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  #61  
Old March 30th, 2017, 09:45
cherokeefan_1 cherokeefan_1 is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

Do you have a smog station nearby? Run it through and get your numbers and we can compare if anyone else has theirs. I keep mine to keep an eye on any possible issues year after year.
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  #62  
Old March 30th, 2017, 09:51
cherokeefan_1 cherokeefan_1 is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

I had a friend that had a set of SBC heads rebuilt once for his Chevelle and it ran hard, low 12's off a stock rotating assembly but it had a slight skip off idle. After about a year we tore the engine down and discovered the valves were not square to the seat. Turns out the last machine shop messed up when they​ either ground the seats or installed the guides. All 16 valves were bleeding off compression but it pulled to 6700 no problem and turn slicks on the strip with eaze. I can imagine it would have made a ton more power with sealed valves.
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  #63  
Old March 30th, 2017, 09:53
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notamos notamos is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

Quote:
Originally Posted by cherokeefan_1 View Post
Do you have a smog station nearby? Run it through and get your numbers and we can compare if anyone else has theirs. I keep mine to keep an eye on any possible issues year after year.
Yeah, we have to have our vehicles emission-tested on a dyno. I just had it run 3 weeks ago. It passed with flying colors. My only problem - I THINK I threw away the paper. Let me look around here. I know my values weren't even 10% of the allowable.
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  #64  
Old March 30th, 2017, 11:25
adamthewebman adamthewebman is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

Xxcx

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  #65  
Old March 30th, 2017, 11:32
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

OK. I finally had time to hook my scanner (Torque Pro) up to it and give it a run. Torque has a website available for the runs, if anyone wants to take a look at it.

http://view.torque-bhp.com/ and login w/ my Device ID (351713082230320).

-The first run, at 11:15 is from a cold start until it was completely warm. I was sitting still the entire time & letting it idle. I checked the engine temp that Torque was seeing against the temp of the thermostat housing - they were both on. For some reason, the graph online is screwed up. Vac @ idle is around 18-20.

-The second run, at 11:42, was after the vehicle was completely warmed up and in closed loop. I went north and did a 1/4 mile run when I turned east. Then, after turning around (you can see it on the map), I did another 1/4 mile run WOT (no overdrive) going north.

One thing to note, some of the units on their website are wrong. For example, where it shows my mph, it is actually showing KPH in one place. You can download the excel files there to get all readings that were recorded.

It takes just shy of 1/4 mile to get to 60mph. 1/4 mile in about 19 seconds, at about 65mph... If that means anything.

Last edited by notamos; March 30th, 2017 at 11:48.
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  #66  
Old March 30th, 2017, 12:04
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

Stock@sea level SHOULD be about 16.5 second 1/4 mile. Don't think the elevation should affect it four full seconds. Definitely sounds slower than it should lol
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  #67  
Old March 30th, 2017, 12:10
cherokeefan_1 cherokeefan_1 is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

Gears and big tires do affect times. Is that corrected speed or is the speedo off due to tires/gears. If it passed with flying colors I'd say the engine and sensors are good. I've got a 01 tahoe that gets 12mpg bone stock where others are getting 16 or so. Some people say the factory could have used different tunes based on who made the ECM.
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  #68  
Old March 30th, 2017, 12:22
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notamos notamos is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

Speedo is with 1%. For some reason, vac didn't log with those runs. I'll have to add it & redo a few things. But, I'm going to do a compression/leakdown test anyway. Can't hurt.
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  #69  
Old March 30th, 2017, 15:03
Green XJ Jeep Green XJ Jeep is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

Do you happen to know what the cc volume of the combustion chamber of the replacement head? Its starting to sound like you are a half a point down in compression
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  #70  
Old March 30th, 2017, 15:06
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notamos notamos is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

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Originally Posted by Green XJ Jeep View Post
Do you happen to know what the cc volume of the combustion chamber of the replacement head? Its starting to sound like you are a half a point down in compression
No, I don't. This was the first engine I ever assembled. I *thought* I did a decent job with it, followed the FSM and other reading to the T. But, I guess I am/was at the mercy of the machine shop who did the work.

What exactly does "half a point down in compression" mean?
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  #71  
Old March 30th, 2017, 17:49
cherokeefan_1 cherokeefan_1 is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

Less horses. But they are low compression engines to begin with so I'm not sure a half point would effect it much. I try to bump compression and cut the quench to no more than .045" to reduce detonation but that's a whole topic on its own and not your problem. Did the head CC's change much over the years? Looking forward to seeing how the compression check goes. Just remember to pull all the plugs, hold the throttle wide open when you do or you get false numbers. Then squirt a bit of oil in each hole and repeat. If those numbers are good not sure you need to do a leak down but knowing how is worth learning.
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  #72  
Old March 30th, 2017, 18:22
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

No real reason to run compression wet or dry, or leakdown. Vacuum reading was well within reason considering the elevation. He stated it runs very smooth, so no reason to suspect a weak cylinder.

With that new info, I'd be moving on to fuel pressure AND volume.
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  #73  
Old March 30th, 2017, 18:28
Green XJ Jeep Green XJ Jeep is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

Quote:
Originally Posted by notamos View Post
No, I don't. This was the first engine I ever assembled. I *thought* I did a decent job with it, followed the FSM and other reading to the T. But, I guess I am/was at the mercy of the machine shop who did the work.

What exactly does "half a point down in compression" mean?
Sounds like you did a fine job on the rebuild. It runs good and is a strong motor so I wouldn't worry much other than the lousy mileage.
A stock 4.0 is around 8.8 to 1 compression ration. If the head had a 10cc larger chamber and if you used a thick head gasket or even pistons with a larger volume dish you could very well of lost .5 point or more in compression. Meaning instead of your 8.8 you would end up having a 8.3 compression ratio. Doesn't seem like much but a 6000'+ in elevation it would be noticable
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  #74  
Old March 30th, 2017, 18:57
cherokeefan_1 cherokeefan_1 is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

That is true. One thing I have totally spaced on is transmission issues. Ford had problems with the torque converter in the 90's that, when bad, could make it feel like you had a boat anchor when taking off from a stop. I'm just throwing stuff out there to maybe get more people to chime in with their experiences.
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  #75  
Old March 30th, 2017, 19:56
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notamos notamos is offline
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Re: Feeling weak (rebuilt 4.0, 4.56, AW4, 31s...), Why?

Quote:
Originally Posted by cherokeefan_1 View Post
That is true. One thing I have totally spaced on is transmission issues. Ford had problems with the torque converter in the 90's that, when bad, could make it feel like you had a boat anchor when taking off from a stop. I'm just throwing stuff out there to maybe get more people to chime in with their experiences.
Trans... I will say that it seems to be much quicker when in 3 and no OD. Also, when in D, it seems to shift into 4 wayyy too soon. I adjusted the TV cable a while back with no change.
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