V6 v I6 v F6

[LotusRising]

Since apparently we have some time to kill on our hands and there seems to be some really smart (and passionate) folks on this message board I was curious about people’s thoughts on the relative pluses and minuses of a V-6 (say somebody was thinking about a Nissan Z ), versus a flat six (maybe a Caymen 4.0?) versus an in-line six engine configuration (why is the Supra so ugly but it is getting a manual soon!). Also, who am I kidding, if I have a chance with a supermodel I’ll wait until 2024 if I have to.

 

[Lolub]

Since apparently we have some time to kill on our hands and there seems to be some really smart (and passionate) folks on this message board I was curious about people’s thoughts on the relative pluses and minuses of a V-6 (say somebody was thinking about a Nissan Z ), versus a flat six (maybe a Caymen 4.0?) versus an in-line six engine configuration (why is the Supra so ugly but it is getting a manual soon!). Also, who am I kidding, if I have a chance with a supermodel I’ll wait until 2024 if I have to.

I have the same curiosity and feelings that you do!

 

[digilotus]

V6 and flat six engines are shorter which means that their crankshafts are shorter with less flex at high rpm. Less camshaft flex also means higher rev limit opportunities. Also a shorter engine is easier to package in a smaller car. An I6 would not fit in a rear engined car like an Emira or 718 Cayman.

However an I6 is simpler with less moving parts. Eg two camshafts not four, one head gasket not two. The layout also allows simpler packaging of intake and exhaust. Eg a V6T generally needs to have a twin turbo due to packaging. An I6T can easily get away with one turbo. Less parts means less weight too.

I6 engines are generally only used for front engined, rear wheel drive configurations (at least for larger displacement engines) as is common in BMWs. I love the simplicity of I6 engines and the ease of working on them.

 

[VL3X]

V6 and flat six engines are shorter which means that their crankshafts are shorter with less flex at high rpm. Less camshaft flex also means higher rev limit opportunities. Also a shorter engine is easier to package in a smaller car. An I6 would not fit in a rear engined car like an Emira or 718 Cayman.

However an I6 is simpler with less moving parts. Eg two camshafts not four, one head gasket not two. The layout also allows simpler packaging of intake and exhaust. Eg a V6T generally needs to have a twin turbo due to packaging. An I6T can easily get away with one turbo. Less parts means less weight too.

I6 engines are generally only used for front engined, rear wheel drive configurations (at least for larger displacement engines) as is common in BMWs. I love the simplicity of I6 engines and the ease of working on them.

Yep.. this brings me back to my 300ZX (VG30DETT V6) vs Toyota Supra (2JZ I6) days. My Z was a beast at ~400WHP with the stock snails and could hit the mid 500s with aftermarket turbos. However my buddy's Supra with it's I6 converted to a big single turbo setup and threw down 800WHP+!

 

[Lolub]

Thank you @digilotus and @VL3X for the excellent details and comparisons! Very helpful!

 

[Eagle7]

There's also the difference in where you can put the different formats. The inline 6 was popular for front engine cars because it could easily be put in between the front wheels, due to it not taking up much space horizontally. The downside was it's the tallest of the 3 layouts so required tall hoods, and they were the longest engines. The Jaguar E type famously dealt with that by putting a hood bulge in the middle.

The flat 6 does the best of having a low vertical profile, but it trades that for a wide horizontal profile which means it can't be used in the front between the front wheels. This is why you see Porsche putting it behind the rear axle. The advantage is low center of gravity and being able to have a low profile body shape. It's also not as long as the i6.

The V6 is the compromise in the middle between the other two layouts. It has a lower vertical profile than the i6, but not as wide as the flat 6, plus the advantage that the cylinders and heads are up high enough that it can be used in the front between the front wheels. The downside is the extra complexity (2 heads, cams) as already mentioned, and the difficulty of balancing the angles. Modern engine technology is so good however, that the balancing issue is no longer an issue. It's the best overall for packaging and layout, being not as long as the i6 or as tall, and not as wide as the flat 6 so it can be used in multiple layouts.

The V layouts, whether a 6, 8 or 12, also work very well for mid-engine configurations due to the way they can be packaged along with the support accessories needed.

 

[LotusRising]

Really great info so far guys. How about engine sound such as pitch and character? Coarseness and vibration (I know the press always raves about the smoothness of the BMW in-line six)? Longevity differences? Interactions with superchargers?
I appreciate everyone’s expertise.

 

[Kwarstler]

Straight 6s generally have fewer moving parts and proven to be robust and reliable. The Supras straight 6 by BMW is a beast with tunes! A manual comes this year but they have limited production to 500 units U.S. which I think is a mistake. I’ve seriously considered one but I can’t get past all the fake vents on the car! I’ve always
Preferred the straight 6 Cummins over the V8 powerstrokes in trucks. They’re simply a proven power plant!

 

[Eagle7]

Really great info so far guys. How about engine sound such as pitch and character? Coarseness and vibration (I know the press always raves about the smoothness of the BMW in-line six)? Longevity differences? Interactions with superchargers?
I appreciate everyone’s expertise.

Coarseness and vibration is what I was referring to as balancing. The inline 6 has the advantage of all the movement of the pistons being vertical in the same direction along the crankshaft. The cam and valves are also sitting right inline on top of all this, so everything is balanced horizontally by being in a straight line along the same vertical plane. This makes for a stable and smooth running engine. It also has fewer parts and weighs less.

The V configurations have the opposite. The pistons on each side are violently moving up and down in opposite directions; the left side is pushing down to the right, and the right side is pushing down to the left. Plus you have two cams each with their own valve sets, hanging out at the top of the end of each side of the V. That's a recipe for a lot of jiggle, wiggle and vibration. The manufacturers use balancers to help compensate for some of that, combined with timing when each cylinder fires so there isn't too much motion at once in either direction. This helps to keep the side-to-side motion down to a minimum in the middle, and the rest is smoothed out with harmonic balancers at the crank. The downside is a lot of extra parts, weight, and things in motion; all of which adds to the overall vibration. The motor mounts help to eliminate the last part so you don't feel it in the car.

As for longevity, modern engines are so well built there probably isn't that much of a difference in longevity, depending of course on how the engine is used. High performance produces high stress and heat, and that can shorten the life of any engine. There are of course fewer parts on an inline 6 to break, so that is somewhat of an advantage.

Here's a good article on the differences between a supercharger and turbocharger:

Turbocharger vs. Supercharger: What's the Difference?

Both turbochargers and superchargers cram extra air into an engine to increase power, and they each have their pros and cons.

www.motortrend.com

A supercharger and turbo both essentially do the same thing, except by different methods. They both force more air into the combustion chamber than the engine would normally pull in on its own. Fuel mixed with air produces the force when it explodes; the more air, the more powerful the explosion. A turbo produces its air from being spun up by the pressure of the exhaust from the engine. Since it's dependent on engine speed, this is why it takes some rpm for it to really start making a difference, and thus feels laggy; it doesn't kick in immediately. The advantage of the supercharger is it forces air immediately because it's not dependent on the exhaust pressure; it's driven separately. This makes it ideal for low speed power and throttle response. Turbos add a lot of power at higher rpms, but how useful that is depends on how and where you're driving your vehicle.

Sound.
There are a lot of factors involved in sound, both engine sound and exhaust sound. Because there are less moving parts, inline engines sound quieter and smoother than a V configuration. V engines are noisy mechanically.

As for exhaust sound, that depends on engine cylinder size (the bigger the bore, the boomier the noise), size and channeling of the exhaust ports, the tubing size, length and shape of the exhaust manifold, as well as the material it's made of, the type of catalytic convertor the manifold exits into, the diameter, bends and length of the exhaust pipes from the cat(s) to the resonator if there is one, the type of mufflers, and finally the exhaust tips. Bigger diameter pipes give a deeper, boomier sound. Smaller diameter pipes give a sharper, barkier sound. Cats, resonators and mufflers can change the tone from sharp to a softer-edged muffled tone, as well as being quieter. They also eliminate harshness in the tone. This makes cars nicer to live with, but the sound isn't as exciting. Louder isn't necessarily better. People make the mistake all the time of thinking that changing the factory exhaust to a 3rd party performance exhaust is going to make their car faster and sound great, then they find out they now have skull pounding resonance in the car. There's a science to a well-designed exhaust system, because it IS a system, not just bigger straight-through pipes.

Because V8's typically have large bore cylinders, they have that typical roaring boomy sound. A lot of fuel and air can be compressed in those large cylinders and that's why those engines are so powerful. The smaller the bore, the higher pitched the sound, which is why V12's have that sharp edged, ripping sound. The bores are smaller than a V8, but they make up for that power-wise, by having more cylinders. A V6 sits in the middle of that; smaller bores than a V8, but larger than a V12, so they have an exhaust sound that's a little deeper than a V12, but not as boomy as a V8. With a good, well-designed exhaust system, a V6 can sound really good. Not quite as sensuous as a V12, but more of an exotic sound than a V8, although a V8 can still sound quite good if the exhaust system is well-designed.

Depending on what Lotus has to cobble in there to meet emissions, the V6 is going to sound very good to really good. The latest clip shows the latest build sounding really good. If that latest clip is production spec, we've got a winner in the sound department. We haven't heard anything definitive about the i4 yet, so it's hard to say, but I expect it to have more of a boomy roar than the exotic rip of the V6. If you've heard a turbo 4, they all seem to have similar sound characteristics; the tone is softer edged with more of a roar than a bark.

 

[Eagle7]

Straight 6s generally have fewer moving parts and proven to be robust and reliable. The Supras straight 6 by BMW is a beast with tunes! A manual comes this year but they have limited production to 500 units U.S. which I think is a mistake. I’ve seriously considered one but I can’t get past all the fake vents on the car! I’ve always
Preferred the straight 6 Cummins over the V8 powerstrokes in trucks. They’re simply a proven power plant!

I notice this is your first post... welcome to the forum!

 

[virtualmacho]

And although off-topic, a rotary engine has even less moving parts. If only there was a transmission that would allow a 3 or 4 rotor engine to be mounted transversely !

 

[LotusRising]

Coarseness and vibration is what I was referring to as balancing. The inline 6 has the advantage of all the movement of the pistons being vertical in the same direction along the crankshaft. The cam and valves are also sitting right inline on top of all this, so everything is balanced horizontally by being in a straight line along the same vertical plane. This makes for a stable and smooth running engine. It also has fewer parts and weighs less.

The V configurations have the opposite. The pistons on each side are violently moving up and down in opposite directions; the left side is pushing down to the right, and the right side is pushing down to the left. Plus you have two cams each with their own valve sets, hanging out at the top of the end of each side of the V. That's a recipe for a lot of jiggle, wiggle and vibration. The manufacturers use balancers to help compensate for some of that, combined with timing when each cylinder fires so there isn't too much motion at once in either direction. This helps to keep the side-to-side motion down to a minimum in the middle, and the rest is smoothed out with harmonic balancers at the crank. The downside is a lot of extra parts, weight, and things in motion; all of which adds to the overall vibration. The motor mounts help to eliminate the last part so you don't feel it in the car.

As for longevity, modern engines are so well built there probably isn't that much of a difference in longevity, depending of course on how the engine is used. High performance produces high stress and heat, and that can shorten the life of any engine. There are of course fewer parts on an inline 6 to break, so that is somewhat of an advantage.

Here's a good article on the differences between a supercharger and turbocharger:

Turbocharger vs. Supercharger: What's the Difference?

Both turbochargers and superchargers cram extra air into an engine to increase power, and they each have their pros and cons.

www.motortrend.com

A supercharger and turbo both essentially do the same thing, except by different methods. They both force more air into the combustion chamber than the engine would normally pull in on its own. Fuel mixed with air produces the force when it explodes; the more air, the more powerful the explosion. A turbo produces its air from being spun up by the pressure of the exhaust from the engine. Since it's dependent on engine speed, this is why it takes some rpm for it to really start making a difference, and thus feels laggy; it doesn't kick in immediately. The advantage of the supercharger is it forces air immediately because it's not dependent on the exhaust pressure; it's driven separately. This makes it ideal for low speed power and throttle response. Turbos add a lot of power at higher rpms, but how useful that is depends on how and where you're driving your vehicle.

Sound.
There are a lot of factors involved in sound, both engine sound and exhaust sound. Because there are less moving parts, inline engines sound quieter and smoother than a V configuration. V engines are noisy mechanically.

As for exhaust sound, that depends on engine cylinder size (the bigger the bore, the boomier the noise), size and channeling of the exhaust ports, the tubing size, length and shape of the exhaust manifold, as well as the material it's made of, the type of catalytic convertor the manifold exits into, the diameter, bends and length of the exhaust pipes from the cat(s) to the resonator if there is one, the type of mufflers, and finally the exhaust tips. Bigger diameter pipes give a deeper, boomier sound. Smaller diameter pipes give a sharper, barkier sound. Cats, resonators and mufflers can change the tone from sharp to a softer-edged muffled tone, as well as being quieter. They also eliminate harshness in the tone. This makes cars nicer to live with, but the sound isn't as exciting. Louder isn't necessarily better. People make the mistake all the time of thinking that changing the factory exhaust to a 3rd party performance exhaust is going to make their car faster and sound great, then they find out they now have skull pounding resonance in the car. There's a science to a well-designed exhaust system, because it IS a system, not just bigger straight-through pipes.

Because V8's typically have large bore cylinders, they have that typical roaring boomy sound. A lot of fuel and air can be compressed in those large cylinders and that's why those engines are so powerful. The smaller the bore, the higher pitched the sound, which is why V12's have that sharp edged, ripping sound. The bores are smaller than a V8, but they make up for that power-wise, by having more cylinders. A V6 sits in the middle of that; smaller bores than a V8, but larger than a V12, so they have an exhaust sound that's a little deeper than a V12, but not as boomy as a V8. With a good, well-designed exhaust system, a V6 can sound really good. Not quite as sensuous as a V12, but more of an exotic sound than a V8, although a V8 can still sound quite good if the exhaust system is well-designed.

Depending on what Lotus has to cobble in there to meet emissions, the V6 is going to sound very good to really good. The latest clip shows the latest build sounding really good. If that latest clip is production spec, we've got a winner in the sound department. We haven't heard anything definitive about the i4 yet, so it's hard to say, but I expect it to have more of a boomy roar than the exotic rip of the V6. If you've heard a turbo 4, they all seem to have similar sound characteristics; the tone is softer edged with more of a roar than a bark.

You the man! Thx for the info!

 

[ksegg]

If it was my choice, I6 TT all day long. (But I am biased)

They're just so naturally balanced and smoooooooth.

 

[Eagle7]

And although off-topic, a rotary engine has even less moving parts. If only there was a transmission that would allow a 3 or 4 rotor engine to be mounted transversely !

Yeah rotaries are amazing. I had one in my RX-8. They're surprisingly small for the amount of power they put out, and they are dead smooth when running. It's like driving a sewing machine. They also easily rev to very high rpm; mine went to 9,000 effortlessly. It was always a surprise when I hit redline, because there wasn't that typical drop-off in power as you got close to it like there is with a traditional type engine. Even at redline it felt like it wanted to just continue pulling. The biggest downside is they aren't very fuel efficient, and they get HOT. Heat was the biggest issue. The coil packs kept getting burned out. The car would be fine then suddenly the power would cut and you wouldn't be able to go any faster than idle, and I'd take it to the dealer and another coil pack had burnt.

Maybe with modern materials and computer controlled engine systems, they could make the rotary work, but since the ICE era is coming to an end, there's probably no reason to justify the development cost. ALTHOUGH, supposedly Mazda has a next generation rotary in the works for a reborn RX-8, but I'll believe that when I see it.

 

[virtualmacho]

ALTHOUGH, supposedly Mazda has a next generation rotary in the works for a reborn RX-8, but I'll believe that when I see it.

I have been waiting 18 years for the RX-9 to come out, but it doesn't look like it will. That's why I put in a deposit for the Emira to replace my RX-8 (which still runs flawlessly).

The biggest downside is they aren't very fuel efficient, and they get HOT. Heat was the biggest issue. The coil packs kept getting burned out.

Agreed. Relocating the coils to a cooler spot in the engine bay is a popular mod, but I haven't done this as I don't track the car nor live in an exceptionally hot area.

'Nuff said. Back to the topic of 6-pistons...

 

[Kwarstler]

I notice this is your first post... welcome to the forum!

Thank you. I’m more a lurker than a poster. A lot of great info on this forum. I have a preorder in for a v6 manual although it won’t be a FE. I’ve been assured I will be able to package it equivalent to a FE plus there’s an additional 6 colors I’ve been told. With the recent update from Lotus I am anticipating a configuration date January 2023, build June 2023 and delivery August/Sept 2023. IF the new manufacturing schedule actually moves forward without a hitch!

 

[Nova]

If we just wanted to build the best engine, the straight six would be the best platform for the engine itself. It's also a good form factor for most RWD platforms because it is long and thin, and fits in naturally in a longitudinal orientation. A straight six has the fewest technical challenges to overcome, and therefore, engineering efforts can push the envelope a bit further.

Plenty of development effort has been put into V6 engines that its space-saving characteristics have won manufacturers over, and there's certainly no shortage of very capable V6s.

Looking back, of the V6 cars I've owned, they've been about half and half I6 vs V6. The most advanced of these is the Mercedes M256, which was indeed a wonderful engine to push around. But to be honest, I think most of these V6/I6 decisions is driven by packaging decisions. An I6 ultimately does take up the least amount of space, and therefore will work better in a long-hood vehicle, allowing space for turbos, hybrid drivetrains, etc. For shorter hood vehicles, a V6 configuration may be better.

In this regard, the engine bay of the Emira is certainly on the "short" side, and therefore, the V configuration is a good fit.