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post #1 of (permalink) Old 03-01-2004, 03:23 PM Thread Starter
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CJ7 258ci installing a offenhauser intakemanafold

I wae wondering if any one has an answer for me?

I got a Offenhauser intake manafold, and on removing the stock manafold I noticed the heater core hose goes through the stock manafold and then to the heater core. now the part I was wondering about is can I bypass this in the new manafold or do I need to run the coolant through it? It wouldn't be a big deal to me, but the taps are very small 3/8in and the hose is 3/4in id would that now restrict the flow for my heater?

any advise would be greatly valued

Dan [img]images/graemlins/scs.gif[/img]
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post #2 of (permalink) Old 03-01-2004, 03:58 PM
 
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Re: CJ7 258ci installing a offenhauser intakemanafold

Do not bypass the manifold, as far as coolant goes. The coolant that warms the manifold helps greatly in fuel delivery/vapor/atomization. You'll still have plenty of coolant to your heater box.

Is it a 4bbl offey manifold? I always thought a 4bbl carb would absolutely drown a 258, but I may be wrong...
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post #3 of (permalink) Old 03-01-2004, 04:54 PM Thread Starter
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Re: CJ7 258ci installing a offenhauser intakemanafold

Yes I will be using a 4bl carb but its a 390 cfm one that shuld work for the 258. this is the first mod on my first jeep 83 cj7

Thanks for the advice
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post #4 of (permalink) Old 03-02-2004, 05:35 AM
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Re: CJ7 258ci installing a offenhauser intakemana

if you have the offy manifold that has the water ports for the heater hose then run it, if you have the one that doesn't then it's fine to switch that line straight to the heater core. either way you can run it without going to the manifold, but you'll be better of running it through if that's how it's designed.

as far as the 390, it's not bad on the 258 as long as you get it dialed in right and do a couple of things to it to make it a bit more jeep worthy. if you don't have the carb yet, you may consider using the offy manifold and doing a mc2100 on top of it with an adapter plate. this gives you better flow characteristics of the manifold, plus a much better carb. but if you have the 390 it's not terrible if set up right.

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post #5 of (permalink) Old 03-02-2004, 06:07 AM
 
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Re: CJ7 258ci installing a offenhauser intakemana

390 just still seems a bit high to me w/out any kind of mods to the head and/or exhaust (H.O. head swap, headers, etc etc.) The 4.2 just breathes pretty terribly and I kind of see it drowning. Let us know how the swap goes, though, I'm very curious.
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post #6 of (permalink) Old 03-02-2004, 07:17 PM
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Re: CJ7 258ci installing a offenhauser intakemana

granted, when i did my clifford intake with the 390 holley on my old 78 i did throw headers on and a jacobs ignition and the engine had been built pretty well within the prior two years, but i will say that the performance on and off the trail, including mileage went up when i put that 4bbl on (as long as i didn't run it WOT, which i really don't do very often anyway)

i was in the process of doing the ghetto fab TBI conversion for the six in the new 78 before i found the 360 and went with that instead. if i still had a six and were going to keep it, i would prbably go with the tbi or mc2100 on top of the clifford or offy manifold. my $.02

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post #7 of (permalink) Old 03-03-2004, 08:34 AM
 
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Re: CJ7 258ci installing a offenhauser intakemana

I have a Clifford manifold with the 390 on a 258 short block with a mild cam, 4.0 head, Borla headers, and a host of ignition mods including an MSD. Haven't seen an Offy up close, but the pictures I've seen make it look fairly different in design than the Clifford... most significantly it looks like the internal plumbing of the runners starts pretty close underneath the carb with a smaller open plenum. IF this is the case, it would make the Offy a stronger manifold for lower-end torque and weaker (by comparison) for mid-range and top-end power.

IN THEORY, a properly tuned four barrel will perform better than a one or two barrel of the same size (CFM) no matter what RPM/throttle opening you are talking about. In practice, you will find an awful lot of people on this board that will trash talk the Holley. You have to know what you are doing to get a Holley tuned properly, but having the power that I do and still being able to get 19mpg on 31" tires sits pretty well with me. [img]images/graemlins/cool.gif[/img]
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post #8 of (permalink) Old 03-05-2004, 11:18 PM Thread Starter
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Re: CJ7 258ci installing a offenhauser intakemana

well Im just getting in to all this and it's a learning experance for sure, I did get the holly carb though. And I put on a pacesetter header, and the offenhauser intake. that is the first small project. thanks for the info though. in the future (when the 258 poops out) I got hold of a 350 to shoe horn in to it.

Dan [img]images/graemlins/scs.gif[/img]
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post #9 of (permalink) Old 09-24-2004, 03:45 PM
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Re: CJ7 258ci installing a offenhauser intakemana

hey Pipe, I have a 83 Cj7 with the 258, i have been debateing for years if i would be wasting my $$ by installing a header or not. I have the Howell TBI, motor bored about .30 over, also have the DUI dist.
Are the headers worth the $$$ any noticable improvement?
Also think about changing intakes as well..
what do you think, or any others who may have done this..
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post #10 of (permalink) Old 09-25-2004, 08:29 AM
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Re: CJ7 258ci installing a offenhauser intakemana

Pipe hasn't posted on this board since this exchange, but has been on a couple of other associated boards. Try sending him a Private Message. Or better, start a new thread asking your questions. A lot more guys will see it and answer that way.

And welcome to the board!
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