JPStreetPerformance

ok im new to this whole forum thing but maybe someone can answer or steer me in the right direction.

I am wanting to build a over squared motor capable of higher Rpms than most Ls motors.. I'm not looking for a ton of power.. Maybe 450-500 range...

I need help with clearance issues that may occur for this 327ish motor
Parts I already own
Brand newLs2 stock block 4.0 bore
Brand new Ly2 4.8 crank
Brand new ls2 stock Pistons

The question is rod length there are zero forged 4.8l rods available 6.278" (without expensive custom ones) so my options are a forged 6.300 or a 6.250

I will be running ported ls3 heads with a Comp 54-502-11 solid roller with required valve train...

So my main question is which rod is recommended and will I have valve clearance with the head/cam set up also compression ratio for this set up?

Also if piston height is slightly tall above deck, what does everyone think about a thicker gasket, if so which one?

Any help is appreciated

MuhThugga

Why not get the 6.300 rod and a custom piston made to fit that rod and stroke in the motor? Or just use the stock 4.8 rods with the factory 6.0 pistons.

Personally, I wouldn't put ported LS3 heads on motor of that displacement. The intake runners are pretty large in stock form, and you want to open them up even further with porting?

No one is going to be able to tell you what your valve clearances will look like. You are going to have to measure. You will also have to measure for pushrod length.

There are also a ton of variables in determining the compression ratio.

JPStreetPerformance

Thanks for the response. Being that we are seeking to build a high rev motor, I was wondering if the stock 4.8 rods would be strong enough, that was my biggest concern, I guess technically i could just cryo treat the rods to give them about a 20% increase in strength.

maybe you can answer this as well.. Did they make the Lq9 heads with a rectangle port?

This is the theoretical build we are going off of with some numbers

Chevy 5.4l "327" Hybrid (Actually 328 ci, but who's counting?)
GM Gen IV LS2 Aluminum Block
Bore: 4.0"
Stroke: 3.27"
GM Vortech LY2 Crank (3.27" stroke) rebalanced for LS2 pistons
GM Vortech LQ9 Heads (wide, rectangular port)
GM Vortech LY2 Connecting Rods (6.275")
LS2 stock pistons (1.34" compression height, no dome)
High-RPM solid roller Cam, springs, and valves:
Exhaust manifolds for higher RPM use

Specs:
Deck Height: 9.24"
TDC: .01" above deck
Compression ratio on Gen IV LQ heads, 0.03" gasket, flat LS2 Pistons: 9.96:1
4350ft/min mean piston speed (max for the 6.0 block stock) at: 8000rpm
Rod/Stroke ratio: 1.92
Bore/Stroke ratio: 1.23
Peak power estimate (with properly timed cam, intake, and exhaust 7500rpm
HP estimate: 480HP @ 7500rpm, around 400 ft/lbs torque between 4000 and 6000rpm.

MuhThugga

The LQ engines came with cathedral heads with large 72cc combustion chambers. The L76 and L92 were the truck engines that came with rectangle port heads.

Are you planning on just being able to hit 7500 RPM in a drag race scenario or sustain 7500 RPM like you would with road racing?

conan

iTrader: (5)

This might be something close to what your looking to do...

https://ls1tech.com/forums/dynamomet...p-8000rpm.html

redtan

iTrader: (5)

If you're going to spin it to the moon don't skimp on the bottom end.

So none of that OEM stuff (even though it's pretty decent stuff).

Forged crank, forged rods, forged pistons etc. This motor is going to cost you a pretty penny in the end, do you really want to put in subpar components? It's going to cost more in the long run than doing it right the first time.

JPStreetPerformance

thanks everyone, after running some compression numbers, i had to change up a few things, just purchased forged lunati rods, and Je pistons.. although im not finding any aftermarket crankshafts for the 4.8 (3.27) stroke. From what i have read the crank is really stout however... opinions?

JPStreetPerformance

thanks pretty much exactly what im doing, looks as if they are running a stock truck crank? i have messaged them to get further details

marks73ta

Looking to do the same except I have two sets of Carrillo 6.2 rods with the Honda rod bearings. They are sets I obtained a long time ago from a Nascar team after they changed combinations. These were back up parts that were blueprinted, balanced, etc but never used. I have to find out if the 4.8 crank can be cut to the Honda bearing (1.88) size and still maintain its integrity/strength.

marks73ta

Just realized the Carillo rods are only .890 wide on the big end. The 4.8 crank I just picked up shows 1.906 wide and the LS are rod big ends are .940 so looks like I can't use the Carillo rods after all. That woild leave around .125 side clearances, way lot too much to overcome. I did get a 4.8 crank so I will be looking into other rod sources. Still not a problem, just too bad that I can't use these great rods. Guess I'll have to make "clocks" out of them, LOL.

Mark

FLYNAVY30

iTrader: (1)

did this build ever go anywhere....very curious