what size injectors for 350 whp?

[dwadia]

This is for an s15 sr20det, although it probably doesn't matter. I have searched this extensively. The most directly relevant info i found is here Inj Size And WHP Output - SR20 Forum (http://www.sr20forum.com/technical-information-library/142897-inj-size-whp-output.html) - that indicates that 555 cc is enough, running at stock pressure.

The problem is, i have found some very different recommendations from other sources, including places that sell injectors. This calculator RC Fuel Injection (http://www.rceng.com/technical.aspx) gives a MUCH different recommendation of 752 cc running at 90% duty cycle (which is an acceptable number for me, since it will not always be making that much power).

So, running with stock pressure (3 bar) at 90% duty cycle on pump gas, what size do i need to make 350 whp? I'd like to hear from some of you guys with experience, what size you are running and how much power you're making.

Lastly, at what size does idle and low-rpm drivability start becoming an issue? This will be using a ROM-tune, no SAFC or anything like that.

[ghost_22_47]

I have a Automotive calculator that made in Excel and I calculated 350WHP to FWHP which is 416.50FWHP, 4 cyliders at .90 Max Duty Cycle. It comes out to needing 728.875cc injectors. I know this isn't personal experience which you were looking for but I did calculate if 350WHP was accidentally used as FWHP which does give a low 600cc calculation which could be why you came out with around 550cc answer.

[codyace]

555 will work fine for your setup at 3bar....and will be in the 90 to 95ish duty cycle range. Most 50lb setups see 95% around 325 whp, so 555 will give you a few more CC at the marginal more HP.



I don't follow that RC chart much as it relies heavily on BSFC (which is not be ignored, but their rating is odd)

I have a cheat way to determine injector size

Take HPx1.15 to get estimated crank hp before drivetrain loss. Divide that by 2, then again by 4..this will give you the theoretical 'lb' of injector you need. Take that result, and multiply it by 10.5 and you'll get CC.

Sure its' crude, but it really works well (on 4 cylinder turbo cars that is)...

For example:
I have 400 whp
400x1.15 = 460
460/2 = 230
230/4 = 57.5 (Which is your lbs of injector)
57.5 x 10.5 = 603.75 (which is the required CC you need)

This really applies well, as on my car, which has 60lb/630cc injectors, fits the math perfectly as my car sees roughly 93% duty at WOT.

Again, it's a rough way to do it, that enables you to be safe with the guess. I've done this on many FWD setups and comapred with logs, as well as RWD and it works oddly well.

(awaiting smart-type engineer guys to explain to me why it's not right...which I'll admit it's napkin math at best...but it translates surprisingly well)

[dwadia]

Thanks to both of you guys... this is actually the thing i have been finding on various forums, people with experience seem to recommend much smaller injectors than virtually all the calculaters i have found (i've been using 410 crank hp in the calc's). Weird, and not sure what to make of it.

If i did go with a larger injector like 740~750 cc, do you guys know whether my idle and low rpm's would suffer badly?

BTW Codyace, i don't know what BSFC is, but since RC recommends that for turbo cars it should be 60-65, i entered a value of 62.5.

[Garber]

brake specific fuel consumption... its an efficiency measurement... fuel consumption divided by power output

[idahotuner]

nice formula cody. the newest dc sport actually had an article on it and used that formula and 1.45 for if your going run e85

[S14DB]

If i did go with a larger injector like 740~750 cc, do you guys know whether my idle and low rpm's would suffer badly?

As long as you stay with a Type2 Denso you shouldn't see a problem with low pulse width.

[codyace]

nice formula cody. the newest dc sport actually had an article on it and used that formula and 1.45 for if your going run e85

It was something we came up with back when I had my Altima, and were learning that the RC calculators and similar using BSFC were really 'overkill' for modern setups. My formula is for cars using a 3 bar pressure setup. You can adapt an injectors lb rating by normally multiplying it by 1.2 per bar

It also applies if you divide by 8 for v8 setups and 6 for v6 cars...it's not as close as the 4 cylinder car but will get you there

(for example a 425ish whp ls1 makes roughly 500 a the crank...500/2 = 250/4 = 31.25 lbs .....and bein that F body cars come with 28's factory (@60psi tho, so they're really like 33/34 lb in a 3 bar setup), you usually see them at mid 90% duty cycle if logging them...supporting the math

Essentially, the math works across the board, and if you can manipulate for the fuel pressure base you can make it work.


If i did go with a larger injector like 740~750 cc, do you guys know whether my idle and low rpm's would suffer badly?

Any of the high or low impedence 72lbers work well at this point...hell there are even 1000cc cars that I've been in that literally drive like grammies buick (well aside from their clutches hehe).

Much of the olrder issues (5-10 years ago) with larger injectors have all been solved through more knowledge and better tuning options. Luckily for you with a MAF and ROM car, it will drive even better than stock.

[dwadia]

Well, thanks guys, this is all very helpful. Sounds like 550's would be ok, but if the idle won't be an issue, just for peace of mind i'll probably go with something between 650-750 cc. After all, the difference in cost will probably be negligible (depending on the brand). So i guess it really can't hurt anything to go with the bigger ones. But if any of you guys disagree with this, please let me know! Thanks.

[codyace]

I don't find any fault with that thought either. Certainly you may be able to find STI or similar injectors cheap, but if you have *any* desire for more power, you're going to need larger injectors, thus making you buy things twice...

[RACETUNE]

This is for an s15 sr20det, although it probably doesn't matter. I have searched this extensively. The most directly relevant info i found is here Inj Size And WHP Output - SR20 Forum (http://www.sr20forum.com/technical-information-library/142897-inj-size-whp-output.html) - that indicates that 555 cc is enough, running at stock pressure.
That is True. (555cc HKS or Tomei)

The problem is, i have found some very different recommendations from other sources, including places that sell injectors. This calculator RC Fuel Injection (http://www.rceng.com/technical.aspx) gives a MUCH different recommendation of 752 cc running at 90% duty cycle (which is an acceptable number for me, since it will not always be making that much power).
That is true if you are running RC injectors. I dont recommend them if you are running a Apexi Power FC.

So, running with stock pressure (3 bar) at 90% duty cycle on pump gas, what size do i need to make 350 whp? I'd like to hear from some of you guys with experience, what size you are running and how much power you're making.
Asuming you are running a Standalone ECU (Apexi Power FC, Haltech, AEM, HKS VPro) The sizes I would recommend-> 555cc HKS or Tomei/ 550cc Nizmo/ 550cc SARD. You would have plenty of duty.

Lastly, at what size does idle and low-rpm drivability start becoming an issue? This will be using a ROM-tune, no SAFC or anything like that.
All the injectors that I stated above will give you very good idle.
**Cannot use RC Injectors with ROM-tune!!!!

[dwadia]

Racetune, thanks for all that info. I'm not using RC injectors, i just found their calculator and thought it would apply to others as well.


All the injectors that I stated above will give you very good idle.

Does this still hold true in your opinion if i decided to use 750's in the above-mentioned brands (probably Nismo), just to have some extra room for future mods or more boost?

Thanks.

[codyace]

Racetune, learn how to quote please.



That is True. (555cc HKS or Tomei)

STI will be the exact same. Brand has ZERO difference. It's a flow rating.


That is true if you are running RC injectors. I dont recommend them if you are running a Apexi Power FC./quote]

Why would you not? RC Injectors are the same as MSD (Rochester style). Again it makes absolutly ZERO difference what injector brand you go with. RC is one of the best in the business, their stuff works, and they stand behind their products.

[QUOTE=RACETUNE;3734378]
Asuming you are running a Standalone ECU (Apexi Power FC, Haltech, AEM, HKS VPro) The sizes I would recommend-> 555cc HKS or Tomei/ 550cc Nizmo/ 550cc SARD. You would have plenty of duty.

550cc would NOT hae plenty of duty at 350 whp...it would be in the mid 90% like I described above. Did you even read my formula??


[QUOTE=RACETUNE;3734378]All the injectors that I stated above will give you very good idle.

Any injector will work fine, so long as it's tuned for the specific CC flow

**Cannot use RC Injectors with ROM-tune!!!!

:Facepalm: Yes, you most certainly can. Why one earth couldn't you?

NO offense RACETUNE, but your information is poor at best.

[RACETUNE]

It's cool..

People only know what they have seen. So when you (or anyone) find something that you can't figure out, let me know I don't mind helping. I am really busy with the Race Team, sometimes it takes me a while to return your messages.

Zilvia is my favorite place for Nissan Slivia Info, but just for reference and never as a fact!

-Frank

[codyace]

It's cool..

People only know what they have seen. So when you (or anyone) find something that you can't figure out, let me know I don't mind helping. I am really busy with the Race Team, sometimes it takes me a while to return your messages.

Zilvia is my favorite place for Nissan Slivia Info, but just for reference and never as a fact!

-Frank

As in the PM, I don't think it was fair to make those claims when I've personally used both and had no issues. No harm no foul, just wanted to ensure it was pointed out that any rochester style injector (obviously in the same impedence) can be used, and have been used now since the advent of the JWT Rom tune programs. Enthalpy ROM tunes also apply, as well as standalone. It's about flow, not brand.

Good luck with your race team, I personally know how stressful even crewing for a ITA car can be. Committment is an understatment. Sorry if my comments were maybe directed the wrong way.