rx7jocke

Got a few questions i cant wrap my head around, the oppinions goes apart considering what my builder/google/and physics say.
Consider that i am restricted to 600hp in my race class and i went with 20b for reliability resons and for maximising powerband and response

1. A 20b needs a bigger turbo then a 13b even that the HP is the same?
(in my head it should be the same..maybe use a bigger a/r just cause you can while still retain spool.500hp is the same amount of fuel and air no mather the amount of rotors, but reading this forum it does not sound that way)

2. A 20b OMFG cut the front end of your car and put a 100" cooler there!!
(why does a 500hp 20b need more cooling then a 500hp 13b? its the same amount of fuel burning? is it the wider range of power?)


3.same as above but with oilcooler/oilcoolers

gxl90rx7

iTrader: (1)

I have no 20b experience, but i will venture to say the turbo sizing should be the same as with a 13b, you size it for the amount of power you want. The difference will be in torque output

RotaryEvolution

iTrader: (30)

all 3 can simply be answered yes

why? because of displacement. does a 4 cylinder 2liter engine require the same cooling as a 6liter V8? no, because the amount of coolant now need to cool has tripled and that tiny radiator for the 4 banger is now not sufficient. for oil, same principle.

same rule as above for turbos, granted the potential to make more power is much greater. say you have a turbo that can produce 96lbs of air, in a 2 rotor that is 48lbs per rotor of consumption, in a 3 rotor each rotor only gets 32lbs to consume but the displacement increases torque output. the numbers will still be relatively equal to a 13B for the turbo, but for the size of the engine the output will not be higher simply because of the displacement of the engine. output is not only rated by horsepower, torque is also a critical figure in how fast an engine truly is.

warpig

Look at the cooling for the 20b more surface area= more area to cool it

Monsterbox

iTrader: (6)

20b does produce more heat. I'm using the same Koyo n flo, it does a great job, but creeps on hills and traffic because of FMIC.

Increasing the radiator size is ideal, but there's limited space. So increasing core size is only going to prolong the heatsoak and temp rise.

If you run a 20b best recommendation is keep airflow path direct to rad. So v mount, water to air intercooler, etc

I'm selling this car for a 4 rotor build, and next go around I've decided a Water-to-Air Core INSIDE Intake Manifold would the best option for the tight engine bay of FD. I'd like to see this on a 20b too.

Dual Oil coolers are a must, as the oil takes a huge temp hit. Take it from me. I ran R1 oil coolers, temps went way up quickly. Installed large 30 rows with 10an lines, temps dropped significantly (water temps that is) meaning the oil temps crashed way down and affected water temps !


These aren't myths. The engine has big center iron, retains a lot more heat, has extra rotor and exhaust at idle/cruising. So even if you're not making "500hp" around town, the thing is a blast furnace. Trust me.


And regarding turbo. Take whatever HP you're looking for and multiply it by 1.3. This is rotary approx. CFM requirement. If you want 600hp, you need 780CFM turbo give or take. Stick it on a 1 rotor, 2 rotor, 3 rotor, 4 rotor. Put it on a 2 rotor, it will make whatever boost it can handle until it maxes out at 780CFM (probably 25+ PSI). Stick it on a 4 rotor, and it will struggle to produce 2psi because the engine is already moving 780CFM, maxing the turbo out. Can't add any more power.

Tuning4life

iTrader: (2)

I would think a 13B is easier to cool than a 20B, the 20B has a middle rotor that is incased by two other rotors. Heat can be pulled outward on the 13B easier than the 20B with the extra rotor incased in the middle.

I also think its easier to package a nice cool V-mount for a 13B than a 20B.

Everywhere the car isn't using the power, it is easier to cool a 13B, idle, cruise, etc as less fuel is being used with a smaller displacement.

same volume of air is needed to make the same power, a larger displacement engine burns more fuel/has more volume of air at lower rpms and can run a larger turbo and spool it quicker at a lower rpm. Hence you can make more power on bigger more efficient turbo's and still spool it well with the larger displacement engine. you can run higher WHP with less stress on the components on the engine side.

since more displacement runs a little hotter more cooling is needed. sometimes what is often forgotten is the low pressure areas where heat can be "sucked" out of the engine. find those spots where you can literally suck hot air out of the engine with excellently thought out duct vents.

rx7jocke

thanks for the input guys, i follow you on the displacement/power at cruise thingy, but will this be noticeable on a racetrack? the 20b wont have to rev as hard as the 13b thats for sure and both will be at WOT alot
i know of thecenter iron retaining heat, my center iron and all 3 housings have added external cooling directly from the EWP and the same with oil to all the bearings so i think it has alittle more margin to keep hotspots to build.
alot of interesting info guys, thanks! vmount, dual oilcoolers without thermostat, ewp and so on is already installed however ill try to reuse my koyo nflow before buying a new all out racing rad :-)

Monsterbox

iTrader: (6)

That will work!