Dyno'ed my GReddy (Peak 16 lbs - then plummets)
 

Hi All!

We had a club dyno day in Tampa this past weekend and had 9 turbo and supercharged Miatas on the rollers. I had the highest numbers (by a couple of hp), but ran into a consistent problem. I would peak at 16 lbs of boost @ 4600 RPM, then it would drop to 12 lbs and creep up to 13.5 lbs. It appears that either the MBC or wastegate is causing the drop. I am adding a helper spring to the wastegate sometime this week to see if that will resolve the issue. Here's a question: How much tension should the spring provide?

My numbers: 190.7 hp / 195 lb-ft torque

I am encouraged by the fact that it should be a simple fix and, once fixed, I should be well into the 200s.

Best thing to do is to attach one end to the wastegate and the other to an eyebolt so you can adjust the tension by lengthening/shortening the eyebolt.

can you post the graphs of your results

Thanks, BRG! That makes sense. I was wondering how I could adjust it. I figured I would add the helper spring and just watch the boost gauge to see how effective it was before I dyno'ed it again. As a bit of background, this was the same kit that made 239hp/255 lb-ft torque on 93Mimi's car http://forums.miataturbo.net/showthr...p?t=1026&pp=10 in March '05. This is the same kit off his car running my stock fuel pump and ECU. I am rich at idle, which I have yet to adjust at the AFM and run stoich to just over lean at WOT @ 16 lbs.


Yep, as soon as I can get these scanned.

It was such a disappointment to be so close to breaking 200hp! :vash:

16psi and only 200whp you have alot of tunning to do.

LOL - indeed! Don't forget, it's the dramatic drop in boost that's killing my numbers! Plus, I am a bit unsure of the numbers provided by the Dyno Dynamics dynamometer we were rolling on.

I know the feeling.

I know that feeling as well.



Get your graph posted, if you have a camera, just snap a pic!

I just need to get my scanner working!

One of our other club member took video as well. I'll give him my graphs to get them scanned and posted.

Dyno plots
 

I got my dyno plots scanned.

I have an assortment of springs, so I'm going to fab something up tomorrow and see if I can keep my boost constant.

I can't seem to move the wategate rod with my hand. Is it supposed to be that stiff?

Let's try this again...

something is way wrong with your fueling those af's are way lean try an fpr or something the bigger injectors can only do so much. please get some fuel to that baby then you will surely get 250 or so whp.

lean? he's running under 12:1 under boost and that reading is at the tailpipe sniffer... he's definetly not lean under boost

I am running rich at idle and leaner, but not 'real' lean at boost. I can adjust for that. Keep in mind also, I am using the RX7 AFM. It has been clocked back from an earlier highly rich state.

In other words, I need to enrichen it for boost and lean it for idle. I should be able to reach a happy medium. It's the helper spring which should be the most 'fun' to tune.

I finally got around to installing a helper spring for the wastergate and completing the install of the EGT temp probe into the manifold. The spring makes a huge difference on the butt dyno and watchful monitoring of the gauges shows the car holding boost pretty well. The car runs like a scalded dog!

I need to schedule some dyno time in the following weeks after the purchase and install of a new downpipe to replace my POS RM dp. :vash:

you need an o2 clamp and work on leaning the mixture now.

btw, dyno dynamics dynos are very very nice dynos. They call them the "heartbreaker dyno" for good reason though. ;) Add about 10-15% to your numbers to figure what you would have gotten on a mustang or dynojet dyno.

uh mustang is 10-15% below dynojet if anything they would be equivalent the dynamics=mustang

I am seriously considering having a 3" DP fabbed up for this car. When the car was on the dyno and, standing behind it by some 20 feet, I was amazed by how much air it pushes out. It was like standing in a wind tunnel!

I may also go with a test pipe and a new custom Flowmaster dual exhaust. I LOVE my present Flowmaster 2.5-inch single outlet (great growl, great flow), and adding an extra 1/2-inch all the way back to a set of duals should really sound great and help the flow.

Agree with the above on the DD dyno-- they make arguably the best dyno on the market, but the numbers are far more realistic than the EgoJet, which unfortunately is what many of the other manufacturers have calibrated their dynos to just to keep people from whining. It's interesting to read into the history of why the Dynojet is inaccurate... but I won't go into it here, they did it on purpose though...

Bottom line is the Dynojet will read 10-17% higher than a Dyno Dynamics machine. I can't speak to the Mustang but I understand them to be closer to DD readings than the EgoJet as well.

If I had an endless bank account I'd own a DD dyno right now. My second choice is a Dynapack which is also a very nice unit. Readings may be a bit on the high side but they are an excellent steady-state dyno making them excellent for tuning just as the DD is. Dynojet's being inertia dynos are about as useful for tuning as a long stretch of road... actually the only thing that makes them better than the road is it's safer and you're less likely to get a ticket. IMO anyways ;)

(Yes Dynojet has started putting brakes on some of their newer Dyno's to allow for steady state tuning, I haven't used one of the new models and can't comment really, their still inertia dynos, but with brakes added... time will tell)

I was just looking at some other threads and realized that post may offend some with DynoJet plots-- that's not the goal at all of course, and the 'EgoJet' nickname just comes from hanging with elitest type tuners that really talk down on inertia dynos period, and particularly DynoJets as they started the whole miscalibration issue. I honestly agree with them wholeheartedly for tuning purposes- for pure HP/TQ curve comparison (at WOT) purposes it really doesn't matter what you use as long as it's a controlled environment and nobody is tweaking the machine to fudge the numbers. (and the numbers are really only comparable on the same machine, and more specifically same exact conditions and even the operator makes a difference)