Variable valve timing for GM?

[Mixedpuppy]

Quick question,

Why doesn't Gm produce affordable performance vehicles with variable valve timing like in thier Northstar engines? Wouldn't that increase the power of thier performance engines significantly? Just a thought.

[Trash man]

cost of production, northstare accord to a couple ppl i talked to is just a tweaked LT4 motor.

[Jay 02 TA ws6]

cost of production, northstare accord to a couple ppl i talked to is just a tweaked LT4 motor.

No way, man.

Northstar is a 32 valve DOHC 4.6L V8 motor.... The LT4 is a 5.7L 16 valve in-block cam pushrod motor....

If you meant to say LT5, I would still want to know where the sources came from... I had never heard that was the case before.

[Jay 02 TA ws6]

In regards to the original question... I believe the ECOTEC 4 cylinder has VVT, doesn't it?

Really the best use for variable valve timing seems to be in getting small displacement motors to make high specific outputs (HP/L) by being able to rev to high RPMs -- this in turn allows for lower gears to be used which increases the torque reaching the wheels. On a single cam pushrod motor like the LS1, revving to 9,000 RPMs is possible, but not without sacrificing driveability in the lower RPMs -- having VVT would allow for smoother operation outside of the powerband.

The reason that a pushrod motor capable of reving to 9K doesn't idle smoothly is because in order for the engine to breath efficiently at such high revs, the valves need to be open for longer durations -- at low engine speeds, this leads to reversion, the A/F gets pushed out of the cylinder because the cylinder pressure overcomes the intake pressure.

It would be nice to have a 9,000 RPM redline and a smooth idle - but that just isn't all that possible unless you take advantage of VVT.

So why not use it?

As someone already said, it is more costly. Not only is it more costly, but it's also more complicated. More parts = more things to break. To me that isn't the biggest reason, however. To me, the biggest reason is the size advantage of the pushrod motors. By locating the cam in the middle of the block, the LS1 uses only one camshaft, whereas the Mustang Cobra motor uses 4 - and they sit on top of the cylinder heads, making for a MASSIVE motor.

The pushrod design has proven to be lightweight, compact, and fuel efficient... it makes torque thanks to it large displacement, so that it can run at highway speeds at extremely low RPMs which allows for that fuel efficiency. You can't beat an LS1's fuel efficiency with a 2.0L Honda S2000 motor (F20C)... and the S2000's motor can't keep up with the LS1 in performance, either. I suppose that a DOHC 5.7L V8 should be able to accomplish all the things the LS1 can as far as power, speed, and efficiency go... plus allow for VVT's advantages... but it would still be much larger.

The best idea is to have a dual in-block camshaft design and run VVT off two in-block cams. I sure hope we see that some day.

Take a look at the pic I attached. It's the 4.6L Mustang motor next to the 5.0L... the 4.6L is OHC, and the 5.0L is pushrod. Note the size difference, even though the 5.0L actually has more displacement

[Injuneer]

There have been rumors for a couple years now of a "dual cam" version of the LS1/2 engine, with the cams located one-over-the-other in the block. The purpose is variable valve timing.

There's a new pushrod 3.9L V6 with VVT, but since its a single cam, its just a matter of moving both intake and exhaust events together, and not being able to alter the lobe separation. The 3.9L V6 will also have a tuneable intake runner.

Check out a thread on the "Advanced Tech" forum at CZ28.com for some info.

http://web.camaross.com/forums/showthread.php?t=368770

[Trash man]

my bad i ment th LT5 motor. and my boss said that(mechanic for over 30 years. but sadly a mopar guy)

[Mixedpuppy]

Thanks Jay and Injuneer!

Thank you guys!

I had this discussion with one of my friends and I told them I didn't know but I could probably get help finding the answers. I probably figured the price for increased complexity. I never realized the increase in size and weight though. I also wasn't sure about performance characteristics across the RPM ranges. I appreciate your help in answering my questions. Way to flex your brains!

[Joe 1320]

The way to do this effeciently would be to use electonically actuated valves. That way the computer could control overlap for low rpms and open them up for monster breathing at high rpms resulting in an huge increase in average power.

[Jay 02 TA ws6]

The way to do this effeciently would be to use electonically actuated valves. That way the computer could control overlap for low rpms and open them up for monster breathing at high rpms resulting in an huge increase in average power.

Absolutely!!!!!

I believe F1 cars use that technology today... I wonder how long before it's affordable and practical enough to be in every day cars.

[94 formula]

my bad i ment th LT5 motor. and my boss said that(mechanic for over 30 years. but sadly a mopar guy)

Didn't the LT5 still use an inblock cam and each pushrod actuated two valves instead of one?

I watched a show on engines using seperate actuators for each of the cylinders. It showed how you could drive your car to the track at just over 1000rpms with the valves having very little lift giving you great torque and gas milage then get there and they can open up to huge lift letting you rev well over 10,000 rpms.

[Christopherrr]

Didn't the LT5 still use an inblock cam and each pushrod actuated two valves instead of one?

LT5's were DOHC engines.

[Jay 02 TA ws6]

Didn't the LT5 still use an inblock cam and each pushrod actuated two valves instead of one?

Look up the Corvette ZR-1.