Point/Counterpoint: DOHC v OHV

[mike100]

Originally Posted by spork2367

...Chevy will likely never build an engine that we think would be comparable to the LT5.

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...

[spork2367]

Originally Posted by Meanmyz

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!

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.

[Meanmyz]

Originally Posted by spork2367

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.

Very true!

[XfireZ51]

Originally Posted by spork2367

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




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.

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.

[spork2367]

Originally Posted by mike100

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.

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.

Originally Posted by XfireZ51

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.

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.

[Meanmyz]

Originally Posted by mike100

The days of big inch lumbering NA engines are not long.

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.

[spork2367]

Originally Posted by mike100

The days of big inch lumbering NA engines are not long. Maybe in trucks for a bit longer...

Most torque under the curve for the future...

[5ABI VT]

Originally Posted by spork2367

Most torque under the curve for the future...

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.

[spork2367]

Originally Posted by 5ABI VT

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.

And the v12 torque curve sucks.

[5ABI VT]

Originally Posted by spork2367

And the v12 torque curve sucks.

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 !!
Would I have rather built an LT5? I think the answer Is obvious !