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J

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Discussion Starter #1
hiya guys

just done a rr sesh for me motor... i am a bit disappointed. only 156bhp and 142lbs/ft. Supposed to be around 166bhp and 150lbs/ft.



:( :(

i've been speaking to my alfa man at lengths and combined with a lumpy idle (approx 750rpm) and a high reading off the emmisions sensor (900 ppm) of fuel and funny things feeling of power since a cem belt was done many moons ago, we reckon the inlet cam is retartded slightly. THis will need to be resetup completely so may as well change the belts as we'll be all apart anyways to do this.

ho hum... more money :(

btw... sorry shug... just wait 'till this gets fixed... i'll really have ya coming out of the hairpin wink :D only joking.

p.s. c'mon wrinx.. i'll have yer pink mobile!

J
 
W

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Still got ya beat J, showing "only" 163 (standard) despite a chip, exhaust and panel filter. Should be loads more but I think the chip is wrong for my car (like Henry's was, chipped but no affect!)

My max torque is at 98mph, max sped 124mph.......whats with yours at only 114mph?

..........and I got 2lb ft more torque :D

wrinx
 
J

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mine was done in 4th gear.. that'll be why the funny speed.

gr wrinx i'm gonna have you... you.. you.. reversing feind!

J
 

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Should be smoother than that. Here is my latest 155 with the wrong chip in, split exhaust and a slightly bent wheel.

All fixed now!!
 
F

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I think I still win in the STD cars gang though wink
 
W

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J

just noticed you've got a saggy bit!!! Around 4500revs everything drops out??

Lets see if I can get my figures up.............



Sorry for the dirty picture, its been kicking around the boot for a while eek!

wrinx
 
M

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Here J.......your car's rubbish. I have more power in my farts wink

A bit worrying though, that means my car is probably only pushing about 50bhp in comparison to yours.

Never mind, I'm gonna buy a Dodge Viper.

PS. J, have you seen the blue Viper razzing about our area yet ????

Marlon
 

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Wrinx & J,

I can't make your plots make sense. Surely the torque and HP should be the same at 5250 RPM?

Look at Henry's plot, that partly makes sense. Even though it's only the 'norm' HP that works out.

I've not had my car done. What exactly do they do? Did they tell you how they arrived at the engine HP figure? Is the torque figure 'at the wheels'?
 
W

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daKlone

Sorry, you've lost me, why would the torque and HP be the same at 5250?

All three of these graphs show car that are not running properly, perhaps thats something to do with it?

Mine is showing standard despite mods and Henry's chip wasn't doing anything, J has already said whats up with his.

I'm confused anyway (not hard!)

wrinx
 

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Wrinx,

Well, how's your algebra?

Since;

HP = Torque x RPM / 5252 (near enough, Taz!) (1)

Then re-arranging (1) you get;

Torque = HP x 5252 / RPM (2)

So it's easy to see that when RPM = 5252, (2) becomes;

Torque = HP (3)

That's why whenever I see a dyno plot that doesn't have power and torque the same at 5252 RPM, I smell a rat :)

The calculation still works no matter how 'badly' the engine is running.
 
W

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Makes sense to me but I know nothing about it!! The figures, can remember algebra ok eek!

So whats happeneing then?

wrinx
 
J

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it works on hery's graph because the scale for power and torque are exactly the same so it's easy to see the crossover, however on mine and wrinx's, we go upto 180 on tre bhp scale and only upto 150 on the torque side, this gives the effect of the crossover being later up the rev range... if the scales were the same i would expect them to be around the right area?

yeah?

eek!

J
 

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J,

That's right. I only had the pictures you posted to go on, but even drawing extention lines from the relevant points to the correct scale using Paint Shop didn't seem to work out. I drew a line straight up from 5250 RPM, then from where this intersects the Torque curve to the right-hand scale and from where it intersects each of the HP curves to the left-hand scale. The numbers aren't the same (can't remember what they were, the picture is at home!).

Perhaps if you have a look at the real plots yourself you may be able to measure it more accurately.

But as I said, no matter how the engine runs, torque and HP must be the same at 5252 RPM.
 
M

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I'm not too sure about all this but..........
if the torque is scaled to fit the 180, it will move the torque curve down and may well cross at about 5250rpm.

For instance, if you look at J's graph.
The torque curve at around 5250rpm = 140 (roughly).
If you plot this 140 against the BHP scale at 5250rpm, you will see it crosses the pink line.

So the graph is correct in my opinion.

Marlon
 

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marlon:
I'm not too sure about all this but..........
if the torque is scaled to fit the 180, it will move the torque curve down and may well cross at about 5250rpm.

For instance, if you look at J's graph.
The torque curve at around 5250rpm = 140 (roughly).
If you plot this 140 against the BHP scale at 5250rpm, you will see it crosses the pink line.

So the graph is correct in my opinion.

Marlon
You know what, Marlon? I think you're right!

(daKlone goes and stands in the corner with a big 'D' hat on)

I don't know what I measured last night, but I've just tried it again and it came out ok! In my defence...it was late...

Apologies to all (but at least you learned something about the relationship between HP and torque.....)
 

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So how would that work on a turbo car? They have bags of torque. My wifes 306 DTurbo won't even get to 5k revs, but it pulls off faster than my Alfa up hills!!!
 

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Neither a turbo nor running on diesel would make any difference to the calculation.

Obviously, if the diesel didn't rev to 5252 RPM then you couldn't double-check the validity of any plot.

But no matter what, there is always this linear relationship between torque and HP.

If by some coincidence, you had a single-cylinder 2-stroke and a 6-litre V8 twin-turbo both making the same torque at the same RPM, they are producing the same HP.

It's that simple.
 

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I used to race a Lotus Sunbeam and used rolling roads to fine tune the set up. The power figures are really only meaningfull when comparing before and after. Even then it should be back to back on the same day since atmospheric pressure can affect readings up or down (colder damper days will show more power due to the greater density of incoming charge). Also different rolling roads tend to give different readings so the same car with the same set up on the same day can read better or worse figures dependant on the rolling road. There are many other factors like higher tyre pressures on the driven wheels will tend to give better readings, however I hope the point is made.

Phil
 
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