Can anyone tell me what this means please?

[Athlon]

On a pre cat Griff, on the plenumn it has a badge, 400 I know but under the 400 it has 250? has this any relevance to the engine?I have not seen this before.

Thanks!

Alex

[Russell Mc]

It had gas flowed heads fitted. 250bhp, well that's what the factory said but should be a slight improvement over a standard 400.

[Athlon]

Thank you.