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Topic: Is the Cosworth geared too tall? (Read 2405 times) |
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faffi
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Is the Cosworth geared too tall?
« on: May 16th, 2010, 9:16pm » |
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Hi!
It's been some time since I last posted - I went to a Mondeo, thinking the Scorpios were getting a bit old when I decided it was time to upgrade on my basic 1997 sedan. Big mistake. After two years trying to fool myself the Mondeo would suffice, I have spotted a low-mileage 2.9 Cosworth sedan and am now in the process of convincing its owner it's a good idea to sell it. To me 
Now to the question - should the Cosworth ideally be geared lower? Looking at the performance figures from Top Gear and Autocar, both the acceleration figures and top speed figures suggests that it's geared too tall for optimum performance. Or it doesn't really make 207 hp. In addition, it seems to have a very tall first and a silly big jump between 2nd and 3rd gear, further reducing acceleraton.
Also: According to a test I found on this site, the Cosworth seems to carry a very tall gearing with 60 mph attainable in 1st, 86 in 2nd and 126 in 3rd. Its top speed is apparently 138 at 5100 rpm. However, this doesn't correspond with the picture on the front page here that indicates 5600 rpm at 142 mph.
So I'm a little confused - does anybody know what's correct, as there is nearly a 7% difference between the two?
Sorry for being so long-winded - I tend to get carried away...
Eirik
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Tons_of_fun
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Re: Is the Cosworth geared too tall?
« Reply #1 on: May 17th, 2010, 8:11am » |
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Hi Faffi. Yep i also think the cossie is a little highly geared. This really isnt a bad thing though as cruising @70 mph in top = 2,500 rpm. Any more than that the fuel economy would be un bearable. I imagine the reason Ford geared them this way was to give the car the most progressive acceleration without compramising the refinment & smoothness of the gear change . If it's quicker acceleration your after a 2.0 ltr diff can be retro fitted which will lower the gearing significantly. A 0-60 time of around 6.5 seconds is easily achieved using this mod ( ask Highlander )   . As for the official performance figures, the information on this site is correct, although ( as some members will confirm ) they do go a little faster then 142 mph ( i couldnt possibly comment ). Hope that helps... Craig
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Lord...Sometimes im not that bright
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Dave2302
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2006 Mercedes S55 AMG, Retired Barefoot Waterskier
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Re: Is the Cosworth geared too tall?
« Reply #2 on: May 17th, 2010, 10:09am » |
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Yes they were overgeared from factory to "tame them".
Stuarts is very sharp with a 2.0 diff, but a little thirsty, an Ideal diff for more general road use is a 2.3 diff.
Remember tho you will need the VSS gear to keep the speedo and trip computer readings "correct", (thats another debate) lol, and also you'll need to pop the cover off the diffs and change the output flanges for the cossie ones as cossie shafts cvs are bigger.
Other than that, doddle to fit and well worth the effort.
HTH
Dave
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Dave "The 'ol Bear" ex Footer !
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faffi
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Re: Is the Cosworth geared too tall?
« Reply #3 on: May 17th, 2010, 12:56pm » |
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Sounds like something to look into - once I wriggle the Cosworth from the owner's hands
Thanks for the replies
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Highlander
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13 Scorpios, XR4x4, Suzuki SJ413 for off road :)
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Re: Is the Cosworth geared too tall?
« Reply #4 on: May 17th, 2010, 5:08pm » |
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Get the 4.27 fitted!
I can get almost 20 to the gallon with it!
I honestly think around town it does better mpg, its only when you get into top it starts to struggle as the revs sit around 1000 higher for the same speed
I like getting off the mark quick, i dont mind someone tearing past me once i level out at 80, its the pulling away bit i like
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on Oct 17th, 2011, 12:35pm, Simmo wrote:I give up !  Too much for an old boy!  |
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tlundkvi
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Re: Is the Cosworth geared too tall?
« Reply #5 on: May 17th, 2010, 7:08pm » |
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Somebody should build a 2-speed diff That would be a nice project
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faffi
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Re: Is the Cosworth geared too tall?
« Reply #6 on: May 17th, 2010, 9:16pm » |
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on May 17th, 2010, 5:08pm, Highlander wrote:Get the 4.27 fitted!
I can get almost 20 to the gallon with it!
I honestly think around town it does better mpg, its only when you get into top it starts to struggle as the revs sit around 1000 higher for the same speed
I like getting off the mark quick, i dont mind someone tearing past me once i level out at 80, its the pulling away bit i like |
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I agree - particularly since I never cruise beyond 80 mph and even that is just a few times when on vacations. Most of the year, I'm limited to 65 mph or less if I want to retain my permit and not throw money into the state treasury 
With a 4.27, the car should accelerate harder than the standard geared car all the way until it hits the rev limiter, I would assume?
4.27, is that from the 2.0 16 valver? 1000 rpm extra at 80 mph sounds substantial, tough - perhaps the 4.09 is a better compromise between relaxed crusing and strong acceleration?
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Matt
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Re: Is the Cosworth geared too tall?
« Reply #7 on: May 18th, 2010, 12:00pm » |
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stick a manual box in it and get the best of both worlds
mine shifts off the mark then at 70 does nearly 40 mpg! as its revving nearly 800 rpm lower in 5th then the autos in 4th
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FDS2000 Scans - Birmingham
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Tons_of_fun
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Re: Is the Cosworth geared too tall?
« Reply #8 on: May 18th, 2010, 12:20pm » |
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Show off :-p
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Lord...Sometimes im not that bright
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faffi
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Re: Is the Cosworth geared too tall?
« Reply #9 on: May 18th, 2010, 12:58pm » |
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on May 18th, 2010, 12:00pm, Matt wrote:stick a manual box in it and get the best of both worlds
mine shifts off the mark then at 70 does nearly 40 mpg! as its revving nearly 800 rpm lower in 5th then the autos in 4th |
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Is there a writeup somewhere about what's required for this? I once did a Granada 2.3 auto -> manual conversion - everything needed for fitting the clutch pedal etc. were in place in the auto chassis. I fitted a complete unit (gearbox and engine) so it wasn't all the much of an issue, but I expect there to be far more involved with the Scorpio?
But 800 rpm less at 70 mph - are you loping along with 1700 rpm at that speed?
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Tons_of_fun
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Re: Is the Cosworth geared too tall?
« Reply #10 on: May 18th, 2010, 3:34pm » |
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You should be sat in the car when the it's doing 6,000 rpm in 4th !!! Scary stuff
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Lord...Sometimes im not that bright
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faffi
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Re: Is the Cosworth geared too tall?
« Reply #11 on: May 18th, 2010, 7:28pm » |
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"And then, just as I hit redline in 4th at 200 mph, I shifted into 5th, floored it and produced a nice burnout on my way into outer space!"
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faffi
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Re: Is the Cosworth geared too tall?
« Reply #12 on: May 19th, 2010, 8:13am » |
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Atschoally, me thinks the two (auto and manual) have (nearly?) the same top gear reduction of 0.75, which should give the same cruising rpm for any given speed regardless of what gearbox is used. Hence, due to the lock-up function, cruising mileage should be very similar between the two. It's in city traffic where a manual gearbox should have a benefit regarding fuel consumption over the automatic - at the cost of having to give the left foot a good workout every morning getting to work
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Tons_of_fun
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Re: Is the Cosworth geared too tall?
« Reply #13 on: May 19th, 2010, 8:17am » |
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LOL. Believe me m8. A manual box makes a HUGE difference ! Matt has converted his cossie to manual & i was daft enough to go for a drive with him when it was finished. It was pulling 110 mph in 3rd before we ran out of road & the brakes got a cooking ( on private road of course.....Officer ) . I think Matt is going to throw a 2.0 ltr diff on...just for a laugh. The real crazy work will be happening a while later as a 4.0 ltr engine is due to be installed soon.....4 ltr engine + manual gearbox + 2 ltr diff = a LOT of very upset Ferrari owners lol
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Lord...Sometimes im not that bright
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faffi
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Re: Is the Cosworth geared too tall?
« Reply #14 on: May 19th, 2010, 9:05am » |
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sounds like a plan
I am definitely not questioning the enhanced performance with the manual - not wasting power on dragging the converter along with all its slip will no doubt give far better acceleration. Just having the extra gear will help.
My 2.3 manual was redlined in each gear as follows (roughly) provided it had the 0.83 ratio for 5th (which, as a 1997 model, it should):
5th: 141
4th: 117
3rd: 81
2nd: 56
1st: 32
So if we continue with that, what do we get if we change the final drive ratio from the 3.91 (I believe I saw that figure someplace recently) of the 2.3 to the 3.64 of the 2.9, we get:
5th: 151
4th: 126
3rd: 87
2nd: 60
1st: 35
Even if we say that the 2.3 had the lowest final drive ratio of 4.27 (which I do not think it has), the 2.9 would still hit 6300 rpm @ 95 mph - a far cry from 110. And if we on top of that say that the gearbox was from the latest edition, 100 mph would still be the limit.
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faffi
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Re: Is the Cosworth geared too tall?
« Reply #15 on: May 19th, 2010, 9:14am » |
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If we continue this theme and assume that the manual is the most common with the 0.83 top gear ratio and that the final drive ratio is 3.91 for the 2.3, which should make my figures fairly accurate, these are the maximum speeds for each gear with a 4.27 final reduction:
5th: 129
4th: 107
3rd: 74
2nd: 51
1st: 29
Be prepared for a lot of wheelspin, I say 
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faffi
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Re: Is the Cosworth geared too tall?
« Reply #16 on: May 19th, 2010, 9:47am » |
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Finally found the reductions on the automatic as well - I do not think they are listed in the specification section, however?
They are:
4th: 0.75
3rd: 1.00
2nd: 1.47
1st: 2.47
So let's see how a stock 2.9 will do at 6300 rpm (the 12V will be limited to 5800 rpm and hence not reach the same speeds):
4th: 168 (you'll get 166 in 5th if you fit a manual from the diesel or late 2.3)
3rd: 126
2nd: 86
1st: 51
As you can see, compared to having a 2.9 converted to a manual with the stock final drive, 1st on the auto ends up somwhere in between 1st and 2nd for a maual whereas 2nd in the auto equals 3rd in the manual and 3rd in the auto equals 4th in the manual. 5th in the manual will be quite a bit shorter than 4th in the auto, giving a better overall ratio.
So not only is the automatic hampered by a tall first gear and a resulting big cap (and drop in revs) between 1st and 2nd gear, it will also suffer above 125 mph due to its tall gearing in top. Add the slurring torque converter, and it becomes clear why the car would accelerate much harder with a manual gearbox, particularly up to 85 mph.
I would say that with the stock final drive and the low geared manual, overall gearing for the 2.9 would strike an almost ideal compromise between performance and economy as well as relaxed cruising.
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faffi
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Re: Is the Cosworth geared too tall?
« Reply #17 on: May 19th, 2010, 9:56am » |
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It's sort pf pathetic to keep on replying to one's own posts, but I need to get this off me chest
My 2.3 was listed to have 147 hp and my former 2.9 Cologne with 150hp. The latter was heavier due to having an automatic gearbox as well as aircon and some other equipment. It also had to fight the same tall gearing as the Cosworth, without the ability to rev past 5800 rpm (I believe mine hit the limiter with 5700 rpm indicated).
Still, they ran neck-and-neck to both 60 and 90 mpg with perhaps the 2.9 marginally quicker according to my unscientific timing. It also felt like it had a little better passing power compared to the small engine from what I could gather. So despite the bigger engine having more torque, which will to some degree aid acceleration, these numbers do suggest that either the 2.9 made more than 3 extra ponies in reality or the autmatic gearbox is more efficient that I have come to believe.
Any thoughts on this?
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Dave2302
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Re: Is the Cosworth geared too tall?
« Reply #18 on: May 19th, 2010, 10:25am » |
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Nice bit of maths but it's wrong.
Matt will be using a hybrid manual built from a Diesel gearbox back end and a 4x4 front half, which gives him a taller fifth gear
Also the lowest diff ratio is 2.0 and the tallest is 24V
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Dave "The 'ol Bear" ex Footer !
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faffi
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Re: Is the Cosworth geared too tall?
« Reply #19 on: May 19th, 2010, 11:25am » |
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If it's wrong, please advice so that I can correct.
Does the 4x4 use a different ratio than the 3.64? If so, you can use that to calculate any changes gear by gear if you want and have the numbers for that ratio.
The 2.0 16 has the lowest ratio of 4.27, but according to a sheet on this site it's shared with the 2.3, which I believe to be wrong. The 2.0 8 has a 4.09 ratio on its final drive. The tallest ratio is for the diesel with 3.35 IIRC.
But if we base this on the diesel manual together with the standard final drive ratio of 3.64, we get these numbers at 6300 for the Cossie:
5th: 166
4th: 126
3rd: 92
2nd: 60
1st: 35
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