They all affect balance and therefore max rpm. In general, things don't like to spin fast if they are not balanced. +1 for common sense
V6 engine questions
- Thread starter JD Cross
- Start date
They all affect balance and therefore max rpm. In general, things don't like to spin fast if they are not balanced. +1 for common sense
Indeed, the mechanical balance is very important factor also in the basic nature of the engine and it's dyno curve.
Not going to go into detail as that would be a very long write up.
Common layouts:
I3 < worst (ever sat in a toyota aygo, IQ or relative? it's horrendous!)
I6 < best (BMW, Skyline, Supra although Skyline's can't rev due to poor quality/deck design stupid things fracture at high rpm)
V12/H12 < even better
R < zero loss but rotory/wankels don't count in this discussion (go to a mazda forum and be amused by the efficiency)
Closest you can practically get to ideal balance is 6 cylinders inline or per bank (there have been numerous I8 cars in the '30,'40,'50)
H4 and H6 have a counteracting feature due to 180 degree bank angle aka boxer aka flat. (Porsche & Subaru)
Crank/firing layout
Take a V8
Flat plain:
+ High revving simple and light
- poor torque and low end drive ability
Cross Plain:
- heavier, doesn't like high RPM (although take a look at a BMW M V8.....)
Not going to go into detail as that would be a very long write up.
Common layouts:
I3 < worst (ever sat in a toyota aygo, IQ or relative? it's horrendous!)
I6 < best (BMW, Skyline, Supra although Skyline's can't rev due to poor quality/deck design stupid things fracture at high rpm)
V12/H12 < even better
R < zero loss but rotory/wankels don't count in this discussion (go to a mazda forum and be amused by the efficiency)
Closest you can practically get to ideal balance is 6 cylinders inline or per bank (there have been numerous I8 cars in the '30,'40,'50)
H4 and H6 have a counteracting feature due to 180 degree bank angle aka boxer aka flat. (Porsche & Subaru)
Crank/firing layout
Take a V8
Flat plain:
- Lotus Esprit
- Italian V8's (except 832 Thema, Maserati)
- F1/Indy car
+ High revving simple and light
- poor torque and low end drive ability
Cross Plain:
- Every other production V8
- heavier, doesn't like high RPM (although take a look at a BMW M V8.....)
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Okay but our topic is V6 engines and we're talking about rpm limits on various configurations of bore and stroke.
Yes clearly having a balanced reciprocating mass is important to smoothness (+1 for common sense as Tangoman so aptly put)
I can understand an unbalanced assembly limiting rpm if it is so out of balance that it wants to self-destruct.
But in this day of OEM engine build quality can we assume most engines are pretty well balanced so it's not balance nor cylinder configuration that limits rpm.
To use your V8 example, we know the flat plane V8 has a higher rpm limit than a cross plane V8 despite the flat plane V8 not being as balanced as a cross plane V8.
Is this due to flat plane V8's being more oversquare and having a lower reciprocating mass than a cross plane V8 and it's heavy balanced crankshaft?
Is reciprocating mass and stroke more important to rpm limits than engine configuration?
Jim
Yes clearly having a balanced reciprocating mass is important to smoothness (+1 for common sense as Tangoman so aptly put)
I can understand an unbalanced assembly limiting rpm if it is so out of balance that it wants to self-destruct.
But in this day of OEM engine build quality can we assume most engines are pretty well balanced so it's not balance nor cylinder configuration that limits rpm.
To use your V8 example, we know the flat plane V8 has a higher rpm limit than a cross plane V8 despite the flat plane V8 not being as balanced as a cross plane V8.
Is this due to flat plane V8's being more oversquare and having a lower reciprocating mass than a cross plane V8 and it's heavy balanced crankshaft?
Is reciprocating mass and stroke more important to rpm limits than engine configuration?
Jim
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Some anecdotal note to add. Adnan knows about this.
The HPD crew ran a special J-Series race engine (I forget the model name) equipped NSX in Pikes Peak last year. My guess is to test for the NSX 2.0.
You can see it sits quite tall in the NSX 1.0 engine bay.
The HPD crew ran a special J-Series race engine (I forget the model name) equipped NSX in Pikes Peak last year. My guess is to test for the NSX 2.0.
You can see it sits quite tall in the NSX 1.0 engine bay.
Ryu
I'm not very knowledgeable about forced induction.
Would you say this engine is turbocharged?
If it is HPD will indeed be gathering great information on a turbo J series with possible NSX application
Do you think if they built a dry sump version it would sit lower?
Jim
I'm not very knowledgeable about forced induction.
Would you say this engine is turbocharged?
If it is HPD will indeed be gathering great information on a turbo J series with possible NSX application
Do you think if they built a dry sump version it would sit lower?
Jim
The J's are always very tall in a other topic i showed a side by side comparison of the height and width difference, it's a lighter engine and you can move it more to the front.
Pictured is a HR28TT, used in ALMS and ELMS Le mans racers regulations require a stock block to be used, it's a short deck version of a J engine with the single exhaust port configuration feeding twin turbo's.
Engine also features dryslump, I have posted hi-res pictures and more details some where on the forum i think in the J-Swap thread.
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It's critical to a engine modern, just basic physics.
Pictured is a HR28TT, used in ALMS and ELMS Le mans racers regulations require a stock block to be used, it's a short deck version of a J engine with the single exhaust port configuration feeding twin turbo's.
Engine also features dryslump, I have posted hi-res pictures and more details some where on the forum i think in the J-Swap thread.
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The piston specs aren't influencing the flat plane V8 even a large flat plane retains the same nature. it's all in power stroke ratio (how many times per flywheel revolution the engine has a power down stroke, that's why 2 strokes rev so insanely)
It's critical to a engine modern, just basic physics.
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I'm not sure if anyone's mentioned this but the 60 degree layout limits space "in the V" (between the cylinder heads) to allow for an efficient induction system to be fitted. Fitting DOHC 4 valve per cylinder heads i.e. physically wide, to a 60 degree V6 reduces the space even further. This size and power advantage would outweigh the inherent smoothness advantage of the 60 degree option for a motorsport application.
It can be done but the engine + induction package gets very tall. Take a look at the Alfa Romeo V6 24 Valve as an example of 60 degree V6 with DOHC 4 valve heads. This is a FABULOUS engine but it is very tall and not that powerful (3.2 Ltr, 250hp). If you ever get a chance I urge you to drive an Alfa with this engine! Also the McLaren F1 V12 motor... magnificent but very tall even with a trick flywheel and clutch assembly.
The overall packaging size of a 90 degree V6 along with the superior induction possibilities make it more desirable to car designers.
I can see how a 90° V engine has better packaging than a 60° V, but if space is not a constraint, both can breathe very well.
As far as I understand it, you ideally want the intake air to enter the combustion chamber pretty much along the axis of the cylinder. That means straight intake runners that make each cylinder bank taller. With such an induction system, the angle between the cylinder banks should be pretty much irrelevant for breathing. However, if you don’t have enough space for such a tall intake system, you may have to go with curved runners. And if you have to make do with curved runners, a 90° V will give you more room to play with than a 60° V would.
If Honda wanted to reduce the height of the C30A engine, curved intake runners drawing out of a central plenum nestled between the banks of the V were one way to do it. It would have been cooler if Honda had fitted a dry sump to reduce the height and then used the space gained to install straight intake runners aligned as well as possible with the axis of the cylinders.
As far as I understand it, you ideally want the intake air to enter the combustion chamber pretty much along the axis of the cylinder. That means straight intake runners that make each cylinder bank taller. With such an induction system, the angle between the cylinder banks should be pretty much irrelevant for breathing. However, if you don’t have enough space for such a tall intake system, you may have to go with curved runners. And if you have to make do with curved runners, a 90° V will give you more room to play with than a 60° V would.
If Honda wanted to reduce the height of the C30A engine, curved intake runners drawing out of a central plenum nestled between the banks of the V were one way to do it. It would have been cooler if Honda had fitted a dry sump to reduce the height and then used the space gained to install straight intake runners aligned as well as possible with the axis of the cylinders.
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I've seen '60's preform superb, take at high performance V12's (there ain't a lot BTW)
Take a look at MG Metro 6R4 that thing fly's with a '60 V6.
But that being said I dislike the height of '60's there TALL.
A novel approach at intake trajectory was done by Bizzarini when he designed the Lambo V12 (2 valve versions)
View attachment 97781
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Take a look at MG Metro 6R4 that thing fly's with a '60 V6.
But that being said I dislike the height of '60's there TALL.
A novel approach at intake trajectory was done by Bizzarini when he designed the Lambo V12 (2 valve versions)
View attachment 97781
View attachment 97782
I agree. This is the one glaring omission from the otherwise excellent technical spec of the NSX.
Great engine but it is in-fact a 90 degree V6
Due to the "odd" angles and therefore the exhaust pulse spacing it's difficult to make 90 degree V6's sound as good as 60 degree ones. Hence the "spaghetti" designs employed by GT-Rom (5.1) etc which attempt to fill the gaps/spaces with out of phase pulses. 90's generally sound a too bass'y for me. The aforesaid Metro is however one of the best... enjoy http://www.youtube.com/watch?v=7s8ydSTj7bo
Cheers
Mark
I don’t understand the uneven exhaust pulses in a 90° C30A. Don’t the offset rod journals in an NSX crankshaft allow for even cylinder firing every 120° of rotation? Is the offset not 30°?
I've always wondered if the NSX should have come in a flat plane crankshaft to deliver:
1. more exotic sounds
2. better acceleration
1. more exotic sounds
2. better acceleration
Flat plane V6 won't work, since you have only 3 cylinders in a line it would give serous vibration and fatigue issues.
BTW flat plane is overrated imho.
1. terrible sound (subject to taste)
2. loss of torque (low end)
2. loss of drive-ability
BTW flat plane is overrated imho.
1. terrible sound (subject to taste)
2. loss of torque (low end)
2. loss of drive-ability
Great thread. Just for reference about piston speeds. I had a k20 head mounted on a k24 block with a 99 mm stroke. stock bottom end. Revving to about 8500. I started at 7k and worked my way up tuning it. It made power to 9k but left it at 8.5 for daily driving purposes. It saw 8.5 k probably ten times a day for over a year. Car was sold two years ago and still running strong. I think it would be safe at the piston speeds mentioned earlier no problem haha. Other factors would also take into play to actually make the power at a higher intake velocity.. We don't wanna outflow the heads and pretend to be productive.
2 and 3 interrelated or is there something else to 3?
Given the right cam combo and intake plenum size, and of course proper port work and combustion chamber design you can carry power much higher than you think. My CRX is an 85mm bore and 87.4 stroke. I rev it to 10,200 RPM on the street and take it to 11K at the track with peak power coming in from 10,100rpm and will hold until 10,700ish before slowly falling to 11k (25hp decrease at 11K). The rods/rod bolts and pistons are properly chosen to handle the G-forces and piston speeds that are the end result. The crankshaft is completely stock and the main/rods bearings are stock as well. The engine will be able to handle close to 10k miles before the rings start wearing out and need refreshed. It's all relative to how much I abuse it. I fully intend to take advantage of the short stroke of my C30. So long as the rotating assembly is assembled with the right frame of mind,(which I will do) I don't see an issue with one of these engines revving significantly higher with a reciprocated power band to boot.
Just what I want to hear.
I can't wait to start tinkering with mine. I purchased my nsx while on a deployment and still have 3 months till I get home, sheesh what a bad one. I would love to rev mine to a conservative 9k daily.
It's very cool to rev so endlessly re minds me of the time i used to ride & modify two stroke motorcycles recall I one of them went 14 or 16k rpm.
2-3k idle and it didn't do anything until 6-8k rpm.
That being said i really really like low down torque.
2-3k idle and it didn't do anything until 6-8k rpm.
That being said i really really like low down torque.
Bumping a great thread with an update. Hopefully not too long from now I'll be able to start tuning my built C30 - 93.5mm bore, 84mm stoke.
So the cosworth Acura engine is a 75 degree engine.
WTH?
WTH?
