Not Supra but a boosted car problem

[GreenChevelleSS]

This is on the 89 Iroc TPI 350
We changed pulleys this weekend to up the boost. we were running at 6-7psi and now we are running at 9-10psi.
Once we got everything fixed up we went for a test drive. It sure pulls hard but in third on the hard pull the car starts lurching Like the computer is shutting off fuel, like fuel cut.

The A/F gauge is showing rich all the way till it lurches then shows lean for that splt second that it lurches and goes back to rich. it keeps doing this too. The car has an 8:1 FMU.

FP is running about 40 at cruse then when you put it to the floor it goes up to about 70-80psi then in third gear the bucking happens and pressure jumps to 90-95psi when the buck/lurch happens. We also watched the Boost gauge....Second gear 9 to 9-1/2psi then thrid gear about 6-7psi the bucking starts.

We unplugged the FMU and tried it. Got very bad detonation under boost so it didnt work out without it.

 

[Supracentral]

The car has an 8:1 FMU.

That could be your problem right there.

You are running 40 psi at cruise. You have an 8:1 FMU You are adding 7 to 9 psi of boost.

Take an average of 8 psi of boost.

8 psi x 8:1 FMU = +64 psi at the rail

Add that to the 40 you are cruising at, you are asking you fuel pump to put out 104 psi @ it's rated flow. That's a tall order. You are probably deaheading the pump.

Which fuel pump are you running?

 

[GreenChevelleSS]

aeromotive Tsunami rated at 100psi +

 

[lagged]

bye bye head gaskets

 

[Supracentral]

aeromotive Tsunami rated at 100psi +

According to Areomotive that pump is only good for 500 HP on a boosted application.

Here's the flow chart:

That pump is down to 300 lbs/hr @ 70 psi - I doubt it can flow any meaningful amount of fuel at 100+ psi.

What are your horsepower goals? What size injectors?

 

[GreenChevelleSS]

well our guess is 330-340hp at the rear wheels... We have stock injectors which i think are 24lbs im not sure
But if we were asking too much from the fuel pump and taking it wouldnt we see it lean out? the A/F guage shows rich all the time except for the second it lurches.
Think it could be something like fuel lines, it also has the stock intank fuel pump to add on top of the inline aeromotive unit...

 

[Supracentral]

Note: for imports, to convert from lbs/hr to cc/min, just multiply the injector size by x 10.5

well our guess is 330-340hp at the rear wheels... We have stock injectors which i think are 24lbs im not sure

Ok, you didn't say auto or stick, but let's guess stick and give a 20% drivetrain loss @ the wheels.

So lets say you are shooting for 400 BHP.

Since we're taking a boosted application we need to use a Brake Specific Fuel Consumption (B.S.F.C.) rating of .60 lbs/hr.

Take BHP multiply by a B.S.F.C of .60 lbs per hour for a boosted car = 240

Take 8 injectors running a max duty cycle of 80% = 6.4

Divide 240 by 6.4 = 37.5 lb/hr injectors - there's our 1st problem - the calcs show you need a bigger injector. You could be going static and that would account for the behavior you describe.

But let's continue with the calculated injector size. Multiply injector flow rate by 8 = 300 lbs/hr fuel.

Considering that chart, the pump can just barely flow that @ 70 psi.

If this were the case, you wouldn't have enough fuel pump for those injectors with that 8:1 FMU.

However since you think the injectors are 24 lb/hr, it's easy to calculate what they support.

Horsepower = Inj Size (lbs/hr) x (duty cycle) / B.S.F.C.

So 24 x .80 / .60 = 32 BHP per injector

32 x 8 injectors = 256 horse (boosted)

Remember that the B.S.F.C is lower for an N/A car - calc for that is easy to run. So 24 x .80 / .50 = 38.4 Horsepower per injector or 307.2 BHP supported for an NA car. Is that close for the old 350? I'm really rusty doing this stuff.

Also, these are all "theoretical" calculations used for fuel system design. I know you can find 101 cases where someone will tell you "well I made more than that" - these are the calculations with built in safety margins that I'm comfortable with when doing motor design.

Overall I'd say you are either deadheading that pump, or you've gone static (or near static) on your injectors - either has the same result, which is a lean spike, a power fall off, then a return to power.

Also I don't even want to think about how poor the spray quality of those injectors would be at over 100 psi at the rail. Injectors are rated at 43 psig - yes, you can up the pressure higher and higher to flow beyond what they were designed to do, but the spray pattern suffers, you get poor fuel atomization, puddling, etc. It gets really ugly. I'd ditch the 8:1 FMU (which in my opinion is a hack) and go with a more resonable 1:1 or 1:2 rising rate regulator. Then spec the proper sized injector and I'll bet you make a shit load more power.

The reason most of the manufacturers sell kits for the F-Body (and Honda turbo kits are guilty of it too) with these bullshit FMU's is to keep the cost down. You really need a bigger injector, but they know a lot of people won't pay for it, so they put in an FMU - it runs the car pig rich and over pressures the injectors.

 

[NashMan]

fmu are not fun at all teh swaping thing get very anoying after aweil

try a afpr you will get better resalts

 

[diy guy]

if youre basing a/f off a narrowband sensor/gauge, 14:1 would likely show as rich, obviously you need to be much richer for boost, hell even n/a

check your plugs and see if youre really rich. my guess, like others have mentioned is your pump is not flowing enough at that high pressure

 

[sleepersupra]

that was quite possibly the most interesting thing i have ever read....ok maybe not but it was something that i didn't know.

thanks for the explaination.

 

[Supracentral]

For those who like to think in cc/min vs lb/hr, the conversion is REALLY easy.

Take the lb/hr injector size and muliply it by 10.50.

i.e. - 24 lb/hr = 252 cc/min injectors

The inverse is true if you want to go the other way, just divide cc/min by 10.50 for the lb/hr rating:

440 cc/min injectors (stock 7MGTE) = 41.9 lb/hr injectors

If you run the math above post you'll see that the calcs come up with a very conservative rating for the stock 7M-GTE fuel system. You can safely go much higher than the calcs tell you. Like I said, these are calcs for building a fuel system that is safe under all conditions, at all altitudes and has a large margin of safety built in as well.

One thing to consider is that an injector working at an 80% duty cycle is working a hell of a lot harder than one working at 60%. If longevity and safety are your goals, use the calcs above and you'll NEVER run out of fuel and will have a fuel system that will last the life of the car.

 

[Supracentral]

And well I'm at it (yea, I know - shut up already!) when discussing rising rate regulators, FMU's etc.

Think about this:

The injector is designed at 43 psig @ atmospheric pressure. If you use a 1:1 rising rate regulator where it adds 1psi of fuel for each 1 psi of boost, you'll always have the same pressure differential. That means your spray patterns are uniform across all boost levels until you reach the limit of the fuel pump.

When you use a non 1:1 regulator, the differential increases as boost goes up. Spray patterns will change radically when you have something as silly as an 8:1 or 10:1 FMU.

 

[GreenChevelleSS]

The car actually has 22lbs/hr injectors on it.
We called procharger and they said to change the injectors, We are asking too much and they are locking up. They recommended switching to the bosch 24lbs/hr injectors think this is enough?

 

[GreenChevelleSS]

That could be your problem right there.

You are running 40 psi at cruise. You have an 8:1 FMU You are adding 7 to 9 psi of boost.

Take an average of 8 psi of boost.

8 psi x 8:1 FMU = +64 psi at the rail

Add that to the 40 you are cruising at, you are asking you fuel pump to put out 104 psi @ it's rated flow. That's a tall order. You are probably deaheading the pump.

Which fuel pump are you running?

The fuel pressure guage is attached to the fuel rail, not in the line before the FMU. So we are getting about 70-80psi of fuel pressure at the injectors with boost. Then the 90-95psi spike only happens when the injectors are locking up i suppose.

 

[Supracentral]

The car actually has 22lbs/hr injectors on it.
We called procharger and they said to change the injectors, We are asking too much and they are locking up. They recommended switching to the bosch 24lbs/hr injectors think this is enough?

I've already given you my opinion on the FMU, which is a way to make little injectors spray more fuel than they were ever meant to do.

Now they are telling you add slightly bigger injectors and have them spray far more than they were ever built to do.

You can get a full set (8) Accel 37 lb/hr injectors from Summit Racing for $389 that are a direct drop in for the TPI LT1:

http://store.summitracing.com/partd...0836&N=4294870762+4294908216+115&autoview=sku

If you are going to go through the expense of buying new injectors, size them right, ditch the FMU and go with something like this for a FPR:

http://store.summitracing.com/partdetail.asp?autofilter=1&part=AEI-13109&N=-86382+115&autoview=sku

And then you'll have more than enough fuel to do what you want.

Remember - pistons & valves ALWAYS cost more than a fuel system. ;p

 

[Dirgle]

Since you have to replace the injectors anyway, you shold listen to Supracentral. It's good solid advice. The fuel system is not a place you want to cut corners, the engine will not forgive you.

I also agree that I don't like the idea of a FMU, forcing the injectors to do a job they were never designed to do is not a good idea.

 

[diy guy]

maybe i'm missing something, but I dont understand the logic of using a fpr to control bigger injectors. supracentral already explained that a 1:1 really doesnt add (or decrease) fuel based on load, it equalizes the pressure differential between the manifold.and fuel rail. the only thing you will be able to change with that fpr is base pressure. i doubt its even possible to adjust fp low enough to make injectors almost twice as big, idle like stock, but assuming it is, they'll flow like stock all the way through redline...no extra fuel for boost.

about fuel pattern, would a big orifice at a lower pressure atomize fuel better than small orifice at high pressure? i'd think the higher the pressure, the better the pattern, unfortunately, it puts more strain on the plunger

now if you were saying he should ditch the fmu for a pulsewidth fuel controller, then yes, i agree, that'd be the better choice.

 

[Supracentral]

maybe i'm missing something, but I dont understand the logic of using a fpr to control bigger injectors. supracentral already explained that a 1:1 really doesnt add (or decrease) fuel based on load, it equalizes the pressure differential between the manifold.and fuel rail. the only thing you will be able to change with that fpr is base pressure. i doubt its even possible to adjust fp low enough to make injectors almost twice as big, idle like stock, but assuming it is, they'll flow like stock all the way through redline...no extra fuel for boost.

about fuel pattern, would a big orifice at a lower pressure atomize fuel better than small orifice at high pressure? i'd think the higher the pressure, the better the pattern, unfortunately, it puts more strain on the plunger

now if you were saying he should ditch the fmu for a pulsewidth fuel controller, then yes, i agree, that'd be the better choice.

An FPR does not "control" injectors. And FPR is not a tuning tool to control added fuel for boost. I'm not really sure what you are getting at. The purpose of the FPR is to provide stable fuel pressure at the rail relative to the boost level. That's all it does.

The larger injectors provide the capability to flow the appropriate amount of fuel at resonable injector duty cycles with sane base pressures.

None of this addresses tuning. This is all foundation work. Building a system that can support power goals. We haven't even addressed the actual tuning of the car.

No tuner who has 1/2 a clue would try to adjust base fuel pressure to "downsize" oversized injectors to achieve a decent idle, that's.. well.. just damned ignorant... The injector sizes we're talking about wouldn't require pulse width changes, just duty cycle tinkering.

For tuning on that car there are a 1/2 dozen decent options and there's always the standalone market as well. Simply running a MAF/MAP fooler would work. (I dont' recall which generation of the TPI he has (early ones were MAF I believe, later ones went to MAP if I remember correctly)) - but there are 101 options to mess around in that arena. I wouldn't be suprised if the MAP-ECU supported that car as well. (I'd have to check the specs on the input output of that old PCM)

 

[GreenChevelleSS]

Simply running a MAF/MAP fooler would work. (I dont' recall which generation of the TPI he has (early ones were MAF I believe, later ones went to MAP if I remember correctly)) - but there are 101 options to mess around in that arena. I wouldn't be suprised if the MAP-ECU supported that car as well. (I'd have to check the specs on the input output of that old PCM)

Its MAF and yes you are correct the early ones are maf and the later ones are MAP.
Ive heard MAF is alot better than MAP, Its more accurate and even more accurate when they are combined.

 

[diy guy]

ok i can see we're on the same page i didnt see anything mentioned about a tuning device in the previous post so I assumed you meant bigger injectors + the fpr posted, alone, would do the trick.

btw, duty cycle is a function of pulse width, if one changes, so does the other