Camshaft Discussion Part III
04-11-2005, 10:36 AM
#101
Found it 
Comp 26921:
# of springs: Dual
Installed Height: 1.77
Outer Spring OD: 1.300
Outer Spring ID: .895
Inner Spring ID: .655
Spring Rate: 408
Damper: No
1.85: 102
1.80: 123
1.75: 124
1.70: 164
1.65: 184
1.60: 204
1.55: 225
1.50: 245
1.45: 265
1.40: 286
1.35: 306
1.30: 327
1.25: 347
1.20: 367
1.15: 388
1.10: 408
Max Coil Bind Height: 1.040
Ti. Retainer (Std Wt): 754
Seat 0.57 OD Guide: 4695 (.500 Guide)
Shims: 4753
Ok, Now what else is needed to see if the ramp on the proposed lobe would be too agressive.
.006 - 260
.050 - 220
.200 - 160
.353 lift (.600 with the 1.7 rocker)
Motor would be seeing 7400-7500 rpm. Again, this would be a hyd motor with Comp R lifters.
Any info needed on the Comp R lifter?
Or the rocker that will be used?
Most likely a reworked stock rocker since they seem to be the lightest over the tip. Possibly a Harlan Sharp roller since I have a set already. The HS's have a pin connecting 2 rockers through the pivot point helping to keep them from from deflecting side to side on the valve and pushrod. Not sure if the stock reworked ones from HS have the same set up, but they get rid of the needle bearings.
Comp 26921:
# of springs: Dual
Installed Height: 1.77
Outer Spring OD: 1.300
Outer Spring ID: .895
Inner Spring ID: .655
Spring Rate: 408
Damper: No
1.85: 102
1.80: 123
1.75: 124
1.70: 164
1.65: 184
1.60: 204
1.55: 225
1.50: 245
1.45: 265
1.40: 286
1.35: 306
1.30: 327
1.25: 347
1.20: 367
1.15: 388
1.10: 408
Max Coil Bind Height: 1.040
Ti. Retainer (Std Wt): 754
Seat 0.57 OD Guide: 4695 (.500 Guide)
Shims: 4753
Ok, Now what else is needed to see if the ramp on the proposed lobe would be too agressive.
.006 - 260
.050 - 220
.200 - 160
.353 lift (.600 with the 1.7 rocker)
Motor would be seeing 7400-7500 rpm. Again, this would be a hyd motor with Comp R lifters.
Any info needed on the Comp R lifter?
Or the rocker that will be used?
Most likely a reworked stock rocker since they seem to be the lightest over the tip. Possibly a Harlan Sharp roller since I have a set already. The HS's have a pin connecting 2 rockers through the pivot point helping to keep them from from deflecting side to side on the valve and pushrod. Not sure if the stock reworked ones from HS have the same set up, but they get rid of the needle bearings.
04-11-2005, 11:57 AM
#102
TECH Resident
Join Date: Dec 2004
Location: K-W, Ontario
Posts: 845
Likes: 0
Received 0 Likes
on
0 Posts
This is what I would recommend:
If the LS1 has a stock height of 1.8", use 1.8" as the install height.
That will yield about 123 lbs. closed, and about 367 lbs. open (1.2")
which is more than enough @ 7500 RPM.
This leaves about 0.140" before bind which will handle pretty much anything
you can throw at this spring.
If you need to shim the spring (~ 0.020") , there is still sufficient clearance.
As for being aggressive on the ramp, the cam MFG. will normally indicate
the maximum rocker multiplier. Since you're sticking with 1.7 ratio, I don't
forsee any danger. The numbers you posted for duration at the lobe are
fairly common.
Finally for the remainder of the valve train components, you have selected
good parts. They are fairly light weight which will help.
The only question I have is the operating range for this cam. Will you need to
spin 7500 RPM?
If the LS1 has a stock height of 1.8", use 1.8" as the install height.
That will yield about 123 lbs. closed, and about 367 lbs. open (1.2")
which is more than enough @ 7500 RPM.
This leaves about 0.140" before bind which will handle pretty much anything
you can throw at this spring.
If you need to shim the spring (~ 0.020") , there is still sufficient clearance.
As for being aggressive on the ramp, the cam MFG. will normally indicate
the maximum rocker multiplier. Since you're sticking with 1.7 ratio, I don't
forsee any danger. The numbers you posted for duration at the lobe are
fairly common.
Finally for the remainder of the valve train components, you have selected
good parts. They are fairly light weight which will help.
The only question I have is the operating range for this cam. Will you need to
spin 7500 RPM?
04-11-2005, 12:19 PM
#103
Being a 348ci large turbo motor I think I am going to have to spin it up there.. The T91 probably isn't going to see full spool till after 5k from what I am hearing. Maybe even closer to 5500.
The profile above was just something I threw out there for the lobe. Trying to just find a definative answer on being too agressive.
I'm really thinking about doing a solid roller though now.
Thanks for the info though..
The profile above was just something I threw out there for the lobe. Trying to just find a definative answer on being too agressive.
I'm really thinking about doing a solid roller though now.
Thanks for the info though..
04-11-2005, 08:39 PM
#105
TECH Resident
Join Date: Dec 2004
Location: K-W, Ontario
Posts: 845
Likes: 0
Received 0 Likes
on
0 Posts
I don't know the equation. I'm sure it would be some sort of "velocity * mass / time " to estimate acceleration of load? It would also be a dynamic
equation as engine RPM increases, reciprocating mass would also increase.
You might have more luck searching the Net (as I'm doing since you've sparked my interest).
In the real world, dyno testing would reveal how much spring pressure is needed
to avoid floating and bounce.
By "rule of thumb", I was taught to add 0.020" clearance over the base clearance (0.040")
for every 500 RPM over the recommended values.
This only applies if the component mass stays the same because the additional
spring travel will account for extra open pressure.
At the point when you come too close to bind clearance, you need to change
install heights, or springs to achieve the same open pressures while keeping
a safe bind buffer...either that, or go to a heavier spring with less clearance.
This is where the cross reference charts come in very handy.
In any case, your setup is fine. You have tons of buffer zone at the open height.
equation as engine RPM increases, reciprocating mass would also increase.
You might have more luck searching the Net (as I'm doing since you've sparked my interest).
In the real world, dyno testing would reveal how much spring pressure is needed
to avoid floating and bounce.
By "rule of thumb", I was taught to add 0.020" clearance over the base clearance (0.040")
for every 500 RPM over the recommended values.
This only applies if the component mass stays the same because the additional
spring travel will account for extra open pressure.
At the point when you come too close to bind clearance, you need to change
install heights, or springs to achieve the same open pressures while keeping
a safe bind buffer...either that, or go to a heavier spring with less clearance.
This is where the cross reference charts come in very handy.
In any case, your setup is fine. You have tons of buffer zone at the open height.
12-08-2007, 12:01 AM
#109
Teching In
Join Date: May 2006
Location: Austin
Posts: 9
Likes: 0
Received 0 Likes
on
0 Posts
Now, if you go over to a solid roller, you can do a tight lash roller, get a slightly more agressive lobe going, but be easier on springs. So you ask, HOW. The simple answer is when you go over to a solid roller lifter you can drop weight. Lower the valvetrain mass, and spring load decreases.
For a given preload and ramp rates and rpm, the spring will always see the same load if there's no valve float; it's the cam which sees less force. The spring puts an identical force as it would have on the retainer at all points on the cycle because, regardless the mass of the valve train, if there's no float, the spring sees exactly the same motion, and the force the spring puts on its retainer is purely a function of how far it's compressed, how fast its accelerating (spends some force internally accelerating itself), its temp, etc.; it doesn't know what's on the other side of the retainer). What is different with a heavier lifter is more of this force is spent accelerating the heavier lifter and less of it is spent pushing the lifter on the cam.
However with a lighter valvetrain, you CAN use less preload or a lighter spring, which I imagine will have the effects you describe.
Another interesting thing to consider is the valves move 1.7x what the lifters/pushrods do, therefore weight lost there is worth more than weight lost at the lifter end, i.e. it will take (ignoring friction) 1.7x the force per valve mass to accelerate it as it does the lifter at a given point in the cycle.
