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Pushrod vs Modern VVT DOHC engines? Which is better Really?

Discussion in 'Other Off Topic Forum' started by Z06Kal, Apr 2, 2004.

  1. Z06Kal

    Z06Kal Karting

    Nov 5, 2003
    154
    I have always been an AVID enthusiest of small displacement high technology engines. I used to own an Mr2 that put down over 400 crank have owned a Supra that put down 420 to the ground out of a 3L with factory turbo's etc.. I love all cars especially Ferrari so please don't see this as a marquee pissing contest. Rather its just a discussion of modern engineering progress in production engine design. This all started when a good friends of mine and I had an interesting conversation about today's state of the art naturally aspirated engines. 4 valves per cylinder and DOHC seems like standard issue for any high performance car but has all this complexity and inovations really yielded us serious benefits in the n/a world? On initial thought I said "OF COURSE!" without even thinking about it. I do drive a z06 but I bought it for bang for the buck I considered it a car that simply gets the job done without getting fancy or expensive. I never thought about how incredible the LS6 engine is when you compared it to manufactures I consider far superior like Honda. But as my friend and I started comparing modern DOHC's to this modern pushrod things started to get blurry. So let me go over what we talked about for some interesting food for thought arguments. Hopefully we'll get some good well minded posts going and not a bunch of mindless troll talk. Please let me know if my accuracy is off I tried to be as fair and accurate as possible.

    So lets compare the modern oldschool pushrod engine in the Corvette Z06 (LS6) to some of the best n/a engine builders in the world...Ferrari and Honda. Ferrari and Honda both have extensive F1 experiance which we would hope would trickle their way into production cars. With inovations such as variable valve timing etc the new designs should blow away the ancient old 2 valves per cylinder push rod engines away in EVERY way right? Otherwise Darwin would turn in his grave..progress must more forward....

    I decided to compare the Corvette LS6 to 4 cars I had solid dyno data from...the Ferrari 360 Modena the Ferrari 456M
    the Honda S2000 and the Acura NSX. The s2000 is one of the highest hp/liter production naturally aspirated engines in the world and so is the 360 Modena. I did not want to cover engines like the Enzo or F50 because I had no real dyno data and price is obviously a big factor in an engines power/weight as that will allow for more exotic materials. Considering an Enzo or F50 powerplant costs I'm sure around 100K I didn't really see its relavance in the general automotive world.

    Lets focus on Power/Weight/Fuel Effeciency/Cost and Physical Size. I won't look at displacement because if an engine is the same phsyical size and weight of a smaller displacement engine then clearly it is superior.

    Weight Fully Dressed:

    Corvette Z06 LS6 (5.7L V8) - 450lbs
    360 Modena (3.7L v8) - 370lbs
    456M (5.5L V12) - 518lbs
    NSX (3.2L V6) - 426lbs
    S2000 (2.0L I4) - 326kbs

    These cars are either mid engine/rwd or front engine/rwd so I'm going to assume that the drive train losses is pretty close for them all with a slight edge to the Modena and NSX for being M/R. I won't go by any factory engine ratings as factory numbers are hardly ever accurate. Ferrari Dyno data comes from this board.

    Average Power Output to the Pavement
    Corvette Z06 LS6 (5.7L V8) - 355rwhp/350tq
    360 Modena (3.7L v8) - 325rwhp/225tq
    456M (5.5L V12) - 370rwhp/360tq
    NSX (3.2L V6) - 260rwhp/200tq
    S2000 (2.0L I4) - 200rwhp/131tq

    Cars with much higher hp then torque numbers indicates peaky power bands which will effect the true usability of its powerband as well as track performance. S2000 for example has very poor corner exit acceleration due to a powerband where its making much less than its peak horsepower through its power band. THus peak numbers does not neccesarily indicate how usable the power band is on the race track.

    Power to weight:

    Corvette Z06 LS6 (5.7L V8) - 1.26 lbs per HP
    360 Modena (3.7L v8) - 0.88 lbs per HP
    456M (5.5L V12) - 1.4 lbs per HP
    NSX (3.2L V6) - 1.6 lbs per HP
    S2000 (2.0L I4) - 1.6 lbs per HP

    The simple Pushrod engine beats all but the 360 Modena in power to weight and loses only by a small margin of .4 lbs per hp. Also its obvious from anyone with experiance of the 360 and Z06 as to which car has a more usable and wider power band on the race track. Well worth the extra 80lbs.

    Now fuel economy is a very difficult thing to determine as the cars are all different weights with different aero. But I'll just post the numbers up.

    Corvette Z06 LS6 (5.7L V8) - 19 City / 28 Highway
    360 Modena (3.7L v8) - 11 City / 16 Highway
    456M (5.5L V12) - 10 City / 16 Highway
    NSX (3.2L V6) - 17 City / 24 Highway
    S2000 (2.0L I4) - 20 City / 26 Highway

    Now the hightech advantage gets even more blurry. The old fashioned engine is the most economical on long trips and in the city looses only to the little 4 cylinder honda by 1mpg.

    Physical Dimensions

    These were hard to come by and I couldn't find any information online as to exact dimensions. Clearly the LS6 is smaller than the V12 in the 456M in every dimension and from straight eye by eye comparisons it definately shorter in height from the crank to the top of the valve covers than all the engines mentioned (which is how it clears that super low hood in the C5 as no DOHC would be able to). This also has the advantage of bringing the center of gravity of the engine to a lower point in the car. Length wise it is also shorter then the 360's V8 and very comparable to the two Honda Engines (Probably within 6-10 inches). So clearly the LS6 is a very compact power plant (for those who have seen it out the car it is amazing how small it really is). Infact people put the same block (LS1) into Rx7's which indicates how small it really is. So for any car builder this would be a very easy engine to build a car around as well as bring the center of gravity for the engine to a much lower point in the car than the DOHC engines.

    Cost/Complexity

    With only 1 cam shaft and 16 valves the LS6 is a very simple engine with very few moving parts. Ask any engineer he will tell you that the fewer parts a machine does to get the same job done the better. This also of course lowers build/operating costs considerably. THe 456M has 4 cam shafts and 48 valves the 360 has 4 cam shafts and 32 valves. The Honda motors have a complex VTEC system. A crate LS6 shipped to your door will run you about $5300. I couldn't find any definiative figures for the other engines but I will assume an NSX engine will be in the $10-11,000 and that the Ferrari engines are considerably more. Even the S2000 crate engine runs in the ball park of $6000 new from factory.

    Reliablity well there are plenty of LS1's that have gone 200,000 miles. THe honda engines will go a long long way as well. The Ferrari engines need constant attention and their reliabilty long term is questionable but that is part of the mistisim of owning such a prestegious marquee.

    So basically all this modern technology and yet this old fashioned engine delivers a superior power to weight than 3 of the 4 engines mentioned in a smaller physical size with the lowest center of mass with better fuel economy at a cheaper build/operating cost with far fewer moving parts...How is this progress folks?
     
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  3. UroTrash

    UroTrash Three Time F1 World Champ
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    Jan 20, 2004
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    Valid point. Forget the Ferrari I'm getting a vette.


    Just kidding about the vette, but I do think your points are valid and can be applied to other areas of human endeavor as well. I have often thought similar thoughts considering longevity of "modern" vs older machinery design. There really is something to be said for stoutness and relative simplicity.
     
  4. FrostCS

    FrostCS Karting

    Mar 3, 2004
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    Christopher
    If you are looking for the most efficient engine, you should be looking more along the lines of horsepower per liter should you not?
    Looking at engine weights and dimensions is really more like poking manufacturers with a stick.. everyone has their own ways to cast/mold/form their engines. Also, as you increase the size of your engine, you are also decreasing the mass needed on a scale. A 2 liter engine will be composed of just so much hollow space, while a 6 liter engine would have much more hollow space. Meaning as the size increases 'normally' the weight to size ratio decreases, yes it will weight more, but it won't weight as much as three , 2 liter engines. Can't really use engine weights when comparing engines, unless you are asking yourself "What engine should I put in this car to make more power, and retain the same weight ratio?"
    Pushrod engines are known for the simple factor, to increase power, you swap out cams, or valves "basically". Which then you are arguing it with variable valve technology, which is designed to lower emissions, and yet, increase power at higher rpm's.
    Basically said, the easiest way to make power, is the most simple route you can take, which would be pushrod. However, your emissions would suffer, and your driveability would suffer. Which is why car manufacturers are opting for variable valve technologies, because most of these engines are produced for cars in countries with high emissions standards.
    There is interesting things to expect from variable valvetrain systems, since we haven't fully mastered it, and there is such a large frontier out there to explore still. GM has actually started with a line up of it's own vvt engines, and companies like BMW, Saab, Toyota, Mitsubishi, and Nissan have been experimenting with full electronic valve actuation (In mean terms, it would have unlimited tuning possibilies for the lowest costs).
    Pushrods are the cheapest to manufacture yes, but are they really the best for the longrun?..
    It doesn't appear so.
    CS
     
  5. Mojo

    Mojo Formula 3

    Sep 24, 2002
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    Joseph
    All I can say is I totally agree with you.
    The facts dont lie.
    Less expensive, more tourqe, less mantanance, Way better fuel economy.
    What can you say?
     
  6. Auraraptor

    Auraraptor F1 World Champ
    Lifetime Rossa Owner

    Sep 25, 2002
    11,392
    MO
    Some issues you forgot:

    How much does the engine weigh with all the added on periphennialia?

    Recall that in the case of the NSX, you are now running off of a comparitively 'old' design for CAMs. The NSX lacks some of the things that would otherwise be present, such as variable value timeing, and a more dynamic variable cam timing...all which would help power. Compare the 97 NSX to the vette engine in 97. (which was really just a tweek in 97, and the heart is still a 91 engine design)

    Same with the 456M. A 575 would have been a better camparo. Same thing, Compare the 98 456M (which like the NSX was really just a tweek, with the heart still a 92 design) to the vette engine in 97.

    Yes, your figures say that the new line of engines are better then the older designed engines. I would like a year to year comparison.

    The key:Was the same year vette a better engine in 91 (NSX), 92 (456), or 97 (minor tweek of the NSX)?
    And..Is the Zo6 a better engine then the current line of 575 engines? (NSXs are making a new engine soon in the new car?


    This data I would be interested in personally.
     
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  8. Nibblesworth

    Nibblesworth Formula 3
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    Nov 29, 2002
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    The biggest advantage to a pushrod motor is valve train stability. A big second is mutiple intake/exhaust valves per cylinder. Although there have been a few 4-valve pushrod engines, none of them were "economically viable", and building a DOHC is much more efficient.

    Anyways, in regards to valve train stability, consider all the points of contact in a pushrod motor, as well as the total distance that force travels. Camshaft lobes push tappets, which push on the pushrod, which push on the rocker arms, which push down on the valves. An OHC motor has camshaft lobes pushing on tappets, pushing on a valve. Much less surface contact, much less friction. The ditance the force must travel in a pushrod motor is greatly increase by both the rocker arm and the pushrod. The creates an instability in pushrod motors at high RPMs.

    If you'll notice, there are very few 6500+ RPM pushrod motors on that market. Reason being, it takes a lot of extra money to make a pushrod motor reliable at those high RPMs, although it can be done.

    Italian motors, and most European motors, for that matter, and Japanese motors, use tiny displacement motors for a myriad of reasons. Regardless of the reasons, in order to get power from these tiny motors, RPMs are used to replace what is lost via small displacement. As a result, most of them use OHC configurations, because they need high RPM power reliably.

    American engines, however, evolved using high-displacement motors. As a result of the massive low end torque and decent mid range HP created, no need to high-RPM applications were needed. Because of this, American pushrod technology is incredibly advanced (hence, the Z06), and Japanese/Italian OHC techonology in equally advanced.

    Now, to decide which one is better, do a test.

    Take a 6.0l V8, and test it with OHC and pushrod technology. I would assume, all else being equal, that a DOHC 6.0l V8 woud out-perform a 6.0l pushrod V8.

    Just my thoughts.....
     
  9. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    6,997
    I will come back later with a point by point analysis on this issue. However, under almost any reasonable* street applications, the pushrod motor of relatively larger displacement is better, and better because of torque not power; torque that gives it not a power peak, but a power plateau.

    *SuperCars and near SuperCars are hard to catagorize as reasonable street applications to begine with.
     
  10. Artherd

    Artherd F1 Veteran

    Jun 19, 2002
    6,588
    Bay Area, CA
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    Ben Cannon
    DOHC and 4 (or 5) valves/cyl will always make more than a comprable* pushrod motor.

    If this were not the case, then F1 would run pushrods. They owe no aligence to any particuliar technology, they are out to win races.


    *an 8 litre pushrod motor is NOT comprable to a 3.5litre DOHC v8!

    GM has done some amazing engineering in the LS6, that is withought a doubt.
     
  11. Paul Vincent

    Paul Vincent Formula Junior

    Apr 3, 2004
    474
    If the pushrod engine is superior than the overhead cam engine, then why is the 2005 Vette (with its low coefficient of drag) only capable of 180 mph? Would not a 5.7 or 6 liter ohc engine push the same Vette to a much higher top end? If the pushrod engine is superior to the ohc engine, then why in 2004 can't GM get as much out of its pushrod engine as can be gotten out of the ZR1's LT5 engine (essentially a 15 year old design)? If pushrod engines are superior to ohc engines, then when will the next pushrod engine win the open class at Le Mans (I think the last time was in 1969)? Don't dohc engines make for better looking engines? By the way, I love the Vette and applaud its success, but it would be even better with a 6 liter version of the LT5.
     
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  13. Mojo

    Mojo Formula 3

    Sep 24, 2002
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    Joseph
    These are all valid points, But the bottom line 405HP and 400 on torque
    Now heres the kicker, ya its more cubic inches and get 28mpg hwy.
    Just think about that. Unbelivable.
     
  14. Mr Payne

    Mr Payne F1 Rookie

    Jan 8, 2004
    2,870
    Bakersfield, CA
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    Payne
    Pushrods are good because of the ultra low production cost (350hp LS1 in the 02 Z28). Has there every been a motor of that power in a car of that price EVER? Simply put, Detroit pushrod engines allow huge power (for N/A standards) with not much cost. With LS6 buildups making 470rwhp N/A and Vipers much more than that, can anyone say it is possible to get an N/A DOHC engine to a comparable power level at a cheaper price? It is not possible. Only when forced induction is in an equation is it possible to compete with the current crop of pushrod engines. Personally, engineering prowess has always meant getting the most results using the least amount of resources. This is what pushrods excel at.
     
  15. Aureus

    Aureus Formula 3

    Gearing. The ZR1 was designed and built to have a high top speed, so it’s gearing reflects that. The 2005 Vette is not designed to sacrifice acceleration for top speed, as the Z51 was.
     
  16. Paul Vincent

    Paul Vincent Formula Junior

    Apr 3, 2004
    474
    Well, if that is so, then how come the standard Vette has a terminal speed that is greater than that of the ZO6? The ZO6 is drag limited; it is not gear limited. I've read several times that if it had the power, it would be capable of well in excess of 200 with its gearing. I think that if the pushrod engine would build power to a higher rpm, that the Vette would climb higher than 175 - 180 mph. Look, I'm not arguing that the Vette's engine isn't wonderful (I've wondered about putting one in a '94 RX7), but what I am saying is that the trade off is there (low end torque in spades, but a reduced capability to run top end).
     
  17. 69stanger

    69stanger Rookie

    Nov 30, 2003
    31

    the ZR1 cost nearly twice the price of a base C4 when it came out, the Z06 on the otherhand cost only a couple thousand more than a base C5.

    also about the comment of why most pushrod engines do not rev past 6.5K rpm is because they dont have too. The 5.7L engine in the Z06 porduces lots of low-end torque do to its large displacement, the 3.6L in the modena on the otherhand has to be revved very high to compensate for a lack of torque.
     
  18. Paul Vincent

    Paul Vincent Formula Junior

    Apr 3, 2004
    474
    Mr. Payne, The Ford Mustang Cobra (yes, I know that it is super charged) develops more hp that the Vette/Z28 engines at at least as good a price (cost per hp of the Cobra is as good as that of the Z28 and better than that of the Vette), and it allows for greater hp increases for far less money. Also, to read/hear the dissatisfaction of Vette owners concerning their current hp deficit ("only 400 hp for the C6?"), I can't believe that too many of them look at the limitations of the pushrod engine as being desirable. Yes, I'll concede that the pushrod engine helps keep the Vette affordable, but if Ford can put a sc dohc in a Cobra for $34,000, GM could also make one available in an affordable Vette (it might change much about the Vette, but it could be done).
     
  19. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    6,997
    The Z06 is REV limited in 5th geat in the low-to-mid 170s, and has such a tall 6th gear that even with the massive TQ of the LS6 it cannot pull 6th gear for more speed.

    The Coupe is rev limited in the low 180s in 5th gear.

    The problem is that 6th gear is set for economy and would rev out in the 240-250 range.

    The Z06 runs out of 4th gear in the high 120s and 5th gear in the low-to-mid 170s.
    The F355 runs out of 4th geat in the low 120s, runs out of 5th gear in the low 150s and holds 6th gear to its power limited 183 top end.
    IF the Z06 gears were chosen to run out of 4th in the 120s, then run out of 5th in the 150s and have a 6th gear set to rev out at 200, it could push (arguably) into the high 180s or low 190s.

    If someone can make a production street pushrod engine rev (and breath well) to 8000 RPMs, all of the SOHC and DOHC street engines would simply become extinct. But as hard as they try, the materials and production techniques simply are not capable of this outside of a race engine. The single valves are too big and heavy, the rocker arms are hard to stabilize at high RPMs, the pushrods and hydraulic lifters comprimize valve timing.
     
  20. PSk

    PSk F1 World Champ

    Nov 20, 2002
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    Not sure about that Mitch. I think manufacturers like Toyota and Honda have got the cost of over head cam engines pretty sorted now ... and that would be the only reason you would resort to pushrod engines.

    With the emissions and economy being so tight, manufacturers need really tight valve timing and control, you just cannot get that with a pushrod engine.

    Now that overhead cam engines have hydraulic lifters too, there is no maintenance hit like there used to be.

    I even think my Toyota Tarago (people move) is twin overhead cam and 4 valves per cylinder, and all it gets is 10000 km oil changes, etc.

    Why Chev sticks with the pushrod I do not understand ... saying that a v8 with overhead cams is a lot more complicated than a straight engine ...

    I think that Chev is the only manufacturer that still produces pushrod engines ???, man that would make a good add ... NOT!

    Pete
    ps: The Ford Ka might still have pushrods ... ?
     
  21. triXXXter

    triXXXter Formula Junior

    Nov 11, 2003
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    Its lots of factors I'm sure but he's what I see.

    Trying making the LS6 fit in an Integra? It's still a big motor. For a lot of countries there cars have to be small. So small higher reving engines are needed to fit and still make good weight balance.
    True the LS6 gets good gas mileage. That's what they have engineered 6th gear for. But get on it and really start running it then to the same to the S2000 and see which one uses the most gas. I'm pretty sure you won't be seeing any Pushrod/electric combo motors.

    Engines have advanced to OHC I think for size and engine placement reasons. Pushrods require a big motor for that power they make. like it's been stated already, Pushrods are not reliable at higher RPM (7k and up).

    Plus correct me if I'm wrong, but there is a lot less control over ignition and spark timing than with a DOHC.
     
  22. PSk

    PSk F1 World Champ

    Nov 20, 2002
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    Not sure what you are saying here?, but in many cases the dizzy is driven off the camshaft, whether a pushrod or overhead cam motor ... thus no difference regarding ignition timing.

    I think many modern engines use a flywheel sensor anyway ...

    Pete
     
  23. triXXXter

    triXXXter Formula Junior

    Nov 11, 2003
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    ok ok sorry I ment control of Valve opening and closing times.

    still may be wrong.
     
  24. Mr Payne

    Mr Payne F1 Rookie

    Jan 8, 2004
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    Forced induction always allows better gains per dollar. I readily concede that. The 2.0L S20DET, 2.0L 4G63, 2.0 3SGTE, 2.6L RB26DETT, 3.0L 2JZ-GTE, and the 3.8L V6 single turbo in the buicks/pontiacs (arguably the best GM engine ever made in power production) all post monster numbers for not a lot of $$$. Of course, the new 03 Cobra brought it to a new level. In fact, forced induction always beats out N/A in power production.

    Of naturally aspirated engines. The current pushrod lineup can not be beaten in power production and the cost it takes to make that power. That is engineering.
     
  25. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    6,997
    When the hydraulic tappets collapse, you do loose valve timing accuracy. However, you loose it in a predictable way, and a way that is good for emissions. You loose timing in the overlap region, thus reducing hydrocarbons in the exhaust.
     
  26. Z06Kal

    Z06Kal Karting

    Nov 5, 2003
    154
    Actually the new Corvette's are actually ULEV compliant (unlike Ferrari and many other high performance OHC engine makers). So that throws out the emissions argument also look at the fuel economy...

    Because if you bothered to read what I wrote the LS6 makes great horsepower and torque with a better power band, in a ultra light engine that is short enough height wise to clear the corvettes narrow slope hood and also short enough length wise to be mid mounted behind the front wheels. Pair that with great fuel ecomony and super cheap production costs and why would they use anything else? It is more powerful than the engine in a 360 Modena or BMW M3 at a near identical weight with a smaller physical size and lower center of gravity (mass of the engine is at the bottom of the car) while being ULEV compliant and getting 28mpg. Oh yea and the cost for a consumer like me to have it crate shipped to my door step is around $5200. So you can imagine what it costs chevy to produce it.
     
  27. Chevarri

    Chevarri Formula Junior

    Jan 20, 2003
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    My freind downloaded a program that will tell you how fast a car COULD go based on its gearing. Lol, if it had the power the Vette is capable of(if I remember correctly) 277mph! The 6th gear is in classic GM fashion, an economy gear. Thats not to say the LSx series engines aren't very good at saving gas/efficent at what they do (they are a very well designed motor), but the final gears help quite a bit. The Richmong trannys they use the 5th and 6th are BOTH overdrives.

    The ZR1s were intended for High Speed, and sacrifice some accel for that.
     
  28. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    6,997
    It does NOT have a lower center of gravity than the 360 engine. In fact, the valve train in the 360 is at the same vertical height off the road surface as the cam shaft in the LS6. Now, it the LS6 were given a dry sump, it could be lowered 5 full inches and then take the advantage.

    It is more powerful in either metric, however it is 1.58 times as big and only has 1.01 times as much HP!
     

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