

Yes, you can run higher compression ratios on boosted motors now thanks to better engine management and tuning practices. I built a two liter watercooled VW than ran 12 psi of boost on the stock 9.6:1 CR. Made 100% more power over stock using 91 octane. Used a p-n-p obd2 e-prom chip from a reliable VW tuner. The tune was conservative and ran modest timing advance and lots of fuel.

I've seen plenty of instances of people running fairly high boost on 10:1 motors. Just be conservative with the tune.

IIRC that's roughly where EFI DIY is for power on his 'salvage' engine (stocker), while he finishes his monster.

I haven't checked back through the whole thread though. Towards the end IIRC.


4200 turbo project...

Edit:

FWIW if you want to run there consistently I would at least change out the sleeves for flanged ones (should be in Marc's thread I linked to, Darton IIRC that way they can't slip) and a set of head studs.

How much power do you want to make - be honest as it will vary my response to you.

Quote: "I am shooting for ~500hp"

well originally said 500, but I'd be happy with 450 at the wheels

I mean honestly, shooting for more than that would just be a waste for what I am going to put it in.

I just look at the numbers efi-diy was able to get for the stock motor + turbo, and they seem awefully low. (maybe a conservative tune?)

Ron,

The early heads exhaust ports are tiny and I'm thinking that they are really killing power.

Anyway, for 500HP your going to need to basically duplicate my short block. Sleeve, rods, forged pistons, head and main studs. Get a '06 up head and port the head - most of the work needs to be done on the exhaust side. Then you need to decide what you want to do for cams - run stock or get custom billet cam made.

So I should be cool to buy a 05 block etc, get the studs, sleves rods and pistons, then buy some 06+ heads and port them and be good as far as motor goes? If so I am going to jump on that immediately.

Also, I dont necessarily want to straight up copy, but I was wondering if you could recommend info on the sleeves rods and pistons... I am familliar with what it takes to install ll of them, but have no idea how to choose the rod lengths and pistons etc. I know typically in boosted applications compression is lower.

btw, I really appreciate your time efi-diy.