Grantura article in Octane
Discussion
It was good to have an article on the Grantura in Octane but it did have some errors. You are correct that the MkIII homologated weight is 600Kg - this is unachievable unless you take the engine out! I suspect like many period homologations they were pure fiction from the manufacturer. You may achieve 700Kg with a light weight body shell and modern chassis of lighter gauge higher spec tubing.
The wheel specs are also wrong for a MkIII - it's 5" or 6" - 5.5" are not homologated.
I'd also question the comments regarding the M16 calipers. When I obtained my FiA papers I had to remove the type 16s that I had fitted in line with what I had had seen on existing cars as the spec is for type 14 calipers according to the FiA papers - the piston diameters dictate this. This info in the article is therefore misleading. I think you can get away with the bigger brakes in some series e.g. Equipe but not in FiA spec series.
The wheel specs are also wrong for a MkIII - it's 5" or 6" - 5.5" are not homologated.
I'd also question the comments regarding the M16 calipers. When I obtained my FiA papers I had to remove the type 16s that I had fitted in line with what I had had seen on existing cars as the spec is for type 14 calipers according to the FiA papers - the piston diameters dictate this. This info in the article is therefore misleading. I think you can get away with the bigger brakes in some series e.g. Equipe but not in FiA spec series.
davegt6 said:
It was good to have an article on the Grantura in Octane but it did have some errors. You are correct that the MkIII homologated weight is 600Kg - this is unachievable unless you take the engine out! I suspect like many period homologations they were pure fiction from the manufacturer. You may achieve 700Kg with a light weight body shell and modern chassis of lighter gauge higher spec tubing.
The wheel specs are also wrong for a MkIII - it's 5" or 6" - 5.5" are not homologated.
I'd also question the comments regarding the M16 calipers. When I obtained my FiA papers I had to remove the type 16s that I had fitted in line with what I had had seen on existing cars as the spec is for type 14 calipers according to the FiA papers - the piston diameters dictate this. This info in the article is therefore misleading. I think you can get away with the bigger brakes in some series e.g. Equipe but not in FiA spec series.
Haven't seen the article but the 600kg homologated weight was based on the engine capacity of 1800cc - same as the Marcos 1800. As Dave says under 700 is just about achievable but only with very light new body and light chassis. Mine is rather more as it has the original tubThe wheel specs are also wrong for a MkIII - it's 5" or 6" - 5.5" are not homologated.
I'd also question the comments regarding the M16 calipers. When I obtained my FiA papers I had to remove the type 16s that I had fitted in line with what I had had seen on existing cars as the spec is for type 14 calipers according to the FiA papers - the piston diameters dictate this. This info in the article is therefore misleading. I think you can get away with the bigger brakes in some series e.g. Equipe but not in FiA spec series.
davegt6 said:
... You may achieve 700Kg with a light weight body shell and modern chassis of lighter gauge higher spec tubing...
As I understand steel, the modulus of elasticity is the same among all the grades you'd want to use for chassis building. What changes, from one type to another is the ultimate tensile strength, effectively making one safer than another. I.e., there isn't any weight gain to be found in type of steel used. You're definitely right about the thickness, though. Today, one could easily conduct a finite element analysis on the chassis, and determine what tobes could be reduced, or even increased in wall thickness, for maximum benefit in stiffness/weight.
Best,
B.
The article contains another inaccuracy in that the Manx-tailed, Cortina tail lights Grantura did not actually appear until very late in 1964. So, contrary to the assertion in the article, the squared off, Kamm inspired tail treatment it did not arrive in September 1963 along with the 1800 engine. Chassis numbers from around 9/660-ish to 9/700-ish were the round tailed car and that is actually what was homologated in FIA papers No. 160 in April 1964. The chassis number format was changed to 65/5/(x)xxx when the Manx tail was brought in later in that year. It seems that this happened at the same time as the Griffith started to get the squared off tail treatment and this 'streamlining' was almost certainly just a way to simplify factory production processes.
The only significant change to the rear of the Grantura that coincided with the fitment of the larger 1800cc engine was some reprofiling around the number plate area. As has been discussed elsewhere, there are some who contest whether the Manx-tailed Grantura should actually be granted FIA papers as there does not appear to be any evidence that it was raced in that configuration in an international class meeting prior to 31 December 1965. But that's probably an argument for another time and place. And probably with the FIA rather than amongst enthusiasts/racers who generally don't seem bothered by the issue. As long as the cars are the same underneath and raced fairly who cares about the pedantry?
One omission in the article is that the permitted track for the SIII 1800 is wider at the front and the back than that permitted for the SIII. The deltas are 30mm and 60mm respectively and this could be quite important from a racing standpoint. Also, the 6 inch rims were allowed under an extension to the FIA papers dated June '65. I'm told that fitting the slightly wider rims sometimes requires the removal of a small amount of material from the inside of the top edge of the wheel arches, which is presumably what racers were doing back in the day if they had been supplied with a car which had originally had the April '64 homologated 5 inch rims.
With regard to brake calipers, davegt6 is quite right and I have been told that he is not the only Grantura racer who was politely asked by the leading MSA approved TVR scrutineer to change to the smaller Type 14 caliper. However, the article is also correct in saying that most people use the Type 16. It is just something that doesn't seem to be enforced very much. Some racers I have discussed this with say that it doesn't much matter in the end as the car is so light it is arguably 'over braked' with the larger caliper size and that they can get it to stop on a sixpence even with the smaller pads. Might be an issue in the Spa 6 Hours where wear and heat could play a role - but everyone knows that lots of blind eyes are turned for that race anyway.
Anyway, good to see the cars being discussed, just disappointing that it would appear even the leading car prep shops still don't fully understand all the details of the homologated spec (and I am not just referring to those mentioned in the article).
The only significant change to the rear of the Grantura that coincided with the fitment of the larger 1800cc engine was some reprofiling around the number plate area. As has been discussed elsewhere, there are some who contest whether the Manx-tailed Grantura should actually be granted FIA papers as there does not appear to be any evidence that it was raced in that configuration in an international class meeting prior to 31 December 1965. But that's probably an argument for another time and place. And probably with the FIA rather than amongst enthusiasts/racers who generally don't seem bothered by the issue. As long as the cars are the same underneath and raced fairly who cares about the pedantry?
One omission in the article is that the permitted track for the SIII 1800 is wider at the front and the back than that permitted for the SIII. The deltas are 30mm and 60mm respectively and this could be quite important from a racing standpoint. Also, the 6 inch rims were allowed under an extension to the FIA papers dated June '65. I'm told that fitting the slightly wider rims sometimes requires the removal of a small amount of material from the inside of the top edge of the wheel arches, which is presumably what racers were doing back in the day if they had been supplied with a car which had originally had the April '64 homologated 5 inch rims.
With regard to brake calipers, davegt6 is quite right and I have been told that he is not the only Grantura racer who was politely asked by the leading MSA approved TVR scrutineer to change to the smaller Type 14 caliper. However, the article is also correct in saying that most people use the Type 16. It is just something that doesn't seem to be enforced very much. Some racers I have discussed this with say that it doesn't much matter in the end as the car is so light it is arguably 'over braked' with the larger caliper size and that they can get it to stop on a sixpence even with the smaller pads. Might be an issue in the Spa 6 Hours where wear and heat could play a role - but everyone knows that lots of blind eyes are turned for that race anyway.
Anyway, good to see the cars being discussed, just disappointing that it would appear even the leading car prep shops still don't fully understand all the details of the homologated spec (and I am not just referring to those mentioned in the article).
Edited by Thurner Fan on Wednesday 7th November 13:30
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