The only „official“ info I know about was this brief brochure, link below, and somewhere else the spec claimed, about 0 - 62 mph in 5 seconds but I can‘t remember where I have seen it.
https://www.morgan-motor.co.uk/mmc/downloads/brochures/+4_supersports__brochure.pdfI have never found a review in any magazine.
I found this page...not exactly you were asking for.
http://hdvds9.com/video/Morgan-Plus-4-Supersport...where are videos to download, also videos I have uploaded on you tube (Morgan Supersports sound), the RAF blue car. Years ago.
