2 Inch Restrictor Vs 3.5 intake pipe
07-22-2017, 05:30 PM
#11
300 whp is roughly 30 lbs/min of airflow, which you can easily pull through a 2" ID hole at roughly sea level atmospheric pressure. Look at turbos for an idea of what sort of area chokes (goes sonic). A 45 mm inducer will easily support 300 rwhp, even with a big compressor wheel nut blocking a decent sized chunk of the area.
Now, I will highlight some reasons why this DID not knock down power, but many people do see a reduction in power with larger restrictors:
1. You put it pretty far ahead of the throttle body, which allowed the intake tube after the restrictor to act as an additional plenum, which really helps restricted engine performance. Essentially you're giving a bigger buffer for the cylinders to have atmospheric pressure to suck in by allowing a larger effective plenum size to fill up with air that might be momentarily going sonic through the restrictor. The intake flow is not constant, it pulses, even at 8k+ RPM, so even if it's going sonic at the very peak of draw through the restrictor, the extra plenum volume helps it. It also reduces the "peak" pressure signal the restrictor sees, which helps it not go sonic.
2. You radius'd the edges of the restrictor very well, which is going to give very low flow losses as the flow constricts through the restrictor then expands out. This will tend to not drop the total pressure of the flow as you saw. If you made the same design with sharp edged corners on inlet and outlet, you would definitely see power going down up top with the 2" restrictor. It won't be a huge amount, but there will be flow losses there, and it will cause the total pressure available to the intake manifold to drop as flow goes up. A thinner restrictor would yield slightly more losses too, but probably not a huge difference vs. your 2". The corner detail in and out is really critical though.
3. As stated above, 2" isn't really choking down a 300 whp engine that much when the flow coefficient in and out of the restrictor are very good.
Now, I will highlight some reasons why this DID not knock down power, but many people do see a reduction in power with larger restrictors:
1. You put it pretty far ahead of the throttle body, which allowed the intake tube after the restrictor to act as an additional plenum, which really helps restricted engine performance. Essentially you're giving a bigger buffer for the cylinders to have atmospheric pressure to suck in by allowing a larger effective plenum size to fill up with air that might be momentarily going sonic through the restrictor. The intake flow is not constant, it pulses, even at 8k+ RPM, so even if it's going sonic at the very peak of draw through the restrictor, the extra plenum volume helps it. It also reduces the "peak" pressure signal the restrictor sees, which helps it not go sonic.
2. You radius'd the edges of the restrictor very well, which is going to give very low flow losses as the flow constricts through the restrictor then expands out. This will tend to not drop the total pressure of the flow as you saw. If you made the same design with sharp edged corners on inlet and outlet, you would definitely see power going down up top with the 2" restrictor. It won't be a huge amount, but there will be flow losses there, and it will cause the total pressure available to the intake manifold to drop as flow goes up. A thinner restrictor would yield slightly more losses too, but probably not a huge difference vs. your 2". The corner detail in and out is really critical though.
3. As stated above, 2" isn't really choking down a 300 whp engine that much when the flow coefficient in and out of the restrictor are very good.
The following users liked this post:
Mrsideways (07-24-2017)
07-23-2017, 12:03 PM
#12
300 whp is roughly 30 lbs/min of airflow, which you can easily pull through a 2" ID hole at roughly sea level atmospheric pressure. Look at turbos for an idea of what sort of area chokes (goes sonic). A 45 mm inducer will easily support 300 rwhp, even with a big compressor wheel nut blocking a decent sized chunk of the area.
Restricting a Turbo induced engine, you can retain or improve serious low end and mid range trq, but cap off the hp to meet regulation requirement. On an engine such as this, your going to lose power nearly everywhere. Simply limiting rpm might be the better option. At the end of the day, some more experimenting on the dyno is going to be required. Math will only get you so far.
Speaking of which, to the OP what hp number are you trying to hit to reach regulation out of curiosity?
Last edited by s2000Junky; 07-23-2017 at 12:13 PM.
07-23-2017, 12:34 PM
#13
I'm not a dynamics flow expert by any means. But logically thinking your statement through, there has to be a distinguishable difference between forcefully pushing air though a fixed opening to get positive pressure to an engine, then relying on a NA engine to draw air in effectively through the same size opening. In other words, a fixed size tube to support theoretical hp figure is really irrelevant here. It falls under its own set of parameters on what this motor can effectively draw from before it starts to pull vacuum and choke, which is what the OP is essentially trying to achieve, pull a vacuum to reduce power.
Restricting a Turbo induced engine, you can retain or improve serious low end and mid range trq, but cap off the hp to meet regulation requirement. On an engine such as this, your going to lose power nearly everywhere. Simply limiting rpm might be the better option. At the end of the day, some more experimenting on the dyno is going to be required. Math will only get you so far.
Speaking of which, to the OP what hp number are you trying to hit to reach regulation out of curiosity?
Restricting a Turbo induced engine, you can retain or improve serious low end and mid range trq, but cap off the hp to meet regulation requirement. On an engine such as this, your going to lose power nearly everywhere. Simply limiting rpm might be the better option. At the end of the day, some more experimenting on the dyno is going to be required. Math will only get you so far.
Speaking of which, to the OP what hp number are you trying to hit to reach regulation out of curiosity?
the turbo engine makes more midrange torque because it can choke the inducer throughout most the rev range, but the NA engine won't see large losses until it chokes assuming a Venturi shaped restrictor with low flow losses.
07-24-2017, 08:28 AM
#14
Thread Starter
300 whp is roughly 30 lbs/min of airflow, which you can easily pull through a 2" ID hole at roughly sea level atmospheric pressure. Look at turbos for an idea of what sort of area chokes (goes sonic). A 45 mm inducer will easily support 300 rwhp, even with a big compressor wheel nut blocking a decent sized chunk of the area.
Now, I will highlight some reasons why this DID not knock down power, but many people do see a reduction in power with larger restrictors:
1. You put it pretty far ahead of the throttle body, which allowed the intake tube after the restrictor to act as an additional plenum, which really helps restricted engine performance. Essentially you're giving a bigger buffer for the cylinders to have atmospheric pressure to suck in by allowing a larger effective plenum size to fill up with air that might be momentarily going sonic through the restrictor. The intake flow is not constant, it pulses, even at 8k+ RPM, so even if it's going sonic at the very peak of draw through the restrictor, the extra plenum volume helps it. It also reduces the "peak" pressure signal the restrictor sees, which helps it not go sonic.
2. You radius'd the edges of the restrictor very well, which is going to give very low flow losses as the flow constricts through the restrictor then expands out. This will tend to not drop the total pressure of the flow as you saw. If you made the same design with sharp edged corners on inlet and outlet, you would definitely see power going down up top with the 2" restrictor. It won't be a huge amount, but there will be flow losses there, and it will cause the total pressure available to the intake manifold to drop as flow goes up. A thinner restrictor would yield slightly more losses too, but probably not a huge difference vs. your 2". The corner detail in and out is really critical though.
3. As stated above, 2" isn't really choking down a 300 whp engine that much when the flow coefficient in and out of the restrictor are very good.
Now, I will highlight some reasons why this DID not knock down power, but many people do see a reduction in power with larger restrictors:
1. You put it pretty far ahead of the throttle body, which allowed the intake tube after the restrictor to act as an additional plenum, which really helps restricted engine performance. Essentially you're giving a bigger buffer for the cylinders to have atmospheric pressure to suck in by allowing a larger effective plenum size to fill up with air that might be momentarily going sonic through the restrictor. The intake flow is not constant, it pulses, even at 8k+ RPM, so even if it's going sonic at the very peak of draw through the restrictor, the extra plenum volume helps it. It also reduces the "peak" pressure signal the restrictor sees, which helps it not go sonic.
2. You radius'd the edges of the restrictor very well, which is going to give very low flow losses as the flow constricts through the restrictor then expands out. This will tend to not drop the total pressure of the flow as you saw. If you made the same design with sharp edged corners on inlet and outlet, you would definitely see power going down up top with the 2" restrictor. It won't be a huge amount, but there will be flow losses there, and it will cause the total pressure available to the intake manifold to drop as flow goes up. A thinner restrictor would yield slightly more losses too, but probably not a huge difference vs. your 2". The corner detail in and out is really critical though.
3. As stated above, 2" isn't really choking down a 300 whp engine that much when the flow coefficient in and out of the restrictor are very good.
Thank you, that was exactly what I was looking for. As I was sanding the edges of the restirctor I was wondering how much I negated it's effect.
07-27-2017, 12:23 PM
#15
Sanding the edges has an effect, which grows more and more pronounced as you approach choke flow when you see more optimized venturi profiles in use. Once you reach choke flow, the only way to increase the mass flow rate is to increase the density ahead of the restrictor (the main reason the restrictor goes in front of the turbo in most classes, for example).
Thread
Thread Starter
Forum
Replies
Last Post
b.r.i.a.n.
S2000 Naturally Aspirated Forum
175
03-28-2018 03:33 PM
beaudin223
S2000 Forced Induction
3
11-07-2016 01:58 PM
WalkingDrunken
S2000 Under The Hood
13
05-23-2004 05:56 AM