Hey guys,

Sorry, I asked this question before but I never got an exact answer from anyone. Does anyone know what the gas mileage on a 3-rotor N/A is?

 

33% worse than an NA 13B?

 

hahaha I know. Thats a good guess but I want numbers.

 

figure out the MPG to HP ratio of the TT20b, and the TT 13b-REW and then you can make a safe comparrison to state how much gas is being used per 1 HP of each engine, or something like that. just be creative.

 

I see what your saying minni but I don't think thats a good way of figuring things out. Im looking for N/A numbers and adding a turbo into the equation while trying to derive numbers for an N/A seems flawed to me. N/As would actually use more gas anyway right? I can see what your getting at though but if I go that route, I need N/A numbers from at least one of the vehicles. I would think its harder to get N/A numbers for a 13b then a 20b.

 

haha i totally forgot youre going NA. well, regardless..........


you could try to make the comparrison between the 6 port 13b NA and the 4 port 13B-T and see what the milage is like, and try to compare that.

how accurate do you want your numbers to be?

 

I dont need the numbers accurate, just a ball park.
I've been told by some people that the mpg would be the same but others say it would be 2/3s of a 2-rotor due to the extra rotor. I have a hard time believing the 2/3s estimate.

Thanks for the info Gordon. Hopefully someone will chime in to confirm your results.

 

Not too many people here will calculate mileage on a 20b. It is safe to say that it can roughly average 33% worse than a 13b simply due to the tranny gearing. Simply put, you spin a larger displacement engine at the same rpms as an engine with smaller displacement, the larger engine will always consume more fuel. Proper gearing is exactly why an American V8 can get 28mpg on the highway in a sports car. Ideally your cruising rpms should be as low as possible to achieve good economy but not so low that the engine is a complete dog. Hope that helps.

 

N/a 3-rotor mileage--- I average 14 mpg when beating on it, and for highway is 17mpg.
So there you go, nice straight answer. Haha (Gordan wins the prize for most accurate estimate )

 

Very informative thread!
Thanks for the answer guys.

 

best mpg on my 3 rotor on the highway, was 19.9mpg. stock fd got 24mpg, gsl-se will do 26mpg. on the same trip.

average cruising mileage with the 3 rotor was in the 14-16mpg range, fd would stay at 18-20mpg, gsl-se would do 22mpg

if you went racing, our na fc would get about 6mpg

 

Depending on what mode you are driving in. N/A will get better gas milage at cruise and light acceleration because the turbo is actually a slight restriction in both the intake and exhaust tracks. Note that the turbo is really not creating boost at cruise speeds or light acceleration. Remember, when the turbo is at 0 psi, this is like an N/A engine at wide open throttle. When have you been at wide open throttle when cruisng at (normal) highway speeds?

When in heavy acceleration (such as WOT) or at top speed runs requiring boost, the turbo theoretically gets better gas milage because the brake specific fuel consumption is theoretically lower, in a thermodynamic sense, but only when at the same power level of an N/A engine (i.e. comparing a 500hp n/a engine to a 500hp turbo engine). Overlap is generally lower on a turbo engine as well as excessive overlap can cause knock (hot exhaust gasses recirculating back into the intake cycle increasing intake temps)

HOWEVER! Because turbo engines are more susceptible to knock due to higher intake temperatures, turbo engines are generally given richer air/fuel ratios, lower compression ratios (which decrease the thermal efficiency of the engine, thus decreasing gas milage) and more conservative timing (also decreases the thermal efficiency of the engine). This comparison only is valid at WOT for 2 engines of the same power level.

HOWEVER AGAIN! When considering a 2 like engines (such as a 20b turbo vs 20b n/a) with similar power outputs (350hp 20b n/a vs 400hp 20b tt, the fuel consumption would likely be higher for the N/A engine as the N/A will generally have more aggressive porting (more overlap).

I guess it all depends on what 2 engines you are comparing and what load situations you are referring to.

 

actually the turbo is kinda funny. the exhaust side is always a restriction, but the compressor isnt. in certain situations, the compressor is actually reducing the pumping losses in the intake.

it depends on the car/setup.

my brothers audi is rated at 18/26mpg, but with the intake/ic/turbo/exhauast it gets more like 24/40mpg.

 

Please explain why the compressor helps with pumping losses during a vacuum situation (when the turbo is not adding any value to the system)

 

How about not producing positive pressure, but still pumping more air into the engine than the engine would be taking in if it were open to atmosphere? Think about it for a second... Just because a turbo is not making boost does not mean its not pushing more air into the engine than would normally be obtained in that situation...

 

did an oil change the other day on the fd,

on my setup I need to get the greedy elbow out to do an oil change,

I started the car b4 I put the elbow back I was suprised how much
air the turbo was pushing @ idle,

this is with 3'' piping big IC and gt4094r turbo,

not sure if that helps any when driving in vacum

 

yep. in some situations it helps pumping, shoing less vacuum on the guage than it would NA

 

I don't have figures but when my car was na is was very very good on fuel. I did one cruise with a car club for around 2 hours, up mountains and used a 1/4 of a tank in a s3 rx-7

Andrew

 

Also.. I found with the extra torque that is far more drivable than a 13b. When I had the stock 20B manifold in, you could hillstart in 3rd gear if you wished, I always took off in second.