Piggybacking off of WRD1972's thread, which began from my own thread about losing fuel pressure in the upper RPM range https://www.camaroz28.com/forums/sho...d.php?t=671487

I am seeing about a 12KPA loss at 100% throttle position in the upper rpm range. I have a K&N cold air intake, then a 4" to 3" reducer to an unmolested stock MAF, then the stock elbow with the air silencer removed. Also have a stock tb. I am losing a lot of hp, hoping you guys can help diagnose the problem.

Engine in sig, 355 with hotcam, 30# injectors and racetronix fuel pump.

 

Whats the reducer look like, what is around the airfilter, is it blocked down below or is the cavity fed.

 

The filter is down near the splash guard. I was thinking of putting the scoop down there to help since the car only comes out on nice days/track days. I was thinking maybe there was not enough volume of air down there. I know it wont be a ram air effect but the increased volume may help. The splash guard is currently untouched.

The reducer looks like a nozzle, which I could see as a restriction but the maf is only 3 inches, and the K&N plastic piece is 4 inches.

 

I'm running a untouched CAI (K&N) on my 383 with a much larger cam and not having issues. So I would look somewhere else unless you managed to clog the filter. (somewhere else may include the MAF which you are already looking at). My main point is, messing with the filter itself should not be the issue.

 

bombebomb - Is your splash guard untouched? Do you have a reducer to connect the k & n to the maf? How is yours connected? I did not plan on modifying the filter or the k & n elbow.

I will clean and recharge the filter when I get a chance and take another log. Other ideas?

 

I was losing 3-4 kPa on the top end of my car when it had Pacesetting LTs with cutouts and a homemade CAI with stock elbow (no MAF as mine is a '93). I replaced the stock TB with a Summit 58 mm and hogged out the manifold holes to match it. I then saw no vacuum at WOT whatsoever, also picked up 0.1 ET, so roughly 10 HP. I know people say the stock TB is good to some huge amount of HP, but on my stock internal engine the 58 picked it up alot.

 

One more thing I forgot: I cut a roughly 4x4 inch hole in the splash guard in front of the left wheel. I am using a cheap cone-type cotton gauze airfilter also.

 

How did you conclusively determine that you did not have any vacuum at WOT whatsoever? It think it is pretty much agreed by most that that is near impossible, especially for the LT1 with the longer intake tract to have no vacuum at WOT.

 

With my findings, I have already reached the conclusion that the MAF nor the filter play any significant role in the intake restriction.

I have read that big overlap cams (mine is a 107 LSA) make it hard to reach closer to zero vacuum. Who knows if thats really true.

 

Hey wrd1972, do you have a good price on a used 52mm stock tb???

 

What I meant when I said 'no vacuum' was that I was seeing nearly atmospheric pressure on my data log (roughly 101 kPa). This was up from 96 or 97 kPa with the stock TB. Of course the world is not perfect and 'absolute' will probably never be achieved for most things. 3-4 kPa was a measured improvement.

 

Its an improvement only if the barometer was the same or less than is was when you measured it on a different day with the stock TB.... if it was not done on the same day, and the "BAR" reading checked so you could calculate the difference between BAR and MAP.

 

I am not sure what you mean when you say calculate the difference between BAR and MAP. BAR is a unit of Manifold Absolute Pressure, as are Kilopascals. 1 bar = 1 atmosphere = 101 kPa. I understand that the barometer plays a large role in MAP readings. What I am trying to say is that the larger throttle body and larger intake openings have shown consistently less vacuum (more pressure) EVERY day on my car.

 

"BAR" is the barometer reading, taken by the MAP sensor BEFORE the engine starts. You compare your MAP reading to the barometer reading, at the time the engine is running. The difference between the two readings represents the pressure loss between the outside air and the intake manifold.

It appears you are comparing your MAP readings to 1 standard atmosphere (14.7psi = 29.95"HG = 101.4lPa). That is not the correct way to measure the pressure loss.

 

UPDATE:

Cleaned and lightly recharged the K&N filter (seemed very dirty), installed a summit 58mm TB and made an air scoop. I know the scoop does not make it a ram air and the car is never driven in the rain. Took a log with all of these modifications done and now at 100% throttle position, at 6200 rpm I was seeing a loss of 3-4 KPA. Since I performed all of these mods at once I can't say which made the most benefit, but either way, I am happy the issue is resolved.