Guest Report post Posted July 21, 2015 When looking at the ratios available on the Samsonas 'box, I see there are a few options available for drop gears or reduction gears? To calculate actual ratios does one just calculate by the chosen reduction gear? Share this post Link to post Share on other sites
DanJ 374 Report post Posted July 21, 2015 Yes, multiply each of the six base ratios by the reduction ratio to get the six engine rpm to propshaft rpm ratios. They've got a little application on the website which does that for you: http://samsonas.com/wp-content/themes/SamsonasNEW/soft/SpeedCalc.zip Share this post Link to post Share on other sites
Guest Report post Posted July 21, 2015 Thanks Dan,How do you know all about the Samsonas site? Do you have experience of them?? Share this post Link to post Share on other sites
DanJ 374 Report post Posted July 21, 2015 I just googled it to see what the ratios were out of curiosity (I'm sad like that being a mechanical engineer!) and spotted their calculator. I'm assuming the reduction ratio is on the secondary shaft to keep the bearing and synchro speeds around their nominal range, it looks like a lovely bit of kit either way. Somewhere on a backup hard drive I've got a tractive effort at the wheels spreadsheet. I wrote it ages ago to look at matching ratios to engine power curves, if I can find it I'll happily send it your way if it will help you decide which option to go for. Share this post Link to post Share on other sites
Guest Report post Posted July 22, 2015 Thanks Dan, I am also a time served Mechanical Engineer, Rolls Royce trained. I now make Dental Burs, which obviously isn't quite as exciting, but keeps me VERY busy. I'm working on giving the car a terminal speed of around 140mph, which should give phenomenal acceleration through the gears? If I need more, I'll change the diff to a 4.44 or even 4.67 which will slow the car down, but make it a rocket off the line!! Share this post Link to post Share on other sites
Church 209 Report post Posted July 22, 2015 Installing different final gear ratio imho is nice mod to gain performance for those staying NA. Share this post Link to post Share on other sites
Tim Radley 18 Report post Posted July 22, 2015 Thanks Dan, I am also a time served Mechanical Engineer, Rolls Royce trained. I now make Dental Burs, which obviously isn't quite as exciting, but keeps me VERY busy. I'm working on giving the car a terminal speed of around 140mph, which should give phenomenal acceleration through the gears? If I need more, I'll change the diff to a 4.44 or even 4.67 which will slow the car down, but make it a rocket off the line!! 140mph in 6th? Or just using 5? If you try and use 6 gears up to 140mph then you may loose more time changing gear than you make up in tractive force. Are you going to run paddle shift? If so then its not as bad but changing gear too often can slow you down Share this post Link to post Share on other sites
Guest Report post Posted July 22, 2015 Good point Tim, but really, what speed would you aim for in 6th? Share this post Link to post Share on other sites
Tim Radley 18 Report post Posted July 22, 2015 Good point Tim, but really, what speed would you aim for in 6th? What are you aiming to achieve with the car? See thing is, if you are twin charging (so circa 600bhp) then a 1st gear with 140mph top is going to have zero traction. If you are running fancy traction control and proper per gear boost control you could maybe live with it in 2nd to some extent. Otherwise you will blow out the first 3 gears in wheelspin. To give you an example, one of the GT-R's i do is 900bhp with 345 michelin cup 2 rear tyres, 4wd, traction control and in 3rd gear i'm pinching the centre of the seat as it's a complete liablity and lighting up all 4 tyres. That does 205mph in 6th. Looking at it the other way, some of my customers only use 3-4 gears at many circuits. 2nd-4th or 2nd-5th. It really comes down to what you want to achieve. 600bhp only using up to 4th or 5th at 140mph in that car is still going to be super fast on acceleration. I've looked at the gearing for mine and would aim for 175mph in 6th on stock diff but use drop gears to change it if required. So give yourself some leaway either side of that on the drops. Try the mfactory gear ratio calculator. Its really useful and gives a graphical overlay of options taking into account tyre size as well as final drive. http://www.teammfactory.com/gear-calculator Share this post Link to post Share on other sites
Fensport 76 Report post Posted July 22, 2015 Hi Nigel, Mine is geared for 156 in 6th at 8,000 rpm. We find that Toyota sprint requires around 145mph top speed but that was in the Celica GT4X but that was running a good 650 - 700bhp. Here is a screenshot of my ratios with 4.4 final drive and 1.0 reduction gear vs a stock car also check out our video from woodbridge, https://youtu.be/WNYrtiYfDNk Although I'm not using 6th at this circuit I am not running full power yet! Its also nice to be able to short shift up a gear especially in difficult conditions (wet / slippy / bumpy) I think my ratios are about perfect for me Best Regards Adrian 1 Tim Radley reacted to this Share this post Link to post Share on other sites
Tim Radley 18 Report post Posted July 22, 2015 What power are you at in that video Adrian? Also what tyres are you running? Getting grip looks to be a real challenge as it is now! Hi Nigel, Mine is geared for 156 in 6th at 8,000 rpm. We find that Toyota sprint requires around 145mph top speed but that was in the Celica GT4X but that was running a good 650 - 700bhp. Here is a screenshot of my ratios with 4.4 final drive and 1.0 reduction gear vs a stock car also check out our video from woodbridge, https://youtu.be/WNYrtiYfDNk Although I'm not using 6th at this circuit I am not running full power yet! Its also nice to be able to short shift up a gear especially in difficult conditions (wet / slippy / bumpy) I think my ratios are about perfect for me Best Regards Adrian Share this post Link to post Share on other sites
Guest Report post Posted July 22, 2015 I've spent hours on that M sport chart after Adrian pointed me towards it.. Still confused.I think I am steering towards version 3 gears but with a .9xx reduction gear? That way I'll be in the ball park where Adrian is on stock diff gears. I also have slightly larger tyres than Adrian.There's then the option of different diff gears or drop gears?Arrrgghh so much money, and only one chance at the decision. Share this post Link to post Share on other sites
Tim Radley 18 Report post Posted July 22, 2015 I've spent hours on that M sport chart after Adrian pointed me towards it.. Still confused. I think I am steering towards version 3 gears but with a .9xx reduction gear? That way I'll be in the ball park where Adrian is on stock diff gears. I also have slightly larger tyres than Adrian. There's then the option of different diff gears or drop gears? Arrrgghh so much money, and only one chance at the decision. Drop gears you can change later. Just choose sensible ratios and a final drive to sit in the middle of the min and max speeds you want. That is the simplest way to do it if you aren't sure what you will use it for. Share this post Link to post Share on other sites
Fensport 76 Report post Posted July 22, 2015 What power are you at in that video Adrian? Also what tyres are you running? Getting grip looks to be a real challenge as it is now! Hi Tim, that was our last run of the day at 1.35 bar boost which was 0.5s slower due to wheelspin etc Woodbridge surface is not great .... car runs fine on smooth surface at that boost level to 3rd gear. We run 0.7 bar in 1st, 1.0 bar in 2nd, 1.35 bar from 3rd up. Plan to run 1.5bar + from 4th gear but that will be later .... Not dyno'd but expect around 450 - 470 at the 1.35 bar. Tyres are R888. I think around 1.5 to 1.6 bar will be enough, any more will likely result in just more tyre smoke Cheers Adrian Share this post Link to post Share on other sites
Fensport 76 Report post Posted July 22, 2015 I've spent hours on that M sport chart after Adrian pointed me towards it.. Still confused. I think I am steering towards version 3 gears but with a .9xx reduction gear? That way I'll be in the ball park where Adrian is on stock diff gears. I also have slightly larger tyres than Adrian. There's then the option of different diff gears or drop gears? Arrrgghh so much money, and only one chance at the decision. lol I know the feeling Nigel .... me too! I reckon you will be fine with V3 and 0.9 drop gear, I doubt you'll need anything else unless forest rallying or top speed running! Best Regards Adrian Share this post Link to post Share on other sites
Guest Report post Posted July 22, 2015 lol I know the feeling Nigel .... me too! I reckon you will be fine with V3 and 0.9 drop gear, I doubt you'll need anything else unless forest rallying or top speed running! Best RegardsAdrianI guess I'd better ring Dan tomorrow then?? Share this post Link to post Share on other sites
Tim Radley 18 Report post Posted July 22, 2015 I guess I'd better ring Dan tomorrow then?? It's only money. You don't have a crack habit nor do you have a crack habit. So get the wallet out Share this post Link to post Share on other sites
Guest Report post Posted July 22, 2015 Wallet is primed and ready for a phone call tomorrow. Looks like number 2 will be getting new 'box internals now? Polished internals too!! Share this post Link to post Share on other sites
DanJ 374 Report post Posted July 22, 2015 The spreadsheet wasn't as user friendly as I remembered so its been revisited this evening. It's got numbers for a standard MT car in it so I've been able to sanity check the results against my own car. https://dl.dropboxusercontent.com/u/87478421/GT86_Ratios_and_Tractive_Effort.xlsx All user inputs are yellow cells, greens are useful output, some of the yellow options are drop downs to quickly select between the different choices. You'll have to put your own engine torque vs speed numbers in, I used the Nm vs rpm from Cosworth's std vs stage 1.x to stage 2 graphs. There's no accounting for speed or torque dependent transmission losses so its only useful as a comparative tool, but is interesting none the less. A standard engine and gearbox but with a shorter final drive must be horrible in the lower gears, the fluctuation in tractive effort as you transistion through the dreaded torque dip is very large! 1 Lee reacted to this Share this post Link to post Share on other sites
Tim Radley 18 Report post Posted July 23, 2015 Wallet is primed and ready for a phone call tomorrow. Looks like number 2 will be getting new 'box internals now? Polished internals too!! You ok Nigel? I just heard a load of sirens heading your way. Do you think they can revive your wallet or is it now officially dead? Share this post Link to post Share on other sites
Guest Report post Posted July 23, 2015 You ok Nigel? I just heard a load of sirens heading your way. Do you think they can revive your wallet or is it now officially dead?No Tim, wallet is buoyant. However, I am totally undecided on the gear set to buy with what reduction gear. Close ratios are cool, but maybe I don't need them with my torquey little boxer?? Share this post Link to post Share on other sites
DanJ 374 Report post Posted July 23, 2015 I don't envy your decision Nigel! If you've got a nice broad torque curve which I guess you should have on a twin charged setup then IMHO the trade-off is ultimately down to flexibility on number of gear choices for driveability into and out of corners vs lost time accelerating with more gear changes to make. From playing around with the spreadsheet I think which ever option you choose will be a big improvement on track vs the standard ratios, which are clearly compromised for more normal road use in 1st and 6th. Share this post Link to post Share on other sites
Guest Report post Posted July 23, 2015 I don't envy your decision Nigel! If you've got a nice broad torque curve which I guess you should have on a twin charged setup then IMHO the trade-off is ultimately down to flexibility on number of gear choices for driveability into and out of corners vs lost time accelerating with more gear changes to make. From playing around with the spreadsheet I think which ever option you choose will be a big improvement on track vs the standard ratios, which are clearly compromised for more normal road use in 1st and 6th.Thanks Dan, I'm glad you understand my predicament!!I hadn't considered that issue.. Obviously a big wide gap between gears will allow less changes in the twisty stuff. I have done auto solo's, and each time I was shifting from 1st to 2nd all the time as I was screaming or bogging down. I guess the right torque curve with the right gearing would allow the whole course to be done in one gear. The SC should give a big gulp of low down grunt whilst the Turbo will mean massive acceleration after 3000 rpm?? (not that I'll be doing solo's in this monster ha-ha)I'll have a relook at my figures.. Share this post Link to post Share on other sites
DanJ 374 Report post Posted July 23, 2015 Indeed, the polar opposite of you describe being a gas turbine which makes huge power but only likes operating over a narrow speed range. Without a torque curve for the twin-charged setup vs supercharged or turbocharged only its difficult to begin to make an objective assessment, but my gut feeling is that twincharged won't be much quicker. My rationale being the extra torque from the supercharger will be at low revs, so would only be of benefit on initial acceleration from rest when you'll likely be traction limited anyway (really need 4wd to exploit it - see Lancia Delta S4!). Once you're rolling then even with relatively long ratios you could easily stay in the region of highest torque. On the flipside of that you may be contemplating a dustbin sized turbo for huge peak power figures, and without a complicated (i.e. expensive!) anti-lag system you're expecting to rely on the supercharger boost to spool up the turbo this side of christmas? One dimensional graphs of dyno plots being useless to assess transient effects. 1 Tim Radley reacted to this Share this post Link to post Share on other sites
Guest Report post Posted July 23, 2015 I know where you're coming from here Dan, on the subject of twin charging. I am only really doing it because I want to and for another reason. I bought an AVO stage 4 set up from Adrian a while back, then the other car came along, fitted with a GTX3071 on JDL pipe work. Adrian has generously agreed to take the stage 4 back, which is still in its original packaging, so I feel obliged to exchange it for a supercharger. At the end of the day, if it doesn't work/ is a waste of time, I'll take the sc off and put it on my other car? With all the work I'm doing on my wide body kit I may even end up with two of em, both wide body, both FI?? This could be beer talking Share this post Link to post Share on other sites
