Dynoed my 427so Cobra today.... interesting to say the least!

[RACER X #99]

Kieth,
I can back up John McMahons comments on you engine as I was also a witness to the HP and Torque numbers on your engine.The headers used on the dyno pull were from my 427 SO and no mufflers were used. Also I don't know if it was mentioned but 110 octane leaded racing gas was also used during the pull.
I had the opportunity to drive this car and it was one bad ass Cobra. I have 13 years experience driving Cobras on the track and if you need more power than you now have you must be a much better driver than I am. I suggest you send your resume out to one of the teams in need of a driver.

BTW, the Richmond 5 speed is a true 5 speed without overdrive, the first gear is very low and that is why Burtis installed a 2.88 rear in your car. You have the best of both worlds. Good gearing for acceleration and a tall high gear for economy.
I can't figure out why Fred sold that car in the first place.

BTW II I can't understand why guys take their cars on chassis dynos anyway, most are usually disappointed just like you were.

RD

[Excaliber]

My dyno work is done 1/4 mile at a time...

[DAVID GAGNARD]

What Roger was saying about headers/fuel and other things on the engine dyno will make a lot of difference..............


For instance;when I dynoed my 331 cu in "race" motor, they told me to make sure I LEFT the water pump at home, the same with my mechanical fuel pump.........a water pump and mechanical fuel pump can "eat" 20 hp depending on their type!!!!!!!!!!!!

I had no choice about the water pump as that was the way the dyno was set-up(they had an electrical water pump,NO engine power loss there), but I did use my mechanical fuel pump and brought my own race gas and used my headers instead of the shop headers............once we made about 8 or so pulls and got the timing/fuel mixture right where it needed to be, I added my air filter and luckily for me only loss 2hp with my air filter........

I specifically used my fuel/fuel pump/headers/air filter cause that's the way it was to be run in my car and it would give me more accurate #'s, the main # I was worried about was the a/f ratio, changing air filters/headers can and will affect that # to some degree..........

Now I run the snot out of the little motor and do not worry about going lean and melting a piston.......I have not had the time to get the car on a chasis dyno, but plan to do so soon.......

David

[ByronRACE]

Why use a chassis dyno? Confirmation of the known and/or measurement of the unknown. The former, is what causes most problems because it causes controversy. There is usually a gigantic discrepency between most engine builder figures and what is actually measured; even when accounting for drivetrain losses. I've personally dyno'd over 1600 Ford powered cars on a dynojet 248 and can count the number times on one hand that a SBF or BBF actually exceeded 1rwhp per cubic inch on pump gas without a power adder. Compare that experience with the number of engine advertisements with power figures that would EASILY exceed 1rwhp per cubic inch in a car, and you have discovered the root of the problem...marketing fudge factor; big numbers sell engines.

As far as dyno accuracy is concerned, I've compared engine dyno to chassis dyno directly, with a variety of transmissions and have a very good idea regarding 5spd drivetrain losses for various transmissions (within 5%). I've also then taken the same car from the chassis dyno to the street, and produced horsepower/torque functions using dataloggers and simple physics...mass, time, speed...and produced the same data (within 5%) of the chassis dyno.

So, for example...

If you had an engine dyno that showed 600fwhp, and put that engine into a car with say a T5 transmission and 8.8 Ford rear, and did a 4th gear pull that that read 400rwhp... and your engine builder is telling you it's because of the water pump, alternator, and drivetrain losses...there's more to the story.

600fwhp
- 13-15% for drivetrain losses (90hp max)
- 5% for max accessory losses (30hp max)
- 5% fudge factor for tire slip, calculation error, whatever (30hp max)

So worst case, the chassis dyno should read at LEAST 450rwhp for an engine advertised at 600fwhp. In reality, it should read higher because the error isn't truly cumulative as shown above; some losses are related.

Most of the time, a 600fwhp advertised engine will dyno at 400rwhp or below. And, the same 600fwhp engine as tested on your own engine dyno will read far less than 600fwhp; which is even harder to explain away. This is all too common and expected.

In your case, after reviewing the dyno graph, peak torque is at at 5200rpm and peak power has been reached by 5800rpm. As advertised, the engine was supposed to reach peak power by 6700rpm. Either the intake/exhaust geometry has changed dramatically; or the cam or cam timing has changed dramatically since it was dyno'd. If you corked the intake with air filters, it would not change the location of the peaks by nearly 1000rpm; it would just change the amplitude of the high rpm portions of the graph. Same is true for exhaust corking (mufflers). My guess is it's not the same cam, or perhaps not the same cam timing. Furthermore, changing the cam timing after achieving a peak number on an engine dyno isn't unheard of...it's done to produce more bottom-end torque to make the car idle better and be more fun to drive in the rpm band you use the most. You can make a better high rpm number by retarding the cam a bunch, but it may not idle / drive worth a damn...so you compromise. If I had to guess, something like this is what took place. Either that, or the cam is the same and they had a very different intake/exhaust system on the car when it was on the engine dyno. Race gas and timing advance would help amplitude as well, and shift the RPM slightly higher...but I wouldn't expect 1000rpm out of fuel/timing alone.

Either way, you' still have a great running engine approaching 1rwhp/cubic inch at the tires...and that's nothing to be ashamed of.

[neverwouldof]

Originally Posted by RACER X #99

Kieth,
I can back up John McMahons comments on you engine as I was also a witness to the HP and Torque numbers on your engine.The headers used on the dyno pull were from my 427 SO and no mufflers were used. Also I don't know if it was mentioned but 110 octane leaded racing gas was also used during the pull.
I had the opportunity to drive this car and it was one bad ass Cobra. I have 13 years experience driving Cobras on the track and if you need more power than you now have you must be a much better driver than I am. I suggest you send your resume out to one of the teams in need of a driver.

BTW, the Richmond 5 speed is a true 5 speed without overdrive, the first gear is very low and that is why Burtis installed a 2.88 rear in your car. You have the best of both worlds. Good gearing for acceleration and a tall high gear for economy.
I can't figure out why Fred sold that car in the first place.

BTW II I can't understand why guys take their cars on chassis dynos anyway, most are usually disappointed just like you were.

RD

Thanks for the info.... I didn't know he was running 110 octane through it at Dyno and with no mufflers and the restrictive 8" filters on top must kill the numbers. However it does need to be looked at because of that lean spike and i need to look into taller 8" filters as well. The way he set the engine in there it has a couple inches room below the hood scoop. Also the car was pulled on dyno in fourth instaed of the 1:1 fifth. So that has some effect. I do like the way he set up gearing, however what is the deal with the clutch and brake placement. Feel like my left knee is touching my chin! it is about 7-8" farther out then gas pedal? Is that normal for contemporary or cobra's in general? can it be adjusted?

Keith

[DAVID GAGNARD]

When I was dynoing my motor, as we were bolting it on the dyno, the operator began asking me specifics about the engine, I told him the cam specs/compression etc.,etc., he then asked what I EXPECTED out of the motor........I told him I would hope for 475 hp, but would be very happy with an honest 450hp with a good a/f ratio(it made 472hp@ 6400rpms)........He told me I would NOT leave disappointed, cause I was being very realistic about my motor!!!!!!!!!!! I DID NOT leave disappointed at all.........

He said he has dynoed a ton of supposedly 600hp pump gas motors that barely made 400hp and made for some very angry owners........

Keith;even as such, you still have one heck of a motor and car, if YOU are satisfied with the performance, that's all that counts, regardless of any dyno #'s..........

David

[neverwouldof]

Originally Posted by 427Aggie

Some of the ones I have seen are the large K&N Filters..but to fit under the hoods you need to have a drop base made for the air cleaner...Rob at Keith Craft Motorsports has made a few for some of keith's cars...he can speak more to what the small 8's will do to your power...Also what mufflers are in the pipes..you should see some of the ones that have been taken off...Rob has a brand he replaces SPF's with and gets quite a HP gain.

Matt

I will look into this..... Thanks!

Keith

[neverwouldof]

Originally Posted by DAVID GAGNARD

When I was dynoing my motor, as we were bolting it on the dyno, the operator began asking me specifics about the engine, I told him the cam specs/compression etc.,etc., he then asked what I EXPECTED out of the motor........I told him I would hope for 475 hp, but would be very happy with an honest 450hp with a good a/f ratio(it made 472hp@ 6400rpms)........He told me I would NOT leave disappointed, cause I was being very realistic about my motor!!!!!!!!!!! I DID NOT leave disappointed at all.........

He said he has dynoed a ton of supposedly 600hp pump gas motors that barely made 400hp and made for some very angry owners........

Keith;even as such, you still have one heck of a motor and car, if YOU are satisfied with the performance, that's all that counts, regardless of any dyno #'s..........

David

I am satisfied with the car by all means, i just wanted to make sure i got what i paid (57k) for..... it sounds like i did and i just need to have it looked over. It has a big hesitation when you get on throttle... not sure if sitting for two years had any effect on lines or pump. The carbs were rebuilt though. we'll see but i'm more optimistic after all the help on here.

Keith

[John McMahon]

Keith,

The car wasn't dormant for two years, just not run a lot as I understand it. I don't know who Fred used on the carbs, he initially had them rebuilt at Holley when the car was built. I would havesome go through the whole drivetrain on that chassis dyno and get a new baseline established. It also has about $75K in it, so you got it at a good price.

Clutch pedal: That's how thay are on Contemporary's, my 289FIA was that way, you may be able to adjust the release point, but all the pedals are hung by the same brakcket, maybe shorten the pedal?

[Excaliber]

Man thats gotta make the heel\toe thing a real bear...

[John McMahon]

...personally, I never even noticed it when driving.

I don't know how tall Keith is or if this is his first Cobra or not, but the pedal thing is just "one of those things" you need to get used to in a Cobra.

While the setup varies from manufacturer to manufacturer, I think we have all had to adjust to the pedals being off center left from a normal driving position.

[neverwouldof]

Originally Posted by Excaliber

Man thats gotta make the heel\toe thing a real bear...

Heel/toe driving is impossible.... i'm going to try and get it set up differently. I'm 6'2 and it has a dropped box in it. but my left knee is still crammed between steering wheel and door sill. Fred must have had short legs or been no taller then 5'10. Also going to have seat position moved 1.5" back which is far as it will go.

[DAVID GAGNARD]

Went to a Mustang Club car show today, brought my race car and my daughter drove my 65 Fastback and I entered it under her name, I only go to 2 or 3 "local" cars shows a year and this is my favorite........good folks and everyone has a good time, great club, they make everybody feel "like family"..........

Well, anyway, they had a couple of guys there with a chasis dyno and was charging 25 bucks a run........it was the kind on wheels (big trailer looking thing) about 6 or 7 feet off the ground.......they probably dynoed 6 or 8 cars and after the judging I tried to get my car on it, been wanting to chasis dyno my car since it has been finished.........well, it did not happen, ramp was too steep and my header collector flanges hit and I needed another 2 inches of clearance to get it up there, we tried adding some boards under the tires, but could not make it work............

So I'm interested in some results and watch them dyno 4 cars, the results were very suprising to say the least.........

Cars 1 thru 3, all 05 Mustang GTs, all 3 bone stock except for maybe a K & N air filter, that's it..........all 3 made from 262rwhp to 267 rwhp, they are adveritsed at 300 flywheel hp!!!!!!!!!!!! that's from 13% to 11% driveline loss, I think either Ford "fudged" those #s a little or else the driveline is very efficent.............

Now the kicker, car 4; 1969 Mach I, 428 Cobra Jet motor, I think these were rated at around 335hp to 350hp???? not sure........anyhow the owner said this motor had about 500 miles on it since a complete rebuild, he added Edelbrock alum heads,headers,big loud Flowmaster dual exhaust,850 cfm Holley, more cam??? not sure how much, not extremely wild, but better than the stock cam, electronic ignition.........now this motor was not an all out motor, but a "healthy" motor, which he estimated to make about 450 hp at the flywheel, never been dynoed, just his estimate, which could be achieved with what he had in the motor.............he ran it up to 6500rpms each of his 3 pulls............

Pull # 1, why he started from a dead stop in 4th gear, I'll never know, but he did, not very good #s, don't remember the exact #, but the owner said it had to be wrong.....I thought the motor loaded up real bad and he probably fouled the plugs some..........

Pull # 2; pretty much the same as # 1, except he starts out before they had the laptop ready and got some wierd readings, so they discounted the whole run.........

Pull # 3; operator told him to start in second gear and do the pull in 3rd gear, again, have NO CLUE why they would do it this way, but they did, I was standing near the rear of the car watching the driveline, he was running WAY,WAY rich by now, both exhaust pipes looked like a diesel truck going up a steep slope loaded down,he made 272 rwhp!!!!!!!!!!!!! when he shut it down and the operatpr showed him the #s and the printout, he was pi$$ed and told them to unhook the car and guide him down......they had a few words and he left, was only charged for 2 runs.........

Later talking to the operator he told me the "average" loss he has seen for late model cars with a stick shift was 15%........

The old Mach I was running a 4 speed toploader and 9" rear end with 3.89 rear gears, he had on a set of drag radials and as I was watching the rear of the car of his last pull, I did not see any signs of his tires slipping or spinning on the drums.........he had a very badly tuned motor, no doubt, but still thought he should have made from 350 to 375 hp at the wheels, he was about 100hp off............

Looks like I will not get a chance to do my car as those portable units are just to steep for my low sitting car............

I was very surprised at the low % of loss for the 05 GTs and very suprised at the high? % loss for a 428 Cobra Jet motor, sure thought it would have done a lot better.............

PS: almost forgot, I took second place with the race car and my daughter took a first place with the Fastback, boy was she proud!!!!!!!!!!!we had a great time together and I think she may be turning into a full fledged waxer now...........

David

[Excaliber]

That Mach 1 pulled in 3rd gear, again, if your not in a 1 to 1 gear ratio you can throw out the results.

[snakeeyes]

Dynos are a great thing, but I think we all tend to place too much stock in the numbers and not enough in how the car actually runs. The post about exhausts and IRS robbing power are dead-on. Research on this site and elsewhere and you'll find that side exhausts, which we all love and believe to be much more efficient than an under-car setup, can actually be a detriment if not carefully designed,

As far as your numbers' I can only offer those of my Beck Lister for comparison, The car has a Corvette IRS, which does rob power vs. a live axle because of the multiple u-joints, the angle of the driveshafts, etc. It also has side exhausts. The builder dynoed the engine on an engine dyno--542 hp/ 508 ft-lbs.

A year or so later, after I got the car together, I had it dyno-tuned on a chassis dyno. I don't have the numbers in front of me, but I think it made around 417 hp and 395 ft-lbs.--losses of close to 25%. I had been expecting about 15%, which the figure you often see, so I was pretty shocked--until I drove it. It ran like a motherf_____. As I said, I think the numbers are much less important than ensuring the car's tuned right. Numbers may give you bragging rights, but they won't keep you from getting waxed by the kid in the chipped Subie WRX.

Get the car tuned, get it to a dragstrip, then decide if it's making adequate power (and getting it to the ground) or not.

[Anthony]

Originally Posted by DAVID GAGNARD

Cars 1 thru 3, all 05 Mustang GTs, all 3 bone stock except for maybe a K & N air filter, that's it..........all 3 made from 262rwhp to 267 rwhp, they are adveritsed at 300 flywheel hp!!!!!!!!!!!! that's from 13% to 11% driveline loss, I think either Ford "fudged" those #s a little or else the driveline is very efficent.............

Pull # 3; operator told him to start in second gear and do the pull in 3rd gear, again, have NO CLUE why they would do it this way, but they did, I was standing near the rear of the car watching the driveline, he was running WAY,WAY rich by now, both exhaust pipes looked like a diesel truck going up a steep slope loaded down,he made 272 rwhp!!!!!!!!!!!!! when he shut it down and the operatpr showed him the #s and the printout, he was pi$$ed and told them to unhook the car and guide him down......they had a few words and he left, was only charged for 2 runs.........

Later talking to the operator he told me the "average" loss he has seen for late model cars with a stick shift was 15%........

The old Mach I was running a 4 speed toploader and 9" rear end with 3.89 rear gears, he had on a set of drag radials and as I was watching the rear of the car of his last pull, I did not see any signs of his tires slipping or spinning on the drums.........he had a very badly tuned motor, no doubt, but still thought he should have made from 350 to 375 hp at the wheels, he was about 100hp off............

I was very surprised at the low % of loss for the 05 GTs and very suprised at the high? % loss for a 428 Cobra Jet motor, sure thought it would have done a lot better.............

I don't think that you can really make any statement about driveline loss only with information from a chassis dyno. I would think that you would have to also dyno the same engine on a stand, using the same dyno, with the same air intake set-up and exhaust system to get a real % driveline loss, otherwise you're just guessing.

Originally Posted by Excaliber

That Mach 1 pulled in 3rd gear, again, if your not in a 1 to 1 gear ratio you can throw out the results.

I don't think it really matters, as the dyno knows the overall gearing from the engine rpm and wheel speed, and I doubt there would be a large percentage loss in the transmission using 3rd gear instead of 4th. Anybody know what the hp loss would be ? Maybe 5-10 hp?

[Anthony]

Originally Posted by snakeeyes

Dynos are a great thing, but I think we all tend to place too much stock in the numbers and not enough in how the car actually runs. The post about exhausts and IRS robbing power are dead-on. Research on this site and elsewhere and you'll find that side exhausts, which we all love and believe to be much more efficient than an under-car setup, can actually be a detriment if not carefully designed, As far as your numbers' I can only offer those of my Beck Lister for comparison, The car has a Corvette IRS, which does rob power vs. a live axle because of the multiple u-joints, the angle of the driveshafts, etc. It also has side exhausts. The builder dynoed the engine on an engine dyno--542 hp/ 508 ft-lbs. A year or so later, after I got the car together, I had it dyno-tuned on a chassis dyno. I don't have the numbers in front of me, but I think it made around 417 hp and 395 ft-lbs.--losses of close to 25%. I had been expecting about 15%, which the figure you often see, so I was pretty shocked--until I drove it.

Get the car tuned, get it to a dragstrip, then decide if it's making adequate power (and getting it to the ground) or not.

Obviously, your 25% loss is not only drivelline loss, but also loss do to the exhaust system, and maybe even the air cleaner as well, so it maybe it's appropriate. In addition, from your post, it appeared that the chassis dyno was not the same guy who built/dyno'd the engine on the stand, which may also enter some fudge factors in determining % hp loss.

Like you said, I think to get optimum performance, you need to have it chassis dyno'd and TUNED, as there can be large performance gains with the engine set-up right. It beats taking the car the strip, and repeatedly drag racing it, adjusting things to try to determine the best state of tune. Probably easier on the car as well.

By the way, I guess you're running a sbc? What is it's displacement ?

[DAVID GAGNARD]

I do believe both engine and chasis dynos are a good thing.......there is plenty of hp/tq to be gained or lost when using a dyno for tuning vs. seat of the pants tuning or guess work........

there used to be a dyno about a mile from my house owned by a good friend, and dirt late model racer.........he ofton would call me on a saturday morning when dynoing race motors to go and watch........on one 635hp race motor I have seen a total gain of 62 hp after a dozen pulls.......this was done with timing and jetting changes and changing out the carb spacer!!!!!!!! they started the session with the timing and jetting that the engine builder suggested and worked from there..........
On my motor,a timing change of 2 degrees made a difference of 8 to 12 hp, nothing else changed, my motor likes 32 degress total and when we went to 34 it lost 12 hp, going to 36 it lost an addition 20 hp, that is something I never would have found without a dyno tune.......

Chasis dynoing can give you an idea of what if any changes you may want to make to the driveline/exhaust system, it has been shown a number of times just how much hp some exhaust systems can "eat"........
I will always dyno my race motors and if I can find a chasis dyno I can get my car onto, I'll chasis dyno it also...........

David

[snakeeyes]

Originally Posted by Anthony

Obviously, your 25% loss is not only drivelline loss, but also loss do to the exhaust system, and maybe even the air cleaner as well, so it maybe it's appropriate. In addition, from your post, it appeared that the chassis dyno was not the same guy who built/dyno'd the engine on the stand, which may also enter some fudge factors in determining % hp loss.

Like you said, I think to get optimum performance, you need to have it chassis dyno'd and TUNED, as there can be large performance gains with the engine set-up right. It beats taking the car the strip, and repeatedly drag racing it, adjusting things to try to determine the best state of tune. Probably easier on the car as well.

By the way, I guess you're running a sbc? What is it's displacement ?

It's a Rodeck 404 cid alloy block with Victor Jr. heads, manifold, and Street Demon carb.

You're absolutely right as far as the different dynos. Both were Dynojets, but other than that everything was different. The engine dyno was in Wisconsin and the chassis dyno was at Keith Craft's Plano shop. I have heard that the Craft dyno tends to be conservative, but have no idea if that's true. I do know that, when Rob dynoed it, I had him remove the sidepipes and check the hp difference. Even with rejetting I think it only picked up 10 hp or so, so I think my pipes are pretty efficient. The air cleaner is a pretty large K & N with a K & N lid, so I think it's pretty efficient, too. I'm running synthetic fluids in the tranny and diff, so I feel I've minimized frictional losses there. It has a bimetal 'Vette flywheel so it shouldn't be losing much there.

I guess the conclusions I draw are that either the builder's dyno was very optimistic or the chassis dyno was very pessimistic. The Corvette tuners all use a 15% loss factor and it seems to be accurate; given that my diff is Corvette I would think it would be similar for me. Maybe the M-22 Cal Metal built for me is still tight and needs some breaking in (1000 miles on drivetrain).

Whatever the case, as I said I think you should use a dyno as a tuning device, not worry about the numbers so much, and judge the car by how it gets down the road.

[neverwouldof]

Originally Posted by DAVID GAGNARD

I do believe both engine and chasis dynos are a good thing.......there is plenty of hp/tq to be gained or lost when using a dyno for tuning vs. seat of the pants tuning or guess work........

there used to be a dyno about a mile from my house owned by a good friend, and dirt late model racer.........he ofton would call me on a saturday morning when dynoing race motors to go and watch........on one 635hp race motor I have seen a total gain of 62 hp after a dozen pulls.......this was done with timing and jetting changes and changing out the carb spacer!!!!!!!! they started the session with the timing and jetting that the engine builder suggested and worked from there..........
On my motor,a timing change of 2 degrees made a difference of 8 to 12 hp, nothing else changed, my motor likes 32 degress total and when we went to 34 it lost 12 hp, going to 36 it lost an addition 20 hp, that is something I never would have found without a dyno tune.......

Chasis dynoing can give you an idea of what if any changes you may want to make to the driveline/exhaust system, it has been shown a number of times just how much hp some exhaust systems can "eat"........
I will always dyno my race motors and if I can find a chasis dyno I can get my car onto, I'll chasis dyno it also...........

David

When you adjust timing on your engine, at what RPM are you running the motor at?

Thanks, Keith