My Vortec Combo disappoints
Le Mans Master
Joined: Dec 2009
Posts: 6,397
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From: Saskatoon Saskatchewan
http://www.gmpartsdirect.com/results...umber=24502476
I think 79Vetter's cam is relatively well matched to his heads and he could get some minor improvements by fine tuning with a different cam but a different cam or advancing his existing one won't make significant differences with his heads, certainly not ones he can feel given that he couldn't feel the roughly 65 net horsepower increase from the vortec/cam changes. Making significant improvements over what he's got now will require well matched significantly bigger cam and bigger heads.
Last edited by Priya; Jan 15, 2013 at 07:49 PM.
Le Mans Master
Joined: Apr 2011
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From: Hermosa
You guys are all way off. GM rated their hydraulic cams @ .000 lift. Aftermarket are rated @ .004 or .006. Duration difference between .000 and .006 would be a lot because the lobe lift is transitioning right there.
A 280 @.006 might work but the others seem a bit long in the duration for 9.6:1.
Looking at the dyno it looks like the cam would benifit from some advance and maybe a 2000-2500 or better stall converter. The chart starts at 2000 rpm but if you were to interpolate the fall in HP and maybe torque,(but that slope were it first shows up on the chart might not be accurate), power would certainly be low for anything below 2000 rpm. It looks about right for a short cam as far at where it peaks (about 5250) and torque comes up by 2000 rpm and is farily flat. But it seems low on the torque overall. Is this the symptom of a low intensity short duration cam, wide lsa? Or is it poor flow somewhere? I'm gonna have to cognate on this one. Maybe like Matt says too tall and too short at the same time.
Last edited by REELAV8R; Jan 15, 2013 at 08:04 PM.
Le Mans Master
Joined: Dec 2009
Posts: 6,397
Likes: 649
From: Saskatoon Saskatchewan
I figured that. Once again, was I mislead all those years ago that only duration at .050" matters with hydraulic lifters as the valve hasn't started moving yet? In other words, what does it matter what duration is at .000" or .006"?
Race Director
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From: Millington Illinois
St. Jude Donor '08-'09
So what do you figure the lift might be at .006? 280,290 even 300?
A 280 @.006 might work but the others seem a bit long in the duration for 9.6:1.
Looking at the dyno it looks like the cam would benifit from some advance and maybe a 2000-2500 or better stall converter. The chart starts at 2000 rpm but if you were to interpolate the fall in HP and maybe torque,(but that slope were it first shows up on the chart might not be accurate), power would certainly be low for anything below 2000 rpm. It looks about right for a short cam as far at where it peaks (about 5250) and torque comes up by 2000 rpm and is farily flat. But it seems low on the torque overall. Is this the symptom of a low intensity short duration cam, wide lsa? Or is it poor flow somewhere? I'm gonna have to cognate on this one. Maybe like Matt says too tall and too short at the same time.
A 280 @.006 might work but the others seem a bit long in the duration for 9.6:1.
Looking at the dyno it looks like the cam would benifit from some advance and maybe a 2000-2500 or better stall converter. The chart starts at 2000 rpm but if you were to interpolate the fall in HP and maybe torque,(but that slope were it first shows up on the chart might not be accurate), power would certainly be low for anything below 2000 rpm. It looks about right for a short cam as far at where it peaks (about 5250) and torque comes up by 2000 rpm and is farily flat. But it seems low on the torque overall. Is this the symptom of a low intensity short duration cam, wide lsa? Or is it poor flow somewhere? I'm gonna have to cognate on this one. Maybe like Matt says too tall and too short at the same time.
Last edited by 63mako; Jan 15, 2013 at 08:54 PM.
Race Director
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From: Millington Illinois
St. Jude Donor '08-'09
1. You can have a cam that has 280 duration @ .006 and 215 duration @ .050.
2. You can have a cam that has 268 duration @ .006 and 215 duration @ .050.
Both will work in the OP's build. Both will operate in the same rpm range. Effective compression or DCR will be much higher in cam # 2 where cam # 1 might have low enough DCR to reduce performance a lot. This could very well be the issue.
Le Mans Master
Joined: Dec 2009
Posts: 6,397
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From: Saskatoon Saskatchewan
Duration @ .006 or 004 does matter for DCR purposes. You need between 7.5 and 8.5 dcr in a street engine to produce best power.
1. You can have a cam that has 280 duration @ .006 and 215 duration @ .050.
2. You can have a cam that has 268 duration @ .006 and 215 duration @ .050.
Both will work in the OP's build. Both will operate in the same rpm range. Effective compression or DCR will be much higher in cam # 2 where cam # 1 might have low enough DCR to reduce performance a lot. This could very well be the issue.
1. You can have a cam that has 280 duration @ .006 and 215 duration @ .050.
2. You can have a cam that has 268 duration @ .006 and 215 duration @ .050.
Both will work in the OP's build. Both will operate in the same rpm range. Effective compression or DCR will be much higher in cam # 2 where cam # 1 might have low enough DCR to reduce performance a lot. This could very well be the issue.
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Race Director
Joined: May 2005
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From: Millington Illinois
St. Jude Donor '08-'09
Yes. Valve starts moving as soon as the lifter hits the start of the ramp. Duration @ .050 will determine what RPM range the cam makes power in.
Race Director
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From: Millington Illinois
St. Jude Donor '08-'09
Race Director
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From: central FL, near the beach.
we don't know the .006" duration for the GM cam. it is 262 for the xe262.
a Cam Dr. would tell it. Or it could be checked with a degree wheel in an engine. I once had a turbo corvair that had crazy long stock duration, even longer than the 476. i checked it when rebuilding it. maybe 330-360, i forget exactly. long time ago. Anyway, the car was such a dog off the line, i sold it. and it was turbocharged! turbo-dog! isn't there a tv show turbo dogs?
GM is going to be way longer than compcams. This is how comp built their business, cams with shorter ramps, etc, make more power.
My guess, the 476 at .006 tappet lift is 280-295 and the valve is open .009, enough to stop it building compression at low rpm. so poor off idle torque.
a Cam Dr. would tell it. Or it could be checked with a degree wheel in an engine. I once had a turbo corvair that had crazy long stock duration, even longer than the 476. i checked it when rebuilding it. maybe 330-360, i forget exactly. long time ago. Anyway, the car was such a dog off the line, i sold it. and it was turbocharged! turbo-dog! isn't there a tv show turbo dogs?
GM is going to be way longer than compcams. This is how comp built their business, cams with shorter ramps, etc, make more power.
My guess, the 476 at .006 tappet lift is 280-295 and the valve is open .009, enough to stop it building compression at low rpm. so poor off idle torque.
Last edited by Matt Gruber; Jan 16, 2013 at 05:04 AM.
Race Director
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From: central FL, near the beach.
there is a guy on speedtalk that says advancing the 962, and 151 6, yes 6, really helps. so i'd go 4-9 if it was convenient. BeeJay has a long ramp GM HotCam roller, i think he advanced it 9 
Le Mans Master
Joined: Apr 2011
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From: Hermosa
Take a look at this dyno. Notice how flat the torque curve is like the op's torque curve. If you subtract 50hp for losses of the trannie you almost have the same torque. The Hp is lower across the board for the op but he is not running a roller extreme energy cam.
http://www.compcams.com/v002/Pages/397/XR282HR-10.aspx
Looking at this page you'll notice a trend that all the high duration cams have very flat torque curves where as the shorter cams have more of a parabola to them. I'd say the ops cam has the torque profile of a 280+ cam with the HP range of a 260 cam, worst of both worlds
http://www.compcams.com/Pages/401/dyno-sheets.aspx
If I were him I would start by advancing the timing 4* to 6* on this cam as long as he could determine that exhaust valve clearence would still be good. This at least would bring the torque up faster and not cost anything but time.
http://www.compcams.com/v002/Pages/397/XR282HR-10.aspx
Looking at this page you'll notice a trend that all the high duration cams have very flat torque curves where as the shorter cams have more of a parabola to them. I'd say the ops cam has the torque profile of a 280+ cam with the HP range of a 260 cam, worst of both worlds
http://www.compcams.com/Pages/401/dyno-sheets.aspx
If I were him I would start by advancing the timing 4* to 6* on this cam as long as he could determine that exhaust valve clearence would still be good. This at least would bring the torque up faster and not cost anything but time.
Last edited by REELAV8R; Jan 16, 2013 at 07:49 AM.
Race Director
Joined: Oct 2000
Posts: 15,071
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From: central FL, near the beach.
I had a 345 scout with a dual range transfer case.
i'd put it in low range in 4x4, and it would LEAP. Top speed was 60mph, but it got there FAST.
that is like a 6:1 rear.
.
I think the long GM ramps are early Torque Management. TM is used on new cars to cut back low rpm torque and reduce warranty claims. So they used the long ramps in c3's to prevent burning the tires at every stop. They even slighty cut down the divider in some cars to further reduce torque. I've also seen iron intakes with passages connecting the 2 planes. What do you think that was for? TM! Sneaky, Huh!?
i'd put it in low range in 4x4, and it would LEAP. Top speed was 60mph, but it got there FAST.
that is like a 6:1 rear.
.
I think the long GM ramps are early Torque Management. TM is used on new cars to cut back low rpm torque and reduce warranty claims. So they used the long ramps in c3's to prevent burning the tires at every stop. They even slighty cut down the divider in some cars to further reduce torque. I've also seen iron intakes with passages connecting the 2 planes. What do you think that was for? TM! Sneaky, Huh!?
Last edited by Matt Gruber; Jan 16, 2013 at 09:15 AM.
Race Director
Joined: May 2005
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From: Millington Illinois
St. Jude Donor '08-'09
I had a 345 scout with a dual range transfer case.
i'd put it in low range in 4x4, and it would LEAP. Top speed was 60mph, but it got there FAST.
that is like a 6:1 rear.
.
I think the long GM ramps are early Torque Management. TM is used on new cars to cut back low rpm torque and reduce warranty claims. So they used the long ramps in c3's to prevent burning the tires at every stop. They even slighty cut down the divider in some cars to further reduce torque. I've also seen iron intakes with passages connecting the 2 planes. What do you think that was for? TM! Sneaky, Huh!?
i'd put it in low range in 4x4, and it would LEAP. Top speed was 60mph, but it got there FAST.
that is like a 6:1 rear.
.
I think the long GM ramps are early Torque Management. TM is used on new cars to cut back low rpm torque and reduce warranty claims. So they used the long ramps in c3's to prevent burning the tires at every stop. They even slighty cut down the divider in some cars to further reduce torque. I've also seen iron intakes with passages connecting the 2 planes. What do you think that was for? TM! Sneaky, Huh!?
The factory timing curve was also set up to reduce low RPM torque and reduce warrantee claims. The slow ramp does the same thing and also reduces cam wear, valvetrain issues and allows the use of weaker springs to further reduce long term wear.
Last edited by 63mako; Jan 16, 2013 at 09:27 AM.
Melting Slicks
Joined: Aug 2012
Posts: 2,548
Likes: 379
From: Woodinville WA
let me get this straight, you're suggesting spending $1,500 to swap rear gears; a problem that could be solved with a $200 cam swap? Not to mention that with the higher numeric gear the car becomes harder to drive, wears parts out faster, and gets much worse mileage.... while I certainly understand the idea of laying out all the options - I wonder about at what point the answer is in the weeds....
Melting Slicks
Joined: Aug 2012
Posts: 2,548
Likes: 379
From: Woodinville WA
I had a 345 scout with a dual range transfer case.
i'd put it in low range in 4x4, and it would LEAP. Top speed was 60mph, but it got there FAST.
that is like a 6:1 rear.
.
I think the long GM ramps are early Torque Management. TM is used on new cars to cut back low rpm torque and reduce warranty claims. So they used the long ramps in c3's to prevent burning the tires at every stop. They even slighty cut down the divider in some cars to further reduce torque. I've also seen iron intakes with passages connecting the 2 planes. What do you think that was for? TM! Sneaky, Huh!?
i'd put it in low range in 4x4, and it would LEAP. Top speed was 60mph, but it got there FAST.
that is like a 6:1 rear.
.
I think the long GM ramps are early Torque Management. TM is used on new cars to cut back low rpm torque and reduce warranty claims. So they used the long ramps in c3's to prevent burning the tires at every stop. They even slighty cut down the divider in some cars to further reduce torque. I've also seen iron intakes with passages connecting the 2 planes. What do you think that was for? TM! Sneaky, Huh!?
2.72 - 4.54 diff gears
low range 2.46
some math.
4500 rpm, 31" tire, 2.72 gears = 62 mph (never mind that a binder would come apart at 3500)
with 4.54 gears - same as above, that's 37 mph @ 4500
Are you certain it was 60 mph? perhaps with the short wheelbase it seemed like 60 but was really only 40?
but yes, in regards to the GM stuff - sneaky, very sneaky.
and yes, it appears I'm being a bit snarky this morning - mostly, I'm sorry about that
Last edited by SuperBuickGuy; Jan 16, 2013 at 10:28 AM.