A forum is no place for a common sense reply based on sound mechanical principles.

 

I thought I remembered what that was and had to look it up. So that means to have crank overlap, and therefore a stronger crank, don't stroke it. It makes sense. Less rotating mass a smaller distance from the centerline of the crank will have less leverage to break. It did say it's ok for less crank overlap if it's a billet crank, but that's over >$2,500 for non lsx and >$3,500 for lsx. Not in my budget lol

What's the CH that was referenced?

 

If your going aftermarket block, 6 bolt heads, and your not turbo limited I would go a little larger. I really like 4.125" bore with a 3.6-4.0" stroke. So 388" to 427" and run enough exhaust turbine wheel and your good to go. Most guys are running a single turbo with a limited turbine so to many cubes choke it.

 

Lol, I hear you

 

If you look at the actual main journal/rod journal overlap of a 3.62x LS crank vs say a 4", it is a substantial difference

We are blessed with a large main and rod journals, giving us nice overlap.

The high power stuff is flexing the crank, and there aren't many CCW options, so putting the stiffest crank in there will keep the bottom the happiest

Sure race car where they tear down often and are doing bearings big deal, but high power street car that has long tear down intervals, it makes a difference

CH is the compression height of the piston, the distance from pin to crown. This is the area you have to work with for adequate lands and ring pack

Good deal less on a 4" vs 3.6 in a standard 9.24 deck block. ~1.3 vs 1.1

 

Here is a pic of a stock crank. Line showing where you are looking at.

I don't have a 4" laying here to take pic of

Good pic of the stock crank showing how much undercut their is at the fillet also

 

^^Thanks for the explanation

 

I personally like bigger cubes. Easier to make power at lower boost levels. More off boost power.

With a good setup car you just need 1000rwhp to run low 8's/high 7's.

 

402 with billet 84. 7s at 170

 

I can tell you this....
with MY 408 Ci
at 12 psi, with a twin 66's ON pump gas 93 octane
I make enough power to run 5.50's and 5.60's in the 1/8th AT 130MPH

Good luck getting there with a 5.3L at those boost levels...


and I'm planning on turning it up to around 20 psi on c16

 

This is why I went with a 370 over a 408 on the same LQ4 block.

A. Stock stroke
B. The difference between the 408 and 370 piston was rediculous.

 

Lolz at "boost" number

Its all about mass flow, mass flow is power

Oh no tell all those mod motor and 2jz guys their crap sucks because they run more boost!

 

If that's your thinking why go any more cubes than stock at all? Just forged it and run more boost? Not being a smartness. It's a legit question because I am in this boat and this next build is where is really starts to get expensive as far as more cubes, better heads, better turbos, setups and so on. I'm trying to get educated to make the best decision. My thought was bigger motor + bigger turbo = more power.

 

I dont' like this logic... If your building a power adder car, let the power adder do the work. The turbo is more efficient at making power. I'd want to make as much power as possible with the turbo. Going through all the trouble to run forced induction and only running 12lbs seems backwards to me.

If the goal was 5.50's, I could easily get the same performance from a 5.3 by dropping base compression and adding boost to make up for difference. Why is manifold pressure relevant? You simply drop your SCR enough to reach your goal with the available octane.

I'd prefer an oversquare motor to a stroked one for a max effort FI build. The larger stroked motors will have more reciprocating weight and more stress on the moving parts. There are large advantages to higher RPM when dealing with FI race engines. A smaller engine will allow more RPM with less back pressure. This will let you extract more power from the turbo.

What class doesn't limit turbo size anyway?

 

the goal is not 5.50's....
the goal is Faster than that.....
but just showing I got there with low boost on a 6.8L vs having to go high boost on a 5.3L to achieve the same thing

when I turn up the boost.....its on like donkey king...

there is a limit to how much cylinder pressure you can get before you start to lift the heads and push water....and you reach it much sooner with a 5.3L on a lot of boost than you do with a bigger motor on less boost

also, your cam is going to dictate how far up the RPM scale you can push the RPM...it doesnt matter how much boost you make if your cam cant support the CFM flow.
so spinning the engine higher doesnt mean didly squat if you dont have a cam that can do it.(and most people have WAY too small of a cam to support high rpm turbo stuff)

 

Lololol. Stick to computers man

Where are these times lips and videos BTW?

 

I've also gone 5.4s on low boost with twin 66s

 

This.

Jack

 

Then why go 370? Why not just do a 4.8/5.3 and run more boost?

 

This is not the reason people say to keep the displacement lower.

In a perfect world, you are correct. Larger engine + larger turbo = more power. The problem with that is, there is not an infinite number of turbine sizes available. You need to size your engine based on which turbos are in your budget that will reach your power goals. Most people don't want to buy a full frame s500 or similar sized turbo. Lots of people need to make their horsepower goal on a single s400 turbo. When you limit yourself in those areas, turbine flow becomes the limiting factor much earlier than compressor.

Look at class racing. There is a reason Carl Stevens is building 480" hemis now when the norm has been 526" for ever and ever. There is a reason you don't see very many unlimited turbo cars over 600". There is a reason Ultra Street guys are getting away from 427" and building smaller engines in the 370-380" range. To be honest I'm not sure why no one has tried to run a 2JZ in that class. With the turbos you're limited to, a 3.0L could dominate that class.

Jack