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The White Bug by pmbrunelle
Started on: 01-03-2019 10:14 AM
Replies: 281 (7379 views)
Last post by: La fiera on 03-05-2021 08:19 PM
wftb
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Report this Post05-11-2020 01:30 PM Click Here to See the Profile for wftbClick Here to Email wftbSend a Private Message to wftbEdit/Delete MessageReply w/QuoteDirect Link to This Post
Use a bigger exhaust pipe and get rid of the muffler. You need more total flow capacity, even if you do everything on your list the 2.5" pipe is still a choke point. I use 2.5" piping on my engine and if I had room I would go bigger. I have a Solstice OEM cat converter and no muffler. Only loud when you build the boost up high, rest of the time it is fairly quiet.

------------------
86 GT built 2.2 ecotec turbo
rear SLA suspension
QA1 coilovers on tube arms

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La fiera
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Report this Post05-11-2020 02:27 PM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
I think you'll need an external wastegate.
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Report this Post05-11-2020 02:40 PM Click Here to See the Profile for ericjon262Send a Private Message to ericjon262Edit/Delete MessageReply w/QuoteDirect Link to This Post
idea:

the inlet and outlet of your muffler are inline, weld a V band to the inlet and outlet, and in between porting the housing, and installing the larger housing, take an intermediate step of installing a straight pipe. if boost control is improved, it tells you your muffler/exhaust is too restrictive, if it isn't improved, you can re install your muffler, and have an alternate exhaust for track days that is an easy bolt in install.
My thoughts:

if the exhaust is too restrictive, it will drastically reduce turbine and WG efficiency, because the pressure drop across the two components is reduced. reducing pressure downstream of the turbine will make boost control easier and more consistent, as well as reduce "spool" time. while straight through mufflers appear to be very free flowing, some actually choke down engines quite considerably.

------------------
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."

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http://www.fiero.nl/forum/Forum2/HTML/119122.html

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pmbrunelle
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Report this Post05-12-2020 08:44 AM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
Considering my main problem now is that the turbine is generating too much shaft power, I don't think that unrestricting the turbine's exit will help it generate less power.

However, the wastegate would do a better job of stealing flow away from the turbine if it dumped to a short non-restrictive exhaust, such as a screamer pipe.

This is what the wastegate passage looks like for exhaust gas entering the inlet flange:


I think that this Saturday I will go to Princess Auto and purchase an electric die grinder + burrs. I need something more powerful than my Dremel to port this.

Even if porting the wastegate passage doesn't solve my immediate problem, the electric die grinder will be a useful tool to have. I don't have a big enough air compressor to run an air-powered die grinder.

[This message has been edited by pmbrunelle (edited 05-12-2020).]

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Will
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Report this Post05-12-2020 09:46 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
If you could add as much radius as possible on the near edge while keeping the far edge sharp, that would help. Not sure if porting the wastegate port can get you where you need to go, but it's worth a shot.
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claude dalpe
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Report this Post05-12-2020 12:23 PM Click Here to See the Profile for claude dalpeClick Here to Email claude dalpeSend a Private Message to claude dalpeEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by La fiera:

I think you'll need an external wastegate.



Your wastegate comes out in your restrictive exhaust which prevents it from operating at full capacity!
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pmbrunelle
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Report this Post05-17-2020 08:38 PM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
I ported the wastegate passage. There is a radius of about 0.4 inches on the inside of the turn. I left a sharp edge on the far side.


Looking into the wastegate hole towards the inlet flange, with a light shining into the inlet flange:


The shape of the turbine housing lent itself to me carving a scoop shape to help divert exhaust gas towards the wastegate passage.

2nd gear pull from 905 RPM to 6131 RPM, followed by a 3rd gear pull:


During WOT, manifold pressure stabilises at about 155 kPa.

To see what would happen without engine acceleration, I brake boosted the car on the highway for a few seconds. Manifold pressure remained stable. I noticed that stock 84-87 brakes heat up quickly!

[This message has been edited by pmbrunelle (edited 05-17-2020).]

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La fiera
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Report this Post05-17-2020 08:53 PM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
. I noticed that stock 84-87 brakes heat up quickly!


Patrick, you being an engineer I thought you have the brakes upgraded for the forecasted HP. How did you spect the stock brakes to keep up with the demands?
Sometimes is a matter of trial and error, I've been there myself! "Keep pounding" like we say here in NC!
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pmbrunelle
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Report this Post05-17-2020 09:04 PM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by La fiera:
How did you spect the stock brakes to keep up with the demands?


I didn't!

I suppose you could build up every system of a project car, and then fire up a finished car and go driving.

In addition to working on the car in the garage, I wanted to drive it even though it's not finished! Driving the car is also how you discover problems.
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La fiera
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Report this Post05-17-2020 09:31 PM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by pmbrunelle:


I didn't!

I suppose you could build up every system of a project car, and then fire up a finished car and go driving.

In addition to working on the car in the garage, I wanted to drive it even though it's not finished! Driving the car is also how you discover problems.


Keep at it!!!! Good job mate!!

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pmbrunelle
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Report this Post05-22-2020 12:21 AM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
There is a small puddle of oil on top of the transmission, and it's not coming from the turbo. The turbo is dry.

The shifter shaft which penetrates the case is wet, and the breather vent also looks wet with oil. I'm not exactly sure.

Any opinions regarding this issue with my Muncie 4-speed?
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Report this Post05-22-2020 02:36 AM Click Here to See the Profile for ericjon262Send a Private Message to ericjon262Edit/Delete MessageReply w/QuoteDirect Link to This Post
possible that the trans was over filled? that would be my first guess, but it's been ages since I looked at an old 4 speed.

------------------
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."

cognita semper

http://www.fiero.nl/forum/Forum2/HTML/119122.html

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Report this Post05-22-2020 09:43 AM Click Here to See the Profile for claude dalpeClick Here to Email claude dalpeSend a Private Message to claude dalpeEdit/Delete MessageReply w/QuoteDirect Link to This Post
and the breather vent also looks wet with oil. I'm not exactly sure.
Like ericjon262 said maybe over filled? Or your breather not working properly ! or your shifter shaft is loose in the case (I suppose you had put a new seal there)
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pmbrunelle
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Report this Post05-22-2020 11:04 PM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
I'll check the transmission oil level this weekend.

Some yahoo put a turbo above the transmission, which makes that job more tricky
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Report this Post05-23-2020 01:09 AM Click Here to See the Profile for ericjon262Send a Private Message to ericjon262Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by pmbrunelle:

I'll check the transmission oil level this weekend.

Some yahoo put a turbo above the transmission, which makes that job more tricky



Engineers are jerks aren't they! lol!

------------------
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."

cognita semper

http://www.fiero.nl/forum/Forum2/HTML/119122.html

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La fiera
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Report this Post05-23-2020 11:07 AM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hey Patrick! How much HP are you expecting your engine to produce? Be gentle with that Muncie, they don't like sudden bursts of torque.
It will last a lot longer if you can program boost by RPM or MPH. Just a thought, keep up the good job!
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pmbrunelle
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Report this Post05-23-2020 12:15 PM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
I would guess in the 250 to 300 hp range when everything is working right. For now though, I am running off the wastegate spring while I solve other problems. Increasing the boost with the electronic solenoid is a project for later.

I remember that you split open the smooth case on your Muncie! I have the ribbed case (from a V6 Fiero) on mine, so hopefully it is stronger than the smooth version.

My hope is that this turbo setup does not shock-load the transmission much more than a stock 2.8 V6. After an upshift at WOT, when I get back on the gas and release the clutch pedal, the manifold pressure should be close to atmospheric. So during the shock-load of the gear change, the engine torque is not too high.

Because of the turbo lag, it takes about 0.3 to 0.4 seconds once I'm in gear for full boost to return. I think that the turbo lag makes the re-application of torque a gentle process for the transmission.

The MS3 has a flat-shift feature to maintain the boost as much as possible during the shifts; I think I will avoid using this feature, to be more gentle on the transmission.

I never had a turbo car before. I thought that maybe I would be bothered by the turbo lag, but finally I think it gives the car a special character. The lag is like foreplay before full boost.
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Report this Post05-23-2020 03:57 PM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by pmbrunelle:

The MS3 has a flat-shift feature to maintain the boost as much as possible during the shifts; I think I will avoid using this feature, to be more gentle on the transmission.

I never had a turbo car before. I thought that maybe I would be bothered by the turbo lag, but finally I think it gives the car a special character. The lag is like foreplay before full boost.


The good thing about Flat-shift is that you can fine tune it to how strong the engine comes into power.
You can also use it to keep the RPMs of the turbo up thus avoing lag.
Another antilag trick is to retard on deceleration (foot off the throttle) at the lower part of the timing table,
lets say from 7000 to 4000 RPMs and at the same RPM window on the VE table you add fuel.

That will create violent explosions between the head and the turbo and as the expanding combusting gas goes past
the turbine at high speed, even with the throttle closed the turbo is turning at high speed and creating boost, once on the throttle again
and hang on for your life!

Yes it creates A LOT of heat in the exhaust, they'll glow RED. But you can have that only at high RPMs like I said before.
To cool down the pipes all you have to do is keep it rich lets say from 3950 to 3500 and advance the timing to about 44-47,
below 3500 go back to normal fueling keeping the timing normally hi.

Every time you do that there will loud BANGS and visible fire out of your exhaust! That's foreplay
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Report this Post05-26-2020 03:30 AM Click Here to See the Profile for ericjon262Send a Private Message to ericjon262Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by pmbrunelle:

I remember that you split open the smooth case on your Muncie! I have the ribbed case (from a V6 Fiero) on mine, so hopefully it is stronger than the smooth version.


From what I remember reading before I put an F23 in my car, the V6 4 speed is slightly stronger than a getrag 282, the downside being that it doesn't have overdrive, so it's not as hwy friendly.

------------------
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."

cognita semper

http://www.fiero.nl/forum/Forum2/HTML/119122.html

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pmbrunelle
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Report this Post05-26-2020 12:13 PM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by La fiera:
That will create violent explosions between the head and the turbo and as the expanding combusting gas goes past
the turbine at high speed, even with the throttle closed the turbo is turning at high speed and creating boost, once on the throttle again
and hang on for your life!

Yes it creates A LOT of heat in the exhaust, they'll glow RED.


I am not ready to start beating the crap out of my exhaust. This build is too new; I am not ready to break it, yet!
However, I suspect a time will come when I have the itch to make the torque come back faster.

For example, now that the MAP stabilises at 155 kPa, I'm convinced that the engine needs more boost...

 
quote
Originally posted by ericjon262:
From what I remember reading before I put an F23 in my car, the V6 4 speed is slightly stronger than a getrag 282, the downside being that it doesn't have overdrive, so it's not as hwy friendly.


For some perspective, here in Québec, the speed limit on highways here is 100 km/h, and the typical maximum cruise speed is 110 km/h. Somewhat slower than the typical 80 mph (so I've read) highway cruise in the USA. My datalogs shows an engine speed of 3240 RPM for a vehicle speed of 110 km/h, which seems quite reasonable to me. I calibrated the VSS reading with a GPS. Eventually I'll probably install taller tires than the 215/60R14 tires I have on the car now.

However, this is the first 4-speed car I have ever driven. Compared to the 5-speeds (and to a lesser extent, 6-speeds) I have driven, I noticed that the wider gaps between gears make the car a bit harder to drive. Downshifts require bigger throttle blips, and it takes more concentration to match the revs right. I'm getting the hang of it though.

Durability-wise, I would guess that the Getrag 282 and the ribbed-case Muncie would be in the same league. People have blown up both boxes. When I was shopping for a replacement planet gear for the differential I found that the Muncie and Getrag 282 share the same part numbers for the differential (planet + satellite) gears.

What's bad for the durability of my transmission is the 1984 M19 gearing (3.53 1st, 4.10 final) vs. the M17 V6 gearing (3.31 1st, 3.65 final). Shorter gear ratios result in greater gear-separating force that can potentially split open the case.
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pmbrunelle
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Report this Post06-10-2020 07:28 PM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
Six weeks after the first start, a number of issues have been resolved, but there is still a lot of work to do before the car is up to my satisfaction!

Here is a WOT run in all four gears, starting from idle in 1st gear:


In the bottom pane, the measured AFR and AFR target are superimposed on each other.

In 1st gear, the measured AFR is leaner than desired.
In 2nd and 3rd gear, the AFR is close to the target.
In 4th gear, the AFR is richer than the target.

This inconsistency in AFR does not cause a WOT driveability problem, but it nags at my sense of OCD.

I think that wall-wetting explains the difference between gears. When the injector wets the intake walls with fuel, the fuel stays on the walls for perhaps ~0.3 seconds before re-evaporating and being sucked into the cylinder. This causes a lag in fuel delivery between the injector and the cylinder.

In 1st gear, it takes about 0.3 seconds for the engine speed to increase from 5000 RPM to 5700 RPM. So at 5700 RPM, the cylinders are finally sucking in the fuel that was sprayed 0.3 seconds earlier, when the engine was spinning at 5000 RPM. Fuel flow at 5000 RPM (on this engine anyway) is less than at 5700 RPM, so the engine operates a bit leaner than desired.

I think I will try the "X-Tau" wall-wetting compensation feature of the MegaSquirt. In addition to making WOT better, I think (hope) it will make all other transient states better. For example, if I go to neutral while engine braking, the engine won't return directly to its 850 RPM idle. Instead, it will go lean and dip down to 750 RPM before the mixture stabilises and the idle returns to 850 RPM.

I could try to patch the idle return problem with a dashpot-type feature on the IAC, but it doesn't address the root cause which I suspect is wall-wetting.

A good video to watch:
https://www.youtube.com/watch?v=0ItkpVofKLw

[This message has been edited by pmbrunelle (edited 06-10-2020).]

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Report this Post06-10-2020 08:09 PM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
Have you tried the "Time-Based Acceleration Enrichment" feature in MS? That's what I use to make my tip in and stomp throttles
nice and crispy. You can tune it by TPS or MAP or a blend of the two.
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Report this Post06-10-2020 08:33 PM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes, for now I use TPSdot accel enrich. However, that can only correct transients caused by a changing throttle pedal.

The AFR error in 1st gear cannot be corrected by TPSdot accel enrich, since the throttle is fixed at 100% during the pull.

I want to make the car run well enough that my dad could get in, start the engine, and start driving to work 5 seconds after starting, without stumbles or hesitation, like a new factory car.

I don't know if I will reach this objective, but that is the challenge I give myself, to tune this engine the best I can (for driveability). I think that wall-wetting compensation will help me reach this goal.

At some point if I can master the driveability aspect, then I may want to add the challenge of also tuning for fuel economy/pollution. But I am not there yet.

Edit to add: On my previous car, I used TPS-based acceleration enrichment. If I do exactly the same thing this time, then I won't be learning anything. If I don't learn new things with this project, then there's no point for me to own this project car. So I want to play with wall-wetting, because I might learn something.

[This message has been edited by pmbrunelle (edited 06-10-2020).]

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Report this Post06-10-2020 09:40 PM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by pmbrunelle:

Yes, for now I use TPSdot accel enrich. However, that can only correct transients caused by a changing throttle pedal.

The AFR error in 1st gear cannot be corrected by TPSdot accel enrich, since the throttle is fixed at 100% during the pull.



In a turbo car I would use MAPdot instead of TPSdot to avoid the problem you have. It has the same problem in every gear
but it is more pronounced in first because the RPMs wind out quicker. If you make the enrichment based on manifold pressure
which varies even if the TPS is 100% it'll be way more responsive beacause you are giving it the fuel it needs as manifold
pressure raises with RPM. Then, when you get to the EAE you can find tune to perfection.

PS. I'm working on a EAE strategy for my engine also but I'm making sure all the other aspects of the tune are worked out.

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Report this Post06-10-2020 10:03 PM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
You should watch this and pay attention to the end
https://youtu.be/KSUUVuSqRCY
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Report this Post06-11-2020 08:52 AM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes, mapdot might work better on my car than tpsdot.

Is wall-wetting the only reason that acceleration enrichment is needed? I don't know of any other reason. For example, does direct injection need acceleration enrichment? I'd think not.

If wall-wetting is the only physical reason that acceleration enrichment is needed, then it makes sense that a wall-wetting scheme could be the only acceleration enrichment scheme, and it would be more accurate in compensating for wall-wetting.

mapdot/tpsdot could be added in afterwards to help mask any imperfections with the wall-wetting compensation, but it would be a band-aid.

I looked at some other videos from Andy Whittle too; he uses the datalogs and plotting features a lot!

[This message has been edited by pmbrunelle (edited 06-11-2020).]

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Report this Post06-11-2020 09:10 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
In a carb, when the throttle is opened aggressively, there's an amount of time required for the mass flow through the venturi to build enough that the venturi vacuum signal is strong enough to draw in fuel. That requires a mechanical means requires to add the fuel the delta airflow needs until the vacuum signal from the venturi catches up.

In a port injected engine, the throttle is some distance from the injectors, meaning that there's a delay between when the throttle opens and when the delta airflow arrives at the injectors and even more of a delay before that signal registers on the MAP sensor... so there needs to be a curve different than directly proportional to TPS involved in ramping up the fueling for snap throttle openings.

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Report this Post06-11-2020 10:13 AM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Will:
In a port injected engine, the throttle is some distance from the injectors, meaning that there's a delay between when the throttle opens and when the delta airflow arrives at the injectors and even more of a delay before that signal registers on the MAP sensor... so there needs to be a curve different than directly proportional to TPS involved in ramping up the fueling for snap throttle openings.


That's why my injectors are located high in the runners. To have about the same time in TPS/Injection, litterally wall-wetting, heat absorption and to give time for the fuel to evaporate before being swallowed by the intake valve. All that equates to improved throttle response, cooler and denser charge and and fuel/air in vapor ready to combust.

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Report this Post06-11-2020 11:05 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
If you really want zero accel enrichment with good mixture quality, then shower injectors above throttle per cylinder is the way to go.
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Report this Post06-11-2020 06:33 PM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
On the subject of mixture quality, I tried end-of-injection timing half-way through the intake stroke (i.e. with the intake valve wide open). The engine did not like to idle like that; it ran very rough.

The MS3's default end-of-injection timing is at TDC just as the intake valve is starting to open. That gave "good" idle quality.

More advanced timing values (on a closed intake valve) did not improve idle quality. It seems like the fuel vaporises rapidly after hitting the intake valve; more dwell time has no effect. The downside of too much advance seemed to be slower throttle response.

I suppose that with "better quality" injectors I might not have to spray on the barely-open intake valve, but I don't know what the spray of my Accel injectors looks like.

Rei, did you consider using a carburetor?

[This message has been edited by pmbrunelle (edited 06-11-2020).]

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La fiera
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Report this Post06-11-2020 07:10 PM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by pmbrunelle:

Rei, did you consider using a carburetor?



Never, ever, ever, never, never, ever never!!

Top fed ITB's throttle bodies I am considering.
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claude dalpe
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Report this Post06-11-2020 07:17 PM Click Here to See the Profile for claude dalpeClick Here to Email claude dalpeSend a Private Message to claude dalpeEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by La fiera:


Never, ever, ever, never, never, ever never!!

Top fed ITB's throttle bodies I am considering.



I can't wait to see it Rei! One day I would like to do that too, it seems that the response to the throttle is great when it is well matched.
And me to : Never, ever, ever, never, never, ever never!!
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pmbrunelle
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Report this Post06-11-2020 07:40 PM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
A throttle body with fuel injectors far from the valves, that's not a similar idea?

Please explain! (I don't know what driving with a carburetor is like, I only read about it in books and on the Internet.)

[This message has been edited by pmbrunelle (edited 06-11-2020).]

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Will
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Report this Post06-11-2020 09:46 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
A carburetor is a calibrated leak
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wftb
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Report this Post06-11-2020 10:34 PM Click Here to See the Profile for wftbClick Here to Email wftbSend a Private Message to wftbEdit/Delete MessageReply w/QuoteDirect Link to This Post
I grew up with carbs. So much fun to have to tune something by bending rods and turning screws in and out. Never again.
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claude dalpe
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Report this Post06-11-2020 10:40 PM Click Here to See the Profile for claude dalpeClick Here to Email claude dalpeSend a Private Message to claude dalpeEdit/Delete MessageReply w/QuoteDirect Link to This Post
Will explained the difference between carburetor and fuel port : In a carb, when the throttle is opened aggressively, there's an amount of time required for the mass flow through the venturi to build enough that the venturi vacuum signal is strong enough to draw in fuel. That requires a mechanical (Acceleration pump) means requires to add the fuel the delta airflow needs until the vacuum signal from the venturi catches up.


Explication:
A carburetor is relatively simple to use but will always remain less precise than the injection even when it is well tuned and it detuned easily.


With a carburetor it's Very difficult to run the engine at the right mixture, it is often too rich or too lean with a carburetor. With a turbo you have to buy a blow in carburetor. With the injection there are many sensors to adjust the mixture. It is not necessarily more efficient at the wide open throttle but more precise.
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Will
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Report this Post06-12-2020 06:19 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
A well developed race carburetor/manifold combo *CAN* deliver better mixture QUALITY--in terms of droplet size and homogeneity--than port EFI... but EFI always has the edge in fuel metering precision.
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La fiera
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Report this Post06-12-2020 07:43 AM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Will:

A well developed race carburetor/manifold combo *CAN* deliver better mixture QUALITY--in terms of droplet size and homogeneity--than port EFI... but EFI always has the edge in fuel metering precision.


Also to add to this very precise explanation, a carburator cannot provide steady performance for long time span. If you let them sit a week, you have to re tune them again.
It used to frustrate me when tuning a Holley on a rotary engine to then find out it ran like junk by the time the customer came to pick the car up. I had to re tune it all over again!
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Report this Post06-15-2020 02:44 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by La fiera:

Also to add to this very precise explanation, a carburator cannot provide steady performance for long time span. If you let them sit a week, you have to re tune them again.
It used to frustrate me when tuning a Holley on a rotary engine to then find out it ran like junk by the time the customer came to pick the car up. I had to re tune it all over again!


As soon as the weather changes, you need to smell like gasoline again. Barometric pressure and humidity both affect a carb's tune. STFT in EFI compensates humidity and the BARO reading taken from the MAP sensor before the engine turns compensates barometric pressure.
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pmbrunelle
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Report this Post06-16-2020 10:29 PM Click Here to See the Profile for pmbrunelleClick Here to Email pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
I worked on the injection timing in the last few days.

In the previous datalog I posted, you'll notice short-duration lean AFR spikes when I got back on the throttle after a shift.

No matter what I did with the acceleration enrichment settings, I could not tune out the lean spikes. I surmised that with the uniform 360° BTDC compression injection timing, the squirt (with the acceleration enrichment shot) wasn't making it into the cylinder on time, leaving the first cycle after a shift lean.

I played with the injection timing in 45° increments. Advancing the 3000+ RPM injection timing to 405° worked best:


Advance beyond 405° was not beneficial. The more the fuel is advanced relative to the intake event, the more time there is for an airflow change to occur between the squirt (and thus fuel mass calculation) and the intake event. Transient response was less good with more advance.

At low speeds / idle, I retained the default 360° timing:


Initially, I thought that I should finish the squirt just before the intake valve closing. This would minimize the time during which a sudden airflow change could cause the injected fuel mass to be incorrect for the air mass that's about to be sucked into the cylinder.

Squirting on a wide-open intake valve gave lean spikes. I think that the fuel was entering the combustion chamber (on time) as large droplets, not burning completely, and then exhausted as unburned HC.

I think that my philosophy for injection timing is to do it as late as possible, while still finishing the squirt on a closed (or barely opened) intake valve. This would apply to the White Bug; other engines may react differently?
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