Let's go kind of crazy in both directions, so we'll have some fun and interesting discussions:

Both motors will have itb's, custom header and exhaust.

We will have to keep the motors streetable, and must be able to use 93 octane pump gas.

Blocks are talldecks (Dart, for example). Bore is 84.5mm.

Motor #1: must have the "perfect" r/s ratio of 1.75.

Motor #2: must have a stroker r/s ratio - at or lower than 1.6. Maybe a 95mm crank?

I'm wondering how these two motors would compare..... given that we put as much attention and detail into each of them.....

I'm starting this thread, because I am thinking of a dart talldeck buildup and am wondering whether a 95mm crank is "ideal," or that perhaps I should be silly and try to get that 1.75 r/s ratio and see what happens.....

 

If you still 1.75 R/S ratio is perfect you some stuff to learn.

 

LMAO

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DonF &raquo;</TD></TR><TR><TD CLASS="quote">If you still 1.75 R/S ratio is perfect you some stuff to learn.</TD></TR></TABLE>


If I could understand wtf you typed, that would be enough.....

 

im confuzed. why would you wnat an al motor buildup without a longer stroke...
there is no perfection. I would probably go with motor 2 and slap some 11.5:1 pistons in it for all motor. i have 12.4:1 and I run 2 bottles of booster with premium to keep it barely running. (yes I know booster only knocks up octane by 1 point maybe a bottle)

 

The bigger displacement (stroke) would def have more torque than the smaller one and reach its peak HP and torque sooner.
The "perfect R/S'ed" engine probably wouldnt make as much HP as the larger one but it could definately get damn close, at a much higher RPM though...
In the end the 1.75 engine would last longer due to less sideloading the pistons into the cylinder walls. (considering both were driven exactly the same).

Basicly face it. Your gonna beat the **** out of this motor. If you dont want to rebuild it in say the next 2 years, go 1.75.
If you want more power and dont mind having to do a teardown within 2 years, go with the large stroke setup.
Ive heard there are some going with even bigger stroke B series like 100mm!

 

why not some REAL big motors like 2.4-2.7. k-series were its going to be. lol just joking but those are some big motors.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DonF &raquo;</TD></TR><TR><TD CLASS="quote">If you still 1.75 R/S ratio is perfect you some stuff to learn.</TD></TR></TABLE>


Whats wrong with a 1.75:1 ratio?

I think that ratio is damn good for a street motor(longevity.) Pure racing engines that have to last hours (formula1, 3000, grandam) are always oversquare designs.

Most drag racing engines (tq is king, its what moves you) have terrible r/s ratios because they dont give a ****. They rebuild engines after every race/pass/event. You can turn a 1.4:1 engine to 13000 rpm if you want to, and if thats what it takes to go faster than the other guy, they'll do it.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Black R &raquo;</TD></TR><TR><TD CLASS="quote">


If I could understand wtf you typed, that would be enough.....</TD></TR></TABLE>

Don left out,

"If you still think the 1.75 R/S ratio is perfect you have some stuff to learn."

He said this because there is no perfect r/s ratio. Determine how you want to use the engine then you design from there.

 

I guess I should have added the requisite .....

But that's why I put the "perfect" in quotes..... seeing as how mathematically it seems to put the least amount of side-loading as someone else mentioned.....

Of course we'll build the motor to our tastes, but why not talk about how r/s ratio affects the power output and longevity of the motor?

Assume 12:1 static c/r.....

 

But a r/s ratio of 1.9 puts even less load, so.

Faster piston speeds and longer strokes get you more torque, that's what accelerates the car. If you are interested in maintaining engine life then stick to a stock engine.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Black R &raquo;</TD></TR><TR><TD CLASS="quote">But that's why I put the "perfect" in quotes..... seeing as how mathematically it seems to put the least amount of side-loading as someone else mentioned.....</TD></TR></TABLE>
An infinitly long rod would give the least side loading, but one might encounter hood clearance problems with the infinitly tall deck required; not to mention the infinite weight of the infinitly long rod.

But personally I'd take a big bore, short stroke, tall deck, long rod, good R/S-ratio, light rotating assembly and lots of RPM. The light gearing and high RPM will still move the car "adequately", and given that the valvetrain and rotating assembly will take that RPM and ask for more; it should last long.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SMSP &raquo;</TD></TR><TR><TD CLASS="quote">But a r/s ratio of 1.9 puts even less load, so.</TD></TR></TABLE>


True, although it seems to sacrifice torque even more so...

Not to mention that there are physical limitations as to what will fit into a b-series block - even with a deckplate...

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SMSP &raquo;</TD></TR><TR><TD CLASS="quote">Faster piston speeds and longer strokes get you more torque, that's what accelerates the car. If you are interested in maintaining engine life then stick to a stock engine.
</TD></TR></TABLE>


Faster piston speeds also seem to be problematic (from the limited reading I've done on the subject), when it is outrunning the flame front. I'm curious about the grey area.....

Maintaining engine life to the point where I can save the rebuild for the off-season would be ideal.

 

Why limit it to an 84.5 mm bore. I'm thinking 86mm.

 

Sorry about not proof reading, but when I read about the "perfect" R/S ratio I know someone had not done their homework. The old B-16 had a ratio of 1.75 and someone proclaimed it "perfect". If it was, then why does the new Civic "R" Honda's most raced production engine in the world, have a R/S of 1.842? It uses the tall block and 5.60 rod length. I have built a tall Dart block with 95mm crank, and R/S of 1.58. It has had over 100 dyno pulls above 9000 RPM's. For a street motor I would have gone to less aggresive cams and a peak of 8300 and it would last as long as anything else. Shorter rods will reach peak VE quicker (lower RPM) than long rods, that is why head and intake flow along with camshaft choice will determine your stroke and R/S ratio choice, or at least your cam timing.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Black R &raquo;</TD></TR><TR><TD CLASS="quote">Let's go kind of crazy in both directions, so we'll have some fun and interesting discussions:

Both motors will have itb's, custom header and exhaust.

We will have to keep the motors streetable, and must be able to use 93 octane pump gas.

Blocks are talldecks (Dart, for example). Bore is 84.5mm.

Motor #1: must have the "perfect" r/s ratio of 1.75.

Motor #2: must have a stroker r/s ratio - at or lower than 1.6. Maybe a 95mm crank?

I'm wondering how these two motors would compare..... given that we put as much attention and detail into each of them.....

I'm starting this thread, because I am thinking of a dart talldeck buildup and am wondering whether a 95mm crank is "ideal," or that perhaps I should be silly and try to get that 1.75 r/s ratio and see what happens..... </TD></TR></TABLE>

a few points to consider, based on my (limited) experience:
- will notice higher rs/ratio is more compatible with "short" stroke (Honda) motors with small diameter manifold runners or ITB runners ... and are rev happy. To put other arguments to context, somehow Mitsu decided to put a 1.74 r/s ratio on their turbo 2 liter motor

-going with a longer rod to achieve a higher r/s ratio is not always ideal as a main factor is adding extra rotating weight or mass, shifting power band, and many seem to use "bolt-on" mods designed more for the 1.5ish r/s ratio type motors. What I'm trying to say is long pairing headers and big diameter intake manifold primaries are all working against you on the high r/s motors, producing an imbalance on the design. Then it doesn;t make power and people get upset and start "dissing" the parts with negative feedback

- I bet a 1.4 r/s ratio motor will outrun the 1.7 r/s ratio motor in a standing start acceleration race. I'll take a 95 stroke B motor with 86 bore over a 87 crank 84.5 bore.
torque will fall off on the top end from the low r/s ratio motor but it'll still be up there making tq for a while even at 8krpm ...

- last point is that you don;t always need a tall deck to get a strong motor, you can do it with stock deck height B series, moved rod pin and slightly longer rod.

one of my all time favorite motor combination for b-series is the 92mm crank with 137 longrod and the Endyn piston with moved wristpin to fit the 137 long rod on stock deck. this motor likes the 4-2-1 long header and fat runner intake manifold.

Greg

 

 

thanks Greg, Dave, and Don.

https://honda-tech.com/zero...age=1

I found some interesting stuff in this thread too.....

 

LOL, I was gonna bring up a thread, but then I noticed you were the one that started it.

https://honda-tech.com/zerothread?id=1088178

To me, application is the most important factor in determining what r/s will work best.

 

one thing you need to leverage off of is look at the r&d results from drag racers who use you engine setup ... talk to them at the track if you can ...
talk to multiple racers and compare their notes to form your own conclusion; if

b-series, talk with bubba, leslie, erick, brad rlz, etc
h-series, norris and brauning
k-series, norris and guys at skunk2
f-series, lol ... you know who = BISI


Good luck and stay away from the "ideal" r/s ratio

Greg

 

People dwell on R\S Ratio wayyyy too much...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Suprdave &raquo;</TD></TR><TR><TD CLASS="quote">People dwell on R\S Ratio wayyyy too much...</TD></TR></TABLE>

I think a HIGHER PERCENTAGE of people DWELL at the TOP of this R/S RATIO discussion. At least 1.74%

Ok, that was lame.

 

I found another interesting link:

http://e30m3performance.com/te...ratio/

http://www.sigmaperformance.com/748-853.html

http://www.theoldone.com/archi...o.htm

http://www.circletrack.com/nls....html

http://www.sportcompactcarweb....part7/

 

After reading all thos articles what conclusion have you come up with?

 

that my car will always be faster than his