Big bore short stroke vs. small bore long stroke

[140Air]

Interesting...so Honda who was always been at a leader in high RPM production engines would compromise the engine to fit it in the chassis? I might be wrong but I would think Honda would redesign the car to fit the engine. It's not like they don't redesign every few years....
The Honda S2000 sports car was a fresh rear wheel drive platform , but Honda chose a long strong engine...

2.0 S2000 was 3.42 bore x 3.30 stroke making it "oversquare". They upped the stroke to increase displacement to 2.2L and bring rpm down. That engine is 3.43 x 3.57 making it "undersquare". ALL Honda 4 cylinder engines have either a 90mm bore spacing or a 94mm bore spacing. This is like ALL small block Chevys have a 4.4" bore spacing. This even carried over to the LS engine even though it was a "clean sheet" design. This limits bore size.

Because of the bore spacing, Honda is unable to go much bigger with bore so the only way to increase displacement is with stroke.

This is the legacy design problem. Eventually Honda is going to have to break out of their block size limits.

[wyrmrider]

Not so
Direct injection, variable valve gear, and turbos will buy them lots of years with current tooling

[289nate]

Interesting...so Honda who was always been at a leader in high RPM production engines would compromise the engine to fit it in the chassis? I might be wrong but I would think Honda would redesign the car to fit the engine. It's not like they don't redesign every few years....
The Honda S2000 sports car was a fresh rear wheel drive platform , but Honda chose a long strong engine...

Keeping the engine compact is absolutely a goal for all engine manufactures.

[Ozonkiller]

the answer is 42

I don't care who you are, that's fully

[BCjohnny]

I'm not privy to any inside information, but the situation at Honda may be a pragmatic consequence.

Changing bore centres is one of the costliest changes that can be made to engine machining plant. Honda engines from the eighties tended to be in the 1.3-1.6l range, so the outgrowth seen over the last couple of decades to 2.0-2.2l could most economically take place by smaller bore increases coupled with larger stroke increases?

As packaging constraints have also become much more important in the same period it may be a happy coincidence to keep to smaller bores anyway, and emissions considerations are certainly made easier with less oversquare/more undersquare engines?

That Honda's pedigree is rooted in high specific output motorcycle engines means that despite choosing a less than optimal, on paper anyway, format, their objectives can be obtained regardless?

WAG & JMO.

Edit: spelling

[Brian P]

VW is even more constrained. Their in-line engines have 88mm bore spacing, and that dates back to the 1970s.

[Truckedup]

I'm not privy to any inside information, but the situation at Honda may be a pragmatic consequence.

Changing bore centres is one of the costliest changes that can be made to engine machining plant. Honda engines from the eighties tended to be in the 1.3-1.6l range, so the outgrowth seen over the last couple of decades to 2.0-2.2l could most economically take place by smaller bore increases coupled with larger stroke increases?

As packaging constraints have also become much more important in the same period it may be a happy coincidence to keep to smaller bores anyway, and emissions considerations are certainly made easier with less oversquare/more undersquare engines?

That Honda's pedigree is rooted in high specific output motorcycle engines means that despite choosing a less than optimal, on paper anyway, format, their objectives can be obtained regardless?

WAG & JMO.

Edit: spelling

I wasn't exactly correct on long stroke Honda/Acura 4 cylinder engines but Honda does use a longer stroke than most of the other engines in the same class. Some of the current 4 cylinder Acura modles have a 8600 rpm redline with equal bore and stroke. I'm no Honda expert but heir high output 4 cylinder engines aren't forced induction like many of the other manufacturers? Perhaps this and fuel mileage concerns also influences engine design..

[140Air]

I'm not privy to any inside information, but the situation at Honda may be a pragmatic consequence.

Changing bore centres is one of the costliest changes that can be made to engine machining plant. Honda engines from the eighties tended to be in the 1.3-1.6l range, so the outgrowth seen over the last couple of decades to 2.0-2.2l could most economically take place by smaller bore increases coupled with larger stroke increases?

As packaging constraints have also become much more important in the same period it may be a happy coincidence to keep to smaller bores anyway, and emissions considerations are certainly made easier with less oversquare/more undersquare engines?

That Honda's pedigree is rooted in high specific output motorcycle engines means that despite choosing a less than optimal, on paper anyway, format, their objectives can be obtained regardless?

WAG & JMO

There is no question it is more economical to raise the deck and stroke an engine than to redesign block, heads, crank packaging of accessories, trans, mounts, engine compartments, etc. And, there is no question that a smaller bore is better for emissions, CR and thermal efficiency, etc. So, if Honda can get equal or better specific power and fuel mileage from their long-in-the-tooth basic engine designs, why not? But, they are old and by the consensus of the rest of the industry, outdated. By the way, as far as I know the most recent engine, the K series, follows similar internal dimensions as their older engines.
But their cars are getting bigger across the board yet they don't have anything in the high power big car market. But then they still can supercharge/turbocharge and hybridization takes some load off the IC engine.

[wideopen231]

I think the big bore make more power.Question whats it going in and what kind of transmission and gearing. Yes pro stock runs biggest bore possible with 5 spd trans.Now take a bracket racers where 2spd glide is the norm. You need wider power band and tq is king. Both are best. 4.600 bore BBC with 4.75 crank 632 ci is very popular in brackets for that reason. Only thing better than ci is forced induction with nitro and again all 3 at once .oops got to clean the screen.

[wyrmrider]

doesn't honda have a v6 for appropriate applications

[Schurkey]

Usually, breathing trumps all other considerations, but combustion efficiency, friction and thermal efficiency can put a stop to how far you can go in the direction of bigger bore, shorter stroke. After pneumatic valve springs "solved" the valve train limit on rpm, F1 designers went for the maximum rpms they could get. But they were limited by the poor combustion chamber shapes they had from the ultra large bore/stroke ratios

The disadvantage to small bores is the small valves and poor breathing. Opening the bore allows bigger valves and bigger ports, leading to better breathing and thus improved power, until the bore becomes so huge that the combustion chamber resembles a contact lens; the engine breathes but cannot burn because the flame travel is too long, and the depth of the chamber has to be too thin (in order to maintain compression ratio).

Late '80's, Suzuki opened the bore of their big-league street motorcycle engine; and found it disappointing. A few years later they built the replacement engine, and went back to a smaller bore to improve efficiency of the combustion chamber.

[teamrude]

I build small single honda race motors. In my vintage "classic" class I am limited to style of head and 150cc + .020 overbore. Original motor was 49.5mm stroke and 56mm bore for 122cc. Valves and head are limiting factor. Fairly deep Hemi chambers with 27 x 21mm valves. With 3 days porting and flowbench testing I found best overall flow numbers I can pull from head. Quite a improvement with a tad over 40% gain average. Exhaust now flows better than original intake and flow keeps increasing to .400 lift on intake.
These motors tend to peak at around 10-11,500 and as i said before the small exhaust valve becomes "cork" in system if I bump cc's over 170 or so. Due to type of racing (vintage MX) I knew I needed response and quick power but also needed broad powerband of 4000 plus spread. Had played with various durations to get it in the ballpark of my needed powerband which is 7-11,000.
First did big-bore 150cc stock stroke and then did a stroke with slight bore 61mm for big bore and 59x57mm for stroker. On dyno made same peak HP at virtually same rpm (10,700). The stroker had better power below peak and on acceleration pulls was noticeably quicker.
My impression is change in rod ratio (2.12 for big bore and 1.70-1 for stroker) helped with poor head design. I have found similar result on similar motor with a different style head with much larger valves and ports.
My question is..... Do you feel rod/stroke ratio or the poor head design is factor for stroker running better? Or as I believe it combo of both. This motor spent 4 hours on dyno just getting pipe design to maximise and I spent time on intake tract length which also was of great benefit. (stepped reverse cone megaphone and 9" from valve was best combo)

[wyrmrider]

nice work rude
you did what you had to do
thanks for the info

[teamrude]

Due to these being one piece rod and press apart cranks. I plug hole for crank pin and re-bore new pin hole 4.75mm off center. Then with special press weheat and shrink rod to desired eye to eye length. Typically to same pin to deck as standard piston. This allows a common standard forged piston to be used. I do some cranks with altered pin height on pistons to save weight or adapt different model.
Due to fixed cam/rocker geometry in head I am kind of limited to lift and duration. Typically .320 and 245 @ .050 was considered max. I now run .395 and low 250's but short total and tight LSA. Even then it requires great attention to things like valve to valve, retainer to guide etc. Heck cam wont even slide into head without some serious work and then have to clearence just to get to spin. I went to beehive/titanium and even valves are handmade titanium 4mm stem specials. Use all coatings and even do exhaust port and 6" of exhaust on inside. This motor was 15.4-1 and ran very very well.

Have a "Batman" project with Porkchop crank, very short rod, short cylinder, relocated valve guide angles with reshaped combustion chamber. Dual plug head with infinitely adjustable timing for each. Piston is basically a silver dollar with a short wristpin. Preliminary on head was remarkable and a flat-top will actually be in the mid 13's for compression. I even went so far as to offset cylinder to crank. Ports were completely filled and now is basically a down draft port. Still technically legal as started with original parts

[140Air]

doesn't honda have a v6 for appropriate applications

Yes they do. Similar to their 4s. Too small for serious power.