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911 turbo ignition advance table

Motor specs:[*]3.2 Carrera motor, now 3.5l with Nickies, was 8.5CR now reducing to 7.5CR[*]twin plug[*]DTAFast ECU S80 Pro[*]Full Width Intercooler[*]Precision turbo PT 5862 CEA T4/0.65 A/R[*]Injector Dynamics 725CC[LIST][*]GT2 EVO cams from Webcams

I live in Denver area and drive between 5000 and 8000 ft altitude, 91 gas. I run max 0.8bar boost. I just blew through some compression rings (and burned some of the cylinders so now getting new Nickies/JE piston set ouch!!) at 8.5:1 CR so on trusted advice am reducing to 7.5:1 CR. On my maps I use TPS as my load and then make a boost correction for the injectors and ignition advance.

Does anyone have an advance table that would be a good starting point for me. I've seen a couple of threads here but not much recently.
Thanks,
Andy
p.s. sorry no photos as motor is in pieces in my garage at the moment, unless you'd like to see ugly pictures of what can happen to a piston and cylinder on a turbo motor
Old 01-04-2018, 03:35 PM
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Im curious, why tps as load?
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Old 01-04-2018, 04:07 PM
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My thoughts exactly. I would definitely be going speed density
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Old 01-05-2018, 02:28 AM
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Quote:
Originally Posted by Andy@Altitude View Post
unless you'd like to see ugly pictures of what can happen to a piston and cylinder on a turbo motor
Ummm, ya.


I'm sure I'm not alone in that I enjoy a good carnage pic or two, or three ...

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Old 01-05-2018, 06:03 AM
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TPS load is probably root cause. You can be at full boost at part-throttle.

I'd change strategy to load for sure!!!

2nd, that turbo is way too small IMO for the size of motor and cams.

I'd definitely try at least 60mm or larger. You're leaving a lot of hp on the table pushing the smaller compressor.
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Old 01-05-2018, 06:48 AM
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Quote:
Originally Posted by dos531 View Post
Im curious, why tps as load?
If the fueling model is VE based, this is fine as the MAP sensor is still an input into the fueling equation and will be compensated for in the model. If the ECU is a pulse-width based model, then you will run into issues.

Edit:
Looking at the DTA Software, it is definitely pulsewidth based fueling. I would heed the advice of others on here and change your load axis from TPS to MAP and get the engine calibrated again once it's back together.
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Last edited by '76 911S 3.0; 01-05-2018 at 07:57 AM..
Old 01-05-2018, 07:50 AM
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Quote:
Originally Posted by Tippy View Post
2nd, that turbo is way too small IMO for the size of motor and cams.

I'd definitely try at least 60mm or larger. You're leaving a lot of hp on the table pushing the smaller compressor.
The turbine (62) is big enough, but it seems like a small compressor (58) for the altitude.

Generally, you would size the turbine 1 or 2 sizes smaller for that altitude, and reduce the A/R. The compressor wheel isn't usually reduced in size.

Also, that CEA compressor is optimized for high pressure ratios -- not ideal for EFI 911s that typically run 1.8 - 2.2 pressure ratios.

That new compression ratio of 7.5:1 is very conservative with the GT2 cams and your altitude.
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Old 01-05-2018, 08:48 AM
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Chris,
At the time I was researching a new turbo the ported compressors and billet machined compressor wheels had just entered the market. Precision was one of the first on the market with their CEA models. After several lengthy phone calls with the factory application guys I was never able to get a compressor map so I am running a bit blind and put my faith in the recommendation of the factory guys. The combination of their CAE, billet machining (acheiveable thinner walls - higher flow areas - lower inertia) and the compressor housing porting supposedly delivered the flow of a 62mm compressor wheel with with lower rotary interia and faster spool up (although am sure the spoolup is mostly dictated by the higher density turbine wheel). Garrett came out shortly thereafter with same features but have to say I am quite happy with the Precision (after years of being frustrated with Turbonetics- garret design warmed over and lousy customer service). The factory guys said they had several customer running this turbo on the VS Golf R32's (3,2l) delivering 600+ HP with good results. I may yet try the next lower AR to 0.45 but seems like a big step.

My driving objective is much more centered on fast spoolup vs. trying to get gonza huge HP numbers as I will take the driveability of fast spoolup over max hp any day in any HPDE or autocross event and top speed ot 180+ is plenty for me. Second reliability matters to me alot and not convinced that my 915 gearbox can take more than 600HP in the long run anyway. So my target is for 500-600 rwhp "only" and not at all concerned about leaving HP on the table. After having tried several other turbos (Hi-fi's, 62mm, etc) I am very happy with the turbo I have. I wastegate quite a bit at 1.8bar (absolute) and if wanted to put in race gas I know I can get well over 2.0 bar.

About being at altitude and pressure ratios. Here are my calcs (please correct me if I am missing something). I live at 7300 feet, ambient is a little below 0.8bar. I have worked hard to keep pressure drop small through the air filter (really big filter element) and plumbing (short run length, minimum bends, 3" dia) to the compressor input. Let's say this pressure drop is 1psi at WOT/full boost) or about 0.07 bar. I have more work to do similarly on the compressor out side (low pressure drop to manifold from the compressor) but let me be optimistic this only is another psi pressure drop. If I am achieving 1.8bar absolute at the manifold then my compressor PR= (1.80+.07)/(0.8-.07)= 2.56. So my PR is quite a bit higher than the normal PR range of 1.8-2.2. Alot it of it driven by the low ambient pressure that I have to work with and why I am very focused on pressure drops to the inlet side of the compressor.

I am comfortable with with TPS load and pressure comp (which is my density correction based on ideal gas law - BTW lots of other posts on other web sites says this is fine - mostly what you are most comfortable with) and getting me the AFR's that I want. I have an AEM AFR gage mounted right next to my steering wheel and so get to watch it constantly in addition to running it into my lambda correction function. At above 1 bar MAP I run 12-12.5AFR reliably regardless of TPS or RPM.

I have now had two times where my top compression rings have failed on the bottom side of cylinders 3 & 6 (this time on cylinder 6). This is the place where it will happen and this time looks like it started right where I put the ring gap ( at about 4PM) and burned a hole through the piston and put a pretty big gouge in the Nickies wall.

I think my problem is heat buildup and detonation (of course linked). I orginally got this car running at sea level and 93 gas so the 8.5CR was OK but think with trying to achieve the same boost (absolute pressure) with the low ambient pressure, 91 gas, and poorer heat transfer also at my altitude that something has to give. So now that I need to buy new Nickies/JE piston set (ouch!) I am reevaluating CR, timing, boost. I'd like to keep the boost level where it is. I know now that 8.5CR is too high so now what? Factory 3.3 turbos were are 7.2/7.5 CR and was told this was the safest bet. However these did not have twin plug (BTW I am running wasted spark - 2 bosch coil 6 packs). I know I am going to lose low/mid RPM throttle response but really do not want to buy yet another set of Nickies! To help offset I have just bought the SACHS power clutch and it is quite a bit lighter than the stock unit so should help some on the throttle response (as well as stock clutch would burn if I did not shift just right under full load). Bottom line not willing to go to 7.2CR but 7.5? 8.0?

I am also taking a hard look at my timing table. I have been conservative not wanting to risk detonation. Based on anecdotal feedback at the time (6-7 years ago when first setting this up) I run only 12deg BTDC at full WOT/boost. Now I'm seeing that this will actually generate more heat and that I should be running more like 18-20degrees? Is this a contributor to my heat problem?

Finally, at these higher PR's air charge heat becomes more of a problem (along with the reduced heat transfer efficiency from the IC at altitude). My IC core is 24"X10"X3" thk and I have focused alot on good sealing between the turbo tail and the top of the IC. I run 2.5"dia pipe in (same as compressor out) and 3.0" out to the throttle body. I can't fit much more of an IC in the engine bay and thinking about a water to air IC with the water radiator in the front spoiler. This is a big change so holding this out as last resort.

I'm really curious what the Pike's Peak hill climbers do? Anyway this is all I got for now. Please put anything on the table for me as with motor apart for the winter and expectations of big spend on complete rebuild now is the time, right?
Thanks,
Andy
Old 01-06-2018, 10:58 AM
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Gentlemen, thanks all for the input!
Chris, let me start with your comments.
I have no concern about leaving HP on the table as I would rather have rapid spoolup and driveability any day over gonzo huge HP for things like daily driving, HPDE, and autocross events. My objective is to “only” have 500-600 rwhp. Plus having a top speed of 180+MPH is plenty for me.
I have had several other turbo’s like most of you: 60, 60 Hi-fi, 62. Mostly Turbonetics product (slightly warmed over garrett designs and lousy customer service). So once I became disgusted with Turbonetics I went about searching for another turbo manufacturer. Garrett of course was one I looked at but at the time (about 4 years ago) Precision was getting a lot of positive comments online and they were one of the first to offer the ported compressor housing along with their optimized CEA design and billet machining of the compressor wheel. After several lengthy phone calls with their factory guys I was never able to get compressor maps so was flying blind on their recommendation but the technical arguments were pretty credible. Their feedback was that the 58mm compressor wheel would deliver the flow I needed for 600HP and the pressure ratio I would need to deliver that mass flow at my altitude and for my displacement. It would deliver the flow of a 62mm wheel but at smaller diameter and with faster spoolup. I know Garrett and just about everyone else now has the ported compressor housings etc but have never gone back to look at their maps for comparison. The Precision factory guys had several customers that had used the 5862 CEA’s on VW Golf R32’s (3.2l) and were reliably delivering over 600HP. I know this is a water cooled V6, 16 valve so different than a flatsix but none the less a good starting point.
When I first got the turbo setup together I was at sea level and 93 gas so the 8.5CR was fine. But now having gone through 2 sets of pistons and Nickies I’m throwing in the towel for the 8.5CR. This last failure was on the bottom side of #6, burned a hole through the piston at about where I put the compression ring gap and took a pretty big bite out of the Nickies wall.
Chris, before I go through options to fix this problem I wanted to go through the PR calculation in my situation. I run max boost at 1.8bar absolute at the manifold. I live at 7300 ft and so ambient pressure is a little less than 0.8bar. I have put a lot of effort into making the input side of the compressor as efficient as possible (meaning low pressure drop) so have huge air filter, 3” dia pipes, short run length and minimum bends from air filter to compressor intake. After all at such low ambient pressure I don’t want to make things worse with poor intake plumbing design. So let’s assume I have 1 psi (0.07bar) pressure drop to the compressor intake. Although I have more to do on the discharge side, let’s assume that I again have only about 1psi pressure drop (is optimistic with the IC, etc). I’m am running 2.5” dia pipe between the compressor outlet (which is also the compressor outlet dia) to the IC and 3” dia pipe from the IC to the throttle body with 2X90 deg bends. So running the PR calculation across the compressor:
PR= (1.8+.07)/(0.8-.07)= 2.56
So I AM running higher PR than the usual 1.8-2.2 CR. I think this is major problem in that the higher PR creates a higher as the higher compression further increases the temperature of the discharge air and also possibility of detonation. So when you put this together with the lower IC efficiency at altitude and the 91 gas and pretty sure something has to give.
These are the options I see it to reduce heat at the top of the cylinders:
• Run lower AFR - BTW Contrary to the posts, lots of guys are using TPS with pressure comp successfully. The pressure comp gives the density correction you need (equivalent to using MAP as load) but also can use TPS in combination with MAP to do some extra things with ignition advance particularly under dynamic throttle situations that you cannot do with just MAP alone. Either way it’s mostly what you are comfortable with as you pretty much get to the same place either way. Anyway I keep an AEM AFR gage right next to my left hand below the steering wheel and watch it religiously as well as using for my lambda correction on the ECU. I run reliably at 12-12.5AFR at any manifold pressure above 1bar and higher below this pressure to help me pass the darn smog test here in Colorado. I am reevaluating this and may just run AFR of 12.5 or below everywhere to help keep engine cooler at all times. Won’t help much directly with detonation but will help take heat away which will indirectly reduce detonation risk.
• Run lower CR - So original factory 3.3l turbos ran at 7.2/7.5CR so I have been told this is a safe betto set CR there. But they did not have twin plug (I run wasted spark with dual Bosch 6 pack coils) nor modern EFI so I am not willing to run 7.2 CR but certainly 7.5? or 8.0? Looking for any input here, however the last thing I want is to do a third motor rebuild!!!! I just want to drive baby drive!!! I know I will pay the price on poorer low boost throttle response. I just bought the SACHS power clutch which is really much lighter than factory cast iron and hoping may help with throttle response a bit.
• Lower boost – simple answer but is my last resort.
• Better IC - I currently run a core that is 10”X24”X 3” thick. I have put a lot attention into sealing between underside of turbo tail and top of IC to make sure I am pushing as much air as possible through the IC. There is not much more room left for a larger IC in my engine bay. I have even looked at going to water to air IC with water radiator in front spoiler. New factory turbos are going in this direction and Chris I know you did this for a mid-engine Porsche (saw in a PCA article). This is a big change however and although not last resort, maybe next to last resort?
• Water/methanol injection - This seems like a nice solution and the newest GT2 press releases say they are doing this at the intercooler (the ones on each side under the wheel wells). However, it is yet another additional system with need for maintenance and refilling (where do you put the water tank ?) and its own set of reliability issues. However there are some nice “pre-engineered” solutions from Snow Performance, Aquamist (the original) and even AEM running for $500-$1000. I think I’ll wait on this for now.
• Ignition timing - This is an area I want to explore right now. Based purely on anecdotal input I got years ago, with twin plug and my kind of boost levels I heard you want to stay below 12-15 deg advance at full boost particularly around where you motor has peak VE. I have been pretty conservative here not wanting to invoke the ire of the detonation beast. But now I’m hearing that even with twin plug full boost advance of 18-20 degrees is better and may in fact my lower advance at 12degs may be contributing to higher heat load? Any input here appreciated!

I’m sure I have missed some things – open to any corrections or ideas!
Thanks, Andy
Old 01-06-2018, 12:17 PM
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