Different bhp readings...

[Dr G]

Ive been on 2 different rolling roads recently after having 2 differnet jobs done on my car and have had some very different readings...

basically i had some head work done (skimmed, gas flowed and ports polished) and had my cams reprofiled to mild fast road spec. The readings i got back where 111 bhp before and 133 bhp after.

Then a week later i had a unichip fitted and tuned and the readings came back at 103bhp before and 112bhp after.

Studyiing the readouts i notied that the maximum speed during test and maximum speed in gear during test where very different, knowing my car and what it can realistically do in each gear i can only conclude that the first rolling road (head + cam work) used 2nd gear to do the test and the unichip one used 3rd. Doed this effect the bhp output depending what gear is used and if so can i assume that i just look at the increases and add them together to get a more accurate bhp figure of what i am running after these 2 new mods?

cheers

DrG

 

[Steveold]

Come on someone im interested in an answer for this.....

 

[Ben H]

My initial guess would be that the first set of figures were based on an "at the flywheel estimate" (derived from an at the roadwheels measure, with tranmission loss calculated) and the second just an "at the roadwheels" measurement.

Some places also do engine dynos, though I understand that these are rarer.

 

[adiclio16v]

when i had mine on it was done in 4th i think, other than that where are the figures taken cos the lower figures could be at the wheels an the higher figure flywheel transmission takes about 20% out

also its better to use the same rolling roads as they vary

adi

 

[steve a]

yeah irecon bens right first set is fly and the second wheels, should be seeing around 140 at the fly then

 

[Pysco]

Yeah first set will be flywheel figures second will be road wheel figures. Theres no way transmission soaks up 20%, No WAY!!! 10% would be closer.

 

[Dr G]

cheers for the responses...

at home now, got the read outs infront of me, reads as follows:

1st rolling road (Head work + reprofiled cam):

Max power speed 5703rpm (67.5 mph in gear used)

Power at flywheel (corrected): 132.4bhp

Power at flywheel (Pwr wheel+Pwr loss): 132.6bhp

Power at wheels: 110.5bhp

Power loss: 22.1bhp

max tourque speed: 5239rpm (62mph in gear used)

max tourque (corrected): 126.7 lbft

max road speed: 77mph

max engine speed: 6506rpm



2st rolling road (Unichip):

Max power speed 5797rpm (89.0 mph in gear used)

Power at flywheel (corrected): 114.1bhp

Power at flywheel (Pwr wheel+Pwr loss): 113.1bhp

Power at wheels: 92.9bhp

Power loss: 20.2bhp

max tourque speed: 5059rpm (85mph in gear used)

max tourque (corrected): 117.6 lbft

max road speed: 106mph

max engine speed: 6309rpm



any other ideas..?



cheers

DrG

 

[Dr G]

anyone?

 

[Steveold]

lol

 

[Ben H]

Oh dear! If you dont mind my saying, I think 140bhp is a lot for some headwork, cams and chip on a NA 1.8 8v engine that makes 110bhp as standard. But then 113bhp is less than Id expect!

 

[Steveold]

No its not Ben.... a 1.8 16v will make 130 standard.... so head work cams etc on a 8v should easily push 140

 

[maciek]

as I said in other post (find and read it.) - its crucial to run the car on the same gear. the differences between 2 and fifth are huge. its because you get far more Nm through the wheels on 2nd than on 5th due to shorter ratio. but the RR doesnt know this... the rolling drag is not differing that much (as the torque at wheels) between 5th and 2nd.

 

[Dr G]

thanks maciek

 

[maciek]

the most accurate gear is usually 4

 

[paddymph]

Mine was done with 4th Gear @ the Bury RR day, i got mailto:152@wheels">152@wheels and the other 172s were anything from 126-152?? Weird eh?

Paddy

 

[Pugboy]

paddy,

bit of deja vu about your post you smug git

what was it again, remind us!

pugboy

(<152 @ wheels but still faster cause im not carrying ballast)

 

[paddymph]

I know, i know !!!!! Ive probably got it coming to me next RR day i go to!

Paddy

 

[Craggy]

you gotta prove it on the strip yet mate! thats where the pub talk ends LOL

 

[Ben j]

on both runs ya transmission loss is near enough the same though! so there is an accuracy

 

[2 live]

hehe well a 149 bhp @ the wheels and a 14.800 1/4 shud be enough to keep the 172 boys quiet lol

 

[Ben j]

yea those new fangled things aint what there cracked up to be are they??!!



< flame suit on >

 

[Frosty]

The reason 4th gear is the most accurate is because it is the closest to a 1:1 ratio, meaning the ramp rate doesnt need much altering (which can produce some funny results in itself).

 

[paddymph]

Ill show yall next year!!!............

Paddy