rexset

Ok here is the question
How reliable is to have an 200 mph Rx-7 FD3s ?

According to my calculations with an 4.444 rear diff with 255/40 r17 at 8500 rpm it should do 198 MPH.
Mi goal is to do that with 15 psi of boost ,and not blow the engine.

What do you think about it?

RotaryEvolution

iTrader: (30)

your calculations of speed are off on gearing, taller rear gearing results in less top speed, not the opposite.

and you would need 400+ whp to get there. how reliable is a 400+whp FD? only as reliable as you build it.

getting to 165 isn't a very difficult task, getting to 200 is leaps and bounds more difficult, stressing the engine to it's limits in that power range which is why it's easier to overshoot in power requirements and get there quicker.

rexset

Yep Thats my goal 400 whp at 15 psi
Well i dont want to do that more than onces
But will be nice to know that i will not blow the engine at 200mph at 8500rpms

RotaryEvolution

iTrader: (30)

stock 4.1 diff gearing is good for roughly 170 mph at that engine speed. the auto 3.9 gears would be good for roughly 179mph.

stock tire diameter 255/50R16 is 26.04"
your tire diameter 255/40R17 25.03"

so the stock tire is actually taller, your chosen tire would also result in lower gearing and less overall top speed. you would need taller tires and lower final drive gearing even beyond the 3.9 gear set to reach that mark.

while maintaining the stock tire dimater you would need a rear gear ratio of 3.44 to get to 200mph, or a taller transmission gearset from another vehicle.

rexset

Well acording to my gps
It goes at 3000 at 70mph with the 4.444 rear diff
So at 8500 it should go at 198mph
Remember that the stock red limit is 7500 rpms meaby
1000 rpms more makes a big difference

RotaryEvolution

iTrader: (30)

spinning the engine that high for that long requires special care in building the engine otherwise it probably won't even get there. there's a reason why the redline is where it is, most seals will not take that sort of abuse. ceramics being the exception but any hint of even light detonation and you just bricked a motor.

overall you're thinking backwards, make more power and use lower overall gearing, not higher gearing and higher revs.

even using the auto differential would save a lot of stress on the engine, use boost not revs.

rexset

Fair
So what do you think will be a safe redlimit for top speed?
My engine is not an oem one , bit still you have a point there
Im not crasy about my car to get 200 mph
I just want to know where is the safe area at top speed
I love my 4.444 rear ratio for many reasons so i will not change it
My point is that at maximum load will be nice to know where is the red limit
I have an Pettit Racing street ported with racing 3mm seals
And everything that they offer there
They told me that to be safe i should not try to get more than 420 whp cause im using the car for the street.
So probably i will set the red limit to 8000 rpms and not to 8500
Still i have a big turbo having in mind low exhaust T at hi speed
Its a Gt3586 hta with an 1.06 t4 exhaust housing, small turbos for top speed just dont work at all.

RotaryEvolution

iTrader: (30)

8k is a relatively safe top limit for a turbo engine, beyond that you run the risk of imabalances, rotor tip scuffing and apex seal chatter with 2mm seals, with 3mm metallic seals less... 7k. 3mm metallic seals aren't good for street driven engines as they tend to chatter and gouge housings the most due to their mass. you might get away with a high speed run with little harm but i wouldn't run them that high regularly.

honestly i don't know why they would put a limit on that engine, 3mm are usually built for drag racing big HP number cars.. perhaps to try and keep you from abusing it and wearing it out rapidly, which sort of defeats the purpose.

rexset

Yep 8000 rpms sounds reasonable
I lnow that in a piston engine is quite hard to go uper than 8500 cause the have an armonic unbalance problem
How is the top speed that you have reach on oem look 93 rx7?
I quite concern about the aerodynamics of the car too

SWAT81

iTrader: (14)

inspired by Wangan Midnight?

rexset

Hahahahaha!
Good one!!
Inpired in what we have here in Chile
Nice hiways and no police
And mountain roads
Will be something like a cross betwin initial D and wangan midnight

Monkman33

iTrader: (28)

Wow. So you want to reach a certain top speed, but are not even willing to change out the rear end? I think you need to pick a priority.


I'll simplify it for you:

Stick with the 4.44, enjoy the faster acceleration, stop caring about hitting 200 mph.

OR

Stick with your goal of 200 mph. Do what is needed instead of doing "just enough" or "will it explode if i only do it once?".




You will not reliably have the best of both worlds with your current setup. Sorry bro.

rexset

To by honest 4.44 rear diff with big turbo es perfect for the street
The aceleration is massive and you can drive it on the traffic jam or in a mountain road with no turbo lag problems
So i will sacrify some top speed and let the rev limit to 8000
I have driven my car at 180 mph and with oem look its scary.
Probably not recomended with out a big spoiler in the rear trunk.
So considering the risk i will by more than happy if i can reach the 185mph mark with the 4.444
Acording to my calculation it will be 186 mph at 8000 rpm