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Best Gearbox ratio for Sylva Fury
Samuele - 22/5/21 at 08:45 AM

I need to have my Type 9 5-speed gearbox overhauled.
So I have the possibility to choose the gear ratio at will.
I have a Blacktop 2.0 engine about 165hp (with a good chance a Rotex compressor will be mounted, but that's another story)
225/50/15 rear tires.
Differential 3.92
What do you recommend?


adithorp - 22/5/21 at 10:39 AM

Without going the maths, my initial thought is your probably going to need a taller diff.

With 165 bhp you're probably good for 130-140mph (210-225kph)plus. Fit a SC later and you'll need gearing to suit even more. Work back from there to find the top gear you'll need for that and also check the RPM you'll get at cruising speeds (120-130kph).

Also with the weight (or rather lack of you'll be best with a "long first" set of ratios.


Samuele - 22/5/21 at 11:18 AM

I was thinking something like this in fact:
1 Gear 2.9=73Km/h
2 Gear 1.8=117Km/h
3 Gear 1.37=154Km/h
4 Gear 1.1=191Km/h
5 Gear 0.93=226Km/h
All 7500rmp

Then in case of engine development you mount a 3.6 differential
The maximum speed is not of the utmost importance to me.
Acceleration and smooth highway driving when you want to go by law


adithorp - 22/5/21 at 12:17 PM

Should be about right.

The Fury is quite comfortable place to be at highway/motorway speeds with a full screen as long as it's not reving it's head off. Your 5th should be OK at around 4000rpm.


pigeondave - 22/5/21 at 01:18 PM

I have a
BGH E8 2.8 Sporting Close
Heavy Duty
Heavy Duty Synchro
Short Input
mech speedo 7/24
1st 2.66
2nd 1.75
3rd 1.26
4th 1.00
5th 0.86

Diff is 3.89 (I think)

I wanted a smaller top gear but Chris recommended against it. I think I'm pulling about 4000rpm @80mph.

Its all mated to a Dunnell Engines Zetec option 3 but then it was changed to injection. Ended up with 224.9bhp on his engine dyno.
Soft cut is at 7500rpm, Hard cut 7700rpm.

If I were to change anything I'd look at the SPC or Tracsport as he's now known gear kits. Steve offers a 1st 2.482 or 2.29.

The only issue I've found with my current box is that I'm a bit between gears on hairpins when doing The Tour of The Alps holidays, but that could be due to wussing out a bit.

You might want to search on here to see if Jeff Wiltshire posted about his ratios. He ended up with a 397bhp phoenix.
I saw the chewed up input shaft on his type 9 so don't go too crazy with the power.

I personally think I've gone far enough with the amount of power I have. If I were to change anything more, it would be to get it as light as your one.


Samuele - 22/5/21 at 02:10 PM

Thanks everyone for the answers.
I have both a 3.6 and a 3.9 differential
I'm mounted the quaife ATB.
So I have to decide which one to take.
If you want to save weight, I recommend making the titanium rollbar.
Almost finished, the weight saving on such a large and very remarkable piece


adithorp - 22/5/21 at 03:21 PM

quote:
Originally posted by Samuele
...titanium rollbar.
Almost finished, the weight saving on such a large and very remarkable piece



obfripper - 22/5/21 at 05:34 PM

What version of the type 9 do you currently have?
If it is the loose needle roller layshaft type, i would suggest to upgrade either to a v6 stub shaft type box, or get a layshaft/gearkit that uses an uprated bearing.

I had the needle roller type with a tran-x gearkit until a couple years ago, and had to rebuild the box 4 times in 10 years, at the last stripdown the bearing surface within the layshaft had spalled and was no longer serviceable.
The tran-x straight cut layshaft is not able to accept an uprated bearing as it is built from separate gears pressed onto the shaft, i believe the quaife gearkits are also built in the same way.
This is fine in a rally car that is stripped on a regular basis, but as i found is frustrating when it fails without much warning, luckily 4th gear is largely unaffected and i was able to manage 100 miles to get home.

I changed to an spc gearkit which offers similar ratios, but uses an uprated layshaft bearing and can be bought with either straight cut or semi helical cut gears.

https://www.tracsport.com/gearkits

I used the following ratios:
1st 2.482
2nd 1.61
3rd 1.225
4th 1:1
5th 0.82
Diff 4.125:1

Gives 138mph (230kmh) top end at 7200rpm, on 185/60r13 tyres, gear ratios are nicely spaced and matched to the cars weight/engine power.

Dave


Samuele - 22/5/21 at 06:04 PM

My gearbox is a simple Type 9 not v6.
3.65
1.97
1.37
1
0.82
I have never used it, I'm not sure even if it works as well as I bought it used not being able to use it until now.
So only that 1 gear would be too short for such a car.
So I thought I'd get it overhauled by changing the ratios as well.
I was offered to assemble a Dog Box with straight teeth.
Only the first 3 gears, 4 and 5 gears instead with crooked teeth.
This is to have a silent gearbox almost like an original on the highway, while in acceleration it will make a lot of noise.
Of what you have honestly explained to me I have not understood anything because of the translation.
But it will certainly be an important thing.
I refer to what you wrote to them.
They will understand what it is.
What I understand is that I don't want to stay on foot either anyway 😁


snapper - 24/5/21 at 06:53 PM

You donít want to high a first as itíll bog off the line.
I like the 3.9 diff but makes 80mph at 4K which can be a bit of a chore on long distances
Ideal is V6 box with 2.7 1st but if you sticking with a standard box then 2.9 1st and 3.6 would probably be right.
Depends on engine redline, one of my Pintos will go to 7k the other near 8k
Get a gear speed calculator then you can check what speed in what gear. 30+ in first 60+ in 2nd is a good starting point


pigeondave - 25/5/21 at 09:28 AM

Thinking more about this.
What with your car being so light for a car engine car, maybe it would be worth looking at what ratios the bike engine cars use.

My car is 610kg with 20litres of fuel, so my experience is based on this. Someone above has mentioned that if first is too long, the car will bog down, but your car will be light so this might not be so much of an issue.


peter030371 - 25/5/21 at 12:13 PM

The Tracsport T9 Semi Helical Gearkit would be ideal for your car by the sounds of it. 2.482 1st and 0.82 5th would be great for fast road use. Its also a very light gearkit so another reason you would like it

They also do some mice alloy parts to save a few more kg


G13BLocost - 25/5/21 at 05:59 PM

I am of the opinion that a flat torque curve and your shift points can make up for, or is more important than, specific gear ratios. Just a thought.

I made a drag race simulation that would suggest that this is maybe the case: http://www.ogilvieracing.com/holiday-drag-racing-part-1-2/


hobbsy - 28/5/21 at 05:14 AM

quote:
Originally posted by adithorp
quote:
Originally posted by Samuele
...titanium rollbar.
Almost finished, the weight saving on such a large and very remarkable piece





I'm curious about a cage / rollbar made from titanium.

What was the weight saving compared to steel and did you redesign it at all based on the different properties of titanium Vs steel?

Hobbsy


procomp - 28/5/21 at 05:25 PM

The better ratios for a lightweight car will be very close to these below if using a 3.9 diff ratio assuming 205 60 13 rubber.
these will get you round every circuit in the UK for trackday and spirited road use. For out right race usage go for a 2.04 1st

1st - 2.39
2nd - 1.69
3rd - 1.21
4th - 1:1
5th - 0.87


stevebubs - 28/5/21 at 09:45 PM

Mine has a 3.89 with Std Type 9 and 3.89 diff. Would prefer a 3.54 for longer distance cruising...


Samuele - 31/5/21 at 08:08 PM

quote:
Originally posted by hobbsy
quote:
Originally posted by adithorp
quote:
Originally posted by Samuele
...titanium rollbar.
Almost finished, the weight saving on such a large and very remarkable piece





I'm curious about a cage / rollbar made from titanium.

What was the weight saving compared to steel and did you redesign it at all based on the different properties of titanium Vs steel?

Hobbsy

I didn't want to change anything regarding the form, the T‹V here would have noticed it immediately and I would have had only problems.
I only worked on the thickness of the tubes.
Titanium is much stronger than iron.
The total weight is now 2.9kg.
Using 38mm tubes.
I do not post more photos of my construction here as every time, after a few months that I have put photos,
then they no longer see each other either because the company goes bankrupt or for other unclear reasons


Samuele - 31/5/21 at 08:09 PM

quote:
Originally posted by procomp
The better ratios for a lightweight car will be very close to these below if using a 3.9 diff ratio assuming 205 60 13 rubber.
these will get you round every circuit in the UK for trackday and spirited road use. For out right race usage go for a 2.04 1st

1st - 2.39
2nd - 1.69
3rd - 1.21
4th - 1:1
5th - 0.87


Anyway, always talking about car engines,
quite right?