A 400 xplorer will do about 60-63mph tops.

 

My Xplorer, on a good day, will just eke out 60 MPH. The engine is stock, except for a Uni filter.
Top speed modified is limited as much by how much you want to spend as anything. I have seen them doing 75+ before.

 

If my speedo is correct,my 99 is doing about 65 mph.Ive yet to find a smooth runway long enuff to see what this will really do.This is plenty fast for me tho.

 

Do you realize that the the Explorer is probabily the the start of the whole Big-bore craze. In it's day it was by far the fastest 4X4 around. It had it's tipicial polaris break-downs, but when it was running nothing coluld touch it as far as ute-bikes were concerned. Now that we have 650 Kawi's and 700Sportsmans and 660 Grizzes the bar is raised. So if you have an Explorer get a pipe and and clutch kit from HPD and you will run about 65-70 and beet all the new big-bore 4 strokes.

 

I live at 5000 feet. For every 1000 foot gain in elevation from sea level you lose about 3% power. With this loss of about 15% of my 400's power, I can still do just over 64 miles per hour anytime and without much road. I do this all the time down a gravel road by my house. This speed was measured very accurately using a Garmin eTrx Vista GPS.

Even without the mods identified in my signature, my stock (+K&N air filter) Xplorer would consistently do 58-60 at this elevation. I can't imagine what it would do out there in the "flatlands"!!! - Dave

 

My 95 Xplorer is modified and on a 1/2 mile track with 18" American Racer tire( with only 1/2 my mod's) is was clocked by a radar at 74 mph. After all current mod's (except heelclicker kit) i have been clocked at 83 mph but this was on a perfect night and track. I'm putting a 38 mm carb on next week and with the heel clicker clutch kit i'm going to see what the top speed is when set up for trail riding.
later
hunt