Advancement of fuel delivery?

Borrowed from the 'Got a nitrous kit!' thread

I covered a very important tuning tip in another thread that I thought I'd copy over to this one. The question that six shooter asks is a responce to a statement I made in regards to controlling the rpm rise rate at the point of nitrous shut down.

What I've found is, if the tuneup is wrong, it will affect the rpm rise rate much more drastically than the map/boost rise rate after nitrous shut down.

Quote:
Originally Posted by six shooter
Are we talking wrong to the rich or lean side ?

Either way. You'll need to search for that mixture that will give you that smooth rise in your particular case. Sometimes that mixture may not be a straight line value too. Explanation below. Don't forget ignition timing too. Although I've found the a/f mixture curve to be the important factor.

Start out on the rich side at nitrous shut off and work lean while looking for changes in the rpm datalog. You may get small lean spikes at the point of nitrous shut down depending on the volumes of your systems plumbing. Just don't let the lean spike get too lean. A lean spike of very short duration shouldn't be a problem. I use a delay box that will keep the fuel side of the system on for a programmed amount of time to control the lean spike due to the accumulative affect of the nitrous gas side of the system pressuring down at the shut off point. I cover that affect in detail in the 'Advancement of Fuel Delivery?' thread.
Even with the use of the delay box, I still allow a short, small lean spike during nitrous shut down. This stradegy has given me the smoothest rpm rise at nitrous shut down. The lean spike will read on the datalog differently from one pass to the next, but generally falls between 12.2:1 to 13.3:1. It is a very short lean spike. You can see a perfect example of it in the datalog examples I posted in the 'Advancement of Fuel Delivery?' thread, post number 201.

With a single nozzle system where the plumbing after the solenoids is usually very short, I'm sure you're not going to be able to finely tune the nitrous system shut off lean spike, if at all. You may not even get a lean spike.
 
Ran the engine today with the new turbo and did a little tweaking of the fuel table. The larger turbine housing freed up some breathing at idle. The engine runs smoother at a lower rpm and at a leaner mixture. The throttle responce is noticeably quicker and sharper. The exhaust tone is lower, deeper and louder.

I did some nitrous hits on the transbrake to start gauging how the turbo is going to spool. Gone forever are 16 pounds of boost in under 1 second. In one second being on the nitrous and the transbrake, I netted less than one psi boost. Maybe one half. Granted the nitrous mixture is as rich as it can get without causing misfiring, so maybe I'll either need to lean the fuel side or increase the nitrous side. I'm going to do some launches next before I make any other changes.

With a new a/f mixture I'm trying at 0 boost (13.3 to 13.6:1), the torque converter is stalling at just over 2600 rpm. It was 2440. When the nitrous hits, very rich setting, 10.2:1 with a warm bottle (975 psi) the stall goes to 3500 rpm and stays pretty level at that point.

A nitrous bottle pressure of under 900 psi will give me some engine miss from a too rich nitrous mixture. 900 psi will give me a miss free hit. Anything over 900 psi, I consider a warm bottle.

There is some work to be done. Arggg!
 
With the turbos (80MM) and larger you need to see atleast 3100-3200 to get decent spoolup.
At 2600 it would take forever.
 
Otto J said:
With the turbos (80MM) and larger you need to see atleast 3100-3200 to get decent spoolup.
At 2600 it would take forever.
Click to expand...

The converter stall is 2600 @ 0 boost, off the nitrous. On the nitrous, and using the present nitrous mixture, the stall is at 3500 rpm after one second of system activation. The boost rising very, very slowly. Only 1/2 psi boost by the one second mark.

I looked at my nitrous system jetting. It appears I have a 4 jet size range to go higher on the nitrous oxide side with the present fuel jet size. I may cut it in half and go for 2 jet sizes higher. Before I make that change though, I'm going to see how the turbo spools on a roll out with the present nitrous jetting. I'm sure I will be leaning the nitrous out regardless. I've always known it was way too rich. I just want to get some base data with this new turbo first.

Changing the stall of the converter is of course an option. That will mean going to a negative angle primary pump, which will significantly hurt top end efficiency. I want to keep this option as a last resort.
 
DonWG said:
The converter stall is 2600 @ 0 boost, off the nitrous. On the nitrous, and using the present nitrous mixture, the stall is at 3500 rpm after one second of system activation. The boost rising very, very slowly. Only 1/2 psi boost by the one second mark.

I looked at my nitrous system jetting. It appears I have a 4 jet size range to go higher on the nitrous oxide side with the present fuel jet size. I may cut it in half and go for 2 jet sizes higher. Before I make that change though, I'm going to see how the turbo spools on a roll out with the present nitrous jetting. I'm sure I will be leaning the nitrous out regardless. I've always known it was way too rich. I just want to get some base data with this new turbo first.

Changing the stall of the converter is of course an option. That will mean going to a negative angle primary pump, which will significantly hurt top end efficiency. I want to keep this option as a last resort.
Click to expand...

It's going to be a struggle. I prefer the smallest turbo I can run to achieve the goals. Anything that large with a low compression alky motor will be a real challenge. Once you have some time to clean up the n2o tune, maybe it will come around. If it still takes a few seconds to get any kind of boost with the n2o, you will be looking at some major changes..converter and/or turbo

I may be able to help with the converter. So far it's Twisted 6/PTC-3...Neil Chance-0:biggrin: Everyone has reported easier spooling and less slip who has made this swap. All 3 situations it was my first shot at the converter verses at least 2 tries for Chance. Either way, you have a big challenge making it come together. Good luck.
 
Check for leaks? You could always stick the 300 shot jets in there:biggrin:
I ended up with 40deg of timing and 13.5a/f to get mine going:eek:



scott wile
 
Dusty Bradford said:
It's going to be a struggle. I prefer the smallest turbo I can run to achieve the goals. Anything that large with a low compression alky motor will be a real challenge. Once you have some time to clean up the n2o tune, maybe it will come around. If it still takes a few seconds to get any kind of boost with the n2o, you will be looking at some major changes..converter and/or turbo

I may be able to help with the converter. So far it's Twisted 6/PTC-3...Neil Chance-0:biggrin: Everyone has reported easier spooling and less slip who has made this swap. All 3 situations it was my first shot at the converter verses at least 2 tries for Chance. Either way, you have a big challenge making it come together. Good luck.
Click to expand...

I'm keeping you in mind, Dusty.
 
Heck with it. I'm going up on the nitrous jets 4 sizes. Should net more than 50 more horses to push on that turbo.
 
Dusty Bradford said:
With that new jet. What is the hp of the hit??
Click to expand...

Before I answer that, I have to explain something about the present jetting. After checking some references I used to come up with the original jetting, I discovered a mis-print in the jetting table. There is an accepted safe mixture range commonly targeted with nitrous systems. In the beginning I was originally targeting the middle of that range. Until just recently, that's where I thought I was. When I discovered the error in the reference, it made perfect sense to me. I had always thought that the system was very close to the rich limit instead of more in the middle of a more conservative range.

Since it was the first time I had ever used nitrous, I had picked a fuel jet size that I thought was two sizes richer than my actual target ratio. A target ratio that was very, very safe to begin with. The reference error caused me to match that fuel jet with a nitrous jet that was too small by two sizes. Now that I've run the system and know just how rich it is, I believe I have plenty of room to go up 4 jet sizes on the nitrous jets to bring the mixture back to my original target ratio, which will remain on the rich side.

The original nitrous jet sizes, as it turns out, are actually sized to provide 30 hp per jet. Times 6, that's 180 hp. BUT! Let's remember that I was running those jets with too much fuel. The richness of the mixture surely killed some of that 180 hp.
With the new jets at 37.5 hp per jet, that will be a 225 hp shot with all six at a more realistic mixture value. So the increase, I believe will be more than the paper value of 45 hp. How much, I can't say.

I realize that the leaner I can run the nitrous system, never mind adding the extra hp value, the better chance of spooling the turbo quicker. There is a limit to how lean you want to push a nitrous system though.

In my experiences with alcohol fuel with this engine, it likes a lambda value of .724 to .731. That would be 10.6 to 10.7:1 for gasoline. Anytime I went richer to 10.3:1 or even richer, the engine became very lazy. A very noticeable loss in hp.
The nitrous system was going to 10.17:1. That is the lowest value my system will read out to me. Chances are very good the a/f was even richer than the 10.17:1. I have to wonder how much hp I was losing out on.
 
I happened to have the jets I need in the trailer. I'll be trying them out this weekend at the track.

Nitrous and methanol together at a very rich mixture. That has just got to be killing the exhaust temp.
 
That's why I was asking. The company spec jet sizes are always on the safe side. Sounds like you'll be fine once the jetting a squared away.
 
Dusty Bradford said:
That's why I was asking. The company spec jet sizes are always on the safe side. Sounds like you'll be fine once the jetting a squared away.
Click to expand...

The table actually had two rows of values that were swapped. Just happened to be the jet sizes I was playing with. I should have noticed it right off the bat. The lb/hr flow values should increase upward and consistently as the jet size increases. The jet sizes column increased correctly, but the flow values for two adjacent jets sizes were swapped. Goes to show you. Check your references very carefully. Double check with other references, if you can.
 
The 40 degrees and 13.5a/f was not on the nitrous said:
Yes, a HUGE 35 (dry of course) shot up to about 138kpa and then back to the standard VE values.

Scott Wile
Click to expand...
 
Just got back in from a long, hot weekend at the track.
The fueling changed quite a bit from 78 kPa on up. When doing my burn out, it wanted a tremendous amount of additional fueling in the non-boost regions (78 to 98 kPa). The lower back pressure of the T6 housing sure affects long camshafts. Even in the non-boost regions. I can run the engine idle at a lower rpm, it's much smoother and I can run a clean, and lean mixture (13.7). The O2 reads much more steady. And reading responce to fueling changes at idle are more clear and stable.

OK. So how did the turbo do? My nitrous jetting is going to need some work. I had to bump up the E injectors about 20% to get the nitrous mixture to a safe starting point. I ran out of nitrous as I was starting to lean it in. I'll wait to report on spooling time until I get the nitrous mixture squared away. I do think I'm going to need more nitrous.

Running without the nitrous, the turbo doesn't want to get going until 2nd gear. When map gets to 135 kPa, get ready. It does spool up plenty quick from that point on. On one of the first non-nitrous runs where the fuel map was still way off, the turbo finally spooled literally at the end of the 1/8. Blew the tires away crossing the finish line.

When I get the fuel map more dialed in, I'll post it so you can compare it to the other fuel map I posted. The difference is quite amazing in the low boost region. I cranked the fuel pump booster to 35% now and finally had to back the E injectors down in the upper boost and rpm region. 4% at this point.
 
Hey Don,

Glad to hear you got it up and running.

When is the next time you plan on taking it to the track? I'd like to check that monster out. I'm mid build-up with my new bullet and could use some motivation :biggrin:
 
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