I've got an LT1 in my 96 Impy SS (duh). It's got the 3" MAF, but I did port it some. I will be swapping the Z06 MAF on soon.

Is it safe to spray straight nitrous through the MAF? I've heard that it freezes the MAF and screwst hings up.

I have also been told that it is safe to spray straight nitrous directly into the throttle body. I would think that this would lean out the mix to unsafe levels since the computer doesn't really have a way to read and compensate for the added air.

What is the TRUTH?

And what way are the dry system users on this board using?

Thank you!

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Cheston P - IM_A_0@yahoo.com AIM:Impalaitis
96 BBB Impala SS "ADIOSS"
91 white Caprice 'n0n 9c1' w/L03

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The NOS dry LS1 kit sprays into the airbox, before the MAF. It works fine. A magazine article from NOS indicated this was possible because the LS1 stays in closed loop at WOT (someone has since told me this isn't so, but this is what NOS claimed) and the LS1 computer has a much faster processor than the LT1. I recently saw a post from someone who had mounted the nitrous spray nozzle directly in front of the MAF sensor, and he had a problem with surging. My thought was that this was because the nitrous and air were not thoroughly mixing to a uniform temperature before they hit the sensor wires. But spraying into the airbox, where the air and nitrous can mix seems to work. I guess the point of all of this is that you aren't going to "freeze" the sensor... the wires are heated and it is the loss of heat that is used to measure the "mass" flow.

In an LT1, generally, dry systems spray after the MAF. The NOS 5176 is an example. That setup typically locates the spray nozzle in the intake elbow, so it is spraying through the throttle body. I used this system for 4 years and never had a problem. I currently spray a 275-shot directly into the TB, with no problems.

A dry system adds fuel by increasing the fuel pressure, to flow more fuel through the injectors when you are spraying. The 5176 did this by taking a small stream of nitrous after the first solenoid, passing it through a pressure regulator to get the pressure down to somehthing manageable, then applying this pressure to the vacuum connection of the fuel pressure regulator. That closes down the regulator, and pushes up the fuel pressure. The pressure level is controlled by a small "jet" that controls now much nitrous pressure bleeds off into the vacuum line to the engine. Works fine, but you need to do some work to make sure it is set up correctly.

I have also seen a number of posts from people who have sprayed before the MAF sensor in an LT1 dry setup, and have not had problems. I would caution you on trying this, because you would have to be extremely careful, starting with a small shot, and montioring A/F ratio very carefully to make sure it was giving the correct fuel flow. The fact that the O2 content of nitrous is 50% greater than air, and that the specific heat of nitrous is different than the specific heat of air will throw the sensor and the PCM calculations "off". Whether the errors cancel each other remains to be seen.... .

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Fred
94 Formula A3: 381/TH400/N2O

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11.513@115.59 on motor; 11.162@127.67, 1.643 60' on a 125-shot. Going with a 275-shot this year

 

Thank you Fred!

I'm trying to use some parts from my TBI nitrous kit on my LT1. A friend gave me a dry nozzle and I was thinking that it should work. The jet in the nozzle is a 28. With just that, I think I should be safe.

There is a certain Hot Air T-type who's azz needs bustin

 

Using a Compucar "Bag Kit", I've sprayed a 135 shot dry system before the MAF with no problems on a LT-1. The key is to make sure you get the spray point far enough back from the MAF sensor that the nitrous is atomized well before it hits the sensor. As said above,....the MAF sensor meters the air coming into the motor by how much the filament wires are cooled off by the incoming air. When the nitrous hits it,...the ECM jumps the fuel up. I've heard and seen people going as large as a 150 shot dry before the MAF on a LT1 car but not on the stock FP, or injectors, or FP regulator.

The jet I use on my dry kit to achieve roughly a 135-shot is a .076

 

How does this affect air temp. sensor in the elbow for those that have not relocated it? Wouldn't the cold N20 cause the sensor/computer to advance the timing which is bad for a nitrous set-up?

In addition, I have an old issue of GMHTP, Nov. '98, where T-Byrne and GMHTP tested out the Compucar Bag O' Nitrous on Tom's then new '98 Z-28 and the kit caused the car to surge and fall off, as well as cause the Check Engine light to come on after 3rd gear. The car actually slowed using the "V8" jetting, so they stepped down to the "6-cylinder" jet, and though the car was still bucking a little and the Check Engine light stayed on in the higher gears, they were able to break into the high 12's. An update and explanation was given in another section of the same issue after Tom had done a head swap and even without the nitrous, "'Track testing of these heads revealed that the mass airflow sensor had been damaged, possibly while testing a nitrous kit, a few weeks earlier. As soon as the tach went past 5700 rpm, the SES light would be triggered and the car would go into speed density operation and lose power.'" Something to think about for us OBDII guys as stated below.
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'81 Turbo T/A
-'75 Pontiac 400
-Richmond 5-speed/3.70's
-Holley 650cfm 4-barrel on 1/2 in. spacer, blocked exhaust crossover, 160* thermostat, Blackjack 1-5/8 in. 4 tube headers, Thrush 2-1/4in. dual exhaust kit w/ Thrush California Turbo mufflers, no A/C-no emission controls; drunk bitch induced front-end damage, placed on indefinite hiatus.

'97 Z-28
-LT1 350
-Borg Warner T56 6-speed
-descreened MAF, blocked off air silencer, TB bypassed, Flow Tech Warlock 3in. muffler w/ built-in cutout, Moroso CAI, custom cold air scoop = 277.7 rwhp/ 301.9 rwtq; add-on's since last dyno = Hypertech airfoil and 160* thermostat, B&M Ripper.

[This message has been edited by ponchoV8 (edited July 15, 2002).]

 

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Using a Compucar "Bag Kit", I've sprayed a 135 shot dry system before the MAF with no problems on a LT-1. The key is to make sure you get the spray point far enough back from the MAF sensor that the nitrous is atomized well before it hits the sensor. As said above,....the MAF sensor meters the air coming into the motor by how much the filament wires are cooled off by the incoming air. When the nitrous hits it,...the ECM jumps the fuel up. I've heard and seen people going as large as a 150 shot dry before the MAF on a LT1 car but not on the stock FP, or injectors, or FP regulator.
The jet I use on my dry kit to achieve roughly a 135-shot is a .076
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I've heard good things about this setup too.

KASR

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94 Z28 Hardtop - (stock: 10.5:1, 5.7L, rated 275hp@5200, 325lb@2400, MFI - Current Rating: ???)
Throwing money at the hungry beast and moddin' away like a mad-man =) Holley CAI, !TB, !MAF, Flowmaster Catback, Monza Quad Tips, 3" cutout, 3.23 gears GU5/G80 perf. axle, QLC, 4L60-E, Spectre Breather and Filter, new plugs, wires, and filter. MODS TO COME: Jet-Hot Hooker Long Tubes, Yank 3000 TC, cc305 cam, 1.6 rockers, NX Gen II

 

Seems to me that you could play around with the MAF tables in the unused range (i.e. high airflow) to control the enrichment, but the MAF isn't extremely precise at high flow rates. Also, eventually you'll hit a "wall" when the MAF maxes out.

One more thing - you'll probably want to do this with an OBDI PCM, as the OBDII PCMs reportedly get kinda flaky with high MAF rates (at least in their stock form - there may be a variety of ways to work around this problem).

I'm not sure I'd feel comfortable spraying before the MAF, but hey, someone's got to be a guinia pig

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1996 Impala SS - LT4 396, T56
1996 GMC K2500
1992 Buick Roadmaster Estate Wagon