I've been playing around with Desktop Dyno 2000 to analyze the effects of various cam profiles on power production. Disclaimer: I know full well that DD2k is not an accurate program for estimating real world output, but it can be useful for comparing two cams in the program.

So I've been looking at the Comp XE 224/230 as I'm looking to upgrade later this year and ditch the CC304 that, while very livable for a daily driver, is costing me a lot of peak power with my combo. I am a stickler for driveability though, so I've been playing with the valve events of this cam and trying to acheive the same power with less overlap.

What I've come up with is that by delaying the intake valve opening and holding it open a little longer, DD2k shows the same peak power at 6000 rpm while putting up slightly better low RPM VE and vacuum #'s. The XE cam is has a 112 LSA and a 108 intake center line. By modifying the intake events, I came up with a 114.3 LSA and a 112.5 ICL. The XE stock has 53 degrees of overlap, my modified version shows only 47 degrees.

My question to you guys is: Are these realistic numbers and is delaying intake valve events a legit way to preserve power while reducing overlap for better driveabilty?

My crude theory is that although overlap is reduced, which should hurt top end power, but delaying the intake timing has the same effect as retarding the whole cam by a couple of degrees? Obviously the low end benefits are from the reduced overlap.

I also observed while browsing Compcams.com that most of their performance LT1 cams have Intake Center Lines of 108 or 110. However, their LS1 cams are all on 112 ICLs, which might explain why most LS1s have great idle manners even with the bigger aftermarket cams (I know much of that is due to great head port velocity, though). What I've done more or less is emulate the popular LS1 grinds and the result theoretically should be good power w/o any less driveability than I have now.

 

Cool. IMO, that's a good way to use an engine design program.
You might consider just moving the intake lobe to change the intake closing point (IC), which may be the most important cam timing event. When you maximize power with the XE 224/230 @ the stock 112 LSA, change the LSA, but keep the IC the same. This may mean advancing or retarding the cam.

If you find improvement, try a different LSA and do the same thing. When you get where you think it's optimum, then try moving the IC again. You should find the IC point and the LSA which maximizes whatever it is you seek: max torque, max power or max average torque and power in your engine's operating range (my choice).

What I'm saying is change only one thing at a time, and hold an important event constant. When you are all done, you might be surprised at the results.

Work in 1 or 2 degree increments, or even more until you zero in on the optimum. Don't bother with 1/2 degree or finer changes.

Keep us posted.

 

Oh, I'll add that the XE's advertised duration is 276/281, my specs result in a 271/281, a bigger split but the shorter intake duration is good for driveability. Probably would be about a 219/230 at .050

 

If your suggesting he does some real world testing of different ICL's (advancing/retarding the cam), than he would need to buy a cam with every ICL he wants to test.


The LT1 cam cannot be installed with offset bushings because it will disturb the opti/crankshaft relationship.

It's cool that you are experimenting with different things on the analyzer. I will say that the later you close the intake valve, the higher the RPM peak hp occurs.

As OldSStroker was saying, you need to decide what you want out of the cam, and then design it around your needs.

If I was after high rpm power and excellent driveability, the XE 224/230 would be at the bottom of my list.

IMO, the majority of off the shelf cams have much too low ICL. (or too early intake closing).

Custom grind is the way to go

 

i agree with what oldsstroker said. only thing he didnt mention is that dd likes to use "lazy" ramp rates and favors the larger cam over the smaller one (which i dont like). theres a lot better programs out there for doing things like this they're more like $400 though. i'm not sure what your heads flow chris i'm pretty sure you're the guy with the cc304 and ported stockers. i'd just assume use a smaller cam than the 224/230 if it was me and keep the lsa tighter (that reads same overlap but more responsive down low) i'd be looking closer to the 212-216 range for intake size and play with the icl and ic. but i'd also consider the dcr just to give me a baseline. what i'm thinking is take a tq based cam thats maybe a little small but will still rpm like you want and then retard it 2 or 4 degrees after you get it maxed out designing it like you were going to install it straight up. its just my idea that it will still keep 98% of the tq you have with the small cam and then it will give peak hp a kick in the pants too. this is just my current thinking on cams. feel free to pick apart my idea.

i also think that getting your i/e lobe ratio right based on head flow is important as well. then tune your ic and lobe size for what you want rpm wise and where you want the power.

 

Yup, I'm that guy, CC304 and bowl ported stock heads (actually GTP "stage 1s").

I have always liked the idea of making good power without having to go big like everybody seems to want to do, I just didn't pick the right cam the first time. If I'm going to pull the one in there out, I might as well go big enough to make it worth the work, though. For that reason alone I'm hesitant to go smaller than 216 intake duration.

I'd like to get more trap speed in the 1/4 mile (times in sig) yet still have the same driveability as I have now. I think with the right grind I can pick up 20hp without having to resort to a bunch of overlap, especially if its not necessary.

 

try doing a search on lift vs duration in advanced tech that might give you a push in the right direction. lots of deep ideas in there for you to chew on. only reason i said go short in duration is because you're on a 350 bottom end and bigger lobes do kill bottom end tq. and you also said you want the same driveability a 14 * increas on the intake lobe probably wont do that sorry. it can be helped with the lsa being wide but then i start to wonder if you're just going too big if you dont want that much overlap. i just think that with the drivability you're talking about that your overlap at 50 will be in the negative range

 

The .050 specs on my imaginary cam end up being 217/228, lift is .544 on both lobes with 1.6rr's for good valvespring/lifter life, and that's probably realistically about the max lift my heads will tollerate. Negative 7 degrees of overlap at .050 also.

 

Sorry, not to be an azz but these programs are basically junk.

Don't get me wrong, they can be fun to play with but I've never seen very accurate results from them. If they were that accurate, the engine developers and high zoot engine guys would be throwing their expensive CFD, FEA and wave dynamics software in the trash and buying Desktop Dyno or EA Pro. Just saying.... I wouldn't put too much faith in the results.

-Mindgame

 

If I had a lot of extra cash to throw away on a real program, I would. But I don't, so I'm making due with what I do have. At least I'm researching and experimenting rather than just buying an off the shelf grind and assuming that's the best there is.

 

It's cool Chris and I agree with your approach. I just think people put a little too much faith in these progs. There are a few guys here locally (I'm pretty close with a big group of racers) and they like to use these progs but they aren't getting the results the software would have them believe they should be getting. The engine torque also always seems to be a good ways off especially when you stray a little more from traditional cylinder heads and parts in general.

Best of luck!

-Mindgame

 

I said in my first post that I know DD2K doesn't provide realistic numbers in terms of real power and torque....so when it says 439 hp I am not expecting 439hp, but it is useful for seeing how changing a cam event changes power relative to another cam in the program.

What I have done is simulate my current engine setup. It computes to 420 hp. You can guess that is sorta close to my net crank hp (322 / .82 = 393 hp), but it really doesn't matter. When you put in cam X and get 439 hp, you can bet that you're looking at 18-20 more hp than you exising setup.

I don't use it to predict real output, just relative output comparing 2 or more profiles.

 

GIGO still applies. Some of it is how you use the tools, not just the tools themselves.

If you give EA Pro good info like Cam Doctor cam data, head + manifold flow, manifold taper, etc.^2, it can come within a few % of dyno results. Getting good data is the challenge.

CFD, FEA etc. are all tools to predict airflow, structural stress/strain, etc. You probably still need to get the airflow data into an engine sim program. Someone with enough hardware/software to do good CFD on a complete engine probably has much more sophisticated engine sim software also.
We're talking orders of magnitude here.
My $.02

 

Thanks Jon but I know what the software does... I worked for Algor Inc. as a lead programmer for a little better than 6 years before starting a consulting business. Still one of the top FEA developers out there as I understand it.

"GIGO", Garbage In Garbage Out for those who aren't familiar with the acronym.

You're working with little Stroker on his engine development stuff. I'm curious.... is EA Pro and Desktop Dyno the extent of your design tool or are you guys using a CFD and FEA software specific to engine design?

-Mindgame

 

CFD and FEA and DD are not used. Rather it's a combination of simulation and dyno testing to verify. Really it is more empirical than analytical. If there are known flow characteristics, measured from hard parts, these are used to simulate what results will emerge. Here is where the correlation is quite good.

SStrokerAce's approach to engine building isn't to reinvent the wheel. He chooses vendors who are experts in their fields, or at least highly thought of. He may run tens or hundreds of combinations, especially valve event timing, and watch the trend of what works, and why.

No basic research in combustion, flame travel etc. going on here. Fortunately there is quite a bit of empirical data on that kind of stuff for popular modern engines. The goal is to specify the correct combination which will produce the desired torque curve, within the available budget. Simulation software like EA Pro was developed hand in glove with dyno data. When dyno data didn't correlate well, the software was changed to more nearly predict what would occur, as I understand it. I've always liked the name "Performance Trends".

Just curious, how were you using FEA with respect to engine airflow and performance simulation? Isn't FEA usually used for design and simulation of mechanical properties of hardware? Maybe I'm out of touch.

It's an interesting group who read/write in "Advanced Tech", isn't it? I had to chuckle that you defined GIGO, but not CFD and FEA.

I may have missed it in past threads, but what kind of consulting do you do?

Regards,

Jon