Hey Tom and Leighton,

I am getting closer to buying injectors for MP-EFI and I want to eventually go turbo and get similar HP numbers to yours (275 RWHP or so). What type/brand of injectors are you using (incl impedance high/low) and what flow rate? I was thinking of ordering a set of Ford Racing high-imp injectors from Summit at 30 lbs/hr. They seem like a great deal at $220 a set (two extras!).

Also, with your injectors, have you found any trouble with idle PW being too small, or any other troubles??

Any other wisdom you can impart would be great.

Lou

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Home of Slant6-powered fun machines since 1988

Lou,
We are running a Siemens 85#/hr injector. Do not forget that we are running alcohol. These injectors appear to be maxed out at about 300hp. They low impedence...if you need the part number I can look it up for you. We bought them from Kinsler. We have not had any idle problems but that is due mainly to the EFI management system(electromotive) and the rising rate fuel pressure regulator.


Tom & Leighton

Here are the formulas and a worksheet for calculating sizes.

Injector Flow Rate (lb/hr) = Engine HPx BSFC
Number of Injectors x 0.8

For example, to calculate the individual injector size for a 650 HP V using 8 injectors and assuming a BSFC of 0.5:

Injector Flow Rate (lb/hr) = 650 x 0.5
8x0.8 = 50.78 lb/hr

If you know an injector flow rate, you can solve the above equation for a rough estimate of fuel system capacity like this:

Engine HP = Injector Flow Rate x Number of Injectors x 0.8
BSFC

For example, using the same estimated values from above:

Engine HP = 50 x 8 x 0.8
0.5 = 640 HP

Here is alink to a worksheet you can fill in and it will calculate it for you.
http://www.rceng.com/technical.htm#WORKSHEET

Tom

Thanks Tom, especially for the alcohol reminder and the rising-rate regulator detail.

I have seen those formulas - that worksheet link doesn't work for me (gives a "reply" screen), but don't worry about it as I already have it in one of my own. Just so no one is confused, the first equation is:

Flow Rate = (HP X BSFC)/((# of injectors) X 0.

I was a little confused the first time I read it without the division slash...

I assume that alcohol gives a much higher BSFC than gas.

Hope the family is truckin' along well,

Lou

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Home of Slant6-powered fun machines since 1988

Sorry. Try the link now.

Cool. That site has some nice info on it.

Lou

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Home of Slant6-powered fun machines since 1988

They think a lot of their injectors too....but everything I have read about them points to the fact that they really know what they are doing.



Tom

Lou,
I don't know if this will help but the '87 3.8L turbo Buick used 28 lb/hr injectors and produced 245 HP @ 4000 RPM. Actually the GNX produced 275 HP @ 4400 RPM but I'm not sure if it used the same injectors. Before you spend $200 you might want to try some of these used injectors. I see them for sale quite often in the "parts for sale" section at www.turbobuick.com/forums/ for $20 to $30 for a set of six. People sell them when they upgrade to a larger turbo and injectors. If you do a search you might find some that have come up for sale in the past month or so but haven't sold yet. I hope this helps.
Bob D

I used 36 # / hr Accells which I believe are actually Bosch made. No problems controlling pulse width at idle. Max duty cycle to date has been around 40 so I still have extra capacity.

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Cheers!
Al T

Bob and Al and Tom,

Thanks very much for your posts. Always great to have more real world input!

I'll keep ya posted on progress...

Lou

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Home of Slant6-powered fun machines since 1988

Tom, another question for ya about the Simca EFI system:

Do you guys measure fuel pressure with that rising rate regulator? What is the max fuel pressure you see at high RPM/max power? Is there a max allowable/achievable pressure for common injectors?

I am getting close to buying MP-EFI injectors.

Thanks much,

Lou

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Home of Slant6-powered fun machines since 1988

Lou,
We see a max fuel pressure of 75psi during the run. If we turn the boost up the the fuel pressure will rise. I have been told that the max that most injectors can be flowed at is 100psi(this came from Kinsler when we bought the injectors) That means that an 84#/hr injector at 100psi would be flowing around 120#/hr.
Fuel pressure at idle is 45-50# I will look at one of the datalog file tonight and let you know.

Tom

Man you're fast... You probably check this site almost as much as I do, addict that I am.

Don't worry about specifics, you gave me plenty of info for my decision. It sounds like 30 lb/hr injectors will be perfect for me in the short term, and should be fine in the long term, at least with a modest turbo and a rising-rate regulator (gas for fuel, < 10psi boost).

I used the calculator you posted earlier, and these numbers check out for 80 psi max fuel pressure, BSFC = 0.6, duty cycle of 0.8, and up to 325 crank HP, using 30 lb/hr injectors.

Thanks again,

Lou

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Home of Slant6-powered fun machines since 1988