Noob,
First, I'll say that I am rather new into Esprits and certainly no guru on the subject.
Not having driven a V8 myself, I'd say from reading here and TLF, and speaking to owners of both, that you should keep your 4-pot. Better steering, lighter, better in turns, and just optimise what you have.
Brakes, Tires, brakelines, optimal coolant, engine oil and gearbox oil. Better pads, and better complete exhaust. Lighten some Things over time, and save time when accelerating.
In my Humble view, the V8 is too heavy and is a brake hard, turn, then accelerate after the turn-car. Well, in some sense of the Word. I'd stick to the 4-pot and optimise that.
In my view, the V8 is more like a sportscar for cruising, and the 4-pot a curve-eater. Anyway, some have written, that the more power you get into a Esprit, the more it will Flex.
The car mag that drove both the Sport300 and Sport350 wrote that the Sport300 is the better car. Power not always the answer. More about driving dynamics.
No offense intended to the happy V8 people out there intended.
There are many small Things to do, and just getting the gearshift perfect all the time, will get you going fast.
Get rid of non-needed weight in the car and get moving
optimising porting, or the inlet manifold's gaskets to aluminium is already something. Everything should be confirmed and tested on a dyno, so you can also read fueling etc. You know, many small Things combined is not 1+1=2, but 3.
I jsut changed to the newish Castrol Edge FST Ti,a s they claim that filmstrength is nearly double. Worth taking. I called Castrol and had a long talk with them on oils.
I used the previous model Castrol Edge FST untill now.
On the other hand, I also feel quite sure, that there are a few things to be done, without the engine exploding right away. There are so many fast engines today, and it's worth lookinginto how they came up with that power. And the Sport300 and the S4s had more punch.
I've been talking to a friend WHO have tuned VW's and Audi's for over a decade, and of course bringing a 250 Hp engine up to 650 Hp shortens the life it can have.
But what mostly breaks Down in all his builds, are the gearboxes, which he already strengthened... 3 runs on a 1/4-mile, and then a new box. Streetdriving every half year.
On another subject, both some of my friends and I have experienced, that driving a beautiful car like the Esprit, kind of provokes other cardrivers to beat the cr.p out of their own car, normal one or sports-ditto, to overtake or stick to the Esprit, in such a way, that it gets dangerous or just killing their car.
Other than that, I think many wise by experience Words were spoken here.
Just my two-pence.
Cheers,
Redfox.