Fuel Injector sizing

[moparman76_69]

Ok so I'm looking at fuel injectors and am wanting some opinions on what direction I should go. I currently am running +40s on a 2.5 with a stock garrett at around 17 psi. I know I'm well in the comfort zone of those injectors but....

I'm planning running a ported intake, head, and exhaust with a holset HX35/30 on 20-25 psi and running E85 so I decided to see what the injector calculators say.

According to the RC injector site's http://www.rceng.com/technical.aspx calculator for 500 crank HP and 55 psi fuel pressure I need 949 cc or 92 lb/hr using a .65 BSFC or 83 lb/hr or 876 cc using a .60 BSFC. Now assuming 30% more for E85 I get either 1234 or 1139 which is basically a 1200cc injector.

My first question is am I being to generous with the BSFC on those calculations? If so what is a more honest BSFC for our engines?

Secondly if those are correct sizing then what brand do I look for? They should be Bosch style low impedance injectors right?

Would these work? http://compare.ebay.com/like/270665154906?ltyp=AllFixedPriceItemTypes&var=sbar&rvr_id=203052480837&crlp=1_263602_304662&UA=WXF%3F&GUID=bd82f96e12d0a0aa11f417c4fffb7f23&itemid=270665154906&ff4=263602_304662

I'm just wanting to make sure I only buy injectors once and don't want to go too small and have to pay more for bigger ones later.

[cordes]

If you're planning on running alcohol I would go any smaller than 95lb. injectors. Those would probably be ideal for what you are going to do. Last I checked you should be able to get alcohol compatible injectors for around $65 if you really search. It's been a while since I've priced them out though.

[moparman76_69]

So 1000cc alcohol compatible low impedance bosch style?

[cordes]

So 1000cc alcohol compatible low impedance bosch style?

Yes. IIRC this may be the place which I spoke with back when that stated these were alky compatible. Double check though.

http://www.injector.com/cart/pc/viewPrd.asp?idproduct=47&idcategory=7

[wallace]

I'm using e85 with a v6. The 120's (Summit TFS brand) were not enough out of injector at 18 lbs. Switched to 160's and dc in the 70% range at 23 lbs. Using MS for tuning and I "fudge" the injector sizing...120's come out to 83's and 160's come out to 96's with e85. Idle is tough with the 160's. What is your dc with current injectors? That should give you a BSFC to work from. I would go big from the start to keep from having to buy another set of injectors and go through the retune process. HTH.

[moparman76_69]

I would go big from the start to keep from having to buy another set of injectors and go through the retune process. HTH.

That's what I was thinking also. My entire setup is changing though so my current DC is useless.

[cordes]

I'm using e85 with a v6. The 120's (Summit TFS brand) were not enough out of injector at 18 lbs. Switched to 160's and dc in the 70% range at 23 lbs. Using MS for tuning and I "fudge" the injector sizing...120's come out to 83's and 160's come out to 96's with e85. Idle is tough with the 160's. What is your dc with current injectors? That should give you a BSFC to work from. I would go big from the start to keep from having to buy another set of injectors and go through the retune process. HTH.


That's some interesting real world experience. Everything I've read says that double the current size of your injectors would be enough for ethanol. I wouldn't have thought that 160lb. injectors would be needed on one of our V6s. How are you feeding those things?

[moparman76_69]

I'm thinking of getting these http://www.summitracing.com/parts/TFS-89095-1/ is that the brand you're using wallace?

[wallace]

Hey, this is a 3.8l ford setup. The cubic inch per cylinder is pretty close to the 2.5L so I was thinking the injector size would be close between the two. I'm using 3 Walbro 255's 2 are continuous and 1 comes on with boost. 5/8" feed and return. Here is the link to the build on the car if you want to check it out: http://www.v6power.net/vb/showthread.php?t=35549

[cordes]

Hey, this is a 3.8l ford setup. The cubic inch per cylinder is pretty close to the 2.5L so I was thinking the injector size would be close between the two. I'm using 3 Walbro 255's 2 are continuous and 1 comes on with boost. 5/8" feed and return. Here is the link to the build on the car if you want to check it out: http://www.v6power.net/vb/showthread.php?t=35549

Thanks for the clarification. I knew you had to be running multiple pumps or one big one. That's a whole lot of fuel.

[wallace]

I'm thinking of getting these http://www.summitracing.com/parts/TFS-89095-1/ is that the brand you're using wallace?

Hey I started with these: http://www.summitracing.com/parts/TFS-89120-1/. I sized the injector in the MS as an 83 lb/hr injector this just compensates for the increased volume and you tune it using gasoline AFR targets. So I started with those 120's and when I ran out of injector I bought the Bosch 160 lb/hr injector I belive they are a CNG injector. The 160's come out to roughly 96 lb/hr (using e85). I would run 2 high pressure pumps one continuous duty and the other to come in at some boost level. On mine the 3rd pump caused an increase in fuel pump pressure below 15 lbs boost so I have it set to come on at 15. It is a great alternative to race fuel my last batch was less than 2.50 a gallon you just need to put a really good fuel system together to run it.

[moparman76_69]

Yeah I heard back from trick flow they are E85 safe and since they're the same price I might just get the larger ones since I can just scale them appropriately in MPTuner.

[Force Fed Mopar]

Remember that our cars run on a higher base fuel pressure than most injectors are rated at. Most are rated at 43.5 I believe, and our cars run on 48-50. +40's are rated at 52 lbs/hr, but at our pressure are actually more like 58's. FWIW I am running E85 on a basically stock engine at 15 psi so far and no fuel issues. Soon as I can get a wideband I'm going to go to 20 psi, so we'll see how far the +40's will go.

[moparman76_69]

Supposedly I need 83 lb/hr or 874 cc/min to support 500 hp on 4 injectors with a bsfc of .6 and rail pressure of 55 and 80% duty cycle. Take into account that e85 will make injectors 30% smaller then a 1200cc injector would be needed to support 500 hp. 1200x.3=360 1200-360=840. 840cc/min will support 475.

Now I understand that using injector calculators are about like using drag time calculators but it's better to use those calculations than to spend money twice.

[cordes]

Remember that our cars run on a higher base fuel pressure than most injectors are rated at. Most are rated at 43.5 I believe, and our cars run on 48-50. +40's are rated at 52 lbs/hr, but at our pressure are actually more like 58's. FWIW I am running E85 on a basically stock engine at 15 psi so far and no fuel issues. Soon as I can get a wideband I'm going to go to 20 psi, so we'll see how far the +40's will go.

From what I understand all of our +xx injectors are rated at 55PSI.

[wallace]

Supposedly I need 83 lb/hr or 874 cc/min to support 500 hp on 4 injectors with a bsfc of .6 and rail pressure of 55 and 80% duty cycle. Take into account that e85 will make injectors 30% smaller then a 1200cc injector would be needed to support 500 hp. 1200x.3=360 1200-360=840. 840cc/min will support 475.

Now I understand that using injector calculators are about like using drag time calculators but it's better to use those calculations than to spend money twice.

That's the same thing I came up with and ended up running out of injector, the actual BSFC is usually not as good as the suggested calculation... The 160's can be had for about the same price as the 120's you just have to look around to get a deal. I never did try and up the pressure for more headroom on the 120's you may be able to go quite a ways with them going that route just make sure you are using enough fuel pump(s) that are capable of the flow rate at those elelvated pressures. The 120's were ALOT easier to get the idle nailed down on. If you're running a sequential setup I would think good idle characteristics would be possible with the 160's. Good luck, once you use the e85 you won't go back to pump gas.

[Force Fed Mopar]

From what I understand all of our +xx injectors are rated at 55PSI.

Apparently not, cause my cal was pretty much spot on fuel-wise when scaled for 58's, whereas when we scaled for 52's we had to pull a bunch of fuel out.

[cordes]

Apparently not, cause my cal was pretty much spot on fuel-wise when scaled for 58's, whereas when we scaled for 52's we had to pull a bunch of fuel out.

Some of the +40s flow closer to 60lbs. I think Rob was working on a rough date range when they were made, but I think they've been back down to a true +40 for a couple of years now. Lots of people do have the higher flowing +40s though.

[Force Fed Mopar]

It would be nice to know for sure what pressure they were originally rated at.

[cordes]

I'm 99% sure they were all rated at 55PSI. The +20s and most +40s flow what they should at the stock FP rating. I suppose I could be seriously misinformed, as that has happened before.

[Force Fed Mopar]

There is a lot of misinformation out there :)

[wallace]

There is a lot of misinformation out there :)

You got that right, most of the people who post "advice" in these threads have no real world experience to go by just some bs they read somewhere else.

To the OP, if you haven't bought injectors yet this guy is selling a set of 8 160's not sure if he would separate or not. http://www.theturboforums.com/smf/index.php?topic=146466.0

[moparman76_69]

I haven't bought anything yet. I did find these though http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=220724657141&viewitem=#vi-content

Thinking of jumping on them looks like the guy is a vendor on dsmtuners. Looking at a Bosch 044 pump and the rest of the fuel system now.