Fuel Cut with 9b's

[BjornRune]

I just returned my engine back to stock/BPU after selling my td05 setup, since this is my DD and I don't ever plan on running race gas I figured I'd go with some 19T's instead. Anyway, I was out cruising with a friend and we thought we'd do a pull in 2nd just to see if the IC clamps would hold as I have an issue with a short coupler on one of the fmic pipes. Well, turned the sbc-id to wastegate pressure and set the gain to 5 just to start out low. Gunning it at around 2200 rpms and even before we hit 3000 rpms the boost came on hard and went through the roof at 18.2 psi Aside from nothing blowing off and being impressed by the rediculous spool time on those 9b's ( ) , I was wondering at what hz # you'll get fuel cut around those rpms? Or is it a fixed number regardless of rpm?

My friend (who was driving) got a little scared, fuel cut is pretty damn violent lol.

I obviously need to check if any vac lines from the SBC are pinched, or that the wastegates actually open at all lol. That aside, I sooo could get used to such instaspool turbos compared to the larger E16G, as I don't plan to track or race the car any at all. Except for the usual assrape murderings of local poser ricers. And bmw 316 owners, seems to be a lot of them around here.

Cliffs :
SBC is iffy, boost spike to 18.2 psi , fuel cut but everybody lived to tell the tale.

-Bjorn-

[cbehnken]

the problem is the loggers can only see ~1600hz from the ECU. Fuel cut doesn't occur until somewhere over 2000 AFAIK.

This is why it is hard to determine exactly where fuel cut is going to occur. Reported IDCs where fuel cut occurs have often been well over 100%. If you calculate the IDCs by hand and reach around 100% you are right on the edge.

[BjornRune]

Thanks for the reply. That's interesting, I wasn't aware of the loggers not being capable of showing more than 1600hz, do you know if that is the case with all loggers?

I suspect my IDC were way past 100%, as I've hit 101-104% according to the logger a few times in the past without any incidents. Probably riding on the edge there as you mentioned. Time to move up on the fuel scale and get some 550's and the lot methinks. I have a maft-pro with speed density just sitting on the shelf as well, should be great once I finally get it in the car hehe.

About the boost spike, turned out the vac hose to the rear wastegate was cracked badly so I replaced that and was able to maintain stable boost pressure. I should probably just get some hardlines, I see more vac hoses that are cracked a little as well
And to think I just replaced them all about two months ago when I did the vac reduction, those rubber hoses just flat out sucked!

[Phattlard]

How does fuel cut work on our cars

[cbehnken]

Originally Posted by Phattlard

How does fuel cut work on our cars

when airflow hits the ECUs pre-programming maximum the ECU simply pulls fuel to prevent more airflow than the stock fuel system can handle from entering the engine.

This was designed on a stock motor with perfectly healthy injectors and fuel pump, so by the time you hit fuel pump you may have already hurt your engine from running lean.

I have personally hit fuel cut several times when I was on 360s without any noticeable damage, but you are at your own risk to depend on it to save you.

That is why you absolutely must have a logger. Even if your damn car is stock spend the money on a logger and see how your engine is doing.

[bjmsam]

Also see here.

[Phattlard]

Ok I read that there, but What are people doing when they go with larger turbos? They must be flowing alot more air how are they getting around fuel cut?

[venik]

Originally Posted by Phattlard

Ok I read that there, but What are people doing when they go with larger turbos? They must be flowing alot more air how are they getting around fuel cut?

they either have a piggy back or an AEM standalone, with a piggyback the car doesn't know you have bigger injectors in, it just thinks you're flowing less air. Naturally the ECU still doesnt see that 2000 hz mark or whatever.

[bjmsam]

Also see here.

[Phattlard]

good read. thanx bro