I have a 305 TPI with a 75 hp shot of DRY ZEX nitrous.
I have an afpr & 255lph fuel pump.
When I hit the n20, the fuel pressure jumps up to 60lbs.
I have had it on a scanner and it did not lean out.
I am wanting to try out a 100hp shot, should i change to bigger injectors(like L98 , 22lb injectors??)

Anyone have experience with this dry kit?

Please refrain from telling me that I should get a wet kit or a bigger engine. I have the dry kit and want to use it to it's full potential.

 

I can't help with your question, but do you have any track times or other performance data with the 75 shot? Good luck with the 100!

 

I had the wet zex on my 305 with the 125 jets and didn't have any problems. My car has ported sr 305 heads, l98 cam, big mouth base, 19lb inj, 255lph fp, afpr, super ram(i know a super ram on a 305, it was free), 2800 stall. When I ran it I had to let off to get it to shft 2-3 and I ran an 8.30 1/8 w 1.85 60ft

 

RSFreak, I ran on my g-tech pro a best of 14.3 in the 1/4, and with the noz, I ran 13.6.

On the 1/8th mile track I ran a best of 9.3 without the noz.

Chikn305, thanks for the reply but I am looking for people with a dry kit for experience with injectors.

LB9GTA

 

Hi, just to clarify I was the guy that said he needed larger injectors on a dry shot. I will explain my reasoning and hopefully someone can chime in and tell me if I am wrong or if LB9GTA needs larger injectors.

For engine mods he already has a Comp cam specs: 480/487 on a 110 LSA with 206/212 duration and headers, no cat, port work and a few other things still on a stock GM bin in a speed density setup. If you use his 1/4 mile time(even tho its a g-tech pro) to calculate HP and you assume his car weighs 3500 and he is 200, a conservative etimate on HP is still close to 280(atleast) at the crank. Then add a 75 shot on dry nitrous brings it up to 355HP conservative. When the nitrous is enguaged the fuel pressure RISES to 60psi.

If you calculate the HP potential of a 19lb injector it works out like this:

injector flowrate(lb/hr) / brake specific fuel consumption(.5 for N/A engines) * number of cylinders = HP at 100% duty cycle

19/.5*8=304HP at 100% duty cycle

Most will agree that you should never run the injector at 100% duty cycle as the injector has a great potential to go static and lock. On top of that you are bumping the fuel pressure up to 60 psi AND hitting 100% DC.

If you use a 80% duty cycle then 304HP*.8=243 hp safely

Now if his FP bumps up to 60PSI when the nitrous is used we can calculate the maximum HP for the injectors with the higher pressure:

square root of new pressure diveded by old pressure mutiplied by old flow =new flow

60/43.5=1.379

square root of 1.379 = 1.174

1.174 mutiplied by old flow(19lb/hr) = new flow
new flow equals 22.31

22.31lb/hr at 100% duty cycle at 60psi.
Thats a bit much correct???
22.31/.5*8=MAX HP

MAX HP from these injectors at 100DC at 60psi is 356hp.

He is atleast at 355HP(conservative) with the 75 shot. I think he needs larger injectors because of this as his stock Multecs can't handle the load of 60psi and 100% DC. Did I calculate things correctly or is he okay with his 19lb injectors???

 

Thanks Razor!

Can anyone help me?
I don't really feel like blowing my engine.

LB9GTA

 

You’re barking up the wrong tree… a dry shot adds fuel by raising the fuel pressure. As long as the thing is running right NA and is jetted correctly then the pressure rise should be enough to cover the fuel needs.

Now here is the thing… How do you know that you’re not running lean? Are you using a wide band or something or are you just assuming that you aren’t because you didn’t blow something up and it ran OK?

60psi is only a 40% rise in fuel pressure, which only works out to be an 18% increase in fuel delivery. 75hp would be 18% of 417hp, so unless you were making about that and delivering enough fuel for it NA, you’re running lean.

Barring having better details, assuming that your car has a race weight of about 3600# (pretty typical for a 3rd gen, mine have come in in the low 3700’s but I’m about 100# heavier then most), your 14.3 is about 243hp at the crank (unfortunately, how accurate that is really depends on the driver and the combination, estimates using your MPH would be more accurate). 75hp should be roughly a 30% increase in power, which works out to require a 71% increase in fuel pressure or about 74psi. Again, imperfect as it is, your ET assuming everything else remained correct should have dropped to around 13.0.

To run a 100hp shot you should expect your fuel pressure to rise to about 86psi when jetted correctly to cover the HP increase, and your ET should drop to about 12.75.

Now will your injectors work at that pressure? Most will, 86psi is the outside range for a lot of GM injectors though… OTOH, ford/bosch stuff is often good into the 100-120psi range.

Why aren’t you getting enough pressure rise? I suspect that you either have the wrong jetting or you have a fuel delivery problem. Really, if I was planning on doing this regularly I’d probably be running an inline pump to boost pressure more then volume

Bigger injectors will not solve any problems unless you’re already running out of fuel NA, and if you did install them you’d have to burn a chip to match the injectors that you’re running. An interesting alternative would be to knock down your base pressure so they flow the same as the stockers at NA and that same, proportionate increase in fuel pressure would actually end up being a lower total pressure which would be easier to keep up with fuel system wise. With 22pph injectors replacing 19's that would invlove knocking down your base fuel pressure to around 32 psi

 

So the stock 19lb Multec injectors will take up to 86 psi safely and are not a concern to run a 75 or 100 dry shot???? Well that should make him happy. I noticed my stock Multecs didn't like it much over 53psi and would start to lock under load. Were they on the way out????

 

Nutshell: they should work, but I wouldn’t consider it a safe setup, since even if they’re right that pressure should be pretty close to where they will start locking up (53 psi is way too low). The big problem is that spiking the fuel pressure like dry kits do is not exactly precise, so hitting those injectors with that pressure spike could work if you get lucky and everything goes well, but say if one of the injectors starts locking up at 88psi and that spike momentarily hits 90 (which is pretty likely), well, you’re carrying your engine home in a bucket…

 

83 Crossfire TA, I have put my car on a scanner(Snap0n).
Now, I am not saying that the 02 sensor is 100% correct, but I took the plugs out and they were fine.

Also, I ran the car without the gas at 14.3. Now with 75hp it should run about 7 tenths better(about 10hp for a tenth), then that puts me at 13.6, where I am at! SO, if I was to add another 25hp(to 100shot) I should be 2 tenths faster or a 13.4.
I have a race weight of 3590 lbs.

Also, I have no problems with the fuel press at the 75hp level,(goes up to 60lbs press) I have an afpr and a 255lph fuel pump. So far no problems.

I guess the only way to find out is to try the 100hp shot and put it on the scanner.(I have to put in non ground strap plugs and a rpm switch and a msd 6al too!) Then put it on the scanner and see.

HAS ANYONE USED A 100HP OF DRY NITROUS ON A 305 TPI SPEED DENSITY???????

Am I just crazy or has no one tried it??

My theory is that with the mods I have now, the fuel press will just compensate for the added nitrous. Am I wrong??

LB9GTA

 

I have run myself and installed the Mustang NOS-5115 on a few TPI cars. But I have always made it a point of switching the 305's to 19# ford injectors, and the 350's to 24# ford injectors.

Some may disagree but from what I have seen in the field, ford injectors are less prone to this pressure lock and general failure all together.

The 5115 works exactly like the Zex kit, you could say that basically Zex has based their whole company on the NOS-5115 kit, which has most of the same parts and all of the same functons as the Zex kit but predates it by about 10-12 years.

The real difference is that Zex has squeezed everything into a little pretty box to hide the components. This is done to protect their proprietary design (yeah right) and avoid the kind of hacking and shadetree engineering that thier main customer base is known for (ricyrs).

Don't get me wrong, I love this system. On a 75 shot, it is very likely that if you dont push things that your engine will last forever on this kind of shot.

I can't speak for how long the 100 shot will last because when I switched to a 100 shot I was running 24 pound injectors on a 85 305 ecm (no tuning) on top of a 415 small block. It ran like a champ, but when I hit the 100 shot detonation occured, probably as a result of the lean condition from having everything so wrong.

On the cars I installed since they werent mine I avoided the 100 shot for not being able to keep an eye on the car for tuning with the 100 shot. I left that up to the customer.

 

George my concerns still are that you are asking the stock 19lb Multec injector to supply a lot of fuel under pressures it is known to have problems with. That and I still don't believe that a scanner can accurately log WOT AFR. You will have to make friends with somebody in Winnipeg that has an LM-1 so that you can datalog a WOT run on a wideband O2. Maybe call Rich at Cruisin Performance and ask him. He was very honest with me about my injectors and seemed to actually care about the advice he gave me. Just my

 

B4Ctom1, that NOS 5115, that is a dry shot right???

LB9GTA

 

So pretty much as I wrote… you don’t really know if you’re running lean, you just didn’t blow anything up.

A narrow band O2 at WOT is just slightly better then using your horoscope, and unless you shut the engine down before you slowed down right after a hard pass and pulled the plugs on the spot… well “they were fine” means nothing WRT to this discussion.



If you’re ever going to learn anything stop messing with “rules of thumb." They're not quite as helpful as a narrow band O2. I gave you accurate numbers, and guessed your race weight within 10lbs. If you don’t like my numbers, fine, that doesn’t make my numbers wrong. If you didn’t run somewhere in that range either your setup is wrong or your driving was.



One more time (can anyone guess what I’m going to say? What did I say the first time?) 60psi isn’t enough, you should be seeing > 74. What I left out is that N2O systems are typically jetted “safe” for a roughly 6:1 A/F ratio with the N2O. If you were anywhere near there you’d be seeing something in the 85-90psi range with your 75 shot.



Woohoo… we have a winner… give that gentleman in the corner a prize… and I quote from earlier:



I’ve gotten the NOS setup to go 175, but that involved running a lower base pressure with bigger injectors (something in the 20’s with 30pph injectors in an LT1), so that an increase in fuel pressure made a much larger difference then it will at the stock 43 psi. It worked fine.

A wet kit is better. And yes, I am a PITA. Tough.

 

yes, I was just reiterating, I know you said it first


yes it is, as I said the same system basically as is contained inside of your Zex "box"

 

Thanks '83 crossfire for your input.

You don't have to be so defensive.

I have my fuel press at about 47-48. I have had the fuel press guage on.

So, I don't care who is right or wrong, but that is what the guage said.

As for my times in the 1/4. I believe that my times are respectable, with and w/o the nitrous. And I have proven my theory about the 10hp for a tenth time and time again with the mods I have done.

Any input from anyone that has roughly the same setup as me would be appreciated. (Injectors with a 305tpi and going to a 100hp shot).

LB9GTA

 

you're semi-blowing off the wrong guy if you want a technically oriented answer to anything.

mark just laid out exactly what you could and should be running with that 75 shot based on actual calculations and not some rule that can't always be applied in the sam manner like 10hp/0.1seconds.

You side stepped it because you believe your car is runnign correctly now, which it may infact be, but i'd be looking into making sure you're not ruining your car with a 75 shot before i bumped it up.

 

I apologize 83 Crossfire.

All I want to know is if anyone has used a dry 100 hp shot of nitrous to a 305tpi with the same mods, not always what works out on paper will work in real life.


(People told me time and time again not to use a 75hp dry shot and I am kicking their butts about now).

LB9GTA

 

The only way you will know about 100 shot on your car is by trying it, seeing if it detonates preferrably with a scan tool looking for a bunch of knock counts when you hit it.

Then by reading the plugs to make sure at the end of a pass they are somewhat showing rich.

 

I'm not too fimiliar with dry kits. How do they add more fuel pressure?

 

they have a regulator to step down nitrous pressure to just a few psi where it presses on the factory fuel pressure regulator just like an boost to an FMU. It begins to close off the return and fuel pressure rises flowing more fuel through the injectors. It is crude but effective.

 

I’m at a complete loss… why would this thing act differently on a 305, 350, LT1, or even a 5.0 mustang? As long as we’re talking about a V8 with the same bypass style regulated high pressure FI setup it’s going to work.

Find/fix your fuel pressure problems and make sure that your injectors will tolerate the pressure necessary to deliver the increased fuel and you’re golden.

If it was me and I insisted on staying with this setup I’d go with either some ford 22.5 or 24pph injectors and an adjustable fpr to give you a wider usable range, run a lower base fuel pressure and go from there. Even a set of stock 19pph injectors from a 5.0 ford would be better then nothing.

Has anyone had a ZEX box open? Does it have 2 N2O solenoids like the NOS kit? If it does I’d setup the second one so that you can disconnect it so you could test fuel enrichment without actually spraying N2O