Super short SRI... Rethink it!
#1
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Super short SRI... Rethink it!
Well I've babbled on in various intake threads about my theories with intake resonance and the TB>MAF>Filter SRIs not being the best way to go for top end power.
Now I have proof!
I made an intake/MAF that is 3.5" in diameter and 31" long, this gives a resonant frequency of roughly 100hz, which equals around 5500-6000 RPMs. I then tested it against the same exact MAF with the filter right on it instead of the full length. The resonant frequency at this length would be over 7500RPMs.
Super short intake is blue, longer one is red.
This is a picture of the length tuned one.
So long story short... Check out this link for a good formula and get some pipe for your intake... gain some power!
http://www.ftlracing.com/tech/engine/intake.html
Now I have proof!
I made an intake/MAF that is 3.5" in diameter and 31" long, this gives a resonant frequency of roughly 100hz, which equals around 5500-6000 RPMs. I then tested it against the same exact MAF with the filter right on it instead of the full length. The resonant frequency at this length would be over 7500RPMs.
Super short intake is blue, longer one is red.
This is a picture of the length tuned one.
So long story short... Check out this link for a good formula and get some pipe for your intake... gain some power!
http://www.ftlracing.com/tech/engine/intake.html
#3
Sounds freaking awesome though.
#4
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I will be cleaning up all the welds, extraneous pieces of metal from fab work, and having it thermal dispersant coated (black). Should look pretty slick, even if it is still a big box.
Regardless, for me, function > form.
Also: No covers are getting stuck on this engine
And to add, although it "only" gave 20 peak WHP, it was over 50whp gains at 7000rpms... and this car will soon be revving to around 76-7800.
Last edited by sparks03max; 02-18-2011 at 07:30 PM.
#7
LOL What's it made out of aluminum? Could polish up nice if there's enough material to bevel the edges a bit.
Thanks for posting this too, verifies that shorter is not always better.
Do you have known gains with the custom IM?
Thanks for posting this too, verifies that shorter is not always better.
Do you have known gains with the custom IM?
#8
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Gains with custom IM.
Last edited by sparks03max; 02-18-2011 at 07:40 PM.
#9
#12
The intake plumbing with stock(ish) set ups is likely to vary greatly, I think, compared to your custom all the way.
Our tiny stock maf and TB would probably still benefit up top with the filter directly on it.
But there's no way around it that those are great gains without losing tq down low-mid.
Would like an SSIM comparison
Our tiny stock maf and TB would probably still benefit up top with the filter directly on it.
But there's no way around it that those are great gains without losing tq down low-mid.
Would like an SSIM comparison
Last edited by Child_uv_KoRn; 02-18-2011 at 08:04 PM.
#13
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The intake plumbing with stock(ish) set ups is likely to vary greatly, I think, compared to your custom all the way.
Our tiny stock maf and TB would probably still benefit up top with it the filter directly on it.
But there's no way around it that those are nice gains without losing tq down low-mid.
Our tiny stock maf and TB would probably still benefit up top with it the filter directly on it.
But there's no way around it that those are nice gains without losing tq down low-mid.
Notice the stock manifold, stock MAF, and the same total length...
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Most people use a velocity stack these days... If they don't, then they're missing out even more.
Also just to note, I still have the stock TB.
#17
Question for you sparks...
I did you ever test the diference between having the intake setup like;
TB>MAF>midpipe>filter
and
TB>midpipe>MAF>filter
I dont recal seing anyone do a direct comparison.
I did you ever test the diference between having the intake setup like;
TB>MAF>midpipe>filter
and
TB>midpipe>MAF>filter
I dont recal seing anyone do a direct comparison.
#19
So long story short... Check out this link for a good formula and get some pipe for your intake... gain some power!
http://www.ftlracing.com/tech/engine/intake.html
http://www.ftlracing.com/tech/engine/intake.html
I read through that whole cluttered page and am struggling to pick out what the key formulas are. Are you using the one under Acoustic Resonance? I don't understand what you'd fill in for "n." Feed me.
#20
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In the case of our cars, N would just be one. What that means is the hamonics of the resonance point. On a high RPM engine, like 9000+ rpms... You can design an intake that resonates at say 4500RPMs, then at 9000RPMs which is a harmonic of 9000. That person would input 2 if they want to see what the second harmonic is. To build an intake that has multiple harmonics at the low RPMs that we turn, it would need to be ridiculously long and certainly acquire pumping losses. (I'm just a former radar/electronics technician that likes math, nothing more)
Last edited by sparks03max; 02-19-2011 at 12:58 PM.
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I have some BC S2s sitting on my shelf waiting for valvesprings, rod bolts, and some other stuff to be installed along with them.
#24
Great thread and info Sparks! I'll be going to a different intake setup soon when I'm tuning, but put me down as interested for a manifold as well. Is there a thread you created regarding that or is this the debut? Props to the work put in for that + the intake research.
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Great thread and info Sparks! I'll be going to a different intake setup soon when I'm tuning, but put me down as interested for a manifold as well. Is there a thread you created regarding that or is this the debut? Props to the work put in for that + the intake research.
There's a link to the dyno thread from there.
#26
I would like one in blue or red jk. Looks real sporty, I like the whole setup, will the engine cover still be able to fit and can the battery and other parts you modified stay stock and in there stock positions?
#27
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This thread is purely about the merits of a very short vs proper length intake piping. As to your questions... Take your time, think it over. The answers are already there.
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I am sure that the nissan techs designed it for optimal acoustic performance. With boltons, however, you would most certainly see gains going to a real intake. I even gained going from a free flowing 3" intake and stock maf to a 3.5" intake and maf.
#33
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The whole acoustic resonance thing does not differentiate between engines or intake manifolds. When determining the length you want, just make sure to add the length of the elbow and TB to the MAF and pipe.
#35
PM'd cause you lost me completely
I love the zip tied reservoir cap on the right side of the Z bay LOL.
That just looks fast.
Have you tried a CAI set up with that IM?
I love the zip tied reservoir cap on the right side of the Z bay LOL.
That just looks fast.
Have you tried a CAI set up with that IM?
Last edited by TunerMaxima3000; 02-19-2011 at 05:11 PM.
#37
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Just to share my response with others...
The length I am talking about is the full length of the air intake into the plenum. This includes the elbow, TB, MAF, and pipe. The formula to determine resonant frequency is pretty simple.
F=V/4(L+(.6D))
F=Frequency. Multiply this by 60 to get RPM
V=Velocity of air. 330-340 is pretty normal
L=Length of intake pipe, in meters. 39inches=1 meter
D=Diameter ofintake pipe, in meters.
So if you want it to resonate at 6000 RPMs with a 3 inch pipe, you do this:
6000/60=100hz
3"/39=.077meters
100=340/4(X+(.6x.077))
100=85/(X+.0462)
100(X+.0462)=85
100X+4.62=85
100X=80.38
X=0.804
L=0.804 meters
.804x39=31.3 inches
So if you want a (roughly) 6000 RPM setup, take length of elbow + TB (use string to measure curves), then subtract that from 31. The remainder is the length that your MAF and intake pipe needs to be.
(hint: if you need PCV, then it can't be before the MAF)
Last edited by sparks03max; 02-19-2011 at 05:55 PM.
#39