My dyno plots - ugly

Keith Quistorff · **Posted:** Mon Mar 21, 2011 9:46 am

Thanks to Rodney, I was able to get my RX-8 dyno'd for cheap on Saturday, which I've wanted to do since buying it a few months ago as the engine warranty runs out in ~5000 miles. The results were pretty ugly, at least above 6300 rpm (the blue plots are a 4th gear pull to 8000 rpm, the red plots are a 3rd gear pull to 7300 rpm. Not sure why the dyno operator shut it down before the 9000 rpm redline, but no matter - it's obvious there's a problem at high rpms):

A normal RX-8 HP plot steadily increases to ~180 HP:

The two dips (at 6300 and 7300 rpm) coincide with opening of auxiliary intake runners. Since my engine takes a dump right at 6300, it seems to make sense that my issue would be related to the function of the secondary runners. I've posted this issue on RX8Club.com, hopefully it's a relatively known/common problem w/easy fix. We'll see.

BriceJohnson · **Joined:** Thu Apr 13, 2006 7:33 am **Posts:** 2230

Ouch. You are making only 10 more whp than a mazda3 (rated at 160 hp). My pull didn't go all the way to redline either (I ran into the 118mph speed limiter since it was a 4th gear pull). Something is most definitely wrong.

Jason Mauldin · **Posted:** Tue Mar 22, 2011 7:07 pm

Keith, on a normal engine :wink:

a broken line like that could indicate a weak ignition system. Ie, spark plugs, wires, etc... And it typically gets worse at higher RPM.

I don't know what's in your ignition system that is serviceable, but if the guys on the RX8 forum aren't any help, you could take a look at some of those components.

Keith Quistorff · **Posted:** Wed Mar 23, 2011 8:11 am

Jason Mauldin wrote:

Keith, on a normal engine :wink:

a broken line like that could indicate a weak ignition system. Ie, spark plugs, wires, etc... And it typically gets worse at higher RPM.

I don't know what's in your ignition system that is serviceable, but if the guys on the RX8 forum aren't any help, you could take a look at some of those components.

Jason - thanks for the suggestion - turns out rotaries are extremely hard on ignition components - the plugs, plug wires, and coils on RX-8s are only good for about 30 kmi. When I bought the car it had well over 30k since the last ignition service so I installed all new OEM ignition parts. So unless I got bad OEM stuff, that shouldn't be the issue.

The other known issue with rotaries is they are very hard on catalytic converters, which could also explain this. According to the service records for my car, the cat was inspected via a Mazda recall at 79 kmi and supposedly was okay - I wonder if it was bad then and missed or has become bad (clogged) since.

Steven Carter · **Posted:** Wed Mar 23, 2011 12:52 pm

Sorry if this is ignorant...wouldn't there be a CEL if there was an ignition or cat problem? If the intake runner thingy you mentioned doesn't open, that wouldn't necessarily throw a code, or would it?

Curious to see what turns up. Obviously it doesn't impact your ability to drive.... :thumbsup:

RodneyWright · **Posted:** Wed Mar 23, 2011 1:11 pm

Just tag along on the dyno info, I was rather pleased w/ my results. In regard to bolt on's for the car, I've added the following items, a JLT CAI, SCT 87/91/93 tune and a set of Stillen axel back mufflers. I had the car set w/ the 93 tune during the dyno. Assuming the 300hp from the factory at the crank and backing off a traditional 15% for the drive train, a stock GT should show about 255hp at the rear wheels.

After the dyno run, I was plot just shy of 295 HP and 302 torque at the wheels. A net gain of 40hp isn't too bad for the bolt on's. I will say the driving the car on the street w/ the 93 race tune is tricky. Seems there is a built in throttle up even w/ static pedal movement.

Keith Quistorff · **Posted:** Wed Mar 23, 2011 1:13 pm

Steven Carter wrote:

Sorry if this is ignorant...wouldn't there be a CEL if there was an ignition or cat problem? If the intake runner thingy you mentioned doesn't open, that wouldn't necessarily throw a code, or would it?

Curious to see what turns up. Obviously it doesn't impact your ability to drive.... :thumbsup:

Not ignorant at all, Steve - you are correct. In most cases like this a CEL should result, but not always - it apparently depends how severe the problem is that causes the power loss. For instance, there are just as many reports on the RX8 forums of CELs with cats going bad as cases where no CEL appeared. And if the intake runner valve failed it would definitely light up a CEL, but there are supposedly cases where the valve is partially working and no CEL appeared.

I'm not getting much useful info from the RX8 forums to help identify the cause, so it looks like I'm going to get Capital Mazda to take a look at it. Given the engine is still under warranty, I figure it's probably best to start there.

Keith Quistorff · **Posted:** Wed Mar 30, 2011 5:12 pm

Update:

I took the RX-8 to Capital Mazda service dept on Monday, reporting lack of power above 6000 rpm. They found nothing obvious wrong and said they could not tell by driving it that it was down on power. They did find the ignition performance appeared to be degraded, which is a very common problem with RX-8s and the reason I replaced all the ignition components with new OEM stuff a couple months ago. They cleaned up the ignition ground and said it appeared to fix the problem. They also uploaded the most recent version of ECU software and sent me on my way. My butt dyno noticed some improvement, but nothing major. A return to the chassis dyno today confirmed the same:

The curves improved significantly from 6300 to 7300 rpm with an increase of 17 peak hp; no improvement in peak torque, but the torque curve looks a bit better above 6300 rpm. Still lacking power, but a definite improvement. This makes me wonder if the ignition system is still not up to par, certainly seems like the most obvious culprit given these results.

JamesShort · **Posted:** Wed Mar 30, 2011 7:16 pm

Well hell, I thought they'd says your intake butterflies were sticky. Hopefully new ignition fixes your issue....then you can continue to dominate

.

Jason Mauldin · **Posted:** Wed Mar 30, 2011 7:34 pm

What is that second dip at 7500rpm?

It looks like what you have going on now is independent of your ignition problem, and is associated with whatever happens at the dip.

Although, you start losing torque after the first dip, compared to the other graph.

RodneyWright · **Posted:** Thu Mar 31, 2011 8:18 am

JamesShort wrote:

Well hell, I thought they'd says your intake butterflies were sticky. Hopefully new ignition fixes your issue....then you can continue to dominate

.

Yeah, hope you continue to dominate in STX Keith!! wait, what :shock:

Keith Quistorff · **Posted:** Thu Mar 31, 2011 10:32 am

Jason Mauldin wrote:

What is that second dip at 7500rpm?

It looks like what you have going on now is independent of your ignition problem, and is associated with whatever happens at the dip.

Although, you start losing torque after the first dip, compared to the other graph.

Hey Jason - thanks for the input - turns out you were right about the ignition. As for the dip at 7500 rpm, that's the final stage of the multi-stage intake runners opening.

Jason Mauldin · **Posted:** Thu Mar 31, 2011 11:22 am

Is it common for those to stick or fail somehow?

Michael Westerfield · **Posted:** Thu Mar 31, 2011 11:25 am

Jason Mauldin wrote:

Is it common for those to stick or fail somehow?

Sounds like "carb cleaner" to the rescue again!

Keith Quistorff · **Posted:** Thu Mar 31, 2011 3:35 pm

Jason Mauldin wrote:

Is it common for those to stick or fail somehow?

It's been reported by a few folks, but not very common, and it should trigger a CEL.

Based on continued searching of the RX8Club forums today, the fact that my power curves show some issues starting well below 7500 rpm (and clearly at their worst above 7500 rpm) suggests a couple other possibilities - Secondary Shutter Valve (another of the many runner valves in the intake manifold) and/or carbon build-up on the apex seals, both of which are addressed in a Mazda Service Bulletin (and both service procedures look like a major PITA!).

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My dyno plots - ugly

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