tomcat

I ran some simulations on Dyno 2000 to optimize cam timing. Starting with a cam card info for an off-the-shelf cam and accurate head flow data, the program was told to optimize power at 6000 by testing many combinations of earlier or later timing for IVO, IVC, EVO and EVC. This is the result:

Crane 138201 (@.004")

Intake duration 310
Exhaust duration 316
Lobe center 110
Overlap 93

Predicted HP 1311 @ 6000
Predicted TQ 1292 @ 5000
Predicted TQ 1083 @ 3000

After the "optimization"

Intake duration 300
Exhaust duration 344
Lobe center 116.5
Overlap 89

Predicted HP 1403 @ 6000
Predicted TQ 1295 @ 5000
Predicted TQ 1039 @ 3000

Not sure how much faith to put in the actual HP prediction, but however the program calculates airflow into the cylinder, it is suggesting that the intake event should be smaller while the exhaust event should be much bigger. I was surprised. The dotted line is the optimized cam.

HARDCORE A/O

This is very interesting Tomcat: 44 degrees more on the exhaust is a hell of a lot more than I've seen on any off-the shelf grind from any cam manufacturer.
What was the Intake to Exhaust flow ratio like? I'm assuming that given the horsepower level (as well the fact that it's you doing it!) it's a supercharged application?
I can't say with certainty that it's an accurate prediction but I personally think that when you're dealing with a high horsepower blown motor that the whole book on what applies to a naturally aspirated engine goes out the window. I mean, if you think about it, you're pushing air into the cylinder, not trying to generate vacuum to pull it in. It therefore goes without saying that you need some means to efficiently get rid of a lot more spent gases than with a N/A application.
That's also the reason that all of the good aftermarket heads with a high exhaust to intake flow ratio (75 + %), like Dart Pro-1s and AFR's can make such good power with a supercharger.
Obviously, it's more feasible to play with cam timing than to hog out the exhaust ports on a set of good heads, so it follows that the cheapest and quickest route would be to experiment with camshafts with a higher duration spread. I recently had Comp Cams do a custom HR grind for me but the spread is only 10 degrees (244 Int. / 254 Exh w/ 114 deg L.S. and .650" Int and .646" Exh.)
I'd like to see somebody do a number of custom grinds with relatively high exhaust duration figures and try em out on a dyno (or a boat) and see what happens.
The problem we have is that most high performance heads and cams on the market were designed for high output naturally aspirated motors, even like the Big Chief and other symmetrical port heads have a poor exhaust to intake ratio for a high output supercharged application, in my view.
The wide lobe desperation figure also helps to make power by reducing overlap because you don't need the scavenging effect from the exhaust side to pull vacuum with a supercharged motor and the more overlap you have with boost the more raw air/fuel mix that gets blown out the cylinder during overlap. Thats my 2 cents

tomcat

Hardcore: Here are the E/I% from 0.200" to 0.700"

84.4
74.7
77.9
76.8
72.1
69.7
69.7

Like most good flowing heads the exhaust does start to lag behind. Is it enough to explain the long exhaust duration predicted I don't know, but it makes me think that off-the-shelf cams may have been put on the shelf back in the days when such high intake flows were not possible. The good intake flow allows a smaller event which makes room for a much bigger exhaust event without increasing overlap. What's also interesting is that the IVC timing did not change in the optimized cam, just the IVO was later.

I'm not sure how much it matters that the engine is supercharged. I ran the simulation again without the blower and the result was very similar. There was a thread a while back in which NOBODY made a good case for the best engine to supercharge being the best NA engine. I agree, especially with centrifugal superchargers.

Yes, somebody needs to experiment with cams. But first I want to talk to the OSO cam experts. I'm not sure I trust Dyno 2000, especially the way it simulates forced induction. Does anyone have the latest Dynomation software with Pro Tools?

tomcat

ttt

HARDCORE A/O

Tomcat:
Thanks for I/E% #s.
Another thing I foud interesting was that the curves for both cams were very similar up to about 5000RPM and then the "smaller" cam pulled away!
I agree that you can't absolutely trust Dyno 2000. I've used it a few times in the past to try to predict some output figures for a street/drag race 350 motor and remember thinking that if I could only make the kind of power that it predicted.
I think you're right about off the shelf cams. The cam profiles that we are using nowadays (like the Crane hydraulic rollers) are probably at least 10 years old, whilst cylinder head port and porting (both CNC and hand) technology has continuously improved in recent years to the point where you can now get flow figures in the 400++CFM range easily sometimes with just a bowl port on the siamesed port (regular style) BBC heads. Also, the full tilt race heads use emphasis on intake flow because they usually end up on on extremely high compression engines with cams with a ton of overlap and I believe that helps exhaust flow.
I'm not sure though about the theory that the best engine to supercharge is the best N/A engine. I mean if you're talking best as in HP, then that would be like a 15:1 598+inch with Big Chief Oval Port Pro stock heads and a monster solid roller cam.
I see the point that a centrifugal s/c is more tolerant of a higher static compression ratio, but how would say an M-5 run on the engine above? Even with 116 octane race gas, I would think it would grenade before you could finish the first dyno pull.
If you're saying that a 9.5:1 540 with a good sized (250ish deg int /260ish deg exh. and .650" lift) N/A cam and good flowing heads will make a ton more power with a Vortech or Procharger - without the need for custom pistons or cam, porting etc., then I'm with you.
(And I hope I'm right because I'm about 3/4 of the way through a 9.5 : 1 509 with AFR heads that I'm hoping to put 8-10 lbs of boost on (w/ a 50/50 pump 93/100LL Av. gas mix)
I'd like to hear from the cam experts too because thats the reason I installed a 3-piece timing cover - because I intend to experiment a bit - maybe with some solid grinds.
In my view, I think it's all a matter of the combination you're dealing with and I firmly believe that the cam should be the last thing you select after considering every part and the intended use of the engine. But, nonetheless there's nothing wrong with experimenting...
BTW: This prediction kinda flys in the face of current cam profiling because for years I've noticed that with a lot of the really big (.750"+) race cams, they actually grind them with less exhaust lift and duration.
I've also noticed that Comp has a new line of Race solid roller cams with the 4-7 firing order swap that they claim increases power (how much they don't say) and reduces harmonics (if you ask me, I think they just sorta copied GM's lead with the 496!)

cobra marty

It all depends on what you want. Peak HP or peak TQ. I see that you lose 44TQ in the mid range 3000rpm with the 'new' cam and only gained 3TQ at 5000. What is the area under the curve between the 2. Which would score higher on an 'engine masters' scoring method.

tomcat

Being suspicious of anything to do with computers I did a cam optimization on a 330 using the head flow numbers provided by Dyno 2000 for a stock iron oval port head (240 CFM in and 160 CFM ex @ 0.500"). The program took a 218/218 cam to 208/251 and picked up 20 HP. I did it again with a much better exhaust system and it went to 216/251 and picked up another 20 HP. This is very educational but if it worked everybody would be doing it. Something's not right with this program.

I think I'll wait for the cam experts to weigh in on this one.

Hi Marty: There is a tradeoff as expected, but the cam timing is a little weird don't you think? I want this tradeoff anyway, because I want to reduce torque in that RPM range. I'm trying to reduce cylinder pressure in the RPM range where detonation is most likely. Check out August 2005 Hot Rod for a good article on maximizing power with pump gas.

HARDCORE A/O

Good Point Marty. The Engine Masters method of scoring is probably a useful tool for boat engine builders because it focuses on average HP (as you say "under the curve") not the overall highest HP reading and it was very interesting to read about some of the methods that top engine builders used to obtain the highest average HP figures. Since most boats only have one gear and operate at less than 6000RPM, the best performer is usually the boat with the the best overall torque and average horsepower.
Tom: I have a correction to make. It's not the duration thats lees on the bigger race roller cams. I went and did a quick check in my Summit catalog and it appears that once it's a Solid Roller with over .725 or so lift the exhaust LIFT is less. But, I also noticed that on the new Comp 4 & 7 firing order swap cams as well as a number of their older designs, that amongst the bigger cams (like .700 upwards), there is a number of cams with greater than 10 degrees spread from Intake to Exhaust. In fact, the largest 4 & 7 cam I found in the Summit catalog had like 30 degrees more on the exhaust and over .848" lift on the intake and quite abit less lift on the exhaust. Food for thought.
It might have something to do with the fact that at some point when you start to approach 100% VE, a N/A engine simply can not make use of any more intake flow and consequently will respond better to more "help" on the exhaust side, especially at higher RPMs. This theory is corroborated by the drop in mid range torque on the "optimized" cam since it is believed that there is a direct correlation between peak torque and peak VE and the second design obviously worked better (in simulation at least) at a higher RPM. Put another way, a cam that achieves best cylinder pressure in the mid RPM range will make more torque and more average power, and that I believe is what most of us need for our typical high performance boat.
Then there's the "practical" limitations on camshaft selection, like too much lift kills valve springs quick, wet exhaust reversion, docking/idling without stalling, shifting without destroying your cone-clutch etc.

NOBODY

Just some food for thought for you guy's
Top Alcohol driver Rick Santos was running the quickest blown alcohol small block in the world and his valve sizes on his 380 inch motor were 2.08 intake 1.625 exhaust. His car was running roughly 5.50s at 230 and I'm pretty sure if they thought they needed a bigger exhaust runner, valve, exhaust duration ect. they would have done it. The only reason he's not running it today is because they kept adding weight to his car to slow him down to the point it just wasn't worth it anymore. He finally had to play follow the leader and get a HEMI like everyone else was running. The point I'm trying to make is this is the same I/E valve ratio for a good N/A engine and is still the same GOOD I/E valve ratio for a blower motor making over 40 pounds of boost.
Am I really FORCING air through my motor or is it just breathing a little easier?