5 replies to this topic

[cartneil]

Hi all,

 

I am just in the process of completing the engine/gearbox set up to go in my mpi, which has been fully restored, but ensure of which FD ratio would be best. I have searched the forums, but the questions asked are for carb models with 4 speed boxes with straight cut gears, where mine is mpi with a minispares 5 speed helical close ratio 'box.

My full spec is -

1330 block

Specialist Components supersports head

swiftune SW5 cam

specialist components typhoon ECU 

Minispares 5 speed gearbox (helical close ratio)

 

I am torn between going with the 3.44 ratio, as most people say it will get off the line without klighting the tyres up, but will give good acceleration to keep up with the more modern hot hatches.

However, with having 5 gears, and the 5th being an overdrive, I'm not sure whether I should go with 3.6? It will obviously get going quicker, but the SW5 cam is supposed to pull well from lower revs, so don't want to 'run out of legs' to quickly in each gear, plus do want to retain the 5th gear to be reasonably quiet and not screaming away at 60-70mph.

With the 3.44 FD, it gives about 3.01 ish FD in 5th. With 3.6, it pushes 5th up to about 3.2 equivalent FD.

This isn't an everyday car, but also not a track car, just a weekend country road blaster, with the ability to cruise without needing ear plugs!

 

Any advice/experience, very much appreciated!

[MiniCarJack]

I think if it were me personally I'd lean toward the 3.44 ratio, with a standard 4 speed box it offers a good compromise between acceleration and comfort at motorway cruising speed. With an overdriven 5th gear it'd make motorways an absolute breeze and would make the car much more drivable on modern roads - of course I'd say this though because I live right by a motorway and use it frequently! With that in mind it really depends on what sort of driving you plan to do with the car, ie if motorways are going to be few and far between, you might find that the 3.6 is actually the better choice. All comes down to personal preference really.

[Cooperman]

With an overdrive 5th I would go with the 3.44:1.
You will then find that you can always keep the engine right in the power band with a 266 and the gap between the gears will be ideal.

[Spider]

I'd suggest working out and comparing overall ratios in all gears to get a better picture here.

From my own experience with 85HP + at the front wheel, when getting shorter than 12:1 in first gear on an open diff, one wheel lights up really easily to the point of being annoying.  You might want to compare all other gears to something you've previously driven with so you have a better picture of what to expect.

 

[Alice Dooper]

Jealous!!  I’d love to have this problem.   

[Midas Mk1]

My sw5 +1.5 rockers pulls hard right upto 6250, limiter set at 6.6k.
Run both 3.2 and 3.1, 3.1 nicer cruising at high speed.