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Unread 04-22-2013, 06:56 AM   #1
Neuner-9R
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258 RPM Range

What is the normal range of rpm's you find you are using with your 258 under typical road driving experience? What feels or seems like 'red-lining' to you?

Mine seems like it is screaming when I'm over 2k. It feels like I don't gain much power after that. I typically drive around between 1000 and 2000 rpm. Only time I'm above 2k is when I get up on it to merge with traffic. Typically I cruise down the highway at 60mph around 1500rpm in 5th. 33s and 3.31 ratio.

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Unread 04-22-2013, 07:04 AM   #2
Matt1981CJ7
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After I got my advance curve worked out, and my Weber 38 tuned, my 258 would rap out to 4K, comfortably.

Usually, I found myself shifting at around 2500 RPM, with 2:73s and 32"s.

Matt

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Unread 05-11-2013, 06:22 PM   #3
Neuner-9R
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Alright - Finally was able to get the timing light and take measurements. I didn't get the chance to measure with Manifold vacuum. Hopefully I can measure it soon.

I have the ported vacuum reading in inHg which I hope doesn't confuse the chart.
timing-advance-chart-051113.jpg  
File Type: pdf Timing Advance Chart 051113.pdf (5.7 KB, 19 views)
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Unread 05-11-2013, 07:29 PM   #4
Matt1981CJ7
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Yep, that looks like a typical 80s emissions curve. Looks like your dealing with a 13 degree advance slot.

You can certainly improve it.

Matt
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Unread 05-11-2013, 08:48 PM   #5
LumpyGrits
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They redline at 4500rpm. I shift most of the time around 2500-2700rpm.
LG
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Unread 05-11-2013, 10:02 PM   #6
Neuner-9R
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Ok Matt. Now what?


Don't want to have to swap out springs if I can help it. Think I can just bump up to 11 BTDC and connect to manifold vacuum like everyone else?
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Unread 05-12-2013, 06:02 AM   #7
Matt1981CJ7
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Well, there's no way to change your advance curve without digging into the distributor.

If that makes you queazy, then you'll have to live with the crappy '80s curve, or find a dizzy with a more aggressive curve.

Good luck,

Matt
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Unread 05-12-2013, 07:17 AM   #8
WindKnot
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I think Matt's Jeep is the exception and not the norm. I have no doubt Matt's Jeep can do it though. but Matt, wouldn't you agree that the torque is at the low end and you don't run the engine constantly at the high end?

I6s are not V8s. They're not high revving engines.
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Unread 05-12-2013, 07:40 AM   #9
Matt1981CJ7
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Windnot,

My thinking is, the redline on a 258 is 4500 RPM, why not give the entire power curve the advance it needs?

I think my video above proves the 258 will rap out easily above 4K, if tuned well. Before I re-curved, mine struggled to reach 3500 RPM, and it sounded like it was about to explode above 3K.

YMMV,

Matt
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Unread 05-12-2013, 08:00 AM   #10
swatson454
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Quote:
Originally Posted by Matt1981CJ7 View Post
Windnot,

My thinking is, the redline on a 258 is 4500 RPM, why not give the entire power curve the advance it needs?

I think my video above proves the 258 will rap out easily above 4K, if tuned well. Before I re-curved, mine struggled to reach 3500 RPM, and it sounded like it was about to explode above 3K.

YMMV,

Matt
Agreed. Torque is done by, what, 2,000 rpm. They'll continue to make power to about 3,500 but they're out of breath after that. They just don't have the head flow or camshaft for anything more than that.

I took mine to 4k a couple of times but you could feel the power drop off after 3,500. You're just revving it at that point. Might as well shift.


Shawn
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Unread 05-12-2013, 08:11 AM   #11
Matt1981CJ7
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Shawn,

What I notice most after re-curving was how smooth 3K RPMs felt. It no longer screamed like a wounded hyena at that range.

With 2:73 gears that was a blessing, as you know all too well.

Matt
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Unread 05-12-2013, 08:29 AM   #12
swatson454
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Quote:
Originally Posted by Matt1981CJ7 View Post
Shawn,

What I notice most after re-curving was how smooth 3K RPMs felt. It no longer screamed like a wounded hyena at that range.

With 2:73 gears that was a blessing, as you know all too well.

Matt
Yeah, me too. It felt like I was about to drive over its tongue at 2,500 before the ignition work.


Shawn
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Unread 05-12-2013, 08:57 AM   #13
Matt1981CJ7
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It really helped on the long, steep grades we have out here. They can be 7-10% for miles. 4th gear won't cut it, so you're forced to rap 3rd out at high RPMs for a long ways.

After the re-curve, I was still in the slow lane, but at least it wasn't embarrassing.

Matt
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Unread 05-12-2013, 09:06 AM   #14
swatson454
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I was just in Colorado Springs last week. It was nice to see snow, pine trees and "deer crossing" signs. The only game we're likely to hit out here is the occasional undocumented democrat.


Shawn
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Unread 05-12-2013, 09:43 AM   #15
Neuner-9R
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Quote:
Originally Posted by swatson454
The only game we're likely to hit out here is the occasional undocumented democrat.

Shawn
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.
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