Hey guys.... TT.net is down, and i was in hopes of hearing from someone who really knows their stuff with really high flow/high hp motors. Last year, i did a ton of work to my car. I went from stock valve train to 1mm oversize ferrea valves, ferrea springs, and JWT500 cams. We did some extensive porting on the heads, as well as port matching the lower plenum. Higher flow Exh manifolds (MS), had the throttle bodies bored to 58 mm, and 2.5 inch boost pipes, and 3 inch intakes from the firewall back, with dual mafs and translator. So needless to say, the flow has increased dramatically. I dont have easy access to a dyno, so I have been driving it for a month or so, taking it easy, checking everything was right, and decided last night wanted to take her out see what she was capable of. Ambient temp of about 55 out last night, and It pulled like a freaking freight train up to about 6500 rpms, then just cuts out, almost like a fuel cut, but I don't have a fuel cut. It didnt buck, or pop, or surge on the way up. I am thinking it is blowout, but unsure. I am running pfr6b-11b's, gapped at .030, no boost leaks, but at 1.1 bar at about 6500 rpm, it is like it hits the rev limiter, which is set to 7500. With these same turbos (gt2560r's), and stock intercooler piping and stock heads, I could push 20 lbs of boost clear to the limiter without issue, but my suspicion is all the extra air, even at substantially lower boost is causing the plugs to blow out. Am I thinking right? Is blowout more a phenomenon based on volume as opposed to overall pressure?
while I am no an expert on this. I may be able to shine a bit of light. The 2 parameters pressure and volume are not singular but interrelated. You need to look at this from the point of view of the number of air molecules at pressure. For example at 1 bar and 20 degrees C, there could be (for example 100 air molecules) at 2 bar there is 200 air molecules. Change the temperature to 40 degree's C the number of air molecules will reduce to half due to the excitation of molecules from the increased temperature. The number of air molecules in a given volume and IS what produces the partial pressure for a given temperature. So pressure and volume are directly related depending on the temperature. IMO your spark is being blown out and may well be a heat range issue or possibly gapping of the plugs. The member that can probably help you is A2zed Eric. He's pretty experienced with this stuff.
Check the fuel pressure at full boost/power ... to be honest I wouldn't be doing any "power" runs without it been checked on a dyno. There is a chance that with all the improved flow the turbos could be too small (just a thought)
Ehhh... I know what you're saying on the dyno. Just that anyone who knows their stuff on these cars, and has the means to tune it would be a 500 mile drive to get to their shop. As far as the turbos, I wouldn't think so. I would think that they would act more like the rebuilds i had before I went to these turbos. They would keep boostin, but just hit a wall above about 6500 where it wouldn't pull hard. Like tryin to breathe through a straw, no matter how hard you blow on it, only so much air will go through. This wasn't that.
My experience is that spark issues will tend to be a miss fire rather than a sudden cut BUT I do know after some testing we did some time ago that the miss fire will most likely be consistent in that it will occur at the same power output. We found that while running 98 unleaded we ran in to a missfire at approx 20 PSI boost and 366Kws at the wheels, when we went to avgas in the same dyno session (drained tank and filled with avgas) we found we got a similar missfire @ 366Kws at the wheels on about 18 PSI boost. We thought this was pretty damn interesting that even with a change in fuel the power output at the wheels was still capped to exactly the same amount by the weakness in the spark system. I later found the plugs had been installed in error at .040" instead of .032" my bad I must have grabbed the wrong set off the bench What you are most likely hitting is (fortunately) a "rich cut" this is where the mixture simply becomes to rich for the spark system at that given point in the tune. A cut like this will be very consistent and will do it the same every pull (in the same conditions), if you do it during daylight with a spotter watching the exh it should be excessively black. A rich cut will be like a brick wall as the mixture can suddenly overcome the spark system in an instant, to much cylinder pressure usually causes a progressive failure of the system - miss fires getting worse and worse, people normally don't leave their foot up it long enough to have the spark go out entirely. A rich cut can dump waaaaay to much fuel in as soon as you hit a given point in the ECUs map IE: X airflow, Y RPM, Z throttle = same cut at same point over and over. GO AND GET IT TUNED BEFORE YOU BREAK IT!! :zlove:
Good advice... Probably oughta just put the controller setting to off and run on spring pressure (about 12 psi or .84 bar) til I can get it tuned. Even on the spring pressure it is a lot of fun with that much flow.
I would also consider putting it on any dyno to get a read out least you will know if its safe to drive.
Living so far from a Dyno or tuner, it might be worthwhile investing in some wideband O2 sensors and gauges. Might give some peace of mind at least while driving around. I did my own road tune on my last Z using WB and gauges. At least I knew it was safe
Spark blowout the motor would stumble to shit,not just cut I'm pretty sure? Sure is not just off the map and stuck outta a lambda range? I reckon you could pop the motor if you don't know what's the deal with the fuel delivery? What ecu and what kind of chip or tune is it? You off the 5v air intake for 'add' function on the translator if that hasn't been addressed.
I sent Ash a couple of blazt data log recordings right after I got it back together... The map that is in it now is pretty much identical to the map in his car.
There are dynos closer.... but no one has Nisstune software close to me. Anybody got reccomendations on a good wideband/gauge setup?
Hey knight... Fuel pressure is good. I ran an extra gauge on a T this afternoon, and it is delivering plenty of fuel. As far as the translator, it is on average.
If it's getting to 6500rpm or there a bouts and suddenly cutting out, I'd assume it's hitting the end of the tp scale. Are you running nistune? Did you change any of the following: Kvalue Afms Injectors ? **edit, just re-read the mod list. Adjust your kvalue to suit and it'll shift the tp scale. Sounds like your engine is breathing a lot easier with all the new mods. If you don't have nistune or access to it, don't stick your boot into it. Chances are it's running lean. Get it tuned asap**
