porkchop-rob

I am new to this, so please bear with me, I have searchd and read a ton, but i seem to be missing some specifics...

If i wanted to build an engine capable of 10 or 11K rpm, what modifications would I need? I assume I will want to balance the engine and have the oil pressure raised, but what else is necessary to be able to wind the snot out of a 13b with some kind of reliability?

Customisbetter

Tons of money.

porkchop-rob

Thanks for taking the time to post such a worthless response.



In all seriousness, I am interested in possibly building a p-port n/a 13b. I understand that I am asking basic questions, and there is a search function, but I have not been able to find answers that are clear cut and experience based.

I keep reading this statement...."a p-port wont make peak power until over 9k rpm, and you need expensive modifications to run that many rpm"

What are these expensive modifications? Lightened rotors? Rotor clearancing? Pinning? Carbon or ceramic seals? Other things Ive never heard of....?

eage8

iTrader: (9)

I made this thread a while ago when I was rebuilding my engine:
https://www.rx7club.com/rotary-car-p...y-rev-1037909/

some good info in there.

ultimatejay

iTrader: (1)

Side clearance rotors and balance rotating assy, ceramic or carbon apex seals, race rotor bearings clearanced to .004",
Hardened stationary gears, you can use stock RX8 gears with stock rx8 E shaft, oil modifications- adjustable oil pressure regulator set to 140-160psi, oil jets in e shaft, by pass stock oil system and come out of from front iron through oil port on side and then go to remote oil filter and then feed oil to front and rear stationary gears directly. If you really want the best and money is no option than get a two piece E shaft.
Aside from the two piece e shaft I have done all the above to my all motor 13b drag car and I shift at 10.5-11k rpm's for the last 4 years without any problems.

ultimatejay

iTrader: (1)

http://youtu.be/-WyeMt9r-0A

porkchop-rob

Awesome info. Thanks!

Now that I have a little more direction, I'll keep researching and learning.

ultimatejay

iTrader: (1)

Here is a good thread on how to do the oil mods I'm talking about. I do this on my street car.
https://www.rx7club.com/showthread.php?t=745594

peejay

After seeing the graphs on stationary gear loading when the rotor gear has 9 roll pins vs. 12 roll pins, I wonder if the fancy hardened gears and rotor gear retention modifications are even required, and are just a holdover from the days before '86-up rotors were available.

With the 9 roll pin rotors (-1985), gear loading goes practically logarithmic over a certain RPM. With the 12 roll pin (1986-), it stays relatively contant. Anyway, I've been running up to 10k on a regular basis with stock GSL-SE stat gears and Series 4 rotors and haven't had a stat gear failure or a rotor gear walk out. Anecdote isn't data but this is data:



Note the double chart. Gear loading is not constant, it's cyclic. They don't mention the frequency, but I would assume that the frequency is one cycle per revolution.

peejay

If you need tons of money, you're doing it wrong If you spent even $6k on a rotary, you'd be in the ballpark of a $20k piston engine of equivalent build.

ghost1000

iTrader: (1)

Is it Na Or turbo? I'm slowly peicing together a turbo build for my car and I'm incredibly disappointed to see so many turbo rx's shifting @7000 rpm. To me this is 1500rpm too soon and a incredible waste of power because the hi revs are the rotaries biggest advantage. I've been looking into rpm based boost controllers to fight boost drop off, I believe its safe to over boost at higher rpm when manifold pressure is say 15psi but combustion psi drops at hi rpm. My understanding is as the rotor spins faster there is less time for air fuel to enter combustion chamber, and with higher exhaust back pressure with the turbo it takes more boost to maintain power at higher rpms. I'm used to seeing hi reving turbo rotaries at the track and anyone with more knowlage or experience please speak up.

ghost1000

iTrader: (1)

The theory, For pump gas where detonation is a problem at lower rpm the engine is more likely to detonate but as rpms increase so should manifold boost pressure as its safer to run higher manifold boost at hogher rpms also fighting boost drop off for higher peak power.

The question why do people use 1 boost pressure say 15psi for the entire rpm range, and Have to shift so early?

I have already opened a thread on this and so far no comments so please anyone who knows speak up.

peejay

Number of reasons I can think offhand are turbo size compromises for desired responsiveness, shifting issues with transmissions strong enough for the added torque, ignition issues, thermal issues...

Drag racers will spin 'em up under high boost but drag racing is also a very lightly stressed form of motorsport.

ghost1000

iTrader: (1)

The reason I think most people don't use rpm boost controlers is because they don't think of it and there is almost no documentation on it. After being in several low reving turbo rotaries I started thinking about why the can't make power at higher rpm. I'm basing my current build on this theory. Ill make it or break it. The only problem I fear is the waste gate opening prematurely do to hi exhaust pressure. I also might have to run the waste gate pressure reference to a low pressure zone like after the intercoller, so I plan on taking baby step with the tuning.

peejay

I wouldn't want the boost curve to go UP with RPM if I could avoid it. I'd rather have something with a lot of midrange boost that tapers off as RPM climbs so tirespin becomes self-limiting - power drops as RPM climbs.

ghost1000

iTrader: (1)

The goal is not make some crazy power but to fight boost drop off and make usable power all the way up to where the engine is balanced. Rotaries can be pushed beyond the rated balance for short periods of time but not continually. The higher you rev the better the use of low gearing. Shifting at 7500 rpm is lame

I've noticed non turbo to turbo conversions make peaCheck out this video on YouTube:

k power at a lower rpm piston and rotary. I guess this is do denser air trying to go through the same size port, back pressure from the turbo and heat. I want find someone who has done this before I pop my motor but I'm in this for experimentation R&D screw sticking to what people know works I want to go beyond that using engineering at some level. First make it work on paper the. Make it work on my car.

madbouncy

Boost is generally falling off because the turbo is going beyond what it can flow, and commanding higher with your boost controller based on rpm won't fix that. As peejay mentioned, people usually size the turbo so it flows just enough to keep power from dramatically falling off at their redline and then run that boost as a constant because of the need for increased anti detonation to ramp to very high boost in the mid range and then trail it off as the engine starts to outflow the turbo.

Basically, as you are entering the part of the compressor map that efficiency starts falling off fast, you're going to be asking more out of the turbo. The solution is to run a larger turbo or turbine, but then you loose low end. For racing, a 4000 rpm powerband is a 4000 rpm powerband, whether it starts at 2000 and ends at 6000 or starts at 6000 and ends at 10000, it makes little difference if you can change the rest of the gearing. However, on the street you aren't in the same boat and if you spend most of your time at 3000rpm, it's not much fun having to always downshift just to get the car moving worth a damn.

Sometimes you don't see people doing what you want to do, not because it won't work, but instead because it's not something anybody else wants. If your turbo can only support a 3000 rpm band at the boost level you want, no magically boost controller is going to be able to change that.


Paper AND engineering?! Plan sounds pretty fool proof to me.

ghost1000

iTrader: (1)

Lots of guys are running low boost on pump gas and get better numbers with meth and higher boost so its not a issue of running out of turbo for the cars I have been in. It's about detination. Also I'm using a Bw362s which has a big pressure map. I bought it for several reasons, reliable inexpensive and will work on my test engine as well as a built motor capable of more. $650 a month day care is killing my project and forcing me to be more carefull. I don't believe running out of turbo is the issue, I believe boost drop off is do to combustion pressure dropping at hi rpm even though manifold pressure is the same and I believe it is at that point it is necessary to raise manifold pressure to maintain combustion chamber pressure. I will post my results I'm my own thread. I'm hoping to have this done by the end of summer. I'm trying to avoid doing more than a street port.

madbouncy

Boost dropping off has nothing to do with combustion pressure. Running the engine out of it's peak efficiency area is what is causing the combustion pressure and power to start falling. The increase in back pressure is from your turbine being unable to flow enough to keep up with the engine.

Most peoples setups aren't being pushed to the very edge of performance. A low boost setup is done to be safe to drive around and if you start running higher boost at high rpm you are defeating the purpose of that setup and might as well just run higher boost everywhere. OEMs will dip down the boost at peak engine efficiency to maintain a flat torque curve and you could do the same but it's more work to just limit yourself from making an extra 10-20 hp and have a flat torque curve instead.

$650 a month for daycare is cheap. In Chicago for a middle range daycare it was over $300 a week and even in Ohio the same daycare is $215 a week for the full 5 days.

peejay

A 2000-6000rpm powerband represents a 200% change in speed from the bottom to the top. A 6000-10,000rpm powerband represents a ~66% change in speed. The higher revving engine has a powerband 1/3rd as wide. An equivalent powerband would be something that made power from 3300-10,000.

If you have to worry about tirespin, you want to have an additional 1000-2000rpm or so of headspace above your powerband. So say your engine makes peak power at 7500, the powerband falls off at 8500, then the engine needs to be safe to 9500-10,500 if you want to be able to drive it without having to worry about hurting the engine. The engine will be so far out of its powerband by that point that you won't go past that. Rev limiters kill engines, don't rely on those.

madbouncy

You're definitely right, thank you for catching that. I should have made my point more directly, the turbo can only flow from its min to its max air amount and it doesn't matter where you put that in the rpm band, it won't change the amount of air the turbo can move.

ghost1000

iTrader: (1)

2,000-6,000 rpm change is a 67% change not 200%
6,000-10,000 rpm is a 40% change not 66%

The turbo isn't out of steam until the waste gate is fully closed and you're running out of boost but as soon as boost drop of hits the turbine will slow causing boost will drop and the waste gate will shut and this makes it seem like its run out of turbo. Like said its hard to separate the two because as combustion pressure drops at hi rpm so does exhaust pressure and the turbo slows, but in theory if u raise manifold pressure just b4 this happens you will maintain combustion pressure =power and as rpms rise so will turbine speed and boost making full use of the turbo and the hi revving balance of the rotary engine. Too small turbo is defiantly not always the case. Most of the time a small turbo will out preform a big turbo because of lag and the big turbo can't make more power because of detonation.

Again at low rpm the air has 67% more time to fill the combustion chamber allowing a higher volume metric efficiency VE or by your math 200% more time which means higher chance of detonation running the same manifold psi a low rpm. At higher rpm. There is 67% less time for air fuel to enter combustion chamber so a higher manifold pressure is needed to maintain power.

You just boosted my confidence this will work

peejay

Indeed. Most turbos only have doubling, maybe tripling of flow from minimum to maximum in the effective flow range at normally seen boost pressures. The ones that are broader, don't tend to work as well at higher boost. The ones that are efficient at higher pressure ratios tend to have narrower flow ranges.

The thing with turbos is that turbo speed makes pressure, not flow, until the turbo starts to run out of steam. This makes sense given that the air compression comes from centrifugal force so you need to throw the air faster in order to make more pressure.

Here's a map with engine load points on it for reference:



As you can see, the turbo is running out of steam already by 5000rpm. The turbo is falling into a zone where it needs to spin faster in order to keep up with airflow, so the air is being overcompressed so it can expand to meet the volume requirements. Efficiency is taking a nose dive, they didn't even bother to make a 55% island since the 60 and 50 percent islands are so close together. Note how close 5000 and 6000rpm are in terms of volume flow, versus where the turbo is at in its happy zone.

The only thing you could really do to extend the powerband would be to make the turbine smaller so as to spool the turbo more quickly, but this poses thermal issues that would need to be resolved, and the top end may wind up being more choked off.

peejay

6000rpm is only 67% faster than 2000rpm? So if I am driving at 2000rpm and am going, say, 50mph, then if I accelerate to 6000rpm I will be only going 87mph?


Long before you get to that point, you will have lost so much power that you will have upshifted already. Turbos that are not free-floating have hotsides that are generally too small to flow enough for the compressor's max output.

TonyD89

iTrader: (10)

You could use a small turbo and a large turbo and have them transition through the RPM range.