While trying to get my new setup sorted out tonight, I logged a Datamaster run and noticed my MAP dropped from about 100.4 KPA at lower RPM , down to about 94 KPA at 6700 RPM. I'm running a 4" dia CAI, a 7" dia X 9" long new K&N, stock rubber elbow (less donkey dong), stock MAF, 58MM Throttle body, LT1 intake bored for 58MM TB and a matched gasket. This system should be capable of flow out the wazzuu.

Does this amount of manifold pressure loss make sense. Seems like a lot to me. I can't hardly believe a lil 355 can move enough air to choke the MAF. Is the design if the intake manifold itself the culprit.

confused

Steve

 

Where does the MAP get it's reading? From the plenum? If so you would not know what the manifold is doing restriction wise. What you do know is that you have a restriction somewhere between the airfilter and the point that your reading is taken. On TPI it is quite common to remove the screens from the MAF to increase flow. Not sure on the LT1 as I thought it was a speed density system. Allen

 

MAP sensor is located in the intake manifold. The sensor port is about 1.5" behind the 58MM throttlebody bores. I also verified that the TB blades are opening to 90 degrees. I think I'll log a run without the MAF and CAI system. Just an open TB with no filter. If my MAP comes back up then, I'll start adding parts back on one at a time to find the culprit. I'll bet the MAF is the restriction.

Steve

 

That's pretty normal. 6kPa ~=2" of mercury. Carbs are sized for a 1.5" pressure differential, and they need it to get a good signal. EFI doesn't, so if you can lower it you may gain a couple of hp. But there will always be some intake restriction.

Rich

 

Yeah unless you enlarge the pleanum volume... and this is happening on a 355 @ 6700rpm under 400rwhp... kinda scares ya what can happen with more airflow demand.

Bret

 

steve,
I have a great deal of information on this issue, I can almost gurantee it is not the maf.

Give me a ring and I can review with you.

Thanks
Dennis

 

It'll do better with a 1300CFM TB and a 4" air intake and a filter to match and not the 6" long K&N it don't have the flow potential.

 

RD,

You'll see in my post, I have a 4" system and my filter has a 4" inlet, is 7" in Diameter, and a full 9" long. Its located in the fender well like typical commercial CAIs. The filter kind fills up that space pretty good , My 4" pipe has a transition down to the MAF. then it's an LE rubber elbow. 58 MM Holly TB, LT1 intake with TB bores bored out to 58.


Stroker,

My sig says 390HP but in theory I should be over that now. It's still not a whole lot of air we're talking about here. Im a heading to the Dyno today to get a couple of pulls on this combo.

Dennis,

I'll give you a call.


To All,

My bad, Should have done the search. This subject has been discussed multiple times, however, no full explanation or solution though. May be its the velocity of air rushing past the MAP sensor hole creating a (mental loss for correct words) pressure change. So maybe its not a real loss of MAP?

Steve

 

RD,

You'll see in my post, I have a 4" system and my filter has a 4" inlet, is 7" in Diameter, and a full 9" long. Its located in the fender well like typical commercial CAIs. The filter kind fills up that space pretty good , My 4" pipe has a transition down to the MAF. then it's an LE rubber elbow. 58 MM Holly TB, LT1 intake with TB bores bored out to 58.


The cleaner ya got doesn't flow enough. The one that does is 12"long and is 12OO?CFM and your TB is a 950 not a 1300CFM.

 

LR,

What is the part number and manufacturer of the cleaner you are talking about?

 

It's a K&N but don't remember the number.Call them they will know.

 

I think he's talking about the KN # re-0870. On my car that filter show's zero restriction when it's on the 4" maf end or the Maf is filter less.

http://www.hotrodhawk.com/images/motor_front.JPG

 

This might be the filter that LR is talking about "K&N RE-0860 Filter (Flows 1357cfm) 4" Inlet". I have this on my K&N setup and had to mock it up just a little bit for it to fit on my non-ram air CAI.

Brandon

 

That's it.No need to put a 1300CFM TB on and the cleaner flows 750CFM--- kinda defeating the purpose.

I had a hell of a time with this '94 getting it to fit in the fender well, it's simple when ya figure it out.

 

The pressure change you see is normal with a stock style intake...or any combo whos heads demand more air than the intake can flow ...Also as any engine, efficiency is greatest at peak torque so you will see more kpa in that area since as it revs past peak torque fuel demand is less meaning the engine isnt as efficient ... If the car has ever been dyno'd and logged you'll see kpa follows the torque curve alot of the times...