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Unread 11-05-2002, 10:41 AM   #1
skirider
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258 Fuel Injection?

First Thank you for the Forum!!

Ok, here is the deal. I'm seriously considering adding fuel injection to my Jeep (79 CJ-7, 258ci, Quadratrac) and am considering the Holley Projection kit to do it (PN 501-12, 1 barrell 300cfm). This appears to be a pretty straight forward application/installation and would I would use the closed loop option.

Here is the quandry. Holley also makes a 670cfm kit for AMC V-8's up to 275hp. Has anyone used this kit on the 258 by adding an aftermarket intake (like an offy) to gain more power and have the added volume for future upgrades?

Give me the good, bad and the ugly!!

Thanks,

skirider

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Unread 11-05-2002, 01:36 PM   #2
CJeep
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Never done what you ask, but I believe that 650 cfm is too much for a 258, especially because the heads have such poor flow.

There is some formula for displacement vs. cfm for optimal performace, but I don't remember what it is.
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Unread 11-05-2002, 01:39 PM   #3
skirider
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That is definately the question of the day (extra cfm's)! I have emailed Holley directly for their input......we'll see what they have to say.

Thanks for the input!

ski
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Unread 11-05-2002, 02:39 PM   #4
skirider
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Well here is the scoop from Holley Tech Support.

The 300cfm unit (made for the 258) is good up to about 140hp. The 670cfm unit will be rich with a stock/near stock setup. To run the 670cfm system you would need: intake, cam, header, head work etc. So unless you are really going to modify the 258 it sounds like the base 300cfm unit is the way to go.

Anybody know what horsepower the 258's made stock?

ski
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Unread 11-05-2002, 06:40 PM   #5
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Quote:
Originally posted by skirider
Anybody know what horsepower the 258's made stock?
115-125 hp. Depending on the year.
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Unread 11-05-2002, 08:21 PM   #6
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Here is your formula... CID X RPM(MAX)
-------------------- =CFM
2 X 1728
Given a 350 CID running 8000 RPM's you would have something like this. 350 X 8000
-------------- = CFM
2 X 1728

2800000
------------ =810 CFM
3456
Remember, you must be realistic about your max. RPM. If you lie to yourself, you will only over carburate causing bogging.
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Unread 11-05-2002, 08:25 PM   #7
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Sigh....... ya know, some day I'll get the hang of setting up these formulas in these posts so they come out the way I typed them.
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Unread 11-06-2002, 07:35 AM   #8
skirider
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Thanks for the info guys!

Looks like with what I want to accomplish the 300cfm unit will work just fine. I'm not looking for a racer just something to improve the offroad characteristics (ie no cough & stumble when the nose goes up or down!).

Thanks again!

ski
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Unread 11-06-2002, 02:58 PM   #9
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Quote:
Originally posted by jeepdaddy2000
Here is your formula... CID X RPM(MAX)
-------------------- =CFM
2 X 1728
Given a 350 CID running 8000 RPM's you would have something like this. 350 X 8000
-------------- = CFM
2 X 1728

2800000
------------ =810 CFM
3456
Remember, you must be realistic about your max. RPM. If you lie to yourself, you will only over carburate causing bogging.
Are you trying to say:

(CID X RPM) / (2 X 1728) = CFM

(350 X 8000) / (3456) = CFM

(2800000) / (3456) = 810 CFM

So .. for my 350 powered Jeep .. I should be using a 800 cfm carb??? I think I have a 650 cfm in there right now .. but its basically stock (for now).
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Unread 11-06-2002, 05:14 PM   #10
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Does anyone know the torque that 258 has? I know HP doesnt really mean as much as torque and 115 sounds bad to the ear. I mean I have a little 4 banger that makes more HP but Im sure the tourque in the jeep murders that little car.
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Unread 11-07-2002, 08:05 AM   #11
skirider
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jeepin,
Torque must be where the advantage lies because those hp numbers are scary low! I'd also be interested in the torque numbers of the 258 mine is a 79?

ski
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Unread 11-07-2002, 07:11 PM   #12
SamFromCO
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The info that you want is here:
258 info
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Unread 11-08-2002, 09:55 AM   #13
skirider
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Sam, Thanks for the link on the 258 info!

ski
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Unread 11-09-2002, 08:40 AM   #14
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Quote:
Originally posted by NaeKid


Are you trying to say:

(CID X RPM) / (2 X 1728) = CFM

(350 X 8000) / (3456) = CFM

(2800000) / (3456) = 810 CFM

So .. for my 350 powered Jeep .. I should be using a 800 cfm carb??? I think I have a 650 cfm in there right now .. but its basically stock (for now).

Are you really running 8 grand? And is that where you want optimum proformance? Remember, these formulas are for MAX RPM at WOT! When carbing, you want to carb to the level of performance you want. If you typicaly run in below 4K with an occasional poke at 6K,Then carb for 4. People tend to carb according to what they think they would like to do, and not what they can do. Oh and thanks for cleaning up my formulas, too much physics and not enough algebra. LOL
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Unread 11-10-2002, 12:40 PM   #15
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Ahh .. ok. So it isn't "magic-number" of 8000 for RPM's.

(CID X RPM) / (2 X 1728) = CFM

(350 X 3500) / (3456) = CFM

(1225000) / (3456) = 350 CFM

Most of my driving is considered highway and slow trails. I don't normally mash on the skinny peddle .. that's not what I built my Jeep for. With that kind of formula, should I change to a smaller carb? That doesn't make sense to me .. but, I am still learning some of the finer details.

Is that 3456 a "magic number"? Or can it change for any reason?
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