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Engine Specific Info and Questions => IDI Engine => Topic started by: Northboundtrain on January 25, 2007, 12:01:14 pm
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Can anyone tell me at what RPM the 1.6 makes peak torque? I'm installing a new engine (and maybe tranny) in my '91 Jetta. The current tranny has a 0.89 5th gear and a 3.94 final drive. By my calculations, with 22" tires, I'm doing about 3,750 rpm at 70 mph, which seems too high for optimal fuel economy. I have an older tranny that I think has a 0.71 5th and a 3.89 final drive. That translates to about 2,950 rpm at 70 mph, which seems better. But would even lower rpms get better torque from the engine and thus better efficiency (that's why I'd like to know the peak torque rpm)? If so, has anyone heard of modifying the final drive ratio?
Information, opinions, suggestions greatly appreciated.
Thanks
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i think peak torque is around 2400
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www.brokevw.com for lots of tranny info
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According to http://www.4crawler.com/Diesel/SAE/vwtdsae.shtml, "The maximum torque is 102 Nm at 2000 rpm." This is in a section on the 1.5/1.6 engine family, so I'm not sure if that is true for the latest versions of the engine. The paper does also mention that "The latest development of the naturally aspirated Diesel engine was concluded in early 1981..."
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my manual states peak torque in the 1.5 NA is at 3000 rpm, and in the 1.6 is at 2800 rpm.
i can certainly vouch for the figure in the 1.5, thats where all the power begins (what little there is).
the only difference is stroke, so i'd say that thats where it'll be, a bit below 3k.
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Hmmm, some different numbers here. Just out of curiosity, what factors affect peak torque rpm, other than stroke length? Here's an engine with a slightly smaller displacement than the 1.6L, shorter stroke, same number of cylinders, and similar compression ratio. It supposedly makes peak torque at 1,700 rpm.
http://www.perkins.com/cda/files/334142/7/404d-15%20engine%20(pn1818%20-%20mar06).pdf
According to the chart on brokevw.com, The tallest gears available are in the code 6G transmission. If I get this tranny, the flanges are 90 mm. So I would have to get new axles, which is no big deal if they will fit into the existing hubs. I just did a front end job to this car, and I know the wheel bearings are a different size than those on the older A1 generation cars that had the 90 mm flange tranny. Are the hubs a different size too? I guess I could also just swap the inner CV joint if the older axles don't fit the newer hubs. Also, what about the tranny mounts -- A1 tranny going in an A2 chassis?
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i've always known perkins to be extremely powerful engines... i know a guy who installed one into a mazda truck.. 4 cylinder. he said the body would give first if dragging something really heavy.
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I would say that the peak torque would depend on the pump and turbo setup. The cam would also dictate it but you could move the torque around a bit with the size of turbo and how your pump delivers fuel. I bet if you run a small turbo yor peak torque may be in the low 2 grand area.
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According to the chart on brokevw.com, The tallest gears available are in the code 6G transmission. If I get this tranny, the flanges are 90 mm. So I would have to get new axles, which is no big deal if they will fit into the existing hubs. I just did a front end job to this car, and I know the wheel bearings are a different size than those on the older A1 generation cars that had the 90 mm flange tranny. Are the hubs a different size too? I guess I could also just swap the inner CV joint if the older axles don't fit the newer hubs. Also, what about the tranny mounts -- A1 tranny going in an A2 chassis?
I'm pretty sure that the hubs are the same (all A2 the same, all A1 the same) You can run either 100 or 90mm cvs with any tranny. All you have to do is swap the flanges on the transmission. It's a good idea to change those seals in there anyways.
A1 tranny will not work in a mk2 unless you make a custom mount. A couple of the holes are missing on the casing as you can see here
(http://www.brokevw.com/pic%20086pp.JPG)
I want to run a mk1 tranny in my mk2 but I haven't tried anything yet
As far as factors effecting torque, the speed that the air is forced into the engine also is a factor IIRC
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Well that's good to know -- that a A1/MK1 tranny won't bolt right in to a A2/MK2 chassis. Can anyone recommend the best tranny to get given that I want the tallest gears possible. From the chart on brokevw.com, it looks like there are several options that have an overall (differential multiplied by 5th) ratio of 2.75:1, which is the tallest listed for 100 mm flanges (I'm assuming 100 mm flanges mean A2/MK2).
Thanks again.
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I have an A1 transmission out of an 84 Jetta in my 85 Coupe. For some reason it has the extra holes. I'm not sure of the gear ratios or final drive but they're much higher than in the tranny I took out. I found myself having to downshift to 4th on hills that I got over in 5th with the old tranny.
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...Can anyone recommend the best tranny to get given that I want the tallest gears possible. ...
for my NA's I prefer ASF or ACN (gas trannies), but... I'm concerned about your altitude, as my NA's have to be pretty healthy to comfortably pull 5th in those tall boxes. (at 500-1500ft altitude) The AGS ('86 TD trannie) is my favorite general purpose diesel ratio. I had a 9A close ratio that I changed to a .75 fifth that was as sweet Mountain trannie (3 gears between 35 and 50).
I took my A2 Jetta w/ 1.9 NA w/ ASF to Montana and it was noticably 'challenged' at altitude, climbing passes. Oh, the TDI likes mtns :D I'm currently making an A2 GTD, and will probably use the (9A with modified (.75) fifth.)
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which is the tallest listed for 100 mm flanges (I'm assuming 100 mm flanges mean A2/MK2).
Dangerous assumption. Most of the mk2s are 90mm, 16Vs for the most part are only 100mm, there are a couple 8vs that were 100mm, but never a diesel (that I know of)
It's been a while since I looked but I think an AGS with a swapped 5th (0.71) would give you the absolute highest gearing in 5th, short of using a 4 speed 4A. I have a 4S and I really enjoy it. I have small winters on my car and am at 2600 at 100kmh (60mph)
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So the ACN will have me spinning 2,950 rpm at 70 mph, which is way better than the current 3,700 that I'm doing at that speed. I'm doing everything I can to get more out of the new engine I'm rebuilding -- ported head, opened up exhaust, giles pump, cold air intake. So I don't think the engine should have trouble with the taller gears.
One thing I don't get: the gasser trannys have taller gears than the diesels. Why?
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According to http://www.4crawler.com/Diesel/SAE/vwtdsae.shtml, "The maximum torque is 102 Nm at 2000 rpm." This is in a section on the 1.5/1.6 engine family, so I'm not sure if that is true for the latest versions of the engine. The paper does also mention that "The latest development of the naturally aspirated Diesel engine was concluded in early 1981..."
That is for the 1.6TD, the 1.6D is 71 ft,lbs. @ 2500 RPM:
http://www.4crawler.com/Diesel/index.shtml#EngineSpecs
I just got done having a 3.67 final drive installed in my FN transaxle. Gives me around 2600 RPM @ 70 MPH. It did take a bit of the pep out of 5th gear (1.9D engine), but is still very driveable.
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One thing I don't get: the gasser trannys have taller gears than the diesels. Why?
I think it is because they rev higher and make more power up top
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[quote="burn_your_mooney]I think it is because they rev higher and make more power up top[/quote]
What?
Gas engines rev higher and make peak torque at a higher rpm, so the gears should be shorter on gas engines. Doesn't make sense to me at all.
I'm kind of curious why VW did this.
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well if you look at a 52hp motor vs a 100 hp motor, the 100 hp motor can have taller gears and still accelerate quite quickly... put that same tranny in a 52hp motor and... slow accel.
those big yellow school buses have really low gearing... bad for highway mileage but they can really zoom up to 50km/h where they normally cruise around town... get it now? :)
its not really until the turbo diesels which achieve more torque at lower rpm's that vw installed some really nice tall tranny's...
(http://img395.imageshack.us/img395/2712/comparison2jl9.jpg)
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Yeah I get it. But it makes you wonder what VW was thinking if they made an engine so underpowered that they put in trannys that required reving to nearly 4 grand just to go down the highway. Kind of defeats the purpose of the diesel engine.
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Yeah I get it. But it makes you wonder what VW was thinking if they made an engine so underpowered that they put in trannys that required reving to nearly 4 grand just to go down the highway. Kind of defeats the purpose of the diesel engine.
tell me about it... my current tranny has to be a swap in from a different type of motor, as even andy2 was saying the gearing is too tall... 3200 rpm gets me to about 100km/h or 60 mph... it just plain SUCKS... back my fuel!!! argh :lol:
but i never have to downshift.. my old jetta i had to on a couple of long steep stretches... but my old jetta also did 160km/h @ 3800 rpm... 8)
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One thing many of the NA diesel transaxles have is a very tall 5th gear. So that makes up for the final drive, giving a 2.77:1 ratio in 5th on the FN transaxle for example. I have a 2.57:1 ratio with my rebuilt FN (3.67 final drive and 0.71 5th gear).
You get the lower overall gearing in 1st to get going, since all the 020s seem to have the same 1st gear ratio (3.45). Ideally you would also like a 6 speed tranny for the diesel, since they can't rev as high, nicer to have more gears spaced closer. Also have to consider that the US speed limit was 55 for much of the time that the early diesels were designed for this market. I know my old '81 did really well @ 55, but when the speed limits went up to 65 it struggled a lot more and MPG fell.
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but i never have to downshift.. my old jetta i had to on a couple of long steep stretches... but my old jetta also did 160km/h @ 3800 rpm... 8)
and what was this jetta my 86 gasser goes 160 at 5000 rpm tell me where do i find this 160 at 3800 (german autobaun) trans
Craig
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hehe i can't quite claim 3800 because the car didn't really have a tachometer... i was mainly going by engine sound... the car still had plenty left and let me tell you... the turbo in that thing ripped! it did 120km/h with ease... 100km/h was hard to hold because the turbo would start to kick in and start doing around 110km/h and if i didnt watch it, it would creep up to 120km/h where it loved to cruise at.
mechanical lifter is definitely more powerful. :) and the turbo must have been a garrett T3... very laggy though... wouldn't come on till 3k rpm or so. (again im just judging by engine sound... but i am a pretty good judge of engine sound/noise)
i believe it was either an ACL or ACN. ACL came with 100mm axle flanges... it was a '86 Jetta GL no a/c... no PS... i loved it!!!!!! get popey arms pretty quick lol... less to break IMO
the sheet says that the ACL or ACN will do 160km/h @ 4000rpm so I wasn't terribly off :)
i recently bought a nice CHE trans with the 0.71 5th gear fitted... now that tranny will do 100mph / 160km/h @ 3800 :D
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So can anyone turn me onto a good tranny rebuilder? I have an old 5 speed that came out of a A1/MK1. Will I be able to send it in as a core for an ACN?
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German Transaxle in Bend Oregon is decent:
- http://www.gtainc.biz/
(looks like they may be having some web server problems right now)
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German Transaxle in Bend Oregon is decent:
- http://www.gtainc.biz/
Thanks, I'll give them a call.
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you can usually be ok with a used gas tranny, as they willl outlast (gas) engine ~ 3 to 1, and the 'cruiser' trannies are less likely to be hammered (not GLI / GTI) You can switch 100mm flanges to 90mm, or use the 100mm shafts. I built a spring compression tool from threaded rod that enables the flange swamp pretty easy. A starter bolt and some shims will work.
Your stock Diesel trannie is in big demand with gas racers, they will usually trade you 2 gas trannies for one diesel with your huge Ring gear. Vortex is a good spot to get trannies, or a local 'u-pull-it', or buy a dead gasser and part it out
The reason VW put this gearing in the '91 and '92 was to meet emission requirements (and they cut out the fuel enrichment on the TD. ) Mine seem to get better mileage running high RPM... but its not good on the ears.