Reasons for not hitting 100 kpa MAP
 

I've done some logging over the last few days and noticed I'm only seeing around 95-90 kpa with the lower at higher rpm's. Now I think this is probably due to an intake restriction? Throttle Body itself? Filter Assy?

But I thought I'd ask if there's anything else that I should be looking for? Does the MAP sensor read more kpa for more voltage? I guess I could be low on voltage to it? a bad earth?

Whats more likely?

Dan

Re: Reasons for not hitting 100 kpa MAP
 

Intake restriction of some sort, could be TB or filter, or combination of both.

Re: Reasons for not hitting 100 kpa MAP
 

I am running a stock TB with a fairly agressive 383ci motor so I was expecting a bit of a restriction there - just wanted confirmation really.

I guess my next question should be... is the expense of a free flowing TB worth the extra power I'm "leaving on the table"

Car feels pretty strong :)

Re: Reasons for not hitting 100 kpa MAP
 

First thing to check is the MAP at key-on, engine-off. That will be the highest the engine can go (unless the elevation is reduced). This is the current barometric reading.

Base all further engine running MAP values from the barometric reading).

In inchs of Hg, a full out race car should have a max of 1" drop.
A hot street car a max of 1.5" - 2" drop.

The drop can be anywhere from the plenum forward. Extra MAP sensors tied in at different locations of the induction system can show where the restrictions are.

RBob.

Re: Reasons for not hitting 100 kpa MAP
 

Ya, mine is 98 engine off. I would graph it. I fudged the range so it only reads 92 to 98.5, to give me a high resolution graph. I've discovered some funky things going on in the low RPMs that have been difficult to explain.

Re: Reasons for not hitting 100 kpa MAP
 

ahh of course engine off is the first thing I will check next time :)

is there a way to work out what kind of difference it would make at 100kpa? I know it more optimum but at what cost do I go to with fixing this. I'm running a completely stock paper filter right now. I do have a K&N panel replacement that I'll chuck in - will be interesting to see if there is ANY difference.

Re: Reasons for not hitting 100 kpa MAP
 

I have two different air cleaner setups. The stock round air cleaner does better in low end, but my modified intake does better in the top end. The difference I am seeing in the low end (below 2500 RPM) is from 97 KPA with the stock air cleaner down to 96 KPA with the modified fresh air intake. The difference in performance is between just barely chirping the front wheels, to a significant screech till I hit about 15 to 20 mph.

In the midrange to top end, The modified fresh air intake does better in the midrange - 3K and above. The stock air cleaner will drop to around 92 KPA above 3K. The modified intake only goes down to around 93.5 KPA The difference there is somewhat more subtle. Yes, you can feel it, but its not huge till above 4K. At around 4500 rpm the engine gags with the stock air cleaner and maxxes out at 4800 rpm. You don't see the KPA climb anymore, but it just tops out. The modified fresh air intake winds out to well above 5200 RPM - OOPS!

Its hard to say what a car will do, this is a 502 in a FWD motorhome, so differences in acceleration are a bit more subtle with a 13K lbs vehicle. Your results may/will vary.

Re: Reasons for not hitting 100 kpa MAP
 

The only time I've seen 100kpa (or slightly higher) was at sea level on a high pressure day (about 103kpa) with the engine off. That was the same reading at our local airport.

WOT I could only hit 98-99. The 4-5 kpa difference represents the pressure differential as the intake system (TPI at the time) is a bit of an overall restriction. I think EVEN if I had the least restrictive intake possible, there would still be a couple kpa difference as nothing is "perfect".

Re: Reasons for not hitting 100 kpa MAP
 

My first question would be location.
If you are above sea level you will not see 100kpa.

You may also just not be logging data at 100kpa if you are in PE mode.

If you log with winaldl does the green box jump to 100kpa with no data shown or does it never jump to 100kpa?