Spit6 Brakes

[the_nutter]

I am rebuilding my Mk2 Spitfire but with a Toyota Supra 7M-GE engine, 200BHP, complete with Toyota Supra W58 gearbox.  I also hope to use the LSD diff from the same car.  The car is intended for reliable summer fun and possibly an occasional track day. 

My query is what to do with the brakes?  I have a set of front vertical links, discs, and calipers from a GT6 but am uncertain whether these will be sufficient.  The other plan was to fit the vented discs from the 2.6L Capri, with calipers from a specialist, but is this really necessary?

At the back I am intending to use the vertical links from a GT3 Rotoflex, but with lower adjustable links back to the main chassis rail (to form a triangle with as wide a base as I can get) and a fixed upper link back to a modifies top turret.  I do not intend to use the doughnuts!  Something more appropriate and CV joint based in the plan, but that's for another time.  I have no parts for the back brakes yet, other than the original Spitfire drums, but was considering either the standard drum set up from the GT6, using the original Mk2 Spitfire front discs with specialist calipers, (plus handbrake) or possibly the discs from either a X1/9 or a MGF.  You can probably tell I am really undecided about this.

Any informed advice would be most appreciated.  For details of what I'm doing please see www.spit6.co.uk.

Many thanks
David

[Clive]

You may well need better brakes, they will be on the limit (or beyond) for 200bhp.

You can use the capri vented discs with the GT6 caliper if you use a spacer and the discs redrilled. Kits are available, try the racing suppliers (I think jigsaw and maybe moss may do them?)
Elsewhere on here 2litre-e is doing a vx red top conversion, and is in the process of doing rear brakes and discs. I think he has used larger calipers at the front too. I have a 150 bhp zetec spit which is fairly basic as far as conversions go, just has 4pot front calipers with drilled discs (came with the project car) and seem ok, but not really tested yet, only normalish driving.

Colin Geer ( I think thats right) has a cossie lump in his GT6 and uses a supra diff, I think with 2000 shafts etc, but can't really remember. I haven't seen him for some time, but maybe somebody out there knows a bit more! He lowered his rack, and to help turned the track rod ends upside down too, to try to keep things a bit sensible wrt bump steer.

Good luck, does sound interesting!

Clive

[Deleted User]

one other point is that you can get (soon) trunnionless uprights at the front from a caterham which will then allow you to have alloy hub and better/more selection of brakes........

[CharlieB]

I think the uprights are the same above the threaded bit so brake choice is the same. You can get alloy hubs to fit already.

[Deleted User]

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[Deleted User]

[quote by=davesideways link=Blah.pl?b=spit,m=1179254254,s=5 date=1179260871]

Canley too, cheaper.

[/quote]

They should be cheap they are a piece of p*** to make. Switch the CNC on, press button and walk away. I can't for the life of me understand why these ever needed to be expensive?

[Deleted User]

[quote by=davesideways link=Blah.pl?b=spit,m=1179254254,s=6 date=1179261044]

No they aren't GT6 uses a removeable brake caliper mount plate not cast lugs...

. but the factory conversion mounts are a bit rare....lucky I have some :)

[/quote]

They just got rarer, we sold the last of ours to another trader last week. Stick em on ebay Dave.

[CharlieB]

I'm pretty sure the Caterham uses modified Spitfire uprights not GT6.

[Deleted User]

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[Deleted User]

[quote by=davesideways link=Blah.pl?b=spit,m=1179254254,s=11 date=117926363 will pr keen to loose the trunnion due to the fact them current repro truns are not the best?
[/quote]

They have just been sorted again look out for the ones with Stanpart cast into them. They should be decent quality,

[Deleted User]

[quote by=CharlieB link=Blah.pl?b=spit,m=1179254254,s=10 date=1179263316]I'm pretty sure the Caterham uses modified Spitfire uprights not GT6.[/quote]

True but we have had Vit/GT6 links machined with the Caterham bit at the bottom. The Chinnmeister is due to trial the first set on his beast next week. The 4 cylinder stuff went all through last winter on my 13/60 estate, or at least one side did.

[Chris]

For what it's worth, I've got GT6 brakes on the V8 - more to handle the increase in weight (which actually isn't all that much) than for the extra speed it's possible to do - and they cope just fine.

Chris

[Deleted User]

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[Deleted User]

post removed on request of author

[GT6Steve]

Do you guys have an Isuzu Impulse over there?  I've got a brake trick if we can identify it...Steve

[chrisspe]

whats all this about power meaning u need more brakes :)  - if you have more power you can accelerate faster, therefore to beat the guy your racing you dont need to put so much effort in to outbraking him.

Pads make a huge difference to brakes, had to fit some halfords papds to my other car cos they were all i could get at the time (the nice pads got chipped in transit) - that was scary 110 - 40 ok - then nothing

[Deleted User]

FYI, I did an AP racing kit some years back and developed it for the TR6 AND GT6.

It's not neccessarily the brake temperatures are the enemy it's the quality of the disk rotors and the swept area of the pad.
This hasn't been available for many (15 yrs+) years, but the performance and progression was absolutely stunning and that used Mintex 171 as a good compromise between track and road.

[Clive]

I assumed when I made my comments about gt6 brakes "being on the limet" that the car would be used at higher speeds than most, and that the supra running gear is heavier. These 2 things make the energy going into the brakes higher, hence getting hotter. Seems obvious that larger brakes capable of getting rid of heat faster would be a good idea.Remember double speed= 4X heat to the brakes.
Vented brakes may well be the best answer, made out of decent materials not cheap tat.

Clive

[Deleted User]

AP rotors are know for being made specially for them.
The quality of cast iron is a major factor in high performance and friction coefficient,- more reason to be suprised that people ignore it so much.....
Keeping the pads cool is not really a big problem with all that air around there.

I remember the main limiting factor on the GT6 was in fact one of space. There's a serious limit to how much disk you can squeeze into a 13" wheel, so that was why I went for a fatter disk with later on, an open back rigid type caliper from a Formula 3/3000.

In that space with relatively low weight and inertia, the next limiting factor became flex of the wishbones and chassis, so in fact it shows the conversion was basically a great success..

...as I can confirm,- on Michelin slicks it became a very very enjoyable experience to drive with great complimentarity between the very good fast initial turn-in inherent to the Triumph cars, and excellent late braking progressivity.
I believe that type of car is at its best at medium speed fast corners (40-90mph), whereas really tight hairpins etc underline the chassis limitations,- a struggle with understeer, poor traction and excessive camber change.
Really higher speeds (90-130mph) show limitations of airodynamic stability

I believe it's all that, that makes the difference between a good driving experience and an outstanding one!

[Deleted User]

Following on from GTEVO's comments re limitations on space under the 13 inch rims, have you considered going to 14 or 15 inch rims - you can then up your disc diameter from standard or even if your using 2.8i Capri discs from 245mm 19mm thick (vented Capri 2.8) to 280mm diameter 24mm thick perhaps even up to 300mm diameter - hence you have more space under the rim - a much wider calliper choice available and pads with much larger swept areas.

Take the GT6 pad it's around 65-70mm square (from memory) - so the pads I'm using are 158.5mm x 58.5mm - that's about double the surface area of each pad - combine this with moving the disc to the outside of the hub you can then dissipate the heat out of the disc/hub much more efficiently - the quality of the disc is also hugely important - pads less so - everyone seems to have this thing about up rated pads when really the disc play such an important factor - I'd rather pay £20 than £60 for a set of pads

Avoid using front calipers on the rear as you will lock up your brakes every time under hard braking - especially in the wet.

The Supra lump has a cast block - not sure what additional weight over the GT6 lump would be - however it looks much heavier than the 6 pot - firstly there is a difference using the car on the road and on the track - you don't tend to suffer break fade on the road where as on the track its a repetitive progression in braking/temperatures (if your trying hard that is!!)

Forget fancy alloy four pots you need a braking system that will stop your car not one that looks good. Princess callipers are not all there cracked up to be - tried them once on my race car and changed them straight away c**p  - a solution that does work really well as used on my GT6 racer was 2.8 Capri discs with 728i BMW four pots (old shape circa 1985) - these callipers bolt directly to the GT6 upright (no adaptor is require) - although you need a spacer between the mounting bracket and the calliper to centralise them over the disc - they are heavy however they will out perform a say a Princess caliper 5x over - if you go this route stick with OE BMW pads as well - I was 14' rims though and also running Fait X19 rear callipers with VW polo discs - however now going across to complete MGF due to availability

Good luck with your project

[Royboy66]

Interesting thread!
Im about to change my worn out mintex 1144's on my gt6 (solid,drilled discs)
Where can I get some of these ds2500's? (couldnt find any listing for gt6? part number?)
Or should I stick with some more 1144's? or something else?

Cheers

Roy

[ferny]

[quote by=GT6Steve link=Blah.pl?b=spit,m=1179254254,s=20 date=1179276891]Do you guys have an Isuzu Impulse over there?  I've got a brake trick if we can identify it...Steve[/quote]

Wiki, she say..

Quote:

The Isuzu Impulse was a small sporty 3-door hatchback (though always classified as a coupé by Isuzu) sold from 1981 through to 1992. The first generation Impulse was a rear-wheel drive car, but the second generation was front-wheel drive and all-wheel drive. The second-generation Impulse was based on the General Motors (GM)-influenced Gemini Coupe or Geo Storm as it was known in the US market, and the engine of the second-generation Impulse is the descendant of the Isuzu engine used in the modern Lotus Elan. The Impulse was also known as the Isuzu Piazza outside of the US, including in the UK where it was the first widely available Isuzu. In Australia it was badged the Holden Piazza, and sold by GM's Australian wing Holden.

I've never heard of it before myself. But the answer is a yes by the looks of it.

[the_nutter]

Many thanks to everyone for the invaluable feedback.

I should of said in my initial question that I am planning to use larger diameter wheels, probably 15" diameter, which should look okay.  The easiest option is to stick with the standard GT6 setup which seems will offer satisfactory braking at least, if combined with good pads.  Which ones seems to be a contentious issue, but changing pads is easy! 

If they're not reliable, or offer poor performance, then I'll try gtr-5's solution of the Capri 2.8 discs with the BMW calipers.  I do like scrap yard stuff, it's so much more satisfying looking at something you've done yourself than taken out of the box (and cheaper) , but thats just IMHO.

Once again, thanks to everyone for taking the time to reply, and share invaluable information.

Cheers
David Squirrell, hence "the_nutter"

[GT6Steve]

Ferny quotes Wiki "The Impulse was also known as the Isuzu Piazza outside of the US, including in the UK where it was the first widely available Isuzu."

This is a ventilated disc that fits the GT6 nicely with a bit of work the first time.  I tapped the original hub to the appropriate metric thread and turned a centering ring to adapt the ID of the rotor.  The caliper is spaced and centered just as on the Capri conversion you have available.

The whole thing ends up a bit lighter than the stock disc with improved air flow thru the disc making up for what it loses in thermal mass.  It might be an alternative to the expensive (over in the US) Capri conversion.

Odd thing with our series, engine mods are wide open but brake calipers must be original...Steve