4.6 Stroker with Sprintex SC, Fuel Injector Size?

[Coffee Commando]

I've been considering purchasing a 4.6 stroker from 505 Performance rated at 285 HP to utilize with my Sprintex. I wanted to build a ministroker with the 232 crank so the HP #'s would be around 330 so I could maintain som streetability, however I don't have the time to build this engine myself.

Hence I've been looking to purchase a turn-key stroker. I was thinking it would be cheaper, and easier, for me to just run a larger pulley on the SC and limit it to 3-4 PSI to try and limit the HP numbers to 330-340 so that I can a smaller injector size in order to make my XJ more streetable. I'm trying to strike a power/efficiency balance with my build.

I also have a 2000XJ with the notorious 0331 Cylinder head which I wouldn't trust any further than I could throw it, especially after the added heat and compression of what I intend to do.

Thoughts, opinions and pointers?

[FlyinRyan]

I've been considering purchasing a 4.6 stroker from 505 Performance rated at 285 HP to utilize with my Sprintex. I wanted to build a ministroker with the 232 crank so the HP #'s would be around 330 so I could maintain som streetability, however I don't have the time to build this engine myself.

Hence I've been looking to purchase a turn-key stroker. I was thinking it would be cheaper, and easier, for me to just run a larger pulley on the SC and limit it to 3-4 PSI to try and limit the HP numbers to 330-340 so that I can a smaller injector size in order to make my XJ more streetable. I'm trying to strike a power/efficiency balance with my build.

I also have a 2000XJ with the notorious 0331 Cylinder head which I wouldn't trust any further than I could throw it, especially after the added heat and compression of what I intend to do.

Thoughts, opinions and pointers?

What are you using for tuning with the Sprintex? Anything less than a true PCM calibration is selling your setup short on power, mileage, and drivability. I can tune big injectors NO problem on these trucks. I am working on a 4.7 Dodge Ram with a ported Eaton M112 with 39 lb Cobra injectors (43.5 psi at our 49 psi pressure system) and it drives like stock, part throttle boost is seamless. I've tuned several I6 strokers now through the stock PCM with excellent results.

[CobraMarty]

Use the right size injectors for the HP you expect to produce. Drivability/streetability will come by the tune.

Ryan- How do you tune for Forced Induction with the 1 bar map sensor?

[CobraMarty]

Which Sprintex? the 210 might be a little on the small side for a 4.6L but if you only want to run 3-4 pounds boost, it would be interesting.

[SilverXJ]

Maybe 30lb or 32lb injectors. Research on here for 505 performance before purchasing from them.

When tuning a stock PCM the 1 bar map sensor is replaced with a 2 bar sensor.

[CobraMarty]

Expected HP = # injectors x inj lb/hr x .8(80%max duty cycle) / .55(BSFC for non intercooled forced ind)

lb/hr = exp HP x .55 / .8 / 6inj ... = 285hp+20%(3-4lbs) = 325-335HP x .55 / .8 /6 = 37.23-38.38 lb/hr, with our 49psi, 37.23-38.38 / sq rt of 49/43.5 = 35-36 lb inj.

I would be concerned about the charge air temp without any type of intercooling but at only 3-4 pounds boost and using some timing retard under boost, you should be ok.

With 30-32 pound injectors you will be pulsing greater than 80% at WOT and leaner than .55BSFC at 325-335HP. Not a good recipe.

[SilverXJ]

I would not put much faith in that calc. Going off of it with a conservative estimate of 250 hp for a NA stroker then adjusting got our 49psi rail it suggests a lb of 26.38. However, it has been shown that strokers like 24lb/hr injectors

[Coffee Commando]

I have a Sprintex setup so it comes with a 7th injector that sprays into the throttle before the compressor so I won't be using 6 injectors at 36 lbs.

I've done the math and gotten it pretty close to figuring it out. The 7th injector is 52 lbs so it reduces the amount of fuel I need for the others in order to make 345 HP.

The sprintex produced a 41% increase in HP on a 2005 TJ with an inline 6. Following those numbers and attaching it to a 285HP engine it puts me at 345 HP (running only 3 PSI, meaning only 20% increase in HP).

The only thing I haven't figured out yet is what the size of the stock Sprintex SC pulley is so that I can adjust for a bigger pulley accordingly.

I found on http://www.billetflow.com/supercharger_pulleys.htm that the SC for the Cobra produces 8 PSI, and for every 7% decrease from the stock 3.65" blower that boost went up 2 PSI (25%). A 15% smaller pulley yeilded 50% more boost.

Based off of those numbers and that logic, I should be able to increase my pulley size to reduce the amount of boost by 3 PSI. The best I can figure this far is that if I increase the pulley size 15% I should be able to drop around 3 PSI. If 7% increased pulley size reduces boost by 1/4th then at 15% I should be down ~3PSI


I feel like there is some sort of mathematical equation that I need to figure out in order to get a better guestimate.

I sent an email to Superchargers of Oklahoma where I purchased the Sprintex. I should ahve an answer from them by tomorrow. I did the math on pulley sizes from 4" down to 2.4" (increasing each by 15%).

[atias]

boost is just a measurement of the resistance to airflow.
whats works for others in a different engine combo may not be the same for you.
its depends on head flow,camshaft,valves,headers,Exhaust system,and cubic inches.

[CobraMarty]

It wasn't clear in your question what setup you were going to actually use. Larger 6 injectors all controlled by the ECU or stock 6 injectors (or slightly larger for your stroker) controlled by the stock ECU and extra fuel and liquid intercooling supplied by the 7th injector and controller. I would do the install in 2 steps. Install the stroker, break it in and debug it if needed , and have Ryan tune it using whatever size injectors work best for the stroker. Get it running just right and then add the supercharger and supporting hardware. The 50lb injector will be fine for you.

[CobraMarty]

The 7th injector- 50 lb/hr @43.5psi injector at .55BSFC and 80%DC will supply 73 additional HP. Yes the fuel system is at 49psi but under boost it will have to 'push' against the boost pressure of ?3-6pounds and effectively 'lose' the higher FP and really deliver at close to 43.5 effective psi.
345HP might be a bit optimistic. I think that most overestimate the real output of a N/A stroker.
I would recommend investing in a 70mm F+B throttle body.
With the 7th inj. you will not use a 2bar MAP sensor for the ECU tuning.

[CobraMarty]

I have a Sprintex setup so it comes with a 7th injector that sprays into the throttle before the compressor so I won't be using 6 injectors at 36 lbs.
I've done the math and gotten it pretty close to figuring it out. The 7th injector is 52 lbs so it reduces the amount of fuel I need for the others in order to make 345 HP.
The sprintex produced a 41% increase in HP on a 2005 TJ with an inline 6. Following those numbers and attaching it to a 285HP engine it puts me at 345 HP (running only 3 PSI, meaning only 20% increase in HP).

The only thing I haven't figured out yet is what the size of the stock Sprintex SC pulley is so that I can adjust for a bigger pulley accordingly.I found on http://www.billetflow.com/supercharger_pulleys.htm that the SC for the Cobra produces 8 PSI, and for every 7% decrease from the stock 3.65" blower that boost went up 2 PSI (25%). A 15% smaller pulley yeilded 50% more boost.
Based off of those numbers and that logic, I should be able to increase my pulley size to reduce the amount of boost by 3 PSI. The best I can figure this far is that if I increase the pulley size 15% I should be able to drop around 3 PSI. If 7% increased pulley size reduces boost by 1/4th then at 15% I should be down ~3PSI

I feel like there is some sort of mathematical equation that I need to figure out in order to get a better guestimate.
I sent an email to Superchargers of Oklahoma where I purchased the Sprintex. I should ahve an answer from them by tomorrow. I did the math on pulley sizes from 4" down to 2.4" (increasing each by 15%).

Good luck on getting them (Superchargers of Oklahoma) to get you an answer.

I will try to answer you question and hopefully no one will get their knickers in a knot over the it.

The Sprintex 210SC puts out .94L/rev. Using the stock pulley given with the kit and 1 complete engine cycle(2 revs) it will put out 4.512L/1engine cycle.
I can tell you that on my stock 4.0L and the sprintex 210SC puts out 7-7.5 pounds boost and up to 8pounds on a cold day where the air is denser. But wait you say, how can that be? This is a 4.0L and SC output is only 4.512L. Well the fact is that these engines only operate at about 75% VE. The TB, intake manifold, head,valves, cam are all restrictive and limit the flow into the engine and effectively decreases the effective displacement to 3.0L. This is backed up by the fact that the SC produces 7.5 pounds boost which is 1.5 times ATM. That means that the 4.512L divided by x-the actual effective engine displace = 1.5 and this is true or else that would be no boost found. the x=3.0L
Another way, the SC 4.512L into a 4.0L engine would only produce .512/4.0 = .125 ATM of boost pressure which = 1.8 pounds of boost and we know that this is not true because it in reality does put out 7.5 pounds boost so the stock 4.0L engine is really acting like a 3.0L.

So how does this answer your question?
Your 4.7L stroker acts like a 3.0L +15% displacement +5% cam,etc = 3.6L effective engine size.
The same SC and standard pulleys which puts out 4.512L now into a 3.6L effective engine displacement we get 4.512L / 3.6L = 1.25 air differential or 1.25 ATM or .25ATM of boost = 3.675 pounds of boost.

So to answer your question, using the Sprintex 210SC on a stroker 4.7L Jeep engine with the standard pulleys should yield very close to 3.675 pounds boost which is right where you want to be. This will be worth a 20% increase in power over your N/A power.

I would try it this way before even considering using larger SC pulleys.

[FlyinRyan]

Use the right size injectors for the HP you expect to produce. Drivability/streetability will come by the tune.

Ryan- How do you tune for Forced Induction with the 1 bar map sensor?

Good starting point is usually 2x the injector the vehicle came in stock configuration. So Ford 42's would probably be pretty suitable considering the plans for a stroker.

I use a 2 bar map sensor (or the SRT4 2.25 bar map,or more if need be) , and rescale all necessary tables for 2 bar use.

Auxilliary injector setups =

Sorry just my .02 , I've seen enough piggybacked setups with garbage drivability and lack of finesse when dealing with part throttle boost. I'll be tuning a 4.0 with a Sprintex this week.

[CobraMarty]

Good starting point is usually 2x the injector the vehicle came in stock configuration. So Ford 42's would probably be pretty suitable considering the plans for a stroker.

Except he said he is not going to use the 6 larger injectors

Auxilliary injector setups =

Not entirely true, daily driver with 5000 miles on system, 'flogged' on daily, running well and strong.

Sorry just my .02 , I've seen enough piggybacked setups with garbage drivability and lack of finesse when dealing with part throttle boost. I'll be tuning a 4.0 with a Sprintex this week.

If you are local, I invite you for a ride. It might just open your eyes and change your mind. Might be true with other, not me.

[FlyinRyan]

Double post, sorry