Observations regarding NA I4 vs V6 engines

[1sttruck]

A lot (most ?) medium and heavy duty diesels seem to be I6. Considering that the cylinders are spread farther out along the length of the engine than in a V configuration, it seems to allow for more bearing support, something important with the high comrpession of the diesels. It also seems to allow for better cooling as again the cylinders are spread out more, again something important for a diesel as they typically run at higher temperatures. The tall engines due to the typically longer strokes potentially make for a stiff block, at least along the stroke axis. Stiffness seems to help with durability, as most seem to get reputations for long life.

My son's 4.9L Ford I6 seems to benefit from the configuration as it too has a good reputation long engine life, even though it's 'just a gasser' :^)

 

[ShiningArcanine]

Originally Posted By: BarkerMan
Try your chart again after you do the same service work on both an I4 and a V6. Try a timing belt or changing the spark plugs yourself and you will begin to see a difference. Front plugs on a V6 in a transverse engine are easy enough but try the rear plugs. But all this is only a concern for the diy owner that keeps his car past the payments or lease. Otherwise just pay a mechanic and don't bother with it all.

A V6 is an exercise in excellence in engineering. Without a computer to help you design such an engine it would never become a successful commercial enterprise. It is strictly an answer to the question how do we get the most power and torque possible without a turbo or blower in this small space at the front end of an automobile. Without that question to work with you would never see such a package developed to the state of the current offerings on the market today. If you told a group of engineers in 1950 that you could design an engine that would develop 200+ horse power and fit in an opening the size of a Honda Accord engine compartment and get 20+ mpg and go 100k miles without oil changes and not much else they would laugh at you. Today that's the least an owner expects.


I have tried changing the spark plugs on my Avalon's V6 with my Uncle's help. We could reach the front ones with minimal difficulty, but the car was taken to the dealership where they changed all six because we could not reach the rear ones.

As for how the amount of power you can fit into a small space, I would suggest looking at turbine engines and AC induction engines, both of which are capable of having higher power output in smaller spaces than conventional engines.

Originally Posted By: sciphi
Too bad more I4 engines are not turbo'd or blown. A blower on a small I4 would fatten the torque curve down low, allowing it to keep up with a larger-engined car while still getting better fuel economy. Same with a small turbo that could be tuned to boost maximally at the RPM's most people are routinely driving at.


This is a bit off-topic but why do people always talk about turbocharging engines? In my mind, super-charging an engine is much better because with super-charging, you can control the increase in airflow with a computer independently of the engine's instantaneous RPM rate, which should be easier to do optimally. I would also imagine that extraction of work from the engine's exhaust would reduce the engine's power output much more than extracting work from the engine's motion via the alternator, which I would think would make a super-charger require less energy than the turbo-charger if the computer controlling it has low power requirements.

 

[XS650]

Originally Posted By: punisher
Originally Posted By: XS650
Originally Posted By: punisher


Don't know what a "flat" V-4" is. It is either a flat (boxer) or a "V", not both.


That would be a 180 degree V.


You're being obtuse now.

 

[javacontour]

You can do the same with a turbo. You can have a variable geometry (may not be the right term) turbo that adjusts boost based on what the computer says.

The turbo is a restriction in the exhaust at times. However, I believe there is more "free" power added by a turbo than by a supercharger.

Of course, it all depends on how the system is designed.

Both can be controlled by a computer, and both are restrictions, either in the intake, or in both the intake and exhaust sides of the equation.

 

[The Critic]

Originally Posted By: ShiningArcanine
I have tried changing the spark plugs on my Avalon's V6 with my Uncle's help. We could reach the front ones with minimal difficulty, but the car was taken to the dealership where they changed all six because we could not reach the rear ones.

I've had no trouble changing plugs on Honda V6s or timing belts on 3.0L Nissans. You really can't blame the design if your skills aren't up to par.

 

[JHZR2]

Skills or no skills, you can in no way compare the ease of servicing spark plugs on a V6 vs. an I4.

JMH

 

[The Critic]

Point is, if you have the skills, it isn't an issue.

This is reminding me of the Honda V6 transmission fill bolt thread we had a while ago.

 

[BarkerMan]

Small airplanes use a boxer configuration because it produces vibrations that an airframe can deal with as opposed to other configurations that may require more structure to dampen.

 

[Spitty]

Ford (Europe) Produced a V4 in the 60's it was used in the Ford Corsair and light delivery vans in 1600cc and 2000cc and also in the Saab as a replacement for a 3cyl 2 stroke engine. In the U.K. the Ford V4 was NOT considered a desirable engine, it was rough and did not have a reputation of longevity. I guess it's main advantage was it's size (proportions), but it was soon replaced by I4's, ether the 1600 cross flow or the OHC Pinto engine.
In the 50's Light I6 engines were common in small up market cars, one of the last was a 1600cc I6 used in the Triumph Vitesse, I think the main attraction was the smoothness, and their ability to 'pull' from low RPM.
I think the limitation of the I6 is the length of the engine as the engine capacity increases (over 3L the engine becomes too long for a car with the normally accepted width, if mounted Transversely, or length if longitudinally mounted) V6's may cost more to manufacture due to duplication of parts (Tow cyl heads etc.) however this cost may be offset if production can use the same machining/components as a V8. However this means the V6 will have an 'unnatural' 90 deg bank angle (60 deg is deemed ideal) unless an offset crank is used.

 

[Dad2leia]

Aren't turbos also easier and more natural on an engine in terms of the boost? I realize that like javacontour said, there is the exhaust restriction, but from what I've learned, a small turbo is the most reliable AND safest way to get more out of a set size of engine, without too much fuss (other than figuring out where the heck you are going to put all of the plumbing involved..

).

I have a question on superchargers though. How are they regulated from constantly shoving boost into the engine. They are directly driven from the crankshaft, so wouldn't boost be directly related to rpms, instead of a spooling up?

 

[BarkerMan]

The original (the good one) MR2 had a two lobe positive displacement supercharger and in not boost conditions the blower could either be disconnected by the clutch much like an a/c unit and it could alow blow against nothing to fine tune the business of running the engine. In this application the heat of a turbo might have been too much for a little car with a mid engine and it might have cooked the driver and passenger. A later, larger MR2 did have a turbo but had more space to deal with the heat. I don't know about the third model.

 

[BuickGN]

Originally Posted By: Dad2leia
Aren't turbos also easier and more natural on an engine in terms of the boost? I realize that like javacontour said, there is the exhaust restriction, but from what I've learned, a small turbo is the most reliable AND safest way to get more out of a set size of engine, without too much fuss (other than figuring out where the heck you are going to put all of the plumbing involved..

).

I have a question on superchargers though. How are they regulated from constantly shoving boost into the engine. They are directly driven from the crankshaft, so wouldn't boost be directly related to rpms, instead of a spooling up?


Superchargers have bypass valves (roots style and screw style) that open if boost goes past a preset limit. They can be set up to open below a certain rpm and at cruise. Generally a positive displacement will stay roughly the same throughout the rpm range without the bypass.

A centrifugal blower like Vortech (looks like a big belt driven turbo) will continue to build more boost the higher the rpms go. People talk about turbo lag but on most of the centrifugal setups you don't get full boost until you hit redline.

Once the turbine is at speed, the turbo poses very little exhaust restriction. With VATN technology common on small diesels, the turbo is not a restriction at cruise. You basically have a variable size exhaust housing. It gets smaller through it's vanes for fast spool and gets larger for top end power and fuel economy.

Power lost from a turbo is only through exhaust restriction which doesn't put any extra strain on the internals.

A supercharger requires power to run. To get the same hp at the wheels, a supercharged engine will actually have to produce more power than a turbo because some of it gets eaten up by the blower. When looking into fuel requirements, for the same output supercharged motors will need more fuel. You engine has the stress of the extra power eaten up by the blower but you will never see it at the wheels.

I've got 20,000 miles on my car in it's current setup, even drove it 210 miles a day for work for a month with 0 problems. Not many people can honestly say they drive a 600hp small displacement V6 210miles round trip with no problems. I credit the turbo with some of this because it allowed me to build the rest of the motor fairly mild and rely on the boost for power.

 

[JHZR2]

Originally Posted By: The Critic
Point is, if you have the skills, it isn't an issue.

This is reminding me of the Honda V6 transmission fill bolt thread we had a while ago.


Id be interested to see, in a vehicle that both the I4 and V6 offerings had timing belts, what the flat rate and actual average time to perform spark plug replacement, drive belt replacement, water pump replacement, alternator replacement and timing belt replacement are.

Id be curious to see if the time required was of the form tv6=1.5*ti4, or if there was deviation in terms of efficiency 1.0>x>1.5 or in terms of complexity x>1.5

Even if you have the skills and the ability, if it takes some inherently higher amount of time, there is an inefficiency to the end user. Not to mention parts, which are absolutelygoing to cost more on a relatively apples to apples engine set.

JMH

 

[The Critic]

Originally Posted By: JHZR2
Id be interested to see, in a vehicle that both the I4 and V6 offerings had timing belts, what the flat rate and actual average time to perform spark plug replacement, drive belt replacement, water pump replacement, alternator replacement and timing belt replacement are.


Timing Belt and Water Pump replacement on a Honda 2.3L I4 is 4 hours, whereas an identical job for a Honda 3.0L V6 is 5 hours.

Part costs are identical...

 

[JHZR2]

Interesting... so it takes about 20% more time to work on a V6 than an I4. That equates to about $100.

I wonder what the comparative time rates are for other stuff that is more unit dependent, like spark plug jobs, etc.

JMH

 

[The Critic]

I know that a spark plug job on a Honda V6 is only 0.5 flat rate.

 

[John K]

On the supercharger vs turbocharger comparisons in 2007 the MiniCooper S changed from a supercharged engine to a turbocharged one. They also changed the engine supplier... It would be interesting to know the reason for the change, I haven't found a detailed discussion. From the web site I got the following (easy to do because the Cooper S convertible still has the old engine, but it messes up the weight and performance comparisons...). Engines have the same bore and stroke, and the latest one is direct injection.

Supercharged: 168HP@6000rpm, 162LbFt@4000, 16.4LB/HP, 134mph top, 7.0 sec 0-60.

Turbocharged: 172HP@5500rpm, 177LbFt@1600-5000rpm, 15.5LB/HP, 139mph top, 6.7 sec 0-60.

The most surprising part to me is the flat torque from 1600 to 5000 rpm.

 

[javacontour]

The engine supplier change came about because I believe they were buying the engine from Daimler-Chrysler, and this did not sit well with the folks at BMW/Mini.

If you look at the early new-mini's, the engine looked a lot like the engine I had in my old '95 Neon. I know it's a smaller displacement. However, I believe it's from the same family.

http://www.autotrader.com/research/car-r...=used&year=2002

http://www.motortrend.com/future/spied_vehicles/112_0503_2007_mini_cooper/

 

[Drew99GT]

The bypass valve on a positive displacement blower like a magnacharger is completely different than the bypass valve on a centrifugal compressor such as a turbocharger or a vortech type supercharger. The difference is in where the throttle is located; on a positive displacement blower, it's in front of the blower and the purpose of the bypass valve is to allow air to enter the engine and bypass the blower so it won't produce boost, and therefore, won't put a drag on the engine, allowing better part throttle driveability and better fuel mileage.

With a centrifugal compressor, the throttle is in between the compressor and engine, so the bypass's function is to release all the boost pressure when the throttleplate slams shut, so it has somewhere to go and not damage the compressor.

Bypass/blowoff valves in no way control max boost pressure. Some positive displacement/roots style systems have a burst panel on the actual blowercase if there's a backfire or something.

 

[gtx510]

http://www.magnusonproducts.com/bypass.htm
Bypass (diverter/recirc) valves also bypass air during idle and light loads (before boost is made), this helps to improve off-boost throttle response. A turbo bypass valve works the same way.
A blow-off valve that is vented to the atmosphere would not do this. And I think some recirc valves can be set-up so that they don't open at idle, iirc, HKS and Greddy.

A bypass valve or BOV will limit boost if it can't hold the pressure and leaks. That's why the DSM guys have the crushed bypass valve "mod".


BMW Mini engines, newer version gets intake Valvetronic?
http://en.wikipedia.org/wiki/Tritec_engine old
http://en.wikipedia.org/wiki/Prince_engine new