Aston Martin Vantage 4.3 & 200 cell race cats
Discussion
Audi quote 295bhp at the fly and 324lbft, albeit that torque is produced at 2.9k rpm. 0-62 is a claimed 5.6 seconds. In the real world (on the road) these 0-60 times are pretty meaningless, and virtually irrelevant when it comes to point to point.
In terms of cross country, especially on damp roads, the 4WD is likely to give an advantage over rear 2WD.
Regarding the cats, you might expect a power increase of 15% or so, maybe a bit higher, so lets say 395 at the fly... If the RR is saying 352 at the wheels then it's only allowing a 10% drive train loss... typically you'd expect around 23% less at the wheels (RR measures at the wheels obviously). Something is amiss!
In any event, on a dry road, if the Aston is slower than the Audi then the Aston driver should be banned from PH (if he/she is a member) and not allowed near a hand built British icon again... like ever..
HTH
Chilli
In terms of cross country, especially on damp roads, the 4WD is likely to give an advantage over rear 2WD.
Regarding the cats, you might expect a power increase of 15% or so, maybe a bit higher, so lets say 395 at the fly... If the RR is saying 352 at the wheels then it's only allowing a 10% drive train loss... typically you'd expect around 23% less at the wheels (RR measures at the wheels obviously). Something is amiss!
In any event, on a dry road, if the Aston is slower than the Audi then the Aston driver should be banned from PH (if he/she is a member) and not allowed near a hand built British icon again... like ever..
HTH
Chilli
Dynos are only good for direct comparisons. In order for the results for the exhaust to be meaningful, you'd need to dyno the car then put on the cats and then dyno again. Same car, same dyno, and as close as possible to the same environmental conditions (especially temperature).
200-cell cats are fairly standard items. You can expect about 15 hp from the cats, so a 4.3L with 200-cell cats will have around 395 BHP instead of the original 380.
Our cars should only have a 15-18% drivetrain loss between engine and wheels. An AWD car will have a 23-25% loss. Regardless, all dynos (rolling roads) are different and saying a car has 352 WHP is meaningless unless you're comparing it to itself on that same dyno or to another car that was measured on that same dyno.
200-cell cats are fairly standard items. You can expect about 15 hp from the cats, so a 4.3L with 200-cell cats will have around 395 BHP instead of the original 380.
Our cars should only have a 15-18% drivetrain loss between engine and wheels. An AWD car will have a 23-25% loss. Regardless, all dynos (rolling roads) are different and saying a car has 352 WHP is meaningless unless you're comparing it to itself on that same dyno or to another car that was measured on that same dyno.
telum01 said:
Dynos are only good for direct comparisons. In order for the results for the exhaust to be meaningful, you'd need to dyno the car then put on the cats and then dyno again. Same car, same dyno, and as close as possible to the same environmental conditions (especially temperature).
200-cell cats are fairly standard items. You can expect about 15 hp from the cats, so a 4.3L with 200-cell cats will have around 395 BHP instead of the original 380.
Our cars should only have a 15-18% drivetrain loss between engine and wheels. An AWD car will have a 23-25% loss. Regardless, all dynos (rolling roads) are different and saying a car has 352 WHP is meaningless unless you're comparing it to itself on that same dyno or to another car that was measured on that same dyno.
I'm totally with you on RWHP being the only real measure of a certain power output. The motor friction of the trans by the dyno to back calculate a BHP trans loss to return a corrected flywheel figure is a totally flawed concept for a number of technical reasons which are too long to go into on here.200-cell cats are fairly standard items. You can expect about 15 hp from the cats, so a 4.3L with 200-cell cats will have around 395 BHP instead of the original 380.
Our cars should only have a 15-18% drivetrain loss between engine and wheels. An AWD car will have a 23-25% loss. Regardless, all dynos (rolling roads) are different and saying a car has 352 WHP is meaningless unless you're comparing it to itself on that same dyno or to another car that was measured on that same dyno.
But, to say the cars have a % drivetrain loss is the wrong way to approach the subject, a trans loss should be quoted as a certain BHP, because, as engine power increases (say from 380 BHP to 450 BHP) regardless of the engine out BHP increase, the trans loss will there-or-thereabouts still be the same power / BHP figure to spin the trans over as it originally took.
Example, on the Graz 6 speed manual the parasitic loss is approx. 65 BHP @ 7500 rpm, so if corrected RWHP was 315BHP, the flywheel figure is 380 - which is what the maker declared at the flywheel for that model. Whilst 65 BHP is 17% of 380, if after modifications the RWHP measured was 450 BHP, using the 65BHP trans loss rule the flywheel power is 515BHP. But, if incorrectly taking a % loss of 17% of the newly measured 450 RWHP as a trans loss, the flywheel figure is incorrectly calculated as being 526BHP.
Yes, the gearbox is a reduction device and by taking engine revolutions at a given torque input, by fact it's working to change ratio / speed, if 50 BHP engine power at 7000 rpm or 500BHP at 7000 rpm, the parasitic loss will change for a number of reasons, but only by a very small amount. Additionally, when the dyno performs a coastdown, the dyno is motoring the trans and not the engine powering the trans, meaning the motored trans loss is not the reality of the road. Which all mean an increasing trans loss (using the % loss rule) is just plain wrong to try and back calculate RWHP to flywheel.
The OEM world states flywheel because they measure engine on an engine dyno. The aftermarket world (mostly) only having chassis dyno should quote RWHP and forget trying to back calculate.
What is an eye opener is the number of aftermarket tuners that confuse the customer by using the % rule as the means to calculate total BHP to sell an overall flywheel BHP, I have seen a V12 kit (same 6speed manual) which apparently had approx. 130BHP trans loss added to result RWHP result! What tosh! So, going back to the start, really means the only number the modifier or end user should be concerned about is RWHP - or better still, the dyno the driver has which is sat underneath him on the seat!
mjk1 said:
Mike, agree with you words but your example calculation is wrong. If you have a transmission loss of 17% and a RWHP of 450 BHP, the flywheel power is 542 BHP not 526 BHP. The difference to the more correct flywheel power of 515 BHP is hence even greater than you suggest.
I had to look at this for a while, yes, I made a mistake which confused even me.In my example I stated a new notional RWHP figure of 450 which following the logic of correctly adding a fixed BHP trans loss of 65 is 515BHP. 450/100*117=526.5, the error in using a % of engine power for a trans loss is therefore 11.5BHP in this example because I'm using the notional 450RWHP number as the feed forward point.
The error in my numbers is that whilst stating the trans loss is 65BHP @ peak power speed (I have measured a ton of them), then concluding 17% trans loss, that is only at 380 and working backwards from the flywheel origin. In my example, had the RWHP figure actually had been 315 and we used 17% means 315/100*117=368
There was nothing wrong with your 380 BHP at the flywheel dropping to 315 BHP at the wheels. This is a 65 BHP loss or 17% (expressed as a percentage of the flywheel power). Applying the same percentage to 450 BHP at the wheels gives 542 BHP at the flywheel (542 minus 17% loss equals 450). Adding 65 BHP loss to 450 at the wheels gives 515 BHP at the flywheel. So using a fixed percentage overestimates the flywheel power by 27 BHP in this example.
These two methods bound the real solution. Assuming a constant gearbox efficiency (fixed percentage) overestimates the improved flywheel power whereas assuming a constant transmission power loss will underestimate it. I agree it will be closer to the latter though i.e the constant power loss assumption.
These two methods bound the real solution. Assuming a constant gearbox efficiency (fixed percentage) overestimates the improved flywheel power whereas assuming a constant transmission power loss will underestimate it. I agree it will be closer to the latter though i.e the constant power loss assumption.
mjk1 said:
There was nothing wrong with your 380 BHP at the flywheel dropping to 315 BHP at the wheels. This is a 65 BHP loss or 17% (expressed as a percentage of the flywheel power). Applying the same percentage to 450 BHP at the wheels gives 542 BHP at the flywheel (542 minus 17% loss equals 450). Adding 65 BHP loss to 450 at the wheels gives 515 BHP at the flywheel. So using a fixed percentage overestimates the flywheel power by 27 BHP in this example.
These two methods bound the real solution. Assuming a constant gearbox efficiency (fixed percentage) overestimates the improved flywheel power whereas assuming a constant transmission power loss will underestimate it. I agree it will be closer to the latter though i.e the constant power loss assumption.
Yes, whilst 542/100*17=92 and 542-92=450, the notional start point was the new 450BHP RWHP which trying to back calculate flywheel power with the assumed 17% trans loss returns 526 theoretical flywheel . The RWHP to achieve 542 theoretical flywheel using constant loss method (65 BHP) would be 477, and using a fixed 17 % trans loss with a notional 542 flywheel figure as a staring point (but it is not) would be the 92 figure and instead of previous method calculating 477 RWHP, mean 450RWHP. But as I say, we start with 450 as the basis for the calculation and to prove the argument apply to that recorded figure either a 65BHP or a 17% addition, so I don't understand 542 which is a 20.5% addition to the 450 notionally recorded starting figure?These two methods bound the real solution. Assuming a constant gearbox efficiency (fixed percentage) overestimates the improved flywheel power whereas assuming a constant transmission power loss will underestimate it. I agree it will be closer to the latter though i.e the constant power loss assumption.
What I stated my error was is correct. I know from measurements the trans loss is 65BHP, that tells me from 380 flywheel, a figure of 17% less is expected at the wheel, but that % is only correct for 380 BHP therefore useless to rely on if we want to increase or decrease engine power. In my example, Yes, 380 minus 65BHP is 315, but if I did record the 315 RWHP, that would mean 368 using the 17% figure. So my theoretical example should have started at 325 RWHP. This outline frames why discussing trans loss as a % of engine power is madness.
I'm intrigued, whilst you say constant loss method will be closer to arriving at a flywheel figure (which is only important to align with what OEM stated because OEM never declared a RWHP meaning RWHP is meaningless in isolation to owner), why then do you suggest the constant power loss method will underestimate (but be closer) than the constant % loss which will overestimate? There must be a right answer with no compromise because the engine is outputting a certain flywheel figure which doesn't care what the trans is up to or if even fitted to the flywheel at all?
So, to attempt back calculate a flywheel figure accurately, by the dyno roller motoring the rear wheels to motor the trans and record a torque to turn figure, is clearly flawed - which is what the dyno test world tries to do!
Next, a nominal engine power, say 380 BHP, if the trans loss 'somehow' had a % loss labelled to it - say 17%, a V8 vantage at 380 BHP has a trans loss of 65 BHP, however, so must a V12Vantage also have 65 BHP trans loss because that model uses the very same identical trans, but 17% of 380 is clearly a lower number than 17% of 510 yet the physical part (the trans) remained the same so this approach makes no sense also.
So, we must take a trans, motor it up under different input torque and oil temps to map its frictional loss, treat it as a box and apply the fixed offset which across that 3d map won't differ much in the window of operation we dyno test at - the 65BHP figure at 7500 rpm I discuss.
Rather than the two methods bound the solution then, isn't the solution, in absence of that 3d map, which only the trans maker might have and probably wouldn't share even to their OEM car maker customers, when testing on chassis dyno, is to actually not use either method and drop trying to back calculate flywheel figures altogether- Just like the aftermarket Motorbike world does. I know we agree that in principal , my question is why do you suggest that there is no perfect answer when the flywheel outputs a number not subject to variation downstream? and why one method to back calculate if it must be done (such as known fixed loss applied) isn't perfect?
elbich said:
Hello.
Last owner of my V8V declares that he install 200 cell race cats. Also he told that car dyno'd at 352.2hp at the wheels on a Dino dynamics dynamometer.
Dealer declares that 4.3 V8V has 380hp, so why is less from dynamics dynamometer??
Surely the question has to be "Are you satisfied with the cars performance ? (regardless of how many horses)"Last owner of my V8V declares that he install 200 cell race cats. Also he told that car dyno'd at 352.2hp at the wheels on a Dino dynamics dynamometer.
Dealer declares that 4.3 V8V has 380hp, so why is less from dynamics dynamometer??
Its all very interesting to know how the HP/BHP is calculated and that different manufacturers can provide it in various guises, but I think the original point has been missed.
Mines a 4.3L with aftermarket Prodrive 200 cell race cats and Tubi rear exhaust. I know its not perfect, it know its not 'tuned' to perfection, but I love the sound, even if the performance is not maximised.
I never bought my car to be fast (why would anyone buying an Aston do that.....), just enjoy the drive and that amazing V8 burble.
leerandle said:
Surely the question has to be "Are you satisfied with the cars performance ? (regardless of how many horses)"
Its all very interesting to know how the HP/BHP is calculated and that different manufacturers can provide it in various guises, but I think the original point has been missed.
Mines a 4.3L with aftermarket Prodrive 200 cell race cats and Tubi rear exhaust. I know its not perfect, it know its not 'tuned' to perfection, but I love the sound, even if the performance is not maximised.
I never bought my car to be fast (why would anyone buying an Aston do that.....), just enjoy the drive and that amazing V8 burble.
Hi Lee ! Its all very interesting to know how the HP/BHP is calculated and that different manufacturers can provide it in various guises, but I think the original point has been missed.
Mines a 4.3L with aftermarket Prodrive 200 cell race cats and Tubi rear exhaust. I know its not perfect, it know its not 'tuned' to perfection, but I love the sound, even if the performance is not maximised.
I never bought my car to be fast (why would anyone buying an Aston do that.....), just enjoy the drive and that amazing V8 burble.
I think it's OK for some nitty gritty to prove diagnosis to be able to draw conclusion - after all, this is a technical forum and not Sky or BBC News which short circuits diagnosis to dumb down and brainwash with their aligned conclusions.
Specifically though, it needed the nitty gritty because the OP was confused that he only had 352 yet had 200 cell cats and stock is 380. For my money his question has now been answered by the nitty gritty in that 352 + fixed trans loss of 65 is 417 and there-or-thereabouts (depending on correction conditions) that's the power for the upgrade he has had. It must be this because 352RWHP for stock is too high and 352 if it did have a trans loss applied is too low and he has 200 cell cats.
The OP's questioned answered and we know now that anybody spouting wild flywheel gains without showing RWHP is talking nonsense - successful thread!
Good afternoon Mike
You are right in that the thread has been answered.
I think there will always be some confusion to us public about what manufacturers put out there in terms of BHP, verses what can actually get measured on a dyno "Where have all my horses gone......
"
I always remember the Top Gear episode where Jeremy's Maserati Merak lost 10's of horse power after he realised the owner had just bought the 'S' badge..........
You are right in that the thread has been answered.
I think there will always be some confusion to us public about what manufacturers put out there in terms of BHP, verses what can actually get measured on a dyno "Where have all my horses gone......
"I always remember the Top Gear episode where Jeremy's Maserati Merak lost 10's of horse power after he realised the owner had just bought the 'S' badge..........
leerandle said:
Good afternoon Mike
You are right in that the thread has been answered.
I think there will always be some confusion to us public about what manufacturers put out there in terms of BHP, verses what can actually get measured on a dyno "Where have all my horses gone......"
I always remember the Top Gear episode where Jeremy's Maserati Merak lost 10's of horse power after he realised the owner had just bought the 'S' badge..........
Yeah, great show. In another test Hampsters own Mustang didn't do too well on dyno either.You are right in that the thread has been answered.
I think there will always be some confusion to us public about what manufacturers put out there in terms of BHP, verses what can actually get measured on a dyno "Where have all my horses gone......
"I always remember the Top Gear episode where Jeremy's Maserati Merak lost 10's of horse power after he realised the owner had just bought the 'S' badge..........
Yeah, I can imagine it's all a bit fuzzy because the test specs the maker is allowed to sign off to don't exactly mean a certain BHP in owners hands, and across the decades the test specs change too. Meaning that along with emissions tests being unrealistic to how cars are actually driven, both represent A big shake up is needed in the industry to be more representative.
Degradation of performance over the years due to wear is another tangent.
BamfordMike said:
I'm intrigued, whilst you say constant loss method will be closer to arriving at a flywheel figure (which is only important to align with what OEM stated because OEM never declared a RWHP meaning RWHP is meaningless in isolation to owner), why then do you suggest the constant power loss method will underestimate (but be closer) than the constant % loss which will overestimate? There must be a right answer with no compromise because the engine is outputting a certain flywheel figure which doesn't care what the trans is up to or if even fitted to the flywheel at all?
Mike, to answer your question, if you put more power through a gearbox without changing the speed the losses will increase slightly. For instance the internal components will elastically deform and relax more which absorbs power ending up in higher gearbox temperatures. The oil films between components will also be forced thinner which also absorbs slightly more power. However the power loss will not go up proportionally to the input power increase (fixed %). This means the true power loss will be somewhere between these 2 bounding cases (much closer to the constant power loss case though as you originally said). I wasn't disagreeing with your words though, just the numbers in your example as I've explained above. Whatever the percentages and power losses are, you have to apply them consistently for both the 315 and 450 RWHP cases. You aren't doing that when you arrive at the 11.5 BHP error between fixed power loss and fixed percentage power loss methods. It's a higher number than that if you work though the figures with consistency.Love the technical inputs. We also need to consider ambient temps, air intake pressure and back pressure inc air/fuel ratio. Most manufacturers operate on a + - 5% power output margin at sign off without parasitic losses. Also whether the cooling is run through a radiator or a heat exchanger which can effect power output as well. Old story of the Friday afternoon engine. I would like to see some datum of actual before and after results of dyno runs of stock car then with replacement cats then remap on same dyno with all atmospheric being equal. Jo public can see the changes then feel through his backside!!!
The engineers here all know the variables and the comments all educational. 1 reason why I like the Aston brand it's an engineers choice, though not perfect in some areas. Rather than the modern Ferrari the look at me brand!
You should see how a 3000hp MTU 4000 series sings when on our dyno during a Lloyds test criteria.
The engineers here all know the variables and the comments all educational. 1 reason why I like the Aston brand it's an engineers choice, though not perfect in some areas. Rather than the modern Ferrari the look at me brand!
You should see how a 3000hp MTU 4000 series sings when on our dyno during a Lloyds test criteria.
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