ben7 Posted January 15, 2003 Share Posted January 15, 2003 Took my 1800 ss k series to a rolling road on Monday. The power output (after temp correction & in 5th gear not overdrive 6th ) was 132 bhp. I was disappointed as CC claim the 1800 ss should produce 140 bhp. The guy at the garage told me that he was actually impressed by the figures and went on to add that the the CC figures are likely to be measured at the fly wheel as opposed to at the wheels as per my test. He went on to say that there is always a lot of confusion about the two methods of measuring. Well the confusion starts here I’m afraid. What is the difference (apart from the fact that one’s measured at the fly wheel and one’s measured at the wheels!!). Is their a rule of thumb for converting one to the other? My car’s a 6 speed with AP lsd. Second question, currently running adj Bilstein dampers with small green springs front and rear. Car is great on the track but is way too skittish on the roads for me. I’m looking to raise the height of the car slightly and soften the ride. (ok ok I can’t believe I’m writing it either!) The garage suggests I go for 8” 180 springs (mine are probably 6.5” 250+) I will be using the car on the road but will also be using it extensively on the track next summer. Is their a happy balance that can be struck? Do I need to consider dumping my lovely billies for a set of dampers that adjust bump and rebound? All and any help would be much appreciated. Link to comment Share on other sites More sharing options...
Seven in SA Posted January 15, 2003 Share Posted January 15, 2003 V500OSV, Not a idiot question but one that has raged through here a bit. I just did a search for rolling road and got a lot of threads that will help you. Biggest one possibly being this one here As for your second question I await someone with superior knowledge to assist you. Nic My first go at a hyper link and it worked Edited by - Seven in SA on 15 Jan 2003 15:24:10 Link to comment Share on other sites More sharing options...
ChrisC Posted January 15, 2003 Share Posted January 15, 2003 OK a number of points 1, I am making the assumption that your 6 speed box is a Caterham article, if it is the 6 gear is not an overdrive, the box does not have one. 2, A manufacture quoted BHP figure is given with perfect conditions. That includes no alternator load, perfect intake air density and temperature etc etc. The reading is given from the Flywheel to remove losses, which occur through the transmission. You will never have this perfect condition, because your engine is install in an engine bay. The clutch, gearbox, prop shaft, diff, drive shafts, wheel bearings, rear brakes are all taking a little of your power. So you always end up with a lower figure at the Wheels. There is something wrong is you don’t. Rolling Road BHP figures will vary from day to day, Rolling Road to Rolling Road, and operator to operator. Rolling Roads should only be used to see if your vehicle is running under load correctly, so it’s a setup tool. Did you gain a power advantage from your first Power Run to the Last? If you did your Rolling Road was worth the money. If you went to the Rollers just to get a BHP figure for the PUB you have wasted you money, you are always better of use the Caterham figures. Anyway if you are looking for a PUB figure quote the Caterham 0-60 or the Caterham Power to Weight, and if anyone dares to question them, invite them to a track day Hope This Helps Chris PS I think 132 BHP on the rollers is good figure for a quoted 140 BHP car. Link to comment Share on other sites More sharing options...
SteveP Posted January 15, 2003 Share Posted January 15, 2003 132bhp at the wheels is almost unbeliveable, since general consensus that transmission losses etc would account for 20 - 25%, so maybe a realistic 'at the wheels' figure might be 105 - 112 bhp for a 140 bhp engine. But like others have said, different rolling roads, conditions, way the test was conducted, coast down adjustment methods all vary the actual result. SteveP Link to comment Share on other sites More sharing options...
stevefoster Posted January 15, 2003 Share Posted January 15, 2003 220lbs can be a compromise on K series cars. What ARB do you have? Softening this may help restore a better balance. Also changing the front will have an effect on the rear. More grip at the front will make the car feel like it will oversteer more. What rear set up do you have springs / ARB. I have some 180's sitting in the garage. If you are near you could try them... If the dampers are inverted then it's only 1 bolt to pop off the springs. I have 250lbs but on a VX which is a match I like. I guess we are talking Bilsteins here. My racing pics, 7 DIY, race prep. Updated often here Photo's of the year here Hants (North) and Berkshire Area club site here Link to comment Share on other sites More sharing options...
ben7 Posted January 15, 2003 Author Share Posted January 15, 2003 Many thanks for the feedback. I took my car to the rolling road in order to baseline what my car was doing prior to potentially upgrading it. My car went from 118 bhp to about 123bhp (from memory) after the mechanic had adjuted the fuelling. Apparently, because it was 14 degrees in the test centre, the figures were then adjusted for temperature. I have no idea what this means, but they came back with a revised set of figures for 132bhp. I thought I'd best ask you guys as opposed to looking like a complete ding in the garage. The car's an ex CC demo car by the way so I have no idea whether CC gave it an extra little bit of uummfff for the benefit of the hacks. It was the car that the fat geezer from Driven managed to drive sideways very slowly round a track a couple of years ago, before complaining that CC were crap handling cars! It is a Caterham 6 speed box, again the guy who was testing the car mentioned the overdrive in top. Thanks also for feedback on springs. Unfortunately I have no idea what arb's I have, looks like I'll be in the garage tonight with a torch and a tape-measure! The rear is wound right down, again on springs that I would guess to be 250+ or above, the front isn't quite as low. When I had the car at Caterham for a check up when I bought it, even they commented that it was very low. Thanks for the offer to lend me the springs, I think I'm about 200 odd miles away unfortunatley. Any idea about the bump and rebound adjustment, and whether it's worth the extra cash? Very impressed with the hyperlink by the way!! Cheers, Ben Link to comment Share on other sites More sharing options...
Bob Corb Posted January 15, 2003 Share Posted January 15, 2003 When I built my 7 18months back I wanted to copy Peter Carmichaels suspension spec to some degree as it got an all round thumbs up in a handling test. Unfortunately Caterham didnt want to sell me the parts as a set with the car as the front springs (green 250lb/") are from a VX race set up and the rears were the std progressive rate jobbies so I plumped for VX race all round together with a 5/8" front ARB. This is how SLR race cars are run on the track apparently. Anyway the rear green (250lb/") springs were far to hard and the back of the car was all over the shop with the rear ARB set one peg off full soft. So I purchased a set of std 7 progressive springs and set the rear bar full soft and on track its just awseome. First time out at Cadwell (7 club day) the car ran very well. The instructor even commented on how well balanced the set up was! Turn in was sharp and the safety margin understeer (mild) could be translated in a drift on demand. Unfortunately (again?) I chose the wrong dampers (SLR race M-1??) so now on the road its still a bit skittish on bumpy bends. I'm looking at replacing the dampers with either Nitrons or Ohlins at some point or other. If you make the car a bit more softly sprung for road use then the bump adjustment in the damper can allow you to prop the car up slightly to prevent roll on track hence giving you a bit more scope for dialling in settings for road or track? I need to look into things a bit further as I'm no expert.. The other thing I heard recently is that Caterham 21 progressive rear springs work well too although I dont know why... ask Miraz.. BC Link to comment Share on other sites More sharing options...
Joe 90 Posted January 16, 2003 Share Posted January 16, 2003 The difference between power at the wheels and power at the flywheel are the power losses. 20% to 25% is realistic, and some rolling roads will make a measurement of losses to try and give a more accurate flywheel power estimate. Corrections should also be made for atmospheric conditions because cold air is more dense than warm air. This effect on it's own gives a 3% change for every 10 deg. In your example, the power at 14 deg is 2% more than the power at 20 deg. Compensating for all these effects should give more consistency between rolling roads. The comments Chris made that the quoted flywheel power is made under unrealistic conditions does not happen much these days. If the figures are measured to DIN standards, alternators and pumps must be connected. In the 70s it was popular to quote SAE gross power figures, which allowed these exagerations. The rolling road corrected flywheel figures should be close enough, and I would agree that 132 BHP at the wheels is ery good. 99,000 miles so far Link to comment Share on other sites More sharing options...
Miraz Posted January 16, 2003 Share Posted January 16, 2003 As far as the choice of rear springs go:- The std progressive spring is 345mm on-shelf-length. The 21 progressive spring is 325mm. This spring is an excellent compromise for those that want stiffer suspension, but don't want to be bounced into the nearest ditch by the race springs. I used to use them and may go back to them. The race linear (green) is 280mm long. Spring Length Rate Standard Rear 345 mm From 0 - 95 mm: 110lb Next 87.5 mm: 130lb Remainder: 200lb 21 Rear 325 mm From 0 - 92.5 mm: 138 lb Next 82.5 mm: 200 lb Remainder: 246 lb Green Rear 280 mm Linear 215 lb The uprated progressive rear will allow you to run a stiffer spring for track use, without making the car feel too skittish on rougher road surfaces - it works well with the 220lb front spring suggested by Steve Foster, but changing the rear will make the most notable difference to the feel of the car. Changing springs is a lot cheaper than changing dampers - have your car flat-floored on the new set of springs and drive it for a bit before even thinking about fitting different dampers. Miraz Link to comment Share on other sites More sharing options...
stevefoster Posted January 16, 2003 Share Posted January 16, 2003 I agree with the right sort of springs up front the rear prog ones will get you far and give a very sure footed balanced car. 250lb rear would be way to stiff imho. On my current VX set up with 260lb fronts I am going to try 180lb rear springs having run all last year with the progressive one. My reasoning for this is that on running the 8.5" rims I cannot run a rear ARB so found the rear a little soft overall on the progressive springs. Going 180 will I hope help here. If not I can always change back. My racing pics, 7 DIY, race prep. Updated often here Photo's of the year here Hants (North) and Berkshire Area club site here Link to comment Share on other sites More sharing options...
ben7 Posted January 16, 2003 Author Share Posted January 16, 2003 Once again, many thanks for the feedback. From what you fella's are saying, I should stick with the green 250's on the front. I'll give the progressive 21 springs a go on the rear for starters, and see how I go. If it's still too hard, I'll try the std springs. Can I buy the 21 springs from CC direct, or should I look elsewhere? Once again, many thanks for all of the help. Now if I could only fix the sodding hot start problem, I might be able to drive the car a bit more!! Cheers, Ben Link to comment Share on other sites More sharing options...
Peter Carmichael Posted January 16, 2003 Share Posted January 16, 2003 I reckon the rolling road geezer has taken the liberty of bull****ting you... Your car did not make 132 bhp at the wheels. The power figures at the wheels will be higher the lower the gear selected, so all these people tugging their beards and saying "ah yes, losses are 20-25 %" are talking rubbish as well. If the rolling road operators did two runs in 6th gear and then a run in fifth gear, the fifth gear figure will be higher. I reckon their rolling road is over-reading by somewhere in the region of 20%. Don't go there again or ask them to give me a call so I can give them a lesson in basic use of dynamometers. And what fuelling adjustments did they make exactly to a MEMS controlled Rover engine? Length of the springs is also irrelevant as long as they don't go coilbound. Ride height is determined by spring platforms. The only problem you have with the car's suspension is the rear spring rate. Try progressives from Caterham or 150lb/in. Your current rear springs will be 225lb/in which is ridiculous. Link to comment Share on other sites More sharing options...
Highlander Posted January 16, 2003 Share Posted January 16, 2003 Nope you engine doesn't produce more power in a lower gear, but it does develope more 'thrust' at the rear wheels. Agree that the dyno operator was BSing though. Link to comment Share on other sites More sharing options...
oilyhands Posted January 16, 2003 Share Posted January 16, 2003 Higlander, you are missing the point The *measured* power at the wheels in a lower gear will indeed be higher, this is because the wheels are turning more slowly so the power losses sustained through the unnaturally high compressions of the tyre wall are lower. The enigne doesnt produce more power in a lower gear, it just sheds less of it through rolling losses. Oily Link to comment Share on other sites More sharing options...
Highlander Posted January 16, 2003 Share Posted January 16, 2003 Oily. Fair point, I was thinking about it after I posted and came to that conclusion. Think that I interpreted PCs comment wrongly. Woops Link to comment Share on other sites More sharing options...
scooby dooby doo Posted January 16, 2003 Share Posted January 16, 2003 250 lbs rear must be INSANELY hard on the road. 180 is quite stiff and a problem on wet bumpy roundabout exits - i have a set here, hardly used if you're interested. 6th is the direct gear on a caterham 6th speeder. If the rolling road guy couldn't see that from the plots in various gears and/or didn't ask you he must be full of ****. 132 at the wheels from a std 1.8 engine is also full of **** remapping with a MEMS ECU is not possible, again he appears to be full of ****. Please tell us the name of the road so we can avoid. and so peter cn inform of the error of his ways. Sorry that your first trip to a rolling road appears to have been a poor one ☹️ As a finger in the air comparison my 1.6 KSS made 100 at the wheels at John Noble Motorsport. Caterham claim the peak figure is similar for 1.6 KSS and 1.8 KSS. OTOH, a road should only really be used for comparisons so overreading by some large number is not such a problem (as long as you don't compare with other roads). HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
Nigel Riches Posted January 17, 2003 Share Posted January 17, 2003 Ben, posted on the wall of our conference room are some rules for meetings, one of these is, "there is no such thing as a stupid question", the same applies on this forum, you will find out if you ask here. regards Nigel. 1982. 5 speed, clamshells. B.R.G / Ali. The True Colours. Link to comment Share on other sites More sharing options...
ben7 Posted January 17, 2003 Author Share Posted January 17, 2003 OK, so the general consensus is that the garage was taking the p!ss. Well the good news is that the whole experience only cost me £60, so it could have been a lot worse!! Re the fueling, I'm desperately trying to recall the exact conversation, but I got the impression that he had adjusted the pressure. Again, I have no idea whether this is possible? I'll dig out the report over the weekend to see what it said. Re the rear springs, they came with the car when I bought it, so all I know is that they are also green like the front. I could therefore be well off the mark by guessing that they are also 250 ish. I don't know, and there was me thinking that all I had to do was learn how to drive it properly! Talking of which, I spent 3 hours of the final day of my holiday i.e. Wednesday, driving around beautiful b roads through glorious open countryside. The sun was shining, the road deserted - simply amazing, but then I suppose you guys know what I mean. Ben Link to comment Share on other sites More sharing options...
scooby dooby doo Posted January 18, 2003 Share Posted January 18, 2003 it is possible to change the fuel pressure by adjusting the regulator. if you have an *adjustable* fuel pressure regulator - these aren't fitted as standard. HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
Miraz Posted January 18, 2003 Share Posted January 18, 2003 The green rear springs are usually 180lbs linear. Miraz Link to comment Share on other sites More sharing options...
scooby dooby doo Posted January 18, 2003 Share Posted January 18, 2003 hmmm... my linear 180s are red. Caterham really don't make it easy do they ❗ HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
Miraz Posted January 18, 2003 Share Posted January 18, 2003 They've changed suppliers again recently - the new ones are just black. Link to comment Share on other sites More sharing options...
scooby dooby doo Posted January 18, 2003 Share Posted January 18, 2003 LOL ❗ HOOPY 500 kg R706KGU Link to comment Share on other sites More sharing options...
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