I have run a -20 on the upper on a 450 hp bbc manual trans iron heads, with no problem. Used a hose for the bottom. Also have done the same thing on a 470 hp ls engine without any problems. Put a lot of miles on both engines without any cooling problems. Power tour every year.
I'm sure a -20 for the bottom will be fine. -16 might be too small for the bottom but might be ok for the top. The thermostat probably has more restriction than a -16 hose anyways

 

I had 16 on top and 20 on bottom with no problems.

 

I have a 16 top and 20 bottom on a 640 hp iron headed small block , it's fine.

 

I would like to install an on my car also. How do you guys connect the fittings, to the slip on tubes at the radiator and engine? Thanks. Any pictures?

 

https://www.meziere.com/Products/Cooling-System-Accessories/Hose-AN-Adapters.aspx

You could do something with these above or do what I'm doing right now, cut the neck off and weld the bungs right to the radiator. In our case we're wanting to get rid of the hose clamps and rubber so no adapter on mine when it's done.

 

I ran 16's top and bottom and was ok.....although it did seem on the small side.

 

I have a 16an upper and a 20an lower with a factory belt driven water pump & no thermostat. The electric fan turns on at 185 and off at 175 and the car is NEVER hotter than 188 street driving in traffic in 85 degree temps. If it's in the 60's or low 70's outside, it has a hard time getting beyond 175 degrees. Car has twin turbos in the engine compartment and is driven anywhere from 2500-4500 miles per year on an 800 rwhp tune and makes somewhere around 1100-1200 rwhp on a race tune. I had my doubts about the an hoses at first. The only regret that I have is not doing it much sooner. They are so nice when you have to take something apart and you never have to worry about one coming off or blowing out.

 

I started running AN hoses on comp elim style cars about 30 years ago & then nitrous pro mods. I initially used 20 & 16AN & then smaller and smaller hose & fittings on successive systems I built. Perhaps you guys need to think of both internal diameter and coolant flow. 16 AN hose & fittings will very likely flow more than any waterpump you have. If that is possible, then why do you want those heavier, big-assed, very-expensive hose and fittings? Especially when something smaller and less expensive is sufficient.

10-15 years ago I remember a 600+ cube nitrous pro mod car running AN cooling lines. The whole system was just 8AN To and From the radiator, & was split down to 6AN going to the heads. Again, it's about the proper amount of cooling flow - not the size necessarily.

 

Did you miss the part about "on the street"?!? Lol
-16 upper and -20 lower would be the smallest I would run for a street/strip deal.
A good pump and system should move 50-60 gpm.

 

I run 16 upper and lower on everything I build.

 

-16 upper and two -12 lowers with remote mount meziere. With regular electric pump I ran -20 upper and -16 lower.