I did search for this... but I would appreciate a definitive answer

Just what is it that allows for the Series-5 13B motor to redline at 8,000 RPMs as opposed to the Series-4 13B motor's 7,000 RPM motor?

I know (Or at least I've heard) that the Series-5 has lighter rotors, but is that the only thing that accounts for the higher redline? Or were there additional changes such as different bearings or transmission changes (I'm talking about the S4 & S5 N/A, not turbo...)

Thanks in advance,
Derek

 

I dont know it all, but the intake manifold also helps

 

The difference's in the redlines i caused by the the intakes. the s4 and s5 have different rotor compression from 9.4:1 and 9.7:! i cant remember the specific name for it but it starts with a V variable injection or something. I saw a write up on it on fc3s.org i think... but ya. thats yoru main reason.

 

hardened gears, better turbo design etc etc god is in the details

 

I've read about swapping the Series-5 Intake Manifold to a Series-4 Motor, however, it's a fairly long and drawn out process -- from what I've read. If I were to retrofit the part, I'd also like to know what else would be required to get the most out of the naturally aspirated engine in a relative reliable manner.

I can't imagine that compression of the rotors would really change much on the redline aside from possibly making more power (or at least not losing power).

What gears were hardened? The gears within the rotor itself (I don't know their proper name, you'll need to forgive me for that), or are the gears in the transmission hardened?

I guess what I'm asking is: What do I need to do, if it is feasible, to enable my N/A Series-4 to rev to 8,000 RPMs safely?

-Derek

 

hardend stationary gears + lighter rotors

 

The better question is why do you need your S4 to rev to 8000rpm?

 

The peak power should be around 6000RPM for S4 NAs right?

 

well i got a question... I just got an S4 turbo II with an S5 motor, tranny, turbo, intercooler, ( not sure about the ECU?) on stock ports, so where do i redline at? i just assumed it was 7k because I'm boosted, but **** if i had another 1k RPM to go.. then my car is definately faster than i think it is

 

You might have an extra 1k rpm, but you probably won't be making any power there. You'd be better served shifting where you're shifting now.

 

ive also heard something about this without being able to flow the air need... probably why the s5 has higher rev line ,and i wouldnt be suprised if rpm at peak horsepower is higher. this may be caused by the intake design. but even with an s5 your not making power at 8000. so i would be more worried about be able to make more horsepower at a higher rpm then trying to achieve a higher rpm without much gain. Better you can flow air the more effective it is at higher rpm with a lower rpm lose. What i konw of that the s5 has that the s4 doesnt is not only lighter rotors about a .5 pound difference plus ther hardened. along with the stationary gearsf(what the rotors mesh to spin in circles with.) and better bearings. and i believe there 3 window bearings that might be the s6 not sure. Also and electric omp maybe be able to meter the oil distrubation better.

 

The manifold and higher compression allow you to make power at those higher rpm's, but they don't do anything to help the motor withstand those extra revs, that comes from the lighter rotors and the hardened stat gears.

All the TII's have a 7k redline, it's only the NA manuals that have the 8k redline (the auto wasn't rated to go that fast).

 

he just said not a turbo...

 

Also, all turbos redline at 7k.
Actually, the rev limmiter is about the same on s4's and s5's, its around 8.5k (trust me, I have found it on my s4). The redline is lower because there is no need to rev the car any higher as it just makes less power. Peak power on an s4 is ~6500, on an s5 its ~7500. Anything past the redline is pointless on a stock ported motor.

 

^^ im thinking ur the one posting the most knowledge because i got my s4 n/a wit a blown rear rotor to rev to 8k.....

 

Thanks for the replies!

Anyway, I suppose that I don't need my S4 to redline at 8,000... I just thought it would be neat to be able to do... I suppose that I like pet projects and whatnot, otherwise my RX-7 would have been long gone. (My goal being a vintage 80's cruiser)

However, even if the motor was losing power after 6,500 rpms, it would still possibly to be beneficial to shift above that point depending on how much power is lost (remember, we're still talking about mechanical advantage and the area under the HP curve). I've never seen a dyno charts for a stock S4 motor vs. S5 (maybe someone could hook me up)

So I suppose that I should have just asked "What do I need to do to have my S4 make S5 power and RPMs" ... which would essentially be to rebuild it using S5 parts. (Intake manifold, rotors, E-shaft... etc)

On a side note, I've heard that the RX-8's Renesis E-Shaft and Rotors work for application in the 13B... would there be any benefit to these parts?

 

I would love it if someone built a older 6 or 4 port 13b NA using rx8 high compression rotors and lightened E-shaft. It would cost a lot of money, but it would b pretty cool.

Im not sure if the rx8 rotors are lighter, but they have higher compression. The only problem is I remember reading that you need rx8 stationary gears and certain other parts. After buying rx8 rotors, seals, gears , etc etc, your engine build cost is a good amount. It would b badass though

 

RX8 stationary gears aren't specific to any series rotor, but they are a nice upgrade for an older engine. The are hardened and have multi-window bearings. iirc

 

I believe that on a stock engine, you should shift about 200 rpm before the redline for optimum acceleration, maybe sooner if you have an older worn out engine. Shifting past the redline on a stock port engine will hurt your acceleration.

 

I believe the previous poster was speaking about shifting past the power peak, not past the redline.

 

Yes. Shifting past peak power, not necessarily redline. On an AP1 Honda S2000, peak power occurs somewhere around 8,500 RPM, yet it redlines at 9,000. No one really shifts before 9,000 because the car is still making decent power and you'd be maximizing the area under the HP/Torque Curve.

So anyway, I included a chart to illustrate this. I think that we can all agree that when I say "Maximize the area under the curve", I'm referring to the overall amount of work that is done by the motor. So even though we may be losing horsepower after a certain RPM, the engine may still be able to do more work thank it would otherwise be able to do.

For example: (I'm assuming that everyone here has taken a basic geometry course or at least knows how to find the areas of objects more complex than a square.)

(I'm using a Horsepower curve here that is somewhat similar to that of an AP1 S2000)

Peak power is 240 Horsepower and occurs at 8,500 RPMs
At 8,000 RPM the engine produces 220 Horsepower.
And, at 9,000 RPM the engine produces 235 Horsepower.

We'll assume that one is shifting from 3rd gear to 4th gear, then to 5th, finally 6th gear; and that one wishes to have the best acceleration from 3rd gear forward. The change in gear ratios between the gears will be 500 RPMs.

To achieve this we need to have the best possible output for 3rd gear, but also to have the engine produce the most horsepower for 4th gear and 5th gear as well... 6th gear is obviously a special case as it needs to be run to the redline as there is no higher gear to shift to. We need to make the most power under the curve to achieve the desired acceleration. Since the amount of work that the engine is producing at a certain point should be defined as: The Horsepower at an RPM * RPMs. This should be extended over an area to give us the overall output for a range of RPMs. So when we look at our chart of Horsepower vs. RPMs (The attached file), the overall amount of work that an engine is producing over a band of RPMs is visualized as an area.

Calculations:

Shifting at 8,500 RPMs would mean that the engine would have to start in 4th, 5th, and 6th gear at 8,000 RPMs. The area that we are calculating is therefore:

(Power at 8,000 RPMs * Band of RPMs) + (1/2)*(Difference of Power between 8,500 RPMs and 8,000 RPMs * Band of RPMs)
(220 * 500) + (1/2)*(500*(240-220))
(220 * 500) + (1/2)*(500*20)
(110,000)+(5,000)

Therefore the overall work produced between 8,000-8,500 RPMs is: 115,000 units

Shifting at 9,000 RPMs would mean that the engine would have to start in 4th, 5th, and 6th gear at 8,500 RPMs. The area that we are calculating is therefore:

(Power at 9,000 RPMs * Band of RPMs) + (1/2)*(Difference of Power between 9,000 RPMs and 8,500 RPMs * Band of RPMs)

(235 * 500) + (1/2)*(500 * (240-135))
(235 * 500) + (1/2)*(500 * 5)
(117,500) + (2,500)

The overall work produced between 8,500-9,000 RPMs is: 120,000 Units

Clearly it is to the advantage to shift at 9,000 in the car to maximize acceleration. Shifting at 8,000 RPMs would be a loss of 5,000 units of work per shift. Most uncool.

 

That's all well and good, but that's not how you determine when the best shift point is. What you do is take the dyno plot and scale it to the gear ratios in the transmission to get a representation of power to the wheels on the Y axis vs. speed on the X axis (1st being tall and skinny, 5th being short and fat). Then you look to see if the power to the wheels in the next higher gear ever gets to be more than the power in the previous gear. If so then the point at which the lines cross is the optimum shift point.

That way you're guaranteeing that the power to the wheels is mazimized at all times. Most of the time, unless power drops off quite substantially, the best shift points are at redline, because even though the power dropped off from the peak, it's still being multiplied by more than whatever power number in the next gear, besides, most of the time the shift puts you well in front of the power peak unless you've got a fairly close ratio transmission.

 

You hit the accelerator until the tach reads 8000rpm.

 

Black91n/a, what have you found are the rpms for shifting in 1st to 5th on a stock port and a streetport motor?

 

You want the s5 intake, rotors, and stationary gears.
But since you're pulling apart the engine anyway, to go even higher you need a street port, finely balanced rotors, better bearings, higher oil pressure and maybe a couple other minor things. I hear the s5 intake doesn't help after you get a street port, b/c the s5 intake is tuned for the stock port.