was looking at the cam i'm going to use. well they have it listed for the LT1 and for the earlier engines. same specs. or so i thought. both are

220/230 @ .050
.510/.510 lift

but i looked closer at the actual cam cards for these 2 ALMOST identical cams. the point at which the valves open and close are different. so, i plugged them into DD2000 and got this difference.

hp compare
http://www.stealthram.com/images/l98lt1hpcompare.gif

tq compare
http://www.stealthram.com/images/l98lt1tqcompare.gif

here are the open and close points for each cam. this is in crank degrees. the L98 style has more below 4500. the LT1 has more above 4500.

07-305-8 L98 cam profile
IO 28 IC 68
EO 83 EC 27

08-305-8 LT1 cam profile
IO 0 IC 40
EO 53 EC -3

 

Look at the cam card specs again more closely.
One is timing at .006" lifter lift or seat duration
and the other is the timing at .050 lifter lift.

it is the same cam grind and installs at the same
110deg intake centerline

the LT-1 and L-98 cam core is a little different.
that iswhy there are two different part numbers.
Performance will be the same.

 

dd2000 put the specs in at the correct spots. one at seat to seat and the other at .050 to match. i used the cam math function. there is a difference in power. just like advancing or retarding the cam. but yes the valve event are listed differently.

 

you have to understand how the DD2000 program works to evalulate the two ways of entering cam specs.

DD2000 actualy uses Seat duration to "Model the cam"

When you choise the enter the .050" method, the program estimates the seat durtation based on your input.
In the program it is a set difference in degrees between the choices.
The "intensity" increases depending on the lifter type you choose.
EG: there is 56 deg difference between the seat duration and .050 duration method choice when you choose a hyd lifter.
This "intensity decreases to 44 deg if a solid lifter is chosen and 34deg for a roller.

Therefore if infact the cam has less or more than a 56 degrees differnence between the two references,
the cam will be modeled wrong using the .050" method.
And give a differnt result.

The seat duration method is the most accurate method.

The "Roller" choice refers to a solid race roller with very quick ramps, not a street hyd roller.
If youre choicing "roller" as the lifter choice its the wrong one to model a Comp Hyd roller.


This is explained in the instructions.

Remember "Garbage in, garbage out"

Do a search on the net for "Harvey Crane" and "Intensity" for a good explaination of "intensity" as it refers to camshafts.

 

well, when you get a program for free, you usually don't get the instruction book. so thanks for the info about the cam choice. i used the 'roller' choice for both. so i should use the 'hydraulic' choice for both then? there is a 56* difference in the cam duration (276-220=56*).

 

F-Bird, I'm so glad someone else has been taking note of which lifter selection to use, besides myself.

mrr23, yes you should use the hyd lifter option with a cam that's otherwise "stock".

The one thing that DD2000 can't do at all is predict the gains seen from the frictional losses of a roller cam over a flat tappet cam.

The nice thing about using the hyd lifter option is the predicted HP and TQ outputs are 'more than likely' to be lower than actual output.

I don't know about you, but if I build an engine, I'd rather put out 350 HP even though DD2000 figured 340 HP, than have it the other way

I've played with that program enough to know it pretty well.

I'm building a 350 for a friend right now. He got a "knock off" cam with the engine kit he bought.

280*/290* adv duration. 112 LSA... 108*/116* .443"/.465"

The .050" duration is 214*/224*

According to my calculations from degreeing the cam, the hyd intensity is 66*. Pretty lame.

If you enter those two duration figures in seperately (adv 'vs.' .050") and compare the outputs, it's amazing the difference.

Make one simple change... input the advertised as 270*/280* (56* hyd intensity) and the results are IDENTICAL!!!

Kind of makes it difficult to know which to use.

 

too bad also that when you click the 'roller' choice it says solid or hydraulic lifter.

 

ok did it f-bird88 way and it's within about 3-5hp and tq. thanks for the info.

 

Trouble with that cam and ones like it is that the "advertized duration" of 280-290 is not the seat duration. It does not a have a reference lift point.
Because it is just an "advertized" number.
If you measured the lobe duration on a Cam Doctor you'd find that cam has a seat duration of about 270/280 at .006" lift.
I've seen the same cam with a advertized duration of 270 and 272 and 280 degrees.

Its not near as lazy as the numbers make it appear.

I went 13.0 on this cam in my F-Bird. Its a good one.

 

Mrrr23 : In truth a Hyd roller cam's Intensity and performance potential as far as DD2000 is concerned will fall some where between the HYD and Solid lifter choice.
A mild design like a stock factory hyd roller will be not much different from a hyd flat tappet cam.
Use the Flat tappet choice to model it.

A hi performance fast action hyd roller like a Comp Extreme Energy hyd roller or one of Cranes Powermax rollers will model best using the solid lifter choice.

A mechanical roller can be more like a solid cam in intensity
(mild roller design)(street roller) or very radical, and really yank the valves around. Roller lifter choice or beyond.

A solid flat tappet cam can fall anywhere from the Hyd choice ( very mild lobe) right up to a roller like intensity.
(radical tight lash race mechanical cam)
And can give near race roller performance.
All depends of the cam lobes' "rate of lift" or shape of the lobe.

You must pay close attention to the reference lift point that the seat duration numbers are taken from to compare two simular cams from different companies.
The lift point reference is not the same so the cam appears different.
There can be a difference between two different cam series
even with in the same cam company.

Cam companies love to juggle the numbers.
Cams with seemingly big numbers, sell...

Take it all with a grain of salt when using DD2000.

Look at the difference between the .050" spec and the
"advertized seat spec" and the actual lift point it is rated at.
Make sure you're comparing apples to apples.

Desk Top dyno does not take into account the shape of the lobe when modeling a cams potential either.
Modern high performance cams have a unsymetrical lobe. The opening side is different than the closeing side.

Newer version of Desk top dyno have more choices for the cam and intake manifolds to better Model the motor.

You can download the instruction and some upgrades from http://www.motionsoftware.com/

 

Not trying to but heads, but what part of
According to my calculations from degreeing the cam..
didn't you understand?

I degreed the cam. I checked it at .006" from open to close. Then I did the math on paper.

It truly is 280*/290* seat-to-seat.

 

i got dd2003 last night. so now i play with a new one. it ahs the manual on disc also. just have to click help then help manual. but again thanks for the info.