whontime

I am running a similar cam in the 227/233 XE and I am shifting it at 6100-6200 rpm in an M6 car. The power peaked at 5900 on the dyno sheet.

stereomandan

Yeah, to be honest, with most aftermarket cams, you are going to have to shift because of the valvetrain capabilities. You never really reach the point where it makes sense to shift due to TQ. If we could, even with the Hotcam, it would be best to shift about 6700-6900 RPM according to the dyno sheets and the gear ratios in a M6. That would maximize the TQ (acceleration) in each gear.

It's difficult to explain the concept of shifting due to TQ and gear ratio, especially by writing it like this, but that's the correct way to judge where your shift points should be.

Dan

Jon A

Read it again. I did account for it using his way. You don't need to account for it using HP (except figuring out the RPM drop of the shift)--that's the point. Both methods result in the same answer. One takes math to undo HP, then re-do HP under a different name. The other just uses HP from the beginning. Maybe that's why they put that line on the graphs? Maybe it does mean something?

No, it couldn't be.

stereomandan

Well, You shift the way you want, but just realize that you will be going slower than you could be.

You don't seem to want to learn.

Dan

FastWhiteTA

If you notice your tqp curve falling off really fast, it's because your springs are not up to the task. The XE grinds take very high spring rates, much more so than a traditional ground cam. I've heard your spring rate should be around 130 to get the most out of those XE cams. Once you have the right springs you could probably shift around 6400 rpm or so w/ that cam.

whontime

I have heard this from several people. I am running the Combo 612 springs and they don't want to hold my XE at over 6K. Some people seem to be able to rev theirs higher, but my power falls off at about 6000 so I shift at around 6200. If I were doing it over I would go with a good dual spring setup for sure. The 612's are nice and plenty of people are using them just fine, but for me I wish I had went with another spring setup.

Jon A

Back to the original question of this thread, a couple people make a really good point. I have yet to see a dyno of this cam where it didn't just die somewhere in the 6000-6200 RPM range. Not that they don't or can't exist, I just haven't seen one. All the ones I've seen do not show the cam to "gradually fall off at high RPM" because it's a small cam (like many I've seen of the CC305 or Hotcam do)--it flat hits a wall. If my dyno looked like that, I would take that to mean at least something in the valvetrain (most likely springs) doesn't enjoy spinning that fast with those lobes. If this was the case, I'd want to shift the car before it hit that wall just to keep from breaking stuff.

With set-ups where the power falls off more gradually find the place where the HP before the shift is the same as the HP after the shift (or do it Dan's way, same difference). With big cams, you're generally going to be the fastest the highest you shift--limited by how fast you're comfortable spinning the bottom end. That's why cams like the CC306 and 847 are faster at the track than their peak numbers would indicate--there's simply more to be gained at high RPM than there is at low revs. Those cams take advantage of this and give you more area under the curve than a cam with the same peak numbers that needs to be shifted at 6K.
You're right, I'm trying to teach. I've tried to keep it simple with the example above but I could also prove it mathematically about 1/2 a dozen other ways. If you want to learn more, you might want to check out this thread (especially the last page):

http://web.camaross.com/forums/showt...0&pagenumber=4

Now you need to put forth some effort and actually look at my example. If we both come up with the same optimum shift points, we'll both be the same speed regardless of how we arrived at those points. My example simply showed that the answer (optimum shift point) will be the same with both methods. One method is just faster, easier and more intuitive. Why it works the same as yours is easily shown mathematically from the equation Force = Power/Velocity. That's right, you can calculate power without even knowing RPM or gear ratios by measuring the end result we all care about--the rate of acceleration of an object. That's what Dynojets do, after all.

stereomandan

First, let me say that Jon A is correct that you can find the shift points the way he describes. You want the HP in the next gear at of above the HP in your current gear before you shift. Previously, I said it had to be TQ, but HP will work too. Either method can be used. Sorry about that.

Is it easier to use HP vs speed for shift points? Yes. Now, is it more intuitive to use HP? Not to me. It gives you no idea of relative acceleration for each gear. If you only plot HP vs speed, you have no idea of how much acceleration you have in each gear. Yes, the shift points come out the same as TQ vs. speed, but to me, it gives no relative performance in each gear. If you really want to see how a car is moving down the track, TQ vs speed is more intuitive, since acceleration follows the TQ curve, not the HP curve.

Just my thoughts.

Dan

LT1ponykilla

Thanks alot guys. Alot of good points here and Ive learned somethings as well. Im dyno'ing my car on a DYNOJET next week and I will let you guys know how everything comes out. Thanks again!

Jon A

I guess different strokes for different folks, Dan. Since the shiftpoints come out the same people can feel confident using either method. Here's why using HP is more intuitive to me:

When one looks at a dyno and thinks about maximizing torque, it seems odd to them that in order for the car to be the fastest you need to use the RPM range where you have the least torque. Looking at HP, it's pretty easy to find the range that will give you the most area under the curve, highest average, etc. Anybody can find that. If we maximize the torque in each gear we'd all be shifting at 4500 RPM and be slow. The rate of acceleration in each gear does follow the torque curve. You will accelerate the fastest in each gear shifting low like that but the car will be slow. What matters is the rate of acceleration vs speed, like you said. In order to use torque for that, one needs to calculate it and use torque @ a speed--which is HP just like torque @ an RPM is HP. At any given speed, acceleration is directly proportional to HP from Power = Force X Velocity. It's done for you.

So by knowing HP, one can intuitively know how fast a car will accelerate without knowing anything else. A car with 400 average HP between shiftpoints is going to be much faster than a car with 300 average HP between shift points. One doesn't need to know the torque or the gears or anything else. At any speed, the 400 HP car will be putting more torque to the rear wheels than the 300 HP car. Because that's what HP is.

whatsup

When you dyno....if you can....post the results here. I would be curious to see them. I just finished installing my 224/230 last week. It pulls hard to 6000rpm....haven't tried going past that yet. I'm running the Crane 10308 double springs.