Help me understand these cam specs
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Hrmm. Lets take things one at a time.
'straight up' means just that. If comp grinds the cam at 106 degrees (2 degrees advanced) when installed straight up the intake centerline will be at 106 degrees. If its ground on 108 degrees, thats where it will be. You can advance it with offset bushings, but we're talking about whats actually ground into the cam at 'straight up'.
On his cam, I assumed he was running an XR268 (though his specs don't seem to match that actually, or any cam I can find now that I think about it...weird) which is ground at 108* ICA. So I was pretty much asking "did you install it straight up, or advance/retard it? (what was the ica?)". Sorry for the confusion.
I'm assuming based on your specs you are running the 280XFI HR13 camshaft?
I cannot find the spec card, but usually comp grinds them on 106 or 108 degrees. If your degreeing it at 108.5 I'm guessing its ground on 108 and your timing set is slightly off. (mine was off by 1 degree advanced).
Now i'm confused about what your saying about 'straight up' being 4.5 degrees retarded on your cam, which is at 108.5 degrees.. The lobe seperation angle has absolutely nothing to do with the intake lobe centerline. Or are you suggesting SBC 'stock' intake centerlines are 113 degrees? I've always known stock to be 108 degrees. ?
As far as the lift goes, the cam I thought he was running has .330/.335 tappet lift, so even with 1.6 rockers thats .528/.536 so I don't know what cam he is running... (but i'd like to know).
And the reason I asked how his cam was installed is, because as we all know, advancing a cam tends to move the powerband up a hair. Though comp claims the cam I thought he was running does infact make power to 5800. *shrug*.
-- Joe
'straight up' means just that. If comp grinds the cam at 106 degrees (2 degrees advanced) when installed straight up the intake centerline will be at 106 degrees. If its ground on 108 degrees, thats where it will be. You can advance it with offset bushings, but we're talking about whats actually ground into the cam at 'straight up'.
On his cam, I assumed he was running an XR268 (though his specs don't seem to match that actually, or any cam I can find now that I think about it...weird) which is ground at 108* ICA. So I was pretty much asking "did you install it straight up, or advance/retard it? (what was the ica?)". Sorry for the confusion.
I'm assuming based on your specs you are running the 280XFI HR13 camshaft?
I cannot find the spec card, but usually comp grinds them on 106 or 108 degrees. If your degreeing it at 108.5 I'm guessing its ground on 108 and your timing set is slightly off. (mine was off by 1 degree advanced).
Now i'm confused about what your saying about 'straight up' being 4.5 degrees retarded on your cam, which is at 108.5 degrees.. The lobe seperation angle has absolutely nothing to do with the intake lobe centerline. Or are you suggesting SBC 'stock' intake centerlines are 113 degrees? I've always known stock to be 108 degrees. ?
As far as the lift goes, the cam I thought he was running has .330/.335 tappet lift, so even with 1.6 rockers thats .528/.536 so I don't know what cam he is running... (but i'd like to know).
And the reason I asked how his cam was installed is, because as we all know, advancing a cam tends to move the powerband up a hair. Though comp claims the cam I thought he was running does infact make power to 5800. *shrug*.
-- Joe
My point is that aligning the dots does not insure the cam is straight up. Only when it checks the same as the LSA is it straight up.
You've got a few other things wrong.
Straight up means that there is no advance or retard from the Lobe Separation Angle. The LSA is the last number shown on Comp's grind number. Considering HR13, the number 13 means the cam is ground on a LSA of 113. The number 12 would mean 112, etc.
If the cam is ground on 113 LSA with no advance ground in, when it's degreed in and the dots are aligned, the reading should be 113. Then the cam is straight up.
There are a few different ways to degree in the cam, one of the methods is called the Lobe Centerline Method, which is the method recommended by CompCams. It's not to be confused with the Lobe Separation Angle, which it often is.
If a cam is ground on 113 and, with the dots aligned, it checks at 108.5, then there is 4.5 degrees of advance ground into the cam. The LSA hasn't changed but the Lobe Centerline has. Lobe Centerline is different from Lobe Separation Angle. This is how it becomes so confusing to many.
When ordering a custom cam, as I did with the cam in my 415, I specified to Comp that NO advance be ground into it. It was ground on 114 LSA and when I degreed it in by first just aligning the dots, it checked at 114. So I didn't have to use a bushing to make any correction. If it had checked at, say, 112 I would have used a 2 degree bushing in the retard position; if 116, 2 degrees in the advance.
Advancing a cam moves the power range lower, not higher in the rpm band. This, too is something often mistaken. It doesn't necessarily cause the engine to make more torque or HP (although it can), it basically moves/jockeys around the power band.
A recent article in the Summer issue of Engine Masters shows the effect of advancing and retarding a cam. Based on the different settings they used, the engine DID make slightly more power at, I believe it was, 105 as compared to the other settings they tried. That setting, 105, doesn't apply to all cams though, just the one they were testing.
I don't recall them listing the power band though, but advancing a cam moves the power range down in the band; retarding it "up".
As an example, I once built a 477 BB for a team and used one of Crane's Inverted Flank rollers, degreed in per Crane's recommended (which is only a starting point - not etched in stone). After a few passes, the car's driver reported back to me that the engine felt slightly flat at the first stripe. I retarded the cam 4 degrees and he then was able to carry it past the last stripe still pulling hard. He left higher so the ET wasn't hurt, but MPH went up.
The cam in my 415 is a custom grind - Serial number V7613, part number 12-000-8, Grind # CS 3192/3315 HR114.0 The 114 is the LSA and the "0" indicates no advance ground in.
The one in my new 388 is Serial number F 3755-05, Part # 07-000-9, Grind # 3016S/3037S HR113+4. It's .577/.572 with 1.6s but I'm running Scorpion 1.7s. If everything was spot on, it shojuld have checked at 109, but it checked at 108.5, meaning it in fact had 4.5 degrees if advance ground in. There's no 1/2 degree bushing, so I couldn't have retarded it 1/2 degree to hit 109.
Jake
Jake
Race Director
Joined: Jan 2002
Posts: 12,264
Likes: 88
From: O'Fallon Missouri
I'm running 605/622 lift, and the car drives almost like a stocker.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
If the durations are very close between the two cams, but one has significantly more lift, that tells you that the cam with the higher valve lift has more aggressive ramps.
Makers don't numerically identify the ramp design so that we can compare the aggressiveness of one cam with another, but there's a little math trick I've used over the years.
Take the advertised duration and subtract the duration at .050. Do that on another cam. The LOWER the difference, the MORE aggressive the ramps. BOTH cams have to have their advertised duration measured at the same point though, otherwise the comparison won't work. Say both at .006. You have to compare "like" camshafts too, HR with HR, not HR with mechanical roller.
If one has a difference of, say, 50 and the other 52, then the one with 50 has more aggressive ramps.
Say one cam has an advertised duration of 280 and a duration at .050 of 230. That gives a difference of 50
Now another one has an advertised duration of 280 and a duration at .050 of 228. That gives a difference of 52.
The first cam has the more aggressive ramps.
Jake
Jake
Burning Brakes
Joined: Sep 2005
Posts: 993
Likes: 3
From: Iowa
The two main things that we look at when we start talking lift is 1, does the cylinderhead actually flow that much more at .600+ to justify a cam/rocker combination of that type and 2, how many miles does the person want to run the engine without changing the springs out. Big lift kills even the best springs; even the $500 ones in a short amount of time. I would stay in the mid .500 area for a street engine that has GM cast heads on it as I've never seen any flow data that showed enough additional flow past .500 to justify it.
Burning Brakes
Joined: Nov 2005
Posts: 797
Likes: 0
From: Bedford Ma.
Let me clarify my statement.When I floor it in drive,it climbs to about 6300 acording to the factory tach.I have never had it on a dyno and have not yet taken it to the track.Other than the mods i`ve mentioned,it has an MSD opti and an MSD coil a set of Taylor wires and most importantly a PCMFORLESS tune.Just from my own SOTP observation and watching the tach,Ifelt that it pulled pretty well up til it shifted it self at about 6300rpm.
Safety Car
Joined: May 2006
Posts: 4,290
Likes: 140
From: Salem NH
'"straight up' means just that. If comp grinds the cam at 106 degrees (2 degrees advanced) when installed straight up the intake centerline will be at 106 degrees. If its ground on 108 degrees, thats where it will be." EXACTLY. If the cam is ground on 113 LSA, that's what it should show when degreed in with the dots aligned. But, if with the dots aligned, it checks at 108.5 - which mine did - that tells me the cam has 4.5 degrees of advance ground into it. The Lobe Centerline has been altered NOT the LSA.
My point is that aligning the dots does not insure the cam is straight up. Only when it checks the same as the LSA is it straight up.
You've got a few other things wrong.
Straight up means that there is no advance or retard from the Lobe Separation Angle. The LSA is the last number shown on Comp's grind number. Considering HR13, the number 13 means the cam is ground on a LSA of 113. The number 12 would mean 112, etc.
If the cam is ground on 113 LSA with no advance ground in, when it's degreed in and the dots are aligned, the reading should be 113. Then the cam is straight up.
There are a few different ways to degree in the cam, one of the methods is called the Lobe Centerline Method, which is the method recommended by CompCams. It's not to be confused with the Lobe Separation Angle, which it often is.
If a cam is ground on 113 and, with the dots aligned, it checks at 108.5, then there is 4.5 degrees of advance ground into the cam. The LSA hasn't changed but the Lobe Centerline has. Lobe Centerline is different from Lobe Separation Angle. This is how it becomes so confusing to many.
When ordering a custom cam, as I did with the cam in my 415, I specified to Comp that NO advance be ground into it. It was ground on 114 LSA and when I degreed it in by first just aligning the dots, it checked at 114. So I didn't have to use a bushing to make any correction. If it had checked at, say, 112 I would have used a 2 degree bushing in the retard position; if 116, 2 degrees in the advance.
Advancing a cam moves the power range lower, not higher in the rpm band. This, too is something often mistaken. It doesn't necessarily cause the engine to make more torque or HP (although it can), it basically moves/jockeys around the power band.
A recent article in the Summer issue of Engine Masters shows the effect of advancing and retarding a cam. Based on the different settings they used, the engine DID make slightly more power at, I believe it was, 105 as compared to the other settings they tried. That setting, 105, doesn't apply to all cams though, just the one they were testing.
I don't recall them listing the power band though, but advancing a cam moves the power range down in the band; retarding it "up".
As an example, I once built a 477 BB for a team and used one of Crane's Inverted Flank rollers, degreed in per Crane's recommended (which is only a starting point - not etched in stone). After a few passes, the car's driver reported back to me that the engine felt slightly flat at the first stripe. I retarded the cam 4 degrees and he then was able to carry it past the last stripe still pulling hard. He left higher so the ET wasn't hurt, but MPH went up.
The cam in my 415 is a custom grind - Serial number V7613, part number 12-000-8, Grind # CS 3192/3315 HR114.0 The 114 is the LSA and the "0" indicates no advance ground in.
The one in my new 388 is Serial number F 3755-05, Part # 07-000-9, Grind # 3016S/3037S HR113+4. It's .577/.572 with 1.6s but I'm running Scorpion 1.7s. If everything was spot on, it shojuld have checked at 109, but it checked at 108.5, meaning it in fact had 4.5 degrees if advance ground in. There's no 1/2 degree bushing, so I couldn't have retarded it 1/2 degree to hit 109.
Jake
Jake
My point is that aligning the dots does not insure the cam is straight up. Only when it checks the same as the LSA is it straight up.
You've got a few other things wrong.
Straight up means that there is no advance or retard from the Lobe Separation Angle. The LSA is the last number shown on Comp's grind number. Considering HR13, the number 13 means the cam is ground on a LSA of 113. The number 12 would mean 112, etc.
If the cam is ground on 113 LSA with no advance ground in, when it's degreed in and the dots are aligned, the reading should be 113. Then the cam is straight up.
There are a few different ways to degree in the cam, one of the methods is called the Lobe Centerline Method, which is the method recommended by CompCams. It's not to be confused with the Lobe Separation Angle, which it often is.
If a cam is ground on 113 and, with the dots aligned, it checks at 108.5, then there is 4.5 degrees of advance ground into the cam. The LSA hasn't changed but the Lobe Centerline has. Lobe Centerline is different from Lobe Separation Angle. This is how it becomes so confusing to many.
When ordering a custom cam, as I did with the cam in my 415, I specified to Comp that NO advance be ground into it. It was ground on 114 LSA and when I degreed it in by first just aligning the dots, it checked at 114. So I didn't have to use a bushing to make any correction. If it had checked at, say, 112 I would have used a 2 degree bushing in the retard position; if 116, 2 degrees in the advance.
Advancing a cam moves the power range lower, not higher in the rpm band. This, too is something often mistaken. It doesn't necessarily cause the engine to make more torque or HP (although it can), it basically moves/jockeys around the power band.
A recent article in the Summer issue of Engine Masters shows the effect of advancing and retarding a cam. Based on the different settings they used, the engine DID make slightly more power at, I believe it was, 105 as compared to the other settings they tried. That setting, 105, doesn't apply to all cams though, just the one they were testing.
I don't recall them listing the power band though, but advancing a cam moves the power range down in the band; retarding it "up".
As an example, I once built a 477 BB for a team and used one of Crane's Inverted Flank rollers, degreed in per Crane's recommended (which is only a starting point - not etched in stone). After a few passes, the car's driver reported back to me that the engine felt slightly flat at the first stripe. I retarded the cam 4 degrees and he then was able to carry it past the last stripe still pulling hard. He left higher so the ET wasn't hurt, but MPH went up.
The cam in my 415 is a custom grind - Serial number V7613, part number 12-000-8, Grind # CS 3192/3315 HR114.0 The 114 is the LSA and the "0" indicates no advance ground in.
The one in my new 388 is Serial number F 3755-05, Part # 07-000-9, Grind # 3016S/3037S HR113+4. It's .577/.572 with 1.6s but I'm running Scorpion 1.7s. If everything was spot on, it shojuld have checked at 109, but it checked at 108.5, meaning it in fact had 4.5 degrees if advance ground in. There's no 1/2 degree bushing, so I couldn't have retarded it 1/2 degree to hit 109.
Jake
Jake
I know what your saying now. I've always considered 'straight up' to be installed at the advertised ICA, and i've always degreed them to ensure the timing set/dots were on right. I *thought* what you were saying was your cam had an advertised ICA of 113, but when you lined the dots up it degreed at 108.
I had the advancing/retarding relation to the powerband mixed up because I'm used to entering the valve timing directly in my simulators, and I'm used to plugging in "-1" to ADVANCE it which results in moving the power band down, but the negative number sometimes makes my brain think i'm RETARDING it..
Sorry!
-- Joe
