Looking at a few calculation I am worried about my injectors. If your making 450rwhp in a H & C car and shooting for an 80% duty dont you need 40lb injectors? The 26lb pea shooters from the factory aint cutting it by far.
Phillip

 

What size injectors are needed for which power levels? Anyone putting down >450 with 26ers or 28's? I have heard of a measly 443 with 26's.

 

Here's a good Injector calc site http://www.rceng.com/technical.htm#WORKSHEET :yesnod:

 

Yup, 42# Bosch - Gm injectors. GM part # 24508208. Same pintle and coil as stock - so you don't have to change the injector offset table. :yesnod: :thumbs:

 

Use 42# "green top" Bosch injectors, excellant drivability and will support 500/500 fairly easily. They also can be have for less than $300 a set :).

Phil

 

Can you IM me with the place you can get this price at? Thanks
Guy

 

You dont need 40# injectors unless you are doing forced induction or dry N20. Use ford motorsport 30#. The are rated at 30# at 40 PSI. On a corvette this makes them 36# injectors which should be a huge improvement over the 26# you have now. Remember to change your injector table with LS1 edit.

Summit has the ford injectors for 220 + shipping.


[Modified by ICULUKN-C5, 8:12 AM 9/13/2003]

 

I kinda disagree. If you use an injector calculator you will find out that 26lb injectors are near 100% duty cycle which is NOT good for any injector. 36lbs will give you some headroom and probably give you more precise fuel enrichment.
Phillip

 

Before my H/C but with my other bolt-ons, I made 322 rwhp through my A4. Running off the chart lean (=/>18:1), I was at 83% duty cycle with 26.4lb. injectors as shown by traces taken during the dyno.

According to the accepted formula: (Inj. Size lb/hr) x (Duty Cycle) / .50 = HP rating per injector (where .50 represents the Brake Specific Fuel Consumption or BSFC), the 28.2lb. injectors will support 390.96 fwhp at 80% duty cycle and 451.2 fwhp at 100% duty cycle.

SVO 30lb. Injectors flow 36.12lb at the LS1 fuel pressure of 58lbs. That means they will support 462.33 fwhp at 80% duty cycle and 577.92 fwhp at 100% duty cycle.

If we assume that a 450 rwhp 6-speed car is putting out about 530 fwhp then the SVO 30lb injectors are undersized at a 80% duty cycle. At 512 fwhp even a 40lb. injector would be undersized at a 80% duty cycle. A 42lb injector would fit the bill, as at an 80% duty cycle it will support 537.6 fwhp.

 

:iagree:


:iagree: Thats what I'm running :cheers:

 

Phil,
I have heard from more than one source that the GM 42# (24508208) injectors are better than the Ford 30's but they are harder to find and a bit more expensive. The spray pattern of the Fords aren't the same as the GM/Bosch. Its not just the lb/hr rate you need to look at. Proper atomization of the fuel is important too. I want my new injectors to match the stock GM spray pattern. I am looking for a set of GM 42# inj. if anyone knows where I can get a set.

 

A few things about injector duty cycle

- Just because a scan tool is reporting x-ms for injector on time, you have to remember it is commanded and may not be actual injector flow. So injector DC calculations may be off.
- If you edit you maf table, injector ms and thus DC will be off if the maf is not matched.
- If you edit injector table, injector ms and thus DC will be off.
- If you edit injector offset, injector ms and thus DC will be off.
(Above assuming pressure does not change)

LOTS of guys tune their ltrims by injector table. No more even close to accurate injector ms.

LOTS of guys put on new injectors (30# bosch for example) and tune them in with injector table or MAF table. Injector ms is now worthless. Not only injector ms, but a lot of other things such as command A/F aren't close, etc.. etc..

LOTS of guys diddle with their MAF table. DO NOT DO IT! :) (Don't ask why.)

Here's my take on injectors and is sometimes in total disagreement with other tuners.

Some tuners will say that if at WOT on the dyno, the smallest injector possible maintains the target A/F, then that is what they use. This could mean that the injector is running fully open. Their argument is that if the fuel is getting their, todays injectors at 100% DC for 1/4mile at a time doesn't won't go bad and rarely do people keep their cars floored for longer than that.

I rather play the cautious size because larger injectors on an LS1 are easy to tune these days. I go by the math and would rather have extra injector room left over.

So, LS1 fuel pressure is 4 bar (58.02psi). Injectors are usually rated at 3 bar (43.51psi). SVO's are said to be rated at 2.7 bar (39.15psi).

The FIRST mistake that most make when putting on large injectors is that they do not know the injector offset for the particular injector, so they solely tune it with injector size table or maf table. The SECOND mistake they make after that is believing that anything coming out of a scan tool such as command injector ms is still correct.

So, a SVO 30lb injector using the "believed" rating of 39.15psi by math should be good for 467 crank HP at 80% DC. Using a conservative test rating of 43.51psi it is 443 crank HP at 80% DC. Both running at 4 bar LS1 pressures. Both using a .50 B.S.F.C . I'm pretty sure the BSFC of an LS1 is more efficient and that's why we are able to get away with smaller injectors a lot of the time.

So, 30lbs SVO's will get you to 554 crank HP at 100% DC w/ a .50 BSFC (43.51psi test). Fine for 450rwhp and with LS1's BSFC "may" hover around oh.... maybe 85% DC or so...

Tuning: USE Chris B.'s injector offset table for the SVO injector. They are very close when combined with a 43.51psi test pressure injector size table. Do NOT modify the MAF. Injector offset table editing should be considered a must.

Here is how close Chris's table is. My 32lb Accel (same style bosch as SVOs) are almost dead on. Meaning the following. PE vs RPM editing is very predictable. So, with Chris's injector offset table and proper injector size table, when the PCM shows a command 14.7 A/F cruise, my incar wideband also displays 14.7 A/F. During warm up, when the PCM is commanding a 13.2 A/F as example, my in car wideband shows 13.2 A/F. And more importantly, during WOT, when I program the PCM for 12.9 A/F, and the PCM displays 12.9 A/F for command target A/F, my wideband is at 12.9 A/F!

Before using Chris's injector offset table, my command PCM target A/F and actually A/F were worlds apart just using the injector size method.

So, if you are NOT using the proper injector offset table, you will have to REALLY REALLY REALLY TWEEK the injector size table something horrible to get proper running ltrims. This also means you will have to tweek the PE vs RPM table something nastly also.

With the proper injector offset, the math for the injectors is accurate and so is the math for the PE vs RPM table. Makes tuning easy, predictible running car and happy owner.

Whew... sorry, I'll stop now... Hope this helps answer your question.

:crazy:


Also, a BIG HUGE thanks to Chris Bennight for always bringing us a little bit more. Thanks Chris!


[Modified by H82BFST, 12:08 PM 9/13/2003]

 

MTWallet, see above for explaination of why most want the same style injector as stock (Bosch 2). Most tuners prefer same style as stock because they have never worked with injector offset table and by using the same style they don't have to in order to still maintain accuracy everywhere else.

 

I dont understand why changing the IFR, maf or offset table would make the injector pulse width read by the scan tool wrong.

It changes the pulse width, but thats the desired effect, not a problem.

Eric

 

H82BFST, Great information and explanation. :cheers:

 

I'm going to add one tidbit to H82BFST and that is we have excellant results with the 42# green tops for drivability etc. We try to recommend them for their tranparent operation and potential to support future mods. Nothing like having to keep purchasing injectors when you could have gotten an injector for the future without the penalty. That being said dont go out and buy 76's..hehe

Phil