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Even and odd fire V6 harmonic issues


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#1 NeilR

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Posted 02 July 2015 - 12:14

V6 engines seem to have unfavourable harmonics in comparison to a straight six. However within the V6 oeuvre does the 90 degree odd fire V6 have more issues than an even fire version of the same engine or a 60deg even fire engine? 



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#2 Greg Locock

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Posted 02 July 2015 - 20:38

90 degree v6s-cut down V8s, are pretty horrible things, I doubt anyone still makes them, we  do not need to discuss them further.

 

Oh well, if you must - if the 'designer' has any self respect he may have fiddled with the crank phasing to improve the firing interval, but so far as i can remember for the GM 90 deg V8 there was a very strong 1.5 order (and multiples) of inertial forcing, which made designing the engine mounts very tricky.I was working on the supercharged version, so that made the engine mounts even trickier. That was for the project which ultimately turned into the Catera - an attempt to import the Opel Omega into the USA. Replacing a nice little I6 with a firebreathing reject truck engine did not sit well with anybody, and in the end they went for a completely different, and equally odd, engine.



#3 NeilR

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Posted 03 July 2015 - 04:02

LOL, thanks Greg. I was looking at the PRV V6, which was originally intended to be a V8.



#4 Greg Locock

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Posted 03 July 2015 - 09:26

Thanks. I never knew anything about that engine. Interesting that they tried both even and uneven firing intervals, I'd really like to hear a comparison of those two alternatives. The cynic in me suggests the difference might not be night and day, as human ears aren't especially sensitive to phase at higher frequencies. I could synthesise the noise but that isn't the same.  It would also be confused by the different balance strategy , and hence inertial, properties of the two alternatives.

 

http://ranwhenparked...-engine-part-3/

 

It certainly powered some interesting cars... and some very dull ones.

 

Now all you have to do is explain why there is a DeLorean, A310 or XM in your shed.


Edited by Greg Locock, 03 July 2015 - 09:28.


#5 NeilR

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Posted 03 July 2015 - 11:35

Explain it? With that level of mechanical punishment ... well I have this strange fetish much like one Max Mosley but cannot afford the private services!



#6 J. Edlund

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Posted 04 July 2015 - 03:08

90 degree v6s-cut down V8s, are pretty horrible things, I doubt anyone still makes them, we  do not need to discuss them further.

 

Oh well, if you must - if the 'designer' has any self respect he may have fiddled with the crank phasing to improve the firing interval, but so far as i can remember for the GM 90 deg V8 there was a very strong 1.5 order (and multiples) of inertial forcing, which made designing the engine mounts very tricky.I was working on the supercharged version, so that made the engine mounts even trickier. That was for the project which ultimately turned into the Catera - an attempt to import the Opel Omega into the USA. Replacing a nice little I6 with a firebreathing reject truck engine did not sit well with anybody, and in the end they went for a completely different, and equally odd, engine.

 

90-degree V6 engines are still made. Audi uses it in I think all their V6 engines, and Porsche have an in house developed 90 degree V6 engine too.



#7 rory57

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Posted 04 July 2015 - 17:33

Four stroke six cylinder engines are all just a pair of (240° firing) three cylinder engines. 

From the point of view of the engine alone, they should have all their cylinders in a line, every other arrangement of six cylinders is a compromise.

 

However, compromise is what engineering design is all about.

 

Today's 90° deg. V6 engines have split-journal cranks, so they have a sort of 6 throw crankshaft. The two banks thereby are phased 120° apart for "even firing".

These crankshafts must be both weaker and more expensive than the true 3 throw crank of the "odd-fire" V6.

The 90° V6 has packaging advantages for an in-line installation, the 60° V6 has packaging advantages for transverse installation.

An advantage of the "odd-fire" V6s is smaller inertia torque peaks, (only one piston at TDC at a time). Another is that short, stiff, cheap, three throw crank.

The PRV V6 in it's "odd fire" forms is certainly not as smooth as other common V6s, but it is a tough old thing at heart.

 

The natural V angle for a V6 is 120°: even firing with all of the advantages of the simple 3 throw crankshaft.

Not as smooth as a flat 6 but a whole lot cheaper and more compact and smoother than any other V6. And almost never used for some reason.



#8 manolis

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Posted 05 July 2015 - 02:30

Hello Rory57

You write:
"From the point of view of the engine alone, they should have all their cylinders in a line, every other arrangement of six cylinders is a compromise."

The Boxer 6-cylinder (like those used in Porsches) is not a compromise, at least no more than the six-in-line. They are both even firing; and they have identical inertia force, inertia torque and inertia moment (versus crankshaft angle) plots.


You also write:
"The natural V angle for a V6 is 120°: even firing with all of the advantages of the simple 3 throw crankshaft.
Not as smooth as a flat 6 but a whole lot cheaper and more compact and smoother than any other V6. And almost never used for some reason."

As compared to the rest Vee-6 arrangements mentioned, the V-120 six-cylinder is not a good choice because it suffers from a very strong first order inertia moment and from a strong second order inertia moment.

As compared to a flat (boxer) 6, the only advantage of the V6-120 is the stronger and cheaper crankshaft. Their external dimensions are not so different (the one is a little longer, the other is taller) neither their complication.

While in the boxer-6 (or V180-6cylinder) the inertia moments from the two banks cancel perfectly each other, in the V120-6cylinder the inertia moments from the two banks are in phase, add to each other and generate strong vibrations.

Take a look at http://www.pattakon....attakonEduc.htm wherein various 6-cylinder arrangements are examined.

Thanks
Manolis Pattakos

#9 Lee Nicolle

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Posted 07 July 2015 - 08:25

Four stroke six cylinder engines are all just a pair of (240° firing) three cylinder engines. 

From the point of view of the engine alone, they should have all their cylinders in a line, every other arrangement of six cylinders is a compromise.

 

However, compromise is what engineering design is all about.

 

Today's 90° deg. V6 engines have split-journal cranks, so they have a sort of 6 throw crankshaft. The two banks thereby are phased 120° apart for "even firing".

These crankshafts must be both weaker and more expensive than the true 3 throw crank of the "odd-fire" V6.

The 90° V6 has packaging advantages for an in-line installation, the 60° V6 has packaging advantages for transverse installation.

An advantage of the "odd-fire" V6s is smaller inertia torque peaks, (only one piston at TDC at a time). Another is that short, stiff, cheap, three throw crank.

The PRV V6 in it's "odd fire" forms is certainly not as smooth as other common V6s, but it is a tough old thing at heart.

 

The natural V angle for a V6 is 120°: even firing with all of the advantages of the simple 3 throw crankshaft.

Not as smooth as a flat 6 but a whole lot cheaper and more compact and smoother than any other V6. And almost never used for some reason.

Apart from routine maintenance I have little experience with V6s. GM made at least 2, the one used in pre 06 Commodores that is at least in part a Buick V8 cut down. The original Buick had even crank pins, and viabrated BUT the Commodore [and others] version had offset pins and viabrated less!. Both little short stroke torquless things. And the offset cranks break when abused, even as a std engine. Then they used the alloytec,, a Saab!

The Chevvy V6, a cut down Small Block again is harsh but can be made to make a lot of power, and stay together. A friend had one doing 12 sec quarters in a full size Holden. Why? Who knows!

 

V6 Mitsis seem to be smoother, though several different styles and some are better than others. Short stroke, long stroke versions

Old V6 Camrys were junk, later ones seem just ok.

 

Apart from packaging a long six is defenitly a better deal. And will make far better torque too usually ,, long strokes ofcourse help. 

The Jap imports make stupid power with turbos and seem reasonably tough too. The 4 litre Ford turbo too is a very powerfull engine,, though when tuned to make more is a bit [lot?]  suspect. Reputedly though there is genuine 800hp ones used in drag cars. Why? To me easier to make 800 from a V8.



#10 MatsNorway

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Posted 07 July 2015 - 20:08

Just make a bigger displacement Straight five if the six is too long. Or do it properly like one the Nissan R35 has. (PS:Leased/rented Ford syl "liner" tech)


Edited by MatsNorway, 07 July 2015 - 20:08.


#11 Kelpiecross

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Posted 08 July 2015 - 03:19


I thought this was interesting:

http://www.leylandp7...b-v6engine.html

Apparently the old Commodore V6 is distantly related to the Rover V8.

#12 Catalina Park

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Posted 08 July 2015 - 08:02

I thought this was interesting:

http://www.leylandp7...b-v6engine.html

Apparently the old Commodore V6 is distantly related to the Rover V8.

Wow, there is some rubbish in that story. The only true bit was Leyland building the V6. The rest of it is rubbish.

#13 bigleagueslider

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Posted 09 July 2015 - 05:14

The I6 has advantages for production vehicles. It is smooth running and even firing. It only requires one cylinder head and intake/exhaust manifold. All of the block and head features are in-line and can be machined in a single setup.



#14 Kelpiecross

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Posted 09 July 2015 - 06:22

Wow, there is some rubbish in that story. The only true bit was Leyland building the V6. The rest of it is rubbish.


Specifically - what parts of the story did you think were rubbish?

#15 Catalina Park

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Posted 09 July 2015 - 11:30

Specifically - what parts of the story did you think were rubbish?

The sequence of events. The V6 was actually going to replace the I6 in the face lifted P76 and the P82 and there was also talk of a slant 4 based on the V8.

The idea that the Rover has a narrower vee angle than the P76, utter rubbish.

#16 Greg Locock

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Posted 10 July 2015 - 00:22

Almost every statement in that story that I knew about failed the sniff test.



#17 Kelpiecross

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Posted 10 July 2015 - 03:29

To be fair to the writer of the article - I am not sure he meant a narrower angle "V" (which would be a bit silly) but that the Rover V8 block was narrower overall. Presumably the Rover block was a bit narrower as it had a lower deck height than the P76.
This Wiki article;
https://en.wikipedia...Rover_V8_engine
appears to confirm the link between the Rover/BOP V8 and the Commodore/Buick V6.
Beside the point a little - but I owned a P76 V8 and I thought it was a great car - apart from tending to rust a lot and the glued-in windows falling out.

The historical links between very different engines is very interesting. I have read that the BMC A-Series engine was very much inspired by the Chev straight six of the 1930s.
Jaguar always swore on the bible that the XK engine was not a twin-cam version of the pushrod mark 4/5 engine - but if you work with both engines you find that the XK pistons and conrods fit the older ender without any real change (I seem to recall the Mark 5 cylinders has to be bored out 40 thou' or so)- so the two engines are not that much different.

Edited by Kelpiecross, 10 July 2015 - 03:31.


#18 Lee Nicolle

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Posted 11 July 2015 - 03:20

I have worked on or at least seem most of these engines in bits.

The VN engine is a Buick front drive engine.  The engine that has the thermostat housing at the BACK of the engine! Made in the US. The late VN-VR engines is a Holden redeveloped Buick. Harsh noisy torqueless thing. The earlier V6 Buick was developed into the late 80s engine. Quite a different version but same base engine and many things interchange, in fact some do with the 3500 Rover and the P38 4.4 too.

 

What was a mild performance series of engines seem to have been misused world wide!   The 215 was abused by Repco and Black Jack!

 

The Commy 3.8 was abused by Formula Holden!

Both broke a LOT of components, The Repco development is very well known and the V6 after the first meeting had to go too a steel single journal crank as they broke about 3 in the first meeting. They had already broken on the dyno too.

In speedway there is a categorie called wingless Sprints, WHY ? Sprints!, stock 3.8 VP VR engines. They are fairly reliable though oil pump seizure!! is common and timing chains have a very short life too.

 

The Ecotec used in VS VT VX VY is quite a different engine. More modern [again] castings though still the same basic design in bore centres, head bolt pattern, oil pump drive etc. Some items do interchange though very few are the same. Eg, alloy sump to stiffen the block in comparison to the tin one used earlier. The VZ onwards 3.6 engine is a Saab.

And if you ever believed the muttering rotters Leyland were going to win Bathurst with the Force 7 P76 Coupe. That was ofcourse dreamworld as the engine would never have been near powerfull enough. Nor reliable enough either. Probably 50hp down on the Holden that was lighter and pushed less air. Even in 5 litre [AFAIK never intended for road use] form such as Mc Cormack used in the 5000 they were not a nice engine but were lighter than the Holden. And 5000s did not do 500 mile raes!


Edited by Lee Nicolle, 11 July 2015 - 03:28.


#19 Catalina Park

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Posted 13 July 2015 - 10:05

Beside the point a little - but I owned a P76 V8 and I thought it was a great car - apart from tending to rust a lot and the glued-in windows falling out.

I was recently talking to one of the Leyland engineers from the P76 era, the glued in windows falling out was a real problem that took a while to sort out. They used a Bostick thermo electric bound sealer to bond the screens, it was like a ribbon of compound that was placed on the body then the glass was placed onto it and then it was heat cured into place by hooking some in built wires in the compound to a battery and it all sunk nicely into place.
The Bostick had to be kept refrigerated before use and this was where Leyland run into problems, the workers on the line didn't want to walk backwards and forwards to the fridge so they would just grab a whole pile and leave them in the work area.
The problem was solved by moving the fridge to the screen fitting area.

Holden had problems with the early HQs with the same type of sealer.

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#20 Lee Nicolle

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Posted 14 July 2015 - 03:27

I was recently talking to one of the Leyland engineers from the P76 era, the glued in windows falling out was a real problem that took a while to sort out. They used a Bostick thermo electric bound sealer to bond the screens, it was like a ribbon of compound that was placed on the body then the glass was placed onto it and then it was heat cured into place by hooking some in built wires in the compound to a battery and it all sunk nicely into place.
The Bostick had to be kept refrigerated before use and this was where Leyland run into problems, the workers on the line didn't want to walk backwards and forwards to the fridge so they would just grab a whole pile and leave them in the work area.
The problem was solved by moving the fridge to the screen fitting area.

Holden had problems with the early HQs with the same type of sealer.

The joke is Ford bonded their screens in too with the same kits. And seldom ever had a problem. HQ-WB flex real bad and break the screens loose all the time. Though modern urethane as used these days seldom causes a problem. That is IF the surround is properly clean.

 

as for those Bostick kits in the fridge?  I have done dozens of them and they never came from the fridge and there was no is no instructions to do so. I think I still have one in stock, only 30 years old, it will be good :stoned:



#21 Lee Nicolle

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Posted 14 July 2015 - 03:37

As for P38 engines,, they truly must be a Holden. When rebuilding the things the original pistons were very expensive and wear out quite quickly too for some reason. [I am sure they were made by Repco in the day as were most OEM in the day]

The 'gun' piston to use was 173 Holden pistons. problem was getting 6 cyl pistons in sets of 8! Though 2 sets were still far cheaper than 8 Leyland ones.

A friend owned a P76 and also his boat had one in it too [dont ask!]. I think he still has 2 in stock from 3 sets! so he can do you a deal!


Edited by Lee Nicolle, 14 July 2015 - 03:38.


#22 Catalina Park

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Posted 14 July 2015 - 11:19

as for those Bostick kits in the fridge?  I have done dozens of them and they never came from the fridge and there was no is no instructions to do so. I think I still have one in stock, only 30 years old, it will be good :stoned:

There was a difference between the factory bonding kit and the aftermarket one.
The factory ones would start to cure as soon at they reached room temperature.