MOT Consultation - 40 Year exemption.

[Douglas Alderson]

If you have a standard engine and have it rebored and for what ever reason it ends up being bored to it's maximum what is the % power increase, anyone know?

[Alan]

I don't know, but as power output is directly proportional to compression ratio, I'd guess the power would rise in proportion to the compression. You would of course have to bear in mind the fact that the true compression is nothing like the calculated one because the volumetric efficiency isn't that good. All this is a posh way of saying the power will increase, but nothing like the 15% talked of here.

[Zetomagneto]

Are you talking about static compression ratio, or dynamic compression ratio, the latter depends on your cam timing.
Are we all to make declarations re our engine mods.Some people buy a car and don't even know it's been "hotted up"

[Alan]

It doesn't really matter which.(although I'd favour the latter) The point is how can it possibly be measured?
The question asked was does a rebore affect power output. The answer is yes but maybe not as much as you'd think.
Something else to consider - if you took a standard engine and rebuilt it, with no modifications, but taking care that all manufacturing tolerances worked in your favour, it would still be a standard engine. I wonder if the power increase might be more than 15%?

[Zetomagneto]

It's called blueprinting

[Bob Culver]

Power will increase in close proportion to the capacity increase and also but in lesser proportion to the consequent cr increase. Boring to .060 increases capacity 5% and cr near same, but only further  2% or so power gained  due the cr component of the increase.

(which in part explains why many supposedly stock Sevens seems to do so much better than the original road tests)

[Rick F]

Morning All,

Has anyone had a chance to read - thoroughly - the latest from FHBVC on this subject, available (to members at least) at www.fbhvc.co.uk/members-pages/newsletter-archive/_file/274/fbhvcnews012018addendum-rtf/


I have been wading through this and it appears to introduce a new category - Vehicle of Historic Interest (VHI). As far as I can understand it, only VHIs will be exempt from MOT testing. A VHI is defined as:

a vehicle which is considered to be of historical interest to Great Britain and which

-     was manufactured or registered for the first time at least 40 years previously;
-     is of a type no longer in production; and
-     has been historically preserved or maintained in its original state and has not undergone substantial changes in the technical characteristics of its main components.’

The last clause is further defined as:

A vehicle will be considered substantially changed if the technical characteristics of the main components have changed in the previous 30 years, unless the changes fall into specific categories. These main components for vehicles, other than motorcycles2, are:

 
Chassis (replacements of the same pattern as the original are not considered a substantial change) or Monocoque bodyshell including any sub-frames (replacements of the same pattern as the original are not considered a substantial change);
Axles and running gear – alteration of the type and or method of suspension or steering constitutes a substantial change;
Engine – alternative cubic capacities of the same basic engine and alternative original equipment engines are not considered a substantial change. If the number of cylinders in an engine is different from the original, it is likely to be, but not necessarily, the case that the current engine is not alternative original equipment.
 
1 If the type of vehicle is still in production, it is not exempt from periodic testing.
 
2 Further arrangements for motorcycles may be introduced, including if core testing standards are considered further internationally.
 
The following are considered acceptable (not substantial) changes if they fall into these specific categories:
•  changes that are made to preserve a vehicle, which in all cases must be when original type parts are no longer reasonably available;
 
•  changes of a type, that can be demonstrated to have been made when vehicles of the type were in production or in general use (within ten years of the end of production);
 
•  in respect of axles and running gear changes made to improve efficiency, safety or environmental performance;
 
•  in respect of vehicles that have been commercial vehicles, changes which can be demonstrated were being made when they were used commercially.
 
In addition if a vehicle (including a motorcycle):
•  has been issued with a registration number with a ‘Q’ prefix; or
•  is a kit car assembled from components from different makes and model of vehicle; or
•  is a reconstructed classic vehicle as defined by DVLA guidance; or
•  is a kit conversion, where a kit of new parts is added to an existing vehicle, or old parts are added to a kit of a manufactured body, chassis or monocoque bodyshell changing the general appearance of the vehicle;
 
it will be considered to have been substantially changed and will not be exempt from MOT testing.
However if any of the four above types of vehicle is taxed as an “historic vehicle” and has not been modified during the previous 30 years, it can be considered as a VHI.

The bold clause above would seem to preclude any rebuilt car or special built during the last 30 years from being exempt from MOT?

Please discuss.

[John Bonnett]

I too have been following this topic very keenly because I have an MGB V8 conversion and a Ginetta G15 with BMW power. It is my opinion having read everything I can find, that in order to qualify for MOT exemption, a self-declaration will have to me made when re-taxing (I know it is free) that the vehicle conforms to the criteria and is MOT exempt. This does not preclude voluntarily putting the vehicle forward for an MOT. For those who's vehicles do not qualify for MOT exemption I believe they will be obliged to have an annual MOT as they do now.

I recently saw a copy of a communication from the DVLA or DOT to the Beach Buggy Club saying that the 8 point rule is going to be superseded by something else which may be more lenient. At the moment, no modifications to the chassis are allowed unless the vehicle goes through IVA. I'm eagerly waiting to hear the next instalment.

[Hedd_Jones]

John

I assume therefore your G15 will need an MOT? is that the only issue you forsee?

[John Bonnett]

John

I assume therefore your G15 will need an MOT? is that the only issue you forsee?

I am hopeful that it will be okay but until we know more cannot be certain. The MG is a grey area because there was a factory V8 and there is an argument for it to be a VHI. Personally I'm not bothered whether it is or isn't so long as it retains its registration and doesn't go on a Q plate.