My Vortec Combo disappoints
Le Mans Master
Joined: Dec 2009
Posts: 6,397
Likes: 649
From: Saskatoon Saskatchewan
Is that the advertised duration on this cam? Good grief that's much too long of a duration for 9.6:1.
I just looked it up and looks like your right.
http://www.gmpartsdirect.com/results...umber=24502476
Ok so maybe it is timed in right. He could still benefit from advancing it some....maybe. Ultimately it needs to be a shorter duration cam. This must be a very old school cam for that slow of a ramp.
Not sure I'm doing this right because the numbers look crazy to me, but when I put in numbers to get a 9.6:1 SCR for a 320* cam with a 112 lsa (guessing that one) it comes up with a DCR of 5.82. Also gives me an intake valve closing angle of 92.5*. That sounds crazy late to me.
I'd say mystery solved. Thanks matt I hadn't bothered to look up the cam and made some bad assumptions. since I'm new to this I had no idea that a cam could be a 320* lash and have a 212@.050. Wow!
You'd have to kick up the SCR to around 12.5:1 to get the SCR up to something reasonable.
I just looked it up and looks like your right.
http://www.gmpartsdirect.com/results...umber=24502476
Ok so maybe it is timed in right. He could still benefit from advancing it some....maybe. Ultimately it needs to be a shorter duration cam. This must be a very old school cam for that slow of a ramp.
Not sure I'm doing this right because the numbers look crazy to me, but when I put in numbers to get a 9.6:1 SCR for a 320* cam with a 112 lsa (guessing that one) it comes up with a DCR of 5.82. Also gives me an intake valve closing angle of 92.5*. That sounds crazy late to me.
I'd say mystery solved. Thanks matt I hadn't bothered to look up the cam and made some bad assumptions. since I'm new to this I had no idea that a cam could be a 320* lash and have a 212@.050. Wow!
You'd have to kick up the SCR to around 12.5:1 to get the SCR up to something reasonable.
Safety Car
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From: anchorage ak
Melting Slicks
Joined: Aug 2012
Posts: 2,548
Likes: 379
From: Woodinville WA
here, let me get that translated for you..... he bought the wrong cam.
Or, put even more specifically, he needs more motor to run that cam
I've said it before, everyone needs to, at least once, buy a cam from the bottom of the page and make it run - it'll teach you everything you need to know about motors (and really, in a good way).
Or, put even more specifically, he needs more motor to run that cam
I've said it before, everyone needs to, at least once, buy a cam from the bottom of the page and make it run - it'll teach you everything you need to know about motors (and really, in a good way).
Le Mans Master
Joined: Dec 2009
Posts: 6,397
Likes: 649
From: Saskatoon Saskatchewan
LOL, that's not much help. Could you give me a bit more detail than that while summerizing what reelav8r said in more generic english?
Le Mans Master
Joined: Dec 2009
Posts: 6,397
Likes: 649
From: Saskatoon Saskatchewan
When I first studied cams there was just total duration given and then they came out with this newfangled @.050 measurement. I thought any duration prior to .050 lift was irrelevant?
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
LOL, that's not much help. Could you give me a bit more detail than that while summerizing what reelav8r said in more generic english?
The last one is more technical and harder to read than the first two.
Safety Car
Joined: Jan 2009
Posts: 3,736
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From: anchorage ak
here, let me get that translated for you..... he bought the wrong cam.
Or, put even more specifically, he needs more motor to run that cam
I've said it before, everyone needs to, at least once, buy a cam from the bottom of the page and make it run - it'll teach you everything you need to know about motors (and really, in a good way).
Or, put even more specifically, he needs more motor to run that cam
I've said it before, everyone needs to, at least once, buy a cam from the bottom of the page and make it run - it'll teach you everything you need to know about motors (and really, in a good way).
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Melting Slicks
Joined: Aug 2012
Posts: 2,548
Likes: 379
From: Woodinville WA
The problem with long-open-times is it reduces the time the cylinder has with the valve closed (I know, duh), but what that does in real numbers is lower the compression. If you have a car with low compression (to begin with), putting that cam in the car would make it difficult to start, and it'd never idle because it just isn't developing enough compression for the resulting bang to make it run.
Ramp - how quickly the valve opens. Obviously, you can "fix" some of the issue listed above by opening the valve more for less time by increasing the ramp. Thus, and for example, you can flow 200 cfm into a cylinder either with a 220 duration and 1" lift and nearly and vertical ramp, or have less ramp and keep the valve open longer with 320 degrees of duration and 1/2" of lift. In the OPs case, the ramp is a low ramp, and long duration which makes the effective compression 5.82 - which would cause all sorts of driveability problems.
There's a very light overview -
Melting Slicks
Joined: Aug 2012
Posts: 2,548
Likes: 379
From: Woodinville WA
this, in no way refers to my just prior post...
it shouldn't be - that's nearly stock.... which to refer all the way back to what I said before - if the cam's too small, any gain with heads would be reduced by too small of a cam - and it's possible that the velocity would be so affected that putting better heads on a motor could actually make the motor perform worse.
it shouldn't be - that's nearly stock.... which to refer all the way back to what I said before - if the cam's too small, any gain with heads would be reduced by too small of a cam - and it's possible that the velocity would be so affected that putting better heads on a motor could actually make the motor perform worse.
Melting Slicks
Joined: Aug 2012
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From: Woodinville WA
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Notice the drastic difference in duration at low lift but not so much once your up on the ramp.
Last edited by 63mako; Jan 15, 2013 at 06:51 PM.
Le Mans Master
Joined: Dec 2009
Posts: 6,397
Likes: 649
From: Saskatoon Saskatchewan
Thanks for the explanation SuperBuickGuy, that helps.
No, I think he's referring to the total duration which is 320 degrees rather than the duration at 50 thou (212/222) if I understand him correctly. Note the listing for the OP's cam:
http://www.gmpartsdirect.com/results...umber=24502476
What confuses me, is people used to give figures for total duration only then suddenly it was duration at 50 thou and I understood the reasoning to be that the valve hadn't moved at all with hudraulic lifters until 50 thou lobe lift therefore the total duration was irrelevant, only the duration at 50 thou mattered. If that's the case it wouldn't seem to me that 79vetter's cam has too much duration.
79Vetter, thanks for posting your dyno sheet.
I see the peak torque is at a relatively high 3500 rpm or so but the torque curve is broad and doesn't drop off that much in the 2000-2500 rpm range, so I still maintain that the performance 79Vetter is getting out of this Vortec/cam combination is about what one would expect and reasonably good given the parts used, i.e. relatively close in performance to the GM330HO (330 gross hp) crate motor he was more or less trying to clone
No, I think he's referring to the total duration which is 320 degrees rather than the duration at 50 thou (212/222) if I understand him correctly. Note the listing for the OP's cam:
http://www.gmpartsdirect.com/results...umber=24502476
What confuses me, is people used to give figures for total duration only then suddenly it was duration at 50 thou and I understood the reasoning to be that the valve hadn't moved at all with hudraulic lifters until 50 thou lobe lift therefore the total duration was irrelevant, only the duration at 50 thou mattered. If that's the case it wouldn't seem to me that 79vetter's cam has too much duration.
79Vetter, thanks for posting your dyno sheet.
I see the peak torque is at a relatively high 3500 rpm or so but the torque curve is broad and doesn't drop off that much in the 2000-2500 rpm range, so I still maintain that the performance 79Vetter is getting out of this Vortec/cam combination is about what one would expect and reasonably good given the parts used, i.e. relatively close in performance to the GM330HO (330 gross hp) crate motor he was more or less trying to clone
Last edited by Priya; Jan 15, 2013 at 07:00 PM.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Safety Car
Joined: Jan 2009
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From: anchorage ak
here, let me get that translated for you..... he bought the wrong cam.
Or, put even more specifically, he needs more motor to run that cam
I've said it before, everyone needs to, at least once, buy a cam from the bottom of the page and make it run - it'll teach you everything you need to know about motors (and really, in a good way).
Or, put even more specifically, he needs more motor to run that cam
I've said it before, everyone needs to, at least once, buy a cam from the bottom of the page and make it run - it'll teach you everything you need to know about motors (and really, in a good way).
Last edited by bluedawg; Jan 15, 2013 at 07:30 PM.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
This what i was refering to. I didnt catch that the advertised duration was 320, it is in fact a crapy cam. If the op doesnt want to buy another cam, he could advance it 4 degrees to raise cylinder pressure and bring the rpm range down by 500 or so rpm, still not the off idle torque he's looking for but would run better or he could buy a descent cam, i say grubbers favorite would work well in this application.