Pauls325

iTrader: (1)

i just looked up the post from when BJ? got his car dynoed before the stage one and after +tune he picked up 30 whp and 18 lbft on a car with intake and exhaust

nmp0098

SM, I agree and still believe my earlier guess of about a 20WHP gain on my otherwise stock engine to be pretty good, and the math still works out to about a 40-45 WHP gain from the stock LS4 to the LS6 manifold on your cammed engine (w/o tune). Because of the exponential thing that you guys have mentioned, I think people won't see the full benefit of other mods without a swap, unless you are using a power adder. The turbo would like the LS6 manifold too, but you can already make really good power with just the kit and it probably isn't worth the effort.

JDMC5, I still haven't decided which direction I want to go with the valvetrain yet and it's cold as all hell right now. But at the moment, it looks like I'll be able to swing either Crane 1.8 rockers or the New Era G8 low-lift DOD cam in a few months when it warms up. I need to call those guys in the next week or two and see what kind of lift, duration and LSA numbers they're running, because I don't want to deal with the MAP issues you get with a lot of overlap. Plus, they might have a stock G8 GT cam (200/208, 116) lying around that I could stab in if the low-lift cam is too agressive for a stockish idle (I know that would be a lot of work for a little gain, but I'd match it with the 1.8s and it wouldn't be a lot of money).

nmp0098

JeremyF is a good tuner, and Panther427 picked up over 20WHP from a good dyno tune. I'm not sure how much to attribute to the porting and how much to the tuning. But SM says he only saw about 18WHP with just the stage 2, and I think his tune will unlock a lot more power if he is setting codes for running lean. Most times CAIs require a tune to reach their potential too. It's just tough because adding gains from different mods usually doesn't work out correctly, and the overall combo plays a big role in how much power you make. I've been reading Marlan Davis articles in Hot Rod and Car Craft for years, and he's shown several examples of a smaller cam or heads making more power because the rest of the setup couldn't feed the bigger heads or cam on the top end and the torque lost lower in the curve was too much to overcome. But before the tune, BJ? only picked up 20WHP, which is similar to SM's 18WHP. The Stage 2 porting apparently didn't add much for SM, and his big restriction was still the narrowing of the throttle neck for the OPSU.

JDMC5

iTrader: (3)

well what ever you decide on the cam let me know and I'll help out. Ever thought of getting the heads ported and maybe bumping compression? That wouldn't affect your DOD or drivability. BTW, I have a copy of that tuning DVD if you want to watch it since I know you're looking for resources.

Count of Monte Carlo

VOYAGER 6 ??????????? We should ask Kirk Unit!

higsy

Kirk would love the blue chick in Avatar....

Sittingmongoose

iTrader: (1)

He did not pick up 20hp from the intake, i would say about 10hp from that was from a tune. Our cars do not tune well until you have MAJOR mods even a before and after tune on my car when i had the cam and heads in there only netted like 10hp when jeremy did it. I would think that the stage 1 port is good for about 10hp. A ls6 intake on a stock car is probally good for about 20hp. If your doing a cam, go big or go home. I saw only little gains from the ls6.
And as far as the heads, i would just send your stock ones in for a port and polish.

JDMC5

iTrader: (3)

Well just remember to take into consideration that you did the cam before the intake. If you would have done the intake then added the cam you would have seen more power from the cam, probably around 20 whp.

Sittingmongoose

iTrader: (1)

yes but than the intake gains are less lol

JDMC5

iTrader: (3)

that answer would be yes....but you see my point.

06 SS

I know...back from the dead post, but increasing plenum volume will (theoretically) increase torque from idle to the peak torque of the engine (any gains beyond that would be minimal). It should pump up the low-mid range and increase the area under the power curve, but not increase peak numbers very much. I would consider this a good cost/benefit for a dd.

JDMC5

iTrader: (3)

I don't want to get into a big argument here but plenum volume is for supplying high rpm power, which is why a single plane makes more topend. In any event I would expect to see a huge gain in topend from the LS6 intake, in fact power gain increasing with rpm.

06 SS

Single plane's give more top end because they act like a short runner intake while the dual plane intakes act like longer runner intakes. Added volume after the throttle body will act as I described.

JDMC5

iTrader: (3)

read the last three sentences in the first paragraph

http://www.popularhotrodding.com/tec..._manifold.html

While the size and shape of runners is the primary tuning device, altering plenum volume also affects where a motor produces peak power and torque. "A general rule of thumb is that the plenum volume should be equal to the displacement of the motor," says Beck. "A smaller plenum gives you more torque, while a bigger plenum makes more power at high rpm."



http://www.circletrack.com/techartic...ech/index.html

here's a snip from this article.

"Smallest Volume Possible In circle track racing, it is generally best to approach manifold development (or modification) by starting with the smallest overall volume possible and increasing volume until no power gain is observed. By having the smallest volume possible, the engine will be more responsive to throttle changes and will generally be easier to drive. By their nature, larger volume manifolds respond less quickly but may perform better at higher engine speeds."

JDMC5

iTrader: (3)

maybe using a single plane intake as an example of the effects of plenum volume was a bad example. There are many reasons why the single plane makes more topend than a dual plane.

But, the facts about plenum volume remain.

06 SS

Yep, they sure do. From your second article nearer to the bottom:

"The plenum acts as an accumulator and holds more mass at the time the valve is opened, allowing for a longer blow-down period than the other manifolds. (Note: This effect is also useful at lower engine speeds on "restricted intake" engines.)"

also you may want to re-read the article, especially what you quoted "Smallest Volume Possible In circle track racing, it is generally best to approach manifold development (or modification) by starting with the smallest overall volume possible and increasing volume until no power gain is observed. By having the smallest volume possible, the engine will be more responsive to throttle changes and will generally be easier to drive. By their nature, larger volume manifolds respond less quickly but may perform better at higher engine speeds."

It advocates the smallest plenum volume possible for responsiveness making it easier to drive (not that there is less power down low). Don't forget, they are focused on a narrow power band that they stay in for the race (and geared for it) and don't care what the engine does down low. Also states that the larger intake 'may' perform better at higher engine speeds, and they might, but they will perform (my definition of perform means output more torque) better below the peak torque RPM of the engine.


On increasing PV in our (closer to a restrictor plated race engine than a non-plated) the net effect is a higher percentage torque increase at engine speeds below the torque peak of the engine. I found an example here: http://www.vetteweb.com/tech/vemp_08...t_results.html

While they do not have a graph of the torque (which would make it much easier to see), we can go off the horsepower graph. The average HP gain over the entire range is 8.2 and the peak gain is 10.2 (not going to get into the possible error factor of a dyno here, the important thing is that the increase at each additional RPM is a decreasing percentage of the total power). Because HP climbs as a factor of RPM quite quickly with similiar torque, what we are seeing is a higher percentage increase of torque/HP at lower RPM and the effect diminishes markedly after 5200 in the example. The biggest gains under the curve would be where the percent increase is greatest. Low to mid-range. The peak torque gain up top would be less of a improvement by comparison. If you gain 6lb-ft at 3900 RPM you get an additional 4.5ish HP, if you gain 6lb-ft @ 5000 RPM, you get about a 25% increase in power over that 4.5. Look at that graph again, hopefully it is easier to see that the torque gains are a much higher percentage at the lower RPM range.

As to the assertion that: While the size and shape of runners is the primary tuning device, altering plenum volume also affects where a motor produces peak power and torque. "A general rule of thumb is that the plenum volume should be equal to the displacement of the motor," says Beck. "A smaller plenum gives you more torque, while a bigger plenum makes more power at high rpm."

Aside from the fact that he appears to be saying a plenum volume larger than the displacement of the engine makes more power and one smaller makes more torque which has nothing to do with our tiny intakes, if you make more power, that means you are carrying more torque at a given RPM, however he also says that a smaller plenum gives you more torque, so he is contradicting himself. Now, if one assumes he is talking about tuning an intake for a specific RPM use, no different than exhaust or cam events, then I completely agree, a larger plenum will shift the torque curve up and to the right, however the shifting up part more than compensates for the shifting right part in a street engine at low low-mid RPM where you see the most benefit.

Short version: Increasing the volume of the intake plenum (up until the point it becomes too large) will increase your low-mid range torque AND your top end power, with the greater percentage gains being seen in the range below the peak torque (and it probably will shift the peak torque up and to the right on a dyno graph).

nmp0098

Here's my $0.02: unless the plenum is really big or small relative to engine displacement (and how much is big or small depends on a lot, and is different for N/A, Turbo, S/C), it's really a tradeoff between throttle response (more important at low RPMs) and cylinder filling (more important at high RPMs). That's obviously oversimplified, but it's IMO too complex to generalize well.

Here's a simplified way to think of it: the plenum is a buffer between each cylinder and the throttle. Some analogies are the an accumulator in a hydraulic system or an inductor in a electrical system (where current = airflow). Each cylinder draws from the the plenum, and not from the throttle directly. The throttle feeds the plenum, and the larger the plenum the bigger buffer there is between the throttle and the cylinder that is filling. So a large plenum hurts throttle response by delaying the time between the throttle opening and the time when the cyinder fills with more air, because it takes longer for the plenum to fill with more air (ie for manifold vacuum to drop). That's why Weber carbs haul a$$.

So why have a large plenum? Well, the cylinders don't draw air evenly. Flow is related to valve lift, and so very little air is drawn into the cylinder at the beginning and end of the intake stroke, and a lot is drawn in during the middle. If the plenum is relatively too small, then cylinder filling during max valve lift is hurt. As RPMs increase, the amount of time the valve is open is less (in time, not degrees), so the plenum needs to have more air in it to feed the cylinder during the brief time it is drawing air. That's why a larger plenum will be able to make more power. Under ideal conditions for power, there would be constant flow through the throttle because the plenum would always have enough air to fill the cylinder and smooth out the pulses.

I hope that explanation was clear. Too big means you step on the throttle and you get power sometime in the future, too small means that your cylinders don't fill well even at low RPM. And it's all relative and tied closely to your displacement, cam, heads, etc.

Based on my experience, the stock LS4 intake's plenum is just too small. I didn't notice any drop off in throttle response (and even if there was a measurable change, my subjective opinion is all that matters for something like that). Now the LS6 intake has more runner volume, more runner taper, reduced runner radius, and more plenum volume! Plus no hated D shaped throttle neck. After I tuned the MAF using LTFTs, I used the MAF output to create new VE tables. My new VE tables show about 0.5% - 1% reduction in filling right around idle, but almost 12% more filling at the torque peak and about 5% more filling at 6000RPM. That means that I gave up almost nothing on the boundaries (which I don't care about anyway), and picked up a ton of torque everywhere it matters. GREAT upgrade. Also, I know that people with stock intakes say the cam pulls all the way to 6000RPM... but not in my car. When the intake doesn't choke off the top end, you can feel it start running out of cam at about 5000RPM. Shifting at 6100RPM, I get a surge after the 1->2 shift (opposite of everyone, I know) because of all the extra midrange torque I picked up without doing much for the top end. Then again, in stock form you could set a straight edge on the torque curve and the throttle response is universally appreciated.

JDMC5

iTrader: (3)

thanks nate..... I know how it works and how it applies here. After reading what you said 06SS I don't know what you're point is now, if you read what I posted the words are written I don't know how you can interpret something different. Long story short: believe what you want but the LS6 intake is going to give you more hp the higher you rev it. To be honest I've lost interest in this topic.

Sittingmongoose

iTrader: (1)

It doesnt really matter, the point is the ls6 is far supior to the ls4 intake. It will be fine up to 6200rpms. If we really start making any power with these cars, like above 450whp, than MAYBE a fast 90mm intake would be good.

JDMC5

iTrader: (3)

thank you.