06 Bu SS 3900 Build

[Joseph Upson]

I'm not clear on whether this engine came with your car or not but if it did you may end up with less or mediocre performance improvement. The intake valve optimizes low end torque and combustion efficiency when closed and high end HP when opened according to GM. The slot in the throat of the intake may seem like a useless aberration but a lot of people ground the fin in the cast iron head down before they found out it was responsible for a ~17% increase in flow ability.

The remark about performance has more to do with the cam than the intake. The LSA has a lot to do with the cam being able to provide proper variation in the power curve. By having the cam reground to a tighter LSA you will also need to limit the cams variation otherwise it will be retarded beyond what is optimum for the camshaft grind. Some fundamentals regarding that were discussed in a thread I linked to in the tech article section.

As long as you can fully tune those parameters you should be okay. I don't know all of the details as far as the precautions you have taken but just be aware if the cam is going to be fully VVT functional you need to be sure the increased lift and head shave is not going to permit interference.

And what's with the head studs and no turbo to exercise them properly.

[IsaacHayes]

114 LSA and that duration, not sure if it will sound lopey or not... I'm going guess it will sound about like stock, but then again I don't know how much the VVT comes into play with that. That lift looks fairly small still, but then again, VVT might limit you on how much lift as Joseph said with interference.

[Joseph Upson]

114 LSA and that duration, not sure if it will sound lopey or not... I'm going guess it will sound about like stock, but then again I don't know how much the VVT comes into play with that. That lift looks fairly small still, but then again, VVT might limit you on how much lift as Joseph said with interference.

He has the equivalent of about .035" more lift than I have with his cylinder head trim. The VVT motors are the only ones with valve reliefs in the perimeter of the piston so they are definately needed at both extremes of the cam location. If the LSA change pulled both lobes inward an equal distance that will serve as a favorable offset to the lift increase.

[gectek]

The engine will produce torque no matter what. that is not a function of that valve. according to GM is funny somtimes, (sorry i use LS engines for comparison but its what i do all day) the VVT and or DOD engines ALWAYS gain power by using components to take them out. IF you use that in conjunction with tuning and a mild build, it will always keep the same fuel economy if not better. this is honest proof that we build every day. this engine put down 170 on a mustang (loaded) dyno. very bad if you ask me. the good thing about being here is, if it doesnt work to take the throat off, i can get a new one and trash/sell the old one. the vvt does nothing honestly. i have driven that car for a while before it sat, and i can tell you that as proof. it will produce torque no matter what at a lower RPM, that is why we decided to change the gear ratio up from 3.69 to a 3.42. it simply did not need it. now i did not get to pick out all the parts, but i did have alot of say in them. i know the cam will idle like stock, because i had almost that same cam in mine and it idled just like stock. afaik the LSA on the stock cam is a 112 or 113, i put it on a 114 to help keep the valve events away from each other so even fully retarded or advanced, they would have no problems. i measured ptv and have no prob.

case in point with the VVt is the new 6.2 L engines. one is the truck engine with VVT and a long runner intake. the other is the LS3 with no VVT and a shorter runner intake.
LS3 http://archives.media.gm.com/us/powe...amSS_SAE_n.pdf
L92http://archives.media.gm.com/us/powe...20Escalade.pdf

and those are stock to stock comparisons.

[Joseph Upson]

The engine will produce torque no matter what. that is not a function of that valve. according to GM is funny somtimes, (sorry i use LS engines for comparison but its what i do all day) the VVT and or DOD engines ALWAYS gain power by using components to take them out. IF you use that in conjunction with tuning and a mild build, it will always keep the same fuel economy if not better. this is honest proof that we build every day. this engine put down 170 on a mustang (loaded) dyno. very bad if you ask me. the good thing about being here is, if it doesnt work to take the throat off, i can get a new one and trash/sell the old one. the vvt does nothing honestly. i have driven that car for a while before it sat, and i can tell you that as proof. it will produce torque no matter what at a lower RPM, that is why we decided to change the gear ratio up from 3.69 to a 3.42. it simply did not need it. now i did not get to pick out all the parts, but i did have alot of say in them. i know the cam will idle like stock, because i had almost that same cam in mine and it idled just like stock. afaik the LSA on the stock cam is a 112 or 113, i put it on a 114 to help keep the valve events away from each other so even fully retarded or advanced, they would have no problems. i measured ptv and have no prob.

case in point with the VVt is the new 6.2 L engines. one is the truck engine with VVT and a long runner intake. the other is the LS3 with no VVT and a shorter runner intake.
LS3 http://archives.media.gm.com/us/powe...amSS_SAE_n.pdf
L92http://archives.media.gm.com/us/powe...20Escalade.pdf

and those are stock to stock comparisons.

Okay. I won't bother the who's right and who's wrong regarding the valve function between you and GM, but I will certainly question a stock LSA rating less than 115 on the 3900 VVT cam which was measured by CNCguy and Delta cams to be greater. That helped eliminate the EGR. Not sure what to say about your dyno results other than something must be wrong somewhere.

I've ridden in a Chevy Uplander with a 3900 and going wide open throttle at 4000 lbs from 55 mph it was no slouch and actually made me smile it accelerated so well. You're the only person I'm aware of that has implied that a VVT engine does not have performance benefits above a non VVT engine in the face of quite a bit of documentation suggesting otherwise. Some of your reasoning suggests GM is wasting good money on this technology.

The engine comparisons you linked to are not quite apples to apples, there are variations between the 3900 applications that probably have more to do with programming than anything else, the covertible vs. hardtop G6 is an example, as well as potential limitations of the DOD components instead of engine tune. If the engines don't sport the exact same intake and cam you can't draw a fair conclusion about a variable intake manifold on one and not the other. If the compression ratio is not the same for both engines that is another mismatch.
Hope what you've built works as planned for the benefit of all of us.

[IsaacHayes]

It does seem that the VVT in GM OHV motors doesn't do a whole lot for performance. Someone mentioned they saw the operations of the VVT and it's doing all kinds of stuff constantly while going a steady speed IIRC. Makes me wonder if it's mainly for emissions.

I drove a 3900 van as well, and it hauled with 3 people and FULL of PC equipment a white board, laser printers, etc on the highway. And it never downshifted on the highway. The new dodge van we took next time was a death trap it was so slow with 2 people and less equipment. That thing had to be floored to barely stay at 70mph for any hill on the highway.

170, damn 70hp loss. I wonder how much torque management is taking out. I know the 4speeds suck power, but damn... It could be the TM sucks a ton out, I've heard the SS trailblazers will just putter along if you floor them from a dig, but roll into it and they are super fast because the TM isn't preventing you from "abuse".

Wait, I thought the smaller the LSA, the more overlap.... Wouldn't a small LSA overlap and then create an EGR function if the exhaust is open long enough for down stroke to pull some back in???

[1988GTU]

Those there 4 speed electric trans are the devil and are known in these neck of the woohoods to be sleezy E's.

[Joseph Upson]

It does seem that the VVT in GM OHV motors doesn't do a whole lot for performance. Someone mentioned they saw the operations of the VVT and it's doing all kinds of stuff constantly while going a steady speed IIRC. Makes me wonder if it's mainly for emissions.

I drove a 3900 van as well, and it hauled with 3 people and FULL of PC equipment a white board, laser printers, etc on the highway. And it never downshifted on the highway. The new dodge van we took next time was a death trap it was so slow with 2 people and less equipment. That thing had to be floored to barely stay at 70mph for any hill on the highway.

170, damn 70hp loss. I wonder how much torque management is taking out. I know the 4speeds suck power, but damn... It could be the TM sucks a ton out, I've heard the SS trailblazers will just putter along if you floor them from a dig, but roll into it and they are super fast because the TM isn't preventing you from "abuse".

Wait, I thought the smaller the LSA, the more overlap.... Wouldn't a small LSA overlap and then create an EGR function if the exhaust is open long enough for down stroke to pull some back in???

Smaller LSA is a compromise for a fixed cam engine in emissions, the wider LSA is necessary for the VVT airflow dynamics to work properly on an in block fixed LSA VVT motor. You have to see the effects in a simulator as well as what happens to torque and HP when the cam is advanced or retarded. Most of us know that a cam biased towards early openning of the intake favors low end torque and idle quality where later valve openning favors high rpm performance so VVT has to offer a broader performance efficiency than a fixed cam.

Ideally less combustion polution with exhaust is better. With oil squirters and more efficient combustion chambers I guess you don't need the EGR valve as much with the ability to maintain a more effective efficiency by retarding the cam to help keep airflow up as the rpm increases. That's what I understand from what I've read about camshaft timing vs airflow relative to piston location in the cylinder.

As I had mentioned earlier, VVT is a very expensive means of applying EGR over the traditional and probably very cheap by comparison EGR valve, so it has to offer more in order to make any sense.

[gectek]

These specs were measured by delta on the stock cam. They are identical to the stock cam i sent them. The lsa is actually at 114.3 if you prefer to get technical. I can tell you exactly that for what the VVT attempts to do, it fails at. Everyday, we take a DOD or VVT engine and revert it back to fixed cam and reg fueling/valvetrain, and they have no problem producing any amount of power over the stock engine. we have taken the 6.0L VVT engines (because we can get them cheaper from GM for some reason) and make them into normal engines like LS2s or L76s and they have always produced more power and had the same drivability in them. Whether this be a stock cam, or aftermarket. Im not talking out of my butt, i am saying it exactly how it is. In this case GM is wrong in their marketing. I am not sure why gm used it in the first place, they seem to love it i guess because the aussies love it. i will post all results i find from this comparo, but believe me, i am not doing this on my own. I am getting alot of feedback from our normal engine builders that work with these designs on the V8 every day.

[Joseph Upson]

These specs were measured by delta on the stock cam. They are identical to the stock cam i sent them. The lsa is actually at 114.3 if you prefer to get technical. I can tell you exactly that for what the VVT attempts to do, it fails at. Everyday, we take a DOD or VVT engine and revert it back to fixed cam and reg fueling/valvetrain, and they have no problem producing any amount of power over the stock engine. we have taken the 6.0L VVT engines (because we can get them cheaper from GM for some reason) and make them into normal engines like LS2s or L76s and they have always produced more power and had the same drivability in them. Whether this be a stock cam, or aftermarket. Im not talking out of my butt, i am saying it exactly how it is. In this case GM is wrong in their marketing. I am not sure why gm used it in the first place, they seem to love it i guess because the aussies love it. i will post all results i find from this comparo, but believe me, i am not doing this on my own. I am getting alot of feedback from our normal engine builders that work with these designs on the V8 every day.

They must have changed the cam specs because Delta told me they had to narrow my LSA down from a considerably higher one. I'll take your word for the results as an overall assessment. I don't doubt that the engine is well below its potential in stock form. Much of what I've read on the variable intake supports better low end torque with no effect on top end. I also noticed in Desktop Dyno that the higher the static compression ratio the less effective the VVT cam is advanced beyond zero degrees and only shows improvement in peak hp and torque band width when retarded.

[gectek]

better low end torque is funny due to us having to change the gear ratio up from the 3.69 to the 3.42 due to it just spinning the tires. i will try to find the dyno graph and post it as well as the cam spec sheet. the 3900 has torque built in with displacement and i see absolutely no reason why it would need a manifold that trys to add to it. its like the TPI intake on the L98 350 engines. torque out the rear from the runner design but nothing above 5k, you could not even pull one in an auto trans above 5100 in 3rd gear on a dyno. I know what GM is trying to do with it, but it is not very successful. if you look at the graphs from one type of manifold to another on the 3900 you cannot see much difference. it is hard to compare apples to apples with one being a flex fuel and showing less HP, but you can look at the curves of the graph and get a good idea, not calling peak to peak.

when i posted those 2 dyno graphs, it was so show how strikingly similar they are in the way the produce power. you see nearly NO difference other than the LS3 on average produces more power everywhere. i was not claiming just peak to peak

[IsaacHayes]

How much more radical is the LS3 cam than the VVT version of the motor though? How much compression is the LS3 running vs that other motor? Weren't the LS2 at 10.9:1 ?

[gectek]

def not radical at all. at all. the ls3 is 10.7 the l92 is 10.5.

[CrimsonGTP]

do me a favor, come to my house and trade motors....kthxbai!

[gectek]

well the engine is complete. brake system is bled. working on aux trans cooler lines now. also placing arp wheel studs on the back and spacers so it does not look retareded lol. the bumper was a bitch to take off, but it will work out alot better this way. UIM is on and everything. ill try to take pics tomorrow.