Dyno Day (miata question)

Yesterday the local Porsche club had a "dyno day" at a new shop in the area. Anyone could come and run their car on their 4 wheel superflo dyno for a pretty reasonable price. I was really expecting a lot less than what they had....

Their shop used to be a strip mall full of offices. It is now a huge L-shaped speed shop. Their lobby/waiting room had a Maserati Gran Tourismo Stradale parked in the middle with nice leather couches, TVs, refreshments, and some wheels on display. In the next office suite: cars waiting to get work done or be picked up. The coolest of which was an E30 widebody with a turbo LS3. Moving on to their garages: 350Z with an LS swap, an old Nascar, some Mustangs and BMWs. Pretty slick, picture links coming soon....

So then I got to run my spec miata on their dyno. It was LOUD. I put down an earth shattering 99.9 RWHP. They also ran an A/F sensor in the exhaust and found my car to be quite lean (15-16.5 before I blew the sensor out). Despite the fact that I've been running it that way for years now, I'm a little concerned and would like to get those readings to be more healthy.

The car is a '91 1.6 with the usual SM "intake" and a springfield dyno exhaust. The bottom end has never been touched.

So what does the braintrust here (paging Keith Tanner) suggest for getting my A/F numbers more in check. My immediate thought is going to the adjustable fuel pressure regulator that is now allowed in SM.

The "sniffers" on the dynos oftentimes aren't real accurate. If you have exhaust leaks before the sensor, then the reading won't be accurate, either.

If you're willing to spend a little money tracking this down, i'd suggest buying a wideband of your own and checking for yourself.

Swank Force One wrote: The "sniffers" on the dynos oftentimes aren't real accurate. If you have exhaust leaks before the sensor, then the reading won't be accurate, either. If you're willing to spend a little money tracking this down, i'd suggest buying a wideband of your own and checking for yourself.

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My bone stock SM motor with 196k miles and Springfield Dyno exhaust made 112.8 rwhp. What kind of intake are you running? I have a tube from AutoTechnik with an AutoZone air cleaner.

Thanks for the input guys. Sounds like I'm going to be buying a wideband AND an adjustable FPR.

As for the result, this was done on a Superflow AutoDyn - 880E AWD Dynamometer. They read lower than Mustangs or DynoJets, which is what most people are more familiar with. Everyone had much lower numbers than they had before. I was actually expecting a little lower. I'm normally around 115 on a DynoJet (without sniffer).

So, any suggestions on what to buy? preferably something that won't kill my tire and brake budget.

Similar thing happened to me. Replaced the original fuel pump and replaced the "tuned" air flow meter w/ a stock one to fix the problem.

Dynos can be quite accurate if the operator knows what they are doing and it is maintained. If it is a newly installed dyno at a high end shop, it is probably accurate.

Is the air flow meter stock / unmodified? A "tuned" AFM can result in a leaner mixture.

What kind of fuel pressure is the car producing? A tired old fuel pump will not keep up with the motor's demands and result in lean AFR.

Suggest you look at that before spending $$ on go fast parts.

I'd also suggest doing a compression check and a leak down test to see what the overall health of the motor is.

My '95 1.8L with an RB intake, 2.5" steel crossover tube, homemade heat shield, and Borla exhaust made 119whp on Pure Tuning's dyno about... 6-7 years ago? I was pretty surprised for a near stock DD miata. Stock clutch/flywheel, 4.10 Torsen rear, 35lb wheel/tire combo. Pure does a lot of SM dynoing, they said mine would've been on the strong end for SM cars. I have a dyno sheet floating around somewhere, but the sucker wanted to pull past rev limiter pretty good. Was a quick car in the 1/4 too, ran a 15.6@89mph at Milan dragway.

Thanks guys. Some good info and things to look at. I'm going to start with a wideband and then cheap parts, including my stock (non tuned) AFM.