How about two tests, The first a 350 cid W/vortec heads and 1970's solid LT1 cam, The second 383 W/vortec heads and 1970's solid LT1 cam. Both with flat top pistons, zero deck height and 5.7 rods.

Carl

 

I made assumptions such as 10:1 compression, a dual plane intake, small tube headers with mufflers, and the cam installed straight up for both.

Comparo Graph:


350 Table:


383 Table:

 

max torque at 2K rpm?

 

I was wondering the same thing. I know DD has some quirks but those numbers don't look right to me either. An LT-1 cam making peak power at 5K in a 350 and at 4500 in a 383? I don't think so. I don't have the LT-1 cam specs to run a DD on it but, overall, peak torque looks high and peak hp looks low for that combo.

 

What can I say. I plugged in the data and this is what I got. Could be operator error, or it could be the program. I've run other curves that look good compared to known engines, but I have noticed similar weirdness in the curves with some combos. It is possible I entered the Cam specs wrong, but I got them off one of the cam builder sites.

 

Brad - that torque curve is too flat for the LT-1 cam, even for a long stroke engine. What did you use for specs?

I have DD2000 cam files for the LT-1 cam based on a lift-crank angle diagram that I took off a new LT-1 cam. The published numbers you see don't mean anything, because DD2000 needs open/close data at .006" actual valve lift. I have that data that is also corrected for actual measured rocker ratio. It's not 1.5:1 and it's not even constant.

Here is the LT-1 cam data you need to set up DD2000 files. Clearance of .021/.026 is rocker ratio adjusted to take up the clearance at the top of the ramps. (The rocker ratio is 1.37 at the top of the ramp.) At max lift the rocker ratio is 1.44:1. Max valve lift is based on lobe heights (.306/.323) minus ramp heights (.016/.020) times 1.44

The .006/006 valve lift file is conventional SAE J604d duration, but I also developed the .006/.010 valve lift file to compensate for the LT-1's asymmetric lobe. DD2000 assumes a symmetric lobe so the .006/.010 file may be a better represention. It gives a little more torque and a little less top end power than the .006/.006 file.

at .006/.006 valve lift: timing 26-71.5/83.5-29.5, max valve lift .418/.436

at .006/.010 valve lift: timing 26-68/83.5-26, same max valve lift.

If you don't use rocker ratio adjusted lifts for other cams then use LT-1 max valve lifts of .435/.455. Non-rocker ratio adjusted lifts will reduce absolute accuracy, but you want to use consistent measuring conventions when comparing cams.

Note that the LT-1 cam has a very early phased exhaust event with about 15 degrees more duration than the inlet side, most of which is at the front end. This early opening exhaust event compensates for the SB head's relatively restrictive exhaust port and is one of the secrets to the LT-1 cam that provides excellent torque bandwidth and peak power. The assymmetric lobe yields a very gentle closing which is very easy on the valves and seats.

If anyone wants the actual DD2000 LT-1 cam files, or the valve adjustment procedure for all OE SB cams that discusses the variation in rocker ratio and why the OE clearances should be "factored", e-mail me and I send them to you.

Duke




[Modified by SWCDuke, 6:02 AM 12/5/2003]

 

Here should be a jpg of a dyno using edelbrock heads and an LT1 cam. I apolgoze if it doesn't come out I'm not so great at posting pictures. Just click the image to read it. You can always go to my website and click on Cam Comparison




[Modified by TTop Tony, 8:34 AM 12/5/2003]

 

Duke,

I got the info from Copm or Crane for what they labeled as the equivalent. It was a .485/.485 lift with 254/254 degrees at .006 and a 114 lobe center. I'll see if I can enter your specs, but if you want to email me you cam file, that would be great. brad@ep.com should work just fine.

 

Usins Duke's specs I got a much more realistic curve. Again, this is with a dual plane manifold. Adding in a single plane should bump up the RPM peak and kill some bottom end torque.

 

OK, since it was easy, I substitued a single plane manifold, which is what I would use if I were going with this setup after looking at the small change in the curve. Bottom end torque is still stout, and the top end picks up nicely.

 

Ahhh, what you have here is some erroneous 30-30 cam data. The duration at 050" lifter lift is 254/254, but the concept of lobe center on both the 30-30 and LT-1 cams is somewhat meaningless because the lobes are asymmertical and the point of max lift does not correspond to the actual center of the lobe. The LT-1 cam duration at .050" is 242/254, gross lift is .459/.485 (which includes the clearance ramps). The points of maximum lift are 110/122, which do not correspond to the "centerlines" because the lobes are asymmetrical. The LT-1 inlet lobe is very similar to the Duntov inlet lobe, but with a bit more duration and lift and the assymetrical closing profile. The LT-1 exhaust lobe is very close to the 30-30 exhaust lobe, but is advanced several degrees relative to the 30-30.

.050" lift timing/duration data is okay for a hydraulic cams, but won't work for a solid lifter cam because a lot of that lift is clearance ramp.

The data I provided in my previous post is what you (or anyone else need)need to generate your own LT-1 cam files, but be sure to adjust other cams peak lift for rocker ratio if you want to compare apples and apples and achieve more accurate results.

Notice that with a dual plane manifold the engine has considerably better 80 percent torque bandwidth. Unless you're building an engine for Bonneville, concentrating on torque bandwidth will yield a better performing street high performance engine or road race engine because it will make more AVERAGE power over the usable rev range.

Whether you punch the throttle on the street at 2500 or come off a corner on a track at 3500 the dual plane manifold is going to pull stronger than the guy behind you with a single plane, and his slight advantage at the top end is not going to be enough to get next to you and try to outbrake you entering the next corner or before you have to brake for the next stop light!!!

Duke




[Modified by SWCDuke, 8:18 PM 12/5/2003]

 

Duke, I knew you'd have the correct info. I'm not sure that I understand the part about .05 lift figures not being comparable though. [QUOTE]
.050" lift timing/duration data is okay for a hydraulic cams, but won't work for a solid lifter cam because a lot of that lift is clearance ramp.
QUOTE]
I understand how actual total duration figures are different due to lash and ramp rate but by .05 lift, don't both cam types function the same?

 

Consider two mechanical lifter cams that have the same lash point and SAE J604D duration (.006" VALVE lift duration), but one has a clearance ramp height of .010" and the other is .020". The second cam will have considerably greater duration at .050" lifter rise because much more of the "duration" is the shallow (typically .0002"/deg. for Chevrolet mechanical lifter V-8 cams) clearance ramps when the valve isn't even open.

Say the first cam has duration at .050" lifter rise of 230 degees, the second will be speced at around 250 degrees. Using the .006" valve lift standard will achieve the same simulation results for both cams because they are the same except for the clearance ramps, but using the .050" lift rise number will give considerably different results.

.050" lifter rise data gives fairly comparable results for hydraulic lifter cams from different sources because ramp height is fairly consitent across the industry, but the .050" lifter rise data for many mechanical lifter cams is not comparable due to considerable ramp height differences from one mechanical lifter cam to the next.

Duke


[Modified by SWCDuke, 12:52 PM 12/6/2003]