How many horses? - JeepForum.com
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post #1 of 13 Old 06-10-2019, 09:16 PM Thread Starter
elchunkogrande
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How many horses?

I have a 90 model YJ with GM TBI and HEI. Surely someone has put a similar set-up on a dyno and can tell me how much horse power it should be making.

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post #2 of 13 Old 06-10-2019, 10:12 PM
Randonexplosion
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Im gonna say you are at approximately 23 zebraforce at the wheels. You may be pushing 30 llamathrust at the crank.



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post #3 of 13 Old 06-11-2019, 12:10 AM
Crazysjeep
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If you ad a mr fusion food processor to the mix you should be close to 1.1 gigawatts
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post #4 of 13 Old 06-11-2019, 01:24 AM
the cueball
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Wish I had some llamathrust!

Is that some sort of off the shelf kit you can buy??
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post #5 of 13 Old 06-11-2019, 06:17 AM
1project2many
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Quote:
Originally Posted by elchunkogrande View Post
I have a 90 model YJ with GM TBI and HEI. Surely someone has put a similar set-up on a dyno and can tell me how much horse power it should be making.
Surely someone can. You should be making stock power at the minimum. With proper tuning a relatively stock powertrain could be expected to make 2-5% more peak power than the original system. If your computer is also allowed to control spark then you will usually see torque gains. It's not that peak torque increases substantially, but torque across the board will usually increase as the spark can be set to a point just prior to onset of detonation. This makes for better acceleration and it makes the engine "feel" stronger.

So what does all this mean?

1) AMC engineers did a good job getting peak power and torque out of the Jeep engines.
2) Computer controlled fuel and spark overcome limitations found in earlier mechanical carburetors and distributors for greater torque and power across the engine's rpm range.
3) The computer needs to be "tuned" to the engine for best results.

Quote:
Im gonna say you are at approximately 23 zebraforce at the wheels. You may be pushing 30 llamathrust at the crank.
Wha??? That graph is crazy! Hp 59% higher than everything else??? Obviously they got numbers from a Mustang dyno...

Quote:
Wish I had some Llamathrust!
llamathrust is really where it's at. Zebraforce is just a number for bragging rights at the mall. Only an a** would worry about Donkeystrength.
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post #6 of 13 Old 06-13-2019, 12:08 PM
daddyjeep87
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The only correct answer is... not enough. I had the same set up years ago. I installed a header, high flow cat and flowmaster exhaust at the same time. My seat of the pants dyno told me that there was a pretty good increase in HP (or ZP if you prefer), but most of that was most likely from the better flowing exhaust. The advantage of the TBI is just smoother operation. All of that money I spent back then on fuel injection doesn't hold a candle to the benefits to swapping in a fuel injected V8. A V8 swap can be much less expensive than the fuel injection conversion too.

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post #7 of 13 Old 06-13-2019, 03:37 PM
Chrisnvegas
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My seat-of-the-pants dyno has the TBI adding only a little more power. It does start and run much smoother.
The biggest gains I felt was from the ignition upgrade. And the reason is RPM. It runs better at higher RPM. Higher RPM is much like increasing displacement.
The stock ignition has the 4.2 pretty much running out of steam at 3500 rpm. The HEI allowed the engine to happily rev to 4500 rpm.

You can get immediate 5% gains by using pure gas. Gas without ethanol. Better economy too.

The combination of TBI and Hei wakes up the 4.2 and increases drive-ability.
How much, I don't know.

I'm perfectly happy with my I-6's and have zero desire for a V-8, in my Jeep anyway.
I'll leave the V-8 in my Mach One.
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post #8 of 13 Old 06-15-2019, 06:43 PM
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Add a weed drawer... Pot smokers drive slow.... They are mellow... Your perceived horsepower gains will be substantial. The easiest mod ever.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #9 of 13 Old 06-15-2019, 08:03 PM
1project2many
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Add a weed drawer... Pot smokers drive slow.... They are mellow... Your perceived horsepower gains will be substantial. The easiest mod ever.
I am never going to pass a slow moving YJ without thinking of this.
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post #10 of 13 Old 06-16-2019, 07:08 PM Thread Starter
elchunkogrande
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I appreciate all the replies guys but seriously, can't someone put a number on it? Isn't it Iowa University that rates tractor engines? I know it's a strong 8N that will make 30 HP and my VAC Case is only about 25 but my 170 AC will pull an honest 62 (4 cyl Perkins). I would just like to know what the little 258 was stock and how much gain do all the mods get me. I bought this project because the PO had spent $15K on it and it still didn't run so it came cheap yet I feel bad about wearing out this set of tires just ferrying kids and chasing parts but an old man deserves something for spending his life raising 2 sets of kids.
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post #11 of 13 Old 06-16-2019, 08:19 PM
jay-h
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Seriously the HEI will do nothing for HP. It may be a stronger spark (better starting mostly) but despite the blurbs in advertising, a properly functioning ignition system already burns all the fuel in the chamber (if it didn't it would NEVER pass emission testing)

The TBI will increase driveability, and misfil\re less at top end but max HP will not change very much.

Only cams, headers, compression changes, stroking or super/turbo charging will actually make a significant difference.

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post #12 of 13 Old 06-16-2019, 09:25 PM
1project2many
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Quote:
I would just like to know what the little 258 was stock
This question can be answered by typing "horsepower torque 258 jeep 1990" into google and following a few links.

https://www.jeeptech.com/engine/amc258.html

Quote:
and how much gain do all the mods get me.
Peak horsepower is a function of airflow. Airflow won't change significantly by replacing the carb with a throttle body because the AMC intake, exhaust manifold, and head limit airflow more than the carburetor that was removed. If the computer is allowed to control spark then timing could be adjusted at all load and rpm conditions to deliver best torque and you'd see a noticeable performance improvement. But simply installing HEI and TBI will not significantly alter power from stock.
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post #13 of 13 Old 06-17-2019, 10:34 AM
daddyjeep87
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Quote:
Originally Posted by elchunkogrande View Post
I appreciate all the replies guys but seriously, can't someone put a number on it? Isn't it Iowa University that rates tractor engines? I know it's a strong 8N that will make 30 HP and my VAC Case is only about 25 but my 170 AC will pull an honest 62 (4 cyl Perkins). I would just like to know what the little 258 was stock and how much gain do all the mods get me. I bought this project because the PO had spent $15K on it and it still didn't run so it came cheap yet I feel bad about wearing out this set of tires just ferrying kids and chasing parts but an old man deserves something for spending his life raising 2 sets of kids.
I really doubt that anyone is going to spend the money for a dyno session for a Jeep with a 258. I believe the factory claimed around 114 or 116 HP.

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