Went to the dyno 12/01/2000

[Donnie]

Here's the dyno report that I got Friday. Just to make it clear to the uneducated, this is my horsepower at the wheels not the flywheel. To calculate the flywheel horsepower, take my fwhp and divide by 0.80 (80%). This assumes a 20% driveline loss.

This pull was made in 3rd gear and does not accurately represent my torque values, but the power values are correct. This is because 3rd gear is not a 1:1 gear.

My graph shows a bad dip in power at 6500rpms. This is because this was not my final pull, therefore the car was not tuned completely and was running very rich at the top end.

http://www.customcurb.com/dyno.jpg

[hipogtr]

Looks like a healthy pull. But that 16G seems to run out of air at 6,500rpm pretty quick.

[ecoli]

Thats the stock 2G cams...

[Donnie]

Those are good guesses but neither is correct. The car ran really rich between 6500-7000rpms. This pull was one of my first and we did a lot of tuning afterwards. It just happened to be my strongest pull of the night.

My turbo (16G Killer) spools to 14psi at 3200rpms (which would be evident if I hadn't shifted out of 2nd so late that pull) and holds steady as a rock all the way to redline.

[Fast16G]

Yes they are correct, "killer" or not, the turbo is dying on the top end. Below you'll find a chart of my small 16G run (21psi, VP-RED fuel). I obviously have more mods than you, but it still falls off. It's just the size of the turbo...nothing you can do about it. You're better off being rich(er) on the top of the RPM band anyway. I wish I started my pull from idle...I'd bet that I have over 300ft-lbs from 2000RPM :)

That was my highest HP, but my highest torque number was 355.2. Still on the stock upper IC hose too :) Since that dyno, I've built the bottom end, raised the compression (JE pistons), switched to a big 16G, removed the balance shafts, finally did the bowl work, 650 injectors, etc. etc. etc. I would really just love to slap a 16G on the dyno and see about 380HP at the wheels someday...

If that was your "first run", why is it PEP file #16? :)

For the helluvit, under the dyno run is a dyno drag pass (basically get the rollers moving in 1st gear and the blast away as if you were at the track). I dunno how the FWD guys do it...my tires lit up on the rollers on more than one occasion. In any event, you can see how the HP is divided into the gears. Notice that in the middle of 3rd and all of 4th, it dies out (small turbo).

http://rossl.home.texas.net/images/sm16gdyno.jpg

http://rossl.home.texas.net/images/gears.jpg

[Donnie]

I'm not quite sure what you're talking about when you say that the turbo ran out of air or is dying on the top end. I saw the data on the dyno computer. It showed the boost graph as jumping to 14psi and holding there like a table top until redline. If you'd like I can call the man that owns the shop and ask to get the boost info send to me.

[Donnie]

Fast16G,

Did you change the gearing in your car? Mine showed 135mph at redline in 4th.

[Donnie]

One last thing... It says pull 16 because that wasn't the first time I had been there.

[Fast16G]

I probably should've been more specific. You're boost won't drop (well, it might if your engine starts flowing *a lot* more than the turbo will supply...mine does). Your engine can take a lot more air at higher RPM, especially in longer gears (3rd, 4th, 5th). This is the prime reason big turbos give you much better top-end.

Let's just say that boost will remain the same, but the engine can use more than you're supplying (volumetric efficiency .vs CFM). Rather than post another chart here, just look at my page http://rossl.home.texas.net/dyno.htm where I have overlayed my friend's Level 5 Frank with my 16G. Notice how the power curve is lower under 4500 and really pops up over that, while my 16G levels off and starts dropping. That is just 110% do to the fact that it flows more air and can keep a good supply of volume (CFM) at a high pressure (boost) when the engine pumping the most (high RPM, long gears).

In essence, a small turbo will "run out of air" to supply the engine...not that it's pushing less, just that the engine can flow more. You really need a turbo big enough to be capable of flowing MORE than the engine can in order for the HP to not drop, or ideally continue upward, by your shift point.

Either that OR there may be too much back pressure in higher gears/higher RPM. Since there's so much air moving in/out of the head, an exhaust restriction (which might not be a restriction at lower RPMs) might actually prevent enough air from exiting, which in turn would cause less air to enter, etc. etc. etc. which would show up as a high RPM drop in HP. This is why people clip their turbine wheels and install 3" exhausts without converters. More times than not, I think it's just from the turbo not flowing enough to keep the engine completely supplied :)

I have an AWD and our gears are much shorter than you FWD people. My 3rd gear tops out at about 90mph and FWDs are somewhere around 108mph?

[Donnie]

Ahhh... I see now. That makes a lot of sense. Does the fact that my power doesn't fall off until just before redline (when it's tuned right) mean that my turbo is ideally sized for the motor as it sits right now?

[Fast16G]

Well, ideally, you wouldn't want to drop HP at all, even near redline. As I said, you'd want it to be level or increasing. The problem is that a turbo large enough to do that requires a lot of supporting mods to make it anywhere near as powerful down low (as seen by the L5/16G dyno chart on my page). He has pretty much the same mods as me, except he has 272 cams and the Frank. As you can guess by that chart, I beat him on the first 1/8 mile and then he catches up on the long end.

Lag is a real problem with a big turbo, and for street driving, it really takes all the fun out of it. It sucks that your car doesn't really go anywhere until 4500-5000RPM and 70mph :) But then again, when it goes, it *goes*. My 16G is as fast in the 1/4 mile as many 20Gs/Franks. I just do it will less trap speed. Difference between spool-up and low end torque.

Your curve definitely isn't any better or worse than any 16G curve I've seen on any DSM. Whether it's the engine VE, back-pressure, or whatever, just be aware that that the high RPM drop won't be something you can tune out or get rid of with cams, porting, or more boost. The whole curve will move up, but that drop on the high-end will always be there with a 16G.