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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!
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by Fast355
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.
Re: Adjustable timing chain for 96-99 Vortec block
That's a pretty tight LSA (bad for idle quality), but the cam is also pretty advanced in timing (good for idle quality).
I've always been curious how those two cam characteristics play together....
Though by the sound of the engine in your video, it does seem to have a very noticeable idle. So the tight LSA may be overriding the advanced cam timing?
Re: Adjustable timing chain for 96-99 Vortec block
Interesting... Crower says to go 2 deg advanced if I had to choose between that or 2 deg retarded. He said if I go 2 deg retard, it'll tend to feel lazier compared to advanced (not a huge difference apparently, but he said I'd be happier on the advanced side).
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by ULTM8Z
That's a pretty tight LSA (bad for idle quality), but the cam is also pretty advanced in timing (good for idle quality).
I've always been curious how those two cam characteristics play together....
Though by the sound of the engine in your video, it does seem to have a very noticeable idle. So the tight LSA may be overriding the advanced cam timing?
I think it will tame out alot when I work on the timing and fueling. Its only idling at 6-8° BTDC in that video. I noticed the idle was very timing sensitive when I had it on the engine stand running it. At 31° idle timing I was pulling nearly 19 in/hg vacuum at 750 rpm.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by ULTM8Z
That's a pretty tight LSA (bad for idle quality), but the cam is also pretty advanced in timing (good for idle quality).
I've always been curious how those two cam characteristics play together....
A tight LSA means little in and of itself. The seat to seat values have to factored in to arrive at the overlap amount. That's where the idle quality comes into play.
To take in all in, LSA (fixed) and duration (also fixed) combine to determine that overlap.
After the overlap, the intake valve closing point is one of those cam events that define an engines running and performance qualities. As you've seen, the IVC part is changeable and with it all of the other valve timing events.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by ULTM8Z
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?
The Timing-Mark is not clear in these images...
The Dowel location without the Timing-Mark shown, does not help.
At least one of the Images clearly shows the back-side of the Gear...
and there is no Timing-Mark normally on the back-side.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by sofakingdom
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.
Yes, I am younger than you.
My certifications/ education only had to go back 10-Years before I started at GM.
I went back 15-Years, so that I would be educated from 1980 to present (being 1995).
I can only really say what I have learned...
I am not well educated in any fine-details prior to 1980.
So you are possibly entirely correct on a 1970-Era Timing-Set.
Re: Adjustable timing chain for 96-99 Vortec block
Lastly regarding Timing-Sets and Camshafts...
These Parts are produced in high numbers and errors in manufacturing occur.
This is one of the more significant reasons why Assembly-Instructions recommend validating the Valve-Events.
Re: Adjustable timing chain for 96-99 Vortec block
Not sure where you ended up with this but am wondering if you've considered the Cloyes Hex-A-Just timing set.
It has multiple crank keyways for adjustment at the crank as well as means to vary the cam timing at the cam.
Plus it's a quality piece.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by skinny z
Not sure where you ended up with this but am wondering if you've considered the Cloyes Hex-A-Just timing set.
It has multiple crank keyways for adjustment at the crank as well as means to vary the cam timing at the cam.
Plus it's a quality piece.
I ended up using a Cloyes L31 Vortec block compatible single roller with -4, 0, and 4 cam timing settings. The problem with double rollers in a Vortec block is you have to grind on the block to get enough clearance for the cam sprocket area and I didn't want to be grinding on an engine that's still under GM warranty and hasn't even been fired up yet.
But I'm now in a situation where I can get to 108 or 112 intake centerline, but not the 110 specified in the Crower cam card. Crower recommended for that choice that I advance to 108 rather than retard to 112 as they said 112 would feel comparatively lazier throughout the useable RPM range vs the 108 setting. So I'm going to set it to 108. For the way I drive the car, I'd rather have it feel peppier where I spend 90% of my time and sacrifice a little at the top end.
Probably will be easier to tune as well... I had my Miniram setup dialed in really well with the 350, so hopefully the change to the 383 with this mild cam (213@.050 on a 114 LSA and 1.6 roller rockers) will be an easy retune (particularly on the AE fueling which was a b*tch to get right with the Miniram).
It was mentioned here earlier too that the chain loosening over time would probably retard the cam timing by 2 deg anyway, so eventually I'd end up at the 110.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by ULTM8Z
The problem with double rollers in a Vortec block is you have to grind on the block to get enough clearance for the cam sprocket area and I didn't want to be grinding on an engine that's still under GM warranty and hasn't even been fired up yet.
Re: Adjustable timing chain for 96-99 Vortec block
Originally Posted by ULTM8Z
Supposedly it's all the Vortec blocks...
Yours is a double roller chain?
I had to use the 9-1157
I have the GM Performance equivalent but it only has one fixed setting, no advance or retard setting. Cannot run a double with a stock reluctor ring.
Also got it good and warm yesterday, idling at about 185°F. I have bolted the exhaust to the collectors and have closed loop enabled. I disabled the catalyst warm up spark retard. Idle tamed out a bit. Open cutouts fwiw. Fuel trims at idle are about -15% currently.
Re: Adjustable timing chain for 96-99 Vortec block
It is going to depend on the Casting used for the particular 1996+ Vortec Cylinder-Block...
and the Brand/ Design of the Double-Roller Timing-Set.
Most Castings will resemble the image below...
Where the surface for the Oil Passage Plugs, is the same surface for the Camshaft Retainer Plate.
The area just above the the center positioned Oil Passage Plug, most often needs to be clearanced.
Not all of these Blocks look like the Image above.
When I Purchase these Blocks in person, I try to pick the one that resembles the Image below:
There is already additional clearance in the area of concern.
I personally find that...
When using a Timing-Set that uses a Torrington-Bearing, instead of a Thrust-Surface with Oil-Grooves...
Less, or no clearancing will be needed.
Also some of the Vortec Cylinder-Blocks sold over the Parts-Counter, resemble older Roller-Camshaft Cylinder-Blocks.
Shown below is what the older Cylinder-Blocks looked like in comparison:
The Surface for the Oil Passage Plugs is recessed compared to the surface for the Camshaft Retaining Plate.
Re: Adjustable timing chain for 96-99 Vortec block
I spent a couple of hours messing with it today. Hooked up a water hose to the heater return on the water pump and dumped the waste water out of the shop to really get all the heater core, and lines really flushed out today. I don't want any pf that crap in my new radiator. I got it dialed in pretty good after adding a 4" MAF into the mixture. Also figured out the bog off-idle when first starting to open the throttle. Transmission abuse mode was kicking in even in Park and cutting the ignition timing to negative 15 or 15 after top dead center. Disabled abuse mode and it rips now. Its taken on some nice exhaust crackle and popping going into decel fuel cut as well. On throttle snap up to fuel kill at 5,200 it leaps up the RPM band. To hit the air/fuel ratio target the MAF is reading 410 gms/sec at 5,200 rpm. Given the formula of 1 gm/sec is 1.2 hp, that means I am feeding it 492 hp worth of fuel. Predicted torque on the torque model is reaching 512 ft/lbs at about 3,700 rpm. The cyl/air reading holds pretty flat at 1.03-1.09 gms/cyl from about 3,000-5,200. It is moving a ton of air through the engine and the exhaust just booms because of it. I have the base idle timing now programmed at about 34 BTDC and it seems to idle best around that. Idle compensation spark has been reduced. Both really seemed to help stabilize the idle.
10-18-2021, 01:34 PM
4° later cam alignment in the later version. I've measured WWWWWWWWAYYYYYYYYYYYYY too many of em to be convinced otherwise.
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