No need to worry about the gate, until you get into boost creep/ not able to get the boost to a lower number. And we can always take you up to a 44mm-60mm in the same area. Just need the pipes back, make some new flanges and bolt it all back together.
The cost difference I would stay with the smaller engine. You can always add a little nitrous if you need more power.
Small engine, better all around in my opinion iwth the single turbo.
BTW you ever get your turbo back from the shop over hauling it.?

 

I'd opt for the 408 and less boost for longevity.

For a few hundred dollars more, you'll increase output by roughly 10%. You're getting a new rotating assembly regardless so I'd go for the 4" crankshaft. It's when you start getting into the 4.120"+ cranks that terrible rotating assembly geometry allows the piston to rock out and eat oil. Also; boost will not upset a motor's insides like high revs do, and as you all know the 370 will need to wind up for this application, so pick your poison; a 408 with the potential to sip a little oil or added stress throughout the life of the 370 from winding high?

I'd much rather make 600-700 horsepower with boost and cubes, and since the OP already has the boost and is in need of a new rotating assembly, a 4.030"x4.000" setup will reduce both the stress and the boost needed to make his goal.

 

Its a bit more than a few hundred dollars.... It will be closer to 2,000 more by the time your all done... The problem with the oil consumption is not only the short pistons skirts but the higher pin location.

 

Am I missing something here? A forged 370 cannot be that mass produced to have an entire 3.622" crankshaft, rods and pistons package cost 2 grand less than a 4" crankshaft, rods and piston package. Texas Speed has the two rotating assemblies priced out within a few hundred of each other.

 

Your motor is a 10:1 370 correct? What kind of power are you making with it, and how much boost did it take you to get there? Also specs on heads and cam?

 

Yeah I got it back. Its bolted to the truck right now. I just have to tune it for the heads and cam, but Im going to go ahead and build the motor before I blow it up and screw up the AFR's in the process.

 

The crank is about $1000.00 vs using a stock crank that I already have. Then add in additional machine work for the longer stroke. Its not $2000 but its a fair chunk of $ over the 370 is the point they arey making.

 

Oh, my apologies then. When you said forged 370 I was under the assumption the whole thing was going to be forged, not just the rods and pistons.

With your current setup, what is your rev limiter set around?

 

It's a new engine, it has 2500 miles on it, no dyno or track times but it feels as strong as the lq4 that ran 11.41 did with 4 pounds less boost. with 8-10 psi I would gestimate around 600 hp. the heads are stock and the cam is very small and tight by turbo cam standards.. There is a ton more info in my build up thread in the projects section...


my 370 build

BTW, at the time if I had the cash it would have been a 408 insted of a 370, but I'm just a broke mechanic trying to keep up with all you rich bastards....

 

Derek and MikeGyver: My cam specs are 226-238 at .050 with 601 on both and 114 LSA. I agree that a turbo and SC can make power differently but it really depends on the turbo setup. Most factory turbo setups like porsche, mercedes, BMW etc make gobs of torque down low. My point, which has been established is that a 408 is designed to make more torque than a 370. I looked at a 370 before my build and due to the weight of the truck went with the 408. I think the price difference on the fully forged rotating assembly kit was less than $300 difference. The machining of the block was little or no difference at the shop. I haven't heard about any issues with burning oil if the engine is assembled with the correct tolerances but I will keep a close eye on it. I just know that boost will eventually kill even the strongest engine so I like less boost more CI.