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Author: Subject: Diff ratios and gearbox
ren

posted on 21/12/17 at 10:31 PM Reply With Quote
Diff ratios and gearbox

Sorry if these questions sound ridiculous this is my first post.
I have a Sylva Striker with Vauxhall Red Top 2.0 engine wihich has been rebuilt and now produces 220 bhp.
Like all things you always want a bit more acceleration which i am looking for rather than the top end speed.
What diff ratio would be best to improve acceleration( i think at the moment it is 3.5 but not sure how to check) and what would i need to do with the Ford r9 gearbox to compensate
on any diff changes,
I live on the Isle of Wight and wondered if anybody knows who would be able to do this in the Southampton area.
Thanks

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JimSpencer

posted on 21/12/17 at 11:46 PM Reply With Quote
Hi

Ok what you really need to decide is what you want the car for.

If it's mainly road use then gear it to hit the aero wall (circa 130ish) at max revs in 4th and keep 5th for cruising along a bit..

If it's for track work then you do the same but for 5th..

So for example using a 5.1:1 diff ratio, my Striker is geared for 127 mph at 8.5k (4AGE and built for it) in 5th.
It's very quick on the track and pulls like a train, but is completely hopeless on the road as at a sensible cruising speed it's doing loads of revs and would drive you nuts..

I would have thought a well built Redtop is good for around 7k revs, so you'd probably be looking at a 4.1 or 4.4 at the most?

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ren

posted on 21/12/17 at 11:52 PM Reply With Quote
diff ratio and gearbox

Thanks for your reply the car is for road not track
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Ugg10

posted on 22/12/17 at 12:27 AM Reply With Quote
What rear axle? Live I guess so currently a 3.54. Options are 3.77, 3.89, true 3.9, 4.1 and 4.4 plus other specials.

For type 9 the usual upgrade is either a bgh heavy duty long first box or a spc semi helical. If you haven’t sorted out 1st gear this is a must (made it longer, something like 2.8 to 2.5 would be good ) or put in the caterham six speed if you can find one, very close ratios though.

There is a good calculator on here http://www.subarugears.com/Ratios/Ratios.html





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1968 Ford Anglia 105e, 1.7 Zetec SE, Mk2 Escort Workd Cup front end, 5 link rear
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ren

posted on 22/12/17 at 10:35 AM Reply With Quote
diff ratio and gearbox

Thanks, does the change in diff and gearbox make a noticeable change in acceleration/
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alfas

posted on 22/12/17 at 08:36 PM Reply With Quote
ok...lots have been said already...but some important things are missing:

first of all: what size of wheels (exact tyre size) are fitted to your car? the bigger the wheels (diameter /circmference) the longer the final drive ratio.
i guess you are talking about a live-axle striker? correct?
than you have a ford escort english / timken axle

3,54 is fitted, 3,77 is rare, 3,89 easily availabe, 4,11 also....the rest (4,4 and plus) are not really suitbale for road use in combi with your engine
the shorter the diff, the better the acceleration.
to compensate the higher rev´s you need to shift earlier and more often...but when you have reached the 5th gear....than you are at the end.
it makes no sense to change gearbox ratios in 1st, 2nd gear....as you will always end in the 5th...and this is THE gear which reduces the revs during cruising.

never heard of uprated ratios for the 5th

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ren

posted on 22/12/17 at 09:20 PM Reply With Quote
diff ratios transmission

Hi

Thanks for your response.
It is is a live escort axle 3.54 the tyres are R195/50.
Garages i speak to say up the diff ratio to 4.1 and leave the gear box as it is.
It all gets a bit confusing.

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alfas

posted on 22/12/17 at 09:46 PM Reply With Quote
195/50 and??? 13,15,17 19, 25 inch wheels?? THE most important info is missing

another question: how do you know the power-output of your engine? have you personaly be present during a dyno run?

you say you have a 3.54 diff, but you dont knwo how to check if its 3.54....so more or less the only sure info we know is that you have an escort diff.

i dont know how many sellers told me "it has a 3,54 diff" and finally it turned out to be a 3,89.....the 3.54 diffs seem to have a bit more value within the ford escort-community...hence lots of sellers are taling about RS200 diff or 3.54....even they dont know if it has been really fitted

also, with "real" 220HP you may not want to have more acceleration?

do you have some specs of your engine?
lots of sellers ttell you 150HP for a Pinto or 135Hp for a x/flow..and whn you put the on the dyno the output is 115 and 105...due to poor settings or tuning-components not matching etc....
your non-existing 220HP might be the reason that you whish more acceleration? i dont know, as i dont know not enough about you and your car.


checking diff-ratio:

jack-up the car, mark wheels and propshaft flange with a white pen or stickers. turn BOTH wheels SIMUTANIOUSLY 1 turn and count the rev´s of the input flange

1 turn of the wheels - 3,5 turns of the flange---> diff rato 3,54:1




[Edited on 22/12/17 by alfas]

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ren

posted on 22/12/17 at 10:15 PM Reply With Quote
diff ratio and gearbox

Hello
THANKS FOR YOUR INFO.
I forgot the R15 on the tyres.
The car was purchased earlier in the year and was RR tested in January from the information i was given.
It has been gas flowed/ported 2.0 Red Top engine running ZX9R bike carbs, Veneer pulleys, Kent Cams, big end bearings , APR bolts and high pressure oil pump.
But i think there is a bit more acceleration to be had.
Thanks

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Ugg10

posted on 22/12/17 at 10:28 PM Reply With Quote
If it’s a 3.54, I have a 3.89 on the shelf and a 4.125 that can be taken out my car if you fancy a swap for either? I am looking to go the other way, more relaxed.

[Edited on 22/12/17 by Ugg10]





---------------------------------------------------------------
1968 Ford Anglia 105e, 1.7 Zetec SE, Mk2 Escort Workd Cup front end, 5 link rear
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ren

posted on 22/12/17 at 10:39 PM Reply With Quote
diff ratio and gearbox

That sounds like a good deal.
I will get my garage to double check the diff ratio, unfortunately even though it has been explained how to check it i am still not sure.
It will be after xmas if that is o.k.
If it is i will contact you.

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Ugg10

posted on 22/12/17 at 10:55 PM Reply With Quote
Sounds like a plan.

As above, if you are single handed, jack up one rear wheel, chock the other wheel and front wheels to stop it rolling (with a brick). Put into neutral.
Put a price of tape on the jacked up wheel, set the tape to the top of the wheel, now put tape on the prop shaft where you can see it. Rotate the wheel ten times counting the number of times the prop shaft rotates. (More accurate than one time).

Once you have that number double it (or half, can’t remember but you are looking for a number between 3.5 and 4.5 in the end) and divide by 10. This is your diff ratio.

If in doubt post the number of times the wheel and prop rotate and I can calculate (hopefully).

If there are two of you the above method turning both wheels is easier.

Obviously the 3.89 would be easier for me but if 4.125 is better let me know and I will take it out.

Whereabouts are you (IoW?), I am just the other side of Chichester and regularly travel the south coast.

Thanks. Speak after Christmas.





---------------------------------------------------------------
1968 Ford Anglia 105e, 1.7 Zetec SE, Mk2 Escort Workd Cup front end, 5 link rear
Build Blog - http://Anglia1968.weebly.com

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Oddified

posted on 22/12/17 at 11:12 PM Reply With Quote
Whilst a different engine and a rev limiter at 8500rpm, i have an SPC semi helical gearset in a type 9 box, and 4.1 diff which is a reasonable compromise using the car on the road, track and drag racing.

I've had a 3.7 cwp, great on the road but lost a bit too much zip on track/drag racing. Also a 4.6 cwp which was great on track/drag racing but a bit mind numbing on the road on a run.

Ian

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procomp

posted on 22/12/17 at 11:18 PM Reply With Quote
Hi. As your on the IOW theres a large group of lads with kitcar experience on the island runing the local motor club.
They will gladley tell you what your diff ratio is with a quick check.

With 220hp and torque of a redtop it may well be a 3.54 diff just to make 1st gear useable assuming its a std 3.65 ratio. If you move to a 3.9 diff ratio 1st gear would become virtualy redundant. The cheap option would be to use a V6 type 9 1st gear ratio to help which is a common upgrade.
The best or ideal ratios would be 1st - 2.04 or 2.2 and a 5th ratio of. 0.87. But those ratios only come in competition boxes that are straight cut and noisy for road use not to mention expencive.

If you want contact details for the group of lads on the IOW u2u and ill pass contact details on.

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snapper

posted on 23/12/17 at 07:18 AM Reply With Quote
Gear speed calculator

3.9 ish is a pretty good ratio to go for as a compromise for road

The limiting factors are 2 fold, maximum engine revs and first gear ratio
Maximum engine revs effectively narrow the gaps between gears as you can hang on to a gear for longer making the lower gears more usable.
1st gear ratio is a compromise between getting off the line cleanly without excessive wheel spin or bogging down and having a usable speed before having to change up.
I run a 3.9 diff on 195 60 14 with a V6 Type 9 gearbox. This has the longer 1st (3.3) 2nd (1.81) and 3rd (1.21) gear, just needs a 4 pot bellhousing and a spacer or cut back the input shaft.

After some years of running the type 9 box I think the ideal 1st gear ratio would be 2.7





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alfas

posted on 23/12/17 at 07:54 AM Reply With Quote
before you make any deals for swaping diffs, make first sure what diff ratio you have and furthermore make sure that you dont have a LSD fitted.
swapng a LSD diff against a standard one woldnt be a good deal. with such a spec of car you may have a LSD fitted.

from wheel size you are ok....means not too big....sure the easiest way to generate more acceleration would be using smaller wheels...but we are talking here of 185/60r13


now to the engine:
you think that a standard 150HP engine (which might not had all HP left when taken out from the donor) is generating 220HP by sticking-in 2 cams and bike carbs?
no way. that might be your "real" problem....i pressume that the engine-output is not more than 170HP.


without a dyno-print out where you have been personally present during the dyno run, i would not bellieve anything.

its already some years ago where i owned a kitcar with xe-engine....45weber carbs...was running really nice....but i always missed some torque.....first i put it fown on the carbs, than in the webcon ignition...indead the webcon ignition showed some problems which we solved....but still no improvement of the torque.....than i checked the cam-timing...and here we go: the inlet cam wasnt perfectly timed (even the engine was running well and smooth)...after re-timing the car went like stink and the intake noise was also much deeper

i could name you another several x/flow engines where the sellers claimed 130 to 150hp and on the dyno they came out with 102-106

since that time i always question what sellers tell me as long i have not got a personal prove of the reality.

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Ugg10

posted on 23/12/17 at 08:31 PM Reply With Quote
http://www.englishdiff.co.uk/uploads/3/8/0/5/3805061/ford_english_diff_information.docx

Link above give the numbers of teeth/splines on the crown wheel and pinion. Once out the the number will be stamped on the side of the crown wheel. If it is a 3.54 this will be 11-39.





---------------------------------------------------------------
1968 Ford Anglia 105e, 1.7 Zetec SE, Mk2 Escort Workd Cup front end, 5 link rear
Build Blog - http://Anglia1968.weebly.com

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ren

posted on 23/12/17 at 08:39 PM Reply With Quote
diff ratio and gearbox

Thanks
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alfas

posted on 27/12/17 at 03:20 PM Reply With Quote
another important info..if you change diff´s ou might not want to disasemble the new one for changing prop-shaft flanges:

there are different diameters of prop-shaft flanges existing...the ideal solution would be that the new diff would have the same flange-size as the existing one.

you can also check with the turbosport guys in their forum about a diff swap....you may get a 3.89 diff, plus some money on top for a 3.54....the 3.54´s are more valuable...

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