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4.8 LR4 dyno results and build evaluation

 
Old 12-22-2018, 12:51 PM
  #21  
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Very interested to hear what the tuner says. 20 is pretty conservative though as others have said so it really sounds like the cam timing is advanced to much. The tq and hp peaks are just way lower than they should be for the parts you've put together.

You should do a quick hot cranking compression test on a few of the easy to reach cylinders and let us know what you find before you open it back up though.
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Old 12-22-2018, 02:18 PM
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Early peak would indicate advanced cam timing. And those drop in truck cams usually have a lot of advance ground in already.
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Old 12-22-2018, 05:52 PM
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Is this a 87 octane tune?
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Old 12-22-2018, 10:42 PM
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Originally Posted by 00pooterSS View Post
Early peak would indicate advanced cam timing. And those drop in truck cams usually have a lot of advance ground in already.
He's got a btr II 212/218 113+2 so that should close the intake valve at 37@0.050 or around [email protected] if it's installed dot to dot with a good timing set.

I really think the cam was just installed incorrectly. At least if it's that its a cheap fix lol

Although, it probably wouldn't have hurt to cc those used heads he bought before putting them on so we would know exactly how much static compression he is working with.

A good cranking compression test with the engine hot would tell us a lot though
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Old 12-23-2018, 07:08 PM
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Originally Posted by stockA4 View Post
He's got a btr II 212/218 113+2 so that should close the intake valve at 37@0.050 or around [email protected] if it's installed dot to dot with a good timing set.

I really think the cam was just installed incorrectly. At least if it's that its a cheap fix lol

Although, it probably wouldn't have hurt to cc those used heads he bought before putting them on so we would know exactly how much static compression he is working with.

A good cranking compression test with the engine hot would tell us a lot though
Yeah I was meaning since they already typically have advance ground in any accidental advance would really show and create issues where you may get away with it with a cam that is less aggressive on advance
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Old 12-24-2018, 08:02 AM
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the tuner hasnt emailed me back yet. dont know if hes on holdiday because of christmas or if he just doesnt want to deal with me.

you guys are making me paranoid about how I did the timing haha. Ive never done any work like this on a chevy so I took my time doing all the work. Plus the timing was super simple on this truck so Id be really embarassed if I did it wrong. I just set the crank gear and cam sprocket dot to dot and checked alignment with a small ruler. Used a Cloyes timing set
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Old 12-24-2018, 08:14 AM
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Also Im out here in Mexico on vacation so I probably wont be doing any testing on the truck for atleast a few weeks. I drove it for a day and a half straight filled to the brim with luggage. The truck has a camper shell on it so it was packed high and tight with tools and appliances with shoes and clothes packed in the crevices.

Truck had almost zero issues in case that says anything about the tune and work done on it. Only issue I had was a tps issue about half way out. in the middle of the night the truck went into limp mode and amd the idle was awful. Turned out to be a loose ground (the one behind the intake on the block. luckily I have smaller hands that could rwach back there) and was quickly fixed. I was back on the road in 10 minutes and have luckily had no issues since then.

When I get back I will see about visiting the tuner in person and doing testing on the engine. Until then I will continue to wait on the tuners response and keep a close eye on the truck for any other assembly errors
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Old 12-24-2018, 08:42 PM
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Whats the fuel mileage?
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Old 12-24-2018, 10:08 PM
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If you did it dot to dot and confirmed with a ruler you're likely fine. There are times the timing set itself or the cam may be a hair off but it's not going to hurt anything it just won't be optimal if the timing is a hair off.

The timing would have to be pretty far off for it to damage anything and you'd know.

Don't get too concerned, we're all just guessing over the internet.
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Old 12-24-2018, 10:08 PM
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Originally Posted by Ls7colorado View Post
Whats the fuel mileage?
14.5-15.5mpg on the hills. hard to get an accurate measurement for standard highway driving because i never spent more then half a tank on flat road. kept hitting lots of hills.

I drove from Sacramento all fhe way to Guadalajara

goes 75 mph @2200rpm on flat ground. I think 1500 rpm let me cruise at 55 mph on the country roads

Last edited by todoslosdiaz; 01-02-2019 at 10:05 PM.
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Old 12-24-2018, 10:13 PM
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Originally Posted by 00pooterSS View Post
If you did it dot to dot and confirmed with a ruler you're likely fine. There are times the timing set itself or the cam may be a hair off but it's not going to hurt anything it just won't be optimal if the timing is a hair off.

The timing would have to be pretty far off for it to damage anything and you'd know.

Don't get too concerned, we're all just guessing over the internet.
thats good to hear. Im glad to hear that I did the correct procedure

I will admit, I did not degree the cam. I had a deadline to meet and felt confident in the tolerances that are upheld by btr/comp cams and decided to throw it in as is. If I had more time I would have liked to degree it; Ill be making sure to do it on my next build so that I have no doubts about my worksmanship

Last edited by todoslosdiaz; 01-02-2019 at 10:04 PM.
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Old 01-02-2019, 09:58 PM
  #32  
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finally got a message back from the tuner. this is his response:

I believe your power is holding fairly flat from 5500-6000rpm. That was
the
powerband the engine made when optimized for area under the curve. I
could
artificially lower power at 5500RPM to make it peak at 6000, but you
would
have less power overall.

I tried advancing timing up to about 28 degrees but there were no gains
above 25 degrees. The power difference between 20 and 25 degrees was
approximately 3-4hp, so I left it around 22-23 degrees as a safe
middleground. A couple hp is not worth the increased cylinder pressures
and
more knock prone nature of the engine when being run at 25+ degrees.

I'm not sure what research you've done, but in general you can get away
with
running leaner a/f ratios at low RPM and run richer up top for
temperature
management. I tried running the engine leaner at 12.5:1 up top, but it
did
not gain any power, so I left it a bit on the richer side for safety and
reliability.
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Old 01-02-2019, 10:03 PM
  #33  
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so by his response it seems the engine was not showing excessive knocking but rather was not making enough horsepower for him to justify leaving it up that high. I still what could have happened if i had taken it to another tuner. I wanted to take it to get tuned at Newtech Performance over in Hayward, CA but they hung up on me when I tried to schedule a tuning session.
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Old 01-03-2019, 01:20 AM
  #34  
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I have a good running 4.8 cam only with a real tune, I'm not speculating, these engines want to rev when you mod them.

Your setup should be pulling strong to 7k, not peaking hp at 5400

Just to be clear, you have a sbe 4.8 Lr4
with 862 heads that you were told were milled 0.020? Anybody want to ballpark the cc of those?

Your cam should close the intake valve at around [email protected] installed straight up on the ground in 111 icl.

That cam in a stock headed 9.5:1cr 4.8 comes out to 7.7 dynamic compression

​​​​​​Even if you have as much as 10.5:1 static if the cam timing was still right on you would only be at 8.5 dynamic

You need to check your cranking compression and then degree the cam as I really think you have the cam timing off.

It would be helpful to know the true static compression ratio of the setup as well to determine your ideal icl.

The tuners generic bullshit response doesn't really help. You need to measure your engine and find someone else that isn't scared to wind it out and make power.

Before you said he told you it was at 20 degrees and now he's saying it's at 25? Which is it? Either way it should be pulling higher.

​​​​
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Old 01-03-2019, 06:16 AM
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Do you have a drag strip anywhere close? That will be better than going straight off duno numbers

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Old 01-03-2019, 08:44 AM
  #36  
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If his cam timing is off, its not from installation.
Each cam gear tooth is ~8 degrees. If a cam that small was advanced another 8 degrees over the built-in advance, it would be peaking at 3600-4000 RPM and would stop accelerating completely by 5500.

Its more likely that the cam timing off of from Comp than it is from an install error.
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Old 01-03-2019, 08:13 PM
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Originally Posted by JoeNova View Post
If his cam timing is off, its not from installation.
Each cam gear tooth is ~8 degrees. If a cam that small was advanced another 8 degrees over the built-in advance, it would be peaking at 3600-4000 RPM and would stop accelerating completely by 5500.

Its more likely that the cam timing off of from Comp than it is from an install error.

Thank you for that, I've always wondered how much each tooth is, had no idea it was that large. Awesome info. And knowing that I would fully agree (not that it matters if I do or don't lol)
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Old 01-03-2019, 09:03 PM
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I'm pretty sure the op replaced his timing set with an aftermarket one so I would hesitate to jump to any conclusions or take cheap shots at cam manufacturers over the internet just yet. Unless he checks his cranking compression and actually degrees the cam it's all just speculation. We know how the combo should perform and it isn't. I'd be more apt to blame the used heads he threw on than comp or btr at this point, I've had great success with their sticks in my stuff.
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Old 01-05-2019, 12:51 AM
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Originally Posted by stockA4 View Post
I'm pretty sure the op replaced his timing set with an aftermarket one so I would hesitate to jump to any conclusions or take cheap shots at cam manufacturers over the internet just yet. Unless he checks his cranking compression and actually degrees the cam it's all just speculation. We know how the combo should perform and it isn't. I'd be more apt to blame the used heads he threw on than comp or btr at this point, I've had great success with their sticks in my stuff.
I used a Cloyes timing set and got my heads from a reputable machinist from Stockton (Jason from Dynicron Cylinder Head Service). The heads were pressure tested, had new valve seals, new guides, 3 angle valve job, nitiride coated valves, 2 intake valves, and gm blue speings with new stainless steel retainers.

At this point the next thing I need to do is to get a compression test done but I am on vacations so that wont be done for a few weeks.

if that turns out fine I will be double checking the timing (even though lined up the dots and checked with a straight edge). If I remember I will take a picture to so that you can all see as well.

Also I will degree the cam while I have the cover off. I believe I read that sometimes they can be off by as much as 3 degrees (from what I remember reading in the pamphlet that came with the cam)

I have no suspicions on the quality of the heads that I installed but I anything is possible so I will keep that in consideration
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Old 01-05-2019, 01:29 AM
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Originally Posted by stockA4 View Post
I have a good running 4.8 cam only with a real tune, I'm not speculating, these engines want to rev when you mod them.

Your setup should be pulling strong to 7k, not peaking hp at 5400

Just to be clear, you have a sbe 4.8 Lr4
with 862 heads that you were told were milled 0.020? Anybody want to ballpark the cc of those?

Your cam should close the intake valve at around [email protected] installed straight up on the ground in 111 icl.

That cam in a stock headed 9.5:1cr 4.8 comes out to 7.7 dynamic compression

​​​​​​Even if you have as much as 10.5:1 static if the cam timing was still right on you would only be at 8.5 dynamic

You need to check your cranking compression and then degree the cam as I really think you have the cam timing off.

It would be helpful to know the true static compression ratio of the setup as well to determine your ideal icl.

The tuners generic bullshit response doesn't really help. You need to measure your engine and find someone else that isn't scared to wind it out and make power.

Before you said he told you it was at 20 degrees and now he's saying it's at 25? Which is it? Either way it should be pulling higher.

​​​​
Yes I have a 4.8 LR4 with 862 heads milled at .020. I think from what Ive read every .007 milled takes of 1cc so milling it .020 should being the ccc to ~58. This in turn would mean that my cr is about 9.94:1. I may be wrong, I do not claim to know this for sure. Its just what I have read on two other forums so anybody feel free to correct me.
Thank you for this bit of information about where the engine should be pulling to. From what I saw reading from other builds on 4.8s I was under the impression that it would be peaking to atleast the 6.5k range so Im glad to hear information that reinforces what I thought.

Youve given me a lot to think about. I will definitely be doing some measuring when I get back home. I have a cranking compression test at the top of my list for things to do and then will go on to degree the cam and set it to its ideal point. Ive been doing a lot of reading about the importance of degreeing a cam and have been seeing several examples of how certain tolerance differences within timing sets combined with tolerances within the cam can combine for a pretty large difference in actual icl and intended icl.

thank you for the information
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