When does the stock 1g intake manifold become a restriction?

[pyro719]

At what air flow/hp does the 1g intake manifold start losing air flow power?

 

[jayson427]

The stock intake manifold is great for street use and autocrossing but in road racing it might become a restriction, especially on tracks with long straights. The power curve levels off at about 6400 RPM and if you have (or are planning to install) cams then you should also plan on changing out your stock intake manifold with one that can support power in the upper RPM range. All of the aftermarket intake manifolds available will have shorter runners and larger plenums, which is what helps increase the power in the higher RPM range but also hurts power in the lower RPM range. This is why it's not an ideal modification for autocross. It's also a modification that you'll want to do after you've done everything else we've discussed above. You won't see much gain in power if you do it in the beginning. The most popular and proven intake manifold on the market is built by Magnus Motorsports.

http://www.dsmtuners.com/1g_dsm_road_racing_setup

heres the link i grabbed the info from hopefully this helps.

 

[LandSpeed-DSM]

Somewhere north of 800whp
http://www.dsmtuners.com/forums/dyno-talk/438871-holset-hx52-dsm-816hp-569tq-38psi.html

If you are asking about what RPM it will start to fall off, that is different.

 

[pyro719]

Im wondering if there is much to gain on my setup. 2.0 Fp red hta 272 cams 10/1 compression e85. Ill be getting tuned in a week and would like to maximize the setup.

 

[jayson427]

is your current intake ported or just straight stock? since you got some good mods anything that will make better flow for the intake manifold will always be good but not absolutely necessary.

 

[pyro719]

Stock intake. Looking to max out this fp red around 500 to 550 whp on a dyno dynamics dyno

 

[camas90gsx]

I hate to say it,but the vast majority of dsms go for the aftermarket intake mani for cosmetic purposes not performance. If anything you will hurt your performance rather than help. It sounds like you have a hood start on your build,but there are many dsms out there running 1 or 2g intake mani's at 500-550hp. If in the future your logs start to show that it is becoming a restriction,then worry about it. Other than hp #'s what are your goals for your build?

 

[bastarddsm]

No. It doesn't choke at a certain mass flow "(HP)" persay. It chokes when the volume flow (cfm), and the cross sectional area, requires the velocity of the flow to approach 1/3 the speed of sound. From then on it chokes harder and harder, meaning the velocity stays the same, but the density of the air making it through falls off.

The density of the incoming air has little effect on the choke velocity. The volume air flow(cfm) is determined by RPM and displacement, mass flow is determined by boost, and volume flow.

It's not choked because of HP, but because of RPM, and displacement.

Based on the cross sectional area of the runners, I'd say it never "Chokes"

It's well established that a 2.0 with a 1g port doesn't encounter choke flow until near 9000RPM, I'd expect the 1g head to follow suit.

The 6200-6500RPM cut off everyone experiences is running out of the ram tuning area of the runners. It is the result of the positive pressure waves in the runners becoming miss timed with an open intake valve.

This is also compounded by the hot-side of the turbo becoming more restrictive, and creating higher residual exhaust gas fractions.

Finally in the case of the HX52, the stock intake doesn't appear to hold it back because of the slow spool causing the torque to peak way after the manifold "peaks" If it made full boost 1000RPM sooner it would be evident. A better intake would defiantly improve the numbers. Not hugely, but improve them none-the-less.

Keep in mine the turbo choice will ALWAYS have the biggest effect on the power curve, followed by cams, and intake last.

To further illustrate the idea of not choking, my intake is a stock one with the plenum and about 4" of runner cut off and a piece of 4" pipe removed. Did not touch the runners at all. With HKS272's and at low boost my power peak went up by about 1800RPM to 8000. Close to what the old rule of thumb says. 7" for 10,000RPM, and add 2" for every 1000RPM you want to bring it down. When I turn the boost up, the power peak falls back to about 7200.

 

[pyro719]

I hate to say it,but the vast majority of dsms go for the aftermarket intake mani for cosmetic purposes not performance. If anything you will hurt your performance rather than help. It sounds like you have a hood start on your build,but there are many dsms out there running 1 or 2g intake mani's at 500-550hp. If in the future your logs start to show that it is becoming a restriction,then worry about it. Other than hp #'s what are your goals for your build?

Id like to run a high 10 at the track and trap in the mid to high 120's

No. It doesn't choke at a certain mass flow "(HP)" persay. It chokes when the volume flow (cfm), and the cross sectional area, requires the velocity of the flow to approach 1/3 the speed of sound. From then on it chokes harder and harder, meaning the velocity stays the same, but the density of the air making it through falls off.

The density of the incoming air has little effect on the choke velocity. The volume air flow(cfm) is determined by RPM and displacement, mass flow is determined by boost, and volume flow.

It's not choked because of HP, but because of RPM, and displacement.

Based on the cross sectional area of the runners, I'd say it never "Chokes"

It's well established that a 2.0 with a 1g port doesn't encounter choke flow until near 9000RPM, I'd expect the 1g head to follow suit.

The 6200-6500RPM cut off everyone experiences is running out of the ram tuning area of the runners. It is the result of the positive pressure waves in the runners becoming miss timed with an open intake valve.

This is also compounded by the hot-side of the turbo becoming more restrictive, and creating higher residual exhaust gas fractions.

Finally in the case of the HX52, the stock intake doesn't appear to hold it back because of the slow spool causing the torque to peak way after the manifold "peaks" If it made full boost 1000RPM sooner it would be evident. A better intake would defiantly improve the numbers. Not hugely, but improve them none-the-less.

Keep in mine the turbo choice will ALWAYS have the biggest effect on the power curve, followed by cams, and intake last.

To further illustrate the idea of not choking, my intake is a stock one with the plenum and about 4" of runner cut off and a piece of 4" pipe removed. Did not touch the runners at all. With HKS272's and at low boost my power peak went up by about 1800RPM to 8000. Close to what the old rule of thumb says. 7" for 10,000RPM, and add 2" for every 1000RPM you want to bring it down. When I turn the boost up, the power peak falls back to about 7200.

Great info! Exactly what I was looking for Thank you.

 

[whe3ls]

on my buddys car 10.5:1 fp4r s366 and e85, i think he hit a wall around 60bls/min. the car pulls the same at 28psi as it does at 40psi

 

[GofaST4life]

Somewhere north of 800whp
http://www.dsmtuners.com/forums/dyno-talk/438871-holset-hx52-dsm-816hp-569tq-38psi.html

If you are asking about what RPM it will start to fall off, that is different.

Well there you have it. Looks like you can spend the money elsewhere.

 

[biglady112]

After what we did with the stock intake manifold, I honestly do not believe that any sort of short runner manifold yields any more overall peak power. It just changes the shape and shifts the power and torque curves. On that same car we were able to make 785hp@30psi just two months later with a home made water injection system that allowed me to lean on the motor that much more. I think with enough boost it could reach nearly 900hp on the HX52 and who knows how much with 7-10mm or more on the turbo.

They do fall off hard after 6500rpm on a "normal" turbo. But as far as holding power back, I do not think there is any sort of restriction. If you open the inlet of the manifold with a larger throttle body and larger opening it should flow anything you cram into it.

 

[arrowhead]

No. It doesn't choke at a certain mass flow "(HP)" persay. It chokes when the volume flow (cfm), and the cross sectional area, requires the velocity of the flow to approach 1/3 the speed of sound. From then on it chokes harder and harder, meaning the velocity stays the same, but the density of the air making it through falls off.

The density of the incoming air has little effect on the choke velocity. The volume air flow(cfm) is determined by RPM and displacement, mass flow is determined by boost, and volume flow.

It's not choked because of HP, but because of RPM, and displacement.

Based on the cross sectional area of the runners, I'd say it never "Chokes"

It's well established that a 2.0 with a 1g port doesn't encounter choke flow until near 9000RPM, I'd expect the 1g head to follow suit.

The 6200-6500RPM cut off everyone experiences is running out of the ram tuning area of the runners. It is the result of the positive pressure waves in the runners becoming miss timed with an open intake valve.

This is also compounded by the hot-side of the turbo becoming more restrictive, and creating higher residual exhaust gas fractions.

Finally in the case of the HX52, the stock intake doesn't appear to hold it back because of the slow spool causing the torque to peak way after the manifold "peaks" If it made full boost 1000RPM sooner it would be evident. A better intake would defiantly improve the numbers. Not hugely, but improve them none-the-less.

Keep in mine the turbo choice will ALWAYS have the biggest effect on the power curve, followed by cams, and intake last.

To further illustrate the idea of not choking, my intake is a stock one with the plenum and about 4" of runner cut off and a piece of 4" pipe removed. Did not touch the runners at all. With HKS272's and at low boost my power peak went up by about 1800RPM to 8000. Close to what the old rule of thumb says. 7" for 10,000RPM, and add 2" for every 1000RPM you want to bring it down. When I turn the boost up, the power peak falls back to about 7200.

I do not understand cutting the runner 4in and 4in pipe removed and then not touch the runners at all, could you provide a picture.
thanks

 

[Steve93Talon]

I do not understand cutting the runner 4in and 4in pipe removed and then not touch the runners at all, could you provide a picture.
thanks

It sounds like he's referring to something like this, where you cut off the stock plenum, shorten the runners, and weld a sheetmetal plenum on:

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I did something similar recently, cut the back open, removed about 3.5" of the runner, and welded it back together. I haven't had a chance to test it out yet, though.

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[bastarddsm]

Ohh I like that. Mine is a PITA cause it's so close to the firewall. I need it tho because I run dual fuel rails.