Chasis Dyno Tuning is A GOOD THING!!

[Rickd]

Got my new ERA FIA 2 weeks ago. Was running a little rough, and turned out to have a bad mechanical fuel pump and alternator. Replaced those and my "mechanic" thought he would tweak the carb and timing. Said "that's where she needs to be". Didn't feel, sound, or smell right so I located a chasis dyno tuning outfit in Pompano Beach Florida - Mustang Specialties. Took her in this morning. This is with a 331 stroker with AFR 165's on it. First pull 210 hp at the rear wheel. My "mechanic" had put a total of almost 58 degrees timing on this motor!! Reset timing to 34 degrees total advance, and leaned the carb a bit. Second pull, 312 rwhp. WOW a little improvement. Then adjusted the carb jetting and ended up at 4th pull with 326 rwhp, and a nice, clear idle sound, and crisp acceleration. On the second pull at 6000 rpm the room filled with black smoke (total miles on the motor 500), so she had been running very rich. After the tuning, put in a new set of plugs. A good chasis dyno tuner can set the fuel / air mix to what it should be. Relying on someone's "ear" can be fatal. Life is good!!!! Rickd

[jdean]

Rickd that is a very good number for a 331. It should equate to around 400hp at the crank. What kind of CR, what are the cam specs etc.?

[J Persons]

Originally Posted by jdean

Rickd that is a very good number for a 331. It should equate to around 400hp at the crank. What kind of CR, what are the cam specs etc.?

I've always read that you loose about 15 to 20% of the HP through the drive train, but lately have questioned that percent of loss. RBT transmissions, who make the ZF trans axle for GT40s and Panteras, say there is only a 16 1/2 HP loss through a ZF. I would be more inclined to say that there is a 20/25 HP loss through the drive train, and not the 20% that some folks claim.

[jdean]

J Persons, the loss from the drivetrain is not speculation, but has been proven with countless comparisons of FWHP compared to RWHP on the same engine. The ZF transaxle is not a fair comparison since it is both the transmission and differential in the same unit, so it is intrinsically more efficient vs a transmission, driveshaft, differential.

The chassis dyno vs engine dyno sometimes introduces sources for addition losses like exhaust systems or other accessories driven by the engine.

[J Persons]

Originally Posted by jdean

J Persons, the loss from the drivetrain is not speculation, but has been proven with countless comparisons of FWHP compared to RWHP on the same engine. The ZF transaxle is not a fair comparison since it is both the transmission and differential in the same unit, so it is intrinsically more efficient vs a transmission, driveshaft, differential.

The chassis dyno vs engine dyno sometimes introduces sources for addition losses like exhaust systems or other accessories driven by the engine.

True, but I was using the referenced ZF as an example only. If the 20% is correct, that would put my 331 at around 420 FWHP, and I just don't think it develops that much power. If someone on the board is a Ford power train engineer, they could answer and put this debate to rest.

[Rickd]

My 331 stoker has AFR 165 heads and the Trick Flow Stage II cam (224 / 232 duration at .050 Lift is 542 intake 563 exhaust). The carb is a Quick Fuel Tech carb that had to be leaned (metering blocks taken off) as it was WAY WAY too rich when I got it. The tuner uses Pro Systems Carbs exclusively and says they're the best available..but he said mine was GOOD and as he tuned it - no problem. KC dyno'd the motor after the build and it showed 426 hp at 6000 rpm on the stand - in ideal conditions not hooked up to a flywheel, no air cleaner etc etc etc. KC's numbers might be on the 'optimistic' side. But I just got in from a 128 mile cruise down to Key Largo and back (with lunch at Alabama Jacks), and the car ran real good, sounded very nice, with a cool melodic idle, and we averaged 18.3 mpg for the trip, mostly in 3rd and 4th gear, with a couple of 5th gear sprints. So it has been "tuner week" for this weeks vacation. We started out super rich, with only 210 rwhp, and 5 mpg on the first 300 miles. Timing adjusted, car leaned, we got a 116 hp increase at the rear wheels, and mileage increased over 13 mpg. I feel a lot better about my new ride, which now has just 650 miles on the odometer. But tomorrow is Saturday!!! Have a great weekend. Rickd

[J Persons]

Rick, well if you have both dyno runs that show the numbers, then I stand corrected.

My engine is a 331, carbed with a Holley 650 DP, and had to be jetted up three sizes on the secondary side to cure a lean condition over 4500 RPM. They also replaced the primary pump shooter with one size larger. No other changes were made. It developed 372 @6100 to the rear wheels.

[Dennis Kelley]

Chassis Dyno is a great tuning device. I dynoed my small block and its amazing the difference in vehicles.
later
dennis

[jdean]

Rickd, if your ERA has an IRS, that will account for some additional loss compared to engine dyno. Good numbers though in both cases for a 331.

[dlang14]

dont forget the loss of hp form the sidepipes. If you have better flowing mufflers in your pipes that 20% can drop significantly.

Daryl

[RICK LAKE]

Both J's You guys are trying to use a shotgun to kill a mouse. There are alot of things you have to take into account. Is the car on or off the ground? Are tires on it? Are the brake pads dragging or touching the rotors? Are the wheel bearing too tight or loose? What kind of tires are you testing with? 10 year old rocks or gummy slicks? I believe you are both right to a point. I think it takes about 20HP to drive the trans and rearend with tires on it up in the air. This is with a posi unit. You put this car on the dyno or street and run it the same way, with tire drag and everything else, about 16-20% of total drag on the motor. You also need to figure out total load on the motor. I would think it is alot easier for a torque motor at low rpms to have an easier job of spinning the drive train than a 600hp motor at 7,000 rpm with no bottom end. The exhaust is another HP killer on cobras. The idea backpressure is about 1-2.5 pounds+ of psi at WOT depending on the motor and size of cam. nything more and the exhaust is costing power. You will also pickup about 10-20 honest HP with a set of webers setup correctly over any carb on the market in the mid range rpm's of the motor. Just my 2 cents. Rick L.

[jdean]

It's not about trying to be right or wrong, just the facts. But you did bring up about 5 other points that could potentially add to the losses on a chassis dyno vs. engine dyno that help explain the range of 15% to 25%.

So far, the least losses I have read about are the less-than-15% losses for the newer Corvettes......but I think the opinion was that the factory understated the FWHP to begin with since the RWHP numbers were so good.

[Rickd]

JPersons. What heads are you running? I have AFR 165's. I know that if I had the 185's I would have about 40 hp additional - or roughly 366 rwhp. And yes I do have IRS, and side pipes with glass pack material. I am very happy with where I ended up this week - it has been a blast. And manana is time for another run!! Have a great weekend!!! Rickd

[J Persons]

Originally Posted by Rickd

JPersons. What heads are you running? I have AFR 165's. I know that if I had the 185's I would have about 40 hp additional - or roughly 366 rwhp. And yes I do have IRS, and side pipes with glass pack material. I am very happy with where I ended up this week - it has been a blast. And manana is time for another run!! Have a great weekend!!! Rickd

I'm using Edel Performer RPM 2.02 heads, that have been professionally ported. They flow better than stock Vic Jr heads. The compression is 9 to 1, and it runs on 87 octane pump gas.

[RICK LAKE]

jdean I am not picking on you, just bring to the table alot of other things that have a drag on the drive train. The more rotating weight that is removed, the more power made. I don't believe all the GM stuff and I work for them for all most 28 years. The trans in the rear of the car was to add weight and balance the car to more of a 48/52% weight change. They are back to tubes for the drive shafts. They are also trying to get more weight on the rear tires for traction. I did leave out the slipage on a tire on a dyno. This depends on the roller and how worn it is. Also the tire and how hard it bites the drum. Don't get me wrong, Dynos are great with limits too. I use them myself but have found that in the end the LM-1 meter with A/F readings on the road is just a little better. I also run Fuel Injection which give me and easier way to adjust the motor. It's a little hard to be driving at 60 mph and trying to change the jets. I am trying to give you just the facts. Rick L.

[jdean]

Rick, I did not take it you were picking on me, in fact the opposite since you just added more stuff to support the point I was making which is that indeed there is 15-20% loss and sometimes more. Dont forget that automatics consume even more.

I totally agree with you on the LM-1. I installed an O2 bung on my Cobra, and used it to verify my AFR at cruise, transition and WOT to be sure things were efficient as far as making the most power. I am helping with a 289 build right now and have already installed an O2 bung in it as well to use the LM-1. If you use the LM-1 and get the AFR tuned correctly across the RPM range. along with optimizing your timing curve, I think this is money better spent vs. a chassis dyno.

[Dennis Kelley]

The chassis dyno that I used had a wide band O2. I would not go to a dyno that didn't have O2 sensor