1275GT Group 1 Air Cleaners

[rich@minispares.com]

straight cut 31 teeth idler gear?

31 tooth is normally jack knight

the st ones are 30 tooth

they will not interchange so you have to run full sets of the gears

[cooper998]

straight cut 31 teeth idler gear?

31 tooth is normally jack knight

the st ones are 30 tooth

they will not interchange so you have to run full sets of the gears

Exactly. I know.
but in homologation papers (28/12E) stands: Idler spur gear ratio 1.044:1. (No of teeth : 23x31x24)
How that can be done

[rich@minispares.com]

Exactly. I know.
but in homologation papers (28/12E) stands: Idler spur gear ratio 1.044:1. (No of teeth : 23x31x24)
How that can be done

a 23 primary and a 24 input does give a 1.044:1 ratio (well, its 1.0434782 if you want to be pedantic),

driven/driver = ratio, so 24/23=1.044:1

early helical stuff was always 1:1, its only the later a plus helical stuff that has some overgearing options (you can walk the 1:1 to .933:1 or .966:1)

[Astro]

Hello to all from Finland,

I'm allso building a similar 1275GT to group 1 period I (-81) and I have exactly the same problems than Astro. I have not found any information about air cleaner box after 2-3 years...
My GT is going to take part on historic rallying in Finland and we follow FIA rules very strictly. So I'm awere that in group 1 car you can only use homologated parts.
And there is allso other similar problems with homologation papers > not a word what kind exhaust should be, C-ARA 334 can be found from ST data sheet. Is it right one?
Or idler spur gear ratio. Have someone ever heard about straight cut 31 teeth idler gear? or 1.044:1 helical set?
Or page 18/9 V. 16.4cm3 is ok for chamber in head and 27.9cm3 is ok for total chamber, but I cannot get CR to 12:1 how many times I count it
(318.75+27,9) / 27,9= 12,423 and a bit higher with 1293cm..


This might be the answer for the problem if normally means original hs4...
You may not change or modify normally mounted carb. Twin hs4/6 is not normally..

Appendic J -81: Art 258
d) Induction: The carburettor(s) or fuel injector pump(s) normally mounted
on the homologated model and described on the homologation form may not
be changed or modified, except for any part which may control the quantity of
fuel fed to the engine, but not those which control the quantity of air, It is
permitted to remove the filtering element on condition that the original air filter
box is retained.

Tero Gronfors
Finnish champion 2009 with Austin Cooper -65

Hi,

if you want, I can send you a pdf of the article testing Longmans car in 1999.

Best

[Astro]

what I even do not understand. The homologation paper quotes helical cut drop gears and helical cut final drives. Nevertheless the Leyland catalogue lists a straight cut gearbox for the group 1 1275 GT. OK, 1 and 1b is a difference. With 1b you can optimize the complete engine, you can use a LSD, an exhaust as you want and so on. These homologations were made for the British Championship with group 1b cars. This may be why we have now a lot of holes to fill.

[Tulka]

Sorry for my bad photo. Two weeks ago in someones garage just for my memory, but fits fine here.

[Astro]

maybe swiftis garage.

[davidnutland]

Paul Shakespear did this illustration from the original car back in the day and it will be correct, he was very meticulous, you should find a spanner somewhere in the picture, the carb to filter inlets were specially cast by Longmans to look like the original 1 1/4's to keep the GT homologated, a few of the modified Dorset cars ran them, it was a good filter fix rather than the horrible pancakes of the period, before K&N's were available.

[Astro]

i feared something like this. But what to do today? these ellbows will probably not anymore be available.

[Astro]

Hi,
these group one 1275 GTs from the late 1970ies are a problematic topic. When regarding the homologation details, they will only work in connection with the former transeuropean 1b regulations, with a free exhaust, with a LSD and much more. However, today’s FIA regulations only allow group 1 or group 2. Following 1, there is no really defined airbox, one should use a 300/300 cam together with a 1 3/4” exhaust manifold but a standard exhaust, standard drop gears, a standard gearbox and diff even when one can add a 1:4.3 final. Last, not least the homologated GKN rims are nowhere available. In the meantime, I am not anymore sure if it was a good idea to follow these ancient steps. Regarding a group 2 GT from 81, it will not be faster than a group 2 S from 71. OK, UK regulations are different but using the international appendix k, makes it difficult to get a competitive car.

[LMM76C]

Hi,
these group one 1275 GTs from the late 1970ies are a problematic topic. When regarding the homologation details, they will only work in connection with the former transeuropean 1b regulations, with a free exhaust, with a LSD and much more. However, today’s FIA regulations only allow group 1 or group 2. Following 1, there is no really defined airbox, one should use a 300/300 cam together with a 1 3/4” exhaust manifold but a standard exhaust, standard drop gears, a standard gearbox and diff even when one can add a 1:4.3 final. Last, not least the homologated GKN rims are nowhere available. In the meantime, I am not anymore sure if it was a good idea to follow these ancient steps. Regarding a group 2 GT from 81, it will not be faster than a group 2 S from 71. OK, UK regulations are different but using the international appendix k, makes it difficult to get a competitive car.

Yes,quite. Well FIA Gp1 inevitably favoured particular models.
One point: FIA Gp1 technically required a standard exhaust but that was normally described only by a blurred photo in the papers. Actual bore and degree of bends in the pipe was not defined so most "Gp1 exhausts" were bigger bore and with slightly less extreme bends in the system...

[Astro]

OK, one may try a RC40 and perhaps a cross pin diff in France. But what is about British scrutineers?