Does anyone have a definitive answer to this question? I have fitted a 1997 engine (VR6) to a 1974 chassis (beetle) what are they going to test the emissions on, the engine or the car? I have searched the internet and can't really find a definitive answer. I always thought it would have to be tested on the engine but came across something on the gov website that says an engine older than the car needs to be tested on the engine, it doesn't say anything about a newer engine in an older car. Someone had quoted this in reply to another person asking the same question and then went on to say if the engine is newer than the car emissions would be tested on the year of the car.
Can anyone enlighten me? Thanks.

To the best of my knowledge, the MOT is always carried out in accordance to the registered date of the vehicle as stated on the V5

There are obviously some exceptions to things like seat belts - if fitted to an earlier car than were required - will be tested.

If your V5 shows 1974 and as long as the engine number and CC are stated (as you are legally required to do), then I have never heard of emissions being tested.

Unsure how this would work with those that have undergone IVA etc though? as Registered date may bring into the realms of modern testing criteria too

Thanks for the reply,V5 has been updated with new engines CC and engine number(V5 was sent off some time ago and came back pretty quickly with no problems), I don't mind wether it needs emissions test or not but as it's a 74 a visual check suits me fine. Thanks again

They tested my Q plate last week and did an emissions that came out at 2.7 the fail for post 75 is 3.75 but they should have done visible smoke only as tested to pre 75 regs however a sniff test shows you mixture so not a bad thing to weak and the motor melts to rich and running costs go up for no gain.

Yes.... August 1975 is the emission check requirement start point. Prior to this it is just what Dvla refers to as a "smoke & idle check". That is to say no visible smoke from exhaust outlets after full engine warm up and although I have never seen this checked the idle part is the vehicle with a carb being revved and the throttle returning to idle promptly.