Bill Ball

That doesn't sound right. We ran out of duty cycle on Dennis' 5L NA using 24 lb'ers.

ShawnSmith

I'm gonna trust the Doc on this one - and heck it's making 350 rwhp on the 19 pounders... 24 seems like it would reach well into the 400's

IcemanG17

Shawn
I WISH my 2008 3 series cost only that much.....................well I guess it did if you add both #'s together.... were did I put my

Hmm....two 928's = $29,000 + all the $$$$$$$$$$$$$$$$$$$$$$$ since then....which makes another $17k or $46k total...... Thats quite a bit of smiles for the $$$$$

123quattro

I was thinking the same thing. My LS1 makes 436 to the tire. It's running (needed) 36lb/hr injectors to be under 80% duty cycle.

ShawnSmith

If I recall the Doc's description, he upped the fuel pressure to help the duty cycle issue on the 19's. This might be part of how it all makes sense in the end...

ARCFLEMING

Shawn,

Greg Brown rebuilt my stroker last year (or should I say rebuilt someone elses mess),I know how you feel-congrats! I have a earlier car than yours that had stock 24lb injectors (too lean) ,we've since installed 30lb injectors. I've learned to trust what Greg recommends.

Brian

GregBBRD

Brian:

That thing is still running?

Good to hear from you. I might be coming to Sebring in February. If I do, perhaps we could get together and do some "Sharktuning" on your car to dial in those injectors?

ARCFLEMING

Greg,

If you are going to be there I'll make every effort to reintroduce your engine to you! I drive it everyday back and forth to work every cent I spent on it was worth it.

THANKS!!!

Brian

Bill Ball

I can definitely see that with the 19s for the shortrun. I know Greg knows what he's doing. It's just that 24s are not what I would expect for 400+HP. With Sharktuner, I go back to normal fuel pressure and run whatever size injector keeps the duty cycle below 90% max. Regardless, have a load of fun with your car.

GregBBRD

Bill:

On street engines, I tend to try and run as small an injector as I can get away with. This always seems to help with the low speed driveability, which is really important with an automatic car, in my opinion. The driveability can get to be really touchy with ported heads and big valves. I think that since the injectors sit very close to the valves, the fuel has a tough time getting mixed, at slow engine speeds. Since an automatic car tends to try and find high gear, before you can get to the crosswalk on the other side of the intersection (when you are cruising), I try to tune for this situation.

So, I tend to like an injector with "bumped" fuel pressure over a bigger injector with lower fuel pressure. It probably tends to all be the same, in terms of fuel quantity, but it is just my personal preference. Of course, this requires the addition of an adjustable fuel pressure regulator.

mark kibort

I tend to agree on my limited experience as well. running 70psi with my stock S4 injectors allowed me to get to 335rwhp /335rwt. I think the better atomization at higher pressures could add to the HP gains, but as greg says, its probably more a factor with the lower rpm street driving mode of operation.

mk

Bill Ball

Although I think the same drivability can be achieved with a stock FPR and larger injectors and Sharktuner, I don't have any experience with strokers.

mark kibort

As it is now, im down in the under 50psi range for mine and still way too rich. I would think that the 24lb injectors would be ideal with the high pressure i was running with the stock bottom end and 19lb stock injector (i.e 70+psi).

Lizard928

With proper tuning a much larger injector should be able to be made to idle just as well as a smaller injector.

I have seen 1.8L turbocharged hondas running 4 1000cc injectors that was able to be driven daily without issues, and had a perfect idle.

GregBBRD

Again, the automatic transmission that seeks to turn 1,500 rpm's with small throttle openings changes the whole thing, in my opinion. Uber low velocity through a port, with poor fuel mixing characteristics can be helped with a higher pressure, smaller injector (basis of my theory.)

I'm not saying that my method is the correct way...just one way that seems to work very well, for me. I've got a bunch of these things running around getting people back and forth to Walmart, in rush trafffic, every day.

My goals might be slightly different than someone else's goals. I'll gladly give up 20 horsepower, on the big end, to get a car that drives perfectly, on the street. One has to be realistic about these projects. Once you have the ability to blow the rear tires loose, at will, more horsepower is just bragging. Not many people can drive these beasts at WOT for any length of time.....they go very fast, very quickly. So driveability becomes one of my primary goals. I'm happy when a customer is happy. If I can give him all the fun he wants and still give him 20mpg, while driving the thing down the freeway, he is more likely to like the car and drive it every day and enjoy it. Shawn's requirements were very specific. He wanted more power, but not at the cost of driveability. I've personally got a few silly cars that spend all their time in the garage, because they have too much power to drive.

If the other approach works better for you, by all means, put in larger injectors and use lower fuel pressures. Both ways will provide equal amounts of fuel, as I see it. I seldom do things by accident. Most of the time, there is a reason for my approach.