Okay for all you engine builders out there, I have a very basic question. I have been modeling my engine in Desktop Dyno 2000 to see what the projected power curves are for my project car. I have entered the published flow numbers, valve sizes, etc for several different "out of the box" aluminium heads, stock E7TE heads and the World Sr. iron heads. I also created a cam profile from the cam card for my Crower Baja Beast cam. The short block is a stock 98,000 mile 5.0 out of an `89 Mustang. Stock comprssion ration with E7TE was 9.2:1. 180LB static compression with less than 2% leakdown over 10 minute test. I'll run it until I see problems or "Need more power". Cam specs are 212 / 212 duration @ 0.531 lift with 114 degrees lobe seperation. I am using a BBK SSI fuel injection intake manifold with a 75mm throttle body, 90mm mass air flow sensor, 19lb per hour injectors, Doug Thorley 1 5/8" shorty headers. I have modeled the combination using AFR 165, AFR 185, World Products Junior Lites, World Products Sr. iron, TFS Twisted Wedge Street as well as the E7TE heads. Using this shortblock and other parts the TFS head provided a better (smoother, flatter) torque curve than the other heads. Even though some of the other heads had much higher flow numbers. (Yes, I did recalculate the compression ration of the combination for each set of heads to make the simulation as acurate as possible. Chamber sizes varied fo 58cc to 64cc so the compression ratio varied slightly.) Here is where I started seeing things that I wasn't sure of. With the above combination, by doing nothing other than retarding the cam 8 degrees, I was seeing 49 more horse power and 41 ft/lbs of torque at 6000rpm with only 4 ft/lbs torque drop at 3000. Does this look reasonable or is this program screwed up?
49HP and 41 ft/lbs??? WOW!!! Be nice to hear from experienced users who can vouch for the computer's calculations...
Interesting how it zeroes out around 9000 rpm...is that when the valves float and the engine falls flat on it face? I never figured it would go to zero until you threw a rod. I always thought it would go up, and hit a high, then level off around 60% or so of the top. Of course, maybe the program thinks your rods are gone by 9000rpm
have your tried a different head with 8* retarded? maybe cause the TFS heads are just a beast...im interested to see if it has the same pattern with the other heads
The cam is not the right one for the combinations. It's to short a duration for the breathing capability of the heads. Try increasing the cam durations at zero advance or retard, and you willl get about the the same increases. This is what shows you the cam is not correct for the combination.
Bluegrass is right. Usually when you retard the cam timing a little, you'll pick up some top end power. To add to that, normally the top end power increase is pretty substantial with a cam that's too small. Another old trick in the book is to tighten up the valve lash, which makes the valves open sooner & close later (adds a few deg or duration & a little lift). If the car picks up, your cam is too small. If it falls off, it's too big. That's for a solid or solid roller cam...that doesn't apply to hyd & hyd roller cams. That said, I wouldn't go by what dyno2000 says. IT's a guide...and a pretty accurate guide, but many times the program "lies" to you on the high side of things. I doubt you'd pick up nearly 50 HP....probably 20-30 at the most. The only sure way to know is to try it & see how it works. Just remember, opening & closing the valves a little later may decrease piston-to-valve clearance. Usually when I am doing a new combo, I'll clay a piston, check it at zero, +4, and -4...that way I know for sure if I can advance or retard it without worries. The one I have now...clearance is already pretty tight so I can't do it. At +4, I have less than .030" intake and .045" exhaust. At -4 I have .080 intake and .030 exhaust. Zero, it's .075/.100...which is fine.
I know that the cam is not optimal for the aftermarket heads. Basically, the car is going to be used with an AOD and 3.25:1 rear gears. Mostly daily driver status with occasional SCCA and Qualcom Stadium 1/8 mile events. What I was looking for from a cam was the best low end torque that I could come up with. SCCA events don't need 7000 rpms and neither does daily driving. When I was playing with the software, I was supprised to see such a dramatic difference in the upper rpm ranges from a cam that I knew was supposed to top out at 3500. Having usable HP and torque at 6000 would be a real nice gift since the torque stayed pretty much flat from 2000 up. I only modeled the aftermarket heads because I wanted to optimize the engine for low rpm torque and was curious which head would cause the best results for the combination and desired rpm range (idle to 3500). I know that the program is too general to be really acurate. I was looking at it as a guide to see what might work, not looking for real world numbers out of it. Good point on the piston to valve clearances. I would check those before making any changes anyway. I have seen way too many "close encounters" to want to pay for one of those myself. Even if it just extends the usable rpm range another 500 rpm, I would be happy.
When I was looking for a cam for my current project I found out that most cams zero is 4 degrees advanced. They are ground this way to account for chain stretch, putting them at 4 degrees retarded is really straight up. BTW my Mustang and Tammy's car are within 10-20 Hp of the desk top dyno and corrected rear wheel Hp
Moving 8° is risky to piston /valve clearence and not normally done. Always check this out for min clearence. An engine with piston valve reliefs may get away with it but one with none, may not.
Hey Ken, I'm not sure if you were refering to me or not so I'll try to explain. What I found is most cams are ground for chain stretch. This is why on the dyno simulations 4 degree retarded give the optimum power. so you have two choices you can put the cam 4 degrees retarded and have the power now or put it at zero and have the power later as the chian stretches. I was in no way saying to move the cam 8 degree just a simple 4, I would still recommend claying it for clearence.
This is especially true of the TW TFS heads...since they are canted valve, running them on factory pistons with alot of lift narrows piston to valve clearance... I have built several engines...I last built a 92 longblock, with b cam, Cobra EFI intake, 24 lb injectors w/calibrated air meter, Ford Racing windage tray (Boss 302 style), longtube exhaust, and an X pipe...with the cam straight up, dyno'd 275 rwhp (over 330 roughly at the crank)...with 4 degrees retarded cam timing, that number jumped to over 290 rwhp...
If you are using a cam that is too small for the rest of the engine why not put parts in that match the cam and save some money. This while getting the same power that your cam will deliver with the more expensive parts. There is little reason to have heads, intake and exhaust that will give you 7500 RPM when you are only going to run it at 5500 RPM. If you tune everything for that 5500 rpm range you will pick up a bit more power there - you will lose it faster after 5500 but if you aren't using that RPM range who cares - Tune it to the RPM that you are going to run at and save some money getting more HP.
Trying to discuss all the areas that need to be addressed and brought togather is difficult unless all have the same understanding of the subject. His motor as listed has forged pistons with valve reliefs if they have not been changed. The cam looks like the Crower 15510 and should give a worthwhile seat of the pants increase in breathing for both Mass Air and SD engine control. The cam is listed for 1500 to 5500 rpm range. This cam should give a good low to mid range power increases along with a little more top end compaired to a stock cam. The stock cam is about done pulling at 5200 rpm in real application with stock heads and intake system. I see no real benifit to the large Mass Air and TB sizes for this engine. The engine can't use that much flow capacity over the full rpm range except for some small amount at the top. The 5L displacement can only pump about 500 cfm of air under ideal no loss conditions at 6000 rpm. Enter the flow losses in the heads and intake and you may get about 85% of that flow at WOT and full rpm. No increases in air meter or throttle body sizes are going to allow more air into the motor with flow losses after them unless the heads and intake are flow improved first, then widen the cam duration a bit to fit the intened application. You just can't think of individual changes unless you include all the other items. This is what makes people wonder why their mods didn't work better than they had hoped for.. This engine is good for about 235 +/- hp as presently speced. The 19 lb injectors are good for 290 hp. They are more than large enough at present time. Going out of design limits with a large meter and TB is not going to hardly get 10 hp or just enough to be felt for the drivability problem they may cause, upsetting the total design.
