ideas on a cam
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
danlee, you can get custom cams for about the same price as a stocker. They are not returnable and take longer tho. Use the intake timing numbers from a 260HR and the exhaust numbers from a 270HR together to make a dual pattern HR cam and check the results.
When you downshift a loss of 50 lb-ft of torque is more than made up with 1000 RPMs.
When you downshift a loss of 50 lb-ft of torque is more than made up with 1000 RPMs.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
Second gear in a stock C6 is 1.46:1. If you were towing at 2500 RPMs and puttting out 440 ft-lbs of torque, and hit a grade that required a downshift your revs would go to 3650 RPM. Since the gear ratio is a torque multiplier you would get the effect of 642 ft-lbs torque at the drive wheels, assuming that there is no loss.
However if your torque drops to 300 ft-lbs, the effective torque at the rear wheels is 438 ft-lbs, the same as it was before the downshift. Your tranny would have to downshift again to maintain speed, or you would slow down until your torque rose to the level required to pull the hill.
This example is a bit extreme, but I just want to demonstrate the necessity of maintaining a flat torque curve out past 3500 RPMs.
However if your torque drops to 300 ft-lbs, the effective torque at the rear wheels is 438 ft-lbs, the same as it was before the downshift. Your tranny would have to downshift again to maintain speed, or you would slow down until your torque rose to the level required to pull the hill.
This example is a bit extreme, but I just want to demonstrate the necessity of maintaining a flat torque curve out past 3500 RPMs.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
This is the torque value for different cams at 2000, 2500, 3000, 3500, 4000 - 3650 RPM. The torque at 3650 is estimated from the curve, so I listed it seperate from the entries at 500 RPM increments.
You can see from this table that the shorter duration cams give the best torque at 2000 RPM, but the longer duration cam produce better numbers at 3650 RPM. The dual energy cams have high low RPM torque and good torque at 3650 RPM. The Rollers are better all over, but follow the same pattern.
With the 260H, I lose nearly 50 ft-lbs torque when the tranny downshifts at 2500 RPMs. The cam with the most torque at 3650 RPM is the 260/270HR dual pattern. I used the lift (0.566) from the 270HR on both lobes of the 260/270HR.
- 260H 444, 433, 424, 407, 369 - 385
- 255DEH 446, 440, 428, 412, 377 - 400
- 268H 429, 427, 421, 411, 385 - 395
- 265DEH 427, 427, 422, 413, 392 - 400
- 260HR 485, 475, 468, 453, 419 - 435
- 270HR 461, 462, 460, 457, 439 - 445
- 260/270HR 477, 477, 470, 462, 439 - 450
You can see from this table that the shorter duration cams give the best torque at 2000 RPM, but the longer duration cam produce better numbers at 3650 RPM. The dual energy cams have high low RPM torque and good torque at 3650 RPM. The Rollers are better all over, but follow the same pattern.
With the 260H, I lose nearly 50 ft-lbs torque when the tranny downshifts at 2500 RPMs. The cam with the most torque at 3650 RPM is the 260/270HR dual pattern. I used the lift (0.566) from the 270HR on both lobes of the 260/270HR.
Last edited by danlee; Mar 16, 2004 at 07:21 PM.
Cargo Master
Joined: May 2003
Posts: 2,561
Likes: 1
From: Earth
What setups are you running on your Dyno? I've got one of the early versions, and I get different numbers (higher actually) with the 265DEH cam. About 440 ftpds torque with a 600 cfm carb, dual plane manifold, small tube headers, and a low compression of just 8.33:1. I put in the exact cam specs from Comp cams as well. Wait a minute, maybe it's the timing your using. I know mine is set for 2* max, as it drops with more or less advance.
Any thoughts? I'm actually hearing from other guys that the 265 cam is a good cam. Decent mileage, and has a slight lope to it (even though Comp. says it is smooth.) I really, really do not want to mess too much with higher compression than what I have it spec'd out for currently, 8.33:1, with a .040 bore. Reason is, I don't want to have to run high octane to prevent detonation. In it's stock form of 8:1, I only detonate when I set my timing too far advanced.
Basically, I'm probably after the elusive "white horse", as I would like a decent cam with a mileage of 12-13 mpg or thereabouts, has more power, and a slight lope at idle. I'm sure one might exist, but it seems less possible really. Mileage though is probably more important than a "lopey" sound.
Any thoughts? I'm actually hearing from other guys that the 265 cam is a good cam. Decent mileage, and has a slight lope to it (even though Comp. says it is smooth.) I really, really do not want to mess too much with higher compression than what I have it spec'd out for currently, 8.33:1, with a .040 bore. Reason is, I don't want to have to run high octane to prevent detonation. In it's stock form of 8:1, I only detonate when I set my timing too far advanced.
Basically, I'm probably after the elusive "white horse", as I would like a decent cam with a mileage of 12-13 mpg or thereabouts, has more power, and a slight lope at idle. I'm sure one might exist, but it seems less possible really. Mileage though is probably more important than a "lopey" sound.
Last edited by 53fatfndr; Mar 16, 2004 at 08:04 PM.
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
I use Desktop Dyno 2000 but you really need the book that goes along with it to understand how to set up the dyno program properly. The name of the book is "Desktop Dyno's" and I believe it is available thru the online store here. -Edit- Just checked and could not find it, you may need to go to Waldens or something.
An example of why you need the manual is the type of cam setting for a hydraulic roller cam: -For mild grinds like we have been discussing here you use the "solid lifter" selection for a hydraulic roller cam in order to get the proper ramp rate for the cam lobes. There are all kinds of other things that have to be set right that don't seem to match up with the settings that are listed.
The newest version of the software may be better tho. I have not upgraded because I can't justify the cost. I might have been able to justify the cost if I had not spent money b4 on the cam disk and other things that have turned out to be absolutely worthless to me.
An example of why you need the manual is the type of cam setting for a hydraulic roller cam: -For mild grinds like we have been discussing here you use the "solid lifter" selection for a hydraulic roller cam in order to get the proper ramp rate for the cam lobes. There are all kinds of other things that have to be set right that don't seem to match up with the settings that are listed.
The newest version of the software may be better tho. I have not upgraded because I can't justify the cost. I might have been able to justify the cost if I had not spent money b4 on the cam disk and other things that have turned out to be absolutely worthless to me.
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Cargo Master
Joined: May 2003
Posts: 2,561
Likes: 1
From: Earth
Thanks for the explanation, Eric. I think I have one of the first copies of that program from when it came out. When I first got it, I was running it in DOS on a 486 machine. This was back in, I believe '95, plus it says '95 on the back of the floppy disk. Oh, well. At least the numbers are close. I never figured this to be dead on, but at least somewhat ball-park.
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
I have about 4 different versions of the program back from my own 486 days. The program is best used to compare camshafts but not for absolute numbers. It is not perfect for camshafts either since the cam manufacturers do a lot of research on the cam profiles that really don't show up in the raw open/close timing numbers.
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