jrhdominos

Hey fellas, and ladies I guess...I have a question. I have a bare b18b block, and also a b17 out of my gsr teg. Im contemplating an LS/VTEC build. My build would consist of - USDM Type R pistons, Eagle 5.531" rods, B17 crank, b17 head (stock or built, dont know yet). This set-up on zeal autowerks calculator nets me a 10.4 cr with a 1.73 rod/stroke ratio. Basically a 1.7 ltr LS/VTEC with b16 revability. I know im destroking the motor, but Im willing to sacrifice a little low end for a screaming top end. Also pretty sure this setup will put better numbers down than that of a stock b17 or b16. Boring the cylinders with forged pistons is also running through my mind to make up for the lost in displacement, and still maintain a near perfect R/S ratio. Any ideas or opinions are welcomed...Thanks in advance.

jrhdominos

bump for somebody with some knowledge on this subject. Thanks.

DDTECH

Rod to stroke to a point is important..All other things being equal, you'd get more torque of out a short rod. The shorter rod engine accellerates faster from TDC so at any given degree of crank angle from 0 to 180, the shorter rods piston is further down in the bore. Longer rods can actually run LESS compression typically, due to the fact that the piston crown dwells around TDC longer than a short rod counterpart. I'm in no way saying that a shorter stroke will make more power.. because all things aren't equal. However.. depending on the use of the motor, you'll want to get the most out of the car.

E.I. if you're using the car for ricer rolls, you'll in turn, be a top end guy...this is just an example.

Higher Rod\Stroke ratio doesn't equal less stress...It equals less piston speed.
There are more important things to worry about then R/S ratio..

Whats the overall use of the car.

jrhdominos

Honestly??? Overall use of the car will be daily driver with it hitting the strip every other weekend. Im a top end guy. My b17 screams at 5500+. I love that. Also the torque was plenty around town. Ricer rolls, thats funny, but I get what you're saying. This motor should see a beating, because I beat on my cars (regularly maintained of course). That's where I figured having a motor designed more for revs, than low end torque, would come in handy. Also I could reuse my b17 pistons, and be boost friendly if I decided after 10,000 miles that I wanted to go that route. Also
keep in mind I have thought about boring the cylinders to make up for the lost displacement. That's just a thought.

DDTECH

I wouldn't destroke the motor.. personally.

jrhdominos

That's what I'm hearing...well I have a bare b18b block no crank. Would using my b17 crank, bore it out, with 84 mm pistons be a just alternative??? I could easily source an LS crank and go from there. I know LS/VTECS have survived all day with the 1.54 r/s ratio. Just figured maybe I'd do something different. Right now I have a full b17. So as far as rotating assembly goes, all I need is eagle rods, I can keep the pistons, and have near stock compression. Also I'll still have a b17(rebuilt) but with the much coveted r/s ratio of a b16. Also the potential to bore it out is still something that I'm considering, because I can have a 1.8 ltr LS/VTEC but with a 1.73 r/s ratio. Reliability is paramount in this build, as it will be my daily driver. Thats really why Im trying to rack up opinions on the build. I know many LS/VTECS have gone the distance, I just know once I build mine, it HAS to go the distance, because I need this car.

DDTECH

Being different, and then going with something proven is two different things.
Over the years, tuning and building habits have changed.. LSVTECs, b20vtecs, all those types of motors can now be just as dependable as a stock gsr. I would suggest you source a LS crank. The Torque you'll get from a 89mm crank will be more then enough to give you the low / mid range without losing top end. It'll allow you to rev as high as you need as well.

EG6 Master

----DO IT----

Build the hybrid using the B17A crank. You can MORE than make up for a loss in stroke by increasing the bore. BORE is factored TWICE as much as stroke (CC=Bore x Bore x Stroke x .7854 x 4) when calculating engine capacity.

By increasing the bore to 85mm you motor will be LARGER (1847 vs. 1834) than an LS VTEC.
This will make your torque production the same or higher than an LS VTEC.


You are on the RIGHT track by using the B17A crank, increasing (bore and stroke) capacity, preserving reliabilty, improving breathing and maintaining a VERY good rod ratio. This combo is a MARVELOUS ALTERNATIVE to the LS/CR VTEC and the GSR/ITR!!!

!!!!AND YOU CAN REV IT LIKE A B16A!!!!


*****Here are two PRIME examples of what maintaining the B16A rod ratio and increasing the bore is capable of producing*****

https://honda-tech.com/forums/showth...ght=b17a+crank
***This is from 2002, an even better combo can be pieced together today***


http://jgenginedynamics.com/_dyno%20...reet%20car.pdf
***77.4mm stroke with 85mm pistons---TORQUE!!***

tagperformance

Its already been proven that a short stroke motor will make more power than a long stroke motor due to having more dwell time at top dead center.

EG6 Master

HHMMM....thats not correct my man.


Higher rod ratios mean EXACTLY that....LESS STRESS on the components in addition to slower piston acceleration.

Less bearing stress, less piston pin stress, less cylinder wall stress, less rod bolt stress, less piston ring stress and MUCH lower crank harmonics.

I agree, its like you said earlier, it depends on what you're using the engine for. For a daily driver this combo will give him EVERYTHING he needs and will be more reliable than the 1.54, 1.52 or lower ratios you are suggesting that are more suited towards a race application.

josephcmiller2

Less stroke = less piston speed.
Higher Rod/Stroke = lower piston speed at TDC and higher piston speed at BDC

Ex: B16A and B16B have the same stroke but the B16B rod is longer
The average piston speed on both is the same.
The B16B piston travels slower than the B16A piston near TDC.
The B16B piston travels faster than the B16A piston near BDC.

Of course, I'm sure ALL_M0T0R already knows this. What we're generally concerned with is piston speed near TDC because of valve timing events and air flow so that's what's usually talked about. However for a noob it is damn hard to unlearn something once they have learned it wrong.

DDTECH

I'll give a recommendation or a opinion.. If someone wants to listen fine.. If not thats fine to.

we still have NO idea what this is used for.. which will determine what route to actually take. R/S ratio is important.. but there are other things to consider.

DDTECH

Displacement - TQ
Stroke - RPM where peak TQ is
Valve Area = max HP
Rod Ratio = not that important.

This is how i tend to see things, why? Because the fact is everthing is a variable, some more important that others.

Here's alittle quote from Dimitri N. Elgin of Elgin Cams.
Somewhat surprisingly, the connecting rod affects intake flow. More specifically, the ratio of the center-to-center length of the connecting rod to the stroke of the engine — termed the rod/stroke ratio or just rod ratio — has a significant effect on Volumetric Efficiency. More surprise: the effect of rod ratio differs for 2-valve vs. 4-valve engines.

Airflow in a normally-aspirated engine is driven into the cylinder only by the pressure difference between the 14.7 psi of the atmosphere and whatever less pressure is inside the cylinder at that instant. The greatest difference in pressure occurs shortly after the piston is moving downward at its fastest. Piston velocity peaks when the rod and the crank throw are at right angles to each other.

The exact number of degrees ATDC for maximum piston velocity can be found in any trigonometry table. The Tangent of the angle ATDC is twice the rod ratio for that engine. Then add 2-3° for time for that news to reach the intake valve at the speed of sound and affect airflow there. The sum should come between 70° and 80° ATDC. The shorter the rod ratio, the earlier that piston velocity peaks.

Airflow in 2-valve heads begins slowly. So airflow through these heads responds to a long rod ratio, close to 2:1, for maximum draw after 75° ATDC.

By comparison, a 4-valve engine flows a lot more air at the lower and mid lifts through its smaller valves and ports. This allows its rod ratio to be smaller without hurting power, more like 1.55:1. Check the rod ratio in a Honda. Airflow demand in the 4-valve engine occurs closer to 70° ATDC.

Another flow difference between 2-valve and 4-valve heads is the ratio of exhaust flow to intake flow. Exhaust valves and ports are always made smaller that the intakes, because exhaust flow gets pushed first by high cylinder pressure, then by the piston on the way up. In 2-valve engines the exhaust port flows between 60% and 80% of the intake. Exhaust flow in 4-valve engines is very high, somewhere in the 80% to 90% region. Later we’ll see how these factors affect cam selection.

I'll leave with that, i'm not slinging mud, just saying other things are more important then R/S ratio now and its been proven.

q16racer

what? proven? lol

long stroke = more displacement = more torque = greater acceleration

its only natural that a motor with bigger displacement will have the opportunity to make more power.

DDTECH

I giggled when i saw you reply btw.

EG6 Master

Bigger bore equals more displacement and more torque also. It is also natural that engines with bigger bores make MORE overall power than engines with large strokes. Less torque but more horse power. I will say it again.... it depends on the intended purpose of the engine.

EG6 Master

Rod Ratio= not that important.

That statement is obviously NOT true.

Otherwise all engines with the highest Horse Power Per Liter outputs would NOT be high rod ratio engines. Also, ALL of these engine have BIGGER bores than strokes.

That being said, it doesnt mean that you cant build an engine with an under square configuration that will have good numbers. Simply put, that all out under square engine WONT produce the overall HP number that an all out over square engine configuration will.

DDTECH

K

TheShodan

iTrader: (14)

Thank god, somebody else said it... Yay!!

CHEETAH

iTrader: (2)

damn, you guys would faint if i told you the RS ratio on my new k-series race motor with big stroke and big bore lol.

94eg!

iTrader: (2)

I haven't got to use these pics on so long I figured I would post them for fun. It's a comparison I made between a 2:1 r/s & a 1.5:1. It really illustrates how r/s effects the position of the piston throughout the entire stroke. Shorter rod = les time at TDC and more time at BDC:

D4MFM4N

Doesn't a higher rod/stroke ratio = higher rpms?

RASE

No. R/S ratio is a non factor in where the motor makes power. That has everything to do with the camshaft/cylinder head/induction side and nothing to do with the bottom end.

Huge stroke, 1.3-1.4 r/s ratio motors are actually preferred for N/A drag applications. The engine is a pump, and the more air it pumps in/out, the more power you can potentially make. Take 2 motors with the same exact bore and stroke, differed by only the r/s ratio, 1 being a 1.75 and the other being a 1.3, the set up with the shorter rod is going to fill the cylinders a lot quicker than the higher r/s ratio motor where the piston hardly travels away from TDC in comparison to the 1.3 r/s ratio motor. But with that being said, I'm talking about an all out drag application. Poor rod angles do cause premature ring wear and show sides of fatigue on the bores a lot earlier.

1.48 - 1.52 is a good trade off IMO for a drag use street/strip motor.

DirtyDA9

Nice avatar


But the only time I would recommend a 84-85mm bore in an LS block is if it was sleeved, you guys forgot to mention sleeving, just mentioned bore.

And I'm not even going to get involved with this arguement, I agree with both sides, but I agree with ALL MOTOR more...

BTW, this is probably one of the best arguements I have seen since I joined HT, it's not just stupid bickering about dumb ****, everyone actually knows what they are talking about, and knows a lot at that. Why do you think most of HT stayed out of this one? haha

snm95ls

You know if you ignore the fluid dynamics relation to R/S issue, and go by shear mechanics, power potential increases with an increase in bore much more rapidly than in increase in stroke.

Methinks that when you account for the huge chunk ignored by the aforementioned model, it tends to become an even race or maybe even flip flop in certain cases.

Interesting thread.