Rotary Engines - FAQ.

[Alchemis]

to every new and potential owner of RE engines....

not sure how do we pronounce this FAQ.. as FACK ? FxCK? ehehhe just joking....
hope you all get your questions answered in this thread...


Lesson 1 Fuel Consumption

Fuel consumption of a Rotary Engine is well know to be thirsty. and it's VERY thirsty. we're talking about a tank of 65 Litre 95 Octane and give you 250 KM in those small roads and traffic jams.... highways will set you up about 300km to 320 KM. these numbers are based on stock twin turbos. because the turbos spin up relatively EARLY around 2.5K RPM compared to Evo or Scoobies, thus alot more petrol is required. and the full twin spins in around 4.5 K RPM.

some of our guys had their car converted to single turbo. some of them are better in fuel milliage. this is due to their turbos are operating like Evo or Scoobies... it starts spinning around 4 K RPM that range.. so.. anything below 4K RPM they are theoritically and practically running like NA.

that's difficult to say as well.. if those single turbo guys were running like 1000 CC injectors all 4 round.... it's different story....

baseline is.... Rotary Engines are damn thirsty....get ready to contribute to Shell, Petronas, Caltex etc... making them rich.... :)

 

[Alchemis]

Lesson 2

Lesson 2 - Maintenance

Basically, maintenance of RE is nothing... very EASY... nothing to be worried off. for a stock car the suggestion is always get a mineral oil only RM50 per 4 litre. and a Mazda oil filter that's around RM 25 to RM 30 per piece....

most important of this lesson... change them every 3000 miles, or 5000 KM THE MOST....

some of the RE folks might say go synthetic, there's a big discussion and argument in the RX7club.com regarding this topic... Logically speaking, our car pumps oil into the engine for lubrication.. it's being burnt.... if the oil burns un-clean... then you'll have alot of dust and deposits. if it's high grade synthetic.. u don't get it burn... i don't know where the oil goes then :)

i know if i use mineral.. it gets evaporated.... so.. i need to top up about 500 ML every half year :) that's not a significant oil lost :) it's normal.

Gear boxes....we're talking about gear box oils, rear axel oils and linkages. if you don't know the history of the gear box oil or the LSD oil, change it once u get the car.... it should last you up to at least 2 years if you're not racing ur car constantly.
how much ? go ask a foreman... gear box oil... usually sell in 1 litre form... you'll need maybe 4 bottles ? and LSD need 2 bottles... and price is depending on what brand u use.

linkages..... as you know, they are wrapped in a rubber piece... greeses are applied inside. once the rubber piece gave up.... time to change the linkages... it'll get worn... you'll be having difficulty getting a right wheel allignment or noises when you drive through rough roads. cross your fingers, this don't happen to you :)

Radiator...... there has been people saying use Water Wetter + de-mineralized water + coolant (25 % only). it does help a little.... but not a significant cash involved.... change them once a year.... it should help your engine to be rust free... and clog free.... this set you off for around RM 50 to RM 80.....

the rest..... brake pads normal question.. finish then change lor.... no need to ask kua :)

i think at the moment that's what i have in my mind for begineers.... i hope some other member could come and post more FAQ for intermediate drivers in term of electronics etc.. what is required in the car... what to do .. what not to do.. what to be careful :)

someone STICK this thread....

 

[SideWaysGrey]

Thanks CB. Very useful information indeed.

 

[Alchemis]

hopefully people don't come and ask the same question ... we'll use this thread for those to join in and ask and for those wanna know more about Rotary engines.

 

[elsm80]

Any advice on tune ups and TPS adjustments?

 

[Alchemis]

URL links from RX7club... for those who don't know where to search

**Useful websites, worthy of special mention**
RX-7 *** Lightning in a World of Thunder *** RX-7
http://www.robrobinette.com
Max Cooper's RX-7 Web Site
TurboRX7.com > Turbo RX7 Main Page
7-UP CLUB HOME PAGE

5th Gear Synchro Fix:
THIS IS NOT MY WRITE UP. I simply saved this for other people so DON'T contact me about the tools


20B info:
RX-7 Owners Club - Where does all the costs come from?
RX-7 Owners Club - 20B Forum


A

Advice for new owners, suggested modifications, etc... look for the long post by jimlab:
RX-7 Owners Club - need questions answered from experienced 3rd gen owners

Air Separation Tank / AST / Coolant Expansion Tank:
Often fails due to heat and pressure. Many people replace them or remove them from the system.
http://robrobinette/coolant_tank.htm
Coolant Air Separation Tank Elimination

Airbox mod (thanks adam c)
RX-7 Owners Club - cheap stock airbox mod

Air to Water ( A2W ) Intercooler How to:
RX-7 Owners Club - my a2w intercooler is done.

Auto to Manual Transmission swap:
RX-7 Owners Club - Automatic to manual swap. How hard is this? Anyone done it?
RX-7 Owners Club - So how many people have done the Auto -> Manual Swap


B

Battery relocation guide (passenger storage bin) w/ photos:
Triple-R: Battery Relocation

Boost Gauge Install:
Boost Gauge Installation

Boost Gauge in stock dash cluster:
RX-7 Owners Club - AutoMeter Gauges in FD Inst Cluster

Brake Bleeding: get rid of air bubbles for improved pedal feel and fade resistance.
http://www.zeckhausen.com/bleeding_brakes.htm

Buying an RX-7 / Buyers Guide / Used Car Shopping:
http://rx7.voodoobox.net/infofaq/bguide3g/bguide3g.html
http://www.marx7.org/infocenter/faqs/3rd_faq_main.html
Buying a Used RX-7
http://www.robrobinette.com/buyaused.htm
Compare Prices and Read Reviews on 1994 Mazda RX-7 at Epinions.com



C

Compression Test:
Compression Test

Coolant Burping Tool/ Radiator Cap Funnel
RX-7 Owners Club - Radiator cap funnel, eliminate air bubbles

Coolant Flush (with pics):
http://www.face2faces.co.uk/RX7/howto/coolflush.htm

Coolant hose part numbers: replace all the rubber coolant hoses in your system.
RX-7 Owners Club - All coolant hose part numbers

Cooling / Radiator Fan Control information:
RX-7 Owners Club - Coolant Recall Fan Controller Schematic/Location

Cooling fan modification. Lets you run your fans when you want to run them:
Cooling Fan Modification
http://rx7.voodoobox.net/howto/fanswitch/fanswitch.html

Cooling system diagram:
http://www.autosportracetech.com/RX-7/coolingsystem.htm

Cooling system info:
RX-7 Owners Club - The Big Fat FD3S Cooling Thread
RX-7 Owners Club - Cooling System flush info:


D

Dashpot : dampens the throttle stop, for smoother on/off throttle transition, less backfiring, bucking
RX-7 Owners Club - Dashpot UIM

Double Throttle removal:
http://www.rotormafia.com/dtc/

Downpipe Install:
Downpipe Installation

Downpipe / Exhaust Gasket issues:
RX-7 Owners Club - Downpipe exhaust leak problems

Downpipe studs & nuts: factory part numbers, also socket-head screw sizes:
RX-7 Owners Club - Downpipe Nut



E

ECU Codes: how to pull and interpret diagnostic codes
Check Engine Light Codes

ECU diagram:
http://www.autosportracetech.com/RX-7/ecu.htm

Engine Components, weighed individually (tons of photos):
RX-7 Owners Club - Engine Bay Weights

Engine Housing / Rotor information, weights, interchangeability:
RX-7 Owners Club - So, it's possible to use 2nd gen N/A housings in our FD'S?

Engine rebuild (DIY style):
RX-7 Owners Club - And the work begins, new engine, lights wheels (pics)

Engine removal & installation:
RX-7 Owners Club - Pictorial write up of my engine pull and re-install.

F

Factory Service Manuals (FSM):
RX-7 Owners Club - 94 FSM's available for download

Fan Switch Mod: run your radiator fans anytime you want, for better cooling at low speeds
Cooling Fan Modification
http://rx7.voodoobox.net/howto/fanswitch/fanswitch.html
RX-7 Owners Club - Fan-mod pointless? I think not.

Front Mount Intercooler Installation Guide (thanks TracyRX7)
http://flathat.woodstream.net/RX7/Docs/Greddy_FMIC.html

Fuel Filter:
Change the stock one every 15k miles, to be safe. Helps regain a little smoothness and MPG:
http://www.robrobinette.com/fuel_filter_replace.htm
RX-7 Owners Club - Fuel Filter Replacement / Upgrade, with pics more pics here

Fuel Leaks or Odor:
http://www.rx7club.com/forum/showth...threadid=113638

Fuel Pulsation Damper Replacement:
RX-7 Owners Club - FPD (fuel pulsation dampner) replacement * write-up *

Full Exhausts (what you need to know):
RX-7 Owners Club - what i need w/full exhaust ??

G

Gauge Installation info, which wires to tap for illumination:
RX-7 Owners Club - Some defi or standard gauge install *facts*

Gauges / Stock Water Temp Gauge Linearization:
RX-7 Owners Club - Temp guage inaccuracy???

Gauge Install: Oil Temp, Water Temp, Boost, DIN panel mount:
RX-7 Owners Club - DIN Panel Gauges


H

Headlight motor mod / sleepy eyes
RX-7 Owners Club - How To: Sleepy headlights on a 3rd gen

Helicoil How-To (repair damaged threads)
RX-7 Owners Club - Stripped manifold stud - Autozone kit?

I

Intercooler/Stock mount installation guide (thanks Gen2n3):
RX-7 Owners Club - GReddy SMIC Install


J

Japanese '99 Rat's Nest solenoid vacuum " black box " info and photos:
RX-7 Owners Club - '99 rats nest replacement block


M

Manual Boost controller / Greddy Profec B II install & review:
RX-7 Owners Club - Profec B spec II install and review

Midpipes and boost control:
RX-7 Owners Club - what i need w/full exhaust ??

N

Non-Sequential Turbo modification:
Non-Sequential Turbo Conversion


O

Oil Cooler cleaning / reconditioning:
RX-7 Owners Club - oil cooler fixing/cleaning - pics and info

Oil Filter Recommendations: K&N , Purolator PureOne, Mobil1
RX-7 Owners Club - K and N oil filters

Oil injectors: different designs 93 vs 94-95:
RX-7 Owners Club - Change in oil injector design?

Oil Pan Leak fix:
RX-7 Owners Club - Mythbusters time - Oil pan and motor mounts

Oil system diagram:
http://www.autosportracetech.com/RX-7/oilsystem.htm


P

Power Steering Pump removal: (thanks jimlab)
RX-7 Owners Club - HOW TO: Remove/Replace Suspension Bushings
RX-7 Owners Club - Powersteering Removal Kit

R

Rear Differential bushings how-to:
RX-7 Owners Club - how to: diff bushings

Reliability Mods:
RX-7 Owners Club - want to buy 3rd gen need reliabilty mod help
Upgrade Stages
RX-7 Owners Club - need questions answered from experienced 3rd gen owners TurboRX7.com > Upgrade Recommendations

Reliability mods / $1000 to spend
RX-7 Owners Club - i have $1,000 to spend..


S

Spark plug photos, with mileage and analysis:
RX-7 Owners Club - Post your spark plug photos here

Spark Plug Replacement:
http://www.robrobinette.com/sparkplug_wires.htm

Suspension bushings removal using hydraulis press: (thanks jimlab)
RX-7 Owners Club - HOW TO: Remove/Replace Suspension Bushings



T

Throttle Position Sensor ( TPS ) adjustment, fix idle / hesitation problems:
RX-7 Owners Club - fixed my idle problems, backfiring, bucking and more...
RX-7 Owners Club - Replaced TPS - now reading 0V

Turbocharger Overview:
http://www.autosportracetech.com/RX-7/TurbochargerOverview.htm

Turbo Rebuild w/ pics:
RX-7 Owners Club - Questions before undertaking Turbo rebuild...

Turbo FAQ's, including sourxe of oil in intercooler / intake pipes:
http://www.autosportracetech.com/RX-7/TurbochargerOverview.htm

Turbo System troubleshooting (Stock Sequential): (thanks spurvo)
http://www.autosportracetech.com/RX-7/rx7stuff.htm
http://www.autosportracetech.com/RX-7/TurboTroubleshooting.htm
Turbo / Boost Problem Troubleshooting

...with higher than stock boost:
RX-7 Owners Club - weird problem with boosting

V

Vacuum hose removal tips:
RX-7 Owners Club - Infamous Vacuum Hose Job

Vacuum hose replacement how to: (thanks Rated R1)
http://rx7.voodoobox.net/howto/vachose/vacjob.html



W

Wastegate Actuator adjustment / modification:
RX-7 Owners Club - Interesting WCA test & potential boost creep solution

Wastegate Porting:
RX-7 Owners Club - how to port wastegate...

Water temperature gauge sender:
RX-7 Owners Club - Water temperature sensor: How to tap and install

Wheels: (stock 'light' vs 'reinforced' version)
RX-7 Owners Club - Difference between light and re-enforced FD wheels

Wheel Fitment:
RX-7 Owners Club - The "Will These Wheels Fit" Question Eliminator 3000

 

[Alchemis]

fueling information

Application Note: You CAN be too Rich
By Klaus Allmendinger, VP of Engineering, Innovate Motorsports

Many people with turbochargers believe that they need to run at very rich mixtures. The theory is that the excess fuel cools the intake charge and therefore reduces the probability of knock. It does work in reducing knock, but not because of charge cooling. The following little article shows why.

First let’s look at the science. Specific heat is the amount of energy required to raise 1 kg of material by one degree K (Kelvin, same as Celsius but with 0 point at absolute zero). Different materials have different specific heats. The energy is measured in kJ or kilojoules:

Air ~ 1 kJ/( kg * deg K)
Gasoline 2.02 kJ/( kg * deg K)
Water 4.18 kJ/( kg * deg K)
Ethanol 2.43 kJ/( kg * deg K)
Methanol 2.51 kJ/( kg * deg K)

Fuel and other liquids also have what's called latent heat. This is the heat energy required to vaporize 1 kg of the liquid. The fuel in an internal combustion engine has to be vaporized and mixed thoroughly with the incoming air to produce power. Liquid gasoline does not burn. The energy to vaporize the fuel comes partially from the incoming air, cooling it. The latent heat energy required is actually much larger than the specific heat. That the energy comes from the incoming air can be easily seen on older carbureted cars, where frost can actually form on the intake manifold from the cooling of the charge.

The latent heat values of different liquids are shown here:

Gasoline 350 kJ/kg
Water 2256 kJ/kg
Ethanol 904 kJ/kg
Methanol 1109 kJ/kg

Most engines produce maximum power (with optimized ignition timing) at an air-fuel-ratio between 12 and 13. Let's assume the optimum is in the middle at 12.5. This means that for every kg of air, 0.08 kg of fuel is mixed in and vaporized. The vaporization of the fuel extracts 28 kJ of energy from the air charge. If the mixture has an air-fuel-ratio of 11 instead, the vaporization extracts 31.8 kJ instead. A difference of 3.8 kJ. Because air has a specific heat of about 1 kJ/kg*deg K, the air charge is only 3.8 C (or K) degrees cooler for the rich mixture compared to the optimum power mixture. This small difference has very little effect on knock or power output.

If instead of the richer mixture about 10% (by mass) of water would be injected in the intake charge (0.008 kg Water/kg air), the high latent heat of the water would cool the charge by 18 degrees, about 4 times the cooling effect of the richer mixture. The added fuel for the rich mixture can't burn because there is just not enough oxygen available. So it does not matter if fuel or water is added.

So where does the knock suppression of richer mixtures come from?

If the mixture gets ignited by the spark, a flame front spreads out from the spark plug. This burning mixture increases the pressure and temperature in the cylinder. At some time in the process the pressures and temperatures peak. The speed of the flame front is dependent on mixture density and AFR. A richer or leaner AFR than about 12-13 AFR burns slower. A denser mixture burns faster.

So with a turbo under boost the mixture density raises and results in a faster burning mixture. The closer the peak pressure is to TDC, the higher that peak pressure is, resulting in a high knock probability. Also there is less leverage on the crankshaft for the pressure to produce torque, and, therefore, less power.

Richening up the mixture results in a slower burn, moving the pressure peak later where there is more leverage, hence more torque. Also the pressure peak is lower at a later crank angle and the knock probability is reduced. The same effect can be achieved with an optimum power mixture and more ignition retard.

Optimum mix with “later” ignition can produce more power because more energy is released from the combustion of gasoline. Here’s why: When hydrocarbons like gasoline combust, the burn process actually happens in multiple stages. First the gasoline molecules are broken up into hydrogen and carbon. The hydrogen combines with oxygen from the air to form H2O (water) and the carbon molecules form CO. This process happens very fast at the front edge of the flame front. The second stage converts CO to CO2. This process is relatively slow and requires water molecules (from the first stage) for completion. If there is no more oxygen available (most of it consumed in the first stage), the second stage can't happen. But about 2/3 of the energy released from the burning of the carbon is released in the second stage. Therefore a richer mixture releases less energy, lowering peak pressures and temperatures, and produces less power. A secondary side effect is of course also a lowering of knock probability. It's like closing the throttle a little. A typical engine does not knock when running on part throttle because less energy and therefore lower pressures and temperatures are in the cylinder.

This is why running overly-rich mixtures can not only increase fuel consumption, but also cost power.

 

[Alchemis]

kindergarden class - before you buy the car

1. Check for proper turbo operation. Problems with the secondary turbo are common. On a test drive with a warm engine at full throttle, the second turbo should kick in with the punch of a jet aircraft's afterburner. Though Mazda didn't install a boost gauge, it's easy to hook up a temporary gauge to the intake manifold. The dial should read 10 psi, then drop to 8 psi at 4500 rpm, then quickly recover to 10 psi. Turbo housings are difficult to obtain, which means that pooped-out turbos can't be rebuilt and must be replaced with new turbos — a pricey proposition.

2. Inspect vacuum lines and wiring. Malfunctioning turbos may also be caused by problems with the RX-7's complex array of vacuum lines and solenoid valves. High under-hood temperatures from the turbos often cause the lines to harden and break, and the solenoids to fail. Ditto for engine-bay wiring and electrical connections.

3. Perform a compression check. Rotary engines require special test equipment available at a dealer or rotary specialist. But a check is especially important as these engines often need rebuilding after only 50,000 or 60,000 miles because the aluminum engine housing warps and/or seals fail and allow coolant to enter the rotor chambers.

4. Examine the cooling system. Rotary engines run hotter than piston engines, and the turbos only add to the heat generation. Proper engine cooling is critical, and if the needle on the temperature gauge rises to "Hot" even once, the engine's probably cooked. On a cold engine, the coolant level should be full and the coolant should be green with no signs of oil. White smoke or the sweet smell of coolant from the tailpipe indicates trouble. The electric fans — there are two — frequently come apart, perhaps launching a blade into the radiator. And the cooling system's plastic air separator often splits, dumping out coolant.

5. Read the service history. The records should show oil-change intervals of no longer than 2000 to 3000 miles. Gasoline residue is more likely to contaminate the oil of a rotary engine than a piston engine, and the oil breaks down more quickly because it's used to cool the turbos, so frequent changes are a must. Oil consumption of a quart per 1500 miles is normal. Oil pressure at idle should be at least 20 psi.

6. Check gearbox for smooth shifting. The manual transmission is generally strong, but a damaged 5th-gear synchro is not uncommon on these RX-7s. Note any crunching when going into 5th gear.

7. Listen for suspension clunks. Noises from the aft end of the car may come from one or more of a dozen deteriorated bushings in the rear suspension, while clunks at the front probably come from an upper A-arm bushing. Any can be replaced with upgraded bushings.

 

[MrPenghulu]

wow cool... thanks learn from you ya... but still we need those rotary experts to help us

 

[ace79]

Hi Alchemis. Errr....this link not working lah :
Intercooler/Stock mount installation guide (thanks Gen2n3):
http://www.rx7club.com/showthread.p...443#post5675443

Hehehe...learning about RX-7's rite now...

 

[Alchemis]

i've changed it...
some error in the link
RX-7 Owners Club - GReddy SMIC Install

 

[BLaCkHoWLiNG]

Re: Re Faq

err... how much u guys top up the 2T oils when u pump; petrol?

 

[Alchemis]

Re: Re Faq

typically...250 ml to a tank full...
that's when we plan to race it hard.. drive it hard... like before track events...

when it's on normaly days.... tend to skip once in awhile.... and that's around100 ML to 150 ML to every tank full...

just to keep it the engine compartment lube nicely...the more we put into the tank... the more smell we get from our exhaust... smells really terrible...

 

[BLaCkHoWLiNG]

Re: Re Faq

yeah..i noticed that... 200ml to 100 bucks petrol yesterday and i can smell it

 

[theseira]

Re: Re Faq

I never use 2t. It's actually for the older rotaries with their inferior seals back in the 70's and early 80's. New seal technology doesn't require 2T oil lube. But again...this is debatable. I've thrashed the FC on the highway a couple of times every other week and engine is as good as ever.

 

[BLaCkHoWLiNG]

Re: Re Faq

kira nasib kwaaaaa

 

[Alchemis]

Re: Re Faq

ahahahah it's true.. kira nasib :P ahahahah

i got this advise from an Apex Seal supplier in USA...
in order to make rotaries last long, premix is required. even oil metering pump is still intact...

i had my powerFC adjusted to pump more oil in the combustion chamber. but sometimes i also put in 2t oil... the reason... petrol nowadays they are mixed with those engine cleaning agent... these agents tend to make ur engine sparkling clean.. oil that got pumped into the engine will most likely disolved and burnt along the combustion...so.. 2T is a safety net there just incase... not enough lube in it...

there's nothing say MUST on 2T mixing.. japanese can run rotaries without premix for like 200k KM...so... like Heath says... it's debattable... lots of debating happen in RX7club.com

 

[Izso]

Re: Re Faq

Does the advice apply for the RX8 renesis engine?

 

[Alchemis]

Re: Re Faq

if you trash it very often... yes u should whenever u think u trashing ur car...
but RX8 rotaries tend to be designed to take synthetic oil... rotary synthetic oils..synthetic oil's behavior tend to be stickier...likes to coat on the metal surface.. so... putting 2T... maybe just for fun :) or waste money on RX8...

 

[savahn]

Info: RON 95

Simple answer - Yes, you CAN use RON 95 with rotaries - SA, FC, FD, SE models.

The lower the octane, the easier it is for the fuel to detonate under compression = easier for engine knock to occur = bad for your engine. This is a design of the fuel itself and adjusted by the petrol companies using special additives and formulations.

Engine knock occurs because of high compression, heat and fuel mixture causes the fuel to undergo premature combustion - i.e. before the power stroke (in piston cars).

All engines are designed with a minimum RON rating. This is usually 91 for most cars manufactured year 2000+

Generally, sportscars should use high octane fuel because they tend to have higher compression in the chambers = turbo, supercharge, high compression NA.

It is very recommended to use as high octane as possible for rotaries because it is generally high compression and high(er) operating temperatures. Especially if you are out gunning it. SA's, FD's and FC's are either turbo-charged or have high compression ratios. SE's (RX8) have high compression ratios.

The main affect is engine knock - which leads to or is an indication of detonation - which is very bad for any engine and can cause damage to crankshafts, the engine block and other moving parts. In the case of rotaries, it can cause apex seal damage/failure or in the worst case, engine blow. It is not fun to replace your rotor housings and rotors. However, the FC's and FD's automatically throttle the fuel the moment it detects knock. I believe it is the same for the RX8.

If you use lower than recommended octane fuel, your ECU will automatically adjust to compensate for knock = less power. But the reverse is not true - using higher octane does not increase power. You must use the minimum octane recommended by your manufacturer.

There are a few places where the above is not true - in mountainous regions. There is less air pressure and hence, the octane of fuel will be lower in those areas. I am told that there are some parts of USA where the available octane is RON 87-89.

[EDIT] Officially, please use the highest RON fuel you can find. Those of you who own a PowerFC will be able to see the direct affect of using lower RON fuel - the Power FC will show you the engine knock detected by the sensor. Any excessive amount of knock must be checked ASAP.

---------- Post added at 02:02 PM ---------- Previous post was at 01:27 PM ----------

INFO: Synthetic, Semi-Synthetic and Mineral engine oil

This is specific to engine oil - NOT transmission oil, axle oil, LSD, etc.

Yes, you CAN use Synthetic. BUT there are caveats. Do use the recommended SAE rating of oil required for your situation.

The main reason for using mineral oil is the fact that it is value for money and widely recommended by large portions of the sports car community. It is also the recommended type of oil by Mazda. With cheap mineral oil, cost-wise, you can change your oil 3-5 times more often than with equivalent synthetic oil.

Mineral oil is extracted from crude oil - the stuff from which petrol, diesel, jet-fuel and other petroleum products come from. Mineral oil is a petroleum distillation that has additives such as special waxes and sealants to prevent it from freezing in cold weather and maintaining its viscosity throughout a temperature range.

The reasons for using synthetic is the belief that synthetic is a superior quality of oil. This is both true and false. Synthetics are man-made using chemistry based on esters. It is designed to have excellent viscosity consistency rating throughout a temperature range without additives. This is the primary reason why synthetics are considered superior. Additionally, some believe there are no additives in it that can cook and leave residues inside the oil system of an engine.

We are also told that if you use Synthetics, you can double or triple the period until the next oil change. This is true to an extent.

The problem is the lack of shear and its fantastic smoothness can be a problem. Engines that have been overhauled or had new parts installed need to be "broken in". This is a process of allowing the internal parts of the engine to wear down a tiny amount at lower engine speeds so as to function smoothly. Synthetics are so fantastic that this does not happen so well and can lead to excessive wear and tear at certain areas.

Idemitsu has a synthetic oil that was used in the Le Man 787 racer. When the engine was broken down after the race, it was found to have literally no wear and tear and in excellent condition. I have to point out that the 787 engine parts were machined and balanced to micro-meters of tolerance. This is an excellent situation for fully synthetic oil. None of that is ever done to a standard sports car.

That said, do use synthetic oil if you can afford it. But the point of mineral oil is so you can change it often. Observing the quality of the waste oil can give you clues as the health of your engine.

Semi-Synthetic is a mineral + synthetic formula. The synthetic portion is 30% or less of the total. This makes it cheaper than fully synthetic while providing an equivalent performance. Again, do use semi-synthetic if you can afford it.

However, if you put your car on a dyno, I sincerely doubt you will find any significant power improvement between synthetic and mineral.

NOTE: do NOT switch from synthetic back to mineral. You CAN switch from mineral to synthetic. You CAN switch back to mineral after a rebuild and then change to synthetic.

The reason for this is the additives in mineral oil do not sit well with synthetic. Semi-synthetics are specially formulated to prevent this, but its not the same as mixing a can of synthetic with a bottle of mineral.