Question on what .050 duration will be after changing events
Thread Starter
TECH Resident
Joined: Aug 2003
Posts: 960
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From: Central, FL
Question on what .050 duration will be after changing events Okay, I was playing with a engine simulator and changing valve events to see the effects on over all power. I started with a cam that has these spec's-
Avd. Duration- 270/276
.050 Duration- 218/224
LSA 111
Lift .544/.544
ICL- 107
ECL- 115
IVO-28
IVC- 62
EVO- 73
EVC- 23
Valve Overlap 51
Ramp Acc. Rate- 3.14
_______________________________
I changed the exhaust closing and LSA a bit, but I need to know what the .050 numbers are now...
here is the new specs...
the specs are comp grind that started life as a 218/224 @ .050...
270/278 adver. duration
Lift- .544 .544
Seat to Seat timing-
28 IVO
62 IVC
73 EVO
25 EVC
Intake Centerline- 107
Exhaust Centerline- 114
LSA- 110.5
Overlap- 53
Acc. Rate- 3.14
Avd. Duration- 270/276
.050 Duration- 218/224
LSA 111
Lift .544/.544
ICL- 107
ECL- 115
IVO-28
IVC- 62
EVO- 73
EVC- 23
Valve Overlap 51
Ramp Acc. Rate- 3.14
_______________________________
I changed the exhaust closing and LSA a bit, but I need to know what the .050 numbers are now...
here is the new specs...
the specs are comp grind that started life as a 218/224 @ .050...
270/278 adver. duration
Lift- .544 .544
Seat to Seat timing-
28 IVO
62 IVC
73 EVO
25 EVC
Intake Centerline- 107
Exhaust Centerline- 114
LSA- 110.5
Overlap- 53
Acc. Rate- 3.14
Seadoo,
By delaying the exhaust closing by 2 degrees, you've increased the duration of the exhaust lobe 2 degrees at .050" and at the advertised value (usually where the valve is virtually fully closed at about .004 to .006" of lift). All of this assumes that you have same lobe series profile.
If your exhaust ports don't flow very well, this 2 degree increase would maybe help HP a tiny bit above 5,000 RPMs and hurt torque a tiny bit in the lower RPM register. I assume that you are looking at an engine dyno simulator software program and this is just a "what if" exercise. You can learn some basic principles from this sort of thing. However, If I already had the cam you're describing and are basically satisified with it, I wouldn't change a thing as the 2 degrees extra exhaust duration won't really do much in the end.
Steve
By delaying the exhaust closing by 2 degrees, you've increased the duration of the exhaust lobe 2 degrees at .050" and at the advertised value (usually where the valve is virtually fully closed at about .004 to .006" of lift). All of this assumes that you have same lobe series profile.
If your exhaust ports don't flow very well, this 2 degree increase would maybe help HP a tiny bit above 5,000 RPMs and hurt torque a tiny bit in the lower RPM register. I assume that you are looking at an engine dyno simulator software program and this is just a "what if" exercise. You can learn some basic principles from this sort of thing. However, If I already had the cam you're describing and are basically satisified with it, I wouldn't change a thing as the 2 degrees extra exhaust duration won't really do much in the end.
Steve
Thread Starter
TECH Resident
Joined: Aug 2003
Posts: 960
Likes: 1
From: Central, FL
Thank you so much Steve! Very informative! The engine simulator I have been running shows this as helping hp and trq about 3500rpm. It should a +2 increase in trq and a +3 in hp.
I do not have the cam yet, I was just playing with the sims to see "what if" as you say.
Oh and the motor is a stock L31, with stock OE vortec heads, 1.94 intake, 1.50 exhaust valves. 9.4:1 compression, Edelbrock Performer RPM Air Gap, 750 carb.
I do not have the cam yet, I was just playing with the sims to see "what if" as you say.
Oh and the motor is a stock L31, with stock OE vortec heads, 1.94 intake, 1.50 exhaust valves. 9.4:1 compression, Edelbrock Performer RPM Air Gap, 750 carb.
