Hey guys,
got my newish engine dynoed last week.
Its a 202 + 40thou, flat top pistons, blue rods, nitrous cam .238 & .248 @ .50, 1.6 inlet & 1.5 outlet ratio roller rockers, 186 YT head big valves etc, straight cut gears, triple 1.75 HIF SU's, elec dizzy and splitfire 8.8mm leads.. etc u get the idea.
anyway it made 151hp at 5500rpm, and it also says it made 780nm at 60kph.
This is what i dont get. 780mn is approx 575.22ft-lb. In the latest street machine, on page 92 theres an article on an elcamino that has 450hp and 470ft-lb of torque. What i dont understand is how my 151hp 202 can have 105.22ft-lb more torque than a 450hp blown 350 chev????
Cheers,
A1
Dyno Report Query
Started by
_draglc_
, Dec 19 2005 06:10 PM
16 replies to this topic
#2
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 19 December 2005 - 07:51 PM
780Nm? at 60kmh, what rpm? doesnt sound right, are you sure the 780 wasnt for some other count like ppm?
Or sounds like it was a full throttle exercise down in second gear only?
Possibly it is just the torque measured on the rollers of the dyno and hasnt been recalculated according to your engine rpm.
Or sounds like it was a full throttle exercise down in second gear only?
Possibly it is just the torque measured on the rollers of the dyno and hasnt been recalculated according to your engine rpm.
Edited by devilsadvocate, 19 December 2005 - 07:54 PM.
#3
_Terrible One_
_Terrible One_
-
- Guests
Posted 19 December 2005 - 07:55 PM
No, it's 780nM of tractive effort. It's common for fairly quick cars to have upwards of 1000nM of tractive effort.
#4
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 19 December 2005 - 08:12 PM
if you look up tractive effort, Ill think youll see it concurs with my explanation about the forces measured on the rollers/wheels and how it can be recalculated according to rpm and gearing/wheel size etc.No, it's 780nM of tractive effort. It's common for fairly quick cars to have upwards of 1000nM of tractive effort.
#5
_Terrible One_
_Terrible One_
-
- Guests
Posted 19 December 2005 - 08:46 PM
Sorry mate I didn't see that part, didn't really read it properly.
#6
_draglc_
_draglc_
-
- Guests
Posted 19 December 2005 - 08:47 PM
it doesnt say anything about tractive effort.. just max torgue = 780nm.
ill put a pic up of the sheets when i can.
A1
ill put a pic up of the sheets when i can.
A1
#7
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 19 December 2005 - 11:16 PM
Terrible One: 
Draglc: Im not particularly fond of the term 'tractive effort'; effort implies a unit of force not the quantity of torque. However, unless the dyno operator keys in such things as your wheel size, gear ratios etc, then the torque at the crankshaft cant be quoted accurately, the figure from the rollers is obviously a real figure and can be used for comparison purposes when tuning the car etc. I hope it wasnt written as 780nm? that would be nanometres! N for newtons, m for metres.(Nm)
Was your dyno run done in 2nd gear?
Draglc: Im not particularly fond of the term 'tractive effort'; effort implies a unit of force not the quantity of torque. However, unless the dyno operator keys in such things as your wheel size, gear ratios etc, then the torque at the crankshaft cant be quoted accurately, the figure from the rollers is obviously a real figure and can be used for comparison purposes when tuning the car etc. I hope it wasnt written as 780nm? that would be nanometres! N for newtons, m for metres.(Nm)
Was your dyno run done in 2nd gear?
#8
_draglc_
_draglc_
-
- Guests
Posted 20 December 2005 - 06:54 AM
No it was written as N.M. and it was done in 4th the print out says. They only went to 180km/h at 5420rpm. Should i give them a call? Basically all im going to be able to say is that they didnt do it right.. and im not gonna make any friends doing that am i?
A1
A1
#9
Struggler
-
- Members
-
- 2,426 posts
Forum Fixture
- Name:Andrew or AJ
- Location:Canberra A.C.T.
- Car:UC Sedan
- Joined: 08-November 05
Posted 20 December 2005 - 10:08 AM
The torque figure you have been given is at the rear wheels. That is engine torque multiplied by your rear end (diff) ratio (assuming the car was dynoed in top or 1:1 gear) and tyre height/m.
This is because the dyno figures torque from road speed, not engine speed.
This is because the dyno figures torque from road speed, not engine speed.
#10
_Yella SLuR_
_Yella SLuR_
-
- Guests
Posted 20 December 2005 - 10:46 AM
I got caught out by that as well.
Struggler, so how do you work it back to actual engine torque? Is that possible? Mine pushed out 1200 lb.ft. of tractive power through 15" rims with 265x60 profile treads through a 3:08 diff in top gear.
Struggler, so how do you work it back to actual engine torque? Is that possible? Mine pushed out 1200 lb.ft. of tractive power through 15" rims with 265x60 profile treads through a 3:08 diff in top gear.
#11
_Yella SLuR_
_Yella SLuR_
-
- Guests
Posted 20 December 2005 - 10:53 AM
Actually make that 1150 lb. Dyno sheet attached from last time. Ignore the bottom two lines, that was the old cam and heads used for comparison of the improvement.
Without hijacking too much, Struggler, the bumps and dips concern me, what is that telling me? Will have to get back into my car one day (damn castle!!!).
Other cars on the day pushed around 800lb fairly consistently. Why was mine so high?
Without hijacking too much, Struggler, the bumps and dips concern me, what is that telling me? Will have to get back into my car one day (damn castle!!!).
Other cars on the day pushed around 800lb fairly consistently. Why was mine so high?
Edited by Yella SLuR, 20 December 2005 - 10:55 AM.
#12
_draglc_
_draglc_
-
- Guests
Posted 20 December 2005 - 12:40 PM
if you can figure out how to get torque back to the engine, im running 3.08 diff with 205/50/13s.
#13
_dansedgli_
_dansedgli_
-
- Guests
Posted 20 December 2005 - 01:56 PM
As was said above the torque get multiplied through all your gears which is why the reading is so high.
The last car I owned that I put on a dyno that read NM pulled 1150nm. It had 202rwkw.
The last car I owned that I put on a dyno that read NM pulled 1150nm. It had 202rwkw.
#14
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 20 December 2005 - 03:47 PM
My calculations suggest that you would need to know the diameter of the rollers on the dyno to get realistic values...........but if someone can show otherwise please post.
Otherwise torque at the crankshaft can be calculated by:
torque(Nm) = power(kW) x 9554/rpm
so if 100kw at 3000rpm , torque = 100x9554/3000= 318Nm
or if using imperial
torque(lbft) = power(hp) x 5256/rpm
Otherwise torque at the crankshaft can be calculated by:
torque(Nm) = power(kW) x 9554/rpm
so if 100kw at 3000rpm , torque = 100x9554/3000= 318Nm
or if using imperial
torque(lbft) = power(hp) x 5256/rpm
#15
_devilsadvocate_
_devilsadvocate_
-
- Guests
Posted 20 December 2005 - 10:21 PM
DragLC: have been scratching my head on this one, your figures just dont seem to be any good, which was why I was suspecting the roller diameter might be a factor.
However looking at yella's data, it doesnt appear to be the case.
Calculating torque from yella's figures at 100kmh, hp =120, rpm = 2335.6(using his wheel and diff data) Torque(using the formula in my last post) works out to be 269lbft.
Using the tractive effort value of 700lbft at the same speed, divide by diff ratio and multiply by radius of wheel in feet. 700/3.08 x (13.8(tyre radius inches)/12)=261lbft. Very comparable.
1200lbft translates to 448lbft at flywheel.
If we do the same for your figs draglc: 780/3.08 x (.56/2)= 70.9Nm, which just doesnt seem large enough for max torque on your vehicle, you could ask them how they reckon they might get the calc looking right....
However looking at yella's data, it doesnt appear to be the case.
Calculating torque from yella's figures at 100kmh, hp =120, rpm = 2335.6(using his wheel and diff data) Torque(using the formula in my last post) works out to be 269lbft.
Using the tractive effort value of 700lbft at the same speed, divide by diff ratio and multiply by radius of wheel in feet. 700/3.08 x (13.8(tyre radius inches)/12)=261lbft. Very comparable.
1200lbft translates to 448lbft at flywheel.
If we do the same for your figs draglc: 780/3.08 x (.56/2)= 70.9Nm, which just doesnt seem large enough for max torque on your vehicle, you could ask them how they reckon they might get the calc looking right....
#16
_draglc_
_draglc_
-
- Guests
Posted 21 December 2005 - 10:04 PM
mmm.. i might stop in there and see what they say when i ask them about it.
Hopefully i can understand it, and remember it long enough to tell yas all about it!
A1
Hopefully i can understand it, and remember it long enough to tell yas all about it!
A1
#17
_thebigsy_
_thebigsy_
-
- Guests
Posted 30 December 2005 - 05:15 PM
Devilsadvocate is on the right track... Don't forget about drivetrain losses between engine and tyres 
1 user(s) are reading this topic
0 members, 1 guests, 0 anonymous users
