: Variable timing question for the 3.6L engine



gohawks63
05-05-13, 08:01 PM
Prior to buying my CTS, I drove Acuras for nearly 20 years. Acura's variable timing system (VTEC) switches to the more aggressive cam profiles when the engine hits about 4,800 RPM. It is a noticeable shift and felt like a very subtle boost.

I was wondering if it's the same way in the GM 3.6L engine. I haven't noticed it and maybe it's a bit more subtle. Anyone know?

OMG
05-05-13, 09:48 PM
It'e very noticeable for me. Both my CTS and my gf's TL share similarities, in putting around town they have just enough torque but stomp it when it hits 4kish RpM's they boyh start doing their hard pulls. The CTS is more linear if it was already in the right gear, so it can be stuble. But if it's a few gears too high there is a noticeable delay from the trans and then it snaps your neck. I kbow it can be tuned out and I will be doing so probably down the road because my passengers are never expecting it and it suprisingly hurts. The TL tends to be better prograbmmed trans which makes it feel very light almost 4 cyl quick in how fast it pulls up revs. But it really isn't any faster revving then CTS. but if it's in the wrong gear it does more of a turbo-lag feel until does hit the right revs and then has the gradual burst of acceleration which gives you the tactile feel of VTEC. sorry for the confusing post and misspellings. On a phone. LoL.

EVH5150
05-07-13, 02:34 AM
Prior to buying my CTS, I drove Acuras for nearly 20 years. Acura's variable timing system (VTEC) switches to the more aggressive cam profiles when the engine hits about 4,800 RPM. It is a noticeable shift and felt like a very subtle boost.

I was wondering if it's the same way in the GM 3.6L engine. I haven't noticed it and maybe it's a bit more subtle. Anyone know?

It's very noticeable on mine at around 4000RPM, from 4000 up it pulls like a demon. I actually did a test with about a quarter pedal through 1st and 2nd, and you can definitely feel the cam phase switchover. From what I can tell it's RPM based as it does it whether you are WOT or just normal acceleration.

I hope this helps buddy.

gohawks63
05-07-13, 01:38 PM
It's very noticeable on mine at around 4000RPM, from 4000 up it pulls like a demon. I actually did a test with about a quarter pedal through 1st and 2nd, and you can definitely feel the cam phase switchover. From what I can tell it's RPM based as it does it whether you are WOT or just normal acceleration.

I hope this helps buddy.

Thanks everyone for your responses. I will have to be a bit more observant to see if I can notice the difference. It's been more of a curiosity thing.

M5eater
05-07-13, 02:59 PM
It's not the same, not even close. Where as Vtec uses individual cam profiles that essentially 'click' over after a certain set of parameters present themselves, the 3.6 uses cam phasing, advancing or retarding the profile to suite the needs at the time. The SOHC Vtec systems(like in your average V6 TL or TSX) basically(until recently) uses a third rocker arm to act like a mini-cam profile in itself, as the normal 'lobe' on the cam essentially will only open the 2nd intake port partially and the 3rd rocker arm acts as the vtec kick-over to open it fully, however, because of the need for a 3rd rocker arm, varying the exhaust ports is not possible since the spark plug tends to get in the way (unlike in the 3.6 where all cams are phased). in 09 they did some neat trickery to allow both profiles to be modified using the 3 rocker arm combination.

DOHC variations actually remove the rocker arms completely and use 3 lobe camshafts to switch between a high and low lift cam lobe, effectively creating 2 different camshafts in a single unit. Where as both intake ports open fully on the normal lobe they open even more on the vtec lobe.
As such, the VVT 'kick over' will be more noticeable than in a normal VVT vehicle, because they can modify lift as well, and when you adjust lift, you can more aggressively adjust fueling and timing, so it gives it a much better kick in the pants.

The VVT in the 3.6 effectively is just advancing or retarding timing on the single cam(s), nothing nearly as complex or entertaining as Vtec. It's such a simple and cost effective solution that most engines have some kind of Cam-phasing built into their design.