Well, I was curious a couple of weeks ago, so for $50 I put the Chevelle on a chassis dyno. It was a dynojet 248. I basically don't care about the numbers but wanted to see where the power dropped off at so I could figure out a better shift point. As you'll see in the graph, I really don't understand right after it peaks the up and downs in the curve. I just thought I would post this up to get some feedback from someone who knows what they are looking at. This is the best pull of the day. I made two other pulls and the best out of those 2 was 381 hp/425 tq. I removed the exhaust and thats when it hit the 400/441. It's obvious my exhaust is definately restrictive, I'll be building a new one. Let me know what you think!

http://i192.photobucket.com/albums/z205/70ss496/DynoGraph-1.jpg

496 CI BBC
4.310 Bore
Scat Internally bal. 4.25 4340 lightweight crank
Scat 6.385 H-Beam Rods
SRP Forged 5cc dome (with my heads works out to be around 11:1)
8" Internal Fluidampner
Ultradyne 288/296 F7, Solid FT
#206 Oval Port Closed Chambered Heads
-Had a bowl grind
-Heads were port matched to the intake
-Valves unshrouded
Edelbrock Victor Jr Intake
"Box Stock" Holley 950HP
Sumped stock tank, -10 line from rear to front into a Carter 172 GPH mechanical pump, -8 to Carb.
Hooker 1 7/8" Comp Headers
3" Exhaust into race-flow flowmasters dumped in front of axle
Stock GM 502 Crate motor water pump
March Billet Aluminum pulleys
Factory Fan w/clutch
Power Steering
Power Brakes

ATI Built TH400
Full manual valvebody
Continental 10" Converter(the best I can tell it flashes to about 4000)

12 Bolt, 4:10 gears
Completely stock 30 year old suspension
Air Bags are the only thing, 0 in left and 6.5 lbs in right
28x10.50 Stiff Sidewall

Matt

looks like a nice street car!

If I'm reading the graph right, you've got some tuning issues. I'm seeing peak torque at about 4700 and peak hp at about 4800. I don't know why it's laying down so early but I'm sure that others here will have some ideas.

The "up and down" in the HP curve is merely the result of the torque falling off REAL FAST from 4700 to 5100, then somewhat levelling out from 5100 to 5600, then tapering off again.

HP is calculated from torque: it's torque times RPM divided by the factor of 33,000 divided by 2pi (Watt discovered that one horse could raise 33,000 pounds one foot in one minute, and therefore created the definition of "horse power" equal to that time rate of doing work; and then since torque is related to linear work by the factor of 2pi, which is the circumference of a circle with a radius of 1, so one revolution of a thing 1 foot in radius does its work over a distance of 2pi feet) which works out to 5252.11. Which is why on graph paper where torque and HP are potted on the same scale (as your graph is), the curves ALWAYS, by definition, intersect at 5252.11 RPM, like yours does.

The worst thing I see about your curves is that the peak torque and peak HP occur at basically the same RPM. In other words, torque falls off FASTER than RPM, once it hits the peak. For a car to go the fastest, you want curves such that you shift at about the peak HP RPM, and you hit the next gear at about the peak torque RPM. The ratio of one gear to the next (1st divided by 2nd, 2nd divided by 3rd, etc.) is usually somewhere around 1.35-1.40 in a wide-ratio trans to about 1.25-1.3 in a close-ratio one, so your trans ratio and your "peak-to-peak" spacing should roughly match (i.e. if you have a real "peaky" motor, where the torque peak and the HP peak occur close together, a wide ratio trans is not the best, and vice-versa). Then, you want a converter as close to peak torque RPM as you can stand and still hook it up at the line.

It'd be interesting to see what effect unhooking the exhaust had on those 2 curves, compared to what they looked like with it hooked up; namely, if it kept the torque from cratering so fast once it passed the peak. Absolute numbers aside, that's the ONE improvement that graph tells you that you can make: is to make changes that spread out the torque band in the upwards direction somewhat.

I made the link to where the graph is horizontal now, so maybe it will be easier to read. If I'm reading it right does my converter flash to 4600?? Here is the combo I forgot to list it.

496 CI BBC
4.310 Bore
Scat Internally bal. 4.25 4340 lightweight crank
Scat 6.385 H-Beam Rods
SRP Forged 5cc dome (with my heads works out to be around 11:1)
8" Internal Fluidampner
Ultradyne 288/296 F7, Solid FT
#206 Oval Port Closed Chambered Heads
-Had a bowl grind
-Heads were port matched to the intake
-Valves unshrouded
Edelbrock Victor Jr Intake
"Box Stock" Holley 950HP
Sumped stock tank, -10 line from rear to front into a Carter 172 GPH mechanical pump, -8 to Carb.
Hooker 1 7/8" Comp Headers
3" Exhaust into race-flow flowmasters dumped in front of axle
Stock GM 502 Crate motor water pump
March Billet Aluminum pulleys
Factory Fan w/clutch
Power Steering
Power Brakes

ATI Built TH400
Full manual valvebody
Continental 10" Converter(the best I can tell it flashes to about 4000)

12 Bolt, 4:10 gears
Completely stock 30 year old suspension
Air Bags are the only thing, 0 in left and 6.5 lbs in right
28x10.50 Stiff Sidewall

There's nothing wrong with the torque curve, you're looking at the multiplication of the converter at the lower rpm's. The stall speed of the converter is increased quite a bit by the 5400# load of the dyno, and the torque multiplication drops rapidly as the converter speeds up.

So the ups and downs after the converter locks up is normal? I thought it was a miss or something. Thanks for the info, any other input!

Matt

I was about to type what onovakind67 wrote. Unfortunatly that means your peak power is about 388 rwhp. What I dont understand is why the run was done at such high RPM. Usually you'll see runs starting around 3000-3500 rpm.