3900 Info

[Joseph Upson]

That's just a nice way to say it was an illegal emissions defeat strategy.

Depends on how they were looking at it and whether or not actual increased emissions or lobbying was the deciding factor. I wonder if they really sat down and did the math or if it was just a hyper-reflex. I'm curious to know if the emissions produced at the higher efficiency/ratio level and decreased fuel consumption providing more distance per gallon, exceeded that of their set standard and all of the emissions expelled in the process of producing and transporting the fuel that would have been saved in order to be used at their standard for that time. I know the higher ratio results in higher temperatures causing a particular pollutant to be higher.

[Joseph Upson]

THANKS for those ever important pictures of the power maker, I guess it would be best for starters to lock it into the straight up position whatever that is because I doubt full retard will be optimum for wide open throttle, at least tampering with cam retard on Desktop Dyno suggested it wouldn't.

[CNCguy]

One of my next steps on this project is to re-install the VVT actuator in the locked position and degree the cam. I want to know where the open and close events as well as lobe centerline is for intake and exhaust. From there I can try to come up with an optimum setting for a fixed location. Then I plan to make an adjustable cam gear to give the end user some adjustability to tweek their cam timing when building the engine. The best way to figure this would be through lots of dyno time but I'm not rich and will probably have to live with only a couple of sessions.

I am really surprised about how few people here work with their cam timing. I have seen very few posts about degreeing a cam to compensate for manufacturing tolerances. During manufacturing, parts have an acceptable dimensional limit. When you add up tolerances in the camshaft, upper gear, lower gear, crankshaft keyway, crank center to cam center distance and chain stetch, the total deviation from what was specified can be off considerably. For a stock engine this is fine but it can affect performance.

Perhaps this is a topic for a thread of its own.

[Joseph Upson]

I'm assuming at idle due to the return spring on the cam the following; either the full return position is straight up, or there is a preload that moves the cam into straight position allowing for positive or negative advance relative to the straight up position.

Next, I wonder if the cam angle changes as a function of rpm, and load, in other words does it change linearly with rpm or does it change relative to the load on a given rpm? When I get my engine I'll subscribe to the Tech site that provides electronic access to the Tech manual for the particular car or better yet ask someone with PCM tunning ability (forgot the name of the company) for a snap shot of the table it utilizes.

Last but not least, valve to piston clearance at TDC in full advance and retard position so that I'll know where to limit a cam regrind. The last spec I got from Crane for a turbocharge regrind yielded .525 lift which I'm sure is too much for this cam because of the way it was assembled and if the base circle is cut to thin the lobe might split at that location or valve to piston contact may occur at that lift.



Looks like HPTuners is the best chance at grafting the stock PCM for this engine into an older vehicle and making it work provided it enables one to disable the necessary PCM requests for items you don't have like anti-lock and a BCM computer. They haven't decyphered the VVT yet from what I read so we won't be getting a picture of the VVT table anytime soon.

[Fiero11]

I took your picture of the 3.9L head on the 3.1L block and scaled it. It seems that the 94mm 3.5L would clear the valves and possibly even the 92mm 3.4L.

[Will'sFiero]

I really think it is somewhat unfair to compare the 3500 and 3900 engines to higher-revving, highly advanced DOHC 3.5 liter engines that are often running with a high enough CR to justify using premium. Those two engines aren't made with the purpose of a high specific output. They're made to be modernized, reliable, economical pushrod engines that produce low-end torque to move some fairly big cars. It just isn't fair to put them on the same scales. They're called a high-value engine for a reason, y'know?

If you want to point to a GM engine to compare to the high specific output v6s in production by other manufacturers, you want the high-feature engines, namely, the 3.6 DOHC with variable valve timing, variable intake manifold geometry, soon to have direct injection. Then you're on level playing ground, in my opinion.

Blast from the past!

My point was that GM WOULD NOT HAVE NEEDED to develop the "high feature" engines if they had put the same development effort into the pushrod 6's as they did into the pushrod 8's. However, GM doesn't take 6 cylinder performance seriously... and obviously doesn't even UNDERSTAND 6 cylinder performance, as evidenced by the fact that they spent a lot of money copying the rest of the market instead of doing what they'd already done successfully (create an advanced pushrod engine: the LS1).

[Will'sFiero]

My understanding of the VVT actuators in the Northstar is that there is no "home" position. IE, the system CAN NOT function without feedback to close the loop. Changing the duty cycle of the valve only results in advancement or retardation of the cam. You have to know where it is first before you can know which way you need to command it to go.

Lean cruise was not used in production vehicles because the lean exhaust would destroy catalysts and increase NOx emissions besides.

[CNCguy]

However, GM doesn't take 6 cylinder performance seriously... and obviously doesn't even UNDERSTAND 6 cylinder performance, as evidenced by the fact that they spent a lot of money copying the rest of the market instead of doing what they'd already done successfully (create an advanced pushrod engine: the LS1).

GM has made some big improvements to the 60V6. This is from GMs site regarding the LZ9:

New cylinder heads apply design features developed for the high-output LS1 and LS6 Corvette small-block V8s. The 3.9L V6’s valves are similar to those in the LS1, as is its combustion chamber design.

When you compare the HP/L the LS2 is 66.67 & the LZ9 is 61.54 there is about a 10% difference. The older 60V6s were less than 53/L. When you add in that it's more turbo friendly because of the oil squirters, it keeps looking better. Not too bad in my opinion considering it is not a completely new design engine.

[Joseph Upson]

I seem to recall someone mentioning in another thread about the closed loop control, plus, I have worked on embedded engine control systems for over 8 years, and I would be amzed if GM was not using closed loop control on the cam actuator. It is pretty fundamental.

The capability of the stamp has nothing to do with how many instructions per second it can handle. The stamp would need to be able to process both the crankshaft and camshaft position signals, and make a determination of a reference point for each signal. This is handled by a timer processor unit in most ECU's, something the very simple stamp does not have. The cam may only have one pulse per rev, but the crank has many (54? I don't recall the exact number). Can the stamp handle interrupts based on the input of each signal tooth? 54 teeth at 6000rpm = 5400 tooth samples required per second.

Open loop may seem good enough, but what happens when you apply a PWM you **think** will give you 10 degrees of retard, but the system actually ends up advancing 15 degrees due to one variable or another? Might not be so good.

I was reading over the progress so far and thought about what you mentioned in the above.

Since most if not all of us wishing to go this route will be using a 7x reluctor wheel the interrupts will only be 7 x rpm instead of 54 x rpm. If that is within the ability of the microcomputer and they offer several with varying capabilities now, there would still be a limitation for effectiveness; resolution.

A crude way of figuring out a rough estimate for cam positioning would be a series of logged power runs at different signal rates and comparing the power curves . Or someone with a friend at GM can have them use one of their scanners to log a few runs in a stock car with appropriate signal inputs and save them to a file for analysis for a pattern.

The PCM may reference several inputs but there can only be one optimum setting for the best airflow at any given rpm and throttle position combination. Some of the inputs are probably redundancy for continued operation in the event of a sensor failure so that the VVT can operate off the next sensor in the loop or values stored in memory. There is probably a power calculator built into the code as well because being hydraulicly operated with a dynamic system that builds and bleeds pressure at the same time to establish a reference means that something as simple as an oil viscosity change can affect its calibration so it has to be able to compensate for that.

[smilinguy99]

Blast from the past!

My point was that GM WOULD NOT HAVE NEEDED to develop the "high feature" engines if they had put the same development effort into the pushrod 6's as they did into the pushrod 8's. However, GM doesn't take 6 cylinder performance seriously... and obviously doesn't even UNDERSTAND 6 cylinder performance, as evidenced by the fact that they spent a lot of money copying the rest of the market instead of doing what they'd already done successfully (create an advanced pushrod engine: the LS1).

1 HP/ci with good emissions, economy, power and reliability shows plenty of understanding. And as far as effort goes, putting VVT on a pushrod engine and getting a good result shows a lot of commitment and some real leadership. No one else makes a pushrod VVT engine for them to copy.

High feature engines would have still been a necessity because pushrod engines still have limitations in the HP/ci department. Yes, this goes for the LSx engines too. And when people are paying more for a vehicle they want more power and more capable technologies in the bargain, like DOHC. Even an ordinary DOHC motor makes more HP/ci than a pretty good pushrod motor. Example: A garden-variety DOHC 2.0 liter Mazda FS motor found in a Protege' makes 130HP. or 65hp/L, or about what a Corvette makes. By comparison, a BMW M3 DOHC 3.0 liter motor makes 300hp or 100hp/L.

But make no mistake, GM isn't doing any of this work on the V660 out of the goodness of their pushrod-lovin' hearts, these engines are a lot cheaper to design, produce, and warranty. And when you consider they are producing over a MILLION V660s a year, it all starts to make sense. Nice thing for us is that they are cheaper to hot rod too.

Perhaps you are right they don't take 6 cylinder performance seriously. If they did they would make an all aluminum version of the 3900 motor, squeeze another 5-10hp/L out of it, and put it in a production version of the Nomad concept car, thereby putting this motor on the performance industry's (parts producing) map. But while there is lots more potential in this motor, GM sees this motor as a "high-value" (read cost-effective) motor. So more power isn't a priority.

Don't get me wrong, I'm committed to this pushrod engine, but give GM some credit for even keeping the thing around, let alone dumping lots of cash into it like they have.

[SappySE107]

I guess its time to get a new flowbench so I can test the larger bore sizes being used. If I can get the port dimensions and gasket dimensions as well as the min port area of the heads, I can do some simulations, including VVT cam timing tests This might help is decide what we want, not what GM programmed initially. Especially useful with mods.

Now to make some money so I can do all this:P

[Superdave]

I guess its time to get a new flowbench so I can test the larger bore sizes being used. If I can get the port dimensions and gasket dimensions as well as the min port area of the heads, I can do some simulations, including VVT cam timing tests This might help is decide what we want, not what GM programmed initially. Especially useful with mods.

Now to make some money so I can do all this:P

you'll have $600 or so coming from me in a month

[CNCguy]

Another update for those following this. I got out my digital indicator, made a degree wheel and checked the valve events with the actuator in the default position (total advance). I plan to do some more measurements as something seems very strange to me. I checked all the numbers 3 times each and got consistent readings.

The vavle timing checked at .050 lift is as follows:
Intake Open: 1 ATDC
Intake Close: 30 ABDC
Intake Duration: 209
Exhaust Open: 59 BBDC
Exhaust Close: 29 BTDC
Exhaust Duration: 210

The duration looks pretty good but what seems strange to me is what is what I calculate the LSA at. By comparing the opening positions of the valves, the LSA calculates to 120 degrees. I know that it isn't the most acurate way to do it but using the Crane Cam spec cards, the numbers usually come out within a degree or two. I did not seen any cams with this much LSA on Cranes site.

I am going to try another method of measuring that I found and see if it comes out differently. It seems as though this would create an issue when it comes to regrinding the cam. Thoughts?

[SappySE107]

Can you get the measurements for .006" lobe lift for intake and exhaust open and close, and then the .050 numbers.

[Joseph Upson]

Wide lobe separation angles are good for boosted/blown engines but I think 120 is a bit much and very likely can only properly be taken advantage of with VVT or boost. The most I've seen recommended with boost is about 116.