258 RPM Range - Page 2 - JeepForum.com

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post #16 of 37 Old 05-12-2013, 09:47 AM
jumbojeepman
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Quote:
Originally Posted by WindKnot View Post

I6s are not V8s. They're not high revving engines.
Has little to do with the engine type, more to do with the engine bore/stroke relationship. For instance, my Camaro and Jeep V8's top out around 4500-5000 rpm, and as definitely down on power at the redline. My BMW and Mercedes I6's redline at 7k rpm, and pull strong all the way there

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post #17 of 37 Old 05-12-2013, 10:22 AM
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Quote:
Originally Posted by Neuner-9R

Now that's funny.

No Matt, not nervous, I'm just the kind of guy that seems to make things worse instead of better when diving into small parts.

Do you have a graph showing the results of your current setup as comparison?

I think it's a bad lifter sound that keeps me from going past 2300. Too long of a to do list to get into that right now.
I'm on my phone now but I'll post it when I get home. Or you could search for my "help with advance curve" thread.
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post #18 of 37 Old 05-12-2013, 10:24 AM
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Originally Posted by Matt1981CJ7 View Post
I'm on my phone now but I'll post it when I get home. Or you could search for my "help with advance curve" thread.
Phone-posting sucks. Here...Advance Curve

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post #19 of 37 Old 05-12-2013, 01:41 PM Thread Starter
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Thanks for the link. I've read it before but with all of the curve graphs it's hard to see which is the latest. Matt, would appreciate you posting.
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post #20 of 37 Old 05-12-2013, 03:32 PM
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My mechanic says the max rpm the 258 would be happy at is about 2500 with standard tuning

1984 jeep cj7, 258 I6, rebuilt T176,rebuilt Dana 300, amc 20 , dana 30, 4.10's Trac-lok in rear , 4.10's detroit soft locker in dana 30, 2.5 inch bds suspension lift, 1 inch polyurethan body mount lift. Line ex. weber carburetor. factory tach. factory clock ,oem replacement speedomter cluster, and oil pressure gauge, factory volt gauge.
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post #21 of 37 Old 05-12-2013, 04:24 PM
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Quote:
Originally Posted by agear
My mechanic says the max rpm the 258 would be happy at is about 2500 with standard tuning
I would look for a new mechanic.

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post #22 of 37 Old 05-12-2013, 05:07 PM Thread Starter
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Set it to 10*BTDC, connected to manifold and CTO per the diagram in another thread and did not like it at all. The power in my low end went away and I was having to give it more gas to get going. Using ported I could easily drive 60 in 5th at around 1500 rpm with plenty of room on the gas pedal to jump up to 70-75. Not with manifold. Even with it floored I lost speed. 2500 rpm was smoother but I don't drive around that high. Couldn't wait to get home to put it back to the way it was.
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post #23 of 37 Old 05-12-2013, 05:08 PM
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Quote:
Originally Posted by firemanjim7

i would look for a new mechanic.

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post #24 of 37 Old 05-12-2013, 05:16 PM
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Quote:
Originally Posted by Neuner-9R
Set it to 10*BTDC, connected to manifold and CTO per the diagram in another thread and did not like it at all. The power in my low end went away and I was having to give it more gas to get going. Using ported I could easily drive 60 in 5th at around 1500 rpm with plenty of room on the gas pedal to jump up to 70-75. Not with manifold. Even with it floored I lost speed. 2500 rpm was smoother but I don't drive around that high. Couldn't wait to get home to put it back to the way it was.
Well after rereading the original post and now this one i would say put it back and enjoy. Doesn't look or sound like you had a problem to start with.

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post #25 of 37 Old 05-12-2013, 05:38 PM
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Quote:
Originally Posted by Neuner-9R View Post
Set it to 10*BTDC, connected to manifold and CTO per the diagram in another thread and did not like it at all. The power in my low end went away and I was having to give it more gas to get going. Using ported I could easily drive 60 in 5th at around 1500 rpm with plenty of room on the gas pedal to jump up to 70-75. Not with manifold. Even with it floored I lost speed. 2500 rpm was smoother but I don't drive around that high. Couldn't wait to get home to put it back to the way it was.
Post up the vacuum diagram you used.

Besides improved cold starts, the only true performance difference anyone should realize switching to manifold vac is at idle, or at very low RPMs with no load. Otherwise, it should be exactly the same as ported.

If there's any change in higher RPM performance, or under load, then something isn't hooked up correctly.

Good luck,

Matt
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post #26 of 37 Old 05-12-2013, 07:23 PM Thread Starter
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It's the last diagram you posted for 'ported vs manifold' thread.

I didn't notice a difference in idle and the performance at the low end was worse from manifold. I'm not buying the voodoo because I now love the way my engine is running. Thought id give it a try just in case it could be improved upon but this has at least removed my doubts. Smooth and lots of power up to 2300. It pulls me up long inclines at <2300. Thicker air down here is probably the difference
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post #27 of 37 Old 05-13-2013, 12:20 AM
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I guess we've found the one guy, out of 100, who prefers ported vac.

I can tell you, however, that the results you claim are not consistent with what should have happened. Not even close. Which leads me to believe you didn't have it setup correctly.

Anyway, it's been a good thread, but this level of tuning isn't for everyone.

Matt
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post #28 of 37 Old 05-13-2013, 06:16 AM Thread Starter
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It's not that hard, and there aren't that many components involved. You may need to make sure your engine is breathing right. Get some better low end so you don't have to make it scream to get up them inclines.

Got me thinking - I had an XJ when I lived in Boulder. It did alright heading to the slopes, about like any vehicle. I got transferred away and several months later my exhaust header cracked. I had it swapped out with a high-flow performance version, changed the exhaust and upgraded the muffler. My MPG improved and when I went back to CO to visit friends, it climbed like a bat out of hell.
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post #29 of 37 Old 05-13-2013, 06:28 AM Thread Starter
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Originally Posted by Matt1981CJ7 View Post
I guess we've found the one guy, out of 100, who prefers ported vac.
Come on Matt, there's a reason it's still debated all over the internet. I found more rodders that preferred ported in my search but the combo of their components and settings were much different than the guys who argued manifold.

It appears to be a difference on how everyone's engine is setup. There isn't an absolute to solve everyone's situation.
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post #30 of 37 Old 05-13-2013, 06:36 AM
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Well, you've had some of the best CJ mechanics on this forum all tell you that manifold is the way to go. If you think they are all just blowing smoke, I guess you're entitled.

BTW, did you know that your 1985 CJ's factory vacuum layout used manifold to the distributer?

Lastly, as I've stated, switching to manifold vacuum changes nothing on the upper-end, it operates exactly like ported vac does except for at idle. Your posts indicate that you still don't quite grasp that concept.

Matt
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