Drivetrain losses

Author
Discussion

stevieturbo

17,229 posts

246 months

Saturday 4th October 2014
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What trap speeds does the Ultima do over 1/4 ?

andygtt

Original Poster:

8,344 posts

263 months

Saturday 4th October 2014
quotequote all
Im not being any of those things... as I say I bench dyno'd my ultima engine and did the speed runs myself... the Ultima 720 is same weight but 1.5 seconds faster than my ultima was so must be more powerful.

To be clear I don't think its 700bhp but I do think its a lot more powerful than mine was as its a lot faster... also the engine was a lot higher spec so should be more powerful as well.

worth mentioning the Ultima has a flywheel 4 times the weight of mine and higher transmission losses IMO, maybe thats a factor?

andygtt

Original Poster:

8,344 posts

263 months

Saturday 4th October 2014
quotequote all
stevieturbo said:
What trap speeds does the Ultima do over 1/4 ?
9.9 seconds @ 143mph which suggests to me 600-650bhp?

regardless its mighty impressive for a car that goes round corners very fast as well?

stevieturbo

17,229 posts

246 months

Saturday 4th October 2014
quotequote all
andygtt said:
9.9 seconds @ 143mph which suggests to me 600-650bhp?

regardless its mighty impressive for a car that goes round corners very fast as well?
Trap could suggest more power I think, depends on weight

andygtt

Original Poster:

8,344 posts

263 months

Saturday 4th October 2014
quotequote all
realistically around 1000-1050 kgs min

Silent1

19,761 posts

234 months

Saturday 4th October 2014
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Just one note... Gareth's old car (what became the first 'factory' gtr720 and did all the records etc) is stroked, with a lot of titanium internals and has a longer first gear whereas all the others are sleeved and a standard g50 gearbox

Edit, i had it the wrong way round.

Edited by Silent1 on Saturday 4th October 23:30


Edited by Silent1 on Saturday 4th October 23:30

stevieturbo

17,229 posts

246 months

Saturday 4th October 2014
quotequote all
andygtt said:
realistically around 1000-1050 kgs min
Power probably is close to that then

reggid

195 posts

135 months

Sunday 5th October 2014
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143mph with 1100kg test weight means its over 100bhp lower than claimed. id say 580-600bhp

Pumaracing

2,089 posts

206 months

Sunday 5th October 2014
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reggid said:
143mph with 1100kg test weight means its over 100bhp lower than claimed. id say 580-600bhp
Spot on. After re-running my simulation program in more detail to put in the inertia of a big V8 with heavy flywheel, setting weight with driver to 1100kg, altering transmission losses to account for this car having an inline engine not a transverse one I get a 143.2 mph 1/4 mile in 10s, 0-100 in 5.33 with 580 bhp flywheel, 498 wheels. Exactly as the dyno clip showed.

Braking from 100-0 including effects of air drag - 3.61s

0-100-0 total time 9.94s.

reggid

195 posts

135 months

Sunday 5th October 2014
quotequote all
i just use the LRT and other equations at bottom of page to get an average

http://www.stealth316.com/2-calc-hp-et-mph.htm

its simple but good enough to spot BS a mile away when you look at trapspeed and mass. forget about ET witt this method it needs something more robust

Edited by reggid on Sunday 5th October 03:36

stevieturbo

17,229 posts

246 months

Sunday 5th October 2014
quotequote all
reggid said:
i just use the LRT and other equations at bottom of page to get an average

http://www.stealth316.com/2-calc-hp-et-mph.htm

its simple but good enough to spot BS a mile away when you look at trapspeed and mass. forget about ET witt this method it needs something more robust

Edited by reggid on Sunday 5th October 03:36
All the ET calculators seem to be based on Yank drag cars, automatic, glued tracks etc etc
So are usually very unrealistic for manual trans cars or any lesser surfaces

reggid

195 posts

135 months

Sunday 5th October 2014
quotequote all
stevieturbo said:
All the ET calculators seem to be based on Yank drag cars, automatic, glued tracks etc etc
So are usually very unrealistic for manual trans cars or any lesser surfaces
thats why i only use it for trap speed

Pumaracing

2,089 posts

206 months

Monday 6th October 2014
quotequote all
reggid said:
i just use the LRT and other equations at bottom of page to get an average

http://www.stealth316.com/2-calc-hp-et-mph.htm

its simple but good enough to spot BS a mile away when you look at trapspeed and mass. forget about ET witt this method it needs something more robust.
Thanks for the link. The Fox and Hale formulae are pretty good for trap speed which is very independent of most variables other than weight and power. ET is very highly affected by grip, gearchange time and how well the driver manages to launch off the line without bogging down or spinning the tyres. As such it's essentially pointless trying to estimate it without full simulation software that can factor in all these things for specific vehicles.

Pumaracing

2,089 posts

206 months

Tuesday 7th October 2014
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A interesting article on transmission losses here.

http://www.carcraft.com/techarticles/ccrp_0311_dri...

Two inline rwd V8 engines tested on both an engine dyno and a Superflow chassis dyno with as far as possible the same exhaust system and muffler combination as used on the actual car which people rarely bother to do in the performance world.

The first engine had an automatic transmission which soaked up a bunch of bhp but the second had a 4 speed manual box which is of more interest to what we are looking at in this thread.

The second engine produced peak flywheel bhp of 329 bhp at 4500 rpm and wheel bhp of 280, a 17% loss. Over the full rpm range losses averaged about 18%.

FWIW my peak power losses equation for inline rwd would predict (329 x 0.88) - 10 = 279.5 bhp. I'm not going to quibble about that last 0.5 bhp. There's obviously no such thing as a simple universal equation which applies to every vehicle as I keep saying but my equations are designed to get one in the ballpark and bust some of the BS out there and I think over the 20 plus years I've being using them they do that very well.

andygtt

Original Poster:

8,344 posts

263 months

Tuesday 7th October 2014
quotequote all
interesting that its a long way from a linear curve, doesn't even make sense to me (less power loss at 3500rpm compared to 3000rpm?)... id always assumed it would be a smooth curve of some kind.

Maybe oiling is playing a part that at certain box speeds the gearbox is more efficient and thus saps less power?



Si1295

362 posts

140 months

Tuesday 7th October 2014
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Claiming peak power from acceleration figures has always been slightly pointless imo as you have no idea what the rest of the power curve is like, so claiming your car is a certain power from the speed obtained over a 1/4 run can vary greatly depending on the power curve and gearing too. So called "Dyno Racing" is also pointless as every dyno owner/operator will claim that there's reads low compared to all the others when in fact they all end up spewing out different numbers without factoring in the various different correction factors DIN/SAE/SAE J1349.

They are however all good for comparing whether you've made gains/losses after modifications, which is what is important at the end of the day

stevieturbo

17,229 posts

246 months

Tuesday 7th October 2014
quotequote all
Si1295 said:
Claiming peak power from acceleration figures has always been slightly pointless imo as you have no idea what the rest of the power curve is like, so claiming your car is a certain power from the speed obtained over a 1/4 run can vary greatly depending on the power curve and gearing too.
In reality...it does not vary greatly, unless you're a buck eejit who cant drive.

Pumaracing

2,089 posts

206 months

Wednesday 8th October 2014
quotequote all
andygtt said:
interesting that its a long way from a linear curve, doesn't even make sense to me (less power loss at 3500rpm compared to 3000rpm?)... id always assumed it would be a smooth curve of some kind.

Maybe oiling is playing a part that at certain box speeds the gearbox is more efficient and thus saps less power?
Given all the vagaries inherent in trying to accurately measure flywheel bhp and wheel bhp under identical conditions given that engine power actually changes due to being fitted in a hot engine bay this isn't the main thing I would have expected anyone to comment on. I was rather hoping someone would spot the stupid errors these mathematically challenged yanks made when presenting their findings.

reggid

195 posts

135 months

Wednesday 8th October 2014
quotequote all
Pumaracing said:
Given all the vagaries inherent in trying to accurately measure flywheel bhp and wheel bhp under identical conditions given that engine power actually changes due to being fitted in a hot engine bay this isn't the main thing I would have expected anyone to comment on. I was rather hoping someone would spot the stupid errors these mathematically challenged yanks made when presenting their findings.
you mean that calculating the % losses as

absolute hp loss/rear wheel hp

may be a load of BS?

and that

absolute hp loss/crank hp

might make a little bit more sense?


E.g

Test A

peak flywheel power 371bhp @ 5000rpm
rear wheel hp 265hp
difference = 106hp

% as calculated by them

106/265 = 0.4 (40%)

proper way

106/371 = 0.286 (28.6%)


Pumaracing

2,089 posts

206 months

Wednesday 8th October 2014
quotequote all
Give the boy a cigar smile

The actual true average percentage losses for the manual box were exactly the 15% of flywheel power that they concluded was too low a figure after dividing the losses into the wheel bhp and also what my equations calculate for an engine of that power. Sadly while engineers might in general be fairly smart, journalists on average are not.