Mike Davis

I would love to do a 6.0l engine.my issue is that i cannot find a reasonably priced 6.0. Looking on car-parts.com has been alright, but thats about it. I have no intentions of spending $2-3k and up for a stock engine unless its an ls3/7. Ebay is full of overpriced con artists, and i have been keeping a pretty close eye on that. Anyone have one for sale or trade? I have an old school 383(all new) and a prs custom guitar

LTX355

iTrader: (15)

I will b shooting for boost in the near future with a 5.3... my choice of cam is a B1.

lq4pwns

iTrader: (6)

I'd use a 04+ z06 cam. Works GREAT, and is CHEAP.

KCS

iTrader: (20)

What's the limit of a 2.00" valve? 2V mod motors are more than capable of producing 1000hp, and they use tiny 1.8x" intake valves and 3.5x" bores...

The cfm gains from a larger valve can be easily offset with a stiffer wastegate spring. Why [pay someone to] do all that work when you can just increase the boost pressure? In the end, the 383ci engine will be able to make more power since it will be able to tolerate more fuel and air to be burned in the cylinder before it detonates.

For most turbo/supercharged engines, the amount of power it can produce is limited by the octane of the fuel. You aren't going to make more power when the engine is detonating. Like I already mentioned, smaller bores resist detonation better than larger bores:



The above is the result of such tests to determine the octane requirements of different bores at different piston speeds. As you can see, the smaller 4" bore required less octane than the 6" bore at every piston speed to keep from detonating. A 3.90" bore would follow suit, and resist detonation better than a 4.00" bore, allowing more power for a given octane. Score one for the 383.

Then you have that extra 13ci in the 383. The main cause of detonation is when the temperature and pressure of the end gases of the flame get too high. That extra cylinder volume allows that air to expand and reduces the cylinder pressure, even though the same mass of air and fuel have entered the cylinder. So now, even more air and fuel can be compressed and burned in the chamber before the cylinder pressure and temperature get high enough to cause detonation, which again means more power for a given octane. Score another for the 383.

Those 13 extra cubic inches will also make a little more power when the turbo is in lag and not providing boost, as well as aid in spooling up a given turbo faster.

So what is the advantage of a 370ci engine? That you can potentially make more power per psi? That's great and all, but for any given octane, you are going to make less power than the 383 because the 370 will have a higher tendency to detonate. Being able to fit a larger valve just isn't an advantage that the 383 can't easily overcome.

99tramsamc/fia

iTrader: (2)

Great info ,But dont forget about piston speed!
I myslef dont like the 4" crank. not only does it incress the speed(1 for the 370), but it mess up rod/stroke ratio(1 for the 370), brings the piston out of the hole(1 for the 370),etc.
With a motor like he is trying to build that **** dont even matter.
Save your money, use the Ls1 block with a stock crank. Spend your money on the upgraded rod bolts.

KCS

iTrader: (20)

Piston speed isn't even an issue. I know of at least one LSx engine that turned 10,000 with a 4" crank. The beauty of boost is that you don't need high RPM.

No it won't.

No it won't. Stock engines stick the pistons out of the hole anyways, so how is that a bad thing?

1CAMWNDR

iTrader: (21)

Very interesting. Good info. Looks like 6 of one and 1/2 a dozen of the other.

NoTractionLS1

Good thread here a lot of good info!

99tramsamc/fia

iTrader: (2)

Out the bottom not the top. The sleeve is only 5.5 long. With a 4" crank the skrit on the piston come almost completely out of the hole> Not to say they dont work millions of them out there.
10,000 is not a big deal if you got the money for pistons. Ever see the skrit on one of them 10000+ motors. about 100 runs if your lucky(got a pile of them). Not the point

Rod goes from 1.68 to 1.52. big difference in side loading.

They both work, but $ for $ 370 all day, Spend your money on a better set of rods and turbo. Jm2c

KCS

iTrader: (20)

How is that an issue? Millions of those 4" (and even 4.10") strokers work because the pistons were designed for it, and they last. The widest point (aka breakover)of the piston is moved up so that the piston is still fully supported at BDC. It works and works well, why bring it up?

Not the point? You did say it "incress the speed". Did you mean something other than piston speed? I just don't see how piston speed is an issue.

So how does that affect the reliability, seal, etc? LS7s have it even worse with a 1.51:1 ratio, which still passes all of GM's 100,000 mile durability testing. What significant impact will this rod ratio have? Can you prove it?

99tramsamc/fia

iTrader: (2)

I didnt say they dont work. Didnt mean to ruffle your feathers.
plot it on your fancy graph, comparing a 3.9 to 4.03 is a lot different the 4 to 6. at 200 fpm incress(3.622 to 4.0) they equal out.
Prove it are you kiding me, pick up a basic physics book. This is not rocket science.

99tramsamc/fia

iTrader: (2)

Not to be a ***, But~~~~~
To go further on the piston speed do some math.
A 4.0 bore @ 1000 fpm requires 97 oct fuel
A 3.875 @ 1000 fpm Requires 96.625 oct(3.875 makes the math easier)
With a incress of 200 fpm( the difference in stroke) the 3.875 bore would require 97.625 oct fuel.
Math dont lie.
Combine that with a long skirt(better heat transfer,cooler piston),Reduced side loading on the piston(better rod ratio, less friction=less heat) the 370 would be able to run more boost on the same fuel and make more POWER.
It as easy as doing some Math.

TurboS10

iTrader: (12)

The main reason to go to a bigger motor is less boost for the same HP and lower rpm for a non race setup.
On street tires, either motor will spin the tires at 3k unless your running a huge turbo that doesn't spool till 4k+.
Back to the original question...
The cam is based on the rpm you want to shift at, the head flow, and the back pressure.
The first 2 are easy. BP is dependent on boost, RPM, and turbine size.
Big turbine = low BP and high rpm so a normal split cam.
High BP from any of a number of things = rev split cam.
Most shoot for less than 2-1 BP ratio. And most cams seem to work ok in that area also.

Your combo- 76mm
383 = no
why, most get a S turbine wheel or smaller. That's not enough turbine to support a 355 efficiently at 5k+. Plenty of posts to support that on The Turbo Forums. This link just does a good job showing it.
example https://ls1tech.com/forums/forced-in...ame-motor.html
A 76mm will be about maxed out on a 383 at 15psi unless your running crap heads. ie you paid someone to screw them up.
By maxed out, I mean it will be way to the right on the compressor map.
Lots of people run in that area and say it's fine. But the compressor will be making the air hotter when running over there and it's harder on the turbo.
also, you don't need 383 unless your shooting for a specific hp/time slip and want lower boost.
Ok, say you want it your way and still run a 76/8HPS. Then a rev split will make more power up top.
What's another way, twin 61mm ptrim .58 or .69 a/r on a iron 347. It uses the cheaper 5.3 block and the twin 61's flow as much as an 88mm.
They will support ~ 1k fhp with that exh.
There was a twin 61/.58 build 383 sbc on TTF's that went 9's w/an M6 in a 4th gen. He ran a CC 218/218 113 lsa HR and ~18psi. He liked the smooth idle it had the best over several other cams he tried.
The small cam worked well with the small exh needed for the m6. Power went flat in the 5k area but the turbos stopped the power from dropping off so he could rev to 7k.

I plugged the LS6 cam into Pat's DCR calculator the other day.
That cam has a late closing intake and low overlap w/the 117.5 lsa. That's why it works well in a turbo.

Best I can tell, these motors come with a nodular iron crank, not cast like a SBC. That's one reason they can handle more HP.
If going with a forged crank, then just go with a 408. - 6.0 w/4.0 crank and an 88mm to keep up.
I decided to go with the iron 347. It's cheaper due to the block and you can find more used heads, intakes, and turbos to support that cid.
And for street tires it's plenty of power unless you want to do 80mph roll ons with the turbo ricers.

KCS

iTrader: (20)

You said going from a 1.6:1 rod ratio to a 1.5:1 rod ratio is bad and makes a "big difference". So I say prove it. How much is this "big difference"? I don't think a physics book is going to tell me about that specifically. Like I said, the LS7 has a 1.5:1 rod ratio, and GM 100,000 mile durability testing seems to disagree with you. What makes you think that it is a "big difference"?

That "fancy graph" was based on results from testing on the equivalent of a lawnmower engine, so applying a mathmatical analysis of this engine to an LSx engine isn't very wise at all. The general trends (like the effect of bore size and piston speed) are relevant, but the slope of the graph probably isn't going to be the same.

Granted, you bring up a good point about piston speed, "the math" doesn't take into account all of the variables. Most of the heat is not transferred out of the pisont skirt, but the piston rings. If you have any "math" that says how much is actually transferred out of the skirt, I'd love to see, but I doubt it's even significant since it's the coolest part of the piston.

Not to mention, you also have those 13 cubic inches to account for, which I highly doubt the design of the piston skirt or "rod ratio" can offset. Like I said, for any given mass of air crammed into the cylinder, it will result in less average pressure and heat since it is a larger volume, resulting in a higher knock threshold.

F8L GTO

This^^^ People make great power on this cam. Sounds factory too!