I just took some boost readings at different places and came up with some alarming news. I recorded over 20psi at the compressor outlet where I have a nipple installed while only seeing 10psi max at the manifold as confirmed by both my power fc and my boost guage which are hooked up to two different locations on the UIM.

What gives.? This has to bad. At 0psi I am seeing 6-7 psi at the compressor outlet and at higher rpms and the same 0psi at the manifold, it has gone as high as 12 psi.

any help!!!!!

I have an rx6b with all the mods including a street ported motor. This explains why my wastegate opened so early when I had it hooked up to this nipple.

 

What kind of IC setup are you running?? Also, check for any and all boost leaks downstream on your compressor outlet.

 

Ok, I placed another boost guage in the IC pipe between the IC and the TB. The two guages are equal meaning no pressure drop from one side of the IC to the other. I have an older greddy Front mount. The one that does not sit up flush but further back in the mouth and is harder to see. Does any one know if this is a 3 row or not?

The pressure drop is at the TB. When at wide open throttle, all the guages are even. My scenario is at part throttle pulls when the butterflies are not fully open. It seems that the turbo is working very hard and easily suppling more air than the engine needs and/or can get past the throttle body and is therefore backing up and creating boost. Does this make sense. I am seeing as much as 15psi in the plumbing with no boost registering at my map or my boost guage. When I floor it, they even out.

Is this normal or is this a sign of a mismatched turbo to engine?

mike

 

I did a test like this on a stock 3rd gen to see what the pressure drop would be. There was a 3psi differance between the turbo outlet and the manifold at WOT. Do you have pics of your setup? By the way, why are you just testing part throttle pulls instead of WOT pulls. I too noticed the same thing when I did mine. The true test is to do a 3rd gear pull and start from 35-80mph at WOT then check the differances in pressure drop. This is how "Sport Compact Car" tested both M2 intercoolers on project Rx7. Doing particial throttle pulls as you stated isn't allowing the turbos sufficiant amounts of time to built boost through out the entire intercooler & piping assembly (espcialy if you have a front mount). Thats why you are getting those really high reading at the turbo outlet and not registering anything at the manifold. This is why front mounts have more lag than the SMIC.

 

I did test under various conditions just to see how everything compared. At WOT pulls all 4 boost guages were similar. I have one on the outlet of the turbo, one on the outlet of the IC (front mount) and one on the UIM where everybody has it, and then the MAP sensor reading on the Power FC.

There was very little difference between the two in the piping whether at part throttle or WOT, meaning very little pressure drop. At WOT the boost was equal on all guages within a +/- 1 psi range. The big discepancy is at part throttle accel. Boost is stacking up in the piping before the butterflies. This could be normal and probably is up to a certain point. Does anyone know how much boost is normaly made in the piping while the manifold is still seeing vacuum. I saw as high as 15psi with 0 boost at the manifold guage.

This is telling me that the turbo is able to supply more air than I need at any given throttle position opening and it is therefore charging the piping. What I don't know is if this is good,bad. or indifferent and what values determine such.

One other thing that I would like to test is back pressure in the exhaust manifild. Does anyone know how much pressure I should see on an idealy sized turbo and what value would be considered too high.

mike

 

Do you not have pics?

 

here are some pics

 

another

 

another

 

one more

 

Well Mike, I have to tell you that your doing some test that hardly no one else on this forum does. So you wont get many answers. When I started that thread in the 3rd gen section(stock intercooler really sucks), I only got a couple replys. Are you just trying to figure out how efficiant your intercooler and piping are?

 

actually I am trying to see if my turbo has to small an A/R and is creating too much backpressure. I am having to pull out more fuel in the mid range than I had with my twins. I supposedly have an apex rx6b. I just do not know why it would require less fuel, less than base maps even.

My next test is to see what kind of back pressure I am making in the exhaust manifold. A propperly sized turbo should be 1 to 1 so I have been told. I also need to check my egt's and see if I am running to much advance.

The pressure drop at WOT is negligable so I am cool there.

mike

 

This is the kind of thread I like to see!!

My car does the same thing and I can see why it happens. At say 20% throttle and 3500rpm my bov is very loud in between shifts and gets louder if I shift higher in the rpm's but same throttle pos. Makes sense really.. I guess with a larger turbine housing this would go away some but I think it will always be there to some degree.

I'm intrested in what your exhaust manifold/intake pressure ratio is. I have a -4 fitting I've been meaning to weld into my exhaust manifold for some time now but been too lazy. I'll probably do it this winter now that the car has to sit out the snow.

It's good to see REAL good questions every once and awhile

let us know what you find!!

 

I have the down pipe out and plan on putting a fitting on the manifold while I am in there. I will keep everyone posted.

On a side note, I plan on wrapping my down pipe with thermo wrap and was wondering what the concensus was on wrapping the mainfold as well?

let me know

mike

 

it seems like a boost leak, but if it's fine at wot, i don't know what it is. change to a different elbow, maybe greddy or custom, see if that makes a difference

 

At part throttle, of course theres going to be a pressure drop across the TB. Thats how throttles work. Ideally, you want the pressure pickup for the ECU in the manifold to get accurate readings, and the pickup for boost control BEFORE the TB so that you don't overspin/overboost your turbo. The RX6 is the fastest spooling turbo commonly used on the 13b, meaning many other singles don't see this kind of problem because they don't really build boost at part throttle. It also means you have to be more careful about over boosting an RX6.

Either that or i misunderstood you and you can disregard the previous paragraph. Barring what I said above, could something be jammed in the intake?

EDIT: To add a few things, turbo + closed WG will create more backpressure than a turbo + open wastegate. If the turbo is trying to build a high amount of boost without it actually reaching the engine, (IE first paragraph) then the backpressure will be higher than if theres minimal pressure drop. This could be creating the tuning flukes your seeing. (They are flukes, right? I'm just a lurker, really. I don't own a rotary yet )

Regarding Exhaust pressure vs. Intake pressure. (Ep and Ip) A more normal ratio (as I understand it) for a street car would be 2:1 (Ep:Ip), especially on a small turbo like the RX6. This assumes no crazy pressure drops, of course. More powerful street cars and race cars should see closer to 1:1. While the very best race setups (mebbee street, too? ) can actually get Ip>Ep! Like .85:1 or there abouts. (I'm talking like LeMans and CART for sure and prolly tons of others.)

 

After thinking it over I don't have nearly as much "pressure build up" at part throttle as you. You say you saw a peak of 15psi, I haven't ever seen anything higher than the wastegate spring on mine (7.25). Otherwise my WG would open slightly and I would hear it because it's open to atmosphere. hmm... maybe that is a bit too small of a turbo that you have.

Welcome to the board CypherNinja, good to see we have a new member that actually knows what's going on.

 

yeah, I do not have a leak and I do not have something clogged in the piping. These were my two first guesses and I checked all this stuff. At WOT everything is normal. The problem as you said is at part throttle. I is just making a ton of boost while none is getting into the intake manifold. I had to move my wastegate source to the intake manifold just to get the wastegate to settle down. After thinking about it. Isn't this the whole reason that the stock set up has pills in the PC and Wg lines coming from the primary turbo dischagre; to help temper the signal going to the actuator so the solenoids could keep up.

My original hook up was straight off the discharge of the turbo and I got all kinds of wastgate openings. It would even open when I let off the throttle. I am assuming from compressor surge not being dumped fast enough, It would also open way early when I was in part trottle pulls in higher rpms. Once again from too much boost in the plumbing but none in the manifold. Think about it. If the map sensor doesn't see boost then it won't activate the solenoid. The solenoid is normally closed so all the boost in the plumbing goes to the side nipple there for opening the wastgate. Under decel there is definately no signal to the wastgate and the surge opens it momentarily till the boost is removed by the BOV. This is why I am going to get a Type r real soon.

mike