Bore/stroke and stroke/rod ratios

[vega]

I've been doing some research on engines for a while now and I have found that a square engine with a higher rod/stroke ratio would be the better motor for a track car, in general, and reliability.

 

Quick list I have been working. (bore/stroke) If there are others - I am unaware of them post um up.

 

BMW

M52B28 84.0 x 84.0

 

Ford

Duratec18 83.0 x 83.0

5.0 L Coyote 92.2 x 92.7

 

GM

20NE, 20SE, 20SEH, C20NE, C20GET (ECOTEC FAMILYII) 86.0 X 86.0

20XE, 20XEJ, C20XE, C20LET (ECOTEC FAMILYII) 86.0 X 86.0

LK9, LNF, LSJ, L34 (ECOTEC FAMILYII) 86.0 X 86.0

gmc 302 (l6 measured in inches vs mm) 4" x 4"

L81 3.0 86.0 x 86.0

LA3 3.2 87.5 x 88.0

Vortec 2200 (RPO codes L43 and LN2) 89.0 x 88.0

 

Honda

B17a1 81.0 x 81.4

K20A 86.0 x 86.0

 

Isuzu

4XE1 80.0 x 79.0

4ZD1 89.9 x 90

 

Jaguar

AJ26 86.0 x 86.0

AJ30/AJ35 86.0 x 85.0

AJ133 92.5 x 93.0

 

Mazda

FE 86.0 X 86.0

ZL 78.0 x 78.4

L8-DE, L8-VE 83.0 X 83.1

 

Mitsubishi

4B11 86.0 x 86.0

4G36 73.0 x 74.0

 

Suzuki

M15A 78.0 x 78.0

M18A 83.0 x 83.0

 

Toyota

2R 78.0 x78.0

3A 77.5 x 77.0

3S 86.0 x 86.0

1RZ 86.0 x 86.0

3RZ 95.0 x 95.0

1AZ 86.0 x 86.0

M 75.0 X 75.0

1G 75.0 X 75.0

2JZ 86.0 x 86.0

1GR 94.0 X 95.0

1GZ 81.0 X 80.8

 

VW

6.2 V12 48v 430-471kW (Lamborghini) 87.0 X 86.8

8.0 WR16 64v4T 736-816kW (Bugatti) 86.0 X 86.0

[MONGO510]

You the list stroke but not the rod length.?

[vega]

I am having trouble finding the rod length on any of these for factory. For your information this did not just take me a half hour do find either.....

Edited November 3, 2010 by vega

[MAG58]

Bob can play this game...

Mercedes-Benz (At least I'm predictable)

M104.941 (C36 AMG Motor) 91mm x 92.4mm Rod = 144mm, B/S = 0.984, R/S = 1.56

Zonda/SL73 M120.98 91mm x 92.4mm Rod = 144mm, B/S = 0.984, R/S =1.56

Edited November 4, 2010 by MAG58

[vega]

Well the point was not just for the bore/stroke but to have a bore stroke that either was square- or to have it so close with in one mm of the bore or stroke that it would not matter. You have an example that is 89.9mm x 73mm which is a much shorter stroke than would be needed to call it square. I went through all of the Benz engine info on bore and stroke- not one was square that I could find.

 

The purpose here is a BASIC starting point for an engine that can not only create tq but can hp at a decent rpm as well as a broader power band. Yes the cam and a compression and a lot of other things as well will come in to this- but this is a BASIC starting point for a good engine IMHO.

[MAG58]

Oh... So you wanted square engines?

 

Annotated...roughly. I'm going to consider them square enough. You can nitpick all you want.

 

And is it of any note that for the past...couple of decades, F1 engines have had bore to stroke ratios coming close to 2:1 and rod/stroke ratios often over 2:1. I feel that boxing yourself into a certain rod/stroke ratio and or bore/stroke ratio as believing those are just better motors for track cars seems a bit constrictive.By your assertion, then the best L series for a track car would be an L24 with a diesel crank?

Edited November 4, 2010 by MAG58

[BRAAP]

I think people get the impression Torque come from stroke alone, HP comes from bore alone, others tend to locked into some variation of this ill conceived logic. Probably started when people were installing longer stroke cranks and their engine wee producing more torque so there for stroke is the only means to gain torque. The 383 SBC is perfect example.

 

All being equal, (engines ability to breathe, rod to stroke, ratio etc), torque comes from the displacement of the engine. Whether that displacement was obtained from an under square bore/stroke, square, or over square combination, if the engine has the same rod to stroke ratio, same ability to breathe, same cam specs, same induction, exhaust etc, it will generate essentially the same torque and HP at all points in the rev range.

 

Where things start to change is when the physical strength of the components are exceeded such as piston speeds due to long strokes and very high RPMs. At that point for a given piston material, stroke and or RPM must be limited to keep the engine together.

 

Since HP is a function of Torque AND RPM, the higher up in the rev range you can produce the torque being developed, the greater the HP created. Look no further than F1 or sport bikes for examples. Liter class bikes, sport or other wise, producing in the neighborhood of 70-80 ft lbs of torques though the engines that produce that torque at higher RPMs are producing more HP.

 

In summation, there is NO magic under square, square or over square combination that is best for all production engines in track environment. Every engine has its strengths and weakness regarding ability to breathe, (heads induction, exhaust), available space in the crank case for stroke length and available deck hight for rod length. While research may uncover trends for a particular engine, those same trends will not necessarily carry over to another engine due to the variables mentioned.

 

In trying to generalize ideal design constraints for making power for a track car, these guidelines are safer bet to follow than a specific "bore-stroke-rod length" combo. What may be an ideal combo for one engine will not be the ideal for a different brand/design, (2 valve vs 4 valve is one variable that changes a lot of "ideal" design parameters). Always build as much displacement as can be built within the engine and/or rules of the class to which you are racing. When limited by displacement, build as much bore as possible to allow as much valve area as possible to allow the engine to breathe, (again within the physical constraints of the engine and/or rules), make up the rest of the displacement in stroke and use as long a rod as possible. Then build the engine to make as much power as high as possible in the rev range over enough RPM range to span the gear ratio drops of the gear box being used. Of course there are other variables that could alter those guidelines due to the fact that not all production engines are created equal, all have weaknesses and strengths. It's how you best minimize the weaknesses and bring out the strengths that will make the difference, hopefully better than the guy next to you on the start online.

 

 

 

Then there is the chassis to contend with, the drivers ability... I digress...

[vega]

I agree with you to a point. One thing you said is about how a square motor is that "it will generate essentially the same torque and HP at all points in the rev range".

 

In my opinion with driving lots of different vehicles (I work in ridgedale mn)ie porsche, bmw, benz, vw, aston martin, jaguar, two ferraris now etc. I have found that if focusing on JUST the engine the vehicles behave very differently based on how the engine is. Where it make power, how it makes power, when it makes power, how fast it makes power- or how slow. I personally prefer peaky motors that are rev happy and that get to that rpm very quickly but have enough tq down low to so it does not bog at launch. the bmw 328is is a great example of this. the v12 850cis is another, one of my personal favorites would also have to be the cayman s, or the g35. these cars have these characteristics for the most part. the cayman s is an amazing car- for the track. Mn roads are horrible so the suspension is WAAAY too stiff in my opinion for road use, and I enjoy stiff suspension as any other sports car nut but it is way too jarring for me and I am 25.

 

I guess I am not sure if I am making my point clear albeit this is my attempt at it.

[Gollum]

I personally prefer peaky motors that are rev happy and that get to that rpm very quickly but have enough tq down low to so it does not bog at launch.

 

You can have a 2.5 liter STI that's not peaky at all, but IS rev happy, and doesn't bog at launch unless you don't know how to launch AWD turbo cars.

 

You can also have a 4.7 liter long stroke Tundra that would "bog at launch".

 

I don't mean to come across as an a-hole, but either you're not well versed enough to explain yourself (which is fine, I'm right there too in a thread me and Tony D have been going back and forth on), or you simply don't know what you're talking about.

 

So much of what you said in that post is car setup specific, and has nothing to do with the bore/stroke ratio or even stroke/rod ratio of the engine in question. From what you've said, what I THINK you actually want is a motor producing at least 100HP per liter, and put into a car in which you have at least a 9lb:HP ratio.

 

This is quite easy in a Z car, but if you insist in a peaky motor, then you're going to want a NA engine making over 100hp per liter. This means you'll either want a DOHC 4 cylinder, 6 cylinder, or even a highly modded L series would fit the bill just fine. I don't say V8 because at over 100hp per liter, and peaky it'll be a beast, and insanely more expensive to build, and most likely way over your power goals.

 

And I say this all in good fun, but I kinda laugh when I hear people say that they like peaky motors... That's exactly opposite of what any veteran race drive would say, and also exactly opposite of what any professional tune shop would say... And there's a very good reason for it. It's not fast! Simple as that. A 240HP S2000 produces LESS NET HP than a 225hp pushrod 5.0 ford, meaning put in front of the same transmission in the same car the 225hp engine would be FASTER!!!!

Edited November 14, 2010 by Gollum

[vega]

go drive an e46 m3 with a 3.2 dohc l6 in it- around a track. than tell me I don't know what i am talking about. To me the m3 or the cayman s- are the best two track cars for daily use I have ever driven. they are setup both engine wise and care wise. the 3.2 has a smaller stroke btw, i can't find much info on the cayman.

 

You are also misunderstanding my point. I said that it is a PART of what I was referring to. NOT the whole. This is hybridz - don't start a flame war please.

[vega]

Just for future ref, BRAAP, your awesome.

[MAG58]

Just to be pedantic...

 

Doesn't the E46 M3 have a bore and stroke of 87mm x 91mm... not square by your definition and a rather pathetic rod/stroke ratio of 1.53 (139mm rod)?

 

The 3.4L Cayman motor has a bore x stroke of 97mm x 77.5mm REALLY not square... (though I expected that, I rarely see a square boxer motor)

 

[vega]

you are correct sir

[vega]

I think one of the reasons it performs the way it does is because the double vanos and the itbs

[MAG58]

Ok so now I'm confused... You said the 'best' motors are square but your two examples for great track motors are not square?

 

 

 

 

Not flaming just trying to figure out what's going on here...

 

 

[Gollum]

Ummm... I wasn't starting a flame war, but as Bob is getting to, you're not making sense. And that's my point... Either you're not communicating what you're REALLY trying to, or you simply don't understand the subject matter.

 

I'm assuming it's the former. Because I'm sure you're aware you could put nearly ANY motor in the M3 and it'd be a great track car. The engine does add a lot of character to the car, but the bore/stroke and stroke/rod are only a sliver portion of what makes the character of the car.

[Leon]

My 2 cents:

 

When "designing" an engine, you have to look at the big picture. There is no magical r/s or b/s ratio that turns something into a great race engine. It is a combination of design parameters that gets you there. As shown, you can have wide ranges of r/s and b/s and still get great results. What matters is how the system is put together.

 

The first thing you do when you want to design an engine is analyze exactly what you're going to use it for, and progress from there.

 

e.g. You're building a race engine. Let's say you build it for autocross. Since autoX courses are usually low speed and tight, you want to maximize area under your power curve at the engine speeds that you'll mostly be seeing (dictated by gearing). Let's assume you want performance in the 4k-7k rpm region. What do you need to do in order to maximize engine performance in that region?

 

You start with a given parameter, and begin designing around it. You have plenty of space for a straight six in you engine compartment so let's start with that, rules of different race organizations will tend to dictate this part. You also take advantage of the 6er's favorable harmonics (in comparison to V arrangement and 4 & 8 hole engines). We picked an engine type and cylinder count, now come engine parameters: bore, stroke, rod length, compression ratio, valve timing, intake and exhaust lengths, among many, many other things that you must make to work in concert with one another. Any choice will have trade-offs.

 

Basically, it's a lot more complex than just finding a couple of magical ratios. Those ratios have to work with the rest of the engine. What works for one, won't work for another.

[vega]

completely agree with you leon

[Touge]

Just to add what I've learned in talking to and reading what has been put out there by people much smarter than myself as well as what I've learned in my own tinkering over the last 10 years. Bottom end geometry does alone dictate an engine's powerband, peakiness, etc. Even basic generalizations are easily disproven. Take the Nissan SR20DE and the Honda B16, archetypes of the small displacement performance engine. Both are DOHC, 4 cylinders, and very close in output but are greatly differing powerbands. The SR20 makes gobs of torque all through the midrange but runs out of steam on the top-end. The honda is almost the opposite. It does nothing until 5000rpm and then charges all the way to the 8000 rpm redline. The odd thing is that the Honda is the under square engine although it does have a 1.75:1 R/S ratio. The 85x85mm SR20 is the torque monster against conventional wisdom.

 

R/S ratio will dictate the max rpm your bottom end can sustain. Longer rods slow the rate at which the pistons accelerate away from TDC and BDC. Long rods also increase the amount of dwell time at TDC which helps with cylinder filling at higher rpms. Cylinder bore wear will be reduced due to reduced piston side loads. The trade off is a taller engine, more reciprocating weight, and reduced cylinder filling at low rpms. The caveat is that all these factors, except for piston speeds, are affected by the rest of the engine components.

 

Larry Widmer at Endyn, who has built some amazing engines (like a 300hp, 285tq, 2.0l Honda B-series), feels that 1.75:1 R/S is a good compromise for a NA street engine and anything below 1.6:1 may benefit from a reduction in stroke to allow installation of a longer rod package. With all that said he is still in favor of getting as much displacement as possible and tuning around it for the performance level you desire.

 

F1 is not the be all end all of engine performance. The rules of F1 tend to dictate engine configuration. The ban on turbos means the engines have to spin to high rpms to make power. High rpm dictate a large bore (for bigger valves). The engine can't be too tall because of aerodynamics so you have to reduce stroke to keep piston speeds down. The added benefit is reduced pumping losses. At 12000+ rpms valvetrain weight and friction becomes a factor. Thats why you don't see 5-valve per-cylinder F1 engines. Almost all are 40 valve, V10's. Honda and BMW were both planning on fielding sub 2.0l turbo 4's when the turbo ban went into effect in the early 90's. As you can see, everything is a tradeoff.

 

When I build my engine, I think I'm going to run an L24 crank in the tallest block I can find (LD28?). I punch the bore out as far as possible and fit it with ITB's, big valves, and a big cam. I'll fit an eaton supercharger making 5-8psi to make up for the lack of low end. My Z is just for my own personal enjoyment and doesn't have to conform to any class restrictions (except my wallet). History has shown that big, low rpm engines are just as viable as small high rpm engines.

 

Sorry for the ramble on.

[MAG58]

 

Larry Widmer at Endyn, who has built some amazing engines (like a 300hp, 285tq, 2.0l Honda B-series), feels that 1.75:1 R/S is a good compromise for a NA street engine and anything below 1.6:1 may benefit from a reduction in stroke to allow installation of a longer rod package. With all that said he is still in favor of getting as much displacement as possible and tuning around it for the performance level you desire.

 

 

NA?

 

I'd like to see this motor, especially if it produces 142.5ft/lb/L of displacement.