poorboybee

HI,

I was just wondering what RPM do you guys ususally shift at? I did a search but couldnt find anything.

thanks

bee

DrunkenBowler

Pretty much whenever you want to shift. Because I think the rotary is moving at 1/3 the time of the e-shaft. For example, your tach will read 3000 rpm and your rotors are moving at 1000 rpm. (I think that is all right.) If I were you, I'd shift it like any other car. If your just crusing the streets, shift around 2k. If your racing, shift at 8500 rpm. Bottom line is, it's a car. Drive it.

spoolin93r1

i usually shift around 8200. my power starts to fall off after 8k, but if i shift any lower, when i get in the next gear, it won't be high enough to get my boost back. in other words, if i shift lower, it'll lag in the next gear

RX7WEEE

iTrader: (16)

damn what sized turbo are u running? a T88?
and are u ported?

spoolin93r1

t78 and yes. it's a somewhat large street port. it's not as bad as that post may have made it seem, but i start making really good power around 5-5.5k. if i let the rpms fall below that when trying to race, it's kinda pointless to continue

DrunkenBowler

Nitrous is the cure for lag. J/k.

rynberg

Your question doesn't make any sense. A single turbo has nothing to do with what's a SAFE rev limit to use, which is what your question was.

Silver7

I found that I had to shift around 7300 to 7500 rpms to get the best 1/4 mile times.

Wargasm

I'm no expert here as I shift at 8000... heheh ... but here are a few factors that come into play to determine your shift point (in no particular order)

1 - Mechanical limits of the parts. Once everything gets spinning, the eccentric shaft flexes. If it flexes enough you can get contact of the rotors against the side housings and the bearings and stationary gears can also fail. You can side-cut the rotors on the edges to reduce this problem, upgrade the bearings, put in harder stationary gears, pin the rotors and rotor gear together, run more oil pressure, etc etc etc to make things stronger if you want to get the maximum potential redline up. Did I mention that most flywheels are only officially rated to around 8000 RPM or so? They will do more, but do you want to see what happens to your legs when a flywheel or pressure plate comes apart at 10,500 rpm? Say hello to Stumpy.

I'm no expert with 8000+ operations, so don't quote me here...

I'll throw out some random numbers here for an FD engine... Again, I'm NO EXPERT here, just giving you some ideas...

8000 - stock redline ... pretty darn safe
8500 - a fair amount of people go to this on a stock block... probably pretty safe in the grand scheme of things. With the possibilities of bad AFR, bad fuel, blown coolant seals, cracked apex seals, overheating of water or oil.... 8500 rpm doesn't seem like the likely cause of engine death anyhow!
9000 - I know you can do it... requires some internal mods as I mentioned above to be safe about it.
9500 - If you're crazy enough and do enough mods to make it happen, you can probably do this too, but by this point, you probably have a pretty crazy FD.

2 - The next factor will be fuel injectors. Or lack of them. As your engine RPM rises, the amount of time to squirt the gas in during the intake cycle goes down. Just some food for thought... at different RPMs, here's how much time your injectors have to get the gas into the chamber:

4000 - 15 milliseconds
8000 - 7.5 ms
9000 - 6.7 ms
10000 - 6.0 ms

So you better have some seriously huge injectors or better yet, at lot of them so that they can open, fire, close that fast! Let's imagine a car that makes peak torque around say 6000 rpm. You may notice that you don't really start running out of fuel injection capacity until 8000? That's because even though you're using MORE gas at 6000, you also have more time to squirt it in. By 8000, you still need a fairly big amount of gas, but not as much as at 6000... but your time to get that gas in there is 25% LESS. So get some big *** injectors.

3 - Power band. OK so you've got this totally built motor that runs 9500 rpm all the live long day. You have a bad *** fuel injector setup so you can dump 2 gallons of fuel per minute into your engine... but you have stock porting and an Apex RX-6 turbo. Hmm. You go to the dyno and notice that your power is dropping FAST around 6000 rpm... By 9000 RPM it looks like your dyno curve is actually going straight down. Heheh. What's wrong? Well you made an engine/turbo combo that doesn't flow enough air at high rpm to necessitate a high redline.

A combo of items 1, 2, and 3 is why I shift my car at 8000.

My engine is built with stock FD parts. Nothing special for high rpm operation... I would not feel safe going over 8500 all the time. So right there I'm going to say to myself, 8000 or 8500 is my max.

My fuel injector setup is hitting around 90% injector duty cycle at 8000-8200 rpm. This is already pushing it a bit. 8000-8500 range is looking like the max here too... hmmm

With my dyno-proven power curve in hand, and MS Excel I can make a graph showing the power put the ground in each gear. I can estimate a little bit (not too far now!) past the end of my dyno graph and see what power I might make a few more hundred rpm later. So if my dyno runs up to 8200 before I lifted, I can probably guess pretty accurately what it might be at 8500... not that far away. So I can make a little spreadsheet... and you know what I found out? Holding out to 8250 or 8500 with MY CAR'S PERSONAL POWER CURVE is only going to get me a SMALL amount of power compared to just shifting at 8000. In other words, I'm not going to push the mechanical limits and the fuel injector limits for what is going to work out to be a VERY small change in the overall peformance of my car.

So anyhow, I know this doesn't answer your question, but I hope it gives you some ideas of what you might think about when picking your redline. I'm sure I probably forgot something too, but forgive me, it's late and I'm tired

Brian

RX7WEEE

iTrader: (16)

Nice little write wargasm!

poorboybee

I dont know.. thats why i asked

poorboybee

thanks for the write up Wargasm!!! that helped a lot

bond007

Stock engine = stock rev limit
How is that for simple and safe?

To raise the rev limit, you have to do modifications to the inside of the motor and at a certain level of RPMS, you'll want a scattershield. You'll also end up having to rebuild the engine more often.

1QWIK7

iTrader: (33)

damn, now im afraid to rev it that high again.. thanks alot hahahah

nah, even now with the minor mods i have, i never hit 8k on the tach yet ever.. i dont even need to, i get alot of power when i shift at like 6-7k

diyman25

is all depend on your PORT and your power band .

For stock 13B RE to W, even thougt MAZDA design this engine to rev up 8500 but the stock peak HP appear at 6000-6500. is point less to rev past that, unless you are in Race condion or got nothing to do .

For different port the power start increase or decrease.

I have two 13B power RX7. one is 13B PP and one mid street port with T04R

On my 13B PP power wont come out until 5K+ and I shift at 8500(on this engine my engine builder already balance every thing and increase oil pressure, so engine is very safe to 8.5K rpm but any thing over this is not a good idea)

My 13BREW street port HKS T04R, with 16 psi of boost my HP start drop at 7k. so is almost point less to drag my RPM to Red line . If I need more HP I can just put more boost into the engine, that why turbo is there.

SO the point is,Stock 13B REW in normal condion (this incl the good oil pressure) you can Rev to 8K Rpm (if any one dont believe it. I got this info from Racing beat)
but is point less with stock port of street port specialy with turbo to drag you engine to red line. I really think If you want to rev pass 8K you should aleast have B port and this will more sense to me