takahashi

My problem:
Towards the end of back straight of my fav race track at about 170-190kmh @4th gear and slightly uphill. In that range I found the car very sluggish, slightly hard to get up there, so car can gain on me. Have not try to shift early to 5th gear though :o

Best Motoring has been commented on the long gear of the RX-8 and many of you have said that before.

Possible solution:
Change of final drive to 4.777 (like the one in Fujita racing)
of course the better solution is to get a new set of gear

Questions:
Will that solve the problem?
Change of odometer reading?
Possibly make some gear better and some worse?

Thx for your advice in advance....

1.3L-of-pure-crack

A slightly lower top speed is the only real draw back. I think it would be a very good upgrade.

RXE16T

Taka, I have posted a thread about potential diff ratio changes.

https://www.rx8club.com/showthread.p...ght=diff+ratio

takahashi

Seen this thx


Still has not answered my question :o

GeorgeH

iTrader: (2)

What RPM are you running in 4th @ 190 kmh? Dropping the final drive will make the car feel more responsive in any given gear, but if you drop it to far you may find yourself in 5th at that speed, in which case you of course have hurt yourself.

Fanman

Might a lightweight flywheel help here. It will help you rev faster through the range. I would like more aggressive gears 1-5 gears, but either leave 6th alone, or lengthen it. I'm already at 4000-4200 RPM when I'm crusing on the freeway. The last thing I need is a higher rev during cruising.

takahashi

It will be about 8000 rpm at 4th gear slightly uphill. I was thinking whether I should shift a bit earlier. Shortening all gear with a final drive will mean I can do 5th gear at the end and hill toe one gear down for the S band ~130 (or 140-150 if I finally decide to go semislick).

Will the 4.777 work - I have it the MazdaSpeed VII in the BM video and I love how the car revs in Tsukuba.

Yes I think it will help. I will eventually change that with the clutch together. I am waiting for the warranty to expire (which still have 2 years to go :o ). Certainly the clutch line and brake line will be done at the same time.

I totally like the 6th gear at present but I am prepare to trade 500rpm, if it means a better 1-5th, since in Australia the speed limit of the city motorway is 100kmh (or 62mph) so I am crusing about ~3200rpm @ 6th gear. I am happy to cruise @ 3700 rpm

Aoshi Shinomori

I don't see why a 6th gear couldn't be changed if the final drive were altered. I know it's been done on other cars so it shouldn't be a problem. I'd like to see a much less aggressive 6th gear, but a much more aggressive final drive. 5:1? I don't really know how it would all get worked out, maybe some of the experts could explain it to us, but I think it is something feasible. If I have posted some misinformation let me know, there's a good chance I rambled about something that made no sense.

GeorgeH

iTrader: (2)

One thing to remember - if you go with the semi-slicks, you will be carying more speed through the corner which leads to the straight, and that will mean more speed down the straight, and you may find 5th gear to be more reachable, even with the 4.444 gears.

Having said that, the 4.777 gears will allow the car to accelerate more strongly down the straight (assuming you are in the same gear in the corner leading to the straight with either gearset), so you should be traveling a bit faster at the end of the straight, all other things being equal. Even if you are "still" only reaching 190 kph, the 7% reduction in gearing will eat up about 600 rpm, so now you should be at about 8,600 rpm. Add a few hundered rpm due to the higher speed, and 5th gear may be a necessity.

But I have to ask - why do you want to be in 5th? If the car is sluggish in 4th, it seems like it would be even worse in 5th, even with the lower final drive ratio.

IZoomZoomI

get smaller wheels...

takahashi

Think of that, I might come out of the 2nd gear corner before the back straight at a higher rev (usually 5000 rpm). That will help.

Yes you are right... I think to solve the problem of acceleration:

1) Go back and tune it properly at 7-8k rpm in 4th gear. I think a mere piggyback/canzoomer is not enough. Need a TSI or even better a replacement ECU.
2) Get the 4.777 and lighter flywheel +/- clutch (since it is nice to change fly and clutch together ).

Hmmm... thx for all the thinking. I think if I will put on the semislick first and try to come out of the corner quicker.... that is what my instructor was telling me to do: "Nail the turn 4 before back straight, so you are in the higher rev before going up the hill (before the end of back striaght)."

I think better traction is good as I power oversteer easily coming out in 2nd gear :D. My right foot is not as that good yet .

:DSilly boy. That will not work since my rotor will be too big for even a 17". Not worth the risk.

RXE16T

I didn't know there were different brake packages?
The US market has a 8 that comes with 16" alloys standard..... are you saying they have different diameter disc rotors?

takahashi

Standard rotor (with 16" in US and Japan) has a dia of 303mm

Our cars (with 18" and in Type S JDM) has a dia of 323mm.

So when you order rotor from Japan - you have to know what dia of disc and caliper you are using

RXE16T

Thanks for clarifying Taka.

takahashi

You see as a preorder customer you get a 200 page RX-8 book.

It is a great toilet magazine... in the days of constipation, I spent hours reading about my car

RXE16T

Way too much info.....

GeorgeH

iTrader: (2)

Good idea to do the semislicks first, and good advice from your instructor.

I did a track day in my Miata last summer. While the power output of my Miata is basically stock, the suspension is highly modified, including (most importantly) a set of semislicks (shaved Toyo RA-1s). I ran in the intermediate group, and I was by far the least powerfull car in the group. There were M3s, Corvettes, STIs, an NSX, and even a Ferrari 360. Only one other car in the group had semislicks - an M30 M3.

Now, I'm not going to say that a Miata can outrun a 360 on a track, but in the final run group, I was the third car out, with all that exotic hardware behind me. The only car to catch me in 25 minutes of driving was that older M3. I'm sure this has allot to do with drivers not wanting to risk their expensive cars (the 360 & NSX drivers said they were keeping it to 120 mph on the straights, where I was barely touching 100), but there were some dedicated drivers in that group, and I'm sure that if I were running street tires like everyone else, I would have been passed by more cars. Corner exit speed can make up for HP defecits, up to a point, anwyway.

takahashi

Although it is out of topic - but this is my thread then who cares

How does Toyo RA-1s compare with others?

So far I found I can get in Melbourne --- Michelin Sport Cup, Potenza RE55S, and Dunlop Direxza (?) D02J - the M1 or the S1.

Per corner: Sport Cup is about $600, Potenza and Dunlop is about $450-550.

Sport Cup feel so soft that it only last 3000km on the road, Potenza are harder compound and can be used on the road. Dunlop D02J M1 compound is about the same as Sport Cup and S1 is for lap racing... I have no idea in grip, and seen no reviews as yet. The only information I have is about the Potenza in the Japanese website... I am very tempted to go all out with the Sport Cup and I am sure it will be the softest compound - but they said it normally last 4 track days in the Porsche up in the Eastern Creek Raceway, Sydney.
I am so Maybe I just forget which one and just get a set first

dmp

fwiw - incase i missed it, by 4th? gear, any advantage to a lighter flywheel would be gone.

takahashi

more information please?

I am interested to know the reasoning. Thank you

dmp

Here's my 'get out of jail' comment:

"At least on PISTON engines..."

Here's a neat little calculator I found online awhile back...in Miata Circles. Enter the gear ratios, etc...displacement...and it shows the 'effective' gain, per gear.

http://www.d-mphotos.com/movies/flywheelcalculator.xls


I'm assuming the physics translate to Rotary engines too. Let me know what you think!

- darin

dmp

what do ya think??

GeorgeH

iTrader: (2)

Yes, dmp is correct. Light flywheels really only help in lower gears, in terms of acceleration. Their benefit is directly proportional to the rate at which the engine accelerates and therefore are most effective in 1st, less so in 2nd, and practially unnoticable in 3rd and higher.

I've never directly compared the RA-1s to any other track tire, but I know they are on the hard side for semi-slicks/R-compounds. Probably not competetive with any of the newer tires you list in terms of sheer stick/lap times. I bought them because they come in a nice size for the Miata, they can be driven on the street, and they are practically impervious to heat cycling, so they last along time compared to other such tires. And they are still faster than any street tire, including Falken Azenis.

takahashi

Sounds like I am heading to the Potenzas RE55S...

And I think the solution is really in the tyres +/- final drive/diff ratio...

I will research a bit more, but I am serious about the advice of changing to semi slick.

Thx for all the advice.

dmp

This is why a lighter flywheel likely won't be measurable on a dyno (most runs are in the gear closest to 1:1 - whichever that is on an RX8)...but will provide real-world results.