Getting the power to the wheels
 

In the past month I purchased a BDR Cobra with a 408 Keith Craft engine. The car was built in 2010 and in that time managed 900 miles. I have added an additional 200, and have been trying to work the kinks out of a motor that has been mostly dormant. The Dino docs it came with indicate the motor produced ~530hp. I recently put it on a mustang Dino and after three passes managed 378 to the wheels. The car was running lean, and timing seems off. Engine had a nice flat power band, but broke up at around 5800. I could not get to the 6250 redline. All this said, what are the chances of getting this thing to where it should be? I was expecting 440 to 450. Just curious if others have had this experience.

All speculation but I watched my engine dyno'd at KC and for a couple things - they are not running air filters, big headers - no mufflers, I think no alternator to drag, may be using your actual distributor or one they have set up for the dyno.

http://i125.photobucket.com/albums/p...aEngine025.jpg

By the time you put an air filter on it (and if using an original S&H filter it's equivalent for a Yugo), add mufflers, add alternator, and driveline losses - it all adds up. But I would have expected you to get to a little over 400 HP - different chassis dynos produce different results. I would compare the power you were getting at 5800 on the engine dyno report and see if it was within 20% of what you got on the chassis dyno just before it started breaking up. If it's tracking pretty closely up to that point then you just need to figure out what's breaking it up at 5800 rpm.

If it was running lean then the air filter probably wasn't holding it back. You may need to confirm your float levels and fuel pump pressure.

Just noticed you said you used a Mustang chassis dyno. I believe they are one of the units that generally produces a little lower HP/torque readings.

My car has a 427 built by Keith. Motor now runs perfect but I had less than stellar rwhp dyno results. My crank dyno was 590HP and 570TQ. My car made made something like 360hp and 350tq at the tires. We pulled the air filter off the car on the dyno and made a pull and it made a whopping 1 hp less.

After getting the car home we found what we thought was an inadequate fuel pump and fuel system. The fuel system was replaced, plugs and wires were replaced and the MSD chip was changed from 6000rpm to 7000rpm. We also changed the springs in the distributor so that the advance would come in much sooner. The car now pulls much harder but I have not stuck it back on a dyno. I also have 2" headers which I think are a major TQ killer on my size motor. If the average guy got in my car and took off he would **** his pants and probably crash.....I'm just a power freak and want more. It takes big power to make close to 500rwhp in one of these things on a mustang dyno. I think you would need around crank hp 675-700hp

Just for comparison, my first 427 small block was a Roush and after putting on 3" sidepipes and a quickfuel 850 mechanical secondary carb, it put down 440 hp to the wheels with no other changes.

Yours should be similar. Start with your timing. A total of 34 degrees is a good place to start. New plugs would be a good idea too. No telling how long they've been in there. That's all there is! Air in, air out! As long as you have fuel and properly timed spark, you should be good to go. Hold a mirror into your sidepipe and see how large or small the interior baffle is. Mine was 1 3/4" inside diameter (really choked the crap out of my motor) before I changed it out to 3". That was the biggest part of my horsepower gain besides the carb.

Good luck. The horsepuppies are there, you just have to figure out how to let them out of the barn.

DanEC has some great points. The dizzy stands out in my mind as far as spark scatter or spark reach issues, especially if your advance comes in late (heaviest springs are not all-in until 5.5k)
The adjustable rotor is a worthwhile investment.
I found this video pretty helpful in setting mine up.
[ame]https://www.youtube.com/watch?v=aWMlNwGW0tM[/ame]

All this assuming your running an MSD dizzy.

Like others have said if the motor is breaking up then your running out of fuel or spark or both. Start with the simple things like checking fuel pressure, check fuel filter for clogs, making sure your plug wires are in good shape and routing to the correct cylinders, checking plug gap and condition of plugs, make sure you have a good ground, etc. Also check you're getting full throttle, but I doubt that's causing the motor to break up.

Good suggestion there. I've seen more than one that the throttle linkage wasn't setup correctly so it was never actually opening all the way up.

How do you change the msd chip? And would it do anything else other than allow for revs up to 7000. There are a lot of useful tips in this thread. This is my First Ford V8 and my first old school motor since the 90s. I'll get to playing with it. Kind of why I bought the car.

Put the 6000 rpm chip back in. It will protect the engine from over revving once you tune it properly.

Whether you have full throttle or not wont be the cause of the engine missing. Your problem is probably corrosion in the distributor, or old plugs. Start with a simple tune up. Who knows when the previous owner tuned it up. And if it's been sitting for any length of time, the internals of the distributor could easily corrode and cause just what you're experiencing. Pull the cap and take a look. Replace rotor, cap and plugs. Check for corrosion and make sure the advance springs and plates move easily.

That will eliminate the basics. It's usually the simple things that cause the most trouble.

That 378 to the rear wheels on a Mustang dyno is probably equal to 425 on a dynojet. Your about 25HP short of your goal. You should be able to get there with a good tune.

Meant to ask you when you say "breaking up" @ 5800, you were on a dyno correct? If so the operator most likely/ should have had a O2 sensor on one of your sidepipes. I'd ask him what the AFR changed to at that moment just prior and then @ the breakup. If it leaned out I'd start looking at your fuel supply (Old hoses, filters and the like). Ethanol is not kind to rubber.

Rear wheel dynos and Cobras just don't mix.

The exhaust is very restrictive on most of these cars, plus you have regular driveline losses.

Your "breaking up" at 5800 is more than likely a valve spring issue....you're probably seeing a little valve float. Most hydraulic camshafts aren't made to turn lots of rpms, unless the engine was setup that way from the get-go.

As a general note from a builder, it's very difficult to dyno an engine, then ship it across the country to a different climate, where the customer sticks it in a car with a tiny air cleaner, and have the A/F ratio be exactly where it needs to be. We can only do so much on an engine dyno. You can generally assume that there will need to be some minor tuning involved. I will dyno the engine with the distributor/carburetor that the customer will have, so it will be as close as I can get it here.

Also, MSD boxes will vary. Most guys don't know this, but you can dyno an engine with one box, then send it to the customer who has another box, and the timing can be off. It always needs to be verified.

Someone mentioned the throttle linkage....that's an easy and important thing to check. Have someone push the gas pedal to the floor while you look down the carb. Both butterflies should be in the vertical position if it's a mechanical secondary carb. Even installation/dyno shops can screw this one up....

From what I've seen, Cobras will lose anywhere from 100-125 hp going from an engine dyno to a chassis dyno. Lots of variables there and the main point is that you use a dyno for incremental testing. You can't expect every dyno to repeat to the same number.

Mustand and Dynojet dynos should really be used more for tuning than for dictating your horsepower output. I recently had my car "tuned" at a facility that had a Mustang dyno. The results were what I considered a bit pathetic. I contacted a friend of a friend that has run the dyno room at an automotive facility near me and asked him why the numbers were so low. He gave me quite the dissertation on dynos. blykins is correct. Dynos hate cobras...especially cheap dynos. No weight in the rear, IRS, high hp, and small rollers make dynos not work real well as they cannot hold the car down. If they have not grooved the rollers on the dyno, there is a real good possibility the tires were slipping.

I took my car to another facility that had a Horiba dyno which is used to give automotive manufacturers certified results for driveline testing. I did nothing to the car since the tune. I magically gained 60 RWHP and about the same in torque. Better dyno and the fact it is calibrated all the time can make huge HP gains.

A few years ago I was talking to Keith Craft about power loss in a Cobra. He said he had dyno'ed motors. Then installed them into Cobra then ran them on a chassic dyno. He typical saw a 20% loss.


Dwight

So that engine has 900 miles on it in 6 years?
I would not only tune it up but drain the fuel from the carb and tank and fill with fresh. Could be gunk in the carb or tank but I'm betting a tune up will bring it back to life. KC 408's are supposed to be good to 6250 rpm, but if it's been sitting for a long time, I guess a valve spring or two could be binding, though I doubt it.

I have a portable dyno made by Pucker Industrial. Keep it in my back pocket. Requires frequent cleaning.

Interesting information by Brent and JoyRidin. It makes me feel better about my 366RWHP on a mustang dyno. The intake rocker studs wicking oil into the runners [ made a mess of the valves had to take them apart and clean them ] and no tune. What I got out of the session was I have a nice broad TQ curve. My desktop dyno with every detail punched in from the Heads, Cam, Intake, Exhaust etc. was 494FWHP. With the info in this thread it makes more sense to me now.

It was leaning out. Car isn't old, and engine had about 1000 miles on it. I had a wide band on the exhaust. Need to get the print off to compare with factory.

1100 miles in 6 years? You may need to "clean" the fuel system including the carb and a complete rebuild. Additionally, if the car is being used in a different climate and/or elevation than where it was tuned, you may need to simply change jets. Read your plugs.

A friend has a Mustang Dyno. We figure about 18%. My 427 usually puts down 440 hp & 430 tq running to 6,700. Good headers and sidepipes and a 14"x3" aircleaner. The last time it was on an engine dyno it was about 530-540 but that was a long time ago and there have been component changes. The atmosphere and other corrections will change things, then SAE or STP output will have significant effects.

As was mentioned in a prior post there are many influences, tune for power & torque and then go out and drive it. Make your last mods, usually carb adjustments for drivability and enjoy it.

Jim