max boost with stock turbo pistons

[berniek]

Put my JDM together about 4 years ago, Cometic 2 mm HG (lowered compression), 550cc, Walbro, Lex, 3" random tech single cat exhaust, HKS catback, 57 trim CT26, Spearco knockoff, hardpipes, Lipp elbow, Aeromotive FPR (42 PSI), Raptor BOV. light Cr-Mo flywheel. Moved oil pickup to rear of pad. Fitted stock turbo pistons loose, but maybe should have gone for Weisco, etc.

I've read all manner of information about how much boost I could run. Never anticipated more than 15 PSI, but.....It feels soooo much better at 17-18. Fuel is always on the rich side. Anyone have a similar setup with stock turbo pistons? I just do short bursts through second and third gear, sometimes through fourth. Curious if anyone has run more boost.


BernieK

[pandrade]

from what iv heard about upgrading the trim on your ct-26 its just not useful. even whith higher trim the turbo regardless after 13 psi will start to blow to much hot air. they dont have the flow chareteristcs to EFFICENTLY push 14+ psi. when it comes to the internals iv heard about 600hp is there tolerance but i would never go that high on factory pistons( sounds like your set up can handle it tho)

[cre]

That's not really true. Any changes you make to the turbo can significantly alter its efficiency. The other aspects of the vehicle's intake and the environment also alter how much extra heat can be dealt with. The figure 14 to 16psi was based on how hot the out coming charge is and the stock intercooler's ability to cope with it before the diminishing return become greater than the risk of damage. The 57 trim is much more efficient and capable of moving a much greater volume of air at higher pressure with less heat. With the compression drop you see from a 2mm HG and a good aftermarket intercooler you can get away with the turbo pumping out much hotter air than normal and still see a reasonable increase in power. It's not all about pressure though, there are a lot of people who push 18 on the stock CT-26, drop i an upgraded CT-26 and are amazed that at only 10-12 PSI they're making the same amount of power.

My concern is the pistons. If they're stock they may be a relatively soft aluminum allow (not even hypereutectic) which makes them a lot more susceptible to detonation damages. Running rich doesn't mean much.... Many people "think" they're running rich but are often in fact running too lean when it counts. Do you have a wideband? What's your AFR range when boosting? 17 to 18psi shouldn't be a problem unless you're driving in killer heat, running lean, using cheap fuel, have excess carbon buildup and so on. I wouldn't try to go much beyond that though... I could get away with more given my altitude.

[berniek]

Thanks for the reply. No, the pistons cannot be hypereutectic from the factory, but most certainly must be eutectic, probably at around 10%-11% Si. From the small amount of metallurgy I know, hypereutectic pistons tend to crack more easily than eutectic, although hypereutectic pistons are stronger. There was (is?) one fellow in Denmark running 30 PSI boost, but don't know any details aside from the stock ignition system not being high enough in voltage to break down the plug gap. Obviously, a casting is not as dense and strong as a forging, but is used in the stock turbo application with oil jet cooling. 17 PSI boost sounds high, but on an absolute pressure basis its only 53% more than the stock 6 PSI boost. But 30 PSI is a different story. If he runs hypereutectic pistons, the stock turbo cast eutectics must be OK for 17 PSI. At least that was my rationale at the time, but I've had lingering doubts about it.

Mixture under boost is about 12.5:1, known by a reworked thermal conductivity A/F ratio sensing cell following a coil of 1/4" cooling tubing run from the Lipp to the front. A small 12V solenoid (stainless) valve blocks it in to retain the last reading, which gas velocity effects through the cell require. Early-on I bought a Dawes 4 LED device which reads the last couple of millivolts at the rich end of the stock A/D ratio sensor. Its got a precision voltage reference and a couple of National voltage to LED drive chips inside. It has matched the thermal conductivity cell exactly. The thermal conductivity cell is not really visible unless the roving (NJ) emission police look under the horizontal sheet which is integrated with the hood latch. The LED readout and small meter for the TC cell are in the ash tray. Speaking of the police, the Raptor BOV is inside the right fender, and is recirculated to the bottom of the accordion hose.

Thanks for the assistance. I'll be happy to send a tip for any further information.


Berniek

[berniek]

Any thoughts about water injection? I have an RV pump which I was going to build a PWM controller for. Still need to get the McMaster nozzle. But this may be one of those things that never gets done. If you believe it to be of value, I'll change priorities.

Thanks again.


BernieK

[cre]

No, 17psi doesn't sound high to me at all. When you do all the math doubling the HP put out by a car only increases the stress on the connecting rods by 20% to 30% not 100%.... BUT as I said, it's not just one thing that's going to destroy something, it's a combination of factors. I think you're fine as long as ambient air temps aren't excessively high. Running a VSV on a thermostatic switch to bypass your boost controller and pull the boost down to 14 or so would be a good safety. Some controllers (not many) have a trigger input to switch boost settings.

To put some perspective on this I've blown holes through TWO low mileage stock pistons at 12psi on a 1.5mm HG running with a mixture of 11:1 (onboard wideband). That really should have been a very safe setup... Matched injectors flowing 480cc/min, new fuel pressure regulator, stock intercooler, full flow oil cooling circuit, REAL cold air intake... Should have been fine. I didn't go lean, had no knock issues BUT I was running GE electronics as a base and the much more aggressive timing map may have been the entire problem. Now, had I been running a more efficient turbo, pulled ignition advance, used water/meth injection, had a better intercooler this probably could have been avoided.

You're being a little more descript than is necessary and I think it's giving me the wrong picture of what you actually have setup. So you're using a narrowband piezoelectric element and offsetting the mixture via creative plumbing to read an approximate range with the 200mA window? If so.... that's madness. Get a real wideband on it and let us know what the mixture is (datalogging hardware would be well advised if you intend on going beyond 18psi). At full boost at that pressure you should be richer than 12.5:1... up to 25% richer. At ~10:1 you really shouldn't have to worry too much. I would recommend you first focus on getting a good intercooler in place, a full flow oil cooling circuit and any intake which DOES NOT pull air from the hot engine bay (stock or aftermarket setup with the filter getting cool air from a neutral or high pressure area (not a wheel well).

I have little experience with water cooling. It is something I want to experiment with soon myself. I do think it would be an excellent addition and would really help ensure that you're getting more of the power that you should be with far less risk but you know all this. Do yourself a favor and look around on the net for information about water/meth injection before the turbo too. I'm kind of of the opinion that running 10 to 20% through a pre-turbo nozzle and the other 80 to 90% after the IC may be very advantageous. I don't think spraying a large volume into the compressor would be a good idea in the long run though (as it's most likely to condense and pool in the IC).



Much to my wife's chagrin, I don't charge for help here and it's really not something which we would allow anyone to do. If someone wants pay for the help they would otherwise give here they should open a shop or start their own web service. As for the 'tip jar' just something I saw used on other forums and since none of the staff here are paid or compensated in anyway well, we took a vote and decided that it would be ok. If we see anyone trying to sell info they will be banned.

[cre]

This may be of use to some. It's not an absolute but it is accurate for most basic setups.