Yeah i got confused.

I bet those rods were a pretty penny. But, with using the stock crank and 2.3 rods, thats still only a 1.56 r/r.

So in the end is it really worth it. Every bit helps but its not going to make a huge difference. This is where the cost might out weigh the gains.

Knowing Chris though, his crank is de-stroked to get that perfect r/r!

Actually someone else did it before Karo.

Here are the specs of Eagle Rods for both the 2.3 and 2.4. Looks like you could shave down the big end of the 2.3 rod to the width of a 2.4 rod. I am not sure I would want to do that to an aftermarket rod. Like Sweetness said, a one off set of rods are going to cost.

Chevrolet LD9 2.4L Quad 4.............Chevrolet LG0/LD2 2.3L Quad4

length: ----------------5.710 in......................5.806 in.
rod journal: ----------1.889 in......................1.889 in.
housing bore: -------2.0145 in...................2.0150 in.
pin size: ---------------0.866 in.....................0.866 in.
big end width: -------0.9120 in...................1.0860 in.
pin end width: -------0.9120 in...................0.8750 in.
thickness above pin- 0.200 in..................0.200 in.
typical weight: --------550g............................590g






Jason
99 Z24 Supercharged
157hp/171tq - NA
190hp/170tq @ 6psi

LG0/LD9 for Life

i love this thread.

to to get the big boys talking makes me proud LOL

so.. gary.. are those pauter rods in your motor the same as karo's?

lol at you chris. im figured out one of your secrets. na na na boo boo.


at this point i am ready to admit that really the only part useful in an ld9 is the crank. lg0 > ld9 all day long. why even bother with a 2.4? put a 2.4 crank in a 2.3 and be done with life.


Edited 1 time(s). Last edited Thursday, August 06, 2009 10:52 AM


Every time I scream "Release", I mean it, you know it. I feel the day. Black 7.

i wanna be in this thread. its gettin me all hot and bothered.

Don't forget to think outside the Quad4 box here guy's. Might be able to find rods from a small block v8 or a nissian or a mitsu or a v6 northstar or whatever that can be resized on the big end or bushed on the small end or you have your quad crank journals turned down some to fit a smaller rod on,cut the holes in the pistons for bigger wrist pins,etc.,etc..

We used to do silly sounding stuff to get what we wanted...





"The FACTS are always subject to CHANGE once the TRUTH is applied"
"In the entire history of man the only stupid questions are the ones that don't get asked"

yea... i did that earlier today with a sbc rod and an ls1 rod my dad had lying around. the ls1 would probably be the right length improvement we'd be looking for but the journals on the big end are quite a bit larger than a 2.4's is. you could definitely bushing the small end and make it work, but the big end would take some ingenuity.



Every time I scream "Release", I mean it, you know it. I feel the day. Black 7.

I'm not really adding anything, but keep in mind deck height is an important dimension too.

there's a formula for finding a bottom end combination that works.

you need the deck height (center of the crankshaft main to the deck)

then add HALF the stroke, the rod length (center of big end to center of little end), and compression height (center of wrist pin to top of the piston.. not including any dome/ dish) together and this must be LESS than the deck height.

Also keep in mind that any change in stroke must be reflected in the compression height by half, and any change in the rod length must be reflected in the compression height equally.

in other words, increase stroke by 4mm, decrease compression height by 2mm
increase rod length by 4 mm, decrease compression height by 4mm

(decreasing compression height means the wrist pin needs to moves UP, towards the top of the piston)


so whatever combination you change things, needs to be reflected in the compression height.


here's an article I often reference when people ask about rod ratio.. I've omitted the V8 specific talk so it mostly refers to engines in general

Quote:

the rod ratio in a gasoline engine determines the piston dwell at TDC. the longer the rod, the less downwards piston motion will be the result of the rod angle changing.

if the crank rotates 10 degrees, then a very short rod will be at a greater angle than if the rod is very long. since the rod doesn't change length then some of the pistons downwards motion will be a result of this phenomenon, so the longer the rod, the longer the "dwell" and the longer the dwell the more complete combustion and higher cylinder pressure. The rod length is limited by other engineering concerns, like block deck height, piston height, and thus inherent stability, and resultant wear. and so on.


Rod Angularity

A longer rod reduces the maximum rod angle to the cylinder bore centerline. Less rod angle will reduce piston side loading; there will be less friction and less bore wear. Less rod angle also gives better average leverage on the crank for a longer period of time.

Piston Pin Height

A higher pin height will reduce piston rock and aid ring seal. please no screaming and name calling about anything about a tighter ring pack, we are talking about pin height and pin height only. Moving the pin closer to the center of gravity of the pistons makes the piston more stable.

Rings

As the compression height is reduced, the space for the ring pack also get reduced. This can be a problem on some engines. It is good for power to have the top ring as close to the top as possible, but this is limited to the strength of the top ring land. As it becomes thin, it becomes weak. High output engines (especially nitrous engines) need a thicker ring land to keep the cylinder pressure from pinching the top ring. In my opinion, if you have to compromise ring location, it would be better to run a slightly shorter rod.

Skirts

Shorter skirts are usually combined with a shorter piston for a longer rod, but they are not really related. There is no reason to reduce the size of the skirts just because the pin location changed. A shorter skirts are used to reduce friction and lighten the piston. The cost is a little less stability, but it is arguable that a lighter piston with a higher pin height does not need the extra stability. For a street car, I would increase the rod length if it meant a reduction is skirt size. Most of the things listed here are for competition motors to gain a few hp, not worth a lot of effort for most street engines.

Piston-to-Valve Clearance

A longer rod decelerates toward TDC and accelerates away from TDC slower than a shorter rod, so piston-to-valve clearances are tighter with a longer rod. This may require deeper valve relief's in the piston. A short rod is just the opposite, there is more clearance because the piston decelerates toward and accelerated away for TDC faster.

Piston Velocity

A longer rod reduces peak piston speeds slightly and delays peak piston velocity until the piston is further down the bore, which gives the intake valve more time to open more. Peak piston velocity is usually somewhere around 75° ATDC and since most cams cannot fully open the cam until at least 106° ATDC, it leaves the valve as a major obstacle when airflow demand is at its greatest. By delaying peak piston velocity, even if it's only 1 or 2 crankshaft degrees, it can allow the valve to open another 0.010-0.015", before peak airflow demand is reached. Not a huge help, but a step in the right direction.

Piston Acceleration / Deceleration

Reducing piston acceleration / deceleration from and toward TDC will reduce tensile loading of the rod, the number 1 cause of rod failure.

Intake Runner Volume

Since it is easier for an engine to breath with a longer rod, less runner volume is needed. This allows more room for an intake system (this is a very small gain, but is real).

Exhaust Gas Scavenging

A longer rod is moving slower at TDC, which reduces the speed of the exhaust gasses during the overlap period. This reduces the scavenging effect at low rpm and reduces low rpm power slightly (makes the engine run more cammie). A short rod on the other hand moves faster past TDC and increases the scavenging effect and help low rpm power.

Ignition Timing Requirements

Due to the fact that the longer rod moves past TDC slower, it gives the charge a longer time to burn. So you need less timing for peak power. Using less timing also reduces the chance of detonation; so higher compression ratios can be used.

Longer Rod Pros

Less rod angularity
Higher wrist pin location
Helps resist detonation
A lighter reciprocating assembly
Reduced piston rock
Better leverage on the crank for a longer time
Less ignition timing is required
Allow slightly more compression to be used before detonation is a problem
Less average and peak piston velocity
Peak piston velocity is later in the down stroke
Less intake runner volume is needed

Longer Rod Cons


Closer Piston-to-valve clearances
Makes the engine run a little more cammie at low rpm
Reduces scavenging at low rpm

Shorter Rod Pros


Increased scavenging effect at low rpm
Helps flow at low valve lifts (a benefit if the heads are ported with this in mind)
Slower piston speeds near BDC
Allows the intake valve to be open longer with less reversion
More piston-to-valve clearance
Can allow for a shorter deck height

Shorter Rod Cons


More rod angularity
Lower piston pin height (if the deck is not shorter)
Taller and heavier pistons are required (again, if the deck height is not reduced)
More ignition timing is required for peak power

some of this must be attributed to grape ape racing...

I've also read that unless you're seeing a change of at least 2-3% sometimes 5%, its not worth the effort.
so changing the rod length alone may not be perceived as any noticeable change (airflow changes)

but rod ratio was a big reason why I decided to swap the LSJ bottom end into the skwirl. The advantages of an engine that has the potential for higher revs structurally, better high-rpm breathing capability, less side loading, and improved OEM internals was more than enough to convince me.