Building a motor with optimal Rod Stroke ratio-
 

So I was aimlessly reading some stuff the other night and came across this,


"In the game of Speed...Torque is KING. To get torque in a Honda you need displacement. What John said about Theres no replacement for Displacement is absolutely true. Since I am no longer building my Big B motor (Cost$$) Ill tell you the design.

B18c1 Block
Crank: B20A (YES A...not B or Z)=95mm
Pistons: 86mm 11.5:1 C/R
Rods: Custom 166.20mm
Displacement= 2207.35cc
This setup would require a Special Deck plate to extend the hieght of the block. Golden Eagle can install the Sleeves to be Taller than the block for an additional $150. (releeving by them is about $750 with Godzilla sleeves). They can make a deck plate...but wont install it. We had come up with a Deck Plate design that might actually work well but its under development right now. You also need a longer timing belt (Already Located one! ) as well as longer head bolt studs (Modified ARPs). All in all you end up with a 1.75:1 R/S and a 12.1:1 C/R. Perfect for all motor. If you wanted to go FI then you would change the Piston from a Dome to a Dish...lower compression .

You must remember that its takes power to make power so reducing the friction in the bottom end is also a good idea. I would suggest Knife-edging the crank micropolishing the journals Moly coating the piston sides while ceramic coating the piston top and going to a light weight flywheel. This is just the bottom end. The head would need extensive work as well just to keep up with the additional flow. Another thing to remember is that if you increase the squish area of the head...you decrease your C/R (just something to keep in mind).

Now if you paid attention you will see that I said 86mm pistons. That WAS NOT a typo. Golden Eagle actually bores out the old sleeves past the actual casting. What does this mean to you? It means you could technically run a slightly larger bore. I wouldnt do this with short rods though as the Side Wall pressures may be to great but with a 1.75:1 or even better yet 2:1 R/S I dont expect there to be a problem.

As far as Piston Speed figured @ 9k RPM:
B16 maxes out at: 5070 M/M
B18C1 maxes out at: 5926 M/M
LS/B20 maxes out at: 6111 M/M
The motor listed above maxes at: 6245 M/M".

This really intrigued me.One of the reasons I love the b16 is its near perfect R-s,but i'd love to have a b20 or a h22,shit give me a K24.
But anyway what this dude is saying,or say some other way that i dont know of,is a plausible way to have a big displacement near perfect r/s frankenstein honda motor? What is the formula when building said motor I need to base my part list around? Obviously the connecting rods and crank,but as you can see Im a little new to this.
My overall plan was to just sleeve the b16 to 85mm,stock knife edged crank shaft,toda cams,among loads of other pocket burning mods,and make power up in the 10krpms.
Of course i'll be at like 115ft/lb if im lucky,but if i Just keep my rpms up past 5-6k,who would even notice lol

Re: Building a motor with optimal Rod Stroke ratio-
 

cool thread, but whats your aim? Many people have had tall deck 95mm setups. Its been going on for years.

Re: Building a motor with optimal Rod Stroke ratio-
 

I'm not a B-series guy so this "tall deck" setup is news to me. Kinda interesting

But also kind of unnecessary. Much of what we think we know about perfect R/S ratio is based upon old train of thought. Take JWEST's old stock block H22 drag engine, for instance. Revving that thing to 9k RPM many times over without mishap defies what we think we know about R/S ratio. There's more to it, so I see this tall deck idea as a waste of time, as far as getting a "perfect" R/S ratio goes.

I was about to type, "it's worth it for the displacement though," but then realized you can get the same displacement or more, with a comparable R/S ratio, by destroking an H22 with an F20b crank and boring the cylinders. Way, way less complicated. Ya this is a waste of time and money

Re: Building a motor with optimal Rod Stroke ratio-
 

lol
thats what i was aiming for.A 2.0l motor with a decent/compareable r-s to the b16 ..Destroked h22 bored sounds pretty sick.Whats the required parts to do that though?will stock rods,pistons etc work?>I'm sure it wont require basically formulating a new motor like the b20 above lol.And whats the possible r/s ratio you can pull?


what if we built a motor with the rod stroke ratios up in the 2s like the f1 cars,got some of the most ridiculous cams grinded,custom intake mani,open headers,knife edged crank,full balanced rotating assembly,among other things(fuel system,ignition etc) It could spin and very welly possibly make power up at 12-14k.Notice I say very welly possibly. I want some f1 cams.
Not for street use

Re: Building a motor with optimal Rod Stroke ratio-
 

Yeah but a drag motor revving that high isnt even remotely practical to a road race motor with the same parameters.

R/S ratio is important because we are trying to achieve the best mechanical angle from the rod on the crank pin during the flame propagation. This creates the most amount of torque which is horse power. Alot of other factors play a part. But for an engine with a practical use besides running for 9-10 seconds, it is very important.

Think of it like this, you are riding a bike. The pedals are the pitsons and rods, your foot is the combustion cycle. You lean your weight into the pedal to push it down when the pedal is at its highest point. If you do it to early, the pedal will travel backwards, too late and you wont have the most efficient return in pedal energy. R/S ratio is important, because we are taking advantage of efficiency. These air pumps we call engines are only truly efficient at 1 single rpm. We are trying to manipulate that.

Re: Building a motor with optimal Rod Stroke ratio-
 

Ah bringing F1 into this, a man after my own heart. Watch out, I just about got laughed out of here a couple years ago by comparing our engines to F1 engines. Whatever, common sense tells us that Formula 1 innovations are certainly applicable.

The modifications you listed (ridiculous cams, intake manis, open headers, balanced and blueprinted blocks, individual coil ignition system) are already done by top race teams and even some more streetable builds (like mine will be). However, off the top of my head, two important things we lack compared to F1 engines are pnuematic valvetrains and like you mentioned 2:1+ R/S ratios. Without these, along with very costly extensive testing, I don't thing we'd be able to advance into F1 category.

But great train of thought, keep thinking that way. F1 is the pinnacle of motorsport, the more we try to emulate them in our engine building, the more we will progress.

I understand how R/S works. I also understand that Higher R/s ratio vs. lower R/S will have much different characteristics concerning airflow, as in how it sucks in air. For instance, since a low R/S ratio engine has a lot of "side to side" piston/rod movement, it sucks in air with greater force than an engine with a higher R/S ratio, since it will only move the piston in a more straight up and down and thus the engine speeds required to forcefully suck in more air need to be greater. This is why you see stroked motors praised in the streets, and high revving motors in race applications. But, the fact remains that
(RPM*Torque)/5252= Horsepower,
So it is always better to have the highest possible RPM assuming you can make enough torque at that RPM, doesn't matter if it's a drag car or road race.

Maybe I missed what you were saying completely, I don't totally follow :P

Re: Building a motor with optimal Rod Stroke ratio-
 

F1 cars definitely are the shit.I'm not going to try to imitate a f1 build with my 90s b16 motor by any means.I just want displacement and high revving reliability.
As far as my knowledge for this goes at the moment, the best I can do to emulate this is what I'm doing with my current build-
Sleeved 85mm b16 (roughly 1.8l)
Stock but knife edged balanced crank shaft = a 1.8l with the r/s of a b16
And prolly another 3-5k$ in supporting mods
Goal-200whp in a stripped eg coupe.I'd like to weigh 2000lbs or less,with that motor and that shell (larger wheelbase than a hatch) I'm hoping to have a SICK street/autocross car.

Re: Building a motor with optimal Rod Stroke ratio-
 

You can do a poormans CTR build, use a sleeved b18 block with the b16 crank. The deck height of the b18 block will give you a better a R/S ratio if that's what you're after. Custom length rods and a raised piston pin height is another way to improve R/S ratio.

Re: Building a motor with optimal Rod Stroke ratio-
 

^^^what he said sounds like a good idea, without getting into custom deck plates and junk.

For revving sky high, R/S isn't quite the end all, be all though, I would at least also get the entire bottom end balanced and use a very high quality oil that meets your needs

Re: Building a motor with optimal Rod Stroke ratio-
 

R/S is best suited for bench racing and marketing hype.

A honda all motor pro engine has a lot more in common with NHRA pro stock than F1.

The reason f1 engine dimensions are what they are is because they kept decreasing deck height to shorten the motor vertically and improve aero. It wasn't because they were after a magic rod ratio...

In pretty much any form of naturally aspirated motorsports you increase the bore as much as the block will allow (or engineer set rebuild allowance), match the crank to the maximum displacement of the class, pick the ideal ring height (usually at a minimum to decrease piston weight), and then you get stuck with your rod length.

I know engine builders for NHRA/IHRA pro stock and NASCAR and anyone of them would tell you they would rather decrease piston weight (and as a by-product a longer rod) then worry about rod ratio. If you are building a shortblock solely on rod ratio you are putting the carriage in front of the horse.

Re: Building a motor with optimal Rod Stroke ratio-
 

Well put... The r/s ratio of our motors is nothing out of line even with stroked setups. I personally think people way overthink it. Keep it simple.

Re: Building a motor with optimal Rod Stroke ratio-
 

I like this, good perspective. That's why I brought jaywest's old build into this, it proves most of what the community thinks they know about R/S ratio is just hearsay and theoretical numbers

Re: Building a motor with optimal Rod Stroke ratio-
 

You could do a jdm f20b, pin moved 5mm up with a longer rod to match makes a 1.7 rs ratio. Just a thought

Re: Building a motor with optimal Rod Stroke ratio-
 

That's another good idea, prolly better than mine. F20b already revs to 9000 but I guess if that's not high enough...

Re: Building a motor with optimal Rod Stroke ratio-
 

Hmm.This thread has opened my eyes up a lot more.My b16 is going to be my first actual all motor build -I'm glad to soak up all the knowledge I can.
As I said earlier with my plan to sleeve/bore my b16 to 85mm...would I be better off swapping the 1.8 block in with a b16 crank? What would be cheaper? More reliable?

Re: Building a motor with optimal Rod Stroke ratio-
 

If it was me i'd do a b20 block, stock sleeves and a cnc werx css, just to help bores from shifting under high rpm and use a b16b crank. Running a 26mm compression height and longer rods nets 1.89 rs which is damn good.

Re: Building a motor with optimal Rod Stroke ratio-
 

^Yeah that sounds sick af!! b20 w a b16b crank = how much displacement?


the b20s sleeves are that bad that youd need the css on stock bore>?

Re: Building a motor with optimal Rod Stroke ratio-
 

I personally don't think the B20 sleeves are bad at all unless you plan on putting big amounts for FI to them (nitrous/superchager/turbo)

Obviously if you beat on your motor 24/7 it will respond to it accordingly. CSS is a nice relatively cheap insurance however. I've considered getting another block for my build, doing CSS and hitting it with a 150 shot.

Re: Building a motor with optimal Rod Stroke ratio-
 

Please explain css to me like I'm 5

Re: Building a motor with optimal Rod Stroke ratio-
 

You're better than that.....

You're welcome.


Cylinder Support System

Re: Building a motor with optimal Rod Stroke ratio-
 

Old school guys would know CSS as sloppy old block guards!

Building a motor with optimal Rod Stroke ratio-
 

Im pretty sure they wont install the css on a b20 block. Every b20 they did cracked at like 400hp or less so it was deemed worthless. Where b18 blocks have been taken to nearly 1k hp

Re: Building a motor with optimal Rod Stroke ratio-
 

They will, they just don't guarantee it. Check the link I posted.

Re: Building a motor with optimal Rod Stroke ratio-
 

I had a lazy moment :p

Re: Building a motor with optimal Rod Stroke ratio-
 

Use anything but the b16 block if you are so determined for this great r/s ratio. Personally I wouldn't even bother sleeving a b16 block, the deck height just really limits the crankshaft you can use.