Crazy Plenum Update - More Sillyness Finding Power
11-24-2009, 07:28 PM
#1
Crazy Plenum Update - More Sillyness Finding Power
If you guys recall a few months ago or so we did a test where we found 336whp by lifting the upper plenum from the lower mid dyno pull. We found that the stock lower non-revup plenum, breathing open air, was able to make a ton more power. Follow up on the thread here if you'd like:
https://my350z.com/forum/na-builds/4...enum-test.html
I did some more reading and first wanted to establish the maximum power available just in plenum volume. As we all know, plenum spacers add power, but obviously at some point it's just got to stop. So we built what we're referring to at the shop as "the box." It's ugly. It's brute, and it pulses with intake manifold vacuum. Yes it's dirty, but that's what tests are for. They are to see if ideas work before you spend a bunch of time on them. Here's a picture of the box:
Yesterday (tuesday) we did 3 tests. Test one was with the stock upper plenum, a Skunk2 spacer (which we had previously dyno'd at 315whp), "The Box" with no spacer, and finally, The box with a 3.5" hole in the top of it, coupled to a 3.5" BPI flow stack to simulate an essentially unlimited, however feasible air supply into the box.
Test 1 - we were only able to get 306-307whp out of the car. There was also less vacuum being pulled in the manifold compared to a few weeks ago AND we've seen some oil in the lower plenum. I suspect the engine is getting tired and the excessive blow by makes me suspect we're losing compression a bit on this motor. That's fine, its got 20 hard hours of racing on it and it's to be expected. Either way, we have our baseline for the day.
Test 2 - the box made about the same power, 305-306whp, but the midrange was much weaker. My best guess at the flow phenomena is that the jagged edges of the box were causing turbulence and the strange shape was causing messed up resonances which were inhibiting the airflow into the runners more than helping them. It's also possible the engine knew it was ugly, and was shy.
Box vs Stock Plenum + Skunk2 Spacer
Test 3 - as soon as we opened up the 3.5" hole and let it rip, the engine totally came to life. Not only did it make more power above 5000rpm (as the other test suggested), it made more power from 4500rpm up. A LOT more. We ended up only 2whp less than the previous test, and that previous test had a much higher baseline.
Box with 3.5" BPI flow stack in the roof
I had to add a lot more fuel to the first bank, which had previously been trimmed lean as it was getting less air, obviously there is some air distribution problem with the current manifold setup. The gains in power only grew as the RPM got higher, and I really wanted to see at what point the power would nose over. Running only to 7200rpm on most runs, the power had just started to fall and I wanted to get a clearer picture of what the power curve was doing.
So, we ran this bone stock OEM block out to 7600rpm. Yes. Stock valve springs too. Craziness? I was expecting the thing to spill its guts all over the shop floor. All in the name of research I guess. Either way, it did nose over around 7100, but not much. It still had 320whp all the way to 7600rpm, and with more compression and perhaps larger cams I'm sure we'd be able to keep the torque up and make even more power up there.
Box with both OE throttle and BPI open vs. Skunk2 Spacer baseline run
Conclusions? 90mm LS1 throttle body coming up, with custom intake plenum? I think so.... But can we make it work for everyone as a bolt-on affair? That is the real question.
https://my350z.com/forum/na-builds/4...enum-test.html
I did some more reading and first wanted to establish the maximum power available just in plenum volume. As we all know, plenum spacers add power, but obviously at some point it's just got to stop. So we built what we're referring to at the shop as "the box." It's ugly. It's brute, and it pulses with intake manifold vacuum. Yes it's dirty, but that's what tests are for. They are to see if ideas work before you spend a bunch of time on them. Here's a picture of the box:
Yesterday (tuesday) we did 3 tests. Test one was with the stock upper plenum, a Skunk2 spacer (which we had previously dyno'd at 315whp), "The Box" with no spacer, and finally, The box with a 3.5" hole in the top of it, coupled to a 3.5" BPI flow stack to simulate an essentially unlimited, however feasible air supply into the box.
Test 1 - we were only able to get 306-307whp out of the car. There was also less vacuum being pulled in the manifold compared to a few weeks ago AND we've seen some oil in the lower plenum. I suspect the engine is getting tired and the excessive blow by makes me suspect we're losing compression a bit on this motor. That's fine, its got 20 hard hours of racing on it and it's to be expected. Either way, we have our baseline for the day.
Test 2 - the box made about the same power, 305-306whp, but the midrange was much weaker. My best guess at the flow phenomena is that the jagged edges of the box were causing turbulence and the strange shape was causing messed up resonances which were inhibiting the airflow into the runners more than helping them. It's also possible the engine knew it was ugly, and was shy.
Box vs Stock Plenum + Skunk2 Spacer
Test 3 - as soon as we opened up the 3.5" hole and let it rip, the engine totally came to life. Not only did it make more power above 5000rpm (as the other test suggested), it made more power from 4500rpm up. A LOT more. We ended up only 2whp less than the previous test, and that previous test had a much higher baseline.
Box with 3.5" BPI flow stack in the roof
I had to add a lot more fuel to the first bank, which had previously been trimmed lean as it was getting less air, obviously there is some air distribution problem with the current manifold setup. The gains in power only grew as the RPM got higher, and I really wanted to see at what point the power would nose over. Running only to 7200rpm on most runs, the power had just started to fall and I wanted to get a clearer picture of what the power curve was doing.
So, we ran this bone stock OEM block out to 7600rpm. Yes. Stock valve springs too. Craziness? I was expecting the thing to spill its guts all over the shop floor. All in the name of research I guess. Either way, it did nose over around 7100, but not much. It still had 320whp all the way to 7600rpm, and with more compression and perhaps larger cams I'm sure we'd be able to keep the torque up and make even more power up there.
Box with both OE throttle and BPI open vs. Skunk2 Spacer baseline run
Conclusions? 90mm LS1 throttle body coming up, with custom intake plenum? I think so.... But can we make it work for everyone as a bolt-on affair? That is the real question.
11-24-2009, 08:10 PM
#2
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experimentation is neat 
problem is, you're ingesting unmetered air - it does go to show you that a proper intake manifold is the name of the game, and getting one to play well with the header is what this engine has always been about. It's all a balancing act
you'll need a new plenum neck to use a 90mm throttle body, and I think what you'll find is its honestly too big unless you are planning on some wicked, wicked cams
problem is, you're ingesting unmetered air - it does go to show you that a proper intake manifold is the name of the game, and getting one to play well with the header is what this engine has always been about. It's all a balancing act
you'll need a new plenum neck to use a 90mm throttle body, and I think what you'll find is its honestly too big unless you are planning on some wicked, wicked cams
11-24-2009, 09:17 PM
#4
experimentation is neat
problem is, you're ingesting unmetered air - it does go to show you that a proper intake manifold is the name of the game, and getting one to play well with the header is what this engine has always been about. It's all a balancing act
you'll need a new plenum neck to use a 90mm throttle body, and I think what you'll find is its honestly too big unless you are planning on some wicked, wicked cams
problem is, you're ingesting unmetered air - it does go to show you that a proper intake manifold is the name of the game, and getting one to play well with the header is what this engine has always been about. It's all a balancing act
you'll need a new plenum neck to use a 90mm throttle body, and I think what you'll find is its honestly too big unless you are planning on some wicked, wicked cams
I am not understanding the bolded portion of your comment. Mainly: doesn't this test show that the stock cams can realize these types gains with the increased airflow SG is going to give it?
11-25-2009, 04:20 AM
#7
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An engine is just an air pump essentially - the more air and corresponding fuel you feed it, the more power it should theoretically make. However, things still need to fit in order to be functional. Packaging is always the great equalizer. The stock plenum neck is only so big, both in its bolt pattern as well as its interior diameter. Anything can be made to fit, it just depends on what functionality it provides once it's in there, and what compromises need to be made in order for that piece to fit.
Last edited by Z1 Performance; 11-25-2009 at 04:28 AM.
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11-25-2009, 07:23 AM
#10
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those are restrictors, which NISMO was required to run per class rules. Also, that is not a common plenum, it houses individual throttle bodies (and that's a V8 too but that's not really important 
)
)
11-25-2009, 10:37 AM
#12
An engine is just an air pump essentially - the more air and corresponding fuel you feed it, the more power it should theoretically make. However, things still need to fit in order to be functional. Packaging is always the great equalizer. The stock plenum neck is only so big, both in its bolt pattern as well as its interior diameter. Anything can be made to fit, it just depends on what functionality it provides once it's in there, and what compromises need to be made in order for that piece to fit.
11-25-2009, 12:36 PM
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If you can get the larger volume of air ingested into the engine, you raise it's ability to make power higher in the rev range with a stock cam. However, you become limited by space. Obviously you can't have a giant hole at the top of your plenum
Then your other option is a more aggressive cam that, has more lift and/or duration, so that more air, being ingested through the smaller orifice, can make it into the combustion chamber per piston stroke
11-25-2009, 12:51 PM
#16
If space is the issue I wonder if one could get rid of the lower plenum and run ITBs up into a box that's built around the lower intake manifold? (not the lower plenum)[/QUOTE]
Something like this ? http://www.fontananissanracing.com/E...ld_Part_3.html
Something like this ? http://www.fontananissanracing.com/E...ld_Part_3.html
11-25-2009, 04:40 PM
#18
The reason the fontana/unitech car can run such a large plenum is because it's dry sump and I'm sure the engine is lower than factory.
All we need to know is exactly where the restrictions are, and find a solution. V style engines with low hoods are nothing new to the world, and I am confident we will be able to find a solution to incorporate a larger throttle body and neck. Whether or not we're able to bring it to production for a reasonable cost will be seen! But unfortunately ITBs aren't an option for most people simply because of the drive by wire issue.
Adam please tell us more about the power you found and why it became too expensive to continue! I hate trying to retrace work you may have already done!
All we need to know is exactly where the restrictions are, and find a solution. V style engines with low hoods are nothing new to the world, and I am confident we will be able to find a solution to incorporate a larger throttle body and neck. Whether or not we're able to bring it to production for a reasonable cost will be seen! But unfortunately ITBs aren't an option for most people simply because of the drive by wire issue.
Adam please tell us more about the power you found and why it became too expensive to continue! I hate trying to retrace work you may have already done!
11-26-2009, 07:51 AM
#19
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unfortunately it's not a conversation that is really for public consumption for a variety of reasons, but over a few beers one day, I'll be happy to share.
I'll be up your way come March with Mike to finalize the tune
I'll be up your way come March with Mike to finalize the tune
11-26-2009, 07:57 AM
#20
How is that Manifold working out for you?
