Gtslo04

Alright if your another diehard stroker fan, please move along. Especially if your aunts cousins brothers son n laws uncle built a destroked Ls and didn't like it. If you have built one yourself I would like to hear feedback.
i recently built a all forged ls1 stroker with all the goodies Cnc heads arp all throughout. Built for nitrous. It just didn't cut the mustard. So I bought a Texas speed 6.0 iron block bored to 4.065 sonic tested ok. With it I bought mahle L92105065P25 pistons -25 cc compression height 1.105 as a package deal for $1400 (pistons alone were 1100) which was a score imo because everything was new. Now I'm going with an lr4 crank and the hard part was finding the correct rods. I'm pasting my notes from last night. Give me your opinion please


L92105065P25
Mahly pistons are suppose to have a 4.000" crank
With a 6.125" rod which produces a 416" 4.065 bore

We are using a 3.268"crank

So the difference between a 4" and 3.268" is .732 (difference in diameter)
Take .732 and divide by two to get your radius difference
Which is .366"

I believe radius is the main difference we are looking for when trying to configure the correct rod size.

So take a 6.125" rod and add .366 to get your new rod length
Which is 6.491

Tall deck LS engines have a rod that is 6.460 which would have the correct "on center" wrist pin, rod journals as well as main journals. This leaves the piston .031 in the bore. Possibly mill the block .030 and check for clearances. Ask Clark about mls head gasket thickness for correct/safe crush thickness. Also ask about material expansion to see if a longer rod will expand with heat as piston rings do.

Compression height is from center of wrist pin to top of the piston. These pistons are 1.105. The eagle rods crs6460O3DL19 are 6.460 the LR4 crank being 3.268 has a radius of 1.634 all totaling to show at TDC to be 9.199
Block deck height is advertised as 9.240
9.240-9.199=.041
Let's check with a kit with same pistons
1.105+2.000"+6.125"=9.23
9.240-9.23=.01 clearance.
With 6.460 rods the clearance would be .041 mill .030 leaving .011 clearance slightly decreasing static compression by ~10%?

Senna

iTrader: (1)

Here is how i see it

Stroke 3.268 / 2 = 1.634
rod length 6.300
piston comp height 1.304

total 9.238


These are common size rods and pistons that would give you options on valve reliefs or dish.

slogo

Yeah, destroying will never work, lol

jhshnh

Go for it, man! I love destroked hi rpm engines. Dare to be different.

8.Lug

The LS is a metric engine, you really should be using 83mm(4.8 crank) and 92mm(your crank) for your calculations.

MY_2K_Z

iTrader: (1)

I would love to see the results. I have an extra gen 4 4.8 crank and rods and if my turbo ly6 ever bends a rod I plan to swap to the 4.8 crank and rods.

Gtslo04

are you being sarcastic? I think so lol because that N/A went 504 hp.

Gtslo04

so your saying throw away a $1000 set of pistons so I can go with a different set of pistons and rods? Is there any geometry behind that? I can order a $590 set of 6.460" rods and have the block milled .030 for less $. If there is any geometrical/durability reason to support your idea I am all ears but I couldn't justify doing that just to go with more common parts. This engine will see 18-20 psi btw

slogo

Yes, I was being Sarcastic, you didn't see the grin on my face.
And it was 540 not 504. I am a fan of big bore short stroke myself.
Seems like there has been debate on ls1tech before about what you are
contemplating, so i thought I would throw that video on here for the fun
of it. Good luck with the build, keep us posted on the build, would love to
see results.

Senna

iTrader: (1)

I'm not a fan of decking the block that far. Limits it's possible future uses. Same with 6.460 rods, limited applications.

It would have been cheaper the way I suggested and not having to deck the block.

P.S. you would'nt have throw the other pistons away, it's possible tp sell theme.

pantera_efi

iTrader: (1)

HI GT, yes I agree most here know LITTLE about PROFESSIONAL Racing.
I acquire my 3.268" crankshafts from David @ Marine Crankshaft, my neighbor.
He's a Kiwi, thus TOP quality Billets.

Your CASE, I would replace the piston, a Racetec 2618.

I will provide a good cost for the EXHATCH piston, I would hope to provide a NPR STEEL ring set.

I would NOT "deck" the block as few intakes will then fit.

The ALMS engine "spec" is COMMON, the chance to fine some "take-out" parts could also be possible.

Lance

KCS

iTrader: (20)

What do you mean tested ok? What was the minimum wall thickness?

Gtslo04

I'm honestly not sure what it tested out to be. It's just what I was told. Now that I think about it that's putting a lot of faith in someone that they speak the truth.

Gtslo04

Good morning everyone!!

hope everyone got a goodnights rest, I have been searching all night for something that will maybe... just maybe.. work! And I found it!! First I just googled 6.500" rod android came up to some forged rods for an old MG 4 cyl. Then right below it.. Howard's cams!!!!! Sbc large journal!!!!! Br6500 is the part number I'll post pics if I can figure out how comparing the ls1 style am for the sbc. If I remember right, when people were first modding ls1's (Jesus I was a kid) they were using 6.125" sbc rods before the aftermarket dedicated ls Rod was made. I remember my stepdad used a set and ran them for over 5 years before selling the car. (They were lightweight titanium and he wasn't about to throw them away) anywho... yeah only difference is a small offset on the pin I believe and the big end had a different size bearing but hey the big end bore Ian the same. Pin side width is .060 wider but what could that hurt? So the math side... 1.634(radius of stroke)+1.105 (comp height)+6.500(rods) 9.239.

Now as as for the lr4 crankshaft I'm finding that there are mixed answers for the stroke I'm seeing 3.268 and 3.270.. anybody know if this is a difference in year or if maybe it was a very used crank they mic'd?.?.

North*power

iTrader: (1)

Destroked LS's are awesome, hoping you've made some headway with the project.

heykw

I would like to see the dyno sheet on this build and a cost breakdown.

Peri00

destroke lq9


if I use the 4.8l crank and rods, with factory lq9 pistons and ls3 heads.. how much do I deck the lq9 block?

G Atsma

Why would you deck the block??

Peri00

Im on a budget
To boost compression and to make sure the pistons is not to far in the cylinder upon tdc..

G Atsma

LS engine pistons tend to come ABOVE the deck a few thousandths.
Mill the heads, not the block