Point/Counterpoint: DOHC v OHV

[spork2367]

Originally Posted by 5ABI VT

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 !

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

[5ABI VT]

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.

[spork2367]

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

[Fully Vetted]

Originally Posted by mike100

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

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

Originally Posted by spork2367

...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...

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...

[32valvesftw]

[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

[XfireZ51]

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.

[Bearly Flying]

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.

[5ABI VT]

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.

[Kevin]

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.

[pantera1683]

Originally Posted by Fully Vetted

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

Big Block?