Why so much nitrous and so low timing? I can't possibly imagine needing 300hp worth of n2o to spool a turbo. The backfires can also be from excessively retarded timing that you need with the large shot of n2o. More timing will help make the engine much more responsive and should reduce the need for that large of a hit.
Most nitrous backfires that blow the hoodscoops off the cars is from excessive timing retard while on the transbrake.
Keep in mind that I'm pairing nitrous with alcohol. A 300 shot on gasoline is not the same as a 300 shot on alcohol. You kinda have to learn to ignore the 300 number with my setup. It's the resulting spoolup that's important.
What would you think a safe retard would be with a 300 shot on alcohol with a tight torque converter? I'm only trying to start out safe with this 300 shot and work up on the timing, but if you say that excessive retard can be just as bad, I'd like to hear more advice. Thanks Dusty.
I did a total of 8 tests. Only the last one gave me a backfire, and only after richening the initial hit area in the map. I was trying to lessen a lean spike that was occurring for a duration of .16 seconds on initial hit of the system that was showing up on the datalog. In the beginning, there were also dips in the rpm rise after the initial lean spike. Rpm rise during the first .16 seconds was actually quite good up to 3300 rpm. The lean spike would start to recover after that point and rpm rise looked like a roller coaster up to 4000 rpm. As I richen the 2800-3800 rpm spread, the roller coaster smoothed out more and more until I reached a point where the rise was perfectly smooth and the sound of the engine was even noticeably 'bitchin'. Since I was now up to 3820 stall at about .55 seconds, I thought I'd try to hit the magic 4000 mark. Understand that up to this point adding more fuel to that 2800 to 3800 rpm spread was working big magic for me. I thought, heck 4% more fuel throughout that rpm spread just might be the ticket to move it up to a 4000 stall in .5 to .6 seconds.
25 degrees retard was what was used for all but I think the first test, which was 30 degrees retard. During the first test with the 30 degrees of retard, I noticed a rather large rpm dip on initial hit. 2410 to 2332 rpm. It recovered in less than .1 seconds. When I stepped up the 25 degrees retard, the dip was still there. The same degree of dip and the same duration. I decided to leave the retard there until I thought I had the fueling more under control. The only thing I changed throughout most of the tests was small increases in fueling in the map at the initial hit area from 2800 to 3800 rpm, 3 to 4% at a time. kPa staying between 95 to 97 kPa through the initial hit, up to just before 4,000 rpm. kPa actually dropped to a small degree on initial hit, 1 to 2 kPa. The engine creating slightly better vacuum from the increase in power from the nitrous. The turbo caught up to the engine by 3587 rpm reading 0 vacuum, 0 boost. 98 kPa with my system. First tiny sign of boost at 3804 rpm, 99 kPa.
This is some data from the test before the 3820 test and the 3820 test.
datalog#17n (test before the 3820 test)
rpm at .529 sec. into the hit: 3690
datalog#17o (3820 test)
rpm at .549 sec. into the hit: 3804
rpm at .496 sec. into the hit: 3757
So you can see that some big power was being gained from just small fueling increases in that 2800 to 3800 rpm range. It was too tempting to see what another 3 to 4 percent of fueling might net.
What I really think happened was, as I increased fueling, engine power increased and rpm rise quickened, putting the engine on the torque converter sooner and harder with each step up of fueling. The engine was not recovering fast enough after the initial lean spike to deal with the higher engine load, and increased combustion temps that were coming sooner with each fueling change.
The lean spike has become a larger problem with the step up of the nitrous system jets. The nitrous gas is getting to the nozzles much quicker than the nitrous system fuel (alcohol). The fuel solenoid is mounted directly to the distribution manifold. the nitrous gas solenoid presently has a one foot hose between it and the distribution manifold. I've ordered a 3 foot and a 2 foot hose to try out. I'll try the 3 foot first to see if I can gauge any change in the staggered feeding problem. It will also mean that I may need to increase the delay time that the fuel solenoid shuts down after the nitrous gas solenoid to allow time for the nitrous gas to blow down out of the longer line.
I don't plan on the timing retard staying at 25 degrees. I've just started this testing and the last thing I want to do is move too quickly and hurt something. After the fueling problem is addressed I'll start bringing in the timing,... a little at a time. Small steps. Small steps.
Achieved in .53 seconds.
