Pecos Pete

Anyone done this before?

4.8L crank stroke (3.268")
4.8L rod length (6.275")
6.0L block bore (4.000")

Yields approximately 327 cid with a huge rod/stroke ration of 6.275/3.268 = 1.92:1



If I use 6.0L pistons made for the stock 6.098" rod length and 3.622" crank stroke, but instead use the 4.8L rod length of 6.275" and 3.268" crank stroke, I believe the piston will end up at the same compression height at top dead center.

If I use 61cc chamber (5.3L) heads, and flat top pistons, I calculate I will end up with a compression ratio of about 12.2:1.

If instead of flat top pistons, I use something like Diamond Racing's domed 6.0L pistons with a 10cc dome, I believe the 61cc chamber heads effectively become 51cc heads, and I calculate I will end up with a compression ratio increases to about 14.5:1.

Would this be a good purpose built LS1, LSx, GEN III E85 motor? E85 is 105 octane alcohol. I believe alcohol likes a high compression ratio and a high rod/stroke ratio. This combination of parts looks to be able to produce both.

If I use stock GM rods and impose a piston speed limit of 3500 feet/minute like typical GM cast connecting rods, this becomes approximately a 6500 rpm red line motor.

If I locate some stronger after market rods and impose a piston speed limit of 4000 feet/minute like typical GM forged connecting rods, this becomes approximately a 7500 rpm red line motor.

Anyone know of a source for forged 4.8L (6.275") connecting rods?

Can anyone find any flaws in my thinking here?

Beaflag VonRathburg

iTrader: (176)

I really like this idea, sounds really good for CI limited racing series. Too bad, I don't know of any places around me where we can get E85. Sounds like it's opening up new possibilities in Gen III/IV performance.

chuntington101

be REALLY nice for a turbo motor to! get the CR down to about 8.5-1 and run GOOD boost and you will have a nice and VERY wide power band!

thanks Chris.

NO-OPTION-2002

iTrader: (2)

This is exactly what i'm planning fo my 2003 S10 swap.

LS2 block, heads, and pistons, 4.8L crank and rods = 328.5 ci.

Good power and great RPM potential. It's going to be setup for open track days at the new Miller Motorsport Park.

under_construction

iTrader: (1)

If anyone is interested, I have a set of 4.8 rods and a 4.8 crank I picked up from valvegod for this combo. Don't need them now (changed classes - need more displacement)


pm me if interested and we can deal.

Stampede4ever

What about using the L92 heads, and intake?

Thanks.

Boggies69

I've got a set of rods, as well as the 4.8 crank...I'm using the 4.8l flat top Pistons to boost up the compression in my 5.3l, basically trying to build an iron L33 my self...if your interested...pm me

Violence.z06

iTrader: (3)

Seems the combo works very well. im doing something similar but turbo with less stroke more bore.

This should show some potential of that combo. Only problem with it all motor is the torque. i was going to go all motor 350 cubes with a 3.185 stroke and big bore. goal was 1000hp at the crank. torque would have been in the 550hp range. Unless you give it a small shot of nitrous it wont really shine until the way upper rpm

Link below--4.8L crank in a 6.0 block. This motor did 1092hp and 755tq @7600rpm.

glu0n

Ya, i don't know why we don't see many screaming LS engines with lightning quick throttle response. I think the firing order change is partially to blame, the old firing order made a better sound imo. The old small blocks have been turning 8000rpm for decades, i love it when an engine screams in pleasure

gnx7

iTrader: (28)

There is no reason a stock 3.62" crank can't turn 7500rpm running good rods/valvetrain. To give up nearly 40ci going from 364ci to 327ci just gives up free torque/hp unless you are restricted to running a class limiting engine size.

A 4" stroke crank should have no issues running to 7500rpm either once you run upgraded rods/valvetrain.

If you plan to run a solid roller cam and even higher RPMs then that is going to make the short stroke combo really shine.... but then most production intakes run out of steam at 6600-6800rpm and just flatline as peak flow has been reached. You need a single plane intake or custom sheetmetal to use the power up top including some very good flowing heads.

I bought a motor that had a 6.0 liter class restriction out of a Bonneville Salt Flats S-10 pickup truck. It was 4.185" bore and 3.27" stroke and just under 6.0 liters. AllPro heads that supposedly flow 430cfm and AllPro single plane intake. It was being revved to 9000rpm+ and made 625rwhp+ with this combo.

JoeNova

You bumped a 9-year old thread.... I don't think they're going to PM you.


He has since went through the engine and switched to higher compression and a bigger cam. I think he made well over 600 HP N/A, and then similar numbers to the old combo on much lower boost.



Most of those high-revving, snappy throttle small blocks are using solid roller combinations with ultra light valvetrain. The same type of setup works just as well in an LS.

albert doty

yes 53 heads suck. 6.0 heads have bigger valves,keep compressiondown souse on street. ot trick flow heads. crane makes a good am ,speedmaster makesrods. use corvette intake. power wellgoodtunegetts you 475hp puton a super charger and get 800+ with low booost

LLLosingit

iTrader: (4)

Keyboard acting up or what This post was started in 2006 by the way.

BigEd_72455

iTrader: (7)

rbiron

Sounds about right but all GM connecting rods are forged so unless you are looking for something better like h beam rods stick with factory parts there's nothing wrong with them one thing though use gen 4 stuff the other gen rods were weak. Find yourself a set of square port heads off a 2500 or 3500 truck the ones I'm using are 823 casting number get em ported pay close attention to the exhaust ports. I'm going with a 6.5 rod and a 4 inch stroke piston in mine for a rod ratio of 2 to 1.

G Atsma

LS connecting rods are NOT forged. They are sintered powdered metal. Different process... but very durable.

Old Buzzard

More engines 101 in the advanced engr forum.....