4.5 speed 6 versus AJP 4.5
Discussion
You've obviously been talking to someone who's had a 400hp plus figure at the wheels and added 18percent losses!
In reality the average of the 4.3 and 4.5 engine tested are in the 410-420hp flywheel range.
We know the good std 4 litres are in the 350/360hp range .. adding 0.5 litres doesn't suddenly add 120hp!
In reality the average of the 4.3 and 4.5 engine tested are in the 410-420hp flywheel range.
We know the good std 4 litres are in the 350/360hp range .. adding 0.5 litres doesn't suddenly add 120hp!
^^^ indeed .. and those people who get a hubs figure, think it's a wheels figure, and add the same losses ,conveniently forgetting they've not got the heavy wheel/tyre to accelerate, nor the tyre/roller losses ..
it's a minefield and no wonder even dyno operators get frustrated.
fact is though, the 4.3s and 4.5s do make for a very rapid car. You'd not be disappointed if you bought one.
it's a minefield and no wonder even dyno operators get frustrated.
fact is though, the 4.3s and 4.5s do make for a very rapid car. You'd not be disappointed if you bought one.
Skellz said:
I’m hearing that the 4.5 speed 6 is doing 482 bhp at the fly. I’m struggling to understand how this can be so when a good AJP 4.5 can hit 400 BHP.
Can anyone help me out here?
Cheers
Steve
As has been covered.. Dyno erm.. Exuberance.. Can anyone help me out here?
Cheers
Steve
A good 4.5 can definitely make more than 400bhp though, FWIW..
Rolling roads are great tools for comparing the relative power (or before and after mods) of cars on the same equipment, on the same day with the same operator, but as a measurement of absolute power, be very careful.
The most obvious variable is the equipment used e.g.
• Lloyd Specialist Developments use a Dynapack chassis dynamometer which is a hub dyno, i.e . connected directly to the drive shaft
• Powers Performance use a Dynojet dynamometer with one large diameter drum
• Surrey Rolling Road use a 4WD Dyno Dynamics dynamometer
• Kits and Classics use a 2WD Dyno Dynamics dynamometer
The power developed by all petrol engines depends on the prevailing atmospheric conditions, particularly amount of oxygen in the air, temperature, pressure and humidity. This is most noticeable when driving up a mountain.
Unless you have an engine on a bench all ‘measurement’ of at the flywheel power are estimates made by the dyno and sometimes the scaling equation from the measured at the wheels/axle power can be tweaked manually by the operator.
I only have personal experience of two dyno’s, Powers Performance and Surrey Rolling Road. There the same car on the rollers gave exactly the same figure (within 1bhp), Great, so they agree, but no. The Powers figure was at the wheels, SRR at the fly. This variation has been bourne out by many others if you look at previous posts. Which is actually correct, if either, I’ve no idea!
The most obvious variable is the equipment used e.g.
• Lloyd Specialist Developments use a Dynapack chassis dynamometer which is a hub dyno, i.e . connected directly to the drive shaft
• Powers Performance use a Dynojet dynamometer with one large diameter drum
• Surrey Rolling Road use a 4WD Dyno Dynamics dynamometer
• Kits and Classics use a 2WD Dyno Dynamics dynamometer
The power developed by all petrol engines depends on the prevailing atmospheric conditions, particularly amount of oxygen in the air, temperature, pressure and humidity. This is most noticeable when driving up a mountain.
Unless you have an engine on a bench all ‘measurement’ of at the flywheel power are estimates made by the dyno and sometimes the scaling equation from the measured at the wheels/axle power can be tweaked manually by the operator.
I only have personal experience of two dyno’s, Powers Performance and Surrey Rolling Road. There the same car on the rollers gave exactly the same figure (within 1bhp), Great, so they agree, but no. The Powers figure was at the wheels, SRR at the fly. This variation has been bourne out by many others if you look at previous posts. Which is actually correct, if either, I’ve no idea!
The best is when we used to have TVR rolling road days and compare cars on the day. Mine always used to make 380bhp so I could always use that as benchmark.
It was quite interesting at Charlies on one of these days when rebuilt cars would come claiming large figures but couldn't achieve. Good 4.5 AJP's made around 420bhp, not the 440 claimed, an expensive speed 6 4.5 rebuild made 384...
TVR Power have an interesting graph for their 4.5
http://www.powersperformance.co.uk/upgrades/supers...
It was quite interesting at Charlies on one of these days when rebuilt cars would come claiming large figures but couldn't achieve. Good 4.5 AJP's made around 420bhp, not the 440 claimed, an expensive speed 6 4.5 rebuild made 384...
TVR Power have an interesting graph for their 4.5
http://www.powersperformance.co.uk/upgrades/supers...
Edited by Byker28i on Monday 18th February 11:19
.Skellz said:
As I have found out from asking about, those figures of 380 at the wheels are the same as others at the flywheel. So I reckon like the 4.7 AJP, the gains are in torque rather than big BHP
Home built 4.7 just made 445bhp.. With a standard exhaust. So there is power in a 4.7 too..Skellz said:
As I have found out from asking about, those figures of 380 at the wheels are the same as others at the flywheel. So I reckon like the 4.7 AJP, the gains are in torque rather than big BHP
Home built 4.7 just made 445bhp.. With a standard exhaust. So there is power in a 4.7 too..I know all dynos are different, but I thought that mechanisms existed to control just that?
If you look up any US dyno pulls, they are always very careful to explain how their dyno is calibrated to SAE or STD, and they will often show exactly what settings were used before quoting their power figures, so that different builders in different states and elevations and dyno types can each compete to show who is making the best parts for motor platforms from Ford, Chevy etc. It strikes me as very odd that we don't do this here.
If you look up any US dyno pulls, they are always very careful to explain how their dyno is calibrated to SAE or STD, and they will often show exactly what settings were used before quoting their power figures, so that different builders in different states and elevations and dyno types can each compete to show who is making the best parts for motor platforms from Ford, Chevy etc. It strikes me as very odd that we don't do this here.
Many dynos will put the corrections used on the bottom of the graph so you can see if something's being fudged by the operator at least (assuming you know what the numbers should be of course) .
Problem is that some dynos are known to over-read no matter what corrections are used. The most obvious is the dynojet, which even the designer admits over-reads, so what hope is there?
Problem is that some dynos are known to over-read no matter what corrections are used. The most obvious is the dynojet, which even the designer admits over-reads, so what hope is there?
450Nick said:
I know all dynos are different, but I thought that mechanisms existed to control just that?
If you look up any US dyno pulls, they are always very careful to explain how their dyno is calibrated to SAE or STD, and they will often show exactly what settings were used before quoting their power figures, so that different builders in different states and elevations and dyno types can each compete to show who is making the best parts for motor platforms from Ford, Chevy etc. It strikes me as very odd that we don't do this here.
Sadly it isn't as clear cut as this. There are simply loads of things that can effect dyno results.If you look up any US dyno pulls, they are always very careful to explain how their dyno is calibrated to SAE or STD, and they will often show exactly what settings were used before quoting their power figures, so that different builders in different states and elevations and dyno types can each compete to show who is making the best parts for motor platforms from Ford, Chevy etc. It strikes me as very odd that we don't do this here.
Different types of dyno also "measure" in a different way.
Most Dynojets use a static weight to load the engine. They essentially measure how fast this is spun up. But not all Dynojets work like this. There is another category of dyno's often known as eddy current dyno's. This type of dyno can vary the load on the vehicle, usually by electrical current. In essence making the rotating mass higher. These are much better for tuning, as in most cases you can apply enough load that you can actually prevent the engine accelerating. Very good for fine tuning A/F, especially on turbo cars. The static weight "inertia" dyno's cannot do this.
This can vary the results however. In the US an interia Dynojet might see 330rwhp, but put the car on a Mustang Dyno (nothing to do with the car), which is an eddy current car dyno and it'll make more like 280-290rwhp. This is just down to the mechanics of how each dyno operates and derives horse power.
If you start including hub dyno's and 4wd dynos into the equation as well, more variance can be seen.
Then there are the differing standards, like you mention STD, SAE. But many dyno's will allow the operator to fiddle with the figures that make up these equations, so all is not always equal. And you may also come across imperial and metric HP, not a massive difference, but enough when combined with something else to make for some interesting variance in numbers.
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