Re: Point/Counterpoint: DOHC v OHV
 

They will be forced to someday by emissions laws. It helps to have two cams per head that can phase exhaust and intake separately to control overlap and therefor cylinder pressure. There has been some though of the camshaft going extinct if some kind of electrically actuated valve technology ever becomes reliable. This will make the argument on how many valves per cylinder rather than cams, but I would venture that the lighter the valve, the better.

Some of this tech will probably preclude engines from going much over 6000 rpm, but if you are torque blending with an electric assist, stored mechanical energy (like KERS), turbos, and all of this, why would you need high rpm? VW used to make a supercharged and turbocharged engine in a very small displacement, but stopped due to costs I think. The days of big inch lumbering NA engines are not long. Maybe in trucks for a bit longer...

Re: Point/Counterpoint: DOHC v OHV
 

But you aren't the average corvette driver, as is evidenced by the fact that you are here on this forum being part of this discussion. :)

Re: Point/Counterpoint: DOHC v OHV
 

Very true! :cheers:

Re: Point/Counterpoint: DOHC v OHV
 

I know that GM tried to put out the message that the LT-4 was "very close" to the LT-5 for performance. I don't buy it for a second. The 4s may have been a strong SBC and EVEN IF they had similar #s, where those peaks took place is vastly different. That's where the rubber meets the road. Its why we wave bye bye to the LT-4 after the first 1/8th mile. As Paul keeps saying, its not the peak number but the area under the curve, and the LT-5 covers a lot more of the real estate on a dyno chart.

Re: Point/Counterpoint: DOHC v OHV
 

Yeah, but it will be in a V6 with a turbo. They aren't likely to pay to costs to design an all new V8 when it won't meet emissions in another 8 years.

And for the average corvette driver, it was. I understand the advantage of the LT5 vs the pushrod engines of the same era, but most corvette customers didn't want to pay for it then, and wouldn't want to pay the premium today if the same technological advances of today were put in a new engine. It's the same reason Porsche built air cooled SOHC flat 6 engines into the late 90's.

That being said, there is not a car with a DOHC engine today in the same price range as the corvette that can trump it. Keep in mind, the LT5 wasn't really the king of the hill in its day. There were faster production cars. F40s and 959s were both faster in acceleration and top speed.

There is a reason there are more mustangs than corvettes, and more corvettes than ferraris. Price. And there is no return on investment for Chevy to retool a plant to build an advanced DOHC engine and bump the price of a corvette up 25% or more.

If there were enough valid counterpoints supporting a DOHC V8, they'd be making one today.

Re: Point/Counterpoint: DOHC v OHV
 

That is sad and probably true. And, you wonder why it should have to be like that. Today's engine's are the cleanest and most efficient they have ever been.

I am with letting the technology take us there through free enterprise and competition...NOT being forced there by a socialistic overreaching big government. ...eh, I have too much to do to get started on this topic, so I won't.

Re: Point/Counterpoint: DOHC v OHV
 

Most torque under the curve for the future...:(

Re: Point/Counterpoint: DOHC v OHV
 

Makes as much of soundtrack as me riding my bike.. Just not cool lol.


Big lumbering engines are imo the direct result of a pushrod architectures limitations. Specifically the single cam. You just can't make an engine with a single cam have a smooth idle.. Torque down low for fuel economy (classic pickup truck formula) and make a high hp number up top that makes an excellent hp/L statistic.

Case in point the Ls7. Huge potential ? Yes because it's 7L. Oem cams have a wide lsa because that one cam has to try and do it all. Want to chase 650-700hp? We're talking a pretty big cam with a choppy idle that sounds like a farm tractor missing a spark plug. Compared to say the F12s v12. Oem form.. 730hp from 6.2L. 505 from 7L. That's a 225 hp difference. The Ferrari v12 is Complex, expensive and spins to the moon which isn't a formula that works for pickup trucks so it's not a path gm chose to follow.

Re: Point/Counterpoint: DOHC v OHV
 

And the v12 torque curve sucks.

Re: Point/Counterpoint: DOHC v OHV
 

Definitely subjective .. But to me I don't care for down low torque. It's not needed. Gearing can give you torque , but can't give you hp. With the right gearing that 510lvs -ft can easily equal a higher torque motor at the tire. For me that torque curve is beautiful !! All that torque up high .. Where the motor will remain under wot through the gears is all that matters to me. If I was towing a trailer.. Sure give me an ls7. If I had a 4000lb pickup .. Sure give me an ls7. For my kind of sports car.. Give me that v12 any day of my life.

My Lt4 I built is a 370ci solid roller.. Makes peak torque at 6400 and peak power at 7400. Idle ? Well I hate choppy idles.. But I'm going to be on the receiving end of that idle lol. What this motor will give me is smiles from 6-8500rpm !! :-D
Would I have rather built an LT5? I think the answer Is obvious !

Re: Point/Counterpoint: DOHC v OHV
 

Sure, but that pretty much craps all over the argument for why DOHCs are the greatest thing ever for the V8.

Re: Point/Counterpoint: DOHC v OHV
 

One funny example I like to use is the L98 c4. Those guys will tell you for days that it's a 'torque monster' and then you should see their faces when they get pulled by a Honda S2000 with enough torque my lawn mower wouldn't even be jealous. Torque from a big cube pushrod motor to me is a recipe for good low speed torque via displacement , excellent fuel economy and greater service life due to low Rpms.
All of which is a formula for gms bread and butter .. Pickup trucks.

Re: Point/Counterpoint: DOHC v OHV
 

That fancy 320k F12 takes 3.6 seconds to make it to 60...:sleepy1:

:)

Re: Point/Counterpoint: DOHC v OHV
 

Which is why I think the 2013 60th Ann. 427 car will be highly collectable. Most likely the last BB Corvette ever produced.

And I wouldn't trust either one of them to get me to the grocery store and back let alone go on a road trip. But I guess that's beside the point...

Re: Point/Counterpoint: DOHC v OHV
 

[QUOTE=spork2367;230703]I'm curious as to what you basis for this comment is?

the OHC arrangement allows for a faster acting valve train, and I think it allows for less overlap. It is overlap that gives the radical cam its lump. Here is a pretty good reference
https://books.google.com/books?id=Dy...ofiles&f=false

Re: Point/Counterpoint: DOHC v OHV
 

The reasons for the tight LSA IS FOR "up top" breathing. But the downside of a tighter LSA AND MORE OVERLAP is a lumpy idle. The 4valve eschews all of that because the 4 smaller valves have more area than the two big ones, therefore there is less lift and duration required. If you look at the LS motors, they had LSAs in the 112-114* range to give a smooth idle and for emissions. BUT they had very high lift. At slow engine speeds that works, but higher revs required lots of energy to move the more massive valves. The 4 valve has less inertia, lighter valve train which is why the valve seat pressure is so much less in an OHC configuration. It also eliminates the pushrod flex present due to transmitting motion in nearly a 180* direction. As Mike pointed out, the twin cam also allows for higher variability in cam phasing whereas the in block cam has a cam phasing that is cast into it(unless you're using a more complex cam ala the Dodge Viper). So the single cam tends to be more of a compromise, although for trucks it's great. The reason OHC make power up top is because they can. The LT-5 was at ~ 5500rpm for over 24hours in the record run. The valve train for the most part was languishing. An OHV config would be much closer to its breaking point at that level. An F1 is turning 15-20k for an hour. Funny cars and dragsters blow up in a matter of seconds.

Re: Point/Counterpoint: DOHC v OHV
 

Compared to say the F12s v12. Oem form.. 730hp from 6.2L. 505 from 7L. That's a 225 hp difference. The Ferrari v12 is Complex, expensive and spins to the moon....



How many Ferrari's do you see with 100,000 miles on them?

How many Ferrari's have set an International Speed Record?

How many Ferrari's change their own oil or work on their engines?

How many Ferrari's are even around from the early 90's?

Nuff said.

Re: Point/Counterpoint: DOHC v OHV
 

It was more of a comparison of dohc vs the ls7 which is pushrod. I believe Ferrari had a failed attempt at the zr1s records ? I believe it was the 550 maranello or maybe the 575 I can't recall. They had tire issues and had to cancel.

Anyhow my thoughts on dohc are this.. Imagine gm chose to continue the LT5 to this day. It sure as hell would have made more than 505hp. I'd have to guess with no bore spacing limitations, dry sump , huge heads, direct injection and 7.0L.. I'd have to say 600-650 hp would have been easily possible in oem pussycat form ? Maybe the c7zo6 wouldn't be suffering thermal issues with a dohc NA motor instead of a pushrod with a blower on top.

Re: Point/Counterpoint: DOHC v OHV
 

friend of mine puts ~10,000 a year on his RedHead. It's a fairly reliable car for him. The reason most ferrari owners don't do their own work is that other ferrari owners want to see records of maintenance from Ferrari dealerships. They don't want to see that Joe's house of tires and waffles fixed a flat or remounted a wheel. It's stupid but when you're dealing with a xx,xxx engine repair bill I can see why they're like that. Of course we're not that far off if you have to send your car out for work.

Re: Point/Counterpoint: DOHC v OHV
 

Big Block?

Re: Point/Counterpoint: DOHC v OHV
 

Im surprised nobody caught it sooner. BB?

ed ramos #3028

Re: Point/Counterpoint: DOHC v OHV
 

thought that was standard short hand.

Re: Point/Counterpoint: DOHC v OHV
 

Although it's a 427, that doesn't make it a big block. It's still an LSx block just a bigger bore. I may be oversimplifying it.

Re: Point/Counterpoint: DOHC v OHV
 

fair point, well made and nicely presented. I'd forgotten that the ls7 was a sbc

Re: Point/Counterpoint: DOHC v OHV
 

My mistake. I thought it was a BB.

Re: Point/Counterpoint: DOHC v OHV
 

The LSx all have the same block dimension, but I took at as any v8 over 400 cubic inches to be a "big block" as the historical packaging generally had its threshold at about that size.

Re: Point/Counterpoint: DOHC v OHV
 

I had a 70 1/2 TA that had a 400 small block (Ram Air III). If I'm not mistaken the "small block/big block" designation was only applied to Chevy engines, tho. But the Pontiac 400 was always referred to as a small block.

Re: Point/Counterpoint: DOHC v OHV
 

396 was a big block back in the day, so displacement was not the determination for the designation. BB cylinder heads would not work on a small block and vice versa.

Re: Point/Counterpoint: DOHC v OHV
 

I thought it had to do with the bore spacing?

Re: Point/Counterpoint: DOHC v OHV
 

Well you could say bore spacing has something to do with it. Here's a very illustrative video of the difference. The name "big block" becomes pretty obvious.

http://youtu.be/LPZuEWli4gQ

Re: Point/Counterpoint: DOHC v OHV
 

Wasn't there both a 396 BB and a 396 SB as well?

Re: Point/Counterpoint: DOHC v OHV
 

402 Big Block
400 Small Block (not to be confused with the Pontiac 400)

Re: Point/Counterpoint: DOHC v OHV
 

Well they actually had a 366 big block chevy for delivery trucks but i think it was designed w a small piston so as to have a thick cylinder bore as they expected extended periods of full throttle operation.

But in my opinion 396 is the same as 400 cubic inches especially since i qualified my statement with the word 'about' haha... The 402 BB was a 396 with a taller deck height for trucks as i seem to recall.

The conversation wouldnt be complete if we didnt talk about the BBC canted valve angles and better rocker ratios, but like the LT5, weight and packaging were a big part of its demise.

Re: Point/Counterpoint: DOHC v OHV
 

Isnt engine size and handgun caliber sayings similar? Your choice should start with a '4'.

Re: Point/Counterpoint: DOHC v OHV
 

I love all the turns this discussion has taken. We have like 5 sub discussions going...lol.

Re: Point/Counterpoint: DOHC v OHV
 

It was meant to be a bit of a catchcan :-D for the way other threads "evolve" or "devolve" depending on your point of view.

Re: Point/Counterpoint: DOHC v OHV
 

I would trust that 959 in a heartbeat. Porsche's are the only true exotic that can be driven daily. 959 was the pinnacle of engineering back in that era. It was only surpassed by the 996 Turbo in performance, and even then the 996 was not as technologically advanced.

True big blocks are designed differently. They have a lot of cylinder material. The LS7 engine has almost paper thin cylinder walls. There is no service life in that engine.

Re: Point/Counterpoint: DOHC v OHV
 

Chevrolet big blocks are an engine family made production from 1958-1972 I believe. Ranging from 348-454 ci then a later year over the counter up to 572 inches.

The LS7's (part of the small block engine family Gen. III & IV) are modern day monsters that are clean from a emissions view and get decent fuel mileage . The cylinder walls are very easily replaced. The service life of an LS engine is an extremely long one.

:cheers:

Re: Point/Counterpoint: DOHC v OHV
 

Don't break his heart and tell him that the 959 was using nikasil plated alloy liners, sodium filled exhaust valves, and a dry sump years before any Corvette...

Big blocks were produced way later than 1972. I had a 2000 Chevy 3500 pickup with a 7.4. My dad still owns his 1997 Chevy Express 3500 van with a 7.4.

Re: Point/Counterpoint: DOHC v OHV
 

Chevrolet BB's were produced until 2007 as Vortec L18 truck engines.

Mark IV which were the performance engines stopped production in Tonnawanda NY in 72.