rx72c

iTrader: (8)

It was still 30psi.
We are going to try and bigger rear housing with the full exhaust and see if that remedies the issue some what. Only time will tell.

We are also doing another rx7 on e85 with an efr 9180, this time with the 1.45 rear. (you would know since your supplying it lol)
We would love to put 40-45psi in it if it can work and see what it makes!.

valley

iTrader: (1)

Just out of curiosity, that's in the post-turbo exhaust, not the manifold?

Slides

Dump pipe pressure.

You could not supply enough compressor energy if pre-turbine pressure was only 9PSI.

rx72c

iTrader: (8)

Thanks for that Slides

I did some more logging and manifold pressure goes through the roof around the time the power goes down, almost double the inlet pressure.

bumpstart

/\ and there is the real scoop.. most of us will have a pressure ratio somewhere between 2 and 3 :1
anything under 2 and you have a very efficient turbo

jetlude

iTrader: (9)

Is this to say that on a restrictive turbo running 30psi boost the exh manifold pressure could be as high 90psi?

Vicoor

That just doesn't even seem plausible. That kind of pressure drop across the turbine would seem to have to "over-rev" the turbo

Monkman33

iTrader: (28)

Because it isn't.

Bernoulli and his principle must me taken into account. As velocity increases, pressure decreases.

bumpstart

dont just take my word for it !
search around!

it is true that some diesels,some older f1 , and some indi cars huge turbine housings with very long extractor type header pre turbo can get down close to 1:1
but these are not street cars with highflows

but your typical stock subie has about 180 Kpa in total exhaust backpressure , or 120 kpa pre turbo , when boost is only 70 kpa .. ratio of 120/70
i.e a ratio of 1.7:1 while only at only 10 psi boost !!

and your average stock 2Jz when wound up is closer to 3:1 backpressure to boost ratios at boost over 1 bar


RX8 Engines

// it is far to big and complicated subject to spell out for a thread like this and relate simply down to Bernoulli without taking in all the mass energy transfers and losses

it is also not a straight line relationship where you can extrapolate a figure like 30 psi boost will equate to 90 psi backpressure,, there becomes a point where the sums go logrithmic after the choke point and simply the backpressure will increase so fast ahead of boost
the boost will flatten out and the motor will have destructed with the heat loads induced by 90 psi backpressure

as for backpressure "over revving the turbo" .. um .. no

the backpressure ratio , expected to be between 1.5 and 3:1 in most examples IS the reason for the large spider washer and the thrust bearing inside the turbo as backpressure will try and load / thrust the turbo assembly axially

valley

iTrader: (1)

Something interesting for those with a bend towards design.

I'm aware of this but was asking as what is being reported is a bit vague.

t-von

iTrader: (8)

Curious, what kind of plug wires you running?

rx72c

iTrader: (8)

Just some Bosch Leads.

t-von

iTrader: (8)

I would check the resistance on them to make sure they have some. Resistorless plug wires are bad for modern day computerized automobiles because they do a poor job of supressing EMI. I was having weird ignition problems with mine that I traced to virtually "no" resistance in the plug wires. They were a universal kit I bought from summit racing. I've recently installed some Magnacor KV85 wires based on some research I did and they work beautifully. You could be having some EMI interference causing hell with the ecu and ignition. Just a thought!

Edit:

For those of you that dont understand what EMI is (eletromagnetic interference) and its effects on modern day electronics, here's some good info.

http://www.magnecor.com/magnecor1/main.htm

Click on "The truth about ignition conductor wires" tab. I don't think I'll ever run a different set of wires on my car again.

Copeland

iTrader: (42)

I've had similar issues with my setup, I'm curious if it's the exhaust housing on the turbo now. I've been assuming it's ignition related for the past few months; it starts at about 26psi and 5500rpm and get progressively worse up to 32psi. Sometimes it doesn't happen, other times it happens all day.

I unfortunately haven't tried logging exhaust manifold pressure since I don't have the appropriate sensors. Where did you get yours?

IGN-1A coils - direct fire
MSD 8.5mm wires, R6725-11 plugs - I've tried several others too
GTX4294R turbo, 1.0 T4 divided exhaust housing
Streetported REW motor, gasket matched intake
Full 4" turboback exhaust, dumped 38mm wastegates
E85 fuel

Guess I'll order a new 1.28 or 1.44 T4 exhaust housing and see if that helps.

jetlude

iTrader: (9)

Is it break-up your having?

rx72c

iTrader: (8)

What mixtures are you running?

Copeland

iTrader: (42)

11.5-11.7 AFR @ WOT - when the issue happens, the AFR's drop into the low 10s though.
15 AFR @ cruise

KNONFS

iTrader: (14)

Do you have a log of the issue?

t-von

iTrader: (8)

Based on your description, how could it be your housing? If the housing was undersized, you would have gradual consistant performance lost and not something that happens occasionally. This only makes since if you had a faulty variable geometry turbo.

rx72c

iTrader: (8)

I agree with t-von. Sounds like you have a fuel supply issue.

Copeland

iTrader: (42)

t-von, you're probably right but I was thinking maybe there was some backpressure issue causing exhaust to be recirulated in the engine somehow. I'll probably still change the turbine housing since it's a little undersized for my plans to raise the boost further.

rx72c, I'm fairly certain it's not fuel related since the issue goes away for a few runs after a fresh set of plugs that are gapped .018" - it still degrades rather quickly though. I'll still check if I can troubleshoot that somehow though.

rx72c

iTrader: (8)

Do you think a turbine housing issue would go away?
There is no logic in that.
You have a tune up/ignition issue.

sleeper7

Try some 10 heat range plugs.

Post a pic of your current plug. The threaded area to see how far the heat is transferring down the threads

Kanho

iTrader: (3)

If it is breakup then the issue is with ignition. You seemed to have enough fuel looking at your AFR. Some have remedy it through spark plugs like you are going to try. But the best and constant solution is to beef up your ignition. I had the same problem but then I bought the M&W ignition box and I swear sometimes I think I could run my car with just water and it will ignited! ;-) it is pricey but it will work every time and the car runs much smother

Just my 0.02 cents

Andrew

rx72c

iTrader: (8)

We did put the M&W ignition which bumped up power to 585rwhp but it is still shutting down after 7000rpm.
Hopefully this rear housing gets here soon and will be seeing if the 1.45 gets us across the line.