Mazda Rotary Club

Had my car dyno'd today using a Maha dyno. Not 100% sure about the results as they seem kind of high to me by about 40-50 bhp but I'm not complaining! The curve is pretty good and the torque curve can't really be improved without more fuel and more boost on the primary.

AFRs at the low end start around 11.4:1 after about 3,000 RPM average about 10.9-11.1:1 to redline.

Air temps on water were low 30's C, off water as you see in the Commander shot.

Stock fuel system. Stock 550/850 cc/min injectors, stock pump hotwired for full 12V, HKS Twin Power and mods in signature.

Ambient temps were about 8 C today. Pretty cold.

398 Bhp (340 Whp) @ 6,036 RPM, 350-360 lb/ft (299-307 Wlb/ft) @ 3,000 - 6,000 RPM.


Video of the dyno and my disbelief



(https://i.imgur.com/N3Y8J17.jpg)

(https://i.imgur.com/oNZPfIb.jpg)

Really nice result!  :13:
I thought that stock REW cant do that kind of power...

95% injector duty is pushing the limits of your current injectors. Might be wise to get some bigger injectors

Maybe, but a few things about that:

• In cold weather like yesterday the duty was 95%, normally it's in the low 90s.
• The injector duty spikes to 95% only around the transition point as it is the most critical and dangerous part of the map. 3,500-5,000 RPM to ensure there is enough fuel there at all times. Everywhere else in the map it's closer to 90%.

[li]I asked several tuners in the UK (Hayward, WGT, Rotor Torque) before deciding to push for over 1.0 bar on the stock fuel system, and every single one said that they have never seen injectors fail or get stuck open even at 100%.
[/li][/list]

Now, that's not to say I shouldn't have a little more headroom but then I'm not 100% sure that even matters. I don't think the Power FC is smart enough to recognise an underperforming injector or low fuel pressure and supplement those types of issues to inject even more fuel. It just reads from pre-loaded fuel tables with temp correction factors to inject more or less fuel depending on intake air temps. So, if an ancillary like a fuel injector fails it is going to pop anyway.

But please tell me if I'm wrong?

In any case, I won't be boosting much in the cold weather as I won't be driving it when the salt arrives so I should be okay. If not, well it's my fault then but I would rather run just under 1.0 bar than swap out my secondary fuel rail and make all of those mods for overkill 1650s.

Nearly 15 psi...when i swapped turbos mine was running 15 to 16psi at the top end of the rpm...its been mapped at this but i subsequently tuned down to 13.5 14psi with an orifice plate in the end of the downpipe...its defo got less power with 1.5psi cut...i thought 400bhp was poss with 16psi tune so your not far off...
How long the turbos last though is debatable...not talking seals but wastgate cracking up with the heat....and in ability to flow through wastegate and boost creep and knock...thats what concerned me but i dont have water injection.
I just had rotary paranoia with it when taking to track so cut it back abit.


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Yeah, that's exactly why I added water. If I was going to try to run c.15 PSI without a huge V Mount then I wanted water to keep things cool. jdmr_neil ran 1.2 bar (17.5 PSI) for over 4 years doing mostly track days with the car and running 500cc/min of water before his twins started to smoke slightly.

Right now I'm using a set of early spec twins and saving my 99s for later so I don't mind potentially cooking the early spec ones that much. When I put the 99s back in the car boost will be turned down to 0.85-0.9 bar as they are too valuable to push too hard.

Yep and tbh i could have easy kept tracking mine as they were still boosting perfect and only a little smoke on overrun. I also had a standard fuel system worth exception to a bosch fuel pump and the base pressure was slightly increased.

Im really pleased with your bhp figure. I always felt my car was around the 400bhp mark judging by the cars i was sitting on the bumper of on the long straight at croft. It would be nice to see some kind of industry standard with dynometer systems and operation so it gets rid of such a variance in results i saw.

All in all, great results on a lovely car.

Mmmm i need water...i miss that extra 1.5 psi lol! Got used to what i got...

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Was you wastegate ported Neil?

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Quote from: neil_jdmr on November 13, 2017, 04:49:35 PM
It would be nice to see some kind of industry standard with dynometer systems and operation so it gets rid of such a variance in results i saw.

Exactly. I dont understand why there is so much difference between dynos...



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Quote from: re japi on November 13, 2017, 05:13:04 PM

Quote from: neil_jdmr on November 13, 2017, 04:49:35 PM
It would be nice to see some kind of industry standard with dynometer systems and operation so it gets rid of such a variance in results i saw.

Exactly. I dont understand why there is so much difference between dynos...



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I had almost 80bhp difference from 1 dyno to another with another reading just north of the middle.

No Jon everything was standard turbo wise

Iirc it was 409bhp, 386bhp and 327bhp all on the same car within a year???

Quote from: neil_jdmr on November 13, 2017, 05:24:25 PM
Iirc it was 409bhp, 386bhp and 327bhp all on the same car within a year???

Well, thats a really big difference.  Usually its about 30-40 horses in 300-400 power range...

Offcourse weather,  circumstances and so on has some effect, but not 80 horses...

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Ive no idea what mines running at circa 320 bhp est now at 13.5 psi..based on some previous owner dyno runs...original tubbys had a blow on flange so replacing them and adding a twinpower..took me 2 15/16psi. Its tuned by Carl at that but i followed his advice and fitted the orifice plate in the exhaust to control the creep..
Seems every car gonna behave different bit like the dynos lol!.

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Quote from: boosted on November 13, 2017, 05:34:56 PM
Ive no idea what mines running at circa 320 bhp est now at 13.5 psi..based on some previous owner dyno runs...original tubbys had a blow on flange so replacing them and adding a twinpower..took me 2 15/16psi. Its tuned by Carl at that but i followed his advice and fitted the orifice plate in the exhaust to control the creep..
Seems every car gonna behave different bit like the dynos lol!.

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What I have heard/read, pre 99 models usually have that about 320 with 1-1,1bar boost. Some have gone up to 350 range...

Dunno much about 99 models, but I think they have better turbos(about 15% better flow) and better ecu than pre 99 models...

But yes, usually I suspect that dynos is not accurate...

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Quote from: neil_jdmr on November 13, 2017, 04:49:35 PM
Yep and tbh i could have easy kept tracking mine as they were still boosting perfect and only a little smoke on overrun. I also had a standard fuel system worth exception to a bosch fuel pump and the base pressure was slightly increased.

Im really pleased with your bhp figure. I always felt my car was around the 400bhp mark judging by the cars i was sitting on the bumper of on the long straight at croft. It would be nice to see some kind of industry standard with dynometer systems and operation so it gets rid of such a variance in results i saw.

All in all, great results on a lovely car.

Well, companies have to make a profit so there are lots of dynos! Dynojet, Mustang Dyno, Maha Dyno, Dyno Dynamics, V-tech, Superflow, and the list goes on. And they all have several settings to adjust load, air temp correction, whp to bhp conversion, etc. Haha.

Quote from: neil_jdmr on November 13, 2017, 05:24:25 PM
Iirc it was 409bhp, 386bhp and 327bhp all on the same car within a year???

Which dynos? Lol. And do you have the graphs? It would be interesting just to see if the curves across your three dynos at least look the same.

Quote from: re japi on November 13, 2017, 05:50:39 PM

Quote from: boosted on November 13, 2017, 05:34:56 PM
Ive no idea what mines running at circa 320 bhp est now at 13.5 psi..based on some previous owner dyno runs...original tubbys had a blow on flange so replacing them and adding a twinpower..took me 2 15/16psi. Its tuned by Carl at that but i followed his advice and fitted the orifice plate in the exhaust to control the creep..
Seems every car gonna behave different bit like the dynos lol!.

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What I have heard/read, pre 99 models usually have that about 320 with 1-1,1bar boost. Some have gone up to 350 range...

Dunno much about 99 models, but I think they have better turbos(about 15% better flow) and better ecu than pre 99 models...

But yes, usually I suspect that dynos is not accurate...

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I don't know for sure because I haven't tested my 99s vs my early ones at the same boost level on my car to see the difference myself. However, from my research online (which kind of means jack shit) the 99s will see full torque around 2600-2800 RPMs (look at my graph and that is about 3000 RPMs), and will hold the flat torque curve to basically the same area of 5500-6250 RPM on a stock port car depending on how the time is tweaked. The 99 spec turbos have a 1mm smaller exhaust wheel however and the abradable seals so do not tend to like more than about 0.9 bar for many miles, and also tend to give up about 10hp at the very top end when running over 1.0 bar compared to the early spec turbos.

A minor difference but the throttle response based on my own experience with both is a huge difference in terms of seat of the pants feel because of the 300-400 RPM of better spool response down low. The car feels more like a supercharged car with the 99s because of how quickly they boost up (and the early spec turbos are already quick). But if you were out on the track or drag racing I don't think there would be anything in it.

Well, as I said, I dont know crap about 99spec cars I just cant understand how so little difference between pre99 and  99spec, can make so much difference in power...

My bro's 94 model had 320 with 1,1 bar and seqwential was deleted...

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True, the 16 bit ECU and harness does help it calculate things at a faster refresh rate so I guess the tune could be more dialed in than the 8-bit cars? Not sure it makes that much difference.

As for the 99 twins vs early spec twins there is no real difference in ultimate power, just that the 99's come on 300-400 RPM sooner in terms of peak torque and hold it for just as long as the early spec twins do. So, they make power slightly earlier but are the same everywhere else basically. And they aren't as robust in terms of taking high boost as early ones are so most tuners do not recommend boosting the 99 twins beyond 0.9 bar.

To get more fuel and cut your duty cycle you could always use secondary's in the primary's and then incorporate a 1.1 fuel pressure regulator, rather than a full 1680 conversion .   

Hmm...but then it won't idle nice with 850s and will be out rich down there.

Roy, I was fitting these into GT35 equipped cars for customers 20 years ago, the cars idle properly and the engines are fed correctly providing the cars is mapped right.

I have 1680's secondarys and 850's in the my Race car and it ticks over like a stock car without loads of fumes ;)     

Whoops modified your post by mistake :-[

Quote from: re japi on November 13, 2017, 06:09:10 PM
Well, as I said, I dont know crap about 99spec cars I just cant understand how so little difference between pre99 and  99spec, can make so much difference in power...

My bro's 94 model had 320 with 1,1 bar and seqwential was deleted...

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A bit more detail on the difference between the 99 spec twins and the early spec ones. As I said, the 99's come on about 300-400 RPM sooner down low yet maintain the same top end as the early spec twins.

Also, I was incorrect in my previous post. It is the compressor housing that is smaller at 50mm and shaped differently on the 99's compared to the 51mm compressor housing on the early spec twins. This aides spool up (hence 300-400 RPMs quicker to reach peak torque). The 99s also have the abraidable seals for better response and the latest Hitachi cartridges and bearings so technically they are a bit more refined even though they don't like to hold as much power as the early spec twins when really pushing them.

Earlier response

(http://www.rx7.net.nz/power1.JPG)


50mm vs 51mm compressor housing

(http://www.rx7.net.nz/turbodia.JPG)


Abraidable seals

(http://www.rx7.net.nz/turboseal.JPG)

Ok, I see. Thanks for info

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Whoops, Roy answering about 850cc injectors I hit the wrong button and modified your post by mistake  :-[, however, see above as the info may still help 

Thanks Clive. No worries. I will keep larger injectors in my back pocket but for now I'm going to try to run without any further upgrades.

Had a long chat with my tuner yesterday to discuss the results in more detail to try and better understand my tune's characteristics and to also contemplate why I showed such a strong result.

According to him (and other tuners I have asked for confirmation) my injector duty is fine and the tune is safe. There should be enough fuel across the entire map for safety and there is definitely enough across the transition (hence the 95% peak injector duty) to protect from detonating in that area where most cars on twins usually let go that are badly tuned. I asked how much room I have to play with colder temps and he said basically on a 0C day (we mapped when it was about 11-13C) you may see an extra 2% injector duty at the very peak. Further, we discussed if there is enough fuel if I boost spike. The fuel cut is set to about 1.15 bar, or another 0.1-0.15 bar above my current settings and thus there should be more than enough fuel to withstand a spike to the fuel cut level if that were to ever accidentally occur.

The Apexi Power FC is very strict in how it operates. It cannot read fuel pressure and it cannot compensate for a lazy or failed injector. It reads the IATs, TPS, O2 sensor (if you have it plugged in), water temp and not much else to determine which part of the fuel and ignition timing tables to utilise (which your tuner will adjust). If your fuel or ignition system is not functioning correctly then the Power FC won't know about it and you may run into issues which may cause pre-ignition or detonation. It is a pretty primitive system.

As for why I made such good power? Well, besides a good tune by my mapper which looks pretty well optimised judging by the graph with only a few small improvements that could be made to smooth the torque curve further, we think it might be the following:

Knight Sports Twin Tube Downpipe

The Knight Sports downpipe has the following dimensions: 60mm (2.36") x 2 pipes feeding into an 80mm (3.15") collector to attach to the mid pipe. This means that the downpipe itself has an internal surface area of somewhere around 90mm (3.54") before the collector.

By contrast, the most popular downpipe for twins, the HKS, has an internal surface area of 75mm (2.95").

After discussion, we believe the larger downpipe has more benefit than initially thought because there is initially less restriction in the exhaust system. However, we cannot say for sure whether the twin tube design itself also has benefits over an equivalently sized single dump like the Australian made SMB 90mm (3.54") downpipe.

(https://www.rx7club.com/attachments/3rd-generation-rx-7-1993-2002-parts-99/655622d1501362825-%7Brx7-boutique%7D-knightsports-dual-60mm-downpipe-ksdp2_zps27278456.jpg)

(https://www.rx7club.com/attachments/3rd-generation-rx-7-1993-2002-parts-99/655623d1501362825-%7Brx7-boutique%7D-knightsports-dual-60mm-downpipe-ksdp3_zps196e4ecf.jpg)

(https://d1vv73x37cbx43.cloudfront.net/media/catalog/product/cache/4/image/9d3082b4bec2d774d16a712307ac9d2a/I/M/IMG_0138_117.JPG)


Water injection but not too much water

As we know, water helps to keep intake temps cool so that the air entering the motor is more dense and you make more power since the ECU doesn't need to inject as much fuel and the combustion process is more efficient. However, there is evidence that too much water does have the effect of decreasing power by a couple percentage points and perhaps by running the smallest jet in the AEM kit I am running just enough to drop temps without having a small negative effect on hp. This might be good for a dyno run, but I won't know if I am injecting the right amount or too little until I do a track day next year and see how well it contains IATs and EGTs over a 15-20 minute period of abuse.

Anyway, that's our thoughts as to why the car was running so strong and surprised me a lot and surprised my tuner a little bit on the day. The larger downpipe and the right amount of water could be some differentiators. Or maybe, I have something else done to my car that none of us have noticed. Some secret engine builder sauce from Japan, even if my results are not necessarily out of the range of what's been evidenced by others around the globe with FDs over the past 20 years.