firebirdStud

So, on the street, I have taken numerous Datamaster scans while at WOT. I see typically a 3-5 KPA drop from 3000 to 6400 rpms. AT the dyno last weekend, I pulled the air filter off, and it still pulled the same vacuum on top end. So, we descreened the MAF sensor, and SAME KPA drop. I have the ws6 ram air intake, with the smooth bellows. The intake is ported for the 58mm AS&M tb, and the runners have all been opened up by AI for my heads.

So, is this just a problem with the LT1 intake manifold?? Is this 3-5KPA drop on the top end just never gonna go away?

Thanks for any input, experience, thoughts...
~Cody

Injuneer

The MAP reading relative to barometric pressure is simply a measure of the air pressure lost between the atmosphere and the MAP sensing point in the intake manifold. That would exclude any measurement of actual pressure loss in the intake manifold, since the MAP sensor is up near the throttle body.

Pressure loss in the intake track, due to friction, increases (approx) with the speed of the air. Double the speed, and you will see 4X the pressure loss. That's why MAP drops as RPM/velocity increases. The difference between MAP and barometer = pressure loss, so you need to look at that number at WOT/max RPM.

With the direct route to the intake that you describe, a 5kPa drop on intake manifold pressure (relative to barometric) seems a bit high. But it isn't irrational. I run the WS6 box with the cover cut completely open, a K&N filter panel, no MAF, the Fernco smooth sewer pipe connector to the throttle body, and a Holley 58mm TB, and don't see more that 3kPa loss up to 7000rpm. I also have both baffles cut out of the hood..... are yours still in place?

firebirdStud

ok, good stuff. Ill have to look at that and see if I can decipher that.


Ok, I have the ws6 box with the louvers still in place, the fernco sewer pipe you suggested to me which is the one you run, a screened maf sensor, and the k and n filter. The hood still has baffles, yes. 3-4 kpa drop is noted while doing a WOT on the street.

Now, here is what baffles me. With the hood up, filter out, I still saw the 3-4 kpa drop. AND, then we pulled out the screen on the maf sensor, SAME drop.

So that tells me it doesn't matter if its on the street fully protected with the baffles and filter and cover with the louvers, or everything removed, its still has the same drop.

So, maybe its time to look at what you suggested with the baro readings, and see if I can figure out what you mean. Maybe I am not even pulling a vacuum if what you are saying about the map is true. ( I highly doubt you are wrong there, you are extremely educated about these motors!)

Injuneer

You don't want to pull a vacuum at WOT. You want MAP as close to barometric pressure as possible. If you have a scanner or scan software, it should show you barometric pressure (BAR on the ScanMaster). If barometric pressure is 100kPa, you want to see high 90's in the intake manifold. Less than that and you are losing HP because the cylinders are filling with less dense air.

Vacuum is the difference between MAP and barometric pressure. You see a high vacuum = low MAP at idle, because you are inserting an intentional flow obstruction (closed throttle blades) between the outside air and the intake manifold. You don't want any vacuum at WOT. You want the absolute pressure to be as high as possible, to push the air in on top of the falling piston.

firebirdStud

Ok, so if I am doing this right....
when I go to WOT at about 2500 rpms, the baro says 97.4, and the map sensor is telling me we are at 97.1.
As we go through the rpms, at 6375 rpms the baro is still 97.4, and the map is at 93-94. So, is this bad, or acceptable?

If its not acceptable, how do I fix it? I already gave it the easiest air intake tract and it doesn't aleviate the problem. So, what needs to be bigger? I already have the 58mm tb, the fernco pipe, the screened maf sensor, and ws.6 ram air intake.

But, with everything removed, so its just the TB, fernco pipe, and descreened MAF sensor I get the identical numbers. So, I am thinkin maybe the pipe or the maf housing itself is causing this?? OR what it its not?

Injuneer

Removing the filter, particularly if its a K&N, might not show much difference. The filter panel may actually smooth air flow into the hole at the rear of the air box.

Doesn't sound like you are all that bad. 97.4 barometer and a 93-94 MAP is only a 3.4-4.4 kPa loss. I don't think you are going to get much below that. Might want to play with the MAF screen to see if removing it makes any difference. With the WS6 box, the air flow into the tube is very symmetrical. GM removed the LS6 MAF screen because of that. I don't run an MAF, so I can't tell you what affect it has. Might be what accounts for the small difference between what you are seeing and what I run.

Numerically, gaining 1kPa in MAP (94 to 95kPa) will produce just a shade over 1% more HP..... or about 4HP on a 400HP engine.

firebirdStud

Yup, I did remove the screen, and it did absolutely nothing. So that leads me to beleive that its about as good as its gonna get for me then, huh??

Like I said, I now have a descreened MAF Sensor. So, Im gonna go make a couple street pulls again for sh*ts and giggles in the mornin and ill post up the results.

Thanks for being so patient and helpful yet again injuneer.

95camaroinok

Not to be an *** here. Im sure you probably have but i'll ask just in case. You said you went to the 58mm TB.... Did you port match your intake when you installed the TB? I havnt done mine yet as its all still in pieces, but I was told that the intake may need to be port matched to the 58mm. Maybe Injuneer can help us both out with the answer on that as he knows more than I do on the subject. just a thought though. Also I've read on here some people having to work over thier aftermarket TBs for flow issues regaurding the butterfly and actual porting on the new A.M. TB.

firebirdStud

Yeah, I opened up the holes on the manifold. If you put on a 58mm TB over 52mm holes, its gonna act like you only have a 52mm tb cuz that is the smallest restriction.
You have to open up the holes on the manifold, or your new TB is worthless.

I have heard nothing bad about AS&M's 58mm TB as far as flow issues... CAre to post a link?

I did have to seal up the IAC port, but that was no biggy.

Injuneer

Good thought... make sure the throttle blades are fully open and absolutely parallel to air flow when your foot is on the floor. I think that's what he meant.

firebirdStud

Oh, I see injuneer! I guess that is worth a shot at this point!
So, if its not, how do you adjust that?? Isn't that something your just stuck with, or do you have to make a manual stopper for the arm to contact when its parrallel?