Compression ratio reduction

[jeff1234]

I am replacing my turbo right now and in the past I have had detonation problems. I have been using the #2006 head gasket which crushes down to .070. My compression ratio cc'ed out at 9.2:1 with this gasket my 782 head and Wiseco pistons. As long as I have the head off I am looking for solutions to the high compression ratio. I wonder if anyone has had any success by un-shrouding the intake valve on this head casting. I also wonder if there is a thicker head gasket available. I am using a stock T2 intercooler mounted between the front facia and the radiator. Could it be this is too inefficient at reducing heat in the air going to the intake (20+ psi). I'm not real sure which way to go here but I want to solve the detonation problem if possible.

[zin]

Copper head gaskets can be had in thicker sizes, and de-shrouding the valves will gain quite a bit in terms of flow, and some in terms of compression. De-shrouding won't gain many CCs, so compression won't drop a whole lot, I'd do the thicker gasket as the main way of dropping compression.

[contraption22]

The stock intercoolers are decent for stock cars. At nearly 2x's factory boost levels, it is not enough to cool the charge well enough on pump gas.

[4 l-bodies]

Jeff,
Why are you running so much CR on your car? Are you sure your compression ratio is really 9.2:1? What do you have, g-head pistons on swirl head? Maybe a heavily resurfaced cylinder head? What plugs are you running? Octane? What calibration? That is a LOT of compression for pump fuel and 20 PSI!
Yes you can heavily unshroud the swirl head to lower compression (both intake and exhaust). Copper head shim can be used with sucess. You can also buy cometic gaskets in various thicknesses too.
Todd

[shadow88]

Same question as Todd, really 9.2:1???

If you deshroud the valves, you'll also loose some quench area. I've done this on my current ported +1 head and I probably wouldn't do it again if I were to do it over.

I've also done the copper shim head gasket and it worked to reduce detonation, but got all damaged when I had to remove it for another reason.

I've also given up on custom cals because of the advanced ignition timing in favour of a ghetto stock 2 bar and cold starts.

Cooler spark plugs worked for me as well. There were non-projected tips that JT suggested from Champion.

I also picked up noticable power and detonation resistance with a larger fmic (srt-4) and a cold air intake (remote front mount filter)

[jeff1234]

Thanks to all,
Todd, the engine machinist decked the block but I am unsure how far he took it down. I thought he may have done that to the head as well so I went out and checked. I couldn't see any of the normal evidence you would see, like cutting tool marks so he probably didn't. I have the WISECO piston that T/U sells for the 8 valve. It has a dish that includes about 80% of the piston top surface. When I assembled the engine I CC'd the head and piston at the deck and included the head gasket in my computations so I am sure of the compression ratio. I use RJ9Y plugs 91/93 octane and Cindy's stage 5 chip. I recently added 2 gallons of Sunoco 110 octane race fuel to about 4 gallons of unleaded 91 and I could still hear some clicks. What should my compression ratio be in the event that I wanted to run as much boost as my stock turbo can produce. (I don't know what that is, I suspect about 24 psi). I looked at Cometic gaskets at T/U, I could increase the thickness of the gasket only .015 over the #2006 which wouldn't be much but combined with un-shrouding might get me enough. Do you recommend a supplier for the copper head shim?
Apparently I also need a larger intercooler, in you guys experience what is the largest you can fit easily into the space between my radiator and front facia? I have space for 22" long 12" high and 4" deep with out modifying anything. I could possibly modify the front crash absorbtion bumper to get more depth.
Jeff

[4 l-bodies]

Jeff,
Attached is a bone stock 2.2 breakdown of compression ratio. Can you fill in the blanks for your application? Nothing should be really very different except how far pistons are down or out of the deck of block. The Wiseco pistons are probably close to this. Gasket is pretty much same. If cylinder head isn't highly modified, CC of head won't change much either. I don't get why you are coming in so high?
BTW I was fighting a detonation issue with a vendors cal. All the the sudden my vehicle got REAL detonation happy. After checking and changing EVERYTHING LIKE THREE TIMES, I put in another cal and problem disappeared. In my case I was running a true 7.8:1 motor. It was rattling bad at 10 PSI! Just changing cals and nothing else it now can run about 21 PSI on pump fuel during the heat of the summer before any sign of detonation. At least something to consider...
I am really not a believer in running turbos in "all of it mode". In most cases you are serously over-spinning them, and it will lead to failure of center section of turbo. Besides, they are not efficient at those speeds either. Ultimate PSI will depend on lots of things. Pressure drop across intercooler, how much CFM head flows, intake, exhaust manifold, etc. I know of one guy that was overspinning his turbo at 15 PSI. His top end of motor was very effcient, the stock TII turbo was about maxed out at 15 PSI. Went through a turbo a year until we bolted on a bigger turbo.
Todd

[Vigo]

You will not need more depth than a 4" intercooler core, as that's the thickest core that's readily available anyway and i think you may run into problems restricting airflow to the radiator if you went any larger than that. I do think the intercooler should be the first thing you address (after you put the engine back together). Everything else you can change externally is relatively incremental (cool air intake, colder plugs) compared to good intercooling. If you're still getting detonation after doing this other stuff i would just retard the timing until it goes away, or add water/meth injection.

[jeff1234]

I went back over my numbers but couldn't find the information on my cylinder head volume. The head was a brand new stock 782 I got from TurboDave and as stated before I can see no evidence of milling. I used a 60 cc syringe to fill the chamber and I seem to remember that it was 58 cc's. What is the stock volume of the 782 head. I have looked all over and can't find the spec's. If 58/60 cc's is about right I am actually around 8.7;1/8.8:1. These numbers were created with a calculator apparently the same as 4l-bodies. I wont go back to a stock cal because I am set up for three bar and it cost way to much to get there, so I have to make this work. Perhaps the stock intercooler has been the problem all along as this motor has detonated with every three bar chip I have tried. I am definitely going to find a different one. 4l-bodies, do you have another chip like the one you solved your problem with?
Jeff

[4 l-bodies]

Jeff,
Unfortunately no I don't have another chip. Currently the car is running a Paul Veccky calibration in it. Actually Jessie Buhr now owns the car. I would try another vendors calibration. As you may or may not know I have ported and flowbenched a lot of cylinder heads. I can say with quite certainty that a NOS stock swirl head will average out around 50cc. 50.4 cc to be exact for mine. I also have a mint (used but uncut) swirl that came in at 51cc average for the 4 chambers. The g-head is around 56-57cc.
I highly doubt the stock intercooler is causing your detonation issues. Have you cleaned it out? Many times they can become saturated with oil. It obviously isn't the ultimate intercooler as it is a little small (flow impaired) compared to a larger FMIC, but many people including me have easily put cars well into the 12's running a stock intercooler or Indy cooler.
Like previously mentioned you can try running a non-projected tip plug. I ran into one friends motor (3 bar cal) that had to run them or it would rattle no matter what I tried. I used a NGK BR6ES (4922) or you could even try colder BR7ES.
Have you read your plugs or had DRB hooked up to see what cylinders are being retarded? Have you had your injectors cleaned or balanced? I've seen brand new +40's be as far off as +/-7% in same batch. Flowed between 520 to 560cc. That could do it right there. I've used Mr. Injector to clean, rebuild, flowbench many injectors for me over the years. At a maximum of $16 per injector, it's too cheap not to do this. He turns them around in 24 hours and charges like 5-6 to ship back. A no brainer for me.
Todd

[shadow88]

All great points and things to consider. I'd like to add the possibility of oil consumption for another possibility for detonation.

As well, is the air fuel ratio rich enough? My own car would detonate if there wasn't enough fuel to help cool the chamber.

I picked up my copper cylinder head shim from car quest. I forget the thickness, but 0.030" rings a bell.

[jeff1234]

4 L-Bodies, I measured one of my chambers and they are indeed 50cc. This means my compression ratio is 9.7 :1 this may explain why the engine always began to detonate at around 7 to 10 psi. I talked with Bill Johnson today and am sending my injectors out. If I need to, after all is back together, I will go with the NGK plugs. In the past I connected OTC 4000 to the engine and it showed that as much as 9degree's were being pulled out of some cylinders.

To get my compression back to 8.1:1 I need to increase chamber volume by 15 cc's. Since a .020 shim is only .9 cc's if my math is correct, I would need a very thick shim. I don't think I can even remove enough from the chamber to get that number. What do you think?

I also considered oil as a source of detonation. The engine was rebuilt a year ago but has seen a lot of detonation. It was using oil but it remains to see if it was the turbo going bad.

My air fuel has always been 10:1 at WOT but the AEM cant sort out an individual cylinder so some cylinders could be lean and you wouldn't know it.
Jeff

[Vigo]

Just as a tidbit to throw in here, I've run a turbo on a tbi 2.5 bottom end with a crappy turbo and crappy intercooler and had no detonation on stock timing and pump gas up to 15-16psi. I believe those have low-9s compression. It's certainly not such a big issue that it detonates at 7psi!

I honestly dont think low 9s compression is a big deal until you are pushing the setup, and even then i think you will uncover many weaker links (cold air intake, better intercooler, colder plugs, timing changes, uneven fuel delivery are all possible issues or improvements) before you can conclusively point to the compression ratio as being the MAIN culprit.


As for the HIGH 9s number, im starting to feel really dubious about the measurements situation. I dont understand how you can run a piston that gives a low 8s compression ratio with stock parts (educated guess on my part that the piston would give same or lower CR compared to stock), have block decking as the only major unknown variable, and end up close to 10:1. If you're using low-compression pistons with a big dish in them i would think they'd have to be ABOVE deck to get that kind of CR and im pretty sure you would have noticed this.

[jeff1234]

Vigo, here is the answer. I was entering information on the online compression calculator incorrectly on head gasket thickness. When I changed the number so it was correct, I came up with 8.1 to 1. Arrgh, so it is not compression if I have it correctly calculated. This stuff can drive me goofy.

[Vigo]

Well, water under the bridge and one less thing to worry about. Still have to figure out your detonation issue!

If you are still getting knock at 7-10 psi i would leave boost relatively low until you figure it out. Obviously you're not going to break it if you havent already but i think it will make diagnosis simpler because we more or less know for a fact that knock counts should be ZERO at 7-10 psi, so if you address the cause and knock counts go to zero it is conclusive, whereas if you run 22psi (for example) and make some improvement, you may only reduce but not eliminate knock counts, which is less conclusive and may leave you wondering if you've fixed the caused or just treated one of the symptoms.

At SOME point knock counts are expected, but you want to know that there is no knock UNDER that so you can tell the difference between the limits of the setup, and an actual problem of something not working right.

[bfarroo]

I'd definitely try another cal, the stage 5 i'm sure is designed for a bigger build with a larger more efficient turbo, larger intercooler and all of the other supporting mods so it probably has a bit more timing added from a stock cal. are you running the 87 electronics? At what pressure are you starting to see the detonation at? Definitely make sure your PCV is working correctly and isn't sucking in to much oil vapor and that your intercooler is clean. Meth / Water injection could be another route to try although some think it is a bandaid and another possible point of failure.

[4 l-bodies]

I'd definitely try another cal, the stage 5 i'm sure is designed for a bigger build with a larger more efficient turbo, larger intercooler and all of the other supporting mods so it probably has a bit more timing added from a stock cal....


Jeff,
...BTW I was fighting a detonation issue with a vendors cal. All the the sudden my vehicle got REAL detonation happy. After checking and changing EVERYTHING LIKE THREE TIMES, I put in another cal and problem disappeared. In my case I was running a true 7.8:1 motor. It was rattling bad at 10 PSI! Just changing cals and nothing else it now can run about 21 PSI on pump fuel during the heat of the summer before any sign of detonation. At least something to consider...
Todd
Jeff,
Try temporarily throwing your stock cal and 2 bar map back in and turn fuel pressure WAY back to around 26-28 PSI (static). If you have a Accufab AFPR it may only go down to around 30, that is close enough. At 28 PSI your +40 injector will be actually flowing around 37 lbs. and not 52 lbs. I bet you will find your problems are gone. Went through this already with my Stage 5 cal. See above post^^^. I even had lower compression (7.8) and it rattled really bad at 10 PSI. IIRC, I think Boostgeek had a cal do this as well 2-3 years ago. In my case cal worked great for a couple years then something changed. Of course I never suspected a cal or LM to go bad, so I checked and replaced everything. Turned out to be the cal and not the LM.
Good luck,
Todd

[Vigo]

I diagnosed an issue down to the chip/cal file on your friend Steve's car down here. That was the first time i had ever been able to point to the chip itself as having failed.

[jeff1234]

Todd unfortunately I no longer have my stock calibration. Here is what I plan to do. I no longer have access to the OTC 4000 so I am going to re-install my cal from Shelgame. It has the detonation indicator still intact. At least I will see an indication which will tell me if I am getting anywhere. I will then follow Vigo's suggestion and turn my boost down and see if I can eliminate detonation below 7 psi. If not I will go to the NGK BR6Es plug. If that doesn't help I will get a different intercooler and see what that does. Additionally I will do the maintenance to my present intercooler that bfarroo (I have 87 electronics) and others have suggested. As long as the engine compartment is wide open I am going to find a way to get the air cleaner out between the nose and radiator support where the cooler air is. It will be three weeks before I can accomplish this because of waiting for parts and other obligations but I will update or create a new thread to let you guys know how I came out. Oh, one other thing, I have created a system of hoses connected to the valve cover, intake manifold and air cleaner that draws on the crankcase when the pcv is closed by boost.
Thank you for taking time to share your knowledge, it is valuable!
Jeff

[jeff1234]

Update, I read an article on intercoolers on enginebasics.com that was very informative. I determined that a part of my det. problem may be related to heat. I ordered a new intercooler from CXRacing. The ic0005 will fit best in my Charger and still increase cooling. I am going to modify the nose and build a duct around it to allow unrestricted air flow. I still haven't figured out exactly how i am going to get my air cleaner out ahead of the radiator support without chopping the car up and running tubing all over the place.

[Vigo]

I admit i dont remember offhand what it looks like, but i would look at whatever Shadow is using in his Charger for the turbo intake.


The intercooler looks good.
http://www.cxracing.com/product/cxracing34/IC0005/images/1.jpg

[jeff1234]

All, here is a picture of my intercooler installation. I sectioned the front bumper. I then cut flat stock in the shape of an "L" welded the pieces and drilled them. The lower braces were made from narrower flat stock, bent on my vice and drilled. I was going to cut the nose piece in places to open it up to air flow but I decided to wait and see if the detonation is suppressed by the larger I/C and the hybrid turbo with a TO4e-46 trim I am putting together. Hopefully the two will lower charge temp enough to tame the knock.

4688446885

[Vigo]

That looks pretty good. Cant wait to hear if the new combo cures the knock!

[jeff1234]

Update, As mentioned in my turbo thread, my turbo is modified and back on the car. I had noticed a reduction in oil pressure recently and so as long as I was under the car I decided to pull the pan and check the main thrust bearing. I found that the detonation problem had pounded the aluminum and copper layers out of the bearing shells leaving small 1/4 inch square patches of copper at the parting line on each side of the shell. Both shells looked that way. So I had to pull the engine (which I hate). The crank needed to be straightened as it was running out about .003. The journals had no significant damage and only required polishing. So, all new bearing, gaskets etc. and the engine is back together and in the hole. I should have it running next week. I am looking forward to testing it for detonation. The pistons and rings were unaffected by the detonation. I added a .020 shim under the head gasket to bring the compression ration down from about 8.4 to 8.1. Considering how much the engine had detonated over time and how little it was damaged speaks to the durability of these engines.
p.s. in case you are all wondering, yes, I removed the core plugs from the head and the block and flushed those area's. I also pulled the cam and inspected and flushed those passages. The oil pump was OK.

[jeff1234]

Well I have it assembled and I am doing the final setup of the new intercooler. In order to get cooler air I am drawing air through the power module like when the car was new. I used a corrugated hose from a Sundance and cut it down about four inches. There isn't much room in the engine compartment so I will rig an air filter at the opening to the radiator support by the power module and I still have to come up with a catch can for the radiator. I hope to test without the nose on the car soon to see if it will detonate now.



4713947140

[zin]

Looking good! I like the use of the flex duct to the PM, it makes things look more "factory", which is something I like to do when possible, lending to the sleeper effect.

Mike

[jeff1234]

I HATE this car. I started IT today, all good, take it down the road and it blows a newly installed core plug out of the oil gallery. Now I have pull the engine to take this thing all apart again, fix that and put it all back together. I hate pulling the motor. I AM TIRED OF THIS CAR. $2000.00 TAKES IT AS IS, YOU HAUL IT AWAY.

[wheming]

Which core plug? Not the one on the flywheel side next to that upper dust sheild bolt??
That's the bugger that leaked on my rebuilt engine. :(

[zin]

I feel for you brother! I felt exactly the same way about my Omni! I was 1/2 step away from "fixing it" with a can of gas and a match! If you hang in there, you'll get through it, and be able to appreciate all the work you've invested.

Mike

[jeff1234]

That would be the one, or it's the rear main. Either way, uuggghhh.

- - - Updated - - -

I'm not going to sell it, I was just so pizzed that I had to spit that out. I should have the motor out tomorrow. I may have to pull the head so I wonder if I can reuse that head gasket, it was new and the motor ran all of ten minutes. Any encouragement or advice?

[zin]

It's not worth the potential headache a blown gasket would induce, so, unless you have to, or don't mind yanking the head later, put on a new one for peace of mind.

Mike

[jeff1234]

Well, I managed to get the engine out without disassembly, saved the head gasket. I could see no problems with the rear main seal but discovered that the oil gallery plug could be moved without much pressure. Couldn't get it out though so I'm going to try and remove the bad plug by using extra strong epoxy to cement a piece of 3/8 NPT pipe into the plug and pulling it. I don't want to drill into it and leave unseen bits of drill material in it. Hopefully back together in about eight more hours.
Any tips for making sure this plug doesn't move again?

[wheming]

You might be able to find my old thread where I delt with it.
To remove use a screwdriver as a lever to try and pry it out. It may be loose because it has already been goobered up a bit from removing the previous plug.
The best way to fix is to tap for a recessed plug. Be sure to use thread sealant when installing.
Someone had replied to my thread with that, and a pic.

I cleaned up the score marks on mine, tried to expand the standard core plug I was going to put in, then used JB weld when I drove it in, and coated with JB after.
I wanted to do the threaded plug but I gained the access by removing trans.

[zin]

I'll file the above remedy under "crude, but effective", and in the end, what you want is an effective fix.

Style points for using a threaded plug, but a sealed hole is a sealed hole, especially if no one will ever see it!;)

Mike

[wheming]

I never said what I did was the optimum fix!
I wish I would have ever heard of that happening before, then I would have certainly had the machine shop use threaded plugs.

[tkelly27]

I have this "aircraft" sealant stuff that makes a thick black paste. I put it on things I never want to take apart ever again.

You might want to make some det cans to be sure you're actually knocking or just getting noise from the sensor.

[wheming]

You might want to make some det cans to be sure you're actually knocking or just getting noise from the sensor.

Can you explain this or post a reference?

[csxtra]

Can you explain this or post a reference?

Wayne,

Here is a reference to what DJ did using a Bosch Wideband Knock sensor from a VW as an electronic det can (it is a long post, scroll to the middle of the post for the knock info):

http://www.turbo-mopar.com/forums/showthread.php?39999-93-2.4l-DOHC-Shadow&p=521051&viewfull=1#post521051

And here is more discussion on using that sensor as an electronic det can:
http://www.turbo-mopar.com/forums/showthread.php?67824-Knock-sensor-gauge-idea!&p=946458&viewfull=1#post946458

[zin]

The term det can refers to a mechanical detonation "sensor", they were/are simple metal cones with a thin metal "drum head" connected by copper tubing with one end hammered flat and connected to the engine at a location suitable to "hear" detonation.

Basically a big stethoscope you attach to the engine.

Mike

[wheming]

Thanks Warren.
In fact I do remember seeing a bit of that discussion before. But I had to read it to get jogged.
I guess I need a yard trip. These off of 4cyl VW?
I may have other questions to post in that thread.

[jeff1234]

Well, I have good news and bad news. The bad news is that on the test run as soon as the engine hit about ten psi oil started coming out of the B
OV, lots of oil, so there is something wrong in my hybrid turbo. The good news is that I didn't get a detonation light so that's taken care of.
I can't go on with the car any longer, I am tired of working on it and spending money on it. Now it needs to come apart and have the oil cleaned out of the new intercooler and piping and fix the turbo and all the other crap that has to be done. I've had it. Send a pm if you are interested.

[zin]

Just take some time off. I know exactly how you feel, like I mentioned earlier, but I also know if you allow yourself a "break", you'll not only feel better about things, but will likely figure out what the problem is, which btw, I don't think is a bad turbo, but rather another manifestation of the half-jazzed PCV system these cars have, sucking up copious amounts of oil into the intake.

Leave it be for a week or two, don't even think about it, until you feel like getting back into it, maybe work on an unrelated project you've been meaning to get to, then revisit this one.

Mike

[jeff1234]

Hi Mike, unfortunately the oil was puddled in the opening to the compressor. I noticed some there during disassembly from the lifter gallery core plug popping out and wondered at the time why it was there. It wasn't much so I connected it's presence to the oil spraying out of the timing window on the bell housing are perhaps thrown up by the air rushing under the car where the oil was leaking out of the inspection plate on the bell housing. I think it is the carbon seal right behind the backing plate inside the cartridge or the o-ring around the thrust plate. I checked the compressor wheel during a procedure to increase preload into the waste gate can. I had installed it with no preload and it wasn't boosting and I guessed that was why. (it was) It boosts now...whoopteedo! The only positive note was that the det. light didn't blink. If I were the man I was 20 years ago I would take a FLAME THROWER to it. (tip o the hat to "Scent of a Woman") LOL.
On another note, Patrick Henry knew what he was talking about.

[zin]

No doubt about Patrick Henry!

On the other subject, if the oil is on the inlet of the compressor, that lends credence to my PVC theory as oil shouldn't be able to get there from the shaft seal, but absolutely will if the PVC (or lack thereof in our case) is to blame.

Try looking further up the intake tract for sign of oil. Might even try running with it disconnected for a time to confirm.

BTW, one might considered as a distraction, a homebrew FLAMETHROWER! LOL.

Mike

[4 l-bodies]

In my experience oil pooled in compressor housing means turbo has failed. Jeff I believe your diagnoses is correct. How is shaft play? I'll bet you will find damage to backing plate during disassembly when it's all said and done. Whether this is cause or effect is another question. Losing that many turbos makes me very suspicious of oiling system. I agree with Mike. Just walk away from it for a while. Doesn't seem like TM cars or parts are selling very good lately anyway. You know your not gonna get much for a non-running vehicle. If I had a nickle for every time I told my friends that I was going to light my GLHT on fire, I'd be at least a few bucks richer (lol)! Hang in there!
Todd

[jeff1234]

4 L-bodies, What I don't understand is how a freshly rebuilt turbo can do this. Shaft play is almost non existent, none on up and down and about .005 in and out. To me it looks like the engine oil pressure is overcoming the shaft seal mounted in the backing plate or blow by is doing it. I suspect that blow by is not the problem because during this situation the valve cover nipple was open so internal pressure should have vented easily. As far as the PCV is concerned, this is how I hooked mine up. I have a Tee on the intake which the brake booster hose is connected to. A hose runs from the other side of the Tee and contains the PCV which is positioned in the hose so that boost will close the valve. The PCV has another hose connecting it to a large plastic Tee which is in turn connected to the valve cover. An additional hose is connected to the Tee that can be attached ahead of the throttle body. During this problem, the hose was open to atmosphere so in effect I had no vacuum during boost and crankcase pressure went to atmosphere. Do you see anything wrong with that set-up? All in all, I expect to see zero damage to the turbo internally as it has only been to boost once since I rebuilt it and as mentioned previously I had noticed oil pooled in the turbo intake after the core plug incident. Additionally two different turbo professionals had looked at that seal and didn't recommend replacement. I didn't replace the carbon seal behind the backing plate during the rebuild because that turbo was supposedly rebuilt by the vendor. When I disassembled it initially both the seal and thrust bearing parts showed no wear. Relative to the oiling system, I pre-oiled the engine and saw that oil was draining out of the return line. I am absolutely confident that there are no obstructions to oil flow and the fact that the turbo blew out about a third of a quart from turbo intake to exhaust tip seems to bear this out. What do you think about the seal?
Any how, the car is in the unheated workshop and winter is here, so I am done until spring.
Thanks for the commiseration and support.
Looking forward to any further ideas or opinions, Jeff

[Vigo]

An additional hose is connected to the Tee that can be attached ahead of the throttle body

If im picturing this correctly then that hose needs to be attached ahead of the turbo.

[csxtra]

What I don't understand is how a freshly rebuilt turbo can do this. Shaft play is almost non existent, none on up and down and about .005 in and out. To me it looks like the engine oil pressure is overcoming the shaft seal mounted in the backing plate or blow by is doing it.

Jeff,

I'm assuming that the freshly-rebuilt turbo is a journal-bearing turbo? Are you running braided oil feed lines to the turbo? Do you have a filter or restrictor in the oil feed path between the engine and the turbo?

The reason for all the questions is that the braided lines allow more oil flow/pressure to reach the turbo than the stock lines do, and this can cause the exact problem you are seeing. Years ago, I had a T3/T4 hybrid that leaked oil out the compressor side, and I was about to sell it as a rebuildable core, but I put a restrictor on the oil feed line and the oil leakage/burning went away. I sold it anyway (I upgraded :eyebrows:) but that same turbo has never been rebuilt and is still running fine 10 years later (even with much abuse with years of drag racing, road courses, and autocrosses).

The restrictor I used was from ATP turbo:
http://www.atpturbo.com/mm5/merchant.mvc?Screen=PROD&Store_Code=tp&Product_Code=ATP-OIL-022&Category_Code=ATP-OIL1

Another option is to put a small inline oil filter on the line from the engine to the turbo, it cuts the flow enough that the restrictor is not necessary. I use this filter from McMaster Race Carr:
http://www.mcmaster.com/#9800k51/=p3bdfh

It is available with different micron filters (the 10 micron filter provides the most restriction and filtering capability).

I hope this helps.

Warren

[jeff1234]

Vigo, yes, before I got the new intercooler I created a air filter adapter with a spigot that the hose would attach to so that when there was boost on, negative pressure was still available at the valve cover. The picture is of the unfinished adapter. I couldn't find the completed picture. It drew air within the engine compartment which wasn't optimum. The new intake gets its air through the power module as in original47310

[jeff1234]

If by journal bearing you mean the brass or bronze full floating bushings that the shaft rides in, that is what I have. I used to have a braided line because T/U wouldn't warrantee their rebuilt turbo unless you used their line. I went back to a stock line in the last couple weeks. It had a larger inside diameter than the braided. I have no restrictor between the oil feed connection on the side of the block and the turbo. It is a factory set up. I'm sure at this point you can see where I might be a little confused. In the past I have always been directed towards making sure there was plenty of oil flow yet you are saying to restrict the flow. I am not disputing your claim, it actually makes sense that with 50 PSI and huge flow the inability to get oil back to the pan and the resulting back up would cause pressure on the carbon seal because that area would be filled with pressurized oil. I don't believe that seal is designed to resist pressure. I think it is only meant to control a small amount of leakage from the thrust bearing. Does that make sense to you?

[Vigo]

Everything i have read suggests that even journal bearing turbos like what you have require a very low volume of flow through the turbo. Even a tiny hose at 50 psi can flow quite a bit of oil.

I have only had one turbo leak oil out the intake side but i cant say why it happened so it's just an anecdote to me. My sample size of having run probably a dozen different garretts on my cars over the years suggests that it's an uncommon failure mode, so i'd be suspicious of a repeat unless you can find a cause.

[jeff1234]

Warren, I plan to get the restrictor, install it, clean up the intercooler system and test before snow fall. This gives me hope that I might be on the right track. My question is, what is the thread design of the stock oil line nut at the oil line fitting, -3 an, -4 an or something else. I know that the screw in distribution block is 1/8 NPT at the outlet for the turbo oil line.
Jeff

[Vigo]

If you still have the old oil feed line you replaced when you went to stock you should be able to take it with you to somewhere that sells fittings and get a 100% accurate answer. I dont know the thread off hand.

[jeff1234]

Update, I moved the car between shop and garage with the intercooler lines disconnected. That burned off some of the oil in the intake system. When I checked the turbo intake side I found no oil. That made me wonder about the way I had intake air coming through the power module as in stock. I tested it again without cleaning the intercooler system out and the air intake to the turbo wide open. Initially there was some oil smoke that probably came from oil pooled in the system somewhere, but that cleared up and I was able to see boost a little over 10-12 psi with one of Shelgames chips. I saw the power loss light around 10 psi so the det problem has not been helped by a bigger intercooler unless oil still in the system is still causing it. It will have to wait until spring. My conclusion at this point is that oil was pulled through the backing plate carbon seal of the turbo because of negative pressure at the compressor wheel. This negative pressure was caused, I believe, by a more efficient turbo system trying to draw it's air supply through the constricted power module. This appears to be evidenced by the absence of clouds of burned oil behind the car during full throttle.

[Vigo]

EXCELLENT!

I think you should not read too much into the detonation until you put more miles on and are sure the oil is all gone.

Hopefully a less restrictive intake will let this turbo stay on the engine and live for a while. You need a break from problems!

[jeff1234]

Amen Brother, Amen!!