RR’d my Cup at 91 degrees

[Gary Brown]

How much affect can air temp have on BHP?

Ive had my Cup rrd today (its first one since I got it in March), and I couldnt help but feel disappointed with the bhp figures - 144.9 at the wheels, and 163.3 at the fly wheel was the best of two runs (144.4 & 163.1 for the first one). It got slightly better when I fitted the green panel filter I bought a month ago (Im a lazy sod) and ran it again - 149.4 at wheels and 167.1 at the fly. Testament to these filters that they make such an immediate difference.

The temperature was 91F (ie hot), but I expected to get closer to 172 given that Ive had my Cup superchipped - superchips claim an 8-10 bhp increase, which I take with a pinch of salt, but I didnt expect the power to be down so much.

Now the confusing bit, which leads me to think the testing gear was having a cant be arsed day:

Before the filter was changed, the peak torque figures were 150.4 lbft and, wait for it, 172.9lbft!!!!. After the green filter was fitted, the torque "dropped" (from 172.9) to 154.6lbft - wtf? Surely the easier breathing would have benefitted torque as much as bhp? So Im lead to think that the 172.9 reading must have been an error - after all, the standard figure is 149 isnt it? 172 is seriously torquey.

So assuming the 172lbft was an error, Im happy with my torque - because it shows that the re-map is having the effect I thought it was, ie increasing torque: even on such a hot day, pre-green filter it gave me 150.4 and then post green filter 154.6, both figures being higher than standard of 149 despite bhp being so drastically down.

Should I just forget these figures and wait for a cold day in October, or are they to be expected given a) the heat, and b) the fact that not all F4R engines produce 172bhp anyway??

 

[rt172]

The Cup at John Nobles a few months back, the MK2 and the MK1 172s all put out 162bhp +/- 1bhp calculated flywheel figures. Im really starting to not trust any rolling road at all. Different places give very different figures for the same car. And yes, the temperature would probably make some difference. Always does when driving.

Same day my Williams 3 put out a supposed 3bhp more than Jon (2Live), whos car is undoubtedly faster than mine. Doesnt boost my confidence in the whole RR thing.

And 172lbft seems pretty optimistic too! Lucky you if it really has that much though.

 

[Tom_16v]

A rolling road will give a measured power reading and a corrected power reading so whether it be hot/cold wont make a difference to the final figure.

As for the increase because of the filter, I would guess half the gain in the fact the new filter is nice and clean, whereas the old one had probably seen a few miles (feel free to correct me on this one).

 

[Gary Brown]

No, you could be right Tom - the mileage is 9200, so yep, the old filter was a little grubby (and very orange). Is it best to try a few different rolling roads, too?

 

[Chris_H]

air temp and barometric pressure and humidity affect power greatly.

The readings corrected but its usually hopeless.

 

[Gary Brown]

Thanks Chris - ambient air pressure was 1011: I think thats lowish isnt it? No idea what the humidity was. Thanks for your comments, too, Rhys.

 

[paddymph]

Im with Rhys Gary, Im also starting to loose faith in the Rollers, too many different results + factors, it seems the only way is on the road and 1/4 mile strip to be 100% accurate.

 

[Chris_H]

1011 what? Need to know what it was measured in.

Not that it matters, best tiem is to compare with another 172 on a rr day or sometting, rollers are not very accurate and are at best a rough guide.

 

[philip]

most 172s even with chip/ik/exhaust struggle to 172bhp. High air temperature will affect the performance considerably. The only relevant measurement is to use the same RR before and after every change you make, and to do that at the same ambient temperature. The absolute bhp number you will get will probably be wrong, but with some luck you will be able to measure the effect of any changes you have made fairly accurately.

 

[Gary Brown]

Cheers all for the helpful comments.

Paddy & Rhys - agree that RRs are crap, but isnt 1/4 miling too dependant on your own ability to be consistent? Do you just have to do plenty of runs each time and average them or something?

Chris H - 1011 bar? I dont know, whatever they use to measure barometric pressure, ie on TV weather forecasts - I think 1080-1100 is high (clear skies) and 950-1000 (low cloud) is low.

Philip - yeah, I agree that best use of one RR is to use it every time you make a change. Im going to re-flash the ECU with the original settings before the 12000 mile service, get it RRd, then reflash with the superchip settings and RR it again; with any luck, 12000 miles and colder weather should coincide around Oct/Nov time.

By the way, whatever effect the green panel filter had or didnt have, it certainly sounds nice.

 

[rt172]

I suppose if anyone has enough goes at 1/4 miling, then there will come a point where they wont be able to beat there own times any more. When it comes down to it, its just accelerating in a straight line, which isnt that difficult. I think it gives a reasonable indicator of your cars performance compared to others there on the same day. It also gives you an idea of what you can take on and have a chance against if they get a crap start or whatever.

Id have a go at an RS focus given that the one at the last York didnt get a run under 15.1 while I was watching...

Youll never get a definitive answer as to how powerful or quick your car is though!

 

[BenR]

THe F4R unit is extreemly sensitive to temps and after doing a bit of temp related testing the diff between max and min inlet temps was a wopping 14bhp.

Peak ambient temperature was 95 deg F, peak inlet temp was roughly 140-150 F, lowest we could get the inlet temp was 104 F.

Plus the the engines only have to leave the factory with 166bhp.

 

[Gary Brown]

Ben - your comments are most reassuring; a power diff of 14bhp is massive, and I was hoping that I was perhaps losing 5 or 6 bhp because of the heat yesterday.



Of course Im only really going on about this because my old L reg 98000 mile totally standard civic vti gave me 167bhp on the same RR (though it was done in mid January!!!)

 

[philip]

I am not the least surprised about 14bhp. I know the difference between a cold winter morning at 3 deg and a sweltering day at 35 deg, and you can definitely feel the 14 bhp!