Take it from someone with experience.

I would get at least a 40lb injector, and tune pulse width accordingly with either a piggy back or full standalone. Keep the fuel pressure stock.

As a general rule of thumb you should pick an injector that is roughly 25% larger than your theoretical need. Hell, we run 150lb injectors on 1.8L honda motors all the time and they idle like stock. Having control over the injectors pulse width is everything.

If you have any questions, feel free to PM or email me.
Bryson

 

What's up man!

 

According to FTC, when using their unit, increasing the MAP bar from 1 to 1.5 would mean that (assuming I intend to run 7 PSI of boost, which is what a 1.5 bar MAP sensor will measure on the boost scale), I need to run 1.5 times larger (50%) injectors for that setup.

That would actually put me at 36 lb injectors. For 7 PSI. I will be on 4.5. Is this wrong then?

 

You keep flipping back and forth on how you want to pick injectors. You need to figure a target HP and base your injectors on that. Realize that your target HP will probably be overestimated, it never works out as expected.

Stock 190HP x .5BSFC / .8%DC / 6 injectors = 19.79 lb injectors

+9lbs boost = (9/18) = 50% HP increased = 190 x 1.5 = 285HP x.6 /.8 /6 = 35.63 lb injectors

Your Hopeful 400HP x .6BSFC / .8%DC / 6 injectors = 50 lb injectors

Notes-
-N/A BSFC = .5, Boosted BSFC = .6
-% Boost HP increase= Non intercooled, stock heads and intake=boost/18 (use 18 when non-optimized)
-% Boost HP increase= intercooled, good heads, good/ported intake=boost/16

 

YO! It's taken a while but I finally joined.


PM'd ya back Coffee.

 

As long as I keep finding conflicting information I will continue to ask questions.

 

And this is all assuming 43.5 PSI at the fuel rail. ? Stock 97+ XJ's have 49. That would mean 46lb injectors based off of the 8% increase in PSI from 43.5 to 49 (an 8% loss of lbs and hour, 4lbs). ?

The reason I can't decide is because I have not yet picked a piggyback unit for sure. So I want a solid starting point.

And I'm using 450HP for my numbers. Just FYI.

 

There are plenty of sites and great books out there with accurate and correct information.

43.5 to 49 psi is not 8% increase in injector output. The correct formula is the square root of 49/43.5 times the injector value.

sq.rt. of 49/43.5 = 1.0613, so it is really only 6% increase in injector output.

450 HP is optimistic, What is your build going to be? 8 pounds boost?
8/18=.444 or 44.4% increase in HP requires a N/A build of 312HP.

312 HP requires a 4.6L(282CID) = 1.106 HP/CID -- Maybe with ported heads, cam, different ported intake manifold, bigger throttle body, compression
312 HP requires a 4.0L (242CID) = 1.326 HP/CID -- NOT ACHIEVABLE!!

Why do you need 450HP in a off road Jeep Cherokee? How much will the trans, clutch, transfer case, Dana 30/35, Chrysler 8.25 axle shafts, drive shafts handle?

450HP will grenade all these stock parts.

 

Hill climbs, 40"+ tires, fun, ect

Trans(aw4) and transfer case will handle it, and id hope he would swap out axles

 

By the time that is installed my drivetrain will be able to handle. I'm putting a dana 44 with chromoly shafts in the front and chromoly axles in the rear. All new Ujoints designed for serious offroading. The ring and pinion are from Nitro gear. Detroit Locker in the rear, and a TruTrac in the front. Still have to look into the driveshafts.

I have a 280+ 4.7 stroker. 260-270 is what it makes according to my build via www.ajeepthing.com . I have many other aftermarket installs.

The same time this supercharger goes on I will be installed the Hesco aluminum head unit that adds 30HP on a stock 4.0 engine. It added 50 HP to the old 4.2 engines.

No one needs anymore horsepower than 190. I do it because I want to. It's a hobby. And it's my dream to make the ultimate Cherokee. Everything that can be done, I will do. With the exception of a turbo of course.

Everything you listed for the "312" HP stroker, I have. Although I don't know that it makes that much. 99+ intake, 1.6 YellaTerra, 62MM TB, APN headers, full 2.5" mandrel bent exhaust, and a snorkel. So the air is cooler as well. I have the MSD 6AL but I doubt that does anything significant besides let me run a larger gap.

The Avenger makes 100 HP on the 4.0. A stock 4.0 with stock cam, and no other alterations than what comes in the kit (fuel injectors and a Diablo Sport tuner). I run a 4.7, will have the Hesco head unit, all the items I've just told you (to include the 206/214 CompCam). There's a lot of variables that aren't accounted for with the advertised 100 HP that accompanies the Avenger. The Avenger assumes none of the variables I have in place. Assuming I only made 100 HP, and I only had 280 at the crank (although 295 is probably more accurate), that's 380. Assuming the Hesco head unit only added the bare minimum 30 (although the percentage ratio suggested 70, although it's very possible it could be even more than that given all the unaccounted for variables in my setup), I would still be sitting at 410. Add the other 40 for the suggested 70, according to the ratio, and I land at 450.

I'm at 9.7 compression, but need to find a thicker head gasket. I'd rather use the .065 gasket and sit at 9.3.

 

Back to the injectors,

Your Hopeful 450HP x .6BSFC / .8%DC / 6 injectors = 56 lb injectors,
if you run it a little leaner than .6BSFC and a little more than 80%DC, 49 vs 43.5psi you can get away with 50 lb injectors.

 

After reading about the AEM F/IC's I'm going to use that in place of the FTC. It allows full control of the pulse width. I guess 56 is the next step up from 50?

Does the amount of boost factor into the BSFC? I noticed it said .55 to .6 for SC, and .6 to .7 for turbochargers. Does this have to do with the boost? I'm only running 4.5 PSI.

 

.6BSFC is for any boosted application. It is a starting point.

At some point you need to determine what your N/A hp is, how much boost do you really want to run- 4.5-8 psi, and what your target HP will be. A good start is to get your current setup dyno'ed.

I think injectors are available 42, 50, 60, 72 lb.
If you want to be able to run 8lbs at times depending on the pulley you use, but mostly for DD you use a different pulley and only run 4.5lbs, you still need injectors for the 8lbs.

 

The HESCO head adds HP to the stock and modified engines but that is compared to stock heads. You have big valve and ported heads? so it won't add so much, some but not full amount. You need to dyno and get an exact baseline/starting point.

Think about it, you have 282CID all done up but with a stock all be it a '99 intake, but realistic HP, not some projected internet site predicted HP, is 1.0 to at max. optimistic 1.1 HP/CID.

So again it your base N/A is 280HP:
4.5 lbs boost = 1+ 4.5/18 = 1.25x280HP =350HPx.6 /.8 /6 =43.75 lbs= 42 injectors will work.

6 lbs boost = 1+ 6/18 = 1.33 x 280HP = 372HP x.6 /.8 /6 = 46.55 lbs = 50 injectors will work.

8 lbs boost = 1+ 8/18 = 1.44 x 280HP = 404HP x.6 /.8 /6 = 50.55 lbs = 50 injectors will work.

Higher boost(9-10) or more base HP(300+) = 450HPx .6/.8/6= 56 lbs = 60 injectors will work

Ok, 49 vs 43.5 psi FP, but again you need a starting point. You are going in uncharted territory. You might need to try one set and then have to buy a second different set once you dyno the thing.

 

I intend to only run 4.5 PSI. I'm not trying to run a ton of boost. I just want a supercharger, with a little boost. If I could keep it at 350 HP that's what I would do. It was originally a 5.5 PSI pulley, but my understanding is that on my 4.7 given the displacement and new head at best I'll have 4.5 PSI. But it will still be moving the same amount of air into the engine, just with less restriction.

I might go with another (larger?) pulley to reduce the boost. My ultimate goal is to have about 50-80 more horses and still get 15-18 MPG. I'm going to do what I can to get there starting with the stock Avenger pulley. I get 18-19 on highways with my current build, and no tune. I don't even have the SAFC-II wired in.