Intake Manifold Pressure dropping at Higher RPM..
Thread Starter
Joined: Nov 2001
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From: Valrico, Florida
Intake Manifold Pressure dropping at Higher RPM.. I was informed that my intake manifold pressure drops at higher rpm. I have a ported TB. Any ideas on what I can do to solve this small issue?
On The Tree
Joined: Dec 2002
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From: Orlando, FL
Re: Intake Manifold Pressure dropping at Higher RPM.. A pressure drop indicates there is a restriction in the intake tract. At WOT you ideally would want to see full atmospheric pressure all the way up the RPM band.
From Vince's last dyno...
@3062 MAP = 14.8
@3821 MAP = 14.6
@4300 MAP = 14.5
@5227 MAP = 14.4
@6000 MAP = 14.2
@6700 MAP = 14.1
Any reduction in manifold pressure will cost HP. If you could eliminate the pressure drops in the intake tract the car would make more HP.
Tim
From Vince's last dyno...
@3062 MAP = 14.8
@3821 MAP = 14.6
@4300 MAP = 14.5
@5227 MAP = 14.4
@6000 MAP = 14.2
@6700 MAP = 14.1
Any reduction in manifold pressure will cost HP. If you could eliminate the pressure drops in the intake tract the car would make more HP.
Tim
Thread Starter
Joined: Nov 2001
Posts: 8,259
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From: Valrico, Florida
Re: Intake Manifold Pressure dropping at Higher RPM.. Thanks Tim.. I am cutting stuff up as we speak to open that path. Just kidding. I will figure out something. Anyone have any ideas..
Re: Intake Manifold Pressure dropping at Higher RPM.. Wow.. it's good to see that in #'s. My dyno software predicted that, but I wasn't so sure. The math works out to be almost a 20 hp loss if you are making 400 hp. I'm putting my motor in my rx7, so it's a hybrid anyway. I'm wanting to use one of the lt1 monoblade style oval throttle bodies that flow 1500 cfm or so... I would slice of the intake manifold "neck", then reshape the opening and attach an oval tube to the tb. I know.. lots of work. It makes me consider the holley piece (easier to weld an oval aluminum inlet to), but I don't like the weight and heat soak issues...
On The Tree
Joined: Dec 2002
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From: Orlando, FL
Re: Intake Manifold Pressure dropping at Higher RPM.. How about this for a restriction... these #s are from Colonels old 422 I tuned a couple of weeks ago. We hit 497 RWHP with the cutout close and 503 RWHP with the cutout open (Magnaflow catback).
@2728 MAP = 14.6
@3350 MAP = 14.4
@4230 MAP = 14.2
@4800 MAP = 13.9
@5400 MAP = 13.6
@6700 MAP = 13.5
The large motors really need some help.
Tim
@2728 MAP = 14.6
@3350 MAP = 14.4
@4230 MAP = 14.2
@4800 MAP = 13.9
@5400 MAP = 13.6
@6700 MAP = 13.5
The large motors really need some help.
Tim
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Re: Intake Manifold Pressure dropping at Higher RPM.. if you have a way to measure volume of air moving, that nosing over along with power production would show a restriction i beleive
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Re: Intake Manifold Pressure dropping at Higher RPM.. If you don't mind putting holes in everything
<img border="0" title="" alt="[Razz]" src="gr_images/icons/tongue.gif" /> the most straightforward way to get your
answer, is to take a vacuum gauge and tap
the intake tract at every intermediate
point (probably selected by the ease of
repair). Under air filter, inside lid, between
MAF & TB, and the manifold itself. The difference
between pressure/vacuum readings down the line
identifies the contribution of each "resistor".
If you used a capillary or very small vacuum
tube, and put it in from the bottom where the
repairs wouldn't show, this would be a good
experiment. Throw some real light on the
relative worthwhileness of various mods.
<img border="0" title="" alt="[Razz]" src="gr_images/icons/tongue.gif" /> the most straightforward way to get your
answer, is to take a vacuum gauge and tap
the intake tract at every intermediate
point (probably selected by the ease of
repair). Under air filter, inside lid, between
MAF & TB, and the manifold itself. The difference
between pressure/vacuum readings down the line
identifies the contribution of each "resistor".
If you used a capillary or very small vacuum
tube, and put it in from the bottom where the
repairs wouldn't show, this would be a good
experiment. Throw some real light on the
relative worthwhileness of various mods.
On The Tree
Joined: Jan 2002
Posts: 107
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From: Australia.
Re: Intake Manifold Pressure dropping at Higher RPM.. We have found on a head and cam car that removing the maf is worth 10+hp and MAP increases from 93kpa to 99kpa...hence the restriction is less.
Get onto Ken Kelly...you guys need mafless tuning over there. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
Get onto Ken Kelly...you guys need mafless tuning over there. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
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From: Objects in mirror no longer matter.
Re: Intake Manifold Pressure dropping at Higher RPM.. </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by HOWQUICK:
<strong> We have found on a head and cam car that removing the maf is worth 10+hp and MAP increases from 93kpa to 99kpa...hence the restriction is less.
Get onto Ken Kelly...you guys need mafless tuning over there. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">How accurate is MAFless tuning? Is that just based on rpm or what?
<strong> We have found on a head and cam car that removing the maf is worth 10+hp and MAP increases from 93kpa to 99kpa...hence the restriction is less.
Get onto Ken Kelly...you guys need mafless tuning over there. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">How accurate is MAFless tuning? Is that just based on rpm or what?
On The Tree
Joined: Jan 2002
Posts: 107
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From: Australia.
Re: Intake Manifold Pressure dropping at Higher RPM.. </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Fenris Ulf:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by HOWQUICK:
<strong> We have found on a head and cam car that removing the maf is worth 10+hp and MAP increases from 93kpa to 99kpa...hence the restriction is less.
Get onto Ken Kelly...you guys need mafless tuning over there. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">How accurate is MAFless tuning? Is that just based on rpm or what? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">based on rpm and map then with the usual parameters. Is as accurate as the tuning you put in it.
Works great for us over here.
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by HOWQUICK:
<strong> We have found on a head and cam car that removing the maf is worth 10+hp and MAP increases from 93kpa to 99kpa...hence the restriction is less.
Get onto Ken Kelly...you guys need mafless tuning over there. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">How accurate is MAFless tuning? Is that just based on rpm or what? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">based on rpm and map then with the usual parameters. Is as accurate as the tuning you put in it.
Works great for us over here.
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Re: Intake Manifold Pressure dropping at Higher RPM.. Yes, maf flows less than TB, so it makes sense that maf wopuld be introducing some of the pressure drop. This is why maf ends are worth it! Maf less tune is called speed density and it is estimation of volumetric efficiency based on rpm and map calculations. Nothing wrong with it if you have all the right info to plug in.
On The Tree
Joined: Dec 2002
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From: Orlando, FL
Re: Intake Manifold Pressure dropping at Higher RPM.. The only issues with SD tuning are that
1) While WOT tuning is pretty easy part throttle will take some time to get accurate (if you're concerned about it)
2) The PCM won't accomodate atmospheric changes well. This will require more attention to the tuning as weather changes.
I'd say if you have a track only car then go SD but if the car must be driven as a daily driver I'd sacrifice the HP and keep the car running as efficiently as possible.
Tim
1) While WOT tuning is pretty easy part throttle will take some time to get accurate (if you're concerned about it)
2) The PCM won't accomodate atmospheric changes well. This will require more attention to the tuning as weather changes.
I'd say if you have a track only car then go SD but if the car must be driven as a daily driver I'd sacrifice the HP and keep the car running as efficiently as possible.
Tim
Thread Starter
Joined: Nov 2001
Posts: 8,259
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From: Valrico, Florida
Re: Intake Manifold Pressure dropping at Higher RPM.. What is Speed Density? I would be pissed after all of this time I was swapping cams for my ultimate setup and all I had to do was buy some $70 MAF ends...
Thread Starter
Joined: Nov 2001
Posts: 8,259
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From: Valrico, Florida
Re: Intake Manifold Pressure dropping at Higher RPM.. I have a 01 LS6 MAF calibrated for the ls1 that has been descreened. What do you guys think? Should I try it and why?
TECH Addict
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From: new england
Re: Intake Manifold Pressure dropping at Higher RPM.. Vince, i will explain pressure drop than you will understand about why maf ends will help make power, atmosperic pressure is free for us to use like a free supercharger, if you can get full 14.7 psi(at sea level) into engines cylinders, and keep it there as motor winds up in its power band. If you keep a stock screened maf in there anmd that causes pressure drop, you may only get like 13 psi into cylinders past maf. So you see its like losing free boost into motor. Now i feel its worth mentioning that real powerful LS1 motors can also start pulling vacuum(pressure drop) because of small intake plenum size and long runner lengths that LS1 style intakes are known for.
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Re: Intake Manifold Pressure dropping at Higher RPM.. </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by LS1derfull:
<strong>Now i feel its worth mentioning that real powerful LS1 motors can also start pulling vacuum(pressure drop) because of small intake plenum size and long runner lengths that LS1 style intakes are known for. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Was wondering if that was going to get mentioned.
<strong>Now i feel its worth mentioning that real powerful LS1 motors can also start pulling vacuum(pressure drop) because of small intake plenum size and long runner lengths that LS1 style intakes are known for. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Was wondering if that was going to get mentioned.