That's fine assuming you are only doing aabotu 40 mph - where your stopping distance and turn-in woudl cope with only seeing 20 feet.
IF the corner ahead is a blind 180 then you need to start swinging the car in a pendulum motion from abotu 30 metres back !!
If it's a corner on a crest then BEST you could do would be to go over at 20mphg unless you've a good nav awho can advise and call the best.
Next time you're out in a car as a passenger, play this little game. Keep your eyse closed, ask the driver to say when they are 20 feet from every corner and ONLY THEN open your eyes and judge what you woudl do. Your heartbeat will hit the top fairly quickly
THEN imagain playing that game with YOU driving. THAT about sums up serious rallying !!!!
On being just as fast without a nav, then it's a BIG difference.
You see it with experienced navs competing at a lower level whilst bringin on a driver. They can go faster then the experienced driver, less experienced nav combo
If you listen to a nav you'll hear they're NOT calling out the NEXT corner but in reality are actually calling oiut what comes AFTER the next corner. That allows the driver to plan to setup the car to make best speed throguh a series of corners. You can't do that on your own
If that's the case he shodl be a circuit driver and forget rallying