Point/Counterpoint: DOHC v OHV

[Paul Workman]

i agree with Mike and Dom and others re their comments and observations relative to the advantages and power delivery of the DOHC vs. OHV. Faced with the superiority of the DOHC architecture, how much longer can GM continue to attempt to mitigate those advantages and embrace what is clearly become a 'damage control' effort (with the OHV architecture)?

Millions was spent on development of the new OHV LT1-4 motors. But, out of the box track performance (and reliability too) has been marginal. And, how much is GM going to bank on the C7's chassis improvements to save the bacon of their latest OHV entry? (Without even touching on the huge swell of reliability issues with LT4's heating PR catastrophe).

In spite of GM hoopla (and excuses), the acid test is going to be performance against European and Japanese in the theater of racing. In view of initial performance (or lack thereof, relative to the latest OHV entries) one has to wonder if we are seeing a repeat of GM's mentality when it stubbornly held to the L98 as being sufficient for Corvette buyers. Or, is there real hope to see an all-out focus on performance as the primary objective?

In the mean time, I've no fear of any match-up with any stock cammed stock-bottomed LS1, or 6.2L LS2, or 3 (LS7s?...maybe them as well, in the right venue?). Just crossing my fingers that GM will endeavor to build a motor and (GT) Corvette capable of the kind of 'take no prisoners' type of car the ZR-1 was when it hit the pavement!

EDIT:

I concur w/ Dom's focus on the MM endeavor. However, that effort (last we saw it) was very preliminary; no variable cam/valve timing or direct injection - IIRC. So, that would also need to be considered.

For example, Ford and Mercedes has a pretty good examples of where DOHC might be had GM continued to develop it (C-link).

[KILLSHOTS]

Originally Posted by edram454

???? what is he talking about?? decided to feel??? the lt5 did pass the 200 hour durability test and did set the record at nearly 176 mph for 24 hours. You dont have to feel it. It is what it is. How about the lt4?? Has it done anything or set any records?? I am perplexed to hear people trying to poke holes in the lt5 on this forum. This is one place I thought that most people would be in agreement but guess not. If its a joke I dont get it. whatever.

Has it done anything or set any records??

The LT platform in the C7.R, which was co-developed with the 2015 Z06, won the Triple Crown of endurance races this year: Rolex 24 At Daytona, Mobil 1 Twelve Hours of Sebring and 24 Hours of Le Mans. According to Chevrolet, “the C7.R and the Z06 represent the closest link in modern times between Corvettes built for racing and the road, sharing unprecedented levels of engineering and components including chassis architecture, engine technologies and aerodynamic strategies.” So yes, the new LT platform has done something. But these facts are easy to escape: just FEEL that Chevrolet is lying about the close link between the production LT4 and the LT in the C7.R.

I have always loved and respected the LT5 as a nearly-bulletproof masterpiece, and I think there’s no question that the DOHC architecture is superior and will re-emerge when the small block has finally reached its limit, technologically. But I continue to assert that if the internet and the various Corvette forums that we frequent today existed back in 1990, we would have all heard instantly about the few LT5 failures that occurred and there would have been at least a few people FEELING that the LT5 is unreliable, despite its performance during the record run.

[spork2367]

Originally Posted by Paul Workman

i agree with Mike and Dom and others re their comments and observations relative to the advantages and power delivery of the DOHC vs. OHV. Faced with the superiority of the DOHC architecture, how much longer can GM continue to attempt to mitigate those advantages and embrace what is clearly become a 'damage control' effort (with the OHV architecture)?

Millions was spent on development of the new OHV LT1-4 motors. But, out of the box track performance (and reliability too) has been marginal. And, how much is GM going to bank on the C7's chassis improvements to save the bacon of their latest OHV entry? (Without even touching on the huge swell of reliability issues with LT4's heating PR catastrophe).

In spite of GM hoopla (and excuses), the acid test is going to be performance against European and Japanese in the theater of racing. In view of initial performance (or lack thereof, relative to the latest OHV entries) one has to wonder if we are seeing a repeat of GM's mentality when it stubbornly held to the L98 as being sufficient for Corvette buyers. Or, is there real hope to see an all-out focus on performance as the primary objective?

In the mean time, I've no fear of any match-up with any stock cammed stock-bottomed LS1, or 6.2L LS2, or 3 (LS7s?...maybe them as well, in the right venue?). Just crossing my fingers that GM will endeavor to build a motor and (GT) Corvette capable of the kind of 'take no prisoners' type of car the ZR-1 was when it hit the pavement!

EDIT:

I concur w/ Dom's focus on the MM endeavor. However, that effort (last we saw it) was very preliminary; no variable cam/valve timing or direct injection - IIRC. So, that would also need to be considered.

For example, Ford and Mercedes has a pretty good examples of where DOHC might be had GM continued to develop it (C-link).

First off, these are all OHV engines....

But comparing pushrod V8's to OHC V8's (whether single or dual cam) isn't a clear cut "this is better and here's why" comparison.

The configuration is largely irrelevant as long as Chevy and Dodge are still putting out pushrod OHV engines that are every bit the equal, if not slightly superior to Ford's modular OHC engines. Let's face it, if someone can build a pushrod engine for a top fuel dragster that makes 10,000 HP, the cam configuration and pushrods aren't the limiting factor. And with variable valve timing we can now compensate for a lot of factors and make a single cam do what it never could in the past.

Direct injection and variable valve timing are far more relevant than cam architecture at this point in time. After that the market is banking on forced induction V6's.

[Paul Workman]

Originally Posted by spork2367

First off, these are all OHV engines....

But comparing pushrod V8's to OHC V8's (whether single or dual cam) isn't a clear cut "this is better and here's why" comparison.

Really? Can you provide data of examples where a NA OHV motor of comparably equal technology and displacement demonstrates equal peak power and superior power under the curve while maintaining a smooth idle? (I referenced the Mercedes M156 6.2L NA as an example of like displacement with like technologies - i.e., cam phasing, etc., and there are others. Example? For example: can you support your claim of comparable OHV being superior to a 25 year old LT5 across the rpm spectrum with a smooth idle?) Point/Counterpoint.

Originally Posted by spork2367

The configuration is largely irrelevant as long as Chevy and Dodge are still putting out pushrod OHV engines that are every bit the equal, if not slightly superior to Ford's modular OHC engines.

*..."engines that are every bit the equal..."*

Showing us the data to support that claim (w/ comparable displacement) would help to provide some validity to that statement...

Originally Posted by spork2367

Let's face it, if someone can build a pushrod engine for a top fuel dragster that makes 10,000 HP, the cam configuration and pushrods aren't the limiting factor.

How do those very special application BLOWN motors (rebuilt every 1/4 mile run) have any relevance to the architecture discussion at hand??

Originally Posted by spork2367

And with variable valve timing we can now compensate for a lot of factors and make a single cam do what it never could in the past.

Granted, VVT is a modern asset to OHV. However, it is even more of an asset to DOHC architecture as the exhaust valve timing can be independent from intake cam lobe timing. Point/Counterpoint.

Originally Posted by spork2367

Direct injection and variable valve timing are far more relevant than cam architecture at this point in time. After that the market is banking on forced induction V6's.

Well, I refer (again) to the example of the DOHC Mercedes NA M156 which shares those same technological advances AND displacement with GM's current OHV NA LT1. I dunno, but most of legit true apples to apples comparisons of DOHC vs. OHV, proving superiority of the latter is pretty thin in the evidence side of the argument.

Far as blown V6's goes, one only has to see one of the 1/2 mile or 1 mile shootouts to see the truth of "If you ain't blowin, you ain't goin!" But, those kick-*** Nissan V6s are also DOHC, by the way... But, as Mike already said, hybrids w/ electric FWD may be what really makes DOHC moot - to your Point/Counterpoint.

[32valvesftw]

One of the pros to the DOHC, is that one can use a more aggressive cam grind and still maintain a good idle.
One of the Cons of the DOHC is that the engine even though it is very well designed is not as simple to work on as a pushrod small block. Assuming you don't have 17 miles of hose and tube on your pushrod V8. What I am referring to for one thing is valve guide seals, with a SBC you can fairly easily change them with the engine in the car.
They say push rod engines make better torque, however I do not understand the physics involved with that assumption. I think it goes back to the cam grind utilized in the DOHC engines and stroke of the engine.

[XfireZ51]

Can someone name a modern day GM Powertrain motor which is NOT a V8 and NOT OHC?

[edram454]

the ls engines will keep making power by increasing power adders, turbo, twin turbo, twin superchargers and ramping up boost until the actual materials wont hold. From what I have seen as soon as they starting ramping up power they start adding better internals so it will stay together. At some point I would hope they would entertain the dohc technology and try to get more power that way and not rely so much on just adding boost. Every auto maker is guilty of adding boost to achieve there horsepower goal.

They might consider the camless engine. Using the computer to electronically open and close the valves. This has been something Lotus was trying to develop but at the time there wasnt a device that would open and close the valves fast enough. This was something Dave McLellan spoke about in his book. Camless?? 1 cam, 4 cam and no cam.

ed ramos #3028

[Paul Workman]

The "Waxer vs. Warrior" question.

I was shocked to learn that as many as 1/3 of ZR-1 drivers have never bumped the rev limiter. And, some admit to never exceeding 5500 (!!) rpm! That being the case, unless balancing a nickel on its edge while sitting on the plenum of an idling motor is what excites them, things like which architecture affords what advantage...is pretty moot. Might as well drive a "Dunwoody Cruiser"! (Our Atlanta friends know what I mean! But, translating for those not from around there, think of the movie National Lampoon's "Family Vacation" and the Family Truckster. That car...driven by soccer moms in tennis outfits)

http://www.autoblog.com/photos/family-truckster/

[spork2367]

Originally Posted by 32valvesftw

One of the pros to the DOHC, is that one can use a more aggressive cam grind and still maintain a good idle.

I'm curious as to what you basis for this comment is?

Originally Posted by Paul Workman

Really? Can you provide data of examples where a NA OHV motor of comparably equal technology and displacement demonstrates equal peak power and superior power under the curve while maintaining a smooth idle? (I referenced the Mercedes M156 6.2L NA as an example of like displacement with like technologies - i.e., cam phasing, etc., and there are others. Example? For example: can you support your claim of comparable OHV being superior to a 25 year old LT5 across the rpm spectrum with a smooth idle?) Point/Counterpoint.

You're trying to make too many comparisons with too many variables. You throw out the Mercedes M156, a small production engine and compare it to an assembly line chevy motor that they make probably 10 times as many of. No, there isn't a fair comparison out there. The LT5 was a small production, hand built engine with tight tolerances and materials that weren't cost effective to bring to base corvette.

*..."engines that are every bit the equal..."*

Showing us the data to support that claim (w/ comparable displacement) would help to provide some validity to that statement...

Closest comparison I could come up with is Ford DOHC 5.4 (lincoln navigator version) vs Chevy 5.3 (truck version). Both have a flat torque curve that makes peak torque that starts at about 2800 RPM. However, the Ford drops off at 4800 RPM while the Chevy holds max torque until 5600 RPM. Both obviously have smooth factory idles. Do I think this is a completely fair comparison? No. There is no data that allows me to say they were shooting for the same goals when they built the engine and that was the best they could do.

How do those very special application BLOWN motors (rebuilt every 1/4 mile run) have any relevance to the architecture discussion at hand??

It seemed like you were implying that the architecture was a limiting factor in some way. If that wasn't what you were saying, ignore that.

Granted, VVT is a modern asset to OHV. However, it is even more of an asset to DOHC architecture as the exhaust valve timing can be independent from intake cam lobe timing. Point/Counterpoint.

Could be done with purpose built hydraulic lifters. It just isn't at this point because it isn't cost effective.

Well, I refer (again) to the example of the DOHC Mercedes NA M156 which shares those same technological advances AND displacement with GM's current OHV NA LT1. I dunno, but most of legit true apples to apples comparisons of DOHC vs. OHV, proving superiority of the latter is pretty thin in the evidence side of the argument.

I'm not claiming one is ultimately superior to the other. They both have their advantages. People in here want to use the reliability of the LT5 as a a defense for DOHCs, but that is nonsensical. The LT5 was reliable because it was hand built to close tolerances using materials that were designed for ultimate reliability. That fact remains that a DOHC engine has far more parts than a pushrod engine. That inherently makes them more prone to failure. If I went out and built an LS1 with aluminum block, aluminum liners, nikasil plated them and the aluminum pistons..etc. You'd have a motor that was more reliable than even an LT5. Why doesn't Chevy build that? Not enough people are going to pay $15,000 more for a corvette because the engine lasts for 250,000 miles instead of 150,000.

Far as blown V6's goes, one only has to see one of the 1/2 mile or 1 mile shootouts to see the truth of "If you ain't blowin, you ain't goin!" But, those kick-*** Nissan V6s are also DOHC, by the way... But, as Mike already said, hybrids w/ electric FWD may be what really makes DOHC moot - to your Point/Counterpoint.

ROI

For the couple hundred or couple thousand people who want a flatter torque curve, with a dead smooth idle and 8000 RPM top end, Chevy isn't going to spend 500,000,000 dollars to retool a plant to build a DOHC V8. And they would piss off more Chevy diehards than they would win over.

You could put the average corvette driver behind the wheel of a 1996 Grand Sport and a 1995 ZR1 and they wouldn't be able to tell you how they felt different. They are selling to the people who are one standard deviation from the center of the bell curve. ZR1 owners are two standard deviations out and Chevy will likely never build an engine that we think would be comparable to the LT5.

[Meanmyz]

Originally Posted by spork2367

You could put the average corvette driver behind the wheel of a 1996 Grand Sport and a 1995 ZR1 and they wouldn't be able to tell you how they felt different.

I am lucky enough to own both a 1996 Grand Sport and a 1995 ZR-1. I sure can tell you the difference between the two... One has a good engine. The other one does a pretty good impersonation of sex (what is that?), but with your cloths on!