3.6 dohc cam specs...somethings not adding up here

[merlot566jka]

ok i was just playing around and trying to figure out what they are doing with the cams in the ly7. and its not adding up right at all! heres what they have listed in the gm spec sheet

• Camshaft Timing @ 0.15 mm (0.0059 in) Lift

• Valve Opens - Exhaust

-229 degrees BTDC

• Valve Opens - Intake

14 degrees
ATDC

• Centerline - Exhaust

111 degrees ATDC

• Centerline - Intake

132 degrees ATDC

• Valve Closes - Exhaust

9 degrees
ATDC

• Valve Closes - Intake

251 degrees ATDC


now how do i get from there to, duration at .050, intake centerline and lsa?
i did the math the old way, and its waaaayyy off. so i tried an online calculator, wayyyy off and entirely diff numbers this time.

whats the deal?

[3100 MPFI]

Just a thought, but could the VARIABLE TIMING have something to do with it?

[merlot566jka]

ha, yes it could. very. im going to have to draw this out to get it right.

damn so much work just to know something

[gpchris]

Sombody should make VVT gears for the lq1... That would be awesome. That could totally make great hp/tq through the entire powerband. We could also raise the redline

[SappySE107]

Its call a 3.6 DOHC. I just saved someone a ton of cash on R&D for the VVT 3.4 concept.

[gpchris]

I would like a 3.6 but finding one is the hard part. Plus all the modding I would have to do to put it into my W. How does VVT work anyway?? how do the gears know when to adjust?

[merlot566jka]

Its call a 3.6 DOHC. I just saved someone a ton of cash on R&D for the VVT 3.4 concept.

lmfao.

[RedZMonte]

I would like a 3.6 but finding one is the hard part. Plus all the modding I would have to do to put it into my W. How does VVT work anyway?? how do the gears know when to adjust?

Not sure if its the same thing but on Honda's Vtec i know (or so i have been told) the larger lobe is locked in by a Pin when the engine reaches a cretin rpm the ECU uses oil pressure to lock in the pin to use the larger lobes... dunno if its the same on the GM's.. Or i could be completely wrong..

S

[LQ1Fiero]

ok i was just playing around and trying to figure out what they are doing with the cams in the ly7. and its not adding up right at all! heres what they have listed in the gm spec sheet

• Camshaft Timing @ 0.15 mm (0.0059 in) Lift

• Valve Opens - Exhaust

-229 degrees BTDC

• Valve Opens - Intake

14 degrees
ATDC

• Centerline - Exhaust

111 degrees ATDC

• Centerline - Intake

132 degrees ATDC

• Valve Closes - Exhaust

9 degrees
ATDC

• Valve Closes - Intake

251 degrees ATDC


now how do i get from there to, duration at .050, intake centerline and lsa?
i did the math the old way, and its waaaayyy off. so i tried an online calculator, wayyyy off and entirely diff numbers this time.

whats the deal?

The way that you have it layed out is confusing as hell. How about this:

Exhaust
Open: 229 BTDC
Close: 9 ATDC
Duration: 229 + 9 = 238
Centerline: 238 / 2 = 119 - 9 = 110 BTDC

Intake
Open: 14 ATDC
Close: 251 ATDC
Duration: 251 - 14 = 237
Centerline: 237 / 2 = 118.5 + 14 = 132.5 ATDC


LSA = (110 + 132.5) / 2 = 121.25


Measuring at .050 will change the duration and open and close events but it should not change the LSA or the centerline unless they are using some lopsided cams.

This engine does have variable timing so the centerlines can move which will change the LSA. I would assume that they would move the lobes closer at the higher rpms to get more overlap and seperate them at low speeds for a good idle and higher torque. I don't think they would put the entire range into those numbers. My guess based on the LSA is those are the numbers for idle and low rpms. "Street" cams have a LSA usually between 104-118. Since this engine has vvt, they can get away with 121. If it was fixed at 121, that engine would have no high rpm power.

[merlot566jka]

thank you. i feel stupid. but that makes perfect sense. i was thinking in a box

[merlot566jka]

Not sure if its the same thing but on Honda's Vtec i know (or so i have been told) the larger lobe is locked in by a Pin when the engine reaches a cretin rpm the ECU uses oil pressure to lock in the pin to use the larger lobes... dunno if its the same on the GM's.. Or i could be completely wrong..

S

thats how honda does vtec. thats not how gm does it on the 3.6dohc. they actually retard or advance the cams relative to the crank. its more like varible cam phasing, and its varible valve timing (perse). when you advance or retard the cam, your changing the valve timing events. honda actually changes lift and duration of the cam. while gm only changes when and where(in time) the valves open. now combine the two...woah.