TomX8

How are cranking RPM's of a starter measured? By cutting off fuel supply, cranking the engine and measuring the RPM? Or during a normal start? I would have done it while cutting off fuel supply.

On this website: The Garage - For RX-8 specialist services and professional rotary engine help | Rotary Revs
I read that the N3H1 starter achieves 220 to 250rpm, and the uprated 2kw starter up to 290rpm. Also, the engine needs a minimum of 250rpm to start, or as I understand it, to combust and provide enough power to start up completely.

Now I am ordering parts, and I want to know whether my starter is shot and is one of the causes of my poor starts, since the engine started this winter to accelerate very slowly. In that case I would just buy the 2kw starter and see.

According to this topic: https://www.rx8club.com/series-i-tec...-speed-252389/
I take it that cranking rpm is measured with the fuel supply off, which gives us a constant and clear reading, not biased by any combustion inside the engine. But I just want to check to be sure. I will measure the cranking speed of my RX8 while I cut off fuel supply and report back.

9krpmrx8

iTrader: (46)

Talking about manual trans starters only:

There were two starters for the S1, the 1.4KW and the 2KW version. Both suck, but both when working correctly can achieve 250RPM, but I have never seen an S1 starter get near 290RPM.

Now, the S2 starter is just larger and also 2KW but I'm not sure why it is so much larger. It will spin the engine at between 290-305RPM.

This is the starter you should buy, for a 2009-2011 RX-8.

https://www.amazon.com/Mitsubishi-St...hi+rx8+starter

9krpmrx8

iTrader: (46)

From 1.4KW to the S2 starter.

dannobre

iTrader: (3)

The new one also has more teeth on the drive gear...that effectively increases the cranking speed of the engine

Nisaja

Get a cheap Bluetooth OBD2 adapter, pair it with an android phone, install the torque app and get the RPM gauge on screen. Now just floor the accelerator pedal and crank. There is a fuel cut when you floor it while starting. About 5 seconds of cranking should be enough to get an accurate reading from the torque app. And no, these cars can start with less than 250rpm. My car has a 2kw starter and for some weird reason it cranks at 180rpm. Still starts in a second.

9krpmrx8

iTrader: (46)

The apps are not really accurate for measuring cranking speed but it will give you a general idea. And Nisaja, you have an auto............

Nisaja

Oh. So autos crank slower than manuals?

nycgps

iTrader: (1)

S2 starter has 14 teeth

And the motor is HD version, so it lasts longer than the light duty type motor found in s1

nycgps

iTrader: (1)

Yes, it cranks slower, aroumd mid 200 is the max speed

Nisaja

Whoa. How's that possible? I changed my battery and now I get around 220rpm. Before the new battery I got around 180rpm lol.

TomX8

Cranked my engine like Nisaja said, and read the RPM's out with my OBD2 Bluetooth ELM 327 with DashCommand (essentially the same). Got about 220 rpm's, shootout to 240rpm's.

The first second it turned sub 200rpm, and it slowly went up to 220, and shootout to 240 (as 9krpmrx8 said, it's good for a general idea) over a 5 seconds period. As soon as I turned the engine after it read 240, the car started in 2-3 seconds. Otherwise I need to crank longer than 5, until the starter gets up to speed... or something like that? No idea what is going on. I ordered a N3Z1 starter and will see what it does. I am now filming almost every start I make this week so I can make a quite good comparison video of before and after.

Nisaja

Yes dash command is the same. It may not be accurate but it is the easiest way to check the cranking rpm. It shouldn't need 250rpm to start though. For about 2 days I drove around with a dying battery. Cranking rpm must have been like 100. It sounded like 50rpm lol, but it still started. 180rpm is more than enough to start the car. I had a mildly weak battery since the day I got the car. Used it for 2 years, and for those 2 years the cranking rpm was 180. Never had trouble starting.

Say 9K, why is measuring the cranking rpm through torque inaccurate? The reading comes straight from the ECU. Flooring the accelerator pedal allows the engine to crank without starting. Whatever the rpm that shows up on torque is the rpm the engine is doing at that moment, so what gives?

9krpmrx8

iTrader: (46)

It's inaccurate because I have compared my torque app to my compression tester. But none of that matters, if you have an S1 and want the fastest cranking speed then you need the S2 manual starter. If you are auto then you are SOL.

Nisaja

Oh ok. Why are the autos slower?

9krpmrx8

iTrader: (46)

Slower cars require slower starters.

Lancr735

Cranking RPM based on compression pulses per second?? I adapted a 0-200 psi = 0-10 volts DC sensor to a Trailing spark plug base (1 volt = 20 psi). So in picture attached of Oscilloscope screen each vertical block = 1 volt = 20 psi and each horizontal block = 200 milliseconds or 1/5 of a second. so PSI is about 120 psi and there are about 5 1/2 pulses in 5 divisions which equals 1 second. I calculate this to be about 330 RPM (5.5 x 60 = 330) In this test both trailing plugs where removed, one plugged with the sensor, the other chamber open while cranking so normal cranking load is reduced by half. This is a 2006 auto RX8 with stock starter, new 850 CCA DieHard battery with new battery terminal connectors, ground connections cleaned along with starter connections on a hot engine. My calculation of 330 cranking RPM with stock starter just does not seem possible from all the threads I have read on this subject. Anyone know is my calculation wrong or right? If right how can I be getting this kind of cranking RPM? I'd be happier if it was 250 RPM !!

Brettus

iTrader: (2)

Nisaja

I think if both cars raced, and if it was a rolling start and the the manual shifted at 8krpm, the auto should win... because of faster shift times. Am I wrong? Has anyone tried that?

9krpmrx8

iTrader: (46)

Science,

Nisaja

Lol. Well I raced a S1 manual way back. Same story. Rolling start. He shifted at 8krpm. I pulled a huge lead! His car had a bad ignition though. I think I told you guys about this back when it happened. I'm planning to do the same with a newer S2 GT or an R3. Just wanna see how much slower mine is compared to them. Who knows! It might be even!

9krpmrx8

iTrader: (46)

That whole scenario is just sad.

Lancr735

I'm beginning to think this whole site is sad, ask a serious technical question and get school boy type replies about stupidity

reni04

For all of us with the automatic starters the N3H2 starter which came on my 2004 automatic is around 200 rpm and if you need the upgraded starter for the automatic it is a N3H2-A
2.62 Hp at 2 Kw.

Brettus

iTrader: (2)

It's called the internet .

I didn't try work out if your calc was right or wrong but yes, you definitely get faster rpms if you have one rotor open. I just use a phone to video my compression tester and then count the spikes over a 10 second period . Multiply by 6 and you get rpm .

dannobre

iTrader: (3)

If you have a scope tracing and you count the pulses per time you should get the correct answer. 😎

Don't try and invalidate your answer just because you don't like it.