4.8 LR4 dyno results and build evaluation
12-22-2018, 12:51 PM
#21
TECH Fanatic
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.
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.
12-22-2018, 10:42 PM
#24
TECH Fanatic
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
12-23-2018, 07:08 PM
#25
He's got a btr II 212/218 113+2 so that should close the intake valve at 37°@0.050 or around 62@0.006 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
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
12-24-2018, 08:02 AM
#26
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the tuner hasnt emailed me back yet. don’t 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. I’ve 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 I’d 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
you guys are making me paranoid about how I did the timing haha. I’ve 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 I’d 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
12-24-2018, 08:14 AM
#27
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Also I’m 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
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
12-24-2018, 10:08 PM
#29
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.
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.
12-24-2018, 10:08 PM
#30
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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
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.
12-24-2018, 10:13 PM
#31
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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.
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.
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; I’ll 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.
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.”
“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.”
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.
01-03-2019, 01:20 AM
#34
TECH Fanatic
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 62@0.006 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.
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 62@0.006 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.
01-03-2019, 08:44 AM
#36
Restricted User
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.
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.
01-03-2019, 08:13 PM
#37
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.
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)
01-03-2019, 09:03 PM
#38
TECH Fanatic
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.
01-05-2019, 12:51 AM
#39
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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.
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
01-05-2019, 01:29 AM
#40
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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 62@0.006 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.
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 62@0.006 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.
Thank you for this bit of information about where the engine should be pulling to. From what I saw reading from other builds on 4.8’s I was under the impression that it would be peaking to atleast the 6.5k range so I’m 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. I’ve 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