The Ultimate Street Skyline?

[SkylineUSA]

I would like to say for the record, English R33 is building The Ultimate Street Skyline, hands down!

[English R33]

Originally Posted by SkylineUSA

I would like to say for the record, English R33 is building The Ultimate Street Skyline, hands down!

Saw the latest car you got, £700 you say well I dont think you bought it,more like stole it from the guy, the clutch is nearly worth that, nice one :

[SkylineUSA]

When I bought it, I knew nothing about the clutch. The owner really told me nothing about the car, other than it did not run right. So, when I bought it, I had no idea of what the car really had, until I got it home.

It also had some HKS springs, tool kit, and a proper 2 ton jack in the boot.

[rev210]

Originally Posted by SkylineUSA

rev210,

Rule of thumb, from what I have learned over the years, 1cc = 1hp when it comes to injectors. So, that means the 550 should be good for 550hp.

I know the GT-SS if they are set up right can put out 550hp, and that is with the stock displacement, now you add the extra displacement, the engine is going to need that fuel from some where. If I am way off base, please let me know, but by my calculations, I would go for at least 600s, or better yet 720s.

Hi,

What fuel pressure is the 1cc = 1hp formula applied to? With a higher than factory base pressure and more aggresive rate on an aftermarket reg like the HKS rising rate you can get quite alot more fuel supply. Fuel supply vs horsepower is the only equation worth concern, 1cc = 1hp is a very blunt instrument ,discard it if it doesn't have a fuel pressure condition (remember that the factory skyline has a rising rate reg so the fuel pressure condition would therefore be mapped and since we can't rely on all factory regs giving the exact same rise in the pressure curve why bother?).

I hope this helps put to death a rather dangerous myth.

Cheers

Dave

[SkylineUSA]

Originally Posted by rev210

Hi,

What fuel pressure is the 1cc = 1hp formula applied to? With a higher than factory base pressure and more aggresive rate on an aftermarket reg like the HKS rising rate you can get quite alot more fuel supply. Fuel supply vs horsepower is the only equation worth concern, 1cc = 1hp is a very blunt instrument ,discard it if it doesn't have a fuel pressure condition (remember that the factory skyline has a rising rate reg so the fuel pressure condition would therefore be mapped and since we can't rely on all factory regs giving the exact same rise in the pressure curve why bother?).

I hope this helps put to death a rather dangerous myth.

Cheers

Dave

You are totally right about the pressure. Do you know what the factory pressure at idel is for the gtr? My Mustang runs around 38-40lbs.

I do not have a fuel pressure gauge on my GTR, do you have one on yours? If so, what are you running under boost? I am very curious.

The 1cc-1hp has been just a basic guide when dealling with injectors. Since you did bring up the pressure part into the equation, I will not make that mistake again.

[rev210]

Someone elses idea of a basic injector size calculation....To convert cc's to lbs/hr divide the rated cc's by 10.5
450cc / 10.5 = 42.85 lbs/hr or rounding up a 43lb injector.
To convert lbs/hr to cc's multiply the rated lbs/hr by 10.5
26lb * 10.5 = 273 cc/min injector.

Brake Specific Fuel Consumption
Locating information about stock injector flow rates can sometime be quite difficult. If you can’t find your car’s injector size you can get a good idea of the injector flow rate using your car’s factory horsepower rating. To do this calculation you will need to determine your Brake Specific Fuel Consumption (B.S.F.C.). The B.S.F.C. is the number of pounds of fuel it takes to make 1 horsepower for 1 hour.

The B.S.F.C. values very from engine to engine depending on its efficiency. The more efficient the engine the lower the B.S.F.C. value, which translates into needing less fuel to make 1 horsepower for 1 hour. This changes for forced inducted applications as the extra fuel is used to cool the combustion chamber helping to prevent detonation. Here are some basic B.S.F.C. values.

Low to medium performance = .50
Performance engine with head work = .45
Performance engine with expert head work = .40 - .45


Supercharged and turbocharged engines = .55 - .60

Injector Duty Cycle
An injectors duty cycle defines how long the injector stays open. Injectors are always rated at 100% duty cycle so, a 26lb injector will put out 26lb's of fuel under 100% duty cycle. You never want to run your injectors above .85 or 85%. Anything higher puts you at risk of the injectors locking up. Choose an injector that puts out your desired lbs/hr at an 85% duty cycle rather than one at 100% duty cycle. If there isn’t an exact match you can raise your fuel pressure, which makes the injector act like a larger one but this trick is only good if you need a few extra lbs/hr.

Now that you have determined your B.S.F.C. and duty cycle it's time to calculate what your stock injector is rated at.

Here is the formula:
( H * B ) / ( C * D ) = estimated injector size.
H = horsepower
B = B.S.F.C.
C = number of cylinders
D = duty cycle

This is what it should look like for a Saturn.
( H * B ) / ( C * D ) = estimated injector size.
124 * .50 / 4 * .80


62 / 3.2 = 19.375 lbs per hour.


If you’ve installed too large of an injector and your car exhibits erratic idle during cold start or stumbling after it is warm you can attempt to remedy this by lowering the fuel pressure. But beware if you lower the fuel pressure to much it will effect your fuel injectors spray pattern so be careful of how much you lower it.

Injector Upgrade
If you want to upgrade your stock 19lb injectors by 10% but your not sure what the new flow rating will be simply multiply the injector’s lbs/hr rating by .10 then add the original lbs/hr rating of the injector. Example:
19 * .10 = 1.9 + 19 = 20.9 or a 21lb injector.
So this means we can upgrade to a 21 lb injector with no problem.

Injector Flow Rate based on Pressure Changes
To calculate an injector’s flow rate at a new desired fuel pressure you will need a calculator that has a Square Root function. Now this one can get a little tricky but pay close attention and this can help you out tremendously. Most of the injectors on the market today are rated at 43.5 psi. So, when you say you have a 19lb injector what you are saying is that your injector puts out 19lbs of fuel per hour at 43.5 psi of fuel pressure. So, how do we find out what our new desired fuel pressure going to be?


Here's an example:
Lets say we want to up the factory fuel pressure to 55psi. You will need to know the following information lbs/hr of the injectors you currently using (19lbs), original fuel pressure (43.5psi), and the new fuel pressure 55psi.

Here is the formula:
The square root of x multiplied by z divided by the square root of y = new injector flow rate

Where:
X = new fuel pressure
Y = original fuel pressure
Z = lbs per hour

First, find the square root of the new and original fuel pressure.
New fuel pressure: square root of 55 = 7.416
Original fuel pressure: square root of 43.5 = 6.595
Then divide the new fuel pressure square root sum by the original.
7.416 / 6.595 = 1.124
Then multiply this total by the size of the injector. In this case we are using the 19lb injectors.
1.124 * 19 = 21.35


At 55psi the injector now flows 21.35lbs/hr

Injector Flow Rate Chart

30psi
35psi 43.5psi* 45psi
50psi
55psi 60psi

16lb
17lb 19lb 19lb
20lb
21lb 22lb

20lb
22lb 24lb 24lb
26lb
27lb 28lb

22lb
23lb 26lb 26lb
28lb
29lb 30lb

29lb
31lb 35lb 36lb
38lb
39lb 41lb

32lb
35lb 39lb 40lb
42lb
44lb 46lb


*Stock injector size 19lb @ 43.5psi

Injector Size vs. Horsepower
Calculating how much horsepower the injectors can support is relatively straightforward using the following four variables:
Injector size: 26lb in this example
Number of cylinders: 4
Maximum duty cycle: .85
B.S.F.C. .50

Here is the equation:
Q * W * E / R = estimated horsepower for injectors.
26 * 4 * .85 / .50 =176.8 horsepower is what four 26 lb injectors will support.

Q = size of injector
W = cylinders
E = duty cycle
R = B.S.F.C.

***********************************

[SkylineUSA]

Damn good post!

I did the equation at the bottom, came up with 178.8. I love math Numbers are your friend.

I did my Stang 30lbs x 8 x .85 / .55 = 371hp, I am take that is at the crank? I have an FMU that will boost the fuel presure to 90lbs, so inturn the injectors will flow enough fuel for 490hp.

So, basically I learned something 1cc does not equal 1hp....Thanks rev for clearing that up.

[SkylineUSA]

Here is a great injector calculator.

http://www.csgnetwork.com/fiflowcalc.html

[SkylineUSA]

So, with the given information about the 550cc = 53lbs x 6 x .85 / .55 = 491hp so in order for the 550 to work with the GT-SS turbos, the fuel pressure will need to be turned up to about 60-70 lbs depending on the tune of course. That shouls be in the 575-620hp range.