Eternal
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| posted on 17/3/11 at 08:18 PM |
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Diff <-> Engine alignment/height
OK i got the engine and gearbox to dead center that was quite easy.
The problem im having is getting the diff and gearbox to line up. Im 15mm out on height but that left 50mm of sump under the chassis rails. I could
get the cast ally sump cut down but its winged and would cost a fortune to get done. Also have a steel sump but that needs baffles and all kinds being
done to it (same height as ally sump).
My question is this... what is the max drop that is allowed from the engine to the diff and over what distance? As if i can raise the engine a little
more that would solve all the problems with clearance. Also the top of the engine is 200mm above the top chassis rails so thats ok the hood im going
to make will have a bulge so can go higher if needed. Any advice more than welcome!
:Also posted on haynes forum:
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adithorp
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| posted on 17/3/11 at 08:42 PM |
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The important thing with prop' alignment is that the center lines of the diff input and gearbox output shafts are parallel to each other,
otherwise the joints will cause vibration. It's also an advantage to have them out of line with small angles on the UJ's. This means the
rollers bearings move in the joint; If they don't have to move they wear out fast with constant pressure in one spot. You should be able to find
reference to the max' angle for the UJ's on Bailey Morris' site.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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Eternal
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| posted on 17/3/11 at 09:08 PM |
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Ok measured the length i would need in its current position.
Using UJ's that are 40mm from the face of the diff and gearbox the shaft would need to be about 500mm from center of UJ to center.
This would give a drive shaft angle of 1.72° over 500mm going 15mm heigh
Idealy i would like to be 500mm going 30mm high that gives 3.43°.
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daviep
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| posted on 17/3/11 at 09:25 PM |
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You need to know what series of propshaft joints you are using and what the max prop rpm will be before you can work out what the max allowable prop
angle will be.
For example: I'm using an 1140 series joints and at 120mph my prop is doing about 6300rpm. Based on this I can run up to 4 degrees of
misalignment, which is roughly 70mm rise per metre.
Links to all the tools I used to work this out:
Flange dimensions to work out which joints you have HERE
Graphs showing speed versus angle
HERE
Triangle calculator for working out maximum rise for a given angle and length of shaft (because I'm too lazy to do trig )
HERE
Tyre circumfrence calc so you can work out prop rpm based on anticipated top speed and diff ratio if you don't know gearbox ratios
HERE
Cheers
Davie
“A truly great library contains something in it to offend everyone.”
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Eternal
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| posted on 17/3/11 at 09:45 PM |
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fantastic thanks for those links. Well it seems that no joints can take 7900rpm that i would get if i got to 6k rpm @5th gear doing 162mph
:Edit: i got prop and drive shaft mixed up heh. Right! Max drive shaft RPM @ 6k in 5th = 2171.74rpm on the drive shaft. So that means looking at that
chart any joints will take upto 5° at that rpm.
But here are my details.
Diff 3.64 LSD
1st - 3.321
2nd - 1.902
3rd - 1.308
4th - 1
5th - 0.759
6k redline
Rims 225/40/18's
Top calculated Ideal speed 162mph
Maby im doing the calculations wrong.
[Edited on 17/3/11 by Eternal]
[Edited on 17/3/11 by Eternal]
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daviep
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| posted on 17/3/11 at 09:59 PM |
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quote:
Originally posted by Eternal
fantastic thanks for those links. Well it seems that no joints can take 7900rpm that i would get if i got to 6k rpm @5th gear doing 162mph
:Edit: i got prop and drive shaft mixed up heh. Right! Max drive shaft RPM @ 6k in 5th = 2171.74rpm on the drive shaft. So that means looking at that
chart any joints will take upto 5° at that rpm.
But here are my details.
Diff 3.64 LSD
1st - 3.321
2nd - 1.902
3rd - 1.308
4th - 1
5th - 0.759
6k redline
Rims 225/40/18's
Top calculated Ideal speed 162mph
Maby im doing the calculations wrong.
[Edited on 17/3/11 by Eternal]
[Edited on 17/3/11 by Eternal]
No you were right the first time when you got 7900rpm (6000/0.759=7905 for 6000rpm and top gear) but unless you have about 500hp then you'll
never manage to do 160 in a 7.
Are you making the prop yourself or buying it? If the latter then your chosen vendor will be able to advise more accurately.
Davie
“A truly great library contains something in it to offend everyone.”
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Eternal
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| posted on 17/3/11 at 10:07 PM |
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Oh yeah simple when you put it that way. The engine will be a max of 350bhp atm its running around 250.
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Chippy
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| posted on 17/3/11 at 11:32 PM |
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Your top speed will be dictated by how many RPM your engine can take without going BANG in a very expensive manner! My V6 for instance has the rev
limiter set at 6250, and with the 3.62 lsd diff tops out at 143 MPH, been there done that, (private road of course). For this reason I am about to fit
a 3.14 diff which apart from giving me a bit economy, will lift the, (in theory), top speed to around 160 MPH, should I ever have the donads to go
there. HTH Ray
To make a car go faster, just add lightness. Colin Chapman - OR - fit a bigger engine. Chippy
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Eternal
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| posted on 17/3/11 at 11:35 PM |
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Indeed. I have stuck to more or less the standard skyline ratio and wheel size. So the top speed ect is about the same. Also whats a real pain is i
dont have the slip yoke for my gearbox >_< SR20DET/RB25DE/RB20DET gearbox. So its kinda hard to tell the prop shaft people what i need and even
if they knew they probably would not be able to supply one. Doh! Who do you guys use?
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matt_gsxr
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| posted on 18/3/11 at 12:00 AM |
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Bailey Morris were good when I used them.
Definitely worth giving them a call, all they do is prop-shafts so they should know some stuff.
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Eternal
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| posted on 18/3/11 at 12:14 PM |
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Just rang Bailey Morris and they said anywhere between 3-5 is ideal. So i can lift the engine by another 15mm with no problems. This allows the bell
housing to be a little higher and also the sump (will mod it at a later date). This will leave me with 35mm of sump below the chassis rail and that is
not too bad.
Next thing i need to do is get the engine sitting parallel to the diff. Anyone have any tips or tricks?
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