: BHP at the flywheel?
08-19-2003, 05:31 AM
Ok, i have recently bought a 1991 2.3 Carlsson, which is fitted with an Abbott racing ECU, i was woundering what BHP she was! well she has been dyno tuned and on the reciept it state's that she is 260 BHP at the fly-wheel, is this the bhp or not?
http://www.saabscene.com/forum/images/smilies/eek.gif Thanks Lee
08-19-2003, 08:35 AM
i was only woundering as i have seen cars for sale and some-times it states X amount of BHP at the wheels? on the dyno tune reciept taken from my carlsson it states BHP at the flywheel, i was woundering if and what the differance in BHP would be from the flywheel and the wheels!
08-19-2003, 08:58 AM
We don't like topic bumping here (see the AUP (http://www.saabscene.co.uk/ubb/ultimatebb.php?ubb=get_topic;f=16;t=000011) ) especially when the original query is only a couple of hours old. But newbies get a second chance...
The figure quoted will almost invariably be flywheel, mainly 'cos it's higher than the roadwheel figure http://www.saabscene.com/forum/images/smilies/rolleyes.gif . Transmission losses vary between about 15-30% dependent upon design, condition, 2WD/4WD etc...
Mark in Ireland
08-19-2003, 09:55 AM
Standard hp for that model is 220bhp at the flywheel, no way will an Abbott racing ECU take it to 260 on its own. I would suspect other tuning mods have been added or the boost just turned up to get a high hp figure for aiding selling. i.e SAAB..260BHP!!!!!!Buy me now!
08-19-2003, 02:47 PM
cheers guys, buy me now!! i bought her because she is a carlsson, not because of the BHP, the dyno tune was done in 2001, i am just trying to make sense of all the reciepts that came with her, thanks for your help.
08-19-2003, 02:58 PM
Originally posted by Mark in Ireland:
Standard hp for that model is 220bhp at the flywheel, no way will an Abbott racing ECU take it to 260 on its own. *I would suspect other tuning mods have been added or the boost just turned up to get a high hp figure for aiding selling. i.e SAAB..260BHP!!!!!!Buy me now! * * * * *[/b]Some of the early 2.3's make more than the factory quoted figures, my 2.3CD (AT LEAST 224bhp on supposedly standard LH/APC unit's) and Scaero's Aero being prime examples. So I see no reason why a Carlsson with an Abbott box couldn't make 260bhp on a good day, but chances are, it's had a few other tweaks.
Mark in Ireland
08-19-2003, 04:05 PM
I spoke to Giles at Abbott and he said I wouldn't see much of a performance gain buying his upgrade for the 2.3 Carlsson, I dare say it is beneficial on lower powered models, but he said the cost of the upgrade wasn't financially worth it for the small gains I would see. Mind you I have a Abbott head, dump valve, mbc valve and 3" JT exhaust.
I would be interested in seeing dyno charts for the upgrades mind, instead of just relying on peoples seat of the pants feelings.
When I had my TCS fault fixed by 2 Stroke to Turbo they said that my car was the fastest Saab they had driven....which was a nice compliment, but to me it wasn't as fast as my other Carlsson. Since putting the JT exhaust on, then a free flowing airfilter and winding the boost up a bit I dare say its at a similar level of performance, but without back to back comparisons its impossible to say. I definitely need to get to a dyno....
08-20-2003, 08:30 AM
I can understand the manufacturer's figures for bhp being "at the flywheel" because it is easy for them to do and a better figure.
When you take your car for a tuneup on a rolling road, surely the figure must be at the road wheels? Engine-out tuneups are possible of course, but only cost effective if other major work has been done - and they have a suitable engine test bed.
Do the tuneup places guess the flywheel bhp or am I missing something here ?
08-20-2003, 08:49 AM
No, they don't "guess". The rolling road basic recording is of power at the wheels, but once max roadspeed has been reached, the clutch is dipped and then it is the friction losses in the transmission that cause the rollers to slow down. These losses are then added to the power at the wheels figure to give "corrected" figure. Other factors may be taken in to account by the software including ambient temperature and pressure.
08-20-2003, 01:55 PM
I had a rolling road test done at Van Aaken in Bracknell and got 225.1bhp @5056rpm, 271.3 lbft @3000rpm.
Peak boost looks to be fractionaly under 1.1bar (no figure given, but it is traced on the graph)
My car is standard and this was with 75% 97 RON, 25% 95 RON.
Does the boost etc sound correct?
08-20-2003, 02:29 PM
Some rolling roads use a "correction factor" to calculate flywheel hp from wheel hp. I suppose this counts as "guessing". However, last time we went to the static rolling road at Wilshers Garage I brought my unmodded 9000 2.0LPT (no intercooler, so no variable results from one run to the next) and it clocked exactly 150hp corrected for flywheel, which agrees with the Saab spec. I don't know what the correction factor was, but my Aero clocked "300+" flywheel hp on the same rolling road (it only goes up to 300hp http://www.saabscene.com/forum/images/smilies/rolleyes.gif ) while Power Engineering clocked it at 305 flywheel hp (243hp at the wheels) using the transmission loss measurement Mark described above. That gives a measured transmission loss of 20% which may sound high, but looking at the plots that are produced during the process, it seems the percentage isn't constant over the speed range. It would be quite a bit less than 20% at, say, 3000rpm instead of 5500rpm.
08-20-2003, 02:30 PM
Originally posted by Skiddins:
Peak boost looks to be fractionaly under 1.1bar[/b]The '96-on 9000 Aero (manual) should peak briefly at 1.08 bar, then settle down to 0.98. Your results sound spot-on.
08-20-2003, 06:14 PM
Hadn't thought of releasing the clutch - perhaps because I've been driving with auto boxes for so long now.
I'm getting mine rolling-roaded soon so I'll try to get the friction loss figures for the auto box as a conmparison.
08-21-2003, 07:30 AM
The rolling road should be able to measure the power loss through tranmission system (clutch to tyre tread) as mentioned by Mark E, at any given wheel speed. In my limited experience of rolling roads, they tend to measure maximum power in third gear, to avoid the road turning too fast. The important point to remember is that the power loss through the transmission, at a given speed, is constant. It's is NOT a percentage of input power. This is an important point for tuning, and one that tuning firms often overlook, as the percentage idea makes their tuning efforts look more impressive. Using an example:-
Power at the wheels 160 bhp @ 5500 rpm
Power loss @ the same speed 40 bhp
Power at flyheel 200 bhp
% power loss 20
Suppose we now tune the car and get the following:
Power at the wheels 200 bhp @ 5500 rpm
Power loss remains 40 bhp (the speed is the same)
Power at the flywheel 240 bhp
However, if you use the % method, as often seen in magazines and tuning firms, you would assume that 200 bhp is 80% of the flywheel figure, and calculate the flywheel figure to be 250 bhp, 10 bhp too much.
Of course, if as normally happens, the peak power figure moves up the rev range, say to 5800 rpm, you need to measure the power loss at the new road speed, eg 84 mph instead of 80 mph. This power loss figure will be slightly higher than the previous figure, but probably only by about two bhp.
By the way, not sure what happens with an autobox, I've not put one on a rolling road yet. Does anyone know?
08-21-2003, 09:47 AM
Originally posted by Mark B:
By the way, not sure what happens with an autobox, I've not put one on a rolling road yet. *Does anyone know? [/b]I thought they just blew up if you knock them into neutral at high speed .
Not sure really, and I haven't got the handbook by me, but I think Saab say something about not going into neutral above a certain speed?
08-21-2003, 07:15 PM
Yup. It says : "IMPORTANT Do not move the selector lever to N when the car is moving, as this can result in damage to the engine and transmission"
So perhaps they won't be able to work out the flywheel bhp on my car after all.