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SPITFIRE DIFF/SUSPENSION

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Hi guys, here's a question for you all. I am fiting the straight six into my 1500 spitfire, and really hadn't looked at any upgrades apart from springs and shocks, but i started going through older posts and it seems many have swapped out the diff and gone to rotoflex uprgades is this something that i need to think about doing, how bad is the swing spring/ standard arrangement for the odd track day. I would rather think about doing it if needed whilst the body is off and before I get the chassis painted, regards wayne.

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Rotoflex / Swing Spring a good idea (I like the Rotoflex more ), but please consider to upgrade the brakes to GT6 / Vitesse spec.

Regarding diff I have the 3.89 in the GT6 and like the acceleration on tracks :) 

Cheers

Martin

Edited by Martin

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Well as the sequence on the GT6 went Swing Axle/Fixed Spring, Rotoflex, Swing Spring this would imply that as I don't think there were any complaints when they finally went swing spring, that its up to the job, and also saves a lot of weight. 

Not sure but I think the GT6 swing spring was heavier duty than the Spit one, but as you are converting a Spit and don't have the extra GT6 rear weight it should be all right.

If you want to keep options open, you could always weld the Rotoflex brackets on whilst body off and easy, keep the swing spring, and if you want to try rotoflex later you are good to just bolt everything on.

I'd concur with Martin upgrade the Front Brakes, you have a lot more weight up there, not to say a few more HP.

Alan

 

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Deffo move away from swing axle, as the half shafts have the design fault that loses wheels (Alan corrected me when I tried to describe it in detail, so I won't risk that again!)

But if you want to consider that, why not avoid Rotaflex donut problems and consider CV jointed transmission?      Well documented in various forms here.

John

 

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Thanks guys that’s most helpful, it has been the threads on here that got me thinking and John it was the cv upgrade that i was really meaning, so I need to do more reading to understand the process, thanks again for all the help Wayne 

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I will add as i can't see how to edit my last post, the breaks will be upgraded and going to vented discs, i have gone from a simple rebuild to going ott but I do want it to handle stop and something to enjoy 

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So after going through posts I have decided to go ahead and fit cv jointed transmition if I go and change the diff at the same time whilst the body is off for a subaru diff and make the plates ect, which ratio would suite the 2l straight six with a gt6 gearbox and overdrive, I am thinking easier to do the mods now than mess around later on, many regards wayne

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Go on, do it!

Ratio is tricky. I started with a 3.7 (1800 zetec) but found it a tad too long so cahnged to a 3.9 which suited the engine/gearing better on track. Changed engine to ST170 with VVT (much better torque curve) and have now swapped back to 3.7....

Trouble is 3.7 is a bit rare, though they are about if you are patient. Other issue is that many sellers are clueless about the ratio, as there is a drop ratio in the gearbox (so I was sold a 3.9 ratio diff, turns up as a 3.54! Seller needed educating) Also worth noting there are different types of CV joint that plug into the diff, you need the correct type to match the diff. That caught me out...

Anyway, ratio depends on what you want to use the car for. 3.9 is a perfect match to the original ratio used in an OD GT6. If you want more relaxed cruising, then 3.7 or even 3.5. I would probably find a 3.7 with overdrive gearbox.

Now, I expect you have found the NZ brackets etc. I fractured the front bracket on my car, and if I had the body off I would have remade the chassis diff mounts to match the front of the subaru diff. It would be a better solution. But I remade the bracket using 8mm steel, and no bends but welded/reinforced angles. Much more rigid. At the rear, I would like to have a go at making a box type structure from steel. A flat plate with a small extra "box" to accommodate the crownwheel.and welded on ears for the rear mounts. Then bring it forwardsto mount the spring, and drop down the sides to attach to the side of the diff. Afraid it sounds confused, but it is all in my head!

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super thanks, I think I understand you with the fixings/Brackets and yes I found the post on making these, which I can do, The back diff plate I will make out of mild steel which is easier for me, I will start looking around for the diffs/joints to match I have the rover 100 shafts and mg vertical links sorted now so it seems silly nort to go the whole way, many regards wayne.

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Ratio depends what you plan to use the car for and the state of tune of your engine.

With a somewhat tuned 2L six in my Vitesse, a 3.63 diff and a 5 speed gearbox with a tallish 5th (0.79:1) it would still pull a taller gear.  Probably (certainly) it would be quicker on the track with shorter gearing and I'd get to use more rpms on the road without out-dragging the speed limit - but it gets mostly used on the open road and long haul at that, so I'd choose the 3.54 from the R160 range,  Spitty/GT6 weighs less and pushes less air out of the way so even more true for them IMO.

There are apparently Subaru diff/inner CV combinations that fit straight in the end of the Rover shafts...... I'd like a pair of those, but not quite sure of the source vehicle(s).

Nick

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Thanks Guys most helpful, Nick it will be tuned with a cam decked block and so on I plan on using it on the track as well as on the road, but nothing serious just fun outings, now to get looking and finalising what I need, I can now get the motor trial fitted to measure up for the mounts and get them folded at work, the last of my panels arrive tomorrow so I can get moving in the right direction, pics and a write up to follow shortly,regards wayne

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I have acquired an R160 diff which is a 3.9 and drive shafts and joints this will get me started so i can get plates made and chassis points welded up then if I need to change I have everything done thanks guys, wayne.

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Look forward to seeing how you tackle the R160 install as it's been on my "one day" list for a while.

Just be a little wary about obvious mods to the chassis as the modifications Nazis are becoming more pushy......

Nick

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I will keep you posted on my progress but I think chassis wise I want to be fairly standard affair, just arm brackets for the vertical links but diff fittings i wan't to keep as a bolt in off original mountings, I will be keeping the original engine and diff boxed up and it could go back to standard state if I ever sell. I will probably just machine up a back plate like the cast ally ones I have seen and make up the winged front mount, maybe strengthened and fold the spring mount like others have done, regards wayne.

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