No7Yet

Just something I wrote a while back and posted to the RXTech and FC's list, but didn't seem to get much response. In another thread in here, Evil Aviator mentioned that he didn't know what the VE of a rotary was... well, hopefully this will help.

As a disclaimer, the calculations were done for a stock-port 88 13B (6PI), and thus are only marginally applicable to a ported 4 port 13B. I plan to dyno sans turbo my car (streetported S5 13BT) after I get the motor built, so I can find these numbers in a more concrete fashion.

Anyway, enjoy:

VE of a rotary

Brandon

No7Yet

In my search for more accurate numbers, if someone could provide the following dyno charts, it would be much appreciated:

stock-port 4port 13B
streetport 4port 13B
pport 13B (w/ port timing)

Brandon

No7Yet

In my search for more accurate numbers, if someone could provide the following dyno charts, it would be much appreciated:

stock-port 4port 13B
streetport 4port 13B
pport 13B (w/ port timing)

Brandon

Lasse wankel

Dyno'd a 13B PP with a 51mm IDA carb, distriburless ignition, 52mm Idia headers 25" long and a 3" exhaust w 1 straight thru muffler. Numbers are as follows at flywheel (engine dyno):
5000 rpm: 129 hp
5500 rpm: 134 hp
6000 rpm: 152 hp
6500 rpm: 165 hp
7000 rpm: 189 hp
7500 rpm: 225 hp
8000 rpm: 269 hp
8500 rpm: 283 hp
9000 rpm:298 hp
9200 rpm: 296 hp
9400 rpm: 289 hp
Max torque: 172ft/lb@8000 rpm

Lasse wankel

Oh sorry forget to tell you that the port timing were Mazda factory PP numbers on intake with a D-port shape and 44mm venturi, the exhaust were opened 4mm earlier but had the same closening timing.

No7Yet

Lasse, if you're still around, do you remember the air temps on that day? Though it doesn't make a huge difference, I forgot to ask...

Also, based on my previous calculations, it looks like your peak VE was 114%. Not too shabby. In SAE 841017 Mazda was getting similar numbers in their "best compromise" timing selection.

Brandon

RICE RACING

You guys are forgeting a major thing, you need the BSFC and the a/f ratio or the fuel flow rates to correctly calculate out the VE% for that given example.

You cannot and I repeat CANNOT use arbitrary figures and make assumptions as this can make a big influence on the actual Ve of the engine.

Only other way on an engine dyno set up is the use a air flow measuring device on the air inlet to measure the amount of air getting into the engine if you cannot get the other data I mentioned.

I have allot of this kind of data An no it's not from "High Performance Honda Hand Book" J/K Your math is pretty close though, good effort

No7Yet

Well, I know that you've got to have more data than I've got in order to accurately calculate VE, but BSFC isn't something that's usually readily available, while dyno charts are plentiful. Besides, I think my numbers were based on sound premises - torque does vary directly with VE, and the number I gleaned from the Honda handbook (okay, I'll admit, a cheesy source, but it was on-hand) has both stood up to the little bit of scrutiny I've put it through and been found elsewhere (or numbers close to it). I've also been able to apply these formulae to known data from Mazda, and ended up close enough for the sort of bench racing it'll be used for. The issue here is one of lack of data. I plan on doing the hard numbers once I have regular access to a dyno. I wouldn't use my "methods" to fine tune a map, but it's certainly more useful than picking a VE number out of the air when sizing a turbo.

With all that said, why not speak up and add to the pool of info here? I'd certainly be interested in hearing what you've got to say about all this.

Brandon

RICE RACING

Brandon, Firstly "hats off for doing a good job" the more analytical people are the better the end result in their modifications.

If you can develope a formular that will take an input of BSFC and air fuel ratio for argument sake, to get the BSFC you will need to data log the fuel flow or you can derive this from the ECU log it will allow you to accurately find out the VE. there is the "odd" SAE report on maily stratified chare rotaries that publish all this measured data. Other than that you need to collect your own as the info is few and far between.

Factors that influence it are basic compression ratio, boost pressure (for turbo cars) porting style, and so on, all can have a great effect on the BSFC and as such can throw out your VE calculations is your generalising. I would say you can expect a "spread" in the result of +-10% or greater if you use general figures.

If you PM me with a specific question I can help you.

carx7

iTrader: (31)

Very interesting stuff. I was wondering about all this as I am begining my turbo selection decision and would rather develope/design my own setup. I'll have to read it more later.

On a similiar, but slightly different topic, do either of you have formula/theory relating to manifold design? I understand with non-turbo piston engines there is a way to determine optimum runner lengths for the headers. Is there such an optimum lenght for a turbo rotary. There seems to be lots of debate on this topic here in the forum, but other than "I've tried this and it worked really well" I haven't seen any "math" on the subject.

This post has lots of potential!

No7Yet

I recommend the book Scientific Design of Intake and Exhaust Systems. It's dry reading, but very worth it. The too-brief summary is that intake reversion pressure waves move at the speed of sound, and without variable length runners, you can only truly tune for one RPM point. There are all sorts of harmonics that come into play here, but it's too dense to go into now.

Brandon

carx7

iTrader: (31)

Thanks! I look for it.

Lasse wankel

The temperature that day was (in celsius) 15 degrees, 1000 baro and 73% hygro. Dyno numbers are i SAE net.
I shall be dynoing 2 more PP engines in March and April so i will coming back with some numbers. The 298 hp engine was tuned with an exhaust temp probe with a peak temp of 830 degrees celsius at 9300 rpm. Plan to tune with a 5V broadband lambda sond next dyno session.

KevinK2

Interesting shot, Brandon.

10 hp from 1 lb/min fuel implies specific BSFC. I backed out some BSFC and a/f ratio values based on this:

10:1 __ .60
11:1 __ .55
12:1 __ .50
13:1 __ .46
14:1 __ .43

BSFC factor includes the engine thermal efficiency, which is low on a rotary due to high chamber surface areas ( I'll post some numbers if desired )

Since max power is typically done at 12-13 ratios, and rotaries usually figure at .5-.6 bsfc, the 1 lb/min air will net less than 10 eng hp ( and more waste heat hp) ... so VE's would be higher that your table.

$.02

No7Yet

That's interesting, Kevin - I hadn't considered using the arbitrary hp per airmass to calculate BSFC. Thinking out loud here, the problem is that if we knew specific BSFCs and power, we'd know VE. Your table is interesting, and I agree, my numbers are slightly low. If I can possibly find the AFRs for the car that I based my numbers on, I should be able to express the VE as a function with one independant, which will be interesting. We can see how much error is built into my calcs.

Fun stuff!

Brandon

Lasse wankel

Have some numbers o a 13B streetport engine i dyno'd a year ago.
4500rpm: 127 hp
5000rpm: 142 hp
5500rpm: 156 hp
6000rpm: 178 hp
6500rpm: 204 hp
7000rpm: 227 hp
7500rpm: 241 hp
7800rpm: 244 hp (peak power)
8000rpm:242 hp
8200rpm: 239 hp
8500rpm: 225 hp

Max torque was 166,7 ft/lb or 229Nm@7200 rpm.
Engine spec: Extended streetport, Hurley 3mm race seals, 51mm IDA carb w/45mm chokes 235main, 160air jets, 2 MSD 6A boxes w/ direct fire Leading 25" primaries, with 1 3" Apple racing straight thru muffler. Exhaust temparature @8200 rpm: 868 degree C
Air temp: 17 deg C 1000 baro and 75% hygro.
Brandon! Can you calculate the VE of this engine ?