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Cam spec discussion

Twisted Steel Performance

Twisted Steel Performance

Anything worth doing is worth overdoing.
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Folks, I have been working with a cam designer looking for a new cam for our motors, so far I have had 1 cam welded up and ground with totally new specs that can't be gotten in a "regrind". I won't post about that as I haven't tested it yet. This person doesn't know much if anything about the 6.x so he is only making guesses at this point...

What I would like this thread to be about is for some of you that know about what a cam really does is for us to discuss the many different factors that "could" help these motors. For this discussion, lets forget a stock motor, we know their isn't much room for things like more lift etc.

I'm not interested in what would only work in stock motors, I don't really build stock motors, heavy towing mostly should be considered...

Lets gear our thinking towards the below basic motor specs...

18:1 compression
valve pockets in pistons
1.5:1 ratio rockers/ higher ratio will only change lift numbers
measured push rods
clearance for high ratio stuff
high output IP's
better turbos
etc..............

Some of my list is

hyd roller lifters
Higher lift, even different lift IN vs EX
a fatter lobe to open the valve faster
no overlap, even negative overlap
different LSA
more duration
split duration IN vs EX

And if anyone knows of a good cam design program list it so I can investigate it... I'm not looking for something to take to market, having a cam welded and ground to test is costly, I'm just doing some R&D....
 
As I stated earlier you need to find out what the specs are when the lifts and duration were measured . The stock cam looks like specs I have measured @ .050 .

Why don't you want overlap ?
 
@EWC , I have this in mind for a fully ported/ both big valve set of heads, ( mine) along with other internal mods... working for a towing cam in the 2000 - 2800 rpm range. And yes I know I don't know a lot about designing cam yet, but I'm trying to learn..

IN - [email protected]" duration
EX - [email protected]" duration
190/220 @.050"


This is considering the following basics with a db2 set up for lots of fuel...

4" turbo back exhaust including the d/p
vgt turbo with controller
custom made intake & I/C
manual tranny

I figure I'm off a bit but that's why I started this thread, I remember "goldsburg" many years ago working on cams but I no longer know how to contact him or any of the others that probably knew more than me...
 
I don't know but I would like to see the specs in a clock graphic form. I assume you have seen
mgispeedware.com

Camshaft Calculator & Valve Overlap Profiles | MGI SpeedWare

An interactive camshaft calculator where engine builders can see how valve overlap (and boost efficiency) is affected by a camshaft’s physical design.
mgispeedware.com mgispeedware.com

I would like to see a shaded area of a bar graph superimposed behind the valve opening curve showing the piston position and or speed of piston stroke. Then some explanation of the benefits adjusting curves.

I can see a little later intake opening increasing combustion cup clean out at lower RPM's???

If you watch this video it shows the fuel injectors firing like looking in the throat of a carburator. If you watch it a couple of times you can see some fogging of the fuel/air depending on air flow RPM and fuel rate.

I would like to see this in slow motion and somehow see the piston postion to see if if the clouds are at say near BDC and then get forced thru on next cycle.

 
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OK , .050 . That's good to know .

Why no overlap ?
 
Because forced induction motors don't like overlap like aspirated do.. and turbo vs blower is also a different need, turbos have the most back pressure, if both valves are open at the same time reversion will happen. Our stock cam has -31* of overlap... that creates sort of a vacuum helping the incoming air rush in...

I think with better turbos, more boost psi, better fueling, etc, a more aggressive lobe design along with more duration, lift, change of lsa, their could be great gains for certain builds... just how much change will be good remains to be seen, sure wish I had a engine dyno....
 
Ok , so here's what I think . As you said , forced induction engines don't like overlap because that blows the mixture out the tailpipe . Keep the overlap down and more of the mixture gets into the cylinder and thus more power . The problem with that line of thought is we have no mixture in the 6.2/6.5 , just compressed air . This is a dry manifold , as opposed to a wet with fuel .

Overlap is used to get the mixture moving . The thinking is that exhaust gases have a " pull " on the intake mixture just as the intake valve is starting to open . This helps to get things started in the intake port .

Reversion is the air mixture hitting the back of the intake valve when it slams shut and traveling back up the intake port . You should look up Jon Kaase and watch the video of his finger in the tunnel ram .

Part of me want's to follow what the experts say about cams and turbos but most of that knowledge is from gas engines . So how does any of that apply ? We have a low RPM diesel and add a turbo . Now what ?

My thinking on the Crane regrind was more overlap was a good thing as the incoming air would help to cool the exhaust valve and lower the EGTs . No overlap would keep more heat in the cylinder and that would help to cause overheating issues and intake air problems .
 
@EWC
I guess your going to need to explain where the overlap is, every cam calculator I have put the numbers into show our stock cam & the crane regrind has no overlap.... they show it as a negative degree and the lines on the graft don't touch...
 
I used this calculator https://mgispeedware.com/camshaft-calculator/

and input the numbers and below is what the calculator shows... if I'm looking at something wrong please let me know...




Stock cam

Exhaust Open: 34BBDC
Exhaust Centerline: 113BTDC
Exhaust Close: 13BTDC
Intake Open: 18ATDC
Intake Centerline: 107ATDC
Intake Close: 16ABDC
Exhaust Area: 18.8
Intake Area: 16.7
Exhaust/Intake Area Ratio: 1.1 : 1.0
Overlap: -31
Overlap Area: 0.0
Overlap/Total Area: 0.0%



Crane regrind

Exhaust Open: 33BBDC
Exhaust Centerline: 113BTDC
Exhaust Close: 13BTDC
Intake Open: 9ATDC
Intake Centerline: 107ATDC
Intake Close: 25ABDC
Exhaust Area: 18.8
Intake Area: 18.4
Exhaust/Intake Area Ratio: 1.0 : 1.0
Overlap: -22
Overlap Area: 0.0
Overlap/Total Area: 0.0%
 
This is kinda where my choice is at this time for my build..

My choice @.050 210/225

Exhaust Open: 51BBDC
Exhaust Centerline: 118BTDC
Exhaust Close: 6BTDC
Intake Open: 5ATDC
Intake Centerline: 110ATDC
Intake Close: 35ABDC
Exhaust Area: 24.2
Intake Area: 22.7
Exhaust/Intake Area Ratio: 1.1 : 1.0
Overlap: -11
Overlap Area: 0.0
Overlap/Total Area: 0.0%
 
No need to explain it . You got it right . My cam card is a little different but only by a degree or two at a few points . Do you have any lift numbers ? Mine is showing around .440 and .450 for intake and exhaust with the 1.5 rockers .
 
I've been looking into cam specs a little myself. I don't see anything to gain on a stock engine. But turbo and head upgrades could definitely benefit from a different cam profile. And those can be tailored to fit the operating range of the engine.

I'm no camshaft expert, but from what I've gathered on a diesel less is more. Pressure development in the cylinders is the key to making power. After all it is a compression ignition engine. Adding alot of lift and duration can actually be a bad thing on a diesel. Our camshaft seems small, but in comparison to other diesel engines its not that bad. R&D performance cam for the 7.3 is 178/190 w/ .410/.412 lift. And if you look at average 12v cam specs they are very reserved. 175/210 for towing, 195/220 for hot street, and 220/250 for pullers and drag trucks. The 6.5s 178/201 isn't far off when you stand back and look at it.

Going from the charts you posted on head flow. There dosen't seem to be much to gain with a cam on stock heads. But with port work and larger values adding some lift and duration to the camshaft can't be a bad idea. But I would be careful how far you take head work on a truck being used for towing. Opening up the heads and increasing flow with bigger valves, rockers, and a big cam might be awesome at 4000rpm. But really fall on its face trying to pull 12k lbs from a dead stop. Port velocity is very important for spooling the turbo. Its a give and take thing with head work. The more you help the top end, usually the bottom end suffers. Its all about setting it up for your application. The race truck and tow truck need two totally different setups.

Modern high efficiency turbos can run a 1:1 or better drive to boost pressure ratio. With numbers like that the LSA can be tighten up and take advantage of the scavenging effect from the valve overlap. You can almost treat a high efficiency turbo engine like a N/A engine to a point. The camshaft overlap is measured at .050" lift. Thats why its negative on the stock camshaft specs. You will have a slight overlap at lower valve lift though. The last few degrees of exhaust and first few degrees of intake do overlap. The factory spec is 110* I think 109* or maybe even 108* would be a nice upgrade.

Changing up the valve timing is another way to get more performance. If the LSA is tighten up, then the cam could be advanced. That will keep the intake timing the same, but push the exhaust valve closer closer to TDC. I remember reading closing the exhaust closer to TDC is a good thing. I don't recall exactly why, but I thought it was for scavenging.

For me I've been looking at something around 185/210 w/ .440" lift(1.5 cast rockers) 109*LSA. Only head work im doing is a port to match and an little polish work. S360 or s362 turbo.

Again im no expert in camshafts. So take what I say with a grain of salt. But I love discussing stuff like this. I dug into it a few months ago, and it been on the back burner till I build the engine. It would be cool to try a few different camshaft profile changes and record it on a lab scope with a pressure transducer. That would be a cool way to see what changes in pressure development where made in real time....
 
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Just refining the duration & LSA a little... and I am think out loud here, the HE351VE & Banshee controller can be programed to build boost near idle, so my thinking is that with near instant boost getting a load moving wouldn't be as labored as well as gear shifts with a manual tranny, I think I could get use to not getting a load moving if I could have excess power in the on road rpm area... I know a "towing" cam is normally for grunt from a standstill, I think I would prefer road speed performance more... not sure tho, just thinking here..

And I still think a faster opening ramp (fatter lobe) would give more flow at low lift of the valve, and a quicker closing ramp would help..

The below chart will have 3* of overlap @.050" lift
I'm using valve lift # of 480/490
Max ex lift @ 108* BTDC
Max in lift @ 102* ATDC

@.050 198/215 LSA 105

Exhaust Open: 36BBDC
Exhaust Centerline: 108BTDC
Exhaust Close: 1BTDC
Intake Open: 3ATDC
Intake Centerline: 102ATDC
Intake Close: 21ABDC
Exhaust Area: 32.7
Intake Area: 29.6
Exhaust/Intake Area Ratio: 1.1 : 1.0
Overlap: -4
Overlap Area: 0.0
Overlap/Total Area: 0.0%
 
A VGT turbo will definitely change how you approach a custom camshaft. Being able to adjust the vanes for low RPM spoiling might help compensate for the loss of port velocity. The key is how much more back pressure will be created while doing so. If your camshaft is set up with a tight LSA and a good amount of overlap. Then you will definitely run into issues in the lower range if the turbo creates alot of back pressure.

I remember correctly most of the VGT trucks have very small camshaft specs. They probably do this to compensate for the higher back pressure at low RPMs. I would imagine you have to be more reserved with specs on a VGT truck vs a standard turbo because of the changes in back pressure.

Its going to take alot of trial and error to get it figured out. Developing a camshaft is going to be time consuming. Its probably better to make small changes and measure its effect before you go crazy with it. I have read about guys making just a 2*LSA change after a turbo upgrade and having great results. Keep it simple is my approach to a camshaft.
 
TSP, anything you can share with us about your cam research- suspicions confirmed, unexpected issues or surprises? (duration,lift,lsa, opening/closing rates)
 
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