Not long ago I picked up a 2016 4runner with VVT (Variable Valve Timing) tech and I've learned much about it since then. This video also shows an interesting system for changing cam profiles on the exhaust side (VVL - Variable Valve Lift).

In a recent Hot Rod they took a GM VVT engine (an L98 - from a truck/SUV I believe) and put nitrous on it. Which got me thinking - has anyone swapped a VVT engine into a C5?

https://www.roadandtrack.com/car-cul...work-benefits/

 

Think of the LS1 being a VVT engine. It's output would've increased significantly. It doesn't do bad for a pushrod motor, and it's simplicity makes it tough as nails, but a VVT would've turned it into beast!

 

The XLR Cadillac version of the C6 had the northstar engine which has four variable cams, the V model added a supercharger.

 

The VVT system wouldn’t really add any power vs just using a little bit better than stock cam.

Theres a reason most people get rid of it on c7’s when trying to make real power

 

Just something else to go wrong lol

 

The LS1 computer will not be able to handle VVT, it will need one of the newer computers.

 

I’ve been watching this carefully on the 4runner forum - numerous people there have 100k miles on these VVT engines. One thing became obvious as I learned more about how this system works - you need lots of oil - it has to be clean - and all your sensors need to be working...

 

It doesn’t change hp that much, it’s a trade off for power and economy. I had two GMC SLT Sierra’s with 5.3 one had VVT one didn’t, the difference was about 3mpg average and 5mpg at the best the power was comparable.

 

On a truck that gets around 15-18 mpg on average, a 3 MPG increase translates to a 15%+ increase in fuel economy, or 18%+ lower fuel costs. That's not trivial.

Also, of course a cam from the factory is going to be geared towards fuel economy. There are performance VVT cams available.

 

is this directed at me? I know firsthand it’s not trivial on economy or power I didn’t say that, both get better.... but it doesn’t make an engine a “beast” imo a beast is 50%-100% more hp/tq and you can do that way simpler and cheaper then modding a C5 with VVT. It’s better technology so there is less trade off but there is always a trade off with economy and power......

btw...my example was from driving both not looking up specs, there were a few other factors like the non VVT truck had 410 gears and a 4 speed the VVT truck I think had 342 gears and a six speed soo it was really less than I stated for economy in my real world example.

 

yeah but the vvt just doesn’t really seem to increase economy in corvettes. The c7 with direct injection, vvt, and cylinder deactivation doesn’t get better MPG in the real world than any c5 or c6, including the ls7 cars.

The lt1 has a little more torque down low than an ls7, which could be potentially attributed to the vvt, but who cares about that? No LS is lacking in torque to begin with.

 

Larger tires and wheels, increased downforce and higher coefficient of drag (C5 coupe is probably the slipperiest Corvette) all decrease fuel economy on the C7.

Also, a C7 is apparently more efficient at hypermiling than a C6: https://www.popularmechanics.com/car...-run-16686407/

However, a large V8 in any car is going to get bad city mileage primarily due to the tendency to accelerate faster than you would without that power. That and the fact that a large engine will consume considerably more fuel than a smaller engine while idling.

 

so you missed a key phrase here: in the real world.

I got a calculated 31.3mpg at 70 miles an hour driving from nc to Florida, including traffic through Atlanta. On the way back I got 30.5 because I was able to move quicker without my parents following me in their mazda3 with kayaks on the top.

He hypermiled a c6 and only got 32? People report that kind of highway mileage at normal driving styles.

Ill say it again, in the real world, vvt and dod don’t really help the corvette.

 

you need a supercharger, you get way too good of gas mileage

 

thats only on long trips, I make sure to overcompensate around the city with many 6500rpm pulls

 

I was just curious if anyone has tried swapping a "variable-anything" engine into a C5. I read that VVT does help with low-end torque which for an SUV that will see the trails is a good thing.

Good points made that VVT probably won't add peak power over a non-VVT - just perhaps "move it around".....

 

It gets the same MPG with higher specific HP. Surely that is not lost on you?

 

460 is now higher than 505?

 

As I said, the LS1 PCM cannot handle VVT functions. You would need a VVT capable computer, which will be a nightmare getting it to work with the BCM at best and downright incompatible with the BCM at worst. If the C5 was stripped down with most factory functions removed, it wouldn't matter as much.

VVT basically just gives you two cam profiles that can be switched on the fly. There are VVT cams available that are more aggressive than the factory cams.

 

VVT isn't just a one description fits all thing. There are many different forms. On GM pushrod engines, they are only advancing and retarding the entire one cam, so both the intake and exhaust centerlines will be shifted together. That means that overlap can not be changed on the fly (more overlap for greater topend and less for greater lowend). Also you have more of a compromise, with single cam vvt, as for any given rpm and load the exhaust centerline may benefit from moving one direction, while the intake may benefit from moving another direction, more or less degrees or simply staying put.

The VVT system on late model dodge vipers actually employs a cam within another hollow camshaft to allow the exhaust centerline of the cam to be adjusted independently of the intake centerline, which allows adjustment of overlap, so you can get hot cam topend with mild cam idle/emissions....

Generally advancing intake adds lowend, retarding intake adds top end, while the exhaust is opposite with retarding exhaust adding lowend and advancing the exhaust adds topend. The intake phasing has more of a profound effect than the exhaust phasing, so with GM's single cam phasing, the rules of intake phasing will apply to GM's overal phasing.

This isn't to say that GM putting vvt on their pushrod engines isn't beneficial. It obviously has its pros. I am sure it helps a good deal with efficiency and emissions. Also they could run slightly hotter cam specs that would normally hurt lowend/efficiency/emissions, but due to being able to adjust the cam phasing on the fly, the engine could keep the lowend/efficiency/emissions of a milder cam, while still benefiting from the added top end of the hotter specs. This also works vice versa, as GM's VVT is capable of advancing the cam up to 7 degrees for added lowend and retarding it up to 45 degrees for added topend.

Most people just delete or lock the cam phasing on these GM engines, when they put a big cam in them, so they don't have to worry about valve to piston clearances, but if you know what you're doing, you can greatly benefit from vvt adjustments. This article explains it better than I ever could:

https://www.hotrod.com/articles/hrdp...formance-test/

https://www.mechadyne-int.com/home/dodge-viper/