Matt Seabrook Posted April 14, 2005 Share Posted April 14, 2005 Er, I make no claims for the torque in that thread at all. In fact, read the last posting 248 x 5252 / 6500 makes 200 but it ain't right, and I wouldn't ever claim it to be. I have also gone on record as stating that I believe that particular set of rollers to be over reading. I claim 235bhp at 7000rpm for the Cossie, which according to my flawed calcs gives me 235 x 5252 / 7000 = 176 which is still high, bit it's a lot closer to the truth than anything posted so far... I do have a torque curve from Northampton Motorsport at home. I'll post up the numbers when I get home... I can see how you can get different power readings from one set of rollers to another but you also have peak power 500rpm apart as well Quote Link to comment Share on other sites More sharing options...
Blatman Posted April 14, 2005 Share Posted April 14, 2005 Yeah, I know. That's 'cos at Northampton Motorsport we didn't have to back off at 6500. We took it to 7000rpm and again, power was still just about rising but as the engine was still quite short of running time, I chose to set a 7000rpm limit. On the Northampton rollers, with the car heavily strapped down (it was free to float at Pete Baldwins place) and a diff problem causing large transmission losses, it made 223bhp. IIRC, the torque figure was over 150 though, but until I get home, I can't remember exactly what it was. All this was two years ago, since when I've had the diff rebuilt (and a fault was found and rectified), and I've been revving well past 7000 were there it still makes power as far as I can tell. Oh, and 223 x 5252 / 7000 = 167, so it's still high, but closer than any other way of calculating it, as far as I can tell 'cos if you substitute peak RPM for peak torque RPM you get numbers in the 250 range. What we need is an expert... Quote Link to comment Share on other sites More sharing options...
Matt Seabrook Posted April 14, 2005 Share Posted April 14, 2005 Hey don't be sorry, we'll not get to the bottom of this without discussion. As i said in my opening post, I stand to be corrected, and educated. However, whilst the numbers may be imprecise, I believe that using the peak RPM figure at least allows us to get in the right ball park for max torque... Peak power is no way to get to peak torque figure R300 Max Power: 160 bhp @ 7000 rpm Max torque: 130 lbs.ft @ 5000 rpm R400 Max Power: 200 bhp @ 7500 rpm Max torque: 150 lbs.ft @ 5750 rpm R500 Max Power: 230bhp @ 8600 rpm Max torque: 155 lbs.ft @ 7200 rpm R300 has peak torque 2000rpm lower the peak BHP. The higher the engine is tuned the nearer the BHP and Torque figures get on the Caterham engines get but even the R500's peak torque is almost 1500rpm less the peak BHP. Quote Link to comment Share on other sites More sharing options...
ian crocker Posted April 14, 2005 Share Posted April 14, 2005 You don't need an expert. Chris has already told you a few posts back. A big problem is all this use of rolling road figures which are generally not very reliable. Fine for tuning an engine on the day but hopeless for comparison with other people using other rollers on other days. Quote Link to comment Share on other sites More sharing options...
ian crocker Posted April 14, 2005 Share Posted April 14, 2005 You can actually get pretty close to peak torque figures if you know the peak power and its rpm. Calculate the torque at peak power, then add on 10%. That will be damn close to the peak torque for most NA engines - just try it with your Caterham figures for example. Quote Link to comment Share on other sites More sharing options...
ChrisG Posted April 14, 2005 Share Posted April 14, 2005 Blatters You only substitute in the peak torque rpm when you're trying to calculate power at PEAK TORQUE rpm, you can't use peak power rpm and peak torque figures, or visca versa!! ie it wouldnt be 223 x 5252 / 4500 = 260lbft it would be [power at 4500rpm] x 5252 / 4500 = maybe 190lbft Quote Link to comment Share on other sites More sharing options...
Matt Seabrook Posted April 14, 2005 Share Posted April 14, 2005 Will have to get my sprint car on another set of rollers as I need to know how the power is coming on about 7000rpm as we got my car up to 6900rpm at 220bhp and stopped. Just be nice to know if its worth revving it to 7800 rpm rev limit I have set. Quote Link to comment Share on other sites More sharing options...
Matt Seabrook Posted April 14, 2005 Share Posted April 14, 2005 Another site peak torque at 4800rpm peak bhp at 6900rpm And one from Mr D V Andrews Quote Link to comment Share on other sites More sharing options...
Blatman Posted April 14, 2005 Share Posted April 14, 2005 Er, I am getting pretty close with the equation though. No-one saId it was going to be 100% accurate, so if you allow a 10% margin on every other calculation then I think you should allow 10% on mine too... R300. Max Power: 160 bhp @ 7000 rpm 160 x 5252 / 7000 = 120ftl/bs. Less than 10% error. R400 Max Power: 200 bhp @ 7500 rpm 200 x 5252 / 7500 = 140ft/lbs. Less than 10% error. R500 Max Power: 230bhp @ 8600 rpm 230 x 5252 / 8600 = 140ft/lbs. Just over 10% error. However, it'll need a new head gasket... Does my equation still look so badly unreasonable? Quote Link to comment Share on other sites More sharing options...
Matt Seabrook Posted April 14, 2005 Share Posted April 14, 2005 Yep the Duratec engine would be about 15% off and I would be p****d off if my power figure was that far out. Maximum Power is 215 bhp @ 6,900 rpm Maximum Torque is 190lbs.ft. at 4,800 rpm Quote Link to comment Share on other sites More sharing options...
Blatman Posted April 14, 2005 Share Posted April 14, 2005 Blatters You only substitute in the peak torque rpm when you're trying to calculate power at PEAK TORQUE rpm, you can't use peak power rpm and peak torque figures, or visca versa!! ie it wouldnt be 223 x 5252 / 4500 = 260lbft it would be [power at 4500rpm] x 5252 / 4500 = maybe 190lbft [power at 4500] x 5252 / 4500 Lets see. Back to graph 1 on page 1. Peak torque appears to be at 6250rpm. Power looks to be about 225-230. So... 230 x 5252 / 6250 = 193 which seems to be more accurate although still well optimistic IMO, and we're back to the basic premise which says that N/A engines will struggle to get above 180ft/lbs... Quote Link to comment Share on other sites More sharing options...
ChrisG Posted April 14, 2005 Share Posted April 14, 2005 LOL, you never claimed you required a 10% error tho, the way I read was "this is how its calculated unless someone proves me wrong" which I thought we did The 10% thing is only a coincidence / trait of some higly tuned engines, it's not something you can apply to any engine with any reasonable certainty that its correct. e.g Merc SL500 (normally aspirated) Max Power = 302bhp @ 5600rpm Max Torque = 339lbft @ 2700rpm torque at peak power = 283lbft which is nearly 20% different Using this "logic" though, does it not also put Scott's figures within this 10% figure too? Quote Link to comment Share on other sites More sharing options...
Blatman Posted April 14, 2005 Share Posted April 14, 2005 Yep the Duratec engine would be about 15% off and I would be p****d off if my power figure was that far out. Maximum Power is 215 bhp @ 6,900 rpm Maximum Torque is 190lbs.ft. at 4,800 rpm Again, I just can't see how the physics of the way the power is produced supports the numbers quoted. I remain sceptical... Quote Link to comment Share on other sites More sharing options...
Blatman Posted April 14, 2005 Share Posted April 14, 2005 Using this "logic" though, does it not also put Scott's figures within this 10% figure too? Matt's figures... Can't remember now, but probably. *Shuffles back to page 1* Adding 10% on to the figure I calculated for Matt (166ft/lb's) makes it 182ft/lbs. How accurate the rollers are is another matter though, so don't gloat too much As arm noted though, it is difficult to believe that an atmo engine is making more than 180ft/lbs. I mean, well done if it is, but it goes against the general laws of physics/mechanics/whatever for these sorts of things and I had that in mind when I started this off. And yes, fair point on the 10% thing. I thought I'd worded subsequent postings carefully enough though. Obviously not... Quote Link to comment Share on other sites More sharing options...
ChrisG Posted April 14, 2005 Share Posted April 14, 2005 Yup, I think we were going along two slightly differerent paths during all that, you were trying to show Scott's figures were optimistic, whereas I wasnt making comment on those, I was just trying to show you where you'd gone wrong in the calcs if you were trying to actually calculate it all Quote Link to comment Share on other sites More sharing options...
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