boost gauge reads 8psi on 6psi kit... is it exhaus

[lilmikey77]

I heard it was because of exhaust restrictions... is that the case?

If so then by installing a header/high-flow cat/catback the boost gauge should read lower, right? So would it read 6 or 7 then?

What I'm getting at is this... If the FMU and whatever else runs off the vacuum/boost signal and now it reads 8psi and say the FMU is supplying 5psi per 1lb of boost so if it reads 8psi its supplying 40psi of fuel, right? so if I got the exhaust less restrictive and then the boost gauge read 6 or 7 psi, the FMU would be supplying less fuel, right? So this could be good and bad... it'd be more accurate per the boost delivered. Also, I'm thinking of getting a BTC, which also adjusts according to boost... Sooo if it retards X amount of timing per 1lb of boost and it retards 8 * X = more timing than I want since its only 6psi...

so if clearing up the exhaust will cause the manifold pressure to be lower, then that would cause everything else to be more accurate and work better (less fuel, less retard, etc.)

or am I just totally wrong about the manifold pressure reading higher because of exhaust restrictions... for all i know it could be this autometer boost gauge is shite.. who knows.

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94 gsr
lots of shite

[217gsr]

Does it read 8 psi all the way up to redline from ANY rpm? Or does it FIRST read 6 psi, and then when vtec kicks in, it reads 8 psi?

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6 psi JRSC GSR: GSS-317, 3" intake -> 217 hp/155 ft-lbs.
New: BTC, MAP controller, and stock timing!
Soon: Endyn stepper?

[lilmikey77]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by 217gsr:
Does it read 8 psi all the way up to redline from ANY rpm? Or does it FIRST read 6 psi, and then when vtec kicks in, it reads 8 psi?

<HR></BLOCKQUOTE>

I dont think it reaches full boost until around 4000rpm, right? and vtec engages at 4400, so I'm really not sure.

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94 gsr
lots of shite

[Holden]

lilmikey77: You are correct. The BTC, FPR, FMU.... all read the actual pressure in the manifold, which is what the boost gauge reads.

You need to calculate settings for all the boost reading mods taking that into consideration.

e.g. You want 16 degrees static timing and 12 degrees final. If you set a retard box to 0.8degree/psi, it will result in 9.4 degrees final. So set it to 0.6 and you'll get 12.2 degrees. You get the picture.

This shows a weakness of the JR FPR. You can't adjust for the difference between actual boost and manifold pressure. The Cartech units can be adjusted to achieve exactly the max FP you want.

As for your setup, I doubt you'll see less than 8psi until you chuck or replace the stock cat (with a bigger one). I had a pretty open exhaust system at 6psi, but I got 8psi too because of the cat.

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Greg Holden
96 GSR, JSRC @10psi, All the Goodies!
Best 1/4 ==&gt; 13.556 @ 105.29mph
My JRSC Install Site

[217gsr]

Excellent. Straight-pipe goes on this weekend. We'll see if it'll drop my psi's down.

------------------
6 psi JRSC GSR: GSS-317, 3" intake -&gt; 217 hp/155 ft-lbs.
New: BTC, MAP controller, and stock timing!
Soon: Endyn stepper?

[lilmikey77]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Holden:
As for your setup, I doubt you'll see less than 8psi until you chuck or replace the stock cat (with a bigger one). I had a pretty open exhaust system at 6psi, but I got 8psi too because of the cat.

<HR></BLOCKQUOTE>

Thanks for the info.

I'll be putting on a comptech header, carsound cat and itr catback. I imagine the carsound cat will make the biggest difference of the 3, and from what I've read they flow almost every bit as well as a straightpipe.

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94 gsr
lots of shite

[SuperTeg]

Would your valve adjustment have anything to do with your "perceived" manifold pressure. Like if you had your intake adjusted at max and your exhaust at the minimum valve lash?

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As long as its fast!

[Syncro]

I think every car is different. With my stock cat the boost never goes over 6 psi.


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'99 GS-R, JRSC 6 psi, DC 4-2-1 Headers, Type R Cat-Back Exhaust, JR HO Fuel Pump, Cold Plugs, J&S Ultra Safeguard v.2, JR MAP Converter, Cartech fmu, H&R OE Sport Springs, Stock Rims, Michelin Pilot 205/50/15 Tires - Yes, its a SLEEPER!

[blownLS]

Hi I am new here to this site. I am a Meteorologist with a bad habit, I spend too much time and money into my 94 LS Integra. I hope some of my weather knowledge of pressure, temperature and humidity helps to answer some questions about my favorite topic, HP and going fast.

So here is the answer to your question:

Yes it would. It changes the amount of overlap in cam timing. Anything can effect boost pressure.

I have adjustable cam gears. By changing the cam timing, I can make my normal 6psi reading (average from 4000-redline) increase or decrease 1psi. Believe it or not, but my fastest times at the track and highest dyno numbers (avg not pk) was at the 5psi setting, not 7. The difference was .4 seconds at the track.

A temperature or dew point difference can also change it. I get 1/2psi more boost in the winter than in the summer, due to cold and dry versus hot and humid. A 50 degree drop in temperature or dew pt (water takes up space) will give you 5% more oxygen molecules per square inch. More air=More power.

Its all relative man.

One important thing to remember, Boost is not a measure of how much air is going into your engine, but just a barometer in your intake manifold measuring pressure that builds up inbetween intake cycles. In a nut shell, what I am saying is, its a false way of measuring how much "extra" air is going into our engines. Think of it this way: Picture 6 people being shoved into a room up against the door. Now when that door opens(vavle) there's only enough time (cam timing) for 3 people to get out before the door closes. So, while those 3 people are in the next room, another 3 people slowly gets added to the room before the process repeats itself. But if you hold the door (valve) open longer (bigger/longer duration cam) you now will be able to get 4 people out the door before it closes. Now you are left with 2 people in the room. This room is where PSI is being read, if less air (people) occupies this space psi will drop. This is why bigger cams, ported heads or anything else that helps more air to get into your engine drops your manifold pressure or PSI.

You want the extra air in your engine, not making pressure in the intake manifold. So more boost does not always mean more power. I proved that on a dyno. No matter what your boost meter measures, the blower is moving at a specific rpm. This blower (M45)is blowing 45 cu inches (.75 liters) of air per 1 RPM. So, if you are NOT increasing the blower speed you are NOT increasing the amount of air that does go into the manifold. The blowers job is done. Its up to the head to determine how much of this air makes into the engine and how much gets left behind.

Chris
94 Blown LS (5psi with engine work)
dyno 181/158
13.98@97mph


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[lilmikey77]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by blownLS:
Hi I am new here to this site. I am a Meteorologist with a bad habit, I spend too much time and money into my 94 LS Integra. I hope some of my weather knowledge of pressure, temperature and humidity helps to answer some questions about my favorite topic, HP and going fast.

So here is the answer to your question:

Yes it would. It changes the amount of overlap in cam timing. Anything can effect boost pressure.

I have adjustable cam gears. By changing the cam timing, I can make my normal 6psi reading (average from 4000-redline) increase or decrease 1psi. Believe it or not, but my fastest times at the track and highest dyno numbers (avg not pk) was at the 5psi setting, not 7. The difference was .4 seconds at the track.

A temperature or dew point difference can also change it. I get 1/2psi more boost in the winter than in the summer, due to cold and dry versus hot and humid. A 50 degree drop in temperature or dew pt (water takes up space) will give you 5% more oxygen molecules per square inch. More air=More power.

Its all relative man.

One important thing to remember, Boost is not a measure of how much air is going into your engine, but just a barometer in your intake manifold measuring pressure that builds up inbetween intake cycles. In a nut shell, what I am saying is, its a false way of measuring how much "extra" air is going into our engines. Think of it this way: Picture 6 people being shoved into a room up against the door. Now when that door opens(vavle) there's only enough time (cam timing) for 3 people to get out before the door closes. So, while those 3 people are in the next room, another 3 people slowly gets added to the room before the process repeats itself. But if you hold the door (valve) open longer (bigger/longer duration cam) you now will be able to get 4 people out the door before it closes. Now you are left with 2 people in the room. This room is where PSI is being read, if less air (people) occupies this space psi will drop. This is why bigger cams, ported heads or anything else that helps more air to get into your engine drops your manifold pressure or PSI.

You want the extra air in your engine, not making pressure in the intake manifold. So more boost does not always mean more power. I proved that on a dyno. No matter what your boost meter measures, the blower is moving at a specific rpm. This blower (M45)is blowing 45 cu inches (.75 liters) of air per 1 RPM. So, if you are NOT increasing the blower speed you are NOT increasing the amount of air that does go into the manifold. The blowers job is done. Its up to the head to determine how much of this air makes into the engine and how much gets left behind.

Chris
94 Blown LS (5psi with engine work)
dyno 181/158
13.98@97mph


<HR></BLOCKQUOTE>

excellent post, thank you.

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94 gsr
lots of shite