My nitrous experience is 20 years old.

Back in those days it was essentially plate systems or high end direct port setups.

Now, with a plate system on an open-plenum manifold, distribution from runner to runner was, it seemed to me, pretty even.

I'm getting back into nitrous now and I'm starting with a Zex dry system and since I have an LT1 with the factory manifold I find myself wondering about distribution issues with the "front loader" design.


Can anyone give me some insight into the distribution idiosyncrasies of the LT1 manifold as it pertains to a dry nitrous shot introduced into the intake tract ahead of the T.B.?


BTW, I did a search on LT1 and DISTRIBUTION in the nitrous section and didn't find what I was looking for.

 

I have extensive engine dyno tuning with a dry setup up to a 300-shot, adding the nitrous before the TB.

http://cjcfo.fbody.com/members/injun...B/N2ONozzl.jpg

The nitrous distribution is extremely uniform, based on numerous pulls from 125-300HP worth of nitrous, inspecting all 8 plugs immediately after the pull. My MoTeC ECU has the capability to tune each cylinder independantly for fuel and spark timing, and we have found no need to depart from identical setting on all cylinders.

When I had suggested a plate behind the TB, the shop (which deals almost EXCLUSIVELY in dry nitrous) indicated they had found distribution problems with the plate on the LT1.

On the shop's own car, a 7.0-second PRO5.0 Mustang, they use the NOS NOSzles for nitrous (only) in a dry setup, so that's another alternative, albeit on the expensive side.

 

Groovy. Just what I was hoping to hear.

 

Fred,
If distribution is not a problem up to 300 dry is there any advantages to going direct port if under a 300 shot? Thanks Ken

 

I asked them why they didn't want to do a direct port dry system on my engine. I assumed that was the best way to set it up for larger shots. But they talked my out of it. Reasoning was that a direct port has one drawback, and that's the fact that even though air is only flowing into the intake runner when the valve is open, cold nitrous vapor is constantly flowing whether the valve is open or closed. Where does that nitrous go when the valve is closed? First the cold nitrous hits the back of the intake valve, and then??? With a short runner like the 3" intake runner in the LT1, I would think there's not much to keep the nitrous from flowing back into the plenum. I would think that a bank-to-bank injection setup would make things even worse, because now you are spraying cold nitrous and atomized fuel on the back of a hot intake valve. Sequential eliminates that issue.

But, when it came time to spray their Pro5.0, they used the NOSzle system, which is a form of direct port. But I "think" they are spraying about 450HP on that car. I know they spent a lot of timing testing the setup to make sure the NOSzle did not interfere with the injector spray pattern.

Since my setup is about as simple and as cheap as you can do a dry system (conveniently overlooking the cost of the MoTeC and the tuning), and it works so well, I didn't want to argue with them..... I bought into their theory.

 

Fred,

It looks like your running in SD mode. I don't see a MAF.

For those of us using a MAF, would you run the nozzle before or after the MAF.

Scott

 

We know the LS1 MAF/PCM combo can handle dry nitrous through the MAF sensor. When NOS first introduced the 5177 dry kit for the LS1, I believe they claimed it was because the LS1 PCM was operating at a much faster speed. And, they also claimed the LS1 stayed in closed loop at WOT, but I've never seen a confirmation of that. I actually doubt it, but have never looked at an LS1 PCM. I know the 5177 works very well spraying through the MAF.

Remember though.... the LS1 system doesn't boost the fuel pressure like the 5176 kit for the LT1. Its relying on the MAF to sense the added mass flow, and for the PCM to add the extra fuel. If you were to spray through the LT1 MAF, you would need to disable the part of the dry system that boosts the fuel pressure.

Whether you could extend that to the LT1 MAF/PCM combo is another question. I have seen a few people post on this forum that they routinely sprayed through the LT1 MAF. But I haven't seen any of those people post here for a couple of years.

It would be a bit of a crap shoot. Can the MAF's internal temperature sensing handle the sub-0deg temps it will see from the nitrous? Is the specific heat (BTU/LB-degF) of nitrous oxide the same as the specific heat of air? The MAF is measuring power (BTU)required to heat the air (at least the air touching the sensing wires) a fixed number of degrees above the incoming air temp (degF), via a Wheatstone bridge, and then calculating the mass flow rate by using the known specific heat of air. Its highly unlikely the specific heat of nitrous oxide is identical to air, but maybe its close enough that it doesn't matter.

Seems like something you could try on a dyno. Introduce a small amount of N2O and see how the A/F ratio reacts on a wideband. Problem is if it doesn't just happen to yield an acceptable A/F ratio, there isn't much you could do about it. You could tweek the PE tables, but then that would throw off your NA tune.

Yes, I run a MoTeC ECU in speed-density, open loop.