ammfab wrote:i just googled stock stroke and rod length for the ld9. i found the rod length to be 5.710 (145.0mm) and the stroke to be 3.700 (94mm). then to find the rod stroke ratio (r/s ratio) u devide the rod length byt the stroke and get 1.54.
when u increase the rod length by lets say .300" to get a new rod length of 6.010 and then when u do th emath again u get a new r/s ratio of 1.62 which is better. it decreases side loading on the cylinder walls like the guys mentioned above which will free up some hp at the same time ur kepping the piston at TDC (dwell) for slightly longer also under the cylinder pressure from the combustion to give it a little more thrust on the way down............ u know what i mean.
as for the new pistons......... yeah u will need new ones with the pin bores moved further up on the piston. they should be moved the same amount as the rod length increase so that it lowers the pistons back down to the original postions, to prevent them from running into the head.
in the event that u have enough room between the head and pistons after u put long rods in and u opt not to run new pistons (because u have enough room), i dont think it will effect the compression ratio at all becaue ur engine is still drawing in the same amount of air as before and the piston dome hasnt changed any. compression ration is changed by the piston dome not putting a longer rod or bigger stroke in.
mike
DaFlyinSkwirl (PJ) - APU wrote:want to know what the skwirl has been up to? I've been doing a lot of homework for this coming year, deciding where I should take the skwirl next. A lot of you will be pleased to know that I plan on staying in the all motor category and mixing it up with ben for another year, and possibly section 8 cav with the 2.6 liter twin cam.
I am doing bottom end modifications this year, but a lot of people may be wondering whats going on... I've been doing TONS of homework the past 6 months, and have finally come to a decision. A lot of people may think I'm trying to accomplish a 2.4 ecotec swap.. and rational thought would agree.. no replacement for displacement right? well I'm going a route that some may think is a bit crazy... but take a look at this article and it may give you a slight idea as to my thought process:
ignore that this is from honda magazine.. those who are savvy know that if you're looking to copy/learn anything for all motor 4 bangers... honda is the company and aftermarket to look at for tips/tricks.
Rod/Stroke Ratio - What's Your Angle?
Dip into the intricate world of internal engine geometry and look closely at something you know very little about: rod/stroke ratios. (C'mon, admit it!) Editor Bob demystifies.
writer: Bob Hernandez
If there's one truth about Honda engines, it's that they like to scream. And Honda enthusiasts like to make them scream. The numbers on the tach reach so high, Honda practically offers the license: Go ahead. Make it sing. It's good at it. So long as you don't miss a shift, all is bliss.
Lightweight components, stronger materials and shorter strokes enable modern four-cylinder engines to spin very fast, yet last longer than ever. A tremendous amount of science goes into engineering and creating these high-spinning machines, most of it rooted in elementary principles of physics and geometry-fundamentals anyone planning to build an engine should know.
Understanding rod/stroke ratio, or the amount that a rod deviates from an imaginary straight line extending from the center of the crank journal to the center of the piston, is key to knowing how these machines deliver power at high rpm.
Determining the Rod/Stroke Ratio
To determine a motor's rod/stroke ratio, divide rod length (distance in millimeters from the center of the big and small ends) by stroke. A B18C1, for example, combines 138mm rods with an 87.2mm stroke for a 1.58:1 ratio.
Most engine builders shoot for a ratio between 1.5:1 and 1.8:1 on a street motor, with 1.75:1 considered ideal, regardless of application. (The most highly developed four-stroke engines in the world-F1 and motorcycle engines-have rod ratios of more than 2:1.)
The rod/stroke ratio affects several engine dynamics, including piston speed and acceleration, piston dwell at top dead center and bottom dead center, piston side loads, cylinder loading and bearing loads. Many of these elements play roles in engine aspiration, combustion and wear.
Generally, a lower ratio means a high rod angle, creating greater potential for accelerated wear to cylinder walls, pistons and rings. A low enough ratio, due to the severity of its rod angle, can drive a piston right into the cylinder wall.
Higher ratio engines, on the other hand, don't have the same friction concerns, but compromise in other areas. Air does not fill the intake ports with the same velocity, and there is less demand for the ports to flow as well since there is more time to fill and scavenge the cylinder (we discuss this phenomenon later). This typically means stagnant airflow at low revs and weaker torque. Hey, you can't have it all.
Lower Ratios-A Honda Characteristic
As the chart on this page indicates, many Honda ratios-designed for economy-fall on the low side. Honda produces compact, short four-cylinder engine blocks that don't require long rods. Most Honda blocks also feature a small bore. When coupled with a short stroke, the rod angle is still harsh, though not as bad as if the piston were larger in diameter.
Some tuners take the geometry into their own hands with longer rods. A longer rod makes more torque with the same piston force, and since it's less angular than a shorter rod, reduces sidewall loading and decreases friction. All of this adds up to more power.
Longer rods also give the pistons more "dwell," the brief periods of time the piston is at top dead center and bottom dead center. A longer dwell allows for better flow of intake and exhaust gases since the piston moves slower between up- and downstrokes.
Longer dwell also offers more time to fill the cylinders during the intake stroke and more time to scavenge during overlap. And since the piston hangs out at or near TDC longer, the combustion stroke has more time to deliver a thorough release of energy on to the piston.
In a stroked motor, the piston ultimately reaches greater speeds to cover the additional stroke. The speed makes intake, compression and exhaust strokes more turbulent and, consequently, more powerful. It also comes with its price in component wear, something to consider when looking into parts that increase stroke.
With a short stroke and a long rod, however, the piston accelerates more gently from TDC. It picks up its greatest speed further down the bore, at the point where the crank pin relative to the rod angle reaches 90 degrees. Since the pistons move from TDC slower, the entire bottom end absorbs less mechanical stress.
Advancing Toward A Thin Line
Even the short-stroke/long-rod combo has its limits. To accommodate extra rod length, some builders will move the piston pin higher into the slug, or opt for a deck plate. Either method requires an experienced wrench with access to a lot of custom parts.
Longer rods in a stroked motor can act to offset any increase in rod angle, but also requires a shorter piston. The deeper you dig into a piston to shorten it, the greater your odds of cutting into the oil ring groove and wreaking havoc with oil consumption. Most piston companies in the sport compact market engineer pistons with tighter ring packs and bridge rings to help avoid this problem.
Regardless of whether you take the stroker route or just run longer rods, you reach a point where you can no longer shorten a piston any further without compromising dependability.
Friendly Advice
Most engine builders believe longer rods are better, but a fringe of enthusiasts still dig the low-rpm torque that shorter rods can make. We advise builders who want a ratio of less than 1.6:1 to use the strongest aftermarket rods they can find, given the angle. We also recommend aftermarket sleeves to better fend off the lateral stress created by the rod angle.
Here's one last nugget to impress your friends with: a formula for calculating piston speed in feet or meters per second. The equation illustrates the point that the longer the stroke, the faster the piston travels at the same rpm.
Take a B16A2 vs. an H23. At 7000 rpm, the B16 slug moves 18 m/sec. At the same rpm, the H23 piston hauls additional ass-22 m/sec. Simply multiply stroke by rpm, and voil-minutes of endless doodling in class.
Stock Rod/Stroke Ratio Information For Some Popular Honda Engines
Block Rod length Stroke Rod ratio
D16A6, Z6, Y7, Y8 137mm 90mm 1.52:1
B16A1, A2, A3 134.4mm 77.4mm 1.74:1
B17A1 131.9mm 81.4mm 1.62:1
B18A1, B1, B20B4 137mm 89mm 1.54:1
B18C1, C5 138mm 87.2mm 1.58:1
H22A1 143mm 90.7mm 1.58:1
H23A1, A4 141.5mm 95mm 1.49:1
K20A, A2 139mm 86mm 1.62:1
K24A 152mm 99mm 1.54:1
by comparison:
block stroke rod ratio
L61 94.6mm 141mm 1.5:1
LSJ 86mm 144.84mm 1.68:1
LNF 86mm 144.84mm 1.68:1
LE5 99mm 143.7mm 1.45:1
you'll notice that the LSJ and the LNF have almost ideal r/s ratios.. (their r/s ratio is actually identical to the small block 350)
they're also very close to the K20A, and the K20A2.. which is starting to become a favorite amongst all motor honda enthusiasts, rivaling the B16A1/A2/A3 series in popularity
you can clearly see, since I'm looking for high rpm stability, top end breathing and less mechanical stress.. my bottom end selection is obvious
oldskool wrote:So do you have a defined numerical goal, or just go all out and see what it does? 180-200 ft/lbs should be obtainable.
I totally respect that you want an N/A torque monster, but if you really want a torque monster, grab a small-ish turbo (like gt28, t3, ect.), and multi-stage electronic boost controller and run high boost from the threshold to ~ 4500rpm and taper down to redline. This is how a stock LNF can make 400 ft/lbs @ 3000rpm safely. However the powerband will be low rpm and relatively narrow (think 2500-5000rpm); power will drop off bit time @ high rpm.
Quote:
If you wanted a high revving high horsepower motor....
You would want a larger bore piston with a shorter stroke. The engine design would be made over square (cylinder bore is greater than stroke) to make it rev higher.
If you wanted a low revving high torque motor.....
You would want a smaller bore piston, with a long stroke. The engine design would be made under square (cylinder stroke is greater than the bore) to make it generate higher torque.
Quote:
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
-MD- Enforcer wrote:
Cam Design....
After talking to a few cam people they recommend something around....
240-260 degrees @ .050" with .375" for the intake
260-280 degrees @ .050" with .375" for the exhaust
but for some reason my brain keeps saying something around
215 degrees @ .050” with .360” lift for the intake
215 degrees @ .050” with .360” lift for the exhaust
Any help would be great!
Blwn LD9 wrote:We should stick with the LG0 then. 3.35in stroke and 5.80" rod length is 1.73 rod ratio
z yaaaa wrote:wait... you had a crate lg0 and you sold it?
shame on you!
Joshua Dearman wrote:Yes, I noticed the same as that article describes when I built the manifold for CSU Fresno's FSAE car. I agree with slowolej with the restriction being the primary factor tho since we dynoed with and without the restriction and the #'s on the unrestricted TB inlet shows no real gains when you increased the plenum volumes beyond a much lower threshold. I ended up running 2.5x engine displacement and ran dynamic runners which lengthened and shortened as the engine revs raised and lowered...just following Helmholtz resonance pulses. Following the secondary pulse showed much better benefits then the plenum volume ever did. So, this basically means runner length makes the most difference, then followed by plenum volume behind a restricted TB...but with diminishing results as the TB becomes more capably of the flow rate needed.
Under boost, I cant say. I only ran boost on the restricted intake on the dyno and since the engine pulls thru the restriction at terminal velocity anyway under NA conditions all it did was level out the torque curve..nothing more. Couldn't aid with more lb/min of flow with the restriction in the way. Still saw vacuum on the plenum while pre-TB was showing boost. I would be willing to say the plenum volume would more lead to drive-ability issues in boosted apps as the plenum volumes got larger. Again this assumes your TB can flow the lb/min your looking for. I do know that while there is resonance in the intake in boosted conditions the pulse front is being bombarded with turbulent airflow in many directions while in the power band. This will basically negate all effects of any wave pulse advantages to speak of since the timing and directions of the waves will now mostly be a function of plenum geometry and not so much straight timing nor be in any reasonably predictable direction . I'd be willing to bet there is no honest answer to this question and couldn't even imagine the amount of processing power it would require to even begin to simulate these conditions....there is no good answer. For boosted apps, build it, cross fingers and dyno it. I'd stick to a reasonable sized N/A plenum of 1.5-2x displacement and get a nice long straight runner to aid the reduction of random directional pulses coming back towards the plenum...help keep them straight into and out of the runners. Make the backside of the plenum rounded to help distribute the pulses back into the plenum the best way possible with least resistance(instead of hitting a wall straight on they hit an angle and slide off instead of hit straight on). Also a nice full rounded runner initiation from the plenum will aid in reducing the possibility of creating turbulence at the entrance of the runners...especially if your going to run some hot cams that pull the air in very quickly.
Hope that helps....my head hurts now.