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DELETED (Inactive)
6 Posts |
 Posted - Jan 19 2004 : 3:17:24 PM
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Hello all, I'm new to the forum, but not new to the rotary, so maybe I'll be of some use to you all.
First some background. I have an '86 model 6-port rotary engine running in a '73 Porsche 914. This make my turbo conversion a bit different than an Rx7 conversion, but it is similar in many ways. I'm using an S5 (89-91) turbo, an intercooler from a 2nd gen DSM, and a Haltech E6K for fuel and timing.
I first ran the turbo conversion last spring and immediately noticed about 15 psi less oil pressure (45 psi at cruise rather than 60) than I had before the conversion. I tapped the oil supply line off the base of the oil filter fitting. I didn't go with Aaron's approach of tapping in ahead of the oil pressure regulator out of concern that the oil pressure might be too high for the turbo seals. I am using a used turbo, but there is no indication that it is leaking oil or performing incorrectly in any way. It makes 8 psi of boost using the stock waste gate.
Did any of you notice a similar drop in oil pressure? Also, do you know if the flow to the turbo should be limited with an orifice in the line? I have found one source that says the Hitachi turbos have a built in orifice and should not require any additional limiting.
Any thoughts will be appreciated.
Danny
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Jan 21 2004 : 09:26:53 AM
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In the "real" 13B turbo engine, the oil is tapped from a hole on the front cover that is fed from the filter. The oil travels through the dowl to the front of the engine. This has the effect of reducing oil pressure at the turbo to about 20PSI.
I can't see how tapping oil off of the filter will reduce your oil pressure. Several others have taken oil the exact same way and not noticed any effects. How are you measuring?
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DELETED (Inactive)
6 Posts |
Posted - Jan 22 2004 : 10:32:17 AM
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I have both electrical and mechanical gauges connected using a T at the standard oil pressure measurement point below the filter.
As for how tapping oil off here will reduce the oil pressure, it could go like this:
I used a fairly large line (-5) from the pickoff point to the turbo, so I probably have full regulated oil pressure to the turbo (45 psi the way it is now). This path is in parallel to the entire NA engine oil system so it could potentially flow enough oil make the oil pump unable to keep up. If my recollection of the formulas for laminar fluid flow is correct, 45 psi vs 20 psi should yield about 50% more flow.
How did you get the 20 psi figure? That is exactly the thing I actually wanted to know, because I'm considering an orifice to reduce the oil flow to the turbo.
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DELETED (Inactive)
6 Posts |
Posted - Jan 23 2004 : 09:29:07 AM
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Correction. My line size is not -5. It is larger than that, but smaller than a -10. I'll find out today what AN size it is. I'm going to buy some parts so that I can reduce the pressue to the turbo and see if that picks my engine oil pressure back up.
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Jan 23 2004 : 09:55:28 AM
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Anything just barely bigger then -10 is pretty huge. -10 is what I used on my oil cooler lines.
Not sure what AN size this works out to, but as I recall I used 3/8" fuel injection line on my turbo oil feed. I am currently replacing with the proper stainless braided.
It makes sense about what you say with regards to the parallel oil flow. However, I have not seen this behaviour in other turbo-NA engines. Are you using the stock pressure regulator?
You might want to consider tapping a hole at the lower banjo bolt on the engine. It will be unfiltered, but also unregulated.
20 PSI is something I read several years ago. I don't remember the source, but it sounds right.
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n/a
DELETED (Inactive)
6 Posts |
Posted - Jan 23 2004 : 11:28:44 AM
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That's "smaller" than a -10. The line is about 3/8 ID I'd guess.
Where I tap off under the filter is before the oil goes into the filter, so it is unfiltered as well. The main reason I went with this spot was convenience/neatness and that I actually wanted regulated pressure.
I am using the stock regulator, and before the conversion I showed the typical 60 psi at cruise and 70 - 75 psi at 7000 rpm.
Because I had to do completely custom oil cooler lines, I didn't use the banjo bolts. I used the Mazda fitting to -10 AN fitting adapters from Mazdatrix. I could still put a T in at that point, but I'm going to figure out what's actually happening first (I hope).
I'll post what happens with my test.
Danny
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n/a
DELETED (Inactive)
6 Posts |
Posted - Jan 26 2004 : 10:22:42 AM
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I did some tests over the weekend and this is what I found.
My drop in oil pressure did, indeed, correspond to my turbocharger install. To show this I put a valve in the turbo oil supply line and an oil pressure gauge on the turbo side of the valve. This let me decrease the flow (temporarily) to the turbo and see what happened with my engine oil pressure. Sure enough, when I limited flow to the turbo I could get 60 psi on the engine rather than the 40 - 45 I'm seeing most of the time.
For the second test I disconnected my oil cooler lines and put in a test line that simply connects the oil cooler supply on the engine to the oil cooler return. With the oil cooler path bypassed as described, I get full spec oil pressure even with the full engine oil pressure applied to the turbo. This is consistent with the fact you guys haven't seen this problem in your Rx-7 installs.
On my 914 the lines to the oil cooler are 13 feet long - one way! Because of the tight path they needed to run I used a flexible 3/8 inch ID hose. This was large enough (though marginal) until I added the turbo. Now the flow requirement is so high that the pressure drop across the cooler and lines is unacceptable (to me, at least).
So, bottom line is I need bigger oil lines to the cooler.
Danny
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Jan 27 2004 : 5:26:39 PM
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Yeah, I guess 26 feet of oil cooler line could do it! Glad you got it sorted out.
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cirvin
Nobel Prize Winner
USA
1542 Posts |
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Jan 28 2004 : 09:42:05 AM
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Engine at the back of the car, oil cooler at front.
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cirvin
Nobel Prize Winner
USA
1542 Posts |
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n/a
DELETED (Inactive)
6 Posts |
Posted - Feb 03 2004 : 11:07:20 PM
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I installed 5/8 inch ID oil cooler lines last Friday night and that seems to have fixed the oil pressure. It's been too cold to get the oil temperature up to a full 180F yet, so I haven't been able to do a completely decisive test, but I think it is going to be OK.
Thanks for the input. I look forward to continuing to check out this forum.
Danny
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Oil Pressure after Turbo Conversion
