LS.

Intro

I had looked over for past threads about LS3 stroker kit options especially the less common one 3.90 stroke, unfortunately there is nothing much about it as we are aware the limitation of LS3 sleeves length by using 4" crank (the most common by now) as it causes piston to be out of bore in BDC know as "piston rocking" which wears piston quicker, nosier,consumes more oil..etc, as this comb suits more for racing application not so perfect for street DD application's .

Bottom line

I'm building an N/A LS3 for street racing perspective and to be my DD vehicle all the time a 3.9 stroke with 6.3 rods theoretically the best combo that i know so far for power/durability ratio as it keeps the piston's inside the sleeves . Not bad for a rod ratio around 1.615, but that kind of combo are not available on shelf the rods and piston should be customized , i'm wondering why this kits are not available on shelf ? most common these days are 4 or 4.125 i believe many people looking for to build a reliable engine am i missing something ?
cons are not sure if it required a supporting rail for pistons !! as it will be around 1" CH , dwell is higher due to rod length which limit the options of CR and cam specs as it take little longer in TDC

the aim of this thread is to open a discussion to hear your opinions of 3.9 stroke and which other combos do you think more subtitle for street DD, N/A engine, for LS3/L92 do you think will be better without significantly sacrificing the durability.

spanks13

iTrader: (5)

Just use a 6.125” rod and you’re golden. I think 3.900 stroke would be a good combo but don’t complicate it by trying to use a 6.30 rod that would require sub 1” compression height.

Ignore rod ratio it literally is one of the least important factors you could waste your time thinking about.

DavidBoren

Use a 6.25" con-rod, and a ~1.040" tall piston. Puts you right at a 1.6 rod ratio.

For a purely naturally aspirated build, you can find lightweight forged con-rods that weigh in under 650g.

The extra dwell at TDC is not enough to hold you back in your desired compression ratio. It might, MIGHT, mean that the tune will be different compared to a lower rod ratio, but I doubt it.

LS.

By using 6.125" rods the piston will still come below the sleeve, but just not as much as a 4" stroke, by using a longer rods it will keep the piston's more inside almost all of it, this guy used it , yes you are right it's exactly 0.99" but using 1" i don't think it will make an issue.

LS.

To be honest is what worries me most is to keep pistons inside as much as possible without giving up much for the stroke. 6.25" is another good choice but makes it better than 6.3 ?
Yes lightweight forged rods is the way to go i didn't dig in it so much but i found manley 6.3 around 690 g as 6.125 is lighter in general

DavidBoren

For me, I have stupid arbitrary limits that I have established.

I won't go below a 1.000" compression height. Nothing to back that up, just my own peace of mind. So, I recommend a 6.25" rod instead of a 6.30" rod. I don't like the idea of the piston pin being that close to the rings.

I also won't go below 1.6 rod ratio, either. I know it really doesn't matter, but it does to me... so I set 1.6 as my absolute minimum.

And won't go over 399ci... 240cc maximum intake runner volume... I put arbitrary hard limits on certain things for whatever reason. It all makes sense to me, but my logic seldom translates to others very well. Lol.

jhshnh

I'm building an N/A LS3 for street racing perspective and to be my DD vehicle all the time a 3.9 stroke with 6.3 rods theoretically the best combo that i know so far for power/durability ratio as it keeps the piston's inside the sleeves . Not bad for a rod ratio around 1.615, but that kind of combo are not available on shelf the rods and piston should be customized , i'm wondering why this kits are not available on shelf ? most common these days are 4 or 4.125 i believe many people looking for to build a reliable engine am i missing something ?

To me no, you’re not missing anything. I agree 100% with you on the 3.9” over the 4” stroke and a 6.3 rod. I guess the reason you see so many 4” kits and no 3.9” kits is I guess bigger is better? But for reliability I can’t agree more with your thinking. Wiseco/K1 started offering a 3.9 crank for this very reason. Here is an interesting article from JE pistons supporting the 3.9 crank:
https://www.jepistons.com/blog/diffe...nk-for-your-ls

KCS

iTrader: (20)

Just go with a 4" stroke. A lot of what you're worried about is complete nonsense perpetuated by people who just don't know any better. Brian Nutter wrote a great article (that you can read here) to help people understand what is really going on in stroker piston design:

"Strokers had a partially-undeserved reputation for wearing out piston skirts and oiling due to lack of support for the piston at BDC. Some identify the piston hanging out of the bore at BDC as the culprit. The real cause is some of the cheaper pistons don’t have the correct taper for stroker applications."

LS.

Yes it's a little CH but what relieves me is the idea that it's meant for N/A and using a forged pistons , as long the logic based on reality nothing wrong with it for me this were the most fun comes in when you see it's actually true.

LS.

Maybe the consequences wasn't so clear in the past as they add some coatings to the skirts not really sure about that, yes it's great article i read it before it has a very useful information's.

LS.

I wish it's nonsense as it will make my life much much easier plus i get an extra HP but it's what it's, JE piston had made blog clarifies the consequences of using 4" as DD otherwise they wouldn't bother doing it if it's not true actuality it will affect badly on there repetition , Nelson Racing has stated as one of aftermarket common mistakes as the piston goes beyond measuring point were the size of the bore are based on it ,the interview as the following skip to 8:40 , how about LS7 if it doesn't affect why GM did extended the sleeves to be 0.350 longer than LS3 ?

DualQuadDave

iTrader: (6)

I do like the 3.900 stroke vs 4.00, but IMO, put the $$$ in the heads/intake/valvetrain and go for power per cube, not just a bigger motor. Really depends on your goals, but LS3's have been mid 500whp with pretty simple topend and we'll thought out cams. That's even w/ ported 821/823 heads. I would reverse engineer it and figure out how fast you want to go and how much power you need to get there. If you really want to go fast, forget the stroker crank and go big bore 388ci.

KCS

iTrader: (20)

I’m very much aware of what both JE and Nelson stated, but they are speaking on very old and very outdated designs. The link i provided shows you the manufacturers are also very much aware of the breakover point on the skirt and where it ends up at BDC in LS blocks. Compared to the OEM LS7 piston, the aftermarket pistons nowadays have the breakover point much higher in the skirt so that the piston is fully supported at BDC.

LS.

Sorry guys the reply approvel took 2 days.

DualquadDave, Head/intake/valvetrain it will be included as i will port the existing heads and order GPI ported intake , cam stage 2 , the overbore i have to do it anyway in order to clean cylinder walls as it will almost at the limit 4.08 or 4.085
thank you for your advice

DualQuadDave

iTrader: (6)

I like the FED 821 heads better than the GPI stuff. For big bore, you can't use the LS3 block unless you resleeve it. I say sell the LS3 block and grab a Dart and go 4.125 bore and get serious. JMO. I am getting ready to do something similar.

LS.

The heads i will port it myself the GPI porting is for the intake not heads, my plan is to re-build an existing l92 engine by just replaceing rotating assmply not to spent much $$ just adding a stroker kit other wise if i plan to spent an extra $$ i will get a resleeved 5.3 aluminum with aftermarket heads.

64post

iTrader: (5)

3.622~2=1.811 + 6.300 + 1.115 CD = 9.226, very easily doable with off the shelf stroker pistons (416) I always thought this might be a good high RPM setup increasing the rod to stroke ratio to 1.74.

ez2cdave

OK . . . Question . . . What is the "correct taper" for stroker pistons ?

ez2cdave

The JE article was written 3 years ago . . . That doesn't sound "very old" to me ( in "electronics", maybe . . . In engine mechanics, no ).

ez2cdave

Are you implying that you believe that Summit Racing produces superior pistons for stroker motors and that the major piston manufacturers "don't know any better" ?

I sure hope that I have been misreading your posts.