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picking-a-cam
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Author:  DadTruck [ Wed Jan 09, 2019 6:38 pm ]
Post subject:  picking-a-cam
For the next engine build for the 68 Barracuda as a strip only car I had a camshaft already selected, a big duration cam that has proven high rpm power potential.
However as I got an urge to make the car a performing strip car that I could drive cross country to the drag races. With that I saw a need for a motor with a
wider HP and torque curve.

I am thinking that if I used a cam in the 250 duration range in a well tuned MPFI motor, I could get an engine with good drag race potential and acceptable street driving characteristicks.

Since I am limiting duration, I will need to pay attention to: port flow, valve lift and valve action.
The summary below addresses valve lift and valve action issues.

I reviewed the Oregon Cam Grind list for lobes in the 250 duration range that have lift above .525

Found six of those, I then compared valve intensity, looking for the lobe that moved the from .020 to .050 in the smallest number of camshaft degrees.
see the second attachment below.

The quicker the valve opens the sooner real air flow starts. The lobe I selected was the 1456.
From there I used the Dyno Sim program to compare various LSA's and installed Intake centerlines.
Ths head I plan to use is at the machine shop (getting another set of seats) so I don't have the final port flow numbers to put in Dyno Sim, so I put in
what I had, and I am thinking the flow will improve with the revised seats, also used a conservative ignition curve. Those were the same for all the trials.

I ran the simulation with many LSA's and ICL's. Performance seemed to drop off once I got away from 108 to a 110 LSA and away from a 100 to 102 ICL.
The final four are on the first attachment below, after writing down the results to decide what was best, I simply went row by row and highlighted the
best performers in each row, then summed up the total number of 'best performers' for each cam setting.

The best performer is the cam with a 108 LSA installed at a 102 ICL.
That is very much in line with what I believe most slant six engine builders target.

Attachments:
scanphotocam10001.jpg
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scancamphoto20001.jpg
scancamphoto20001.jpg [ 127.24 KiB | Viewed 8901 times ]
Author:  Dart270 [ Thu Jan 10, 2019 3:43 am ]
Post subject:  Re: picking-a-cam
Interesting results. Many Slant racers have chosen 104-106 LSA as being best, but 108 will be very close. 102 CL is about perfect, and many use 100. Did you try EXH lobes with less duration/lift? I wonder how your program handles that? I assume you input port flow curves for both INT and EXH of your head?

I have driven my 64 Dart since 1996 with a cam 250 @ 0.050" or bigger on the street. I advise using at least 10:1 static comp and more like 10.5:1. You will want a 3000 RPM stall converter or higher. Modern high stall converters do not lose much efficiency at light throttle. What trans and rear axle ratio?

Honestly, EXH profile will likely make less difference than INT, but many racers find less EXH duration is good. Mike J was a notable exception, I believe, and used longer EXH duration.

Best and thanks,
Lou
Author:  DadTruck [ Thu Jan 10, 2019 10:05 am ]
Post subject:  Re: picking-a-cam
added results from 104 and 106 LSA to the spread sheet that had the 108 and 110 LSA info.
and increased the RPM range from 5500 to 6000

the narrrower LSA does show an advantage from 5500 RPM and up however the narrower LSA gives up
HP and TQ across the midrange to up to 4000 RPM ,, that was the drop off that I mentioned previously.

generally as long as the HP - TQ curves are going up, the difference between the best and worst is
one to five counts. It is after peak has been reached and the tail off has begun that the spread gets large.
So this exercise is about matching the HP and TQ curves to the rpm range and expected use.

and remember, this study is this cam grind. I would expect larger grinds to react different.

and concerning the Reverse Dual Profiles, I did not see much difference with that when I was planning the
cam for the 83 D150, but went that way to see what it was like,,,,

I will do some more looking at running a smaller exhaust duration, but for today, I think it is best to run the valve duration
that fits the torque curve and overlap that you want. If the overlap was getting too big, I can see where it may be best to
reduce the exhaust duration and preserve the intake duration, but if the overlap fits in the window, and the torque and HP are
where you want them, why artificially reduce the exhaust duration?

Attachments:
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Author:  Dart270 [ Thu Jan 10, 2019 11:00 am ]
Post subject:  Re: picking-a-cam
Makes sense. Thanks for the extra data. Of course, any program will not be a perfect prediction of reality, but this one looks to have things in the ballpark.

Lou
Author:  DadTruck [ Thu Jan 10, 2019 3:37 pm ]
Post subject:  Re: picking-a-cam
I called Oregon Cam Grinding and spoke with Ken

concerning the 1456 grind, he does not know if it was ever put on a slant motor
but he agreed that it is a fast ramp, he said it would not work with a Chevy lifter,
the notes on the shop sheet says it requires a .875 minimum (Ford lifter) so it would work with a
.904 Mopar lifter. Ken offered that IHRC, the 1456 was done for a circle track motor.

Ken said he can do the 108 LSA, but I will need to degree the cam to get the 102 ICL.

I guess the Holy Grail would be finding a cam shop that specializes in Mopar cams that
take advantage of the large .904 lifter.
Author:  emsvitil [ Thu Jan 10, 2019 9:43 pm ]
Post subject:  Re: picking-a-cam
Something is wrong with one of the charts.

How can the 106LSA 102ICL have both the highest hp and lowest tq at the upper rpms?
Author:  Dart270 [ Fri Jan 11, 2019 2:49 am ]
Post subject:  Re: picking-a-cam
Keep in mind that fast ramps are not necessarily better performers and you want to drive this thing on the street. Tilley said he tried some fast ramp cams and they did not work for him (dyno). Durability should likely be a consideration. When Hughes and others first released the fast ramp cams, tons of Mopar guys wiped cam lobes and lifters. I have stayed away from them. Getting 2-5 HP (maybe) at the cost of broken parts and an unreliable engine is not my idea of fun.

Just my 2 cents,

Lou
Author:  DadTruck [ Fri Jan 11, 2019 4:39 am ]
Post subject:  Re: picking-a-cam
Quote:
How can the 106 LSA 102 ICL have both the highest hp and lowest tq at the upper rpms?
that is because the combination of 106 LSA and 102 ICL moved the torque curve down in the RPM band.

note that the peak torque for the 106 LSA 102 ICL occurred at 3500 RPM, in fact
it was the best torque performer at 3500 and 3000 RPM, and the worst TQ performer
from 4500 to 6000 RPM. Once the motor spins beyond peak the curves drop off quickly.
Author:  DadTruck [ Fri Jan 11, 2019 4:59 am ]
Post subject:  Re: picking-a-cam
Quote:
Tilley said he tried some fast ramp cams and they did not work for him (dyno)
engines are air pumps, the further the valves are opened per given crank degree the more air they flow.

Not sure what Mr Tilley was testing, but his result is counter to the fundamental process of an engine,
possibly there was a need to optimize fuel-spark timing to work with the cam change,.

Concerning durability, yes the faster the ramp speed the more risk. The 30 intensity value on this cam is

faster than a 32 or a 34,, but it is not a high 20. Remember the one advantage of a Mopar engine is the

large diameter lifter. And the .904 lifter is what makes the steeper ramp angles possible. Not going to a faster
ramp leaves the large lifter diameter on the table.

On a related topic, the reverse dual pattern cam with the shorter exhaust duration. IIRC when Doc wrote of that
he mentioned that a 'Mopar' exhaust lobe was used on those cams.

If it was a Mopar lobe, it was designed to be used with the large .904 lifter, and probably was a fast ramp. Then the

fast ramp may have been the secret ingrediant, not the reduced exhaust duration. Or to say it another way, the fast ramp allowed the

reduced duration to function. Just a thought.
Author:  drgonzo [ Fri Jan 11, 2019 5:52 am ]
Post subject:  Re: picking-a-cam
Quote:
Quote:
On a related topic, the reverse dual pattern cam with the shorter exhaust duration. IIRC when Doc wrote of that
he mentioned that a 'Mopar' exhaust lobe was used on those cams.

If it was a Mopar lobe, it was designed to be used with the large .904 lifter, and probably was a fast ramp. Then the

fast ramp may have been the secret ingrediant, not the reduced exhaust duration. Or to say it another way, the fast ramp allowed the

reduced duration to function. Just a thought.
I think you may be on to something there. Doc used the same Mopar exhaust lobe on two different grinds. On the smaller grind (210/212) the exhaust was not smaller than the intake and on the larger grind (218/212) it was. I think he was using a very efficient exhaust lobe on both and the cam design was not driven by the split in duration.
I don't know anything about the simulator you are using but I do know the Desktop Dyno does not reward advancing the cam or running a smaller exhaust lobe. I believe this is true because that program is written from SBC and other popular V8 data and I suspect most simulation programs would be the same, but that's all just speculation.
Still, there are many ways to skin a cat. (This is a very interesting thread. Thanks for posting it.)
Author:  Dart270 [ Fri Jan 11, 2019 6:44 am ]
Post subject:  Re: picking-a-cam
Quote:
Quote:
Tilley said he tried some fast ramp cams and they did not work for him (dyno)
engines are air pumps, the further the valves are opened per given crank degree the more air they flow.
Nothing in this Universe is this simple. Every theory and every principle you/we/humans have ever learned is an approximation. Yes, even Newton's Laws. Consider turbulence, transient air response, reversion in a port, and many other non-idealities. I am not saying this "rule" is not true a lot of the time, but given how much people have changed what are "optimum" cam profiles over the last 30-40 years, and how much boosted cam thinking has changed in the last 10 or 20 years, I would say we still have plenty to learn.

That said, it is possible that other optimizations (like ign timing, induction or fuel delivery type...) might show that faster ramp cams on a Slant work better than slower ramps, if everything is optimized. Tilley (and potentially Team Green) have done dyno/race testing showing that RDPs worked a bit better under their conditions. Of course, there are a huge number of variables, so it is hard to say any one thing does anything unless you optimize the other 100 or 1000 variables to find another (more global) maximum for each cam profile, LSA, etc...

In short, I agree with your scientific and computational approach, John. Just some thoughts to consider.

Lou
Author:  drgonzo [ Fri Jan 11, 2019 7:02 am ]
Post subject:  Re: picking-a-cam
What Lou said. :D
Author:  DadTruck [ Fri Jan 11, 2019 11:33 am ]
Post subject:  Re: picking-a-cam
Quote:
What Lou said.
That most recent conversation underscores the intrigue to building a slant six.
No one that frequents this forum can go to an online site and order a dyno certified slant six crate motor.

It is up to each individual to pick and choose from the few performance slant six parts that are available. And to find a
way to adapt other performance parts and current trends in engine design to our slanted motors.

For me, and I believe I can speak for others,, what makes building and racing slant motors interesting, is that there are different approaches.

I posted what I am doing and my thought process that got me to that decision. Is it the right way or the wrong way,
don't know, in the end its like Frank S said "I did it my way"

https://www.youtube.com/watch?v=r377iPPbvVA
Author:  drgonzo [ Fri Jan 11, 2019 11:47 am ]
Post subject:  Re: picking-a-cam
Well put DT.
SlantSix guy, not one of the sheeple.
Author:  Dart270 [ Fri Jan 11, 2019 2:38 pm ]
Post subject:  Re: picking-a-cam
Nicely said, John. If I could order all the parts I wanted or just use a formula, I would find a different engine.

Lou
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