asoduk
asoduk New Reader
5/12/13 10:25 a.m.

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.

Swank Force One
Swank Force One MegaDork
5/12/13 10:38 a.m.

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.

oldeskewltoy
oldeskewltoy Dork
5/12/13 11:32 a.m.
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.

this

racerfink
racerfink SuperDork
5/12/13 6:54 p.m.

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.

asoduk
asoduk New Reader
5/12/13 8:53 p.m.

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.

amg_rx7
amg_rx7 Dork
5/12/13 9:13 p.m.

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.

beans
beans New Reader
5/13/13 8:32 a.m.

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.

asoduk
asoduk New Reader
5/14/13 8:42 p.m.

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.

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