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View Full Version : Valve lift VS. Port velocity question.

EHardy1971
10-06-2009, 04:12 PM
Ok guys, most of you know I'm running GT40 Irons on my car, with the E303 cam (set @ 4* ADV), and the Crane/Cobra 1.7 RR's. When I went with the 1.7's, I understandably lost a tiny bit of bottom end torque due to changing the powerband of the cam. I know as valve lift increases, port velocity decreases. According to this, the GT40's make power all the way up to .600" of lift.http://www.allfordmustangs.com/Detailed/630.shtml However, they don't make THAT much more at .600" than they do at .500". Do you think the 1.7's are hurting me more than they're helping? I know bigger isn't always better in some cases.:shrug: When I dynoed it a couple of months ago, it made power up to 5200 RPM's, which I know is mostly the intake.
SilverBack
10-06-2009, 04:16 PM
You also have to consider that changing the rocker ratio effectively changes the opening & closing event timing, not just the maximum lift at the valve.
EHardy1971
10-06-2009, 04:56 PM
You also have to consider that changing the rocker ratio effectively changes the opening & closing event timing, not just the maximum lift at the valve.
:yup:It also increases the duration IOW.:nice:
SilverBack
10-06-2009, 05:44 PM
:yup:It also increases the duration IOW.:nice:
Yep, I guess that's what I was getting at. The opening and closing happen faster. You've basically got a "bigger" cam than with the 1.6s and shifted your torque curve later in rpm range, possibly losing some down low.

How does it feel in the higher rpms?
EHardy1971
10-06-2009, 05:51 PM
Feels plenty strong and torquey from around 2400 and up.
89five0Gt
10-06-2009, 07:12 PM
Feels plenty strong and torquey from around 2400 and up.

If it don't have enough torque, then put a bigger shot on it :jester:
QWKSNKE
10-06-2009, 09:03 PM
Doesn't the 4 degrees cam advance you have bring the powerband back down or am I thinking backwards
EHardy1971
10-06-2009, 09:49 PM
Doesn't the 4 degrees cam advance you have bring the powerband back down or am I thinking backwards
No, you're right. I was planning on putting it back at 0* awhile back, but since the Explorer intake drops off after 5200 anyway, I decided to leave it alone.
itlepeanut
10-06-2009, 10:08 PM
If it don't have enough torque, then put a bigger shot on it :jester:

Are we gonna see what kind of "shot" you have at trackday this year?:jester:
coupe
10-06-2009, 10:16 PM
Not much more you can get out of a 220º duration cam (E303). If you wanna really benefit, put some more camshaft in it. I wouldn't hesitate to go somewhere around 228º duration, but I wouldn't mess with anymore than about .500 lift on the heads.

As for your question, the 1.7's are not hindering the E303 on your combo.
EHardy1971
10-06-2009, 10:29 PM
Not much more you can get out of a 220º duration cam (E303). If you wanna really benefit, put some more camshaft in it. I wouldn't hesitate to go somewhere around 228º duration, but I wouldn't mess with anymore than about .500 lift on the heads.

As for your question, the 1.7's are not hindering the E303 on your combo.
Yeah, I see a new cam in my future. I was checking out the AFM cams, and they have a couple that are designed around GT40's. I know Bandit has had good performance with his AFM cam.
89five0Gt
10-07-2009, 08:17 AM
Are we gonna see what kind of "shot" you have at trackday this year?:jester:

Not unless there is water involved. I haven't touch my car in a couple off months. Just burnt out on it I guess. Hell I've even considered selling it
itlepeanut
10-07-2009, 10:57 AM
Not unless there is water involved. I haven't touch my car in a couple off months. Just burnt out on it I guess. Hell I've even considered selling it

Nah...you will never sell that car you are like Eric you get aggravated or burnt out on it and you go with something else for a while, don't let it get to ya...:chug:
EHardy1971
10-07-2009, 03:20 PM
Not unless there is water involved.
When did you get a Subaru?:think:




































:jester: