I don't know much about engines...

[Zenmervolt]

Originally posted by: andylawcc

Originally posted by: Zenmervolt
See above. When the focus is on power and torque production at lower RPM (below 6,000 RPM) there's little to no practical value to a DOHC setup.

ZV

what if you add high-revving capability (like an S2000) to those V8s? won't you create a heck of a monster motor?

No, you'll lose low-RPM torque. You can get high horsepower through RPM or displacement, but depending on RPM sacrifices low-end torque, reagardless of engine size.

ZV

 

[Zenmervolt]

Originally posted by: Howard

Originally posted by: Random Variable
I read an article somewhere about moving to electronic actuators or something.

Impossible with current technology.

It's been done.

It is, however, incredibly expensive right now and also incredibly noisy.

ZV

 

[cavemanmoron]

Originally posted by: Howard

Originally posted by: Random Variable
I read an article somewhere about moving to electronic actuators or something.

Impossible with current technology.

Not impossible,only expensive,air would work too,as would oil pressure
actuation.

Oh Honda is using something like it already.
http://www.hondanews.com/CatID3025?mid=2005090151253&mime=asc
Torrance, Calif. 09/01/2005 --

Introduction

An advanced powertrain is essential to meet the MDX's goals of providing V-8-like performance, class-leading low emissions, and excellent fuel economy. To that end, the MDX is powered by an advanced 3.5-liter, VTEC V-6 engine. The MDX powerplant produces 253 horsepower SAE net (8/04)at 5800 rpm, and 250 lb-ft SAE net (8/04) of torque at 3500 rpm. Acura's Variable Valve Timing and Lift Electronic Control (VTEC(TM)) valvetrain, first used in the NSX supercar, adjusts the timing, duration, and lift of the intake valves according to engine speed. In conjunction with a two-stage intake manifold, VTEC yields muscular response at low- and medium-rpm, high peak-rpm performance, very low emissions, and superior fuel efficiency. A dual exhaust system increases horsepower and torque while helping to minimize emissions.



Link to an article.From GM Delphi.

Warning its a PDF file.You will need acrobat reader.

http://www.delphi.com/pdf/techpapers/2003-01-0029.pdf

 

[tboo]

Originally posted by: redly1
corvette ZR1
LT5 DOHC engine..it was ONLY a $27,016 option in 1990
of course, it was designed by a boat manufacturer

 

[Zim Hosein]

Originally posted by: redly1
corvette ZR1
LT5 DOHC engine..it was ONLY a $27,016 option in 1990
of course, it was designed by a boat manufacturer

Isn't the Taurus SHO a Yamaha DOHC engine too?

 

[Ornery]

Originally posted by: Howard

Originally posted by: Malfeas
One of the advantages of a pushrod engine is the smaller size. You will notice that the LS7 in the vette is ALOT smaller than an equivalent output DOHC european or japanese engine.

Size of the engine, or displacement?

They are not as tall as OHC designs, allowing for a lower center of mass, or a more wedge shaped vehicle profile.

 

[Slickone]

I took these pics of a brand new ZR-1 & it's LT-5 back when the ZR-1 first came out in 1990. I knew the service/parts/body shop mgr who called me when they got it. The mechanics were doing a new car inspection. The owner told them to leave the coating on the glass, carpet protector/cover stuck on, and the steering wheel cover on.
1
2
3
4
5
6

Sorry the pics aren't very good. No digital camera back then. My scanner isn't very good either. And I didn't spend the time touching up.


BTW, here's a cutaway view of the LT5.

 

[Zim Hosein]

The ZR-1 has a sexy a*s, second only to Jessica Alba! :heart:

 

[ElFenix]

Originally posted by: andylawcc

Originally posted by: Eli
lol, the cam's location has nothing to do with how much power the engine can produce.

well, it is a gross generalization on my part; i mean, almost all high performance European and Japanese cars have DOHC, why not American too? Cost shouldn't be a main concern in builting a sports car right?

cost maybe not, but weight should be, and DOHC designs are very heavy for the power output, not to mention the sheer size.

After extensive measurements, it is obvious that the factory BMW 2.5-3.2L, crossflow head Inline-6 engine is MASSIVE in height, length, and width. With an iron block and uber-long crank, it is also one heavy mutha. Hell, a lightweight V8 swap could LOSE weight in this car! This is not unheard of - Ford 302's with aluminum heads, swapped into Datsun 240-280Z cars, can lose a few pounds. Cross-flow head Inline-6 engines are not at all space or weight efficient.

http://www.vorshlag.com/ls1bmw1.asp

 

[ElFenix]

Originally posted by: Howard

Originally posted by: Malfeas
One of the advantages of a pushrod engine is the smaller size. You will notice that the LS7 in the vette is ALOT smaller than an equivalent output DOHC european or japanese engine.

Size of the engine, or displacement?

size of the motor

 

[IGBT]

..the Toyota Tundra v8 is a 32 valve DOHC 4.7 liter. To meet emissions requirements the total displacement must be reduced so more valves are needed to flow more air/fuel mix to get similar HP/torque. The primary objective is to reduce tail pipe emissions and compromise HP/torque .

 

[rbrandon]

Originally posted by: andylawcc
if the LS7 and Ford GT can produce 500hp, what if GM and Ford can add DOHC to those engine? elventybillion HP?

umm.. the northstar engine in my caddy IS DOHC. Cadillac is a division of GM. They've been making this engine since 93

 

[Howard]

Originally posted by: Zenmervolt

Originally posted by: Howard

Originally posted by: Random Variable
I read an article somewhere about moving to electronic actuators or something.

Impossible with current technology.

It's been done.

It is, however, incredibly expensive right now and also incredibly noisy.

ZV

Really? Link?

 

[Howard]

Originally posted by: cavemanmoron

Originally posted by: Howard

Originally posted by: Random Variable
I read an article somewhere about moving to electronic actuators or something.

Impossible with current technology.

Not impossible,only expensive,air would work too,as would oil pressure
actuation.

Oh Honda is using something like it already.
http://www.hondanews.com/CatID3025?mid=2005090151253&mime=asc
Torrance, Calif. 09/01/2005 --

Introduction

An advanced powertrain is essential to meet the MDX's goals of providing V-8-like performance, class-leading low emissions, and excellent fuel economy. To that end, the MDX is powered by an advanced 3.5-liter, VTEC V-6 engine. The MDX powerplant produces 253 horsepower SAE net (8/04)at 5800 rpm, and 250 lb-ft SAE net (8/04) of torque at 3500 rpm. Acura's Variable Valve Timing and Lift Electronic Control (VTEC(TM)) valvetrain, first used in the NSX supercar, adjusts the timing, duration, and lift of the intake valves according to engine speed. In conjunction with a two-stage intake manifold, VTEC yields muscular response at low- and medium-rpm, high peak-rpm performance, very low emissions, and superior fuel efficiency. A dual exhaust system increases horsepower and torque while helping to minimize emissions.



Link to an article.From GM Delphi.

Warning its a PDF file.You will need acrobat reader.

http://www.delphi.com/pdf/techpapers/2003-01-0029.pdf

I didn't think he was talking about variable valve timing/lift, which almost every manufacturer has a version of nowadays.

 

[Howard]

Originally posted by: Zenmervolt

Originally posted by: andylawcc

Originally posted by: Zenmervolt
See above. When the focus is on power and torque production at lower RPM (below 6,000 RPM) there's little to no practical value to a DOHC setup.

ZV

what if you add high-revving capability (like an S2000) to those V8s? won't you create a heck of a monster motor?

No, you'll lose low-RPM torque. You can get high horsepower through RPM or displacement, but depending on RPM sacrifices low-end torque, reagardless of engine size.

ZV

I figure it's possible to rev high and still maintain high levels of low-speed torque. All you need is high volumetric efficiency, right?

EDIT: I need to learn to put my replies in one post.

 

[Ornery]

1. Link

 

[Howard]

Originally posted by: Ornery

1. Link

Interesting. I wonder how much power is required for that system.

 

[johnnqq]

if honda ever made a big block i would sh it my pants . if people are still squeezing over 300 reliable hp out of a 10 year old b16, why can't they make an 8 cyl car!!

 

[Ornery]

Who cares? It's more bulky and complicated than what it replaces. Technolgy for the sake of technology. I belieive in the KISS principle myself, which is why I'm not too keen on OHV engines in the first place. If it ain't broke...

 

[Slickone]

The Nissan VK56DE V8 that comes in the Titan, Armada, and Infiniti QX56 and Q45 is 32V. So was the VH41DE, and the VH45DE that came in the Q45 starting back in 1990.

 

[Zenmervolt]

Originally posted by: Howard

Originally posted by: Zenmervolt
No, you'll lose low-RPM torque. You can get high horsepower through RPM or displacement, but depending on RPM sacrifices low-end torque, reagardless of engine size.

ZV

I figure it's possible to rev high and still maintain high levels of low-speed torque. All you need is high volumetric efficiency, right?

EDIT: I need to learn to put my replies in one post.

Not really. There's a certain amount of optimization that will benefit both, but for the most part what helps low-end torque hurts high-RPM power and vice-versa.

For example, low-end torque likes small-bore and long stroke with smaller valves for higher intake and exhause velocities at low RPM. The long stroke gives the pistons more leverage against the crankshaft, but it increases the mean piston velocity at any given RPM and makes it harder to keep the pistons under control at higher RPM. The smaller valves to keep intake and exhaust velocities high help make sure that exhaust scavenging is fully utilized at lower RPM and that the intake is swirling properly but this chokes the engine off at higher RPM. There are similar issues with cam tuning.

When 4-valve cylinder heads were first coming on the market it was very common to read enthusiast magazines talking about how much damage the new 4-valve heads did to low-end torque, even though the car was making more HP since all the added HP came near redline and at the expense of power down low. Road and Track in 1986 even went so far as to prefer the SOCH 8-valve Porsche 944 (147 hp) over the DOHC 16-valve Porsche 944S (188 hp) because the former had more power in useable RPM ranges.

ZV

 

[Zenmervolt]

Originally posted by: Ornery
Who cares? It's more bulky and complicated than what it replaces. Technolgy for the sake of technology. I belieive in the KISS principle myself, which is why I'm not too keen on OHV engines in the first place. If it ain't broke...

OHV or OHC?

OHV is a HUGE improvement over side-valve engines and has been in near-universal use since the 1950's. Side-valve engines have vast inefficiencies and they have a propensity towards overheating since the location of the valves on the side of the cylinders makes it much more difficult for them to dissipate heat.

OHC has its benefits and drawbacks, but it actually has _fewer_ moving parts than pushrod designs since the camshaft is acting directly on the valves instead of through pushrods and rocker arms.

ZV

 

[Howard]

Originally posted by: Zenmervolt

Originally posted by: Howard

Originally posted by: Zenmervolt
No, you'll lose low-RPM torque. You can get high horsepower through RPM or displacement, but depending on RPM sacrifices low-end torque, reagardless of engine size.

ZV

I figure it's possible to rev high and still maintain high levels of low-speed torque. All you need is high volumetric efficiency, right?

EDIT: I need to learn to put my replies in one post.

Not really. There's a certain amount of optimization that will benefit both, but for the most part what helps low-end torque hurts high-RPM power and vice-versa.

For example, low-end torque likes small-bore and long stroke with smaller valves for higher intake and exhause velocities at low RPM. The long stroke gives the pistons more leverage against the crankshaft, but it increases the mean piston velocity at any given RPM and makes it harder to keep the pistons under control at higher RPM. The smaller valves to keep intake and exhaust velocities high help make sure that exhaust scavenging is fully utilized at lower RPM and that the intake is swirling properly but this chokes the engine off at higher RPM. There are similar issues with cam tuning.

When 4-valve cylinder heads were first coming on the market it was very common to read enthusiast magazines talking about how much damage the new 4-valve heads did to low-end torque, even though the car was making more HP since all the added HP came near redline and at the expense of power down low. Road and Track in 1986 even went so far as to prefer the SOCH 8-valve Porsche 944 (147 hp) over the DOHC 16-valve Porsche 944S (188 hp) because the former had more power in useable RPM ranges.

ZV

With a 100% volumetric efficiency (meaning in theory) and all else equal (this includes fuel type, head and block material, compression ratio, heat loss from coolant, rod length/stroke ratio, piston/piston crown coating material, cylinder liner material, flame front speed, etc.), torque depends solely on cylinder displacement and compression ratio.

Torque = r cross F, so let's assume that r is perpendicular to F for ease of math so
Torque = r*F

F = combustion pressure * piston crown area

Piston crown area is dependent on bore
Combustion pressure is dependent on the temperature of the gas inside the chamber, whose temperature rise can be calculated from the displacement (since we're assuming 100% volumetric efficiency) and compression ratio (more displacement = more energy, higher compression = higher pressure)

Since combustion pressure stays the same, now

Torque = r * piston crown area

r * piston crown area = displacement

Am I doing the math right? Now, to get 100% volumetric efficiency at lower speeds you can use forced induction, or variable valve timing/lift.

Variable lift can be taken care of by this infinitely-variable-lift system:
View in IE
The animations are self-explanatory. I'm not sure how one would achieve infinitely-variable timing (and equivalently, duration) - electromagnetic/hydraulic actuation might work.

 

[Zenmervolt]

Originally posted by: Howard
With a 100% volumetric efficiency (meaning in theory) and all else equal (this includes fuel type, head and block material, compression ratio, heat loss from coolant, rod length/stroke ratio, piston/piston crown coating material, cylinder liner material, flame front speed, etc.), torque depends solely on cylinder displacement and compression ratio.

Torque = r cross F, so let's assume that r is perpendicular to F for ease of math so
Torque = r*F

F = combustion pressure * piston crown area

Piston crown area is dependent on bore
Combustion pressure is dependent on the temperature of the gas inside the chamber, whose temperature rise can be calculated from the displacement (since we're assuming 100% volumetric efficiency) and compression ratio (more displacement = more energy, higher compression = higher pressure)

Since combustion pressure stays the same, now

Torque = r * piston crown area

r * piston crown area = displacement

Am I doing the math right? Now, to get 100% volumetric efficiency at lower speeds you can use forced induction, or variable valve timing/lift.

Variable lift can be taken care of by this infinitely-variable-lift system:
View in IE
The animations are self-explanatory. I'm not sure how one would achieve infinitely-variable timing (and equivalently, duration) - electromagnetic/hydraulic actuation might work.

That's all very nice. But in the real world, all else is not equal. Even holding as much equal as possible there are subtle differences in conbustion chamber shape as more valves are added, the angle at which those valves can sit is influenced by practical concerns of camshaft location, etc.

And you can't just double the number of valvesin an engine while leaving everything else equal and expect the VE to remain the same. If the engine is at 100% VE with 2 valves per cylinder, then adding more valves only slows the intake and exhaust charge velocity and you lose power because you're not getting the full scavenging effect from the exhaust header design.

Fewer valves generally mean that peak VE is achieved at lower RPM while more valves moves the point of peak VE higher.

It's a trade off. Just depends on the characteristics one wants in the car.

ZV

 

[Ornery]

OHV or OHC

Nice, I meant OHC. Fewer moving parts, but the ones it has are more expensive, take up more space, and for what? Nothing that concerns me in any way. Hell, if Ford had stuck with OHVs, they might have been able to fit a decent cubic inch engine under the hood of the Marauder.