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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Anyone know of an adjustable timing chain that can get 4° at the cam? Somehow my factory GM chain is resulting a 4° retarded cam install.
There seems to be some mystery regarding what chain will fit a Vortec block, so I'm looking for first-hand experience. Anyone with a ZZ series engine would have this block...
All the single roller chains I'm seeing only get me 2° at the cam, so I'd need a double roller I see double rollers that would give me the 4° at the cam, but I keep hearing about interferences with double rollers and the block.
Re: Adjustable timing chain for 96-99 Vortec block
Altering cam timing is done by either using an offset crankshaft key or offset bushings in the camshaft gear.
The only different timing chains that I am aware of are slightly shorter chains for the situation where a block's main journals have been excessively line bored.
This is the grinding you need to do for double roller timing set clearance.
Last edited by NoEmissions84TA; 10-15-2021 at 07:37 PM.
Re: Adjustable timing chain for 96-99 Vortec block
Grinding on the block is something I'm not really inclined to do. It's a GM ZZ/HT 383 short block that hasn't been fired yet and is still under warranty.
Yeah, I'm 100% positive. I've degreed in two cams with 110° intake centerlines advertised on the cam cards (one Crower and one Comp) with the factory GM timing chain that came with the short block and they're both measuring at 106°.
Re: Adjustable timing chain for 96-99 Vortec block
Lobe separation angle and intake centerline are two different things.
If your lobe separation is 110°, ground 4° advanced, then you will actually measure 106°.
And while you are measuring, you MUST rotate the crank in the clockwise direction only.
If you go backwards, then all bets are off.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by NoEmissions84TA
Lobe separation angle and intake centerline are two different things.
If your lobe separation is 110°, ground 4° advanced, then you will actually measure 106°.
And while you are measuring, you MUST rotate the crank in the clockwise direction only.
If you go backwards, then all bets are off.
Please post some pictures of what the pointer is showing on the degree wheel.
LSA on this cam is 114. With 4 deg advance I should read 110, no?
Here's my entire process documented. And yes I only approach measurement points in the clockwise direction.
Re: Adjustable timing chain for 96-99 Vortec block
LSA is irrelevant to "advance".
LSA is the # of CAM degrees that the exhaust valve reaches peak opening, RELATIVE TO peak intake opening.
"Advance" is the relation between intake peak opening, and ... something. Problem is, there's NO STANDARD WHATSOEVER for what constitutes "0°" for that "something".
Best we can do is, compare the end result of some combination of cam and timing set, to the end result of some random stock cam and timing set.
That said, in the early days of emissions, 71 or so and maybe earlier in the California cars when those were still different, GM basically dropped all cams except the 929; and introduced a "new" timing set, that retarded the same old 60s 929 by 4°. This was the original attempt at EGR without using external devices, and/or augmenting device-based EGR.
So, in 2021, WHAT REALLY IS 0° of intake lobe centerline? If you don't have a hard nailed-down number for THAT, then any number you claim for "advance", is ... pretty much garbage.
So, if you want to talk about your cam timing, FORGET that "advance" garbage meaningless term altogether; and instead, discuss your cam's INTAKE LOBE CENTERLINE, aka ICL.
In 2021, one might claim that "0°" intake lobe centerline, is 110° ATDC. (keeping in mind that ICL is in CRANK degrees, whereas LSA is in CAM degrees) Or, maybe some other number. I'm no authority on that; I'm not going to declaim that 110°, or any other number, is "straight up". But that seems to be some kind of a consensus, so even if not a "standard", it's possibly a good place to start. Regardless, your cam grinder will tell you he designed his cam to be installed with its ICL at xxx°, so THAT'S 0° for YOUR CAM.
Of course, if your intake centerline is, let's say, 110° ATDC (i.e. the intake reaches peak opening 110 CRANK degrees after the TDC where the int valve is starting to open, i.e. the piston a bit more than halfway down the bore), and your LSA is 114 CAM degrees (i.e. 228 CRANK degrees BEFORE the intake lobe centerline, i.e. a bit before the piston reaches halfway up during the exhaust stroke BEFORE TDC), then at least you have some hard factual numbers as to when this happens with respect to that other thing.
"Advance" is just about worthless as a meaningful cam design parameter these days. Instead, focus on the ACTUAL valve event timing, and whatever adjustments you need to make to your timing set (bushings and whatnot) to achieve that.
EFFFFF "advance". What ICL are you attempting to achieve?
Re: Adjustable timing chain for 96-99 Vortec block
If using the Lobe Center method of degreeing, cam should be installed on an intake centerline of 110°
You have used that GM timing set for all of these measurements, correct?
I suspect that the timing set is mismarked. 1 tooth on the cam gear is 10° IIRC.
If I am right, then there should be 36 teeth on that gear. I suspect the dot got marked 1 tooth off.
So indulge me here - the purple line is where you should be - nearly 10 degrees off.
Reset the timing set to be 1 tooth off to get the pointer to match the purple line. Forget about the dot.
Then recheck everything again to see if it agrees with the cam card. I suspect you will only be within 1 degree off.
Last edited by NoEmissions84TA; 10-15-2021 at 10:13 PM.
Re: Adjustable timing chain for 96-99 Vortec block
I had bought a Cloyes adjustable timing chain set and decided to try it out this morning. Supposed to give -4, 0, and 4 crank deg adjustablility.
Something seems off though...
When I have the piston at 0 TDC, the dots are lining up like the photo below. However the instructions are showing the crank dot at 12 and the cam dot at 6.
In order to get the dots to line up like the instructions I have to rotate the crank 4 deg CCW from TDC. Maybe that's where the 4 deg advance comes from?
Re: Adjustable timing chain for 96-99 Vortec block
Looks to me like both the cam and the crank are somewhat past TDC in your photo. Might wanna try a straightedge between the centers of the crank and cam, for more precision. Might have been A Good Idea to verify the crank key location before the heads went on: the keyway is supposed to be EXACTLY aligned with the #1 rod throw, which if the block is bored right (cylinders not offset one way or the other as they often are) then it should point EXACTLY 45° past straight up (1:30) when #1 & #6 are at TDC. Obviously if that's wrong, then everything to do with the timing set and its "marks" is going to be skewed as a result. Or if they're not on yet, go ahead and do that.
If there were 10 teeth on the crank sprocket, then each tooth would be 36°. (the new math: 360 ÷ 10 = 36)
Looks to me like there's ALOT more than 10 teeth on the crank sprocket, in any case. I don't know offhand how many though; I've never had occasion to count them. Looks kind of about like 20 or 22 or thereabouts.
LSA is ground into the cam. It's the amount of rotation, in CAM degrees, between the int lobe center and the exh lobe center. Can't be changed by the installer. Only the ICL is subject to that. Remember also, ICL is specified in CRANK degrees, but LSA is given in CAM degrees. Each of which is 2 crank degrees.
20° would only be right if there are 18 teeth on the crank sprocket and 36 on the cam one. Which might be true as far as that goes; you can count them and see. Then, 1 tooth on the cam would be 10 degrees of cam rotation, which is also 20 degrees of crank rotation.
If you have to rotate the crank 4° past "the right place" to get the cam to "the right place" intake lobe centerline), then the cam is RETARDED 4 crank degrees from "the right place". You need 4 more degrees of "advance".
Keep in mind also, as the engine breaks in and wears and ages and the chain "stretches", the chain DOES NOT tighten up. The ONLY direction in which the cam timing will change, is to RETARD from wherever you left it at installation. If you're doing nothing but racing it, i.e. it will get VERY FEW miles put on it, then that's probably not a real big deal. For a street car though, you probably want to install it something around 4° ADVANCED from wherever you think it should be (the cam mfr's recommendations for example), such that as time goes by and things slacken up, it will end up near about where it was designed to be. Otherwise, if you put it at that spot at installation, after a few trips to the moon and back, it'll be significantly retarded, for the whole rest of its life. IOW it'll be right for the first day or 2 then retarded for forevermore.
Re: Adjustable timing chain for 96-99 Vortec block
Just put the crank gear to full retard on the adjustable set and the Comp Cam mostly came in to spec
110 ICL per the cam card.
22 deg intake valve open at .006 tappet lift per the cam card.
66 deg intake close point .006 tappet lift vs 62 deg on the cam card. A little off. If I put the degree wheel at 62 deg, I get .008 tappet lift. So I guess the closing ramp is pretty sensitive to measurement error... 4 deg for .002 lift...
But if I can get everything this close on the Crower, I'll probably call it day on that.
I'll reinstall the Crower later today and see what I get.
Re: Adjustable timing chain for 96-99 Vortec block
https://www.chevydiy.com/cam-drives-...ps-techniques/
From the article:
The small block relies on a crank gear with exactly half the number of teeth on the crank as on the cam. This spins the crankshaft at exactly half engine speed. The stock Chevy crank gear counted a mere 18 teeth on the crank gear with 36 teeth on the cam gear using a link belt type chain to connect the two. The Achilles heel of this system focused on the aluminum cam gear that employed a nylon covering over the teeth to prevent wear and reduce noise. The problem was that eventually, the nylon succumbed to heat and wear, which caused the plastic teeth to crack, allowing the cam to easily slip a tooth or two. Chevy redesigned the cam drive in 1967, going to a steel gear with excellent durability. But this also spurred the aftermarket to create its own versions.
Along with much stronger single-roller and double-roller chain designs, racers also wanted an adjustable drive mechanism that would allow the builder to easily change cam phasing relative to cylinder Number One and top dead center (TDC). This phasing requires precise location of the cam since a mere 0.005-inch movement of the camshaft changes the cam phasing one degree. In the early days, machinists created offset bushings that could advance or retard the camshaft between 1 and 8 degrees. You didn’t need to create more than 8 degrees of freedom since on the original small-block camshaft gear each tooth represented 10 degrees of camshaft movement since the stock wheel had 36 teeth. Since then, manufacturers have added more teeth for more strength, reducing the degree spread even further. For example, a 44–tooth cam gear offers a mere 8.18 degrees between teeth. This is another reason why missing the proper location by even one tooth on the cam gear makes such a drastic difference in cam phasing.
Re: Adjustable timing chain for 96-99 Vortec block
I suggest you use the intake centerline method only. If using the Lobe Center method of degreeing, cam should be installed on an intake centerline of 110°
It's just like finding true TDC (which I saw that you can do accurately), except you are checking some distance down on either side of the cam lobe at max lift.
For example, let's use .050" down on either side of your lobe. You read, let's say, 100 and 120 degrees. Then halfway between is 110 degrees. KISS method.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by ULTM8Z
Grinding on the block is something I'm not really inclined to do. It's a GM ZZ/HT 383 short block that hasn't been fired yet and is still under warranty.
Yeah, I'm 100% positive. I've degreed in two cams with 110° intake centerlines advertised on the cam cards (one Crower and one Comp) with the factory GM timing chain that came with the short block and they're both measuring at 106°.
If you measured 106 degrees where you installed the above Camshaft... then it is 4 degrees advanced in relation to the 110 Intake Center Line.
If this Cam has a 110 ICL and 110 LSA (the ECL will also be 110, and there is no advance "ground into the Cam").
Comp cams may grind the cam with a 106 ICL and a 110 LSA (4 degrees "ground into the Cam").
Last edited by vorteciroc; 10-16-2021 at 07:17 PM.
Re: Adjustable timing chain for 96-99 Vortec block
The Gen-1 SBC is an "Over Head Valve" Engine with one Camshaft (without being able to be phased into another relative position).
This makes the Lobe Separation Angle a fixed angle that can not be changed unless the Camshaft is reground.
To keep things simple, LSA is represented as the angle (camshaft degrees, not crank degrees) between the center of an Intake Lobe (peak Lift), and the center of an Exhaust Lobe (peak Lift).
Now what confuses people are the Terms Intake Center Line and Exhaust Center Line.
In reality both of these numbers can not change unless the Camshaft is reground.
Just as the LSA can not change, neither can the ICL or ECL...
The Camshaft Lobes can not move.
Because of the terminology used in the process of Camshaft degreeing... confusion occurs.
When the term ICL is used here, it is actually incorrect.
When degreeing the Cam; the term ICL is just a reference point of the valve events in relation of crank position.
It is the position that the Camshaft is installed in, compared to the Crankshaft position.
If the Camshaft being used has a 110 ICL and you installed it in the position of 106 degrees...
You did not actually move the ICL (it can not be moved).
You are simply installing the Camshaft 4 degrees ahead (advanced) of the intended position (the actual center of the Intake Lobe being measured).
Think of it as the Camshaft is installed 4 degrees before the actual ICL (the math does not always work this way, but for simplicity it works).
Also do not confuse the ICL and LSA.
If I have an ICL of 110 and a ECL of 110, the LSA will be 110 (add ICL and ECL, then divide by two).
If the ICL is 106 and the LSA is 110...
The ECL has to be 114.
Last edited by vorteciroc; 10-16-2021 at 07:13 PM.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by NoEmissions84TA
I suggest you use the intake centerline method only. If using the Lobe Center method of degreeing, cam should be installed on an intake centerline of 110°
It's just like finding true TDC (which I saw that you can do accurately), except you are checking some distance down on either side of the cam lobe at max lift.
For example, let's use .050" down on either side of your lobe. You read, let's say, 100 and 120 degrees. Then halfway between is 110 degrees. KISS method.
I hear ya...
I just wanted to make sure everything is correct on the cam before I commit to putting it in and then the engine in the car. I only want to to this once.
Just finished measuring the exhaust lobe and checking LSA on the comp cam. I got 112.5 where the cam card says 112.
At least that validates my process...
Put in the Crower just now...
Had to move the crank gear to full advance, but...
I got 108.5. That's as far advanced I as I can get this evidently. But I'm not going to sweat 1.5 deg at this point. I'm just glad I convinced myself finally that I'm doing it correctly.
The factory setting on the cloyes crank gear had the intake centerline at 112, so looks like the 110 is not achievable. So I have to choose between being a couple deg advance or retarded. Figure I'll go retard and help the top end a bit. With the 114 LSA I already know this thing will idle smooth.
Actually measured the exhaust centerline and then calculated LSA... should be 114... I'm getting 114.5. Nearly dead nuts.
There must be something funky with that GM L31 Vortec crank gear that came with the engine. What constitutes the "factory setting" on that gear is pretty different than what is the "factory setting" on the Cloyes. Which is what was probably throwing me for a loop earlier...
Re: Adjustable timing chain for 96-99 Vortec block
For a double check, you can do #6. Pistons #1 and #6 are at TDC at the same time. It's just that one is on the intake stroke and the other is on the firing stroke.
I agree - "something" is off with those gears. Who cares about the dots or marks. What is important is that you got the thing installed as it was designed to be.
This is exactly why you should degree the camshaft. You will never know it's right unless you actually measure.
Last edited by NoEmissions84TA; 10-16-2021 at 07:44 PM.
Re: Adjustable timing chain for 96-99 Vortec block
I have degreed a few camshafts. NEVER was I able to exactly match the numbers on the cam cards.
The ISKY cam in my 334 ended up "OFF" by something like 1.5 degrees in opposite directions - if you know what I mean.
You can only compensate in one direction, so I had to call it good.
FWIW, I had to drill the cam gear to use a bushing.
Last edited by NoEmissions84TA; 10-16-2021 at 08:07 PM.
Re: Adjustable timing chain for 96-99 Vortec block
Yeah I didn't do this with the comp cam when I installed it about 20 years ago and discovered now that I've been running it 4 deg retarded all this time. Which now explains why it seemed like it idled a tad bit rougher than I would have expected for a 212@.050 in 5.7 with a 112 LSA. It was smooth but not as smooth as I would have expected...
Also seat of the pants it felt stronger above 5500 than I would have expected for a cam that small too...
Re: Adjustable timing chain for 96-99 Vortec block
interesting comparison between the L31 gear and the Cloyes "factory" setting...
The Cloyes is the installed one and the L31 is out by itself... There's a ~5-6 deg relative retarding on the L31 relative to the factory setting on the Cloyes. Which probably explains how the L31 resulted in a 106, and the Cloyes 4 deg advance resulted in a 108.
Re: Adjustable timing chain for 96-99 Vortec block
Leave the protractor as it is, but rotate the crank so that the woodruff key is where it is in the first image - on a clock, the 1:30 position.
In other words, make the two images match. Then you can do a true comparison. It looks like you need to rotate the crank 120 degrees clockwise to do this.
Last edited by NoEmissions84TA; 10-16-2021 at 10:11 PM.
Re: Adjustable timing chain for 96-99 Vortec block
You need #1 to be at TDC, which is when the key is at 1:30.
Your gear has 3 positions - 0, -4, and +4 degrees.
Each position will have a different "dot" symbol at the 12 o'clock position.
Make sure that tooth aligns with 90 degrees on the protractor.
You're a little off here, but this is what I need you to do. The "dot" at 12 o'clock will be an "A". Line that up and see what the protractor reads.
Last edited by NoEmissions84TA; 10-16-2021 at 10:27 PM.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by NoEmissions84TA
You need #1 to be at TDC, which is when the key is at 1:30.
Your gear has 3 positions - 0, -4, and +4 degrees.
Each position will have a different "dot" symbol at the 12 o'clock position.
Make sure that tooth aligns with 90 degrees on the protractor.
You're a little off here, but this is what I need you to do. The "dot" at 12 o'clock will be an "A". Line that up and see what the protractor reads.
This image above is with the piston at TDC. The image below is with the cam sprocket dot lined up with the triangle on the crank sprocket. The triangle represnts the 4 deg advance position.
I tore down the setup this morning, re-set everything up, re-established TDC at the piston, then remeasured everything again this morning and I'm still getting the 108 ICL and the same intake/exhaust open/close events. Just to make sure I wasn't going crazy yesterday.
Re: Adjustable timing chain for 96-99 Vortec block
Factory cam degreed in 5° advanced on the L31 I bothered to degree with the factory timing set. May be why the marine cam that has similar specs but 2° tighter LSA had a much more noticably thumpier idle with the GM performance timing set. I had to advance it 4° with an offset bushing to get it close to the 106 ICL GM calls for.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by ULTM8Z
interesting comparison between the L31 gear and the Cloyes "factory" setting...
The Cloyes is the installed one and the L31 is out by itself... There's a ~5-6 deg relative retarding on the L31 relative to the factory setting on the Cloyes. Which probably explains how the L31 resulted in a 106, and the Cloyes 4 deg advance resulted in a 108.
I think you are saying advance and retard backwards. Lets say the spec is 110 ICL. If it drops in at 114 ICL that is 4° retarded. If it drops on at 106 ICL, that is 4° advanced. My L31 timing sprocket has 5° advance built in. That 5° of built in advance is probably why so many people that cam L31s think they cannot build good power on the top-end. Drop a cam in it that is ground 4-5° advanced and it is suddenly 10° advanced and acts way smaller.
There are also two different L31 timing sets. The later ones could have negated the 5° cam advance and been why the HP rating changed in 97. 250 hp in 96 and 255 hp in 97.
Your protractor angle is off on the Cloyes set because you are not measuring relative to the keyway slot you are actually using. Your crank is 1/3 turn off from TDC. Need to measure from the keyway slot you are using to drive the sprocket.
Re: Adjustable timing chain for 96-99 Vortec block
These pictures are all academic at this point for the most part.
But I was thinking a little more....The Crower cam was designed around a 350, so I figure with a 383, retarding the cam by 2 deg will probably help adapt it more to the 383 since the 383 doesn't need as much low end help with the longer stroke.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by ULTM8Z
These pictures are all academic at this point for the most part.
But I was thinking a little more....The Crower cam was designed around a 350, so I figure with a 383, retarding the cam by 2 deg will probably help adapt it more to the 383 since the 383 doesn't need as much low end help with the longer stroke.
The cam that is now in my 383 was spec'd and ground for a 350. It is 218/228 @ 0.050 on a 108 LSA and 104 ICL. It lined up 2° retarded from spec with the GM Performance ala ZZ4 timing set. I just chose to run it as is. 11:1 383 with Rhoads V-Max lifters has plenty of low end cylinder pressure even with the 2° retarded cam. Actually about to breathe life back into it today. Have a starter, a header and a few other things to bolt on it before I hit the key for its first time to run under the factory L31 intake. Just porgrammed the 2004 6.0L Express van Green/Blue P59 PCM with a 2005 Mexican 1-ton GMT800 L31 tune for a startup tune to run it last night. I pulled the 232/244 @ 0.050 Lunati Bootlegger out to give me more low-end torque, smoother less noticeable idle for less questions at smog time and a powerband more suited to the L31 truck manifold. Had to go with the mexican L31 file because the factory based ignition is going back onto it.
My cam should have been at 104°. Its at 106.5°. Its 2.5 degrees retarded but I don't even stress the 1/2 degrees.
At 225 psi cranking compression I am not going to lose any sleep over 2.5° retard even if it wears to be 4-5° within the next 20-30K miles. With the 2,800 high str stall its going to be an beast on the low end anyway compared to a L31 with a stock stall.
Re: Adjustable timing chain for 96-99 Vortec block
ugh... my head hurts from all of this... lol.
Any rate, I re-did the crank gear to the "factory" setting and now I'm at 112.
Wow, so that means with the factory L31 gear, sitting at 106, I would have been 4 deg advanced on top of the 4 deg already ground into the cam. This 383 probably would have fallen on its face above 4500...
Definitely glad I degreed this thing in and got it right, but this is my last cam install!!! lol...
Re: Adjustable timing chain for 96-99 Vortec block
I'm glad this is finally solved.
And we potentially discovered why so many 383s fall flat on their face above about 5200 rpm --> the L31 timing sprocket has 5° advance built in. That 5° of built in advance is probably why so many people that cam L31s think they cannot build good power on the top-end. Drop a cam in it that is ground 4-5° advanced and it is suddenly 10° advanced and acts way smaller.
There are also two different L31 timing sets.
Thanks for confirming this Fast355.
Re: Adjustable timing chain for 96-99 Vortec block
ULTM8Z - look back to # 14 to the last part of what Sofa wrote.
The timing chain will stretch with use - and this will RETARD the cam timing as a result.
You might want to set it back to 108 degrees, because after a little break-in, you will be at 110 degrees.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by NoEmissions84TA
ULTM8Z - look back to # 14 to the last part of what Sofa wrote.
The timing chain will stretch with use - and this will RETARD the cam timing as a result.
You might want to set it back to 108 degrees, because after a little break-in, you will be at 110 degrees.
Yeah but over what period of time? My guess is this car will not even see 1000 miles per year...
Re: Adjustable timing chain for 96-99 Vortec block
BTW, the 2 images below show the apples-to-apples comparison I was looking for.
This clearly shows the 5 degrees advance built into the GM L31 timing set >>> 51 vs 45 degrees.
Or maybe now I am confused. My head hurts too.
Last edited by NoEmissions84TA; 10-17-2021 at 04:06 PM.
Re: Adjustable timing chain for 96-99 Vortec block
First, GM never altered the Timing-Sets with any Valve-Event Advance.
Second, the Crankshaft Sprocket alone can not be used to establish an Advance or Retard.
Both the Camshaft Sprocket and Crankshaft Sprocket have to be used for comparison.
If that GM Crank Sprocket is (lets call it 5 degrees for simplicity) advanced...
The GM Cam Sprocket may be 5 degrees moved, compared to the aftermarket Gear-Set.
Both Gears are needed to establish Cam to Crank relationship/ position.
Re: Adjustable timing chain for 96-99 Vortec block
GM never altered the Timing-Sets with any Valve-Event Advance.
Pretty sure that's not true.
Pretty sure you're younger than me. Maybe ALOT younger.
GM changed their timing set in the early, VERY EARLY, emissions era. 71 or so for 49-state cars, possibly earlier for California cars. 4° later cam alignment in the later version. I've measured WWWWWWWWAYYYYYYYYYYYYY too many of em to be convinced otherwise.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by vorteciroc
First, GM never altered the Timing-Sets with any Valve-Event Advance.
Second, the Crankshaft Sprocket alone can not be used to establish an Advance or Retard.
Both the Camshaft Sprocket and Crankshaft Sprocket have to be used for comparison.
If that GM Crank Sprocket is (lets call it 5 degrees for simplicity) advanced...
The GM Cam Sprocket may be 5 degrees moved, compared to the aftermarket Gear-Set.
Both Gears are needed to establish Cam to Crank relationship/ position.
I wonder...
The positioning of the dowel hole directly opposite one of the bolt holes appears to be typical, as well as alignment of that hole centerline to the teeth. It seems like all the cam timing is controlled by the relationship between the keyway on the crank sprocket and the teeth.
What I know for sure is that the L31 timing chain set advances the cam by 4-5 deg over what the cam grinders appear to expect to see out of factory setting.
This the L31 cam sprocket that I currently have.
This is a Summit brand sprocket, part of a double roller adjustable set that bought, but will be sending back since I don't need it.
This one is an image of some SBC sprocket I found online...
Even the LS cam sprockets seem to follow the same basic formula?
Re: Adjustable timing chain for 96-99 Vortec block
Small cam seems to behave quite well for me with the EFI.
First startup of the 383 in the Express with the factory L31 based manifold and ignition. Running on a Green/Blue P59 out of a 2004 DBC 6.0L van. So far I have segment swapped the 4L85E, turned the VATS off, set the injector flow rate to match the AUS Injection 48 lb/hr spider and copied the MAF table from a 2002 L31 van into the 2005 Mexican tune. Had to populate the idle tables that were not used with the manual trans. Other than that the mexican cal is relatively stock GM issue. Still needs some fueling work and some timing advance as its running about 4-8° BTDC at idle.
10-15-2021, 07:11 PM
If you don't have a hard nailed-down number for THAT, then any number you claim for "advance", is ... pretty much garbage.
You got it! 
4° later cam alignment in the later version. I've measured WWWWWWWWAYYYYYYYYYYYYY too many of em to be convinced otherwise. 
