Disappointing Day on the Dyno

I ran my '67 Mustang on a Dyno Dynamics chassis dyno today, and I certainly had higher expectations for the results! First of all, we had less than ideal conditions since it was so hot and muggy today (96 deg with 80 - 100% humidity and it was storming by the 3rd pull). However, instead of trying to explain away the numbers, I will just put the data out there and see what you guys have to say.

424W- 6.2" H beams - KB Forged 10.2:1 - AFR 205's- flow balanced Victor Jr. intake -Mighty Demon 825cfm -Comp Cams XE hyd roller .236/.242 @ .050 .555/.576 lift -Miller 1.6 mid-lift rockers- MSD ignition - 1 3/4"Hooker Super Comps - Gene Hughes AOD with a non lock-up 2800 stall


Notes:

• Max HP - 357.2 @ 5400 rpm
• Max Torque - 383 @ 4500 rpm
• 38 deg total timing / 14 deg initial timing
• Fuel mixture: 12.25 @ WOT / 14.7 @ idle
• Jets - 80 primary / 92 secondary
• Converter stalled at 3400 rpm

On the upside, once we got the carb jetted right and changed the advance springs in the distributor it ran very smooth and had a lot of throttle response. I'm wondering why my converter stalled so high which also makes me wonder how much power I'm losing in the AOD and converter. The guys at Carter Racing did say that on a cooler, dryer day we would see atleast 20 to 30 more HP/TQ.

Cam is too mild.

and 12.25 at WOT seems too rich.
You want to see more like 13.5

I would play with fuel and timing and see about a custom cam.

Originally Posted by rbarn351

Cam is too mild.

and 12.25 at WOT seems too rich.
You want to see more like 13.5

I would play with fuel and timing and see about a custom cam.

It was actually running lean until the last jet change. We made three jet changes going up two sizes at a time. Maybe I could go back down one size.
I know that the cam is too mild to put up big numbers, but there are guys making 500 to 550 flywheel HP with the exact same cam and heads in 408's. I'm not sure exactly what my numbers equate to in terms of flywheel HP considering the rest of my drivetrain, but I was expecting to go north of 400 at the rear wheels.

You can fiqure a 17%-/20% loss thur the drive train for flywheel HP,with that kind of humidty, you could easily be losing 100 or more CU FT of air, yes it would be a rich pig ,A/F is calulated using usable air after the water content is subtracted out, I really like to see the intake vac at WOT. from 0 to about 1.2 is really good. no restrictions.the 825 may be a little small. but still give you a good throttle response. . with that much timing and such a early intake valve closing the engine may be working against pressure buildup in the cylinder after the plug fires . some other usuable fiqures are the BMFC/in LBS per HP per hour, and BMEP, I really hope these figures he got are the measured HP and Torque, not corrected

a) You're way down on power -- you knew that
b) Your cam is too small for that engine
c) Throttle is not opening 100%???
d) Carb sucks

Your combo should be putting a MINIMUM of 450RWHP to the ground!

Search for my dyno numbers and find the link to my cam specs...

As much as the car seems down on power, there must be multiple things wrong with the motor. Don't expect to change just one thing and then gain 100hp. No cam change is going to get you there. Something else is wrong. As it is, that motor combination should be putting out a minimum of 400hp at the wheels without breaking a sweat.

I suggest first starting with the basics to determine the health of the motor. Do a compression/leak down test. What vacuum reading do you get at idle and at a higher, steady RPM?

38 degrees total timing sounds a little excessive for an efficient combustion chamber like the AFR's have. I would think that it should be less than 34 degrees. I wonder if the cam is installed correctly. Did you determine true top dead center before installing the cam?

Chassis Dynos...

They can be like a 'box of chocolates'. Don't rely on them for absolute numbers, as they are more of a tuning tool, and not that great of one at that.

That being said, engine dynos measure gross output. Your car may have a lot of 'parasites'.

Start from the front of the engine and work your way back, eliminating anything that sucks power. Do you have an electric fan and waterpump? The AOD absorbs a TON of power! If you remember when the 5.0 mustangs came out, the 5-speeds would RUN CIRCLES around the AOD cars. Major power hogs.

Now, how about the engine? What exhaust is on the car? With that large of an engine, it NEEDS MANDREL BENT 3" PIPE and muffler that you can see straight through. If it doesn't have it, you'll be WAY down on power. Nice headers aren't worth a sh*t if they are hooked up to a crappy exhaust. An Olympic runner isn't going to do well if he has to exhale through a straw. LOL

One option with exhaust, (it's hard to do 3" tailpipes on an early stang) is to run 3" back to 3" mufflers, then weld some 3-bolt collector rings to the muffler outlets. The tailpipes can them be attached with simple header reducers. Speaking of tailpipes, 2.5" mandrel bent flowmaster tailpipes are around $100, and work/fit really well. Being removable allows the car to take on a lot of different personalities. Tailpipes on for quiet cruising, or off for being rowdy. The removable tailpipes also make it easy to remove the entire exhaust system for transmission service. One tip, don't use long mufflers on a mustang, as there may not be enough room for the tailpipes to make an efficient bend up and over the axle.

Good Luck!

Originally Posted by DynoTomS

I really hope these figures he got are the measured HP and Torque, not corrected

Fortunately, the numbers are not corrected.
The dyno operator kept saying things like "This dyno hurts a lot of people's feelings" and that it tends to be very "conservative". I don't know enough about dynos to know how much difference there can actually be from dyno to dyno. Maybe they were just trying to spare my feelings, but they were not alarmed by the numbers and did not think there was anything wrong with my engine. Although the numbers were not outstanding, they felt like it ran very well and performed just fine considering the temp and humidity we were running in. How much HP could I have realistically been losing due to the temp and humidity?
They estimated my drivetrain loss to be around 20% and possibly even more with my AOD and converter. Figuring 20%, the FWHP would be about 450. At 25% it would be more like 480. If you assume that I could pick up another 25 HP on a cooler, less humid day, then that would at least clear the 500 HP mark. Am I being realistic at all here?
That being said, there is no denying that my cam does not peak at a high enough rpm to really take advantage of my heads and induction. I guess that's what I get for trying to walk that line between street engine and race engine. Those of you who predicted that my peak power would be around 5400 rpm were right! I'm just wondering how someone else's 408 peaked at 5900 with the exact same cam, heads, and intake. I didn't think the extra 16 cubes would have that much effect on the power band. A cam swap may very well be in the cards for me!

Cam installation can have a big effect.

What exhaust is on the car?