damian

iTrader: (2)

I have seen many posts with people who have mods that would demand an ecu, however waiting to install a modded ecu it is rationalized by the concept of controlling boost to stock levels (ie, ~10)

I question this practice based on my limited understading of airflow physics and the posts I have read on here.

Anyone correct me if I make an incorrect statement:

Anytime you add an intake or exhaust mod that 'opens' or creates 'less restriction', you are in essense expanding the virtual 'pipe' that is the pathway of air from the intake filter all the way to the tip of the muffler.

So, a car with an intake mod and catback mod is flowing more air at 10lbs than a stock car at 10lbs. (Just like 10lbs in a garden hose is flowing much more than 10lbs in a mcadonalds straw.)

The problem is that the ecu regulates fuel based on the boost pressure (map sensor) and not by volume (or air flow). So, in a car with intake/catback mods, the ecu does not know that the 'pipe' is more open that stock and it still delivers the same amount of fuel for 10lbs at the stock 'pipe' air flow rate.

Most experienced gurus will say that there is the 3 mod rule, once you get to 3 intake/exhaust mods you need to upgrade the ecu, but if it just 2 (like catback+intake, or intake+dp) then you will be in the safe zone since the stock ecu provides plenty of extra fuel for this state.

BUT... what about having somthing like intake, dp, and catback....and then regualting boost to 10lbs with a boost controller?

seems like a lean condition to me, even though the boost is set to 10lbs. the air flow is condicerable more that the stock 10lbs in this situation.

So, just set the boost to 8lbs and that solves it right? I don't think so, the stock ecu will just deliver the fuel it should at 8lbs, and this is not the same as needed for the flow at 8lbs with the new open 'pipe' from 3+ intake/exhast mods.

Ok, I'll stop rambling now, for most this is probably obvious.

reza

I got K&N filter, catback, downpipe, high flow cat.
STOCK ECU with HD Boost controller.
I put wideband on and do the 3rd gear boost pattern test. I got 10-8-10 boost pattern with Wideband showing 10.9 all the way to 7K rpm.
I believe even with those mods, the stock ECU still has plenty fuel in it.

The only problem is boost spikes, it even can happen with boost controller.

Reza

damian

iTrader: (2)

Ahh, good info reza, that is what we need to see, air/fuel data wiht these mods and stock ecu at stock boost levels.

PS
What is the 'HD Boost controller'?

Dannis

everyone kept talking about getting aftermarket ECU... what about piggy back add-ons like S-AFC?? will it solve the problem and don't have to change the ecu???

SilverRX7

I believe the problem is we cant properly regulate the psi to 10, and therefore it rises above that with creep and spikes... and the ECU cannot handle any further... therefore we run lean.

So the intake and exhaust are designed with 10psi @Pman... but when we open up the intake and exhaust, Pman increases and gives increased mass air flow rate which we cannot match with our mass fuel flow rate.. therefore running lean, causing knock, and then blowing an apex seal...

Mahjik

iTrader: (1)

Hey damian,

I hear what you are saying, but people are basing that one the tests that Wade has done:

http://www.newwave.net/~flanham/wlan.../3modrule.html

If you take a look at his chart, you'll see that even with mods that the stock ECU has plenty of fuel for 10 PSI. So that rule of "being safe at 10 PSI even with mods" is based on someone doing some real tests, not just something "thinking" is should be ok.

damian

iTrader: (2)

ohh, thanks Mahjik, good point :-)

yzf-r1

iTrader: (1)

SCC magazine claimed their car ran lean with just a downpipe, and supposedly they measured the ratio with a wideband, so go figure

anyway, I agree that the three mod rule seems to be fairly reliable....I ran my car like that for a couple of years with no problem

damian

iTrader: (2)

wow, if it ran lean with just a dp then they had somthing wrong to start with

rynberg

Many of us have data to back up Wade's tests.

My A/F ratios with a downpipe and cat-back at 10 psi dipped below 10:1 at the transition and stayed there until 7500 rpm when they rose all the way up to 10.2:1. If there's nothing wrong with your fuel system, you can run a lot of bolt-ons safely at 10 psi.

As reza pointed out, the only risk is doing enough mods to worry about boost spikes. That is one reason I wouldn't even consider running a midpipe on the stock ecu (the other reason being it would be very, very difficult to control boost to 10 psi with a midpipe). Also, a streetport requires timing changes to be truly safe, so again, I wouldn't run a streetport with the stock ecu (many have done so though).

yzf-r1

iTrader: (1)

rynberg,

any comments on running a streetport with a pettit or M2 ECU?

MakoDHardie

I believe that open exhaust- dp, mp, catback- allows for maximum (with the exception of a race pipe) spool up capability of the exhaust turbines, building more boost in the intake tract. With a low restriction intake system, less vaccum pressure is present at the compressor wheel which allows for the turbo to swallow more air per revolution. Also builds boost. If tuning compensation is not made to prevent the a/f ratio from leaning out, then the higher boost is not a good idea. Boost control opens the wastegate sooner and/or more frequently under lower boost settings on a car with full air flow mods. Modifying a car so that it has minimal air flow restriction doesn't serve much of a purose performance wise if you're going to be spilling all that extra boost you paid for through the waste gate. You'll have a lot of carbon build up in the waste gate after driving like that for a while.

Another issue that has to do with ppm and boost is intercooler upgrades. You'll see specs on single turbos for 400-450hp @ 15psi. Those of you who are wondering why this is so is because with a single turbo setup, you will be using a larger intercooler than stock. Larger cooling capacity allows for the air to cool- and decrease volume between the intercooler and throttle body. You will still have the same ppm of air molecules going into the intake ports, but you will be doing so at a lower psi. For people who have setups along the lines of: intake, dp, mp, catback and are using the stock intercooler, you will most likely see boost spikes, even if you have reprogrammed ecu's or boost controllers. 'Die For MX' has that set up with an XS remapped ECU and he will spike from the set 12 psi up to 15 psi on a cool night without the exhaust baffle in. Upgrading the intercooler along with the air flow mods is a good idea with the right fuel system adjustments, but don't expect your waste gates to open in time to balance an insufficiently cooled surge of boost to creep from your IC to your engine's combustion chambers. Creep and spiking happens very quickly. You can install pop off valves and boost controllers all over the place, but what's the point if you're only running stock boost? And for those people who know what they're doing, disreguard that statement because they know they have the parts and the programming to run at different boost levels at any given time. For the sake of keeping the rotaries running, do your homework before you make your investment. Make sure you have all the parts you need to handle everything you are running. Air, fuel, and timing are all linked in the car. Expect to compensate for all of them when you bolt something on. Don't expect not to have reliability issues when bolting something on is the only work you do. Every car is different. Some people get away with raping their engines, while others pop a seal with nothing more than a K&N drop in filter. So help yourselves and your cars and remember that you too can run higher levels of boost safely, but only with all of the proper equipment.

rynberg

I know some people have done it but M2 doesn't recommend it. I don't know about Pettit's chip, it seems to be more versatile so maybe they can set it up to run a streetport.

yzf-r1

iTrader: (1)

yep, M2 doesn't even recommend a midpipe with their chip

GoodfellaFD3S

iTrader: (213)

Home Depot. Basically a pair of T fittings, one for boost and for pre-control spool. I hated adjusting it on the side of the road--my Profec B is worth every penny.

reza

HD Boost controller is the Home Depot boost controller.
I had to close the wastegate more to keep 10-8-10. I had a ported wastegate that is opening too much.
I still have stock intercooler, that is what I want to change next. PFC is on hand as well, but I want to know the stock ECU capabilities. I guess its pretty good. But I will change to PFC at 10psi, and tune it out, then move to bigger boost 12psi later.

Reza

PraxRX7

The speed at which the compressor/turbo "spools" up to is directly related to the air-flow in/out of the engine. By increasing air-flow, the pressure is directly increased as well.

For example if X volume of air causes the compressor to spool to Y RPM causing Z boost then X and Y are directly related.

Essentially, I believe that at 10Psi boost you are running a fixed amount of "Air-Flow" that doesn't change based on the restrictive intake etc. and in order to increase boost, air-flow must be increased.

Of course I am just speculating, and I haven't really taken into account the waste-gate etc.

Tim Benton

iTrader: (1)

Someone already beat me to it concerning Wade's data, but also Max Cooper has some relevant data due to open exhaust, pressure drop and fuel related data on his site.

www.maxcooper.com
Good time to say thanks to both Wade and Max for their contributions to the big list and forum. Both were active on the big list back when I was on it regularly a few years ago.

Tim

LAracer

As damian said, pressure and flow rate can be changed independently. There is no doubt about this. There are alot of variables at work here, but the point is that "10psi" doesn't tell us very much about what our A/F ratio might be.

SilverRX7

For increased mass air flow rate... (assuming temp is instantaneously constant), if density is increased, your pressure is increased.

Having said that, more flow means more boost ... so if your a/f ratio is off, that means either your manifold pressure or your density has increased... so if you are going to eliminate restriction... you will get more boost and will need to increase mass flow rate of fuel to compensate... and the stock ECU cant do this adequately.

LAracer

Maybe. Depends how much the density increases. Like I said, this stuff is complicated. I think the best we can do is admit that a complete understanding is out of reach and buy an A/F gauge.

yzf-r1

iTrader: (1)

Essentially, I believe that at 10Psi boost you are running a fixed amount of "Air-Flow" that doesn't change based on the restrictive intake etc

totally wrong

uncorking the exhaust and intake causes a significant increase in flow through the engine, a portion of which on the exhaust side is diverted to spool up the turbos, which is why you can see as much as a 2 psi boost increase by adding a dp alone

I believe the stock computer can compensate for a small window of flow increase, and/or it is tuned rich from the factory in the first place

SilverRX7

Vzf... right.

LARacer, its not impossible to understand... just take your masters in powertrain modelling and control and it all falls into place But you're right, get a boost gage and a/f meter... and you will protect yourself.

turbojeff

iTrader: (30)

I've seen cars hit fuel cut with just a DP. The problem here is the DP caused the car to get much more than stock boost. Keep the boost to 10psi, it'll be fine.

My 93 R1 is one of Wade's test subjects.

Jeff

13brv3

Say we open up the intake and exhaust, then limit the boost to 10 psi, and keep the intake temp the same for the sake of simplicity. At this point, we are saying that we have more airflow through the engine than when it was stock. So far so good.

The ECU only sees temp, and pressure, which are the same as before. Doesn't that mean it's supplying the same fuel as before? If that's true, why wouldn't we be running lean if more air is passing through? Was the stock AFR ridiculously rich, like 8 or 9?

Are we really making more power if we keep the boost at 10 psi? The only way I can imagine this is if we're removing some of the restriction on the engine, thus making it more efficient. Are we really just reclaiming power that was being wasted on pumping losses before?

Sorry for all the questions, but I've been trying to make sense of all this for some time now, so this thread is really helping.

Cheers,
Rusty (NOT a thermodynamic guy)