Interesting cam timing observation
Thread Starter
Joined: Aug 2011
Posts: 4,729
Likes: 814
From: Portland, OR
Interesting cam timing observation For you motor heads who do your own work.
I added forged internals to the L33. I let my builder assemble the short block since the clearances etc are his work. He will stand behind it.
I assembled the rest. Installed cam, heads and so forth.
When I took it apart, the once tight Cloyes chain had loosened as expected. Since it is the hex adjust setup, I obviously had to re-degree it.
Originally set it up according to the cam card. Loose chain adds a bit of retard for sure.
So I advanced it 1 degree this time around.
The only change in the short block was forged pistons/rods. Lost a smidge of compression due to the valve reliefs. Didn't really need them with my combo, but they were there none the less.
Supposedly the L33 is now 9.75:1. And supposedly the stock L33 is 10:1.
Things I never verified with actual measurements.
The heads have been milled just .005" to get them flat. But this didn't change during this latest build.
Anyway.......
On the two step before, at 3300 it made 7 psi.
Now it makes 10psi. Very easily.
This is a Martin Smallwood cam. You listening Martin?
I got this together in time to make 4 passes, I drove like crap. Short shifted every pass, and the track was toast so it spun every pass.
But was surprised that it made more boost on the two step compared to last year. With a maybe 2 degree change in actual cam timing.
Stuff I pay attention to .......in slow motion. Ha!
Ron
I added forged internals to the L33. I let my builder assemble the short block since the clearances etc are his work. He will stand behind it.
I assembled the rest. Installed cam, heads and so forth.
When I took it apart, the once tight Cloyes chain had loosened as expected. Since it is the hex adjust setup, I obviously had to re-degree it.
Originally set it up according to the cam card. Loose chain adds a bit of retard for sure.
So I advanced it 1 degree this time around.
The only change in the short block was forged pistons/rods. Lost a smidge of compression due to the valve reliefs. Didn't really need them with my combo, but they were there none the less.
Supposedly the L33 is now 9.75:1. And supposedly the stock L33 is 10:1.
Things I never verified with actual measurements.
The heads have been milled just .005" to get them flat. But this didn't change during this latest build.
Anyway.......
On the two step before, at 3300 it made 7 psi.
Now it makes 10psi. Very easily.
This is a Martin Smallwood cam. You listening Martin?
I got this together in time to make 4 passes, I drove like crap. Short shifted every pass, and the track was toast so it spun every pass.
But was surprised that it made more boost on the two step compared to last year. With a maybe 2 degree change in actual cam timing.
Stuff I pay attention to .......in slow motion. Ha!
Ron
TECH Resident
Joined: Sep 2013
Posts: 994
Likes: 119
From: Mechanicsburg, PA
Very interesting. Makes you want to move it around and check the results each time. Any notable difference in the power curve? Less top end maybe? Guess you said you short-shifted so hard to tell.
Thread Starter
Joined: Aug 2011
Posts: 4,729
Likes: 814
From: Portland, OR
For you motor heads who do your own work.
I added forged internals to the L33. I let my builder assemble the short block since the clearances etc are his work. He will stand behind it.
I assembled the rest. Installed cam, heads and so forth.
When I took it apart, the once tight Cloyes chain had loosened as expected. Since it is the hex adjust setup, I obviously had to re-degree it.
Originally set it up according to the cam card. Loose chain adds a bit of retard for sure.
So I advanced it 1 degree this time around.
The only change in the short block was forged pistons/rods. Lost a smidge of compression due to the valve reliefs. Didn't really need them with my combo, but they were there none the less.
Supposedly the L33 is now 9.75:1. And supposedly the stock L33 is 10:1.
Things I never verified with actual measurements.
The heads have been milled just .005" to get them flat. But this didn't change during this latest build.
Anyway.......
On the two step before, at 3300 it made 7 psi.
Now it makes 10psi. Very easily.
This is a Martin Smallwood cam. You listening Martin?
I got this together in time to make 4 passes, I drove like crap. Short shifted every pass, and the track was toast so it spun every pass.
But was surprised that it made more boost on the two step compared to last year. With a maybe 2 degree change in actual cam timing.
Stuff I pay attention to .......in slow motion. Ha!
Ron
I added forged internals to the L33. I let my builder assemble the short block since the clearances etc are his work. He will stand behind it.
I assembled the rest. Installed cam, heads and so forth.
When I took it apart, the once tight Cloyes chain had loosened as expected. Since it is the hex adjust setup, I obviously had to re-degree it.
Originally set it up according to the cam card. Loose chain adds a bit of retard for sure.
So I advanced it 1 degree this time around.
The only change in the short block was forged pistons/rods. Lost a smidge of compression due to the valve reliefs. Didn't really need them with my combo, but they were there none the less.
Supposedly the L33 is now 9.75:1. And supposedly the stock L33 is 10:1.
Things I never verified with actual measurements.
The heads have been milled just .005" to get them flat. But this didn't change during this latest build.
Anyway.......
On the two step before, at 3300 it made 7 psi.
Now it makes 10psi. Very easily.
This is a Martin Smallwood cam. You listening Martin?
I got this together in time to make 4 passes, I drove like crap. Short shifted every pass, and the track was toast so it spun every pass.
But was surprised that it made more boost on the two step compared to last year. With a maybe 2 degree change in actual cam timing.
Stuff I pay attention to .......in slow motion. Ha!
Ron
Just saw this post, thanks!
TECH Fanatic
Joined: Jun 2013
Posts: 1,163
Likes: 16
From: Avon, Ohio
There is gains to made in cam timing on 95% of cars. Issue is, unless your sitting on an engine dyno (or have a motor that can have them manipluated while on a chassis dyno) its basically impossible to go and test gains. Its all trial and error.
TECH Fanatic
Joined: Feb 2015
Posts: 1,080
Likes: 178
I've read where some sprint car guys would set cam timing based on cranking pressure. It seemed to fall around 3-4 degrees advanced. I've always degree'd per grinders recommendation. Next time I'll check this out for data collection purposes.
Maybe the cam guys can comment on this?
Maybe the cam guys can comment on this?
TECH Enthusiast
Joined: Apr 2009
Posts: 723
Likes: 4
Running easily changed belt drives for a period I can say this, what the stated "Ideal" valve curtain is related to ICL is a misnomer & not always optimal for every combination. It's really that simple.
Vaporization, homogenation & compression, as well as rod to stroke ratio & flame propagation rates, all play a role here.
Cranking compression is a good reference but not a true indicator of dynamic compression. As a variable, ideal valve curtain is a range of ideals.
Vaporization, homogenation & compression, as well as rod to stroke ratio & flame propagation rates, all play a role here.
Cranking compression is a good reference but not a true indicator of dynamic compression. As a variable, ideal valve curtain is a range of ideals.
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9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
More importantly...
How repeatable was the 3300/7psi, over how many tests ? Same conditions etc ?
And likewise the 10psi ? No other tuning changes ?
And what was the cam timing with the loose chain...vs the new cam timing +1 ? How much had the chain stretched by ?
How repeatable was the 3300/7psi, over how many tests ? Same conditions etc ?
And likewise the 10psi ? No other tuning changes ?
And what was the cam timing with the loose chain...vs the new cam timing +1 ? How much had the chain stretched by ?
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Thread Starter
Joined: Aug 2011
Posts: 4,729
Likes: 814
From: Portland, OR
Stevie,
No tuning changes at all.
I did not measure cam timing at disassembly. So my numbers are an educated guess.
I log every pass, so I'm confident in the data.
I'll know more when we get back to racing in 2017.
Forced
I never tested cranking compression prior to adding the forged internals. I did test that after the race and got very low and confusing numbers.
then discovered my compression gauge was busted.
Other than short shifting the dang thing at 6k instead of 7k, the car ran normal.
No tuning changes at all.
I did not measure cam timing at disassembly. So my numbers are an educated guess.
I log every pass, so I'm confident in the data.
I'll know more when we get back to racing in 2017.
Forced
I never tested cranking compression prior to adding the forged internals. I did test that after the race and got very low and confusing numbers.
then discovered my compression gauge was busted.
Other than short shifting the dang thing at 6k instead of 7k, the car ran normal.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
You would wonder are quoted cam timings/grinds done to allow for some chain stretch...or is that up to the builder to decide.
But more importantly in the real world...does it really matter ?
I've never really seen many people test stuff like this, which you'd think for such a popular chain driven setup....there would be loads of testing done that would suggest how to install a new cam/chain.
That would make me think it really does make very little difference in most cases.
Even cars with VVT etc, they need to swing the cam sometimes 20-30deg to make a measurable difference. So a couple of degrees ? Would be hard to measure any difference, if any at all. Although I guess that might change the more extreme the build, and longer duration etc the cam.
But more importantly in the real world...does it really matter ?
I've never really seen many people test stuff like this, which you'd think for such a popular chain driven setup....there would be loads of testing done that would suggest how to install a new cam/chain.
That would make me think it really does make very little difference in most cases.
Even cars with VVT etc, they need to swing the cam sometimes 20-30deg to make a measurable difference. So a couple of degrees ? Would be hard to measure any difference, if any at all. Although I guess that might change the more extreme the build, and longer duration etc the cam.
FormerVendor
Joined: Aug 2014
Posts: 473
Likes: 1
The ambient air temp or something else about the motor found you those 3 extra PSI on the step.
In my experience you gotta swing one way more than a degree or two to be able to give credit to the cam timing for making a change like that.
In my experience you gotta swing one way more than a degree or two to be able to give credit to the cam timing for making a change like that.
Thread Starter
Joined: Aug 2011
Posts: 4,729
Likes: 814
From: Portland, OR
:-)
Going from 5.5* retarded to the cam card to 1* advanced from the cam card I picked up almost 12mph at the same boost level. No other changes made. Also went from 160ish cranking to almost 200 cranking compression. 4-5* made a HUGE difference in my case. (5.3)
Should have advanced it another 6.5* and picked up another 12mph lol. Do you know your IVC before and after? Edit. I think you were running a zr1 cam which already has a late IVC of 48 and if it was retarded 5.5 that would make it 53.5. That IVC is way late for a turbo car and a 5.3 if your not spinning it hard. Look at we're stock48 has the IVC on his turbo cams. It's in the 30s. The Zr1 has a blower so it can use a later one to make the power leak later.
Last edited by sbcgenII; Dec 10, 2016 at 04:24 PM.
Should have advanced it another 6.5* and picked up another 12mph lol. Do you know your IVC before and after? Edit. I think you were running a zr1 cam which already has a late IVC of 48 and if it was retarded 5.5 that would make it 53.5. That IVC is way late for a turbo car and a 5.3 if your not spinning it hard. Look at we're stock48 has the IVC on his turbo cams. It's in the 30s. The Zr1 has a blower so it can use a later one to make the power leak later.
It's definitely not as simple as retard the cam for more top end and advance for more power and less top end.
Assuming you started out with the optimal cam timing and advanced the cam 2*. You will still put out roughly 99.7%. Yet 2* retarded can drop output by as much as 3%. It's also not linear, so a 4* drop may drop output 5-6%. Also have to add break-in into the equation. Chains tend to retard another 1/2* or so. So I could have been as much as 7* retarded from the card, and as much as 8-9* away from optimal timing. Obviously whatever it was robbed me of a TON of power. Went from 139 @ 21lbs to 150.8 @21lbs... No other changes. 160-195ish cranking compression.
9 Second Club
Joined: Nov 2003
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From: Norn Iron
Thing is...without actual testing on our own engines, there is no way to say what cam timing will work best. And that isnt really practical for most. So we just stick to what the card suggests and hopefully it will work well.