Jimny VVT less power at low revs than non-VVT?

Hi, all,

I don't know much about power and torque and gear ratios, so perhaps a stupid question.

I have a 2005 VVT Jimny with 235/75/R15 tyres and my friend who has the same tyres on his non-VVT drove my car the other day and said it felt like it was down on power. I have 17% reduction gears (high range) in my car and he does not, so I would expect my car to feel better (also VVT is supposed to have slightly more BHP).

I have a fairly steep hill near where I live and when I'm going up at ~3k revs in fourth gear at about 40mph, I can't accelerate without dropping down a gear.

I'm trying to understand, is the VVT more likely to get "stuck" in low-power/economy mode (with less fuel and air), and be unable to increase RPM (forcing you to drop down a gear) compared to a non-VVT (operating at full power all the time)?
i e.- the VVT is operating with less power than the non-VVT until the revs are up to ~4k(?), and with the big tyres, going up hill, I can't get the revs up to that band.

Or am I totally misunderstanding something?

Thanks in advance
Lee

 

I think that compared to the tyres and gearing the VVT should not be noticable.
Having driven one VVT alot with 17% and 235 's and a mates non vvt with 215 and no gearing change, I would say they where pretty similar, both m16. 

How ever, my vvt with broken catalytic converters was pretty slow. Cat no 1 disintegrates and clogs up cat no 2.

 

Thanks, yakuza. Although my friend has the same 235 tyres as me and says my car feels underpowered. We both have 1.3 engines, so the only difference I could imagine was that mine is VVT.

I would have expected that my 17% gears should make my car better able to power up hills with low-ish revs, not worse. So I am trying to understand whether it is the VVT that makes the car feel underpowered until the revs get higher, compared to my friend's non-VVT. My rough understanding is that the VVT effectively reduces power output at lower revs e.g. for fuel consumption etc.

Thanks
Lee

In theory VVT increases power and torque by allowing more valve overlap at high revs.  If the cams were set for a lot of overlap without VVT, the engine would be unable to idle at low revs.  However, manufacturers may use it for other purposes, such as emissions control.

VVT is designed to spread the torque and power over a wider rev range by flattening the torque curve and is generally more effective at the mid to higher revs. There is probably very little difference in the lower revs. If the VVT and non-VVT produce the same amount of torque at lower revs and the vehicle speed is the similar (you might be using a higher gear?), then they will feel the same.

The point of using a 17% reduction in gearing is to compensate for the bigger tyres so you can get the engine spinning in the torque and power band (>3,000 rpm), not slugging around at 2,000 rpm.

However, agreed it shouldn't be worse, but I doubt that is the fault of VVT, more likely to be something else.

tomlil01 wrote:

Hi, all,

I don't know much about power and torque and gear ratios, so perhaps a stupid question.

I have a 2005 VVT Jimny with 235/75/R15 tyres and my friend who has the same tyres on his non-VVT drove my car the other day and said it felt like it was down on power. I have 17% reduction gears (high range) in my car and he does not, so I would expect my car to feel better (also VVT is supposed to have slightly more BHP).

I have a fairly steep hill near where I live and when I'm going up at ~3k revs in fourth gear at about 40mph, I can't accelerate without dropping down a gear.

I'm trying to understand, is the VVT more likely to get "stuck" in low-power/economy mode (with less fuel and air), and be unable to increase RPM (forcing you to drop down a gear) compared to a non-VVT (operating at full power all the time)?
i e.- the VVT is operating with less power than the non-VVT until the revs are up to ~4k(?), and with the big tyres, going up hill, I can't get the revs up to that band.

Or am I totally misunderstanding something?

Thanks in advance
Lee



 

Well no, that isn't how VVT works. I'm not exactly sure how the Suzuki version works, although most car makers have offered something similar. Earlier examples being the Honda VTEC and Rover VVC engines. The main difference here being the Rover's was continuously variable while the Honda was more of a stepped approach.

Most of the systems allow an engine to run essentially different cam profiles at low rpm vs high rpm. This however is almost entirely done for emissions reasons and to a lesser extent improved drivability down low.

On nearly every engine using this kind of tech, switching to the more aggressive profile will nearly always improve power and performance everywhere which is what a lot of remaps do.

As for your vehicle. I'd say yes the gear reduction should help. But you'd need to see a dyno plot of a VVT and non VVT engine to see if there is any difference in power/torque for a given rpm.

Subjective feel is not very accurate. Ways you can measure would be to use an app on your smartphone. Or even just a GPS speed readout and a stop watch. Don't do a standing start, just measure acceleration over a set range, ideally in a single gear. Such as 30-50mph roll. Then get your friend to do the same on the same road.

The other way to measure would be line both cars up side by side and do a roll race from a set speed. It will be very clear to see if one is faster than the other.

In standard cars the the VVT engines pull slightly better than non-VVT but the difference is barely noticeable. With gear reduction yours should have the upper hand.
Aside from servicing and mechanical issues, the engines do lose performance if never driven hard. Having owned a few ex-pensioner Jimnys, I've found a tank of V-Power and hard driving with regular visits to the rev limiter will restore lost performance.
 

Thanks for this. That's helpful, but doesn't it fit with what I was saying? E.g. At 3k RPM my car will be in the "low-performance cam profile", and may feel less powerful than a non-VVT at the same revs? If I drop down to a lower gear to increase the revs the car will switch to "high-performance" cam profile and will feel the same or faster than the non-VVT engine?

Does a remap allow for the VVT to switch to the high-performance cam profile at a lower RPM?

Thanks
Lee

tomlil01 wrote:

Thanks for this. That's helpful, but doesn't it fit with what I was saying? E.g. At 3k RPM my car will be in the "low-performance cam profile", and may feel less powerful than a non-VVT at the same revs? If I drop down to a lower gear to increase the revs the car will switch to "high-performance" cam profile and will feel the same or faster than the non-VVT engine?

Well sort of, but there is no way to know numbers without seeing some official dyno plots or output at a given rpm. There is nothing to say the VVT would be less, more or the same output as the non VVT engine down low. It could be any of them.

Although in any instance I'd expect it to be mild difference, not a huge one.

tomlil01 wrote:

Does a remap allow for the VVT to switch to the high-performance cam profile at a lower RPM?

Thanks
Lee

I believe yes, although it depends how the system is controlled and what access the mappers have to the settings. Probably best to contact and speak to some to see what they say. One mapper said that this was the case for the 4th Gen however, so I'd assume it is for the Gen 3.

I might be wrong but i am under the impression that the lobes on the cam are static on a suzuki so it is not how long it is open but how early or late. there is allmost no difference and no very noticable power gain, it just occurs at a bit different rpm.
Not like the Honda system where there is different lobes coming into effect at diffrenet times. (from wiki)
I would say that even if the VVT system is stuck and static there would be little noticable difference.

My Swift is a non VVT but it has 90hp on the m13 and my jimny had 80hp on its m13. Yes the swift feels like there is more hmmpf than the jimny but still no racecar and it is lighter than the jimny I think.

if there is a very noticable difference in power it must be something else.

I think it's just intake cam phasing on most Suzuki VVTs.  The ECU uses the cam and crank position sensors to decide what to do, and oil pressure is used to actually rotate the pulley.

Correct, it's just intake cam timing that changes. I wouldn't describe it as high power and low power modes. It adjusts the timing slightly so it's better optimised at higher and lower engine speeds. You won't gain a boost in power by adjusting the transition point.
I think this is a distraction anyway. The difference in performance your friend has noticed is unlikely to be related to the VVT.