an email from 95naSTA, this thread by MyLittleBlackBird, and the LN3 piston thread by clm2112 (HERE
), along with wilwren'* incessant search for power gains
, have combined to make me think that people may actually be realizing that there are gains to be had by improving rotating assembly geometry...
ya'll know that Iím the nut working on a hybrid of the tall deck SI (EV6) block with the much better symmetrical port heads of the SII (Ecotec) bolted on (I am also looking at several improvementsí to the oiling system/windage as well as more involved roller cam bearings...)
So maybe I can lend a hand...
first off I donít have all the info (I'm kind of half done with a REALLLY long write-up of my work thus far) of the GN and LN3 and EV6 blocks, but I donít mind finding out more info! (I already have 3 3800'* in my garage, and i would love to have an LG3 and LN3 along with the SI and SII L67 for comparison purposes...
but Iím not sure I have the room
as Wilwren stated in the thread by clm2112 the SI (EV6 or earlier even the GN) loses all power potential at a fairly low rpm, this is sad because the tall deck long rod rotating assembly makes for a good mid/high rpm Tq curve and breathing (aka more HP as well) the problem is simple...poor head design that doesnít flow well
the SII engines have the opposite problem, a head that flows extremely well but on a short rod bottom end that lacks the geometry for better induction at high rpm but is very good for low rpm grunt, which also seems to make our FWD trannies cringe
I saw this first hand looking at the flow charts of a seriously worked over set of EV6 (aussie SII which is our SI) heads with spread guides for larger valves and serious port and seat work, which were still out flowed by a set of mildly ported SII heads on the aussie forums...
my thoughts are that for the eventual development of max effort racing 3800'* the best of both worlds needs to be utilized, that said, lets get to work.
The SI (EV6) NA specs
Connecting Rod Bore B/E = 60.295mm - 60.312mm or (2.3738" - 2.3745")
Length Center to Center = 162.052mm - 162.154mm or (6.3800" - 6.3840")
Piston Pin Diameter = 22.995mm - 23.000mm or (0.9053" - 0.9055") Pin to Rod fit = 0.018mm - 0.043mm Interference or (0.0007" - 0.0017")
I do not have the info pertaining to the SC SI L67'* specs or the LG3/LN3 GN engine readily available...
The SII (Ecotec) has some interesting differences...
The connecting rods will fit the crank (SI EV6 or SII Ecotec cranks) as the n/a & */c conrods have the same size connecting rod big end bore of = 60.295mm - 60.312mm or (2.3738" - 2.3745")
Now for the differences
*/C con rod length center to center = 143.256mm or (5.640")
N/A con rod length center to center = 145.80mm - 145.90mm or (5.740" - 5.744")
*/C piston pin Diameter = 22.981mm - 23.002mm or (0.9048" - 0.9056")
N/A piston pin Diameter = 21.995mm - 22.000mm or (0.8659" - 0.8661")
this means that there are differences in the piston compression height as well, particularly because of the ring package spacing due to the differences in the dished area of the piston as well as ring land strength requirements.
now on to my thoughts (which I Knooowww that 95nasta is interested in...lol)
unfortunately there isnít much that can be done to the SII NA (L36) piston compression height that will allow for a longer rod other than maybe a dykes ring setup or a radial gas ported 2 ring design, but this would call for very good oil control to keep from overtaxing the oil scrapper and keep oil out of the chamber (a good bet would be a Variable displacement AC compressor utilized as a "on demand" vacuum pump to improve this)
Utilizing a EV6 tall deck block (really...who wouldnít love an extra inch?
) and ditching the tall compression height SI pistons and running a set of aftermarket (and fairly cheap I might add compared to custom jobs, though I hate standard dishes and would prefer a chamber mirror dish design for maximum quench characteristics) forged L36 pistons would let you run a rod that is a full inch longer than the L36 rod,
6.740 > 5.740
as well as being almost 3/8ths of an inch longer than the factory SI rod.
a side by side pic of a 93 EV6 L27 rod and piston next to a 98 SII L36 rod and piston:
L36 on the left 93 EV6 on the right (note the differences in dishes on both NA engines this relates to the difference in combustion chamber volume as well)
Now for my question...
Originally Posted by MyLittleBlackBird
Then for chits and giggles I laid one of my forged H-Beam rods next to it for a little comparison. The H-beam is 6.658" long..... Just about the same length as the piston and rod of the L36...
this REALLLY interested me.. the C to C is 6.658 inches correct?
so this rod (given proper big and small end sizing) would work well with a set of SII L67 pistons with the crown cut down .018 inches which increases the quench area a bit as well as lowers the dished area'* volume while having a negligible effect on top ring land strength (the additional material removal required by radial gas porting is minor as well)
what application are those sourced for?
I have looked into the Eagle rods but have focused on the Pauter rods more windage efficient x beam rods $$$ (very close to a diamond shaped beam) since I have been looking at the whole engine design from a max effort point of view...
while it may not me the longest rod you can fit in there it may prove to be a good compromise with a non stroked 3800...
Can you give me more info on that rod?