usd2bfst

Ok Ben. You're right, run 4 was a little weird with some spikes that skewed the numbers, so I'll use run 3 which was clean. Both runs are corrected. Igor's run was at 160 Kpa solid (uncorrected), 12 PSIg (corrected for altitude). Your run was at 162 kPa sagging to 156 kPa at redline (uncorrected), which is 12-11 PSIg (corrected for altitude).

Joe Perez

iTrader: (8)

Excellent work on these back-to-back comparisons, and props.

I continue to be seriously unimpressed by the Euro-spec flattop manifold. The differences from one to another aren't all that dramatic, but if a winner can be said to exist, either of the US-spec manifolds clearly show better performance in the mid-RPM band that matters most for a daily driver.



I still can't quite see why this would be the case, or why it would seem to make sense.

One of the few advantages to using a mass airflow sensor as opposed to MAP-based operation is that MAF cars tend to be extremely forgiving of modifications which greatly improve the airflow characteristics of the engine.

In other words, you can move all of the extra air you want to, and since it's all flowing through the MAF sensor, it's going to be accounted for in the load computation.

The only scenario in which this would fail to be the case would be if you are flowing so much air through the engine that you have pushed the ECU "off the edge" of the load table, so to speak. While I haven't actually seen a realtime analysis of the NB ECU's load table, I cannot imagine that it could have been designed with so little headroom as to allow this scenario to occur on a naturally-aspirated engine.

usd2bfst

From experience with the old piggyback Link ECUs on NB turbo cars, they would throw a CEL for the MAF going out of range somewhere around 12 PSI. (Which was a terrible idea for a Link piggy, btw..) The stock injectors will support more power than most N/A builds will ever produce so who knows what the real reason is.

FWIW Yolk has stock 2001 purple injectors in all the Mazda intake manifold testing.

EO2K

iTrader: (37)

Definitely not arguing with you, it just seemed plausible. The question becomes "how forgiving?"

For the sake of argument, air for 140hp sounds like M45 JRSC territory and we know the stock ECU needs help with that. That being said, there is some anecdotal evidence that the stock NB fuel pump can't keep up with the stock motor anyway. Lots of variables and not a lot of data

Joe Perez

iTrader: (8)

Granted- I can't argue with you on that.

I'm thinking of this in relative terms, though. For any given engine, I find it hard to believe that switching from the US manifold to the EU manifold is causing an increase in airflow which even begins to approach the significance of adding even a minor amount of boost.

If one were comparing a bone-stock engine with a US-spec manifold to an engine with significant headwork, aftermarket camshafts, an extremely free-flowing exhaust system, etc., then I can obviously accept what's being proposed here. But comparing two identical engines with the intake manifold being the only difference? I'd need to see actual flow-bench data to convince me that the flattop, by itself, is promoting a 20-30% increase in airflow.

emilio700

iTrader: (3)

Probably more like 4-5% after the torque peak. Not relevant for a street driven car with a stock engine but quite relevant to a tightly restricted race class where we almost never drop below the torque peak while on track.

Torques is great but even with an engine having copious low end grunt, you still shift at or just after the power peak if you want to accelerate at the maximum rate possible.

We use USDM manifolds on some of our race cars where we don't need all the top end the car is making are limited in gear ratio choices. On other cars where we run a 6 speed and need more top end power, we use the square tops.

Dollar for dollar, the square tops or a decent, if not stellar value. 5-9whp on an NB engine for about $400. That fits in with the other simple bolt on mods that folks typically do to NB engines. When combined with a BP5A cam in a BP4W head, we see in the neighborhood or 10-15whp over USDM bits.

Yes I know Joe, turbos make more torques/$. Great for the street guy but not always the best solution for a track rat.

Joe Perez

iTrader: (8)

No argument there.

I'm responding specifically to the folks who are talking about stock MAF sensors and stock ECUs. To me, that implies a street-driven car with very few related modifications as opposed to a highly engineered track rat.

For such an engine, I just can't see how switching from a stock US-spec manifold to a stock EU-spec manifold is going to throw the fueling off.

RotorNutFD3S

iTrader: (33)

A local friend has a '99 with a BP5A cam, EUDM manifold, DDMWorks "stage 2" intake kit, Racing Beat header, FM midpipe, and Car Make Corn's exhaust and he has no issues with the car. In fact it runs very well and is definitely quicker (well in terms of an n/a Miata anyway). All still on the stock ECU and fuel system.

18psi

iTrader: (76)

Eh you're probably right. That's why I said "supposedly".

Sav was the one that I saw post that statement fwiw.

EO2K

iTrader: (37)

To be fair, I did say cam, manifold, exhaust, etc, not just manifold

Good to know! Any chance he has a wideband? LC-1 will let you do some rudimentary datalogging

RotorNutFD3S

iTrader: (33)

Not yet. I want to install my LC-1 in his car temporarily, especially when he takes it to the dyno to get some numbers, but I need to get a replacement sensor first.
I also want to be able to dyno my '99 at the same time to see how they compare considering that while we don't have all of the same name parts, we have the same modifications, except for the intake manifolds.

scenturion

iTrader: (9)

Awesome - so in this single scenario of an slightly bolt-on-modified '99 Miata, flattop>VICS? I got the flattop for relatively cheap (<$200), and my car is primarily a track car, so it seems to be a good modification over the VICS.

codrus

Heh. I ran my car at 12psi with the Link piggy for about 5 years. The MAF would overvoltage around 230-240 rwhp (dynojet, sea level), and when it set the CEL the stock ECU would cut the fuel through the stock injectors (with piggyback injectors still flowing), which was kinda scary.

--Ian