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

[Power Surge]

Originally Posted by avanti-176

Also remember ...different dynos say different things.
But it does sound like something is a little off. I would agree with power surge and start with the timing. Pay attention to power surge I have read an awful lot of his posts....he knows his stuff.

Good luck,
Dan

Why thank you . It does help that I dyno tune for a living .

[John McMahon]

I was in the shop when that motor was run in on the dyno, did Fred give you the dyno sheets?

I have driven that car on both the street and track and its got an awesome powerband.

Fred did not drive that car much, so I would start with a complete tune on the dyno.

You got what you paid for, I know that is the engine that was dynoe'd. I watched that car being built from the ground up, all quality pieces.

[neverwouldof]

Originally Posted by John McMahon

I was in the shop when that motor was run in on the dyno, did Fred give you the dyno sheets?

I have driven that car on both the street and track and its got an awesome powerband.

Fred did not drive that car much, so I would start with a complete tune on the dyno.

You got what you paid for, I know that is the engine that was dynoe'd. I watched that car being built from the ground up, all quality pieces.

Do you remember what gear it was pulled on then?

at 3000rpm on dyno it was 18 air/fuel ratio which is strange to me because it flattens out near 4000 into i guess what would be considered normal. Idles around 1100rpm and when driving it acts shaky at anything under 2000rpm.

[Power Surge]

You want whatever gear is 1:1. On most 5 speeds, that's 4th. If the Richmond is different, I am not sure.

[neverwouldof]

Originally Posted by Power Surge

You want whatever gear is 1:1. On most 5 speeds, that's 4th. If the Richmond is different, I am not sure.

Yes i now see on his post that it is a 1:1 ratio for 5th gear and i didn't know that. But i still want to get it checked out before i take it back there to dyno. Wonder what kinda difference that makes... have to research it i guess

Keith

[John McMahon]

Keith,

You must understand that those numbers were on an engine dyono on a stand, those are flywheel numbers. Typically, you will suffer 15 to 18% loss thruogh the drive trains and it sounds like the 1:1 ratio for the RG may suffer some loss too. I don't think the car was ever chassis dynoe'd though.

Don't forget you've got dual 4 barrels there which could probably use a thorough going through. The car sat more than it was driven the last two years or so.

I don't know what Fred did to prep it prior to the sale r what you have done thus far, but I would start with a thorugh tune of the engine and carbs, find the sweet timing spot, get those carbs tweaked and then leave them alone.

[neverwouldof]

Originally Posted by John McMahon

Keith,

You must understand that those numbers were on an engine dyono on a stand, those are flywheel numbers. Typically, you will suffer 15 to 18% loss thruogh the drive trains and it sounds like the 1:1 ratio for the RG may suffer some loss too. I don't think the car was ever chassis dynoe'd though.

Don't forget you've got dual 4 barrels there which could probably use a thorough going through. The car sat more than it was driven the last two years or so.

I don't know what Fred did to prep it prior to the sale r what you have done thus far, but I would start with a thorugh tune of the engine and carbs, find the sweet timing spot, get those carbs tweaked and then leave them alone.

He had the carbs rebuilt during the process of us negotiating.... then he said he had it tuned up by someone nearby. yes i understand the 15-18 loss. but that would be a 34% loss. Hopefully the engine guys down here can help me out....

[Anthony]

Originally Posted by John McMahon

You must understand that those numbers were on an engine dyono on a stand, those are flywheel numbers. Typically, you will suffer 15 to 18% loss thruogh the drive trains and it sounds like the 1:1 ratio for the RG may suffer some loss too. I don't think the car was ever chassis dynoe'd though.

Once you install the engine, with air cleaner - exhaust system, you get a different system than on an engine dyno'd on a stand to some degree. I recently just completed an engine, 427 SO, stock stroke, 0.017" overbore, 10.5:1 CR, about 430 ci. I had built the engine, installed it in my car without ever dynoing it, then had a coolant leak I had trouble finding. Took my car to an engine builder, who fixed my leak, and exchanged my low performance side piipes with higher performance ones, and then chassis dyno'd it, and tuned the carb. The intake is a factory single 4 bbl dual plane, and the carb is an original holley 780 vacuum secondary with Lemans bowels. Initial chassis dyno run had max RWHP 392 and RWtorque 406. After tuning the carb, setting the timing, he then got max rwhp 454 @5900 rpm's and still climbing, and max rwtorque 488 @3800 rpm's. Just for a refernce, he also chassis dyno's roush 427R's, and the best he has ever got was max RWHP 413 and max rwtorque 435.

He said he was impressed with the max torque, and the flatness of the curve. I had asked him about dynoing engines, and he said he likes to dyno them on the stand just to make sure the engine is OK, and get it somewhat close, but he really likes to dyno the engine in the car, to really tune it to the best, with all the equipment installed.

Considering I was using mostly factory ford parts, heads, intake, carb, I figured my engine came out pretty good.

[Hal Copple]

recently my SPF was on a Mustang Chassis dyno for some tuning, basically a 392 Windsor, performer RPM, 750 holley Pro, trick flow heads, match ported, MSD, standard SPF side pipes. roller lifters over a flat tappet A351 Motorsports cam (pretty aggressive). Peak hp was 391 at 4960 rpm, where it also flattened out, peak torque 451 at 4000rpm, pretty flat torque curve. AF ratio was adjusted a bit with jets, althought for street use, i down jetted the primary two sizes, it was just to "gassy" on the street with their rich jetting. It is also a very tractable motor, for street and track.

Just thought i would post what a non-exotic Windsor could put out.

[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

[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 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

[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

[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.