TTAC commentator edgett writes:
Since the current pushrod LS-X engines reportedly offers a better power-to-weight ratio than an equivalent Porsche engine, and returns excellent fuel economy, why aren’t other manufacturers emulating the same kinds of evolutionary upgrades which GM applied to their small-block V8?
Sajeev answers:
Naturally aspirated Porsche boxers may be lighter than an LS-X, but don’t bother comparing their power bands (i.e., area under the curve). The Porsche turbos are comparable, but weight is not their friend.
But your question is kinda wrong: all manufacturers apply evolutionary upgrades to their motors. It is do or die, even if GM Powertrain couldn’t save the Mothership from bankruptcy. But I digress. The LS-X thrives with fewer and lighter materials, lower center of gravity and abundant torque from a physically simple design with massive displacement: even with (fuel economy) taller gearing. Plus, they are cheap to make and getting more common in junkyards.
Which makes for a great power/economy combination in Frankenstein heart transplants. [If the Houstonian who owns the LS-6 powered Porsche 914 is reading: I want a ride in your car. E-mail me.] Speaking of evolution, wait until the LS-X gets direct injection and/or variable valve timing like its competition. They could be unstoppable, if GM Powertrain gets the money to make it happen. Start holding your breath . . . NOW!
Bonus! A Piston Slap Nugget of Wisdom:
The LS-X’s modern OHV architecture is the key to its success. Yes, I said “modern.” The 1949 Kettering/Oldsmobile OHV V8 is some 50 years newer than Karl Benz’s Boxer, 30-ish years newer than the first OHC motors. Just remember that when someone says that Detroit V8s are ancient dinosaurs.
[Send your technical queries to mehta@ttac.com]
How about a 911 with a Chevy smallblock?
Sajeev I think LS series engines already got variable valve timing. If not the LS, I’m sure the HEMI got. If Chrysler did, GM should be near.
Sure, they may not be available at the junkyard, but it’s a matter of time.
I’d like to see this slapped into them:
http://www.araoengineering.com/Chevy/chevybb.htm
And, check this:
http://www.hotrod.com/techarticles/engine/hrdp_0902_motown_ls_engine/index.html
Not including AFR heads, STS turbos, conventional twin turbos, racing blocks, and a long long etc…
I’ve seen pics of them swapped in almost everything. Even Mustangs =)
On Mr. edgett: every manufacturer does. Quick example: Mitsubishi’s 4G63 engine, VW TDI, Porsche’s boxer. An engine represents a HUGE investment and pays more to evolution it than make one from scratch every 5 years for example.
I love engineering variety, love high-tech stuff, but I believe that having too broad a variety of engines (pushrod AND OHC AND others) within one manufacturer’s lineup has an eventual impact on the customer’s experience.
With all due respect to dealer service technicians out there, wouldn’t the customer’s service experience tend to be better if the people servicing the vehicles don’t have to know all of the possible variations of engine architecture?
On the other hand, Volkswagen (for the most part) uses a fairly common design for all of its engines, and also suffers from abysmally low dealer experience scores. But I’m not sure if that has so much to do with service experience as it does with the one for sales.
Just remember that when someone says that Detroit V8s are ancient dinosaurs.
When did reciprocating mass cease being a problem?? I don’t see anyone in the various F1 engine departments trying to use pushrods.
“When did reciprocating mass cease being a problem??”
A DOHC V-8 engine has four camshafts and the gears/sprockets to drive them. A cam-in-block V-8 has one camshaft. The reciprocating mass of a well designed cam-in-block V-8 is much lower than for a comparable DOHC design.
F1 engines are built to run at insanely high RPMs where push rods are a problem. F1 design criteria has just about nothing to do with the demands place on normal road cars.
PeteMoran:
Ever so slightly different design objectives & constraints yielding different outcomes.
Sajeev,
It is interesting that you cite Porsche. They have applied untold engineering and design hours making an essentially unstable basic design, (ie. rear engine, hung out behind rear axle) into one of the most admired and best perfoming cars in the world. I find it a shame that Porsche dumbs down its likely more capable car, the Cayman/Boxster, for marketing purposes. Given the same drivetrains of the 997 it would likely clean house. The 911 devotees and Porsche designers are prisoners of the cult of the 911. Even the new Panamera suffers from awkward styling as result of this misplaced “brand heritage.”
GM has spent 60 years fine tuning the 90 degree V8
Nascar still uses pushrods. 9 grand all day long.
I thought GM was becoming the electro-green hybrid battery car company? Has Obama been notified they have V-8 engines still?
The King will not be pleased
GS650G: Nascar still uses pushrods. 9 grand all day long.
Oh, yes, the pinnacle of technology. Or they were when they stopped allowing development 40 years ago. Pushrod engines, carburetors, live axles and square-tube roll cages. Oh, wait, that wasn’t modern even in the 1960s.
Do you really think Toyota would have developed a cast-iron pushrod engine for NASCAR if it didn’t have to?
@ John Horner
Eh? Is that without the pushrods themselves? Have they become toothpicks while I wasn’t paying attention?
I have a Popular Mechanics magazine somewhere with an exploded (as in “diagram”, not “bang”) 2L DOHC I4 comparing it against one bank of a pushrod V8 (both Ford I think). The DOHC value-train parts were significantly lighter.
@ rm
Engine guys I deal with say that you wouldn’t start a clean-sheet design using pushrods. I’ve dealt with a few over the years, from Briggs & Stratton all the way to Wartsila.
GM/Ford/Fiatsco’s use of the design is about existing tooling and R&D cost. So the key constraint is “cost”, nothing more.
“why aren’t other manufacturers emulating the same kinds of evolutionary upgrades which GM applied to their small-block V8?”
The LS_X engine actually was more of a revolution than an evolution, compared to the original small block chevy.
If you are asking about pushrod engines then there are really only two companies still using them, GM and Chrysler. Ford abandoned the pushrod engine in the 1990’s, mostly for marketing reasons in my view.
Both GM and Chrysler are making constant improvements to their pushrod engines. GM has applied variable timing to the Vortec V8 truck engines, and Chrysler made variable timing available on some Hemi V8s this year. The Viper V10 has had variable timing for a while. Variable lift might be more difficult to accomplish on a pushrod engine. However, direct injection is not going to be any more difficult with an OHV (overhead valve / pushrod) engine than with an OHC (overhead cam) engine, and displacement on demand (running on 4 or 8 pistons) is easier with an OHV engine. Both GM and Chrysler offer displacement on demand with their OHV engines.
Both OHV and OHC engines have reciprocating mass issues, and reciprocating mass is not the same issue at 19,000 RPM as it is at 7,500 RPM. F1 is becoming much more like NASCAR, basically a spec series with huge technical restrictions. If F1 was unlimited, like in the past, the debate would not be between pushrods or overhead cams, but between cams or no cams at all.
OHV and OHC are both very old technologies; both use ancient cams instead of more advanced methods of moving poppet valves up and down, and it is a bit embarrassing that both haven’t been replaced yet.
For the things that matter for a street engine – power, torque, outside dimensions (not displacement except in countries that tax it as a very poor proxy for fuel economy), weight, and fuel economy – OHV vs. OHC does not matter nearly as much as the fine tuning and development of the particular engine.
Nascar still uses pushrods. 9 grand all day long.
When you analyze the data, those engines get zinged to 9 grand for about 10 seconds per lap. Even with that, hundreds of thousands of dollars are spent on development each year to keep the pushrods inside the valve covers.
Johnny Canada :
July 14th, 2009 at 9:45 am
Nascar still uses pushrods. 9 grand all day long.
When you analyze the data, those engines get zinged to 9 grand for about 10 seconds per lap. Even with that, hundreds of thousands of dollars are spent on development each year to keep the pushrods inside the valve covers.
And, how long do any race engines run without being torn down and rebuilt? Top fuel dragsters are torn down and rebuilt during an event. NASCAR engines might last a few races in between rebuilds. What happens in F1, Indy, CART circuits?
All racing engines take a beating. Using racing engines to make points about street going vehicles seems kind of silly to me.
I recall that OHC engines enjoy this advantage over pushrod engines. An OHC engine can be smooth from idle to maximum engine speed, but a pushrod engine will have a lumpy idle if it is designed to be smooth at high rpms or will have a smooth idle, but will be rough at high engine speeds. Is this so? Furthermore, because European and Asian vehicles typically have small-displacement, four-cylinder engines and must be revved high, car makers favor OHC engines. A big, lazy engine doesn’t need OHC if the maximum engine speed is low.
wait until the LS-X gets direct injection and/or variable valve timing
The intake and exhaust are on the same cam, so the benefits of variable phasing are dimihshed compared to DOHC with full on discrete phasing for intake and exhaust. How much that limits the beneftis is not something I could speak on.
I guess it is possible to make a dual cam-in-block setup with seperate phasing but that could be complex. Also the valvetrain mass is still a problem with OHV, as well as optimal valve angles being limited by the geometry of the design.
Not that OHV isn’t still a viable design notable for its great power density.
SLLTTAC : I recall that OHC engines enjoy this advantage over pushrod engines. An OHC engine can be smooth from idle to maximum engine speed, but a pushrod engine will have a lumpy idle if it is designed to be smooth at high rpms or will have a smooth idle, but will be rough at high engine speeds. Is this so?
In certain situations…ones that rarely involve street cars that pass Government mandated restrictions.
Counterpoint? Go drive a new 7.0L Corvette Z06.
Tell me how rough that idle is compared to a 911 Turbo, and THEN go zing it up to 7000rpm.
Stingray : Sajeev I think LS series engines already got variable valve timing. If not the LS, I’m sure the HEMI got. If Chrysler did, GM should be near.
Chrysler did it on the Viper V-10. GM did it on their 60-degree V6s. Direct injection is more important (to me) than VVT on an LS-X, but who knows when either will show up given GM’s current situation.
Certain versions of the 5.7 liter Hemi have variable valve timing for 2009, in addition to cylinder deactivation:
http://www.reuters.com/article/pressRelease/idUS141622+07-Jan-2009+PRN20090107
The 6.2 liter GM Vortec OHV V8 has had variable valve timing since 2007:
http://en.wikipedia.org/wiki/GM_Vortec_engine#6200
According to Autoblog:
“While installing the VVT system on a single-cam OHV engine doesn’t offer up any adjustability of intake/exhaust overlap timing, it should be noted that simply advancing or retarding the overall valve timing can have significant effects on an engine’s powerband, as hot-rodders have known for decades. Typically speaking, advancing the cam timing offers more low-end power, while upper-end performance benefits from retarding camshaft timing. I’m sure that GM employs this system in other ways as well, such as to improve cold-start emissions.”
http://www.autoblog.com/2006/02/21/gms-l92-and-ls2-v8-engines/2
Which makes sense, since there are also single overhead cam (SOHC) engines with variable valve timing.
The Viper V10’s Variable Valve Timing actually uses a cam within a cam so that exhaust timing can be changed independently from intake timing:
http://www.sae.org/automag/technewsletter/070402Powertrain/04.htm
Direct injection is sure to come.
Speaking of evolution, wait until the LS-X gets direct injection and/or variable valve timing like its competition.
I’m surprised that Dart, Edelbrock, or the other aftermarket companies haven’t developed a DI head for the original small block Chevy V8.
Is the OP’s increased p/w spec just because of lighter block materials, like Al-alloy?
(doesn’t the Z06 have one?)
I always thought that Porsche engines always had the highest hp/l spec of any prod. car, even in Naturally Aspirated version. -like 100hp/l and over, esp in the GT3.
It’s funny to hear that OHC is actually the same vintage or older than OHV, because the latter always seemed more primitive.
@John Horner: I thought that since a great deal of it moves symmetrically around the rotational center, most of a camshaft’s mass is considered Rotating, not Reciprocating (ie: like a piston or conrod)
-But otherwise yeah, 4x the weight in camshafts. Ask any VW 16V or 20V owner about the stress that puts on timing belts and tensioners.
(though multivalve heads are nice w/o the rocker arm+pushrod steampunk;
-right up until the belt breaks, and they are multi –bent– valves! :P )
willman:
Porsche probably had the most absolute HP per liter in a production car at certain points in history with its 911 Turbo engines, but I doubt that Porsche has ever had the most HP/Liter in a naturally aspirated engine. Honda, BMW and Ferrari usually trade that title around.
@no_slushbox: Oh, ok. -I read the ~114/l at one point for the GT3, and had thought that was tops.
I know Honda did like 108+ in the s2000 and BMW did ~107 in the E46 M3; -but what were some of the other high marks?
—
*Hey! -> Post Idea for Piston Slap: “HIGHEST EVER N/A HP/L SMACKDOWN!”
The original S2000 was a 2l. motor with 237 hp. After 2004 they added 200 ml but did not increase the nominal hp.
With respect to the 911, isn’t it’s single largest advantage weight transfer during braking? As in the braking force is more evenly distributed between the front and rear wheels?
Of course, the flat engine helps here as well with its low center of gravity.
A few months back Hot Rod did a comparison test of a series of crate motors using a ’70 Chevelle. That was a seriously interesting article. I kept thinking about the LS engines as possible aircraft powerplants. Even the LS-9 is cheap compared to a garden-variety Lycoming 0-360. Of course you need to work out cooling and deal with a PSRU (prop speed reduction unit) to keep the prop from going supersonic at max output….
Ronnie Schreiber :
I’m surprised that Dart, Edelbrock, or the other aftermarket companies haven’t developed a DI head for the original small block Chevy V8.
There is so much more to DI thank just putting the injectors into the head. The entire fuel system is different the engine control system is vastly different, even the pistons are different. It really isn’t in the scope of an aftermarket company to do.
Sorry, this is long….
I’ll quote from Keith Duckworth, the guy who invented the modern cylinder head. The book is “Cosworth” by Graham Robson. Pages 81 and 82.
“The hemispherical head was correct many years ago, when engine strokes were very long, and the compression ratio you could get on available fuels was fairly low. Therefore, with a flat topped piston, and two large valves fitting nicely into the chamber, and a spark plug fairly near the center, you got rather a nice chamber. Flame travel near the plug was good, and the whole chamber was a nice shape.
Once bores starting getting bigger, and the usable compression ratio went up, then people started adding lumps to the top of the pistons, and if there was a 90 degree included valve angle, what remained was really a pent roof chamber anyway. The chambers became orange peel shaped with pockets in the side of the pistons.
Even the first 4-valve engines of the 1960s which were motorcycles (and Honda did an F2 engine to compete with our SCA) still had 80 or 90 degree included angles.
When I came to design my first 4-valve head, I looked around and said, ‘Well, hemi heads, they should have been turfed out years ago, they’re wrong, and those angles are all wrong’. My criteria were that I didn’t want any surplus combustion chamber area, I wanted to use a pent-roof combustion chamber with the valve angles adjusted to make a flat top piston reasonable at a compression ratio of about 10:1.
It means that I am responsible, by a completely original piece of thinking, for the modern narrow angle 4-valve head..”
Can’t do it with pushrods. Can’t get the cylinder filling with only two valves, can’t match the gentle acceleration of the valve train with OHC, so can’t get the low overlap, thus can’t get the bmep or specific fuel consumption. Just ain’t possible. Sure, you can fiddle about with a two valve head and make it very good, maybe better than a lackadaisical OHC design.
My dream is seeing what a Toyota Tundra 5.7 liter V8 would do for a Corvette. Because it makes a 5700 lb 4wd truck get a 14.7 sec quarter mile. That’s power. And I bet it would get better highway mileage idling along in sixth.
Unfortunately, as Duckworth is deceased, he is no longer available to argue with armchair experts! I recommend the book highly. Get a copy, it’ll broaden your engine knowledge horizons. Pushrods will allow sufficient revs for a civilian engine, but they cannot match the combustion chamber efficiency allowed by a narrow angle 4-valve head and overhead cams.
Heck, even the new EX stationary one lunger engines Subaru makes for generator/industrial duty (Trademarked as Robin, robinamerica.com) have an OHC and 4-valves. Don’t think they’re doing that just for fun. First listed feature? “Pent Roof Combustion Chamber”. Nice cutaways, too, and power curves going only to 4000 rpm.
wmba : My dream is seeing what a Toyota Tundra 5.7 liter V8 would do for a Corvette. Because it makes a 5700 lb 4wd truck get a 14.7 sec quarter mile. That’s power. And I bet it would get better highway mileage idling along in sixth.
The only reason the Tundra does that well is with its 6-speed tranny and AWD. Put a 6-speed in the Chevy truck, and I betcha the numbers will be similar. Except they won’t, because the engine is lighter, smaller, has a lower center of gravity and costs far less to make.
wmba : Unfortunately, as Duckworth is deceased, he is no longer available to argue with armchair experts! I recommend the book highly. Get a copy, it’ll broaden your engine knowledge horizons. Pushrods will allow sufficient revs for a civilian engine, but they cannot match the combustion chamber efficiency allowed by a narrow angle 4-valve head and overhead cams.
That book is old, and Duckworth would have a tough time fighting the the CFMs that flow out of an LS7’s heads. I wish I remembered the actual CFM, but the number was unbelievable for a pushrod motor that passes EPA tests…and its right on par with production 4v heads.
Times have changed, that’s all there is to it…
Styles79:
“It really isn’t in the scope of an aftermarket company to do.”
I don’t buy this argument, at all. Where’s your proof?
Hydrodynamic modeling packages in the $10K range can turn any M.E. into a DI genius in a year or two. The aftermarket heads will come, however, initially we won’t gain no-throttle designs, that will come after the aftermarket injection heads are perfected, and they can justify aftermarket piston design.
They can easily start out with any current DI design’s pistons to get a start with the software.
Nope, sorry, just don’t buy it. It will just take a bit before the first systems arrive.
@Sajeev:
Don’t forget that the Tundra 5.7L V8 runs a 4.30 final drive ratio. I bet that’s the biggest for the Tundra’s crazy times.
The Ram 1500 is usually stuck with either a 3.55 or 3.92. Except for the Ram R/T which gets 4.10 gears. It runs a 14.3 quarter mile with a 5-spd.
The 6.2L Sierra and Silverado have a 6-speed transmission and run just a few ticks slower than the Tundra. Amazingly they only have a 3.42 final drive. A 4.30 on the GM trucks would make them leave everything for dead.
@ Aqua225
Sorry, perhaps I should’ve been a little more expansive on that, and said it’s just not in the scope of aftermarket companies at the moment, hence the fact that they have not been developed yet.
I just don’t think that an aftermarket head company is likely to see a return on getting into DI work for a very long time. Redesigns of extant DI heads perhaps, but all new DI systems for old (non-DI) engine designs I just don’t see paying off. I don’t think the market would be big enough for the developer to get a return, and the massive cost of the componentry to set DI up on an engine wouldn’t make it worthwhile for the engine builder/owner. I see this being the case for the near-mid term (the next 10-15 years), after that, who knows?
wmba:
Don’t buy your argument either, however, in my explanation, I will say I am a CPE, not a ME.
All 4 cycle ottos have valves in the heads. A camshaft in the valley can always drive those valves at any angle. Period. There is no “magical” OHC driving ability for the valves, just easier angles. There may be weight penalties, but in general, high RPMs are useless unless you plan to dog the car and ring it out for every little need for power. Which is ridiculous and uncomfortable to me (personal desire really influences this choice). My LS1 pushvalve motor an make just about anyone grin.
OHV (but not with a OHC) designs tend toward two valves due to size, complexity, and upper limits on lobe strengths on the cam itself. What GM engineers have found (and other OHV engine manufacturers), is that you get better fuel mixing in a port injection or carb setup at the ports of a OHV engine (or even a 2 valve OHC design), which will typically mean more low end torque (except for Ford, who has totally screwed the pooch in the 4.6L design, the thing has no low end torque, despite having only 2V/C).
Over the years, car lovers were influenced by the Germans and Japanese though, that to get into a high rev region with a small engine, you had to go to overhead cam design. This was true for a while, until material science brought the weight down on the old pushrod valve train.
Now, for the regions a passenger car operates in, there is no real advantage to the OHC. If anything, its a disadvantage — requires belts or long chains, which are more prone to breakage and catastrophic engine damage. Notice I am NOT saying this can’t occur in a OHV engine either, but simple physics says a shorter drive chain for the valve gear is a distinct advantage in reliability.
Even better though — if you have a OHV design that you need to go into the stratosphere, you just put a big turbo on it, because nowadays, you can trust the valve train to track the cam shaft in a OHV, even at high speeds. Put a turbo on there, and there is no advantage that the DOHC screamers can possibly claim. Not only will a large displacement small block OHV beat a DOHC on low end torque normally aspirated, but turbocharged, and you are really getting into ridiculous power levels that traction becomes the key player in.
If you want to see what OHV is capable of in racing extremes, check out the mercedes V6 turbo they ran in Indy for exactly one year before all the bars were lowered to keep the motor out.
A stock block V6, that had a OHV design, could turn 11.5KRPM ALL_DAY_LONG. Except it didn’t need too. I believe little Al got to drive the thing that season, and he drove at the top of the pack at about 8.5KPRM ALL_DAY_LONG, and then embarassed the field when he turned up to 11.5KPRM for the final few laps of the race. The motor had so much extreme power, there was absolutely no competition that year for their car. Most of the technology they built the OHV valvetrain with in that engine is still “classified” under numerous patents and trade secrets.
The only reason OHC is so popular, is that it is (or was, I should say), cheaper to build, and made the mechanics who had to work on them a lot cheaper.
Nowadays, there isn’t an advantage in production cars.
Finally, I have to agree with a previous poster: F1 is a bum sport, like nascar now. It used to be where all the cool stuff was, now its where all the rules are. I miss the heady days of 4 cylinders with a 1000bhp/L specific outputs, traction control, abs, and other engineering marvels. F1 made the mistake of thinking they needed to keep the bar low to get in, and killed the interest in the sport for gearheads like me.
wmba, I will admit you are correct that the 4 valve pent roof combustion chamber is a “better” cylinder head design, but you need to look at the engine as a whole and actually the whole vehicle system as a whole. The LS series (and the modern Hemis) use essentially pent roof combustion chambers.
More valves do give you more valve area, but you need to think how useful that is. Notice how all the variable valve lift systems (VTEC, etc) increase the valve lift at high rpm and load? If maximum flow was always better, at highway cruising and maximum power, why don’t they always run the valves at maximum lift? Or on the old DOHC ZR-1, they only flowed to one intake valve during highway cruising for fuel economy reasons, if max flow was always better why did they not use both intake valves for highway cruising? Essentially, for low RPM operations, you want to restrict the flow for optimum fuel economy.
Lets go to my point at looking at the vehicle as a whole system. I will grant you the DOHC advantages, but pushrods have advantages. I do not think they are inherently lighter than DOHC, just because the LS series are so light, does not mean pushrods are inherently lighter. They are more compact in both width and height, they also have a lower cg. When the C5 corvette was being designed they had to make a decision if they wanted a DOHC engine. They figured a DOHC engine would be 100lbs heavier and in vehicle design for every lb of engine weight, the entire vehicle weight goes up by 2 lbs. So the corvette would weight 200lbs more pounds. Another factor was they would need to accommodate a wider engine. During the build of the vette, the chassis is lowered onto the engine, so the frame rails need to be wider than the engines. A DOHC engine would mean the frame rails would have to be farther apart, this would impact the suspension design forcing the upper control arms to be shorter or the car to be wider. Also a taller engine would raise the hood. If the hood was raised, the driver would have to sit higher. If the driver sits higher, the roof needs to be higher. All of this increases the frontal area, which would increase the drag. The corvette has a very low frontal area for a front engine car, just compare it to the GT-R. Then there is the cost, the pushrod motor is cheaper to build than a DOHC. Sure the Northstar works in the corvette, but is it is a very compact DOHC engine because of its origins on FWD Cadillacs, but it is more expensive and heavier than the more powerful LS engines.
Aqua225:
The advantages of pushrods fall away with inline engines, so for the common inline 4, DOHC makes much more sense. On a V8 you get to put the cam in the valley between the two banks, an inline engine really loses the packaging advantage because the cam and the pushrods start to take up useful space. Sure you have a shorter chain or belt, but have added all these extra parts compared to a OHC design.
The indy engine you mention was not a “stock” block by any defintion expect the rules. It was a full on race motor, they just found a loop hole in the rules that allowed larger displacement if the engine used pushrods, so they designed a pushrod motor. It had nothing to do with inherent advantages of the pushrod design, it had to do with the rules.
Didn’t say it was a “advantage” of the pushrod in terms of design. However, it was a definite advantage that year: it allowed them to run higher boost. All the other manufacturers had abandoned pushrod motors for the appeal of the DOHC, and mercedes proved beyond a doubt that they were all wasting their time.
Not only will a large displacement small block OHV beat a DOHC on low end torque normally aspirated,…
Not sure if I’m misinterpreting what you’re saying here. But a 2v design in of itself does not produce more torque than a 4v configuration –all things being ~ equal. I think it’ a myth because larger OHV engines are being compared to smaller DOHC engines. Producing power is mostly about getting air + fuel through the combustion chamber, and a 4v head DOHC generally does this better than the 2v design of the OHV engines, so it will generally produce more torque and hp across the rpm band.
Compare the same displacement 3.3L engines …(from a few years ago) …
Dodge Caravan 3.3 OHV (2v) … … 180hp/210 ft-lbs @ 4000 (torque)
Toyota Sienna 3.3 OHC (4v)… 230hp/242 ft-lbs @ 3600
The Sienna engine has a higher compression ratio (10.8 vs 9.3) which accounts for some of the difference. But nevertheless, the 4valve design produces better torque, and will do so basically across the rpm range. The only way to compensate for that is to give the OHV 2v design a larger displacement. This is typically what GM was doing, selling a larger ~ 200hp 3.8 OHV versus 200hp+ 3.0 OHC-4v designs from Japan. At a certain point, the increased displacement of the OHV engine will produce more torque, but you’re then comparing a substantially larger engine displacement to a smaller one.
Most of the 2v OHV designs like GM’s 2.2l, and the V6’s simply weren’t competitive against the competitors 4v DOHC designs. And there were a lot of poor performing 2v OHV engines, like the 2005 Dodge Durango which had a 4.7l V8, rated 230hp. Less than DOHC 3.0l V6’s, although more torque.
In this edmunds dyno test, the Silverado 6.0-liter L76 V8 against the Tundra and Tiatan, the L76 was easily out-powered at 5k rpm or less by the DOHC 4v engines. Is the L76 being run at lower power levels because the cam-in-block setup can’t dissipate heat from that area of the engine in a heavy running (towing) environment..????
I’ve also heard complaints that many OHV engines don’t have as good NHV (noise, harshness, vibration) as their DOHC counterparts. MT complaned that the Malibu V6 was “a bit thrashy” at high rpm.
That being said, GM has done an excellent job with its V8 OHV designs. And their smaller displacement V8’s like the 4.8l in the Silverado are excellent engines for their purpose. In a sports car like the Corvette, yes these engines can be made to produce good power with big heads, valves, high-lift, but in some respects they are not as good a DOHC setup.
@ Blastman
Great post. Thanks.
It would be interesting to see the Caravan/Sienna engine weights. I might have them in a data book somewhere, but I’m guessing the materials are different anyways.
ajla : Don’t forget that the Tundra 5.7L V8 runs a 4.30 final drive ratio. I bet that’s the biggest for the Tundra’s crazy times.
The 6.2L Sierra and Silverado have a 6-speed transmission and run just a few ticks slower than the Tundra. Amazingly they only have a 3.42 final drive. A 4.30 on the GM trucks would make them leave everything for dead.
Well that is quite interesting! And that explains the GM’s ability to better the Tundra (4wd to 4wd) by 2 MPGs on the highway.
@Blastman:
And there were a lot of poor performing 2v OHV engines, like the 2005 Dodge Durango which had a 4.7l V8, rated 230hp. Less than DOHC 3.0l V6’s, although more torque.
The Chrysler 4.7L V8 is a 2v SOHC design.
___
Also, from that Edmunds dyno test article you linked to:
“As it turns out, the explanation boils down to an engine calibration strategy. GM calibrated the 367-hp 6.0-liter V8 to remain in stoichiometric “closed-loop” fuel delivery mode for 4 seconds after the throttle is floored. This fueling strategy helps keep emissions in check (and saves fuel) at the expense of reduced power — about 40 hp less at the peak. Once the driver lifts his right foot from the wide-open throttle position, the 4-second clock resets.”
So it sounds like GM hamstrung the truck L76 (for three seconds) for environmental reasons- with disastrous results.
I know that the auto L76 that goes in the G8 GT doesn’t suffer from this, and I’d bet if you look at a dyno graph of the LY6 6.0L that goes in the Silverado 2500 (and isn’t calibrated this way), the lines would be comparable to the Tundra’s V8.
@ ajla
So it sounds like GM hamstrung the truck L76 for environmental reasons- with disastrous results.
No, Edmunds say that the engine still delivers the advertised power, just with the 4-sec behaviour. So the graph would not change. I wonder where-else GM use that “trick”.
“The Chrysler 4.7L V8 is a 2v SOHC design.”
Good catch! You are indeed correct. I always think 2v = OHV these days. It’s still a good example of a 2v engine not producing near the power one would expect for that displacement and compared to a 4v design.
” I know that the auto L76 that goes in the G8 GT doesn’t suffer from this, and I’d bet if you look at a dyno graph of the LY6 6.0L that goes in the Silverado 2500 (and isn’t calibrated this way), the lines would be comparable to the Tundra’s V8.”
The L76 in that Silverado does seem to be hamstrung somewhat. But why? Problems of the 2v -OHV design meeting high power and emission requirements at the same time? I don’t know, the 2v could be drawback here. You could be right about a better calibration producing better power below 5k, but I still have doubts that the L76 could completely match the torque numbers of the Titan/Tundra below 5k rpm.
@Robert Schwartz: Aha!!! -I think i used the 239/2.2 for my s2000 guess.
So, that puts the 237/2 s2000 above the GT3 @ ~119hp/l.
Thx; Good info!
This has been one of the most enjoyable threads on TTAC.
BTW, does anyone read TDC, Kevin Cameron’s column in Cycle World? He routinely writes about all sorts of deply technical subjects in an exceptionally clear manner. I bring it up because a few months back he was writing about the evolution of pistons and engine design. It was a very interesting read. One point he made was that the limiting factor in OHC engine design is piston acceleration resulting from material strength. Good stuff.
chaparral66 : and
Aqua225:
The loop hole described was the amount of boost allowed for DOHC vs. pushrod. Chaparral is correct, it was just a case of mercedes finding a loop hole in the rules that had never been shut bc it was assumed that no one would ever go back (was originally done for teams running the old Buick V6’s I believe). Similar to what F1 was trying to do with giving the low-budget teams a variable wing, it wouldn’t matter what the high budget teams did, they couldn’t compete with that. The differential in boost allowed meant that no matter what was done with an OHC engine within the rules there was no way it could compete with the pushrod in that situation (personally the most boring Indy500 in history)
Interestingly,
Corvette Coupe LT1 6.2L V8 (pushrod)
Power: 430 @ 5900 RPM
Torque: 424 @ 4600 RPM
C-Class C63 AMG Sport Sedan 6.2L 451 hp V8 (OHC)
Power: 451 @ 6800 RPM
Torque: 443 @ 5000 RPM