Tuner thinks I might have an intake restriction that is causing MAP KPA to dip a bit lower than it should at WOT. I get 96-98 at low to mid RPM and 92-94 at WOT. Not sure this is even a problem.

I have a stock ported 52mm TB, air diverter, 1LE rubber elbow and Arizona Speed & marine CAI. All components look good and the filter does not look unusually dirty.

I have Scanmaster and Datamaster to log MAP KPA.

 

It's a problem if you want maximum horsepower. Idealy you want the plenum to be equal to atmospheric pressure at WOT. You should be able to get 99KPA. However it depends on far you want to take things.

I would take off the air tube in front of the throttle body and see what that does for your KPA. It could be you need a combination of things. You just need to trouble shoot by testing the componets and see what they do to your KPA. Again it is just a matter of how far you want to take things.

It could be enough to get you close to 400rwhp.

 

TY. It is on my to do list.

 

I have the same problem as you, but have also had some other issues so I haven't worried about it yet. I saw a post on here by a guy that also had this problem and went to a monoblade to help the situation.

 

Your MAP readings don't mean anything unless you reference them to the barometer reading (BAR) that the PCM is indicating. The pressure loss in the intake track is equal to barometric pressure minus MAP. That equals vacuum. Both numbers are available in a data scan. Barometric pressure depends on altitude, air density, and weather conditions.

Take your data log and post both numbers to determine how severe the problem is. Each kPa you lose represents approx a 1% loss in engine HP.

 

Injuneer,
Thanks for the explanation. Makes perfect sense.

Here is some data that I have from a run at the strip last year.
BP= 101.1
3025 RPM = 98.2
4025 RPM = 97.8
4500 RPM = 97.4
4925 RPM = 95.6
5575 RPM = 96.7
6075 RPM = 95.2
6375 RPM = 94.0

So it appear that pressure loss at redline is 7.1 which could potentially = 7% power loss.

Is this about right or excessive?

 

At your max rpm that is just over 2" of vacuum (in hg) using standard atmospheric pressure. This is excessive even for a carbed motor.

A good place to start may be to verify with a vacuum gauge during a run that you're actually seeing that much. With the map sensor located where it is at real high rpms its subject to the vacuum pulses created by the two intake ports located directly under it. My map readings are somewhat eratic at wot. If you are friendly with somebody who has a flow bench, start flowing your throttle body then start adding your intake pieces to it. You may be suprised on how little performance some filters are capable of providing. It takes a big filter to flow enough for 400rwhp. To move 350g/sec (common for h/c lt1's) through the maf at standard conditions and room temp you have to move about 872cfm, 400g/sec is right at 1000cfm (doubt you made it near here unless your maf calibration is way off based on your hp).

I have the same problem as you only worse mid 80's on map at upper 5000rpm. Taking the filter and maf off does nothing for it. Since I already have a 58mm tb I am thinking of changing intakes to one that will allow me to use an ls1 tb or go to a 4150 style tb.

Just as a side note, if you're running a regular old stock configuration style catback you may want to rethink it even at your power levels. I found a lot of hp when I ditched the 3" pipe for a set of duals. The cross section of a 3" pipe just aint getting it for any significant hp in my opinion.

 

Thanks for the response. Now we are getting somewhere.

Dont know anyone with a flow bench, so thats out.

My AS&M CAI uses a 3.5" hard pipe and piece of rubber hose to connect the hard pipe to the MAF. This rubber hose is squeezed between the radiator and the ABS module meaning the hose is pinched and no longer totally open like one would want. The filter is round and about 8" in height.

Maybe part of the problem is the AS&M CAI. Maybe because of the pinch and the smaller filter, it is incapable of flowing what I need. I know the K&N FIPK or the LPE CAI should flow more air through the plastic tube than my current setup. Those kits also have the great big K&N filter which is the biggest that will fit down in the hole.

I will assume that the MAF is calibrated properly, tuner knows his stuff plus he commented last year that he thinks there is a restriction in the intake somewhere. The MAF is stock with the screen FWIW.

I have been thinking about duals too BTW. But i want to resolve this intake issue first.

What do you guys think about my comments on my CAI? Would the K&N or LPE be worth the investment?

 

so more pressure in manifold is better? I datalog some and notice my bar is at 1.01 and my map is either 1.01 to .99 at WOT. That's good?

 

Stock maf with screen is not a problem as far as restriction goes unless you're boosted and even then its debatable.

As to wether or not your maf is calibrated properly. If your pe is flat along the rpm range and is commanding what you're getting from the wideband, then it is. If your pe values are all over and its commanding some wild number, then it isnt. The difference is that if the maf is calibrated correctly and pe/rpm values are constant, when you make a change to the engine later the tuneup will still be dead perfect. In either case if the thing makes power and the air fuel ratio is safe dont worry about it too much. Every tuner has thier way, mine is to adjust maf and ve until the air fuel matches whats commanded.

Try the bigger filter on your current cai if you want to spend the cash on that. Or if your tuner gave you a speed density tune that works try running just the filter attached to the tb or maybe no filter or maf on the dyno to see if theres a power diff if it picks up you know where to spend the cash or if it doesnt.... you will still know.

 

One more thing. Look at the two pinches inside the 3.5" rubber hose for my CAI. These two pinches are between the radiator and the ABS module. What are your thoughts on this?

 

Not good. Those pinch points will create a lot of turbulence which you do not want for good air flow. They could even screw up the MAF reading where you want good laminar flow. I was told of where ribbed tubing was used in front of the MAF and everything went to hell. Anyways that is a problem and should be corrected.

 

Here is my 3.5" cold air intake on my 3rd Gen. With my next motor I'm hoping for well past 400rwhp so I need all the air I can get. By the way that is an AS&M monoblade throttle body. I get between 99 to 100kpa at WOT with the current motor.

By the way the air filter is capable of 1300CFM, the 3.5" tubing is capable of 1300 CFM and the throttle body is rated at 1300CFM. So with the accumulated losses maybe 1100 CFM at the plenum area.

 

Any chance at all of moving that up some to get rid of the pinch without hittin the hood. Sorry long time since I messed with a stock hood or cai since I use the ram air box which is a straight shot into the tb.

Also it doesn't look like your filter works too well with all dirt on the inside of the tubing. When your maf gets dirty it will send your air fuel ratio rich real quick.

I would want it as straight a shot as possible with a nice large cross section. If you can modify what you have and get a larger filter on it you may pick up some power. Honestly unless you can sell your current cai for about what a new one would cost I wouldnt lose sleep over it. You can spend a whole load of money chasing that last few hp that may or may not be there, up to you of course. I would find it hard to justify the cost.

 

I cant raise the tube up any higher to reduce the pinches. Dont think thats dirt in the tube, the flash looks to be exposing the stuff that just does not look like dirt. Maybe its a release agent that was used when making the rubber tube.

When its nice outside, I am going to play with the data logger and pull the CAI and do some testing. I am leaning toward getting K&N FIPK to take advantage of the better flowing tube. I can get one dirt cheap new and sell my current CAI.