Need help on EFI

[John S]

Hi everyone, I need some help and advice. I've been reading through posts here and on several other boards but have not found the direct answers to my questions so please bear with me and help out wherever you can.
I'm in the prcess of having my new engine built, its a 427 SBC, solid roller setup that I may eventually put a centrifigal blower on. I've been pretty set on using the Holley Stealthram for induction on this engine and was about to order today when some questions were raised that got me thinking. So this is where I need help.

I understand the difference between hi/low impedance injectors, but what are the real benefits or disadvantages between them and specifically on my engine combination?

I estimated that I would need 46lb/hr injectors based on the motor specs and considering that I may force induction at some point. Summit says that I would only need 42 lb/hr injectors but I think they are saying that because that is the largest injector they offer. Knowing this what injector would be my best choice?

I am also torn between the Holley Commander 950, and the Accel gen VII controller. I have not found anywhere whether or not the commander has rev limiting functions built into it, does anyone know if it does?

Lastly, it appears that there is no significant price break for buying the StealthRam as a kit. In fact I think that the kit would come with things I wouldnt even be using such as the inline fuel pump and the hoses and fittings ( I use all braided). Could this system be pieced together using the Holley intake and plenum, and a different (better) set of fuel rails, injectors and choice of ECU.
thanks.

[64duece]

I might be able to help in this area.

Higher fuel pressures (like those found is boosted applications) work against the fuel injector opening. No matter it's design, pintle, disc as the orfice get's larger so does the need for fast repsonse and control. Having the low impedance helps improve the large injector's opening respose time. The low impedance flows more current to "kick" it pintle off it's seat.

Next, 46lb gets you 550hp worth of fuel on a supercharged application (higher BSFC). Not really getting it there on a supercharged 427. The 42's are plenty even for a hot 427 w/o boost.

Cmdr950 does have rev limiting.

You are correct, it might be best to peice together the specific peices to get you where you need to be. Don't worry about the rails etc. I've used the standard rails and rail mounted regulator w/ an A1000 to 850hp on a 355 w/ Procharger's D1. The pump gave up before anything else did.

[Doug F]

You need to know what the HP of you engine is to properly choose injectors.

The Commander has a rev limiter.

You could buy just the intake, not sure why you want different fuel rails as far as the extrusions go.

It is possible that low imp. injectors could have better high pressure characteristics which you'd want with a lot of boost which will raise the line pressure that the injectors operate at. I've seen some high z injectors start to open slowly as low as 55 PSI.

Which ever you choose, get a wideband as you'll need that for the SC to safely tune it.

[Doug F]

Geez Dennis, we think alike and at the same time!

[ProdigyCustoms]

If supercharging is in your future, I would suggest the Stealth Ram and A FAST XFI or Gen 7, something with some advanced tuning capabilities. I can supply you with all of the above with competitive pricing, including the ProCharger when your ready. We are distributors for all these products. And we also provide a start up program. We almost always use the Holley intakes fuel rails and crossover kits. Most important will be using a system that you can find a tuner in your area that is familiar with the product. Ultimately, you will need a tuner, especially when you boost it, to dial you in 100%. Call me tomorrow, four zero seven 832 1752 and we can answer all you questions and get you going.

[John S]

Good information, thanks guys.
Dennis you really cleared up the differences between the injector types for me.

The engine should come in at about 550 - 560 HP at the flywheel NA. because the compression will be right at 11-1 if I do boost the engine it would be limited to 5-6 lbs. I dont think I could go any higher then that without some serious risk. Also, because this is an infrequent driver the use of high octane fuel is likely.
I think I would be better off going with larger injectors with the intent of either boosting or juicing the engine at a later date instead of purchasing injectors a second time when the time comes. If 46 lb injectors are good to 550hp bosted, then I will need to go even larger since I should be closer to 700hp.
Thoughts on this?

I know that BSFC numbers are pretty much a constant for for different engine types ( 0.4 - 0.44 mild engine) but how do you determine what the best BSFC number to use for your specific engine? This would help me in determining proper injector size.

Doug;
Not that I would want different fuel rails, I just have not found a kit listed for the Stealth Ram with intake, plenum, rails, proper size injectors, wb O2 and the commander and harness without all the other unnecessary items such as fittings, tubing and fuel pump. I guess the big thing is I do not want to pay for 42 lb. injectors if I will have to buy 46 or larger anyway. (the cost of the injectors would keep me in fuel for the summer :))

Bill;
I'll give you a call later today. You may be able to help me out and I would much rather buy parts from someone here than Summit or jegs. I do not think I would go for the Fast system though.

Thanks again everyone.

[Doug F]

There is actually a PN for a stealthram that I believe has no pump and injectors but everything else including a ECU and wideband.

I think I did it special for Dennis once! But it is an orderable PN.

I'll take a look.

[64duece]

Forgot about that Doug.

John,
The Cmdr950 is a very capable ECU and will handle anything you throw it's way. I've tuned dozens of these units over the years from 300hp 4cyls to 1600hp turbocharged SBC w/ 160lb injectors.

We have one on a turbocharged Nova running 8.48 to 8.52 every pass down the track! Talk about consistency.

I would reconsider your thoughts about sizing injectors for boost on this deal until you are serious about making power with it. Enjoy what you have for awhile, when the time comes, lower the static CR and make a cam and injector change to take advantage of the power found in supercharging. For BSFC, I always errr on the high side for supercharged applications .600. It may fall in at .550-.580 when it's done but, you need to be sure your fuel system is covered. I've done some back to back testing with different superchargers, they use vastly different amounts of power which greatly affects BSFC.

[EFI69Cam]

Good information, thanks guys.
Dennis you really cleared up the differences between the injector types for me.

The engine should come in at about 550 - 560 HP at the flywheel NA. because the compression will be right at 11-1 if I do boost the engine it would be limited to 5-6 lbs. I dont think I could go any higher then that without some serious risk. Also, because this is an infrequent driver the use of high octane fuel is likely.
I think I would be better off going with larger injectors with the intent of either boosting or juicing the engine at a later date instead of purchasing injectors a second time when the time comes. If 46 lb injectors are good to 550hp bosted, then I will need to go even larger since I should be closer to 700hp.
Thoughts on this?

I know that BSFC numbers are pretty much a constant for for different engine types ( 0.4 - 0.44 mild engine) but how do you determine what the best BSFC number to use for your specific engine? This would help me in determining proper injector size.

Doug;
Not that I would want different fuel rails, I just have not found a kit listed for the Stealth Ram with intake, plenum, rails, proper size injectors, wb O2 and the commander and harness without all the other unnecessary items such as fittings, tubing and fuel pump. I guess the big thing is I do not want to pay for 42 lb. injectors if I will have to buy 46 or larger anyway. (the cost of the injectors would keep me in fuel for the summer :))

Bill;
I'll give you a call later today. You may be able to help me out and I would much rather buy parts from someone here than Summit or jegs. I do not think I would go for the Fast system though.

Thanks again everyone.


I have a Gen VII DFI system, but if I was buying now I'd go with a XFI or BS3.

[John S]

Thanks for all the input guys, thats what is so great about these forums, the wealth of information that is available. I've taken evyones comments and suggestions into consideration and have decided on the following. After speaking with Frank @ Prodigy I orded the Stealth Ram manifold and FAST XFI ecu. I did not think that the fast system would be within my budget but the total cost came out to about the same as the complete Stealth Ram kit. One of my deciding factors was that I could not find anyone in my area that was familiar with tuning the Commander but there is a shop near me that has experience tuning the FAST system on their chassis Dyno. Frank also convinced me to abandon my MSD billet distributor and crank trigger in favor of the Accel dual pulse distributor. I'll get a refund of over $500 from summit for those parts so there is nothing lost in that change.
OPnce this all comes together I'll post on the details.
Thanks again for all the help.

[yohinan]

Uhh is this the guy with the last name that goes along the lines of the Cat in the hat? If not then sorry for the interruption.