Thanks for clearing up the VE reference. It did seem like you were referring to the engine's base VE.
I have never heard anyone say they want more complexity in an engine management system. I've heard specific complaints with different calibrations. Complaints like "I want more resolution in the spark tables" or "can we make the VE table extend to the rpm I run the engine at" are common. It's also common to hear a variation on "Why can't the factory make these things simpler to tune" which goes a long way toward explaining why the aftermarket systems are so simple.
I'll put in a bid for OE management. The Sunbird turbo calibration has 2079 variables (a table is considered a variable for this claim) to adjust. Some are relevant only to factory hardware used for testing, but there are still over 2000 possible values to adjust. This ecm is from a family of ecm's known as a "P4." There are specific hardware variations between P4 ecm's, but the basic architecture is usually similar enough that code from one ecm can be used in whole or in part in another ecm. This allows you to import sections of code from at least 3 other vehicles which used turbocharged engines including the Pontiac McClaren turbo Grand Prix and 2 different models of Lotus. And finally, since the code is written in a well documented assembly language, it's possible to write your own custom code to perform tasks exactly as you feel they should be performed. Combine this with some published ecm "mods" such as extra memory, better peak and hold injector drivers, and the ability to "finish" populating various boards with components not originally used in that application, and the factory ecm seems to have a high degree of flexibility.
I actually have a 'Woo / Delco pcm on my desk. I'm hoping to have time to start trying to get the calibration out of it to see if it matches anythign used in a GM vehicle. Might be nice.
I'm a mechanic simply because that's the trade closest to what I want to do for fun. I've spent 3 years pursuing an EE degree, but had to leave when both my wife's parents became terminally ill. I've worked in race shops, high performance shops, dyno shops, a corvette and muscle car dealership, new car dealerships, and I had a business repairing farmer and rancher's equiment for several years in Montana. I've had piles of GM training and a whole lot of hands on experience. I currently maintain a fleet of school buses (easy work and doesn't get in the way of my fun time).
The rest of this post is the reply I typed yesterday. I have to meet family for breakfast. Enjoy your daughter's birthday. Family is far more important than "car stuff."
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I haven't ever told anyone to try and follow in my footsteps, nor have I implied that 17 psi boost is an easy goal to reach. There were a few things I read in this thread which caused me to post my response.
To get 200whp out of the C20GET you would need to port the head, replace injectors (stock size will work fine...don't take a chance with used injectors ), install an intercooler, get stronger valve springs (to combat valve float) and run the engine at about 14psi of boost.
if you ask anyone, the rocker arms are the first thing to blow if you up the boost.
I also worry about bad information floating around. Porting the head will help tremendously, but it isn't needed. I've never heard of the rocker arms failing simply because the boost is increased. I'm not sure what pressure level constitutes "overboost" but I know of a few engines including mine which should be considered fairly high boost. Stronger valve springs will provide good insurance against damage, but I feel good stockers will hold up. The cam really stops making power below the redline and there's no need to run significantly higher. You're better off not to use the stock size injectors at this power level even though it is possible.
Although this one rang so true I had to laugh:
At 180 whp you shouldn't have to worry about the tranny... and frankly.... unless you have a limited slip I doubt very much that you can put that to the ground.
As far as timing, my experience is that GM in the 80s and early 90s loved to use excess timing both in turbo and NA applications. I feel this was probably to help improve off the line acceleration and seat of the pants feel. The best indicator I've found of excess timing before detonation is engine oil temp. Before detonation occurs, engine oil temps will rise. When the crank is too close to TDC for the cylinder pressure to be efficiently converted to mechanical energy, it's the engine oil which takes most of the abuse. As a result the oil temp rises, sometimes considerably. If you back off timing and the temp drops, it's an indication that you probably have timing too far advanced. Yes, you often can increase timing without detonation. But that doesn't mean you're making the most power or that you're doing the best you can for your engine.
Starting in 92 with the LT1, GM really did a much better job with ignition timing.
I have no idea what kind of power my LT3 is producing. The last time the car was on the dyno it was non intercooled and producing around 10 psi. I intercooled it shortly after but I've never returned to the dyno. I use 87 octane fuel and add 4 ounces of Marvel Mystery Oil to every gallon of gasoline. I use MMO in all my cars. AFR's start around low 12's but peak in the high 12's heading for 13.0 at the top of the rpm range. It's very important to keep the rpm to fairly low levels because higher rpm doesn't allow enough time for the injectors to deliver fuel. I try very hard to observe the stock redline.
I don't doubt the engine's base VE is low. The only real way to tell is to estimate from fuel usage and hp produced. GM's tuning leaves indicated VE greater than 100% even before the boost is applied. I'm fairly sure my 8V engine didn't achieve Indy or Formula 1 engine VE numbers when new. But if you try using the base hp numbers for a 92-94 NA PFI to guesstimate base VE of the turbo engine I'd have to say it's probably closer to 80%. It's sad to think my engine may have lost an additional 10% VE over time.
I am not using a stock TB. I'm using a ceramic coated throttle body and intake from a 92 - 94 pfi engine adapted to the LT3. Tony posted flow numbers for both intake / TB combinations on Darkmuck's site.
I misquoted deliberately. I wanted to address the detonation issue. I agree that lower intake air density is reducing hp from what it could be.
Compressor outlet temp depends on temp change across turbo. Temp change relates inlet temp, outlet temp, pressure rise, and compressor efficiency. Outlet temp is directly proportional to inlet temp. The amount of change is affected by efficiency and pressure rise.
You may have done it.... but as far as I'm concerned your specific tuning of the PCM and careful monitoring of all parameters is the only thing keeping the engine from going "boom" at any given moment.
Yes, it is because of my tuning. I mentioned careful changes and extensive datalogging.
As far as how you've had to retard timing..... I have to think it's a problem your particular engine has due to low efficiency.... a well designed C20GET should be able to advance timing off baseline factory maps without risking spark knock.
Discussing proper timing can occupy an entire thread. When the knock sensor sees knock you've gone too far. It's the ecm's way of catching an "uh-oh." You need to prevent knock, and often this means looking at timing values at lower rpm and lower loads than where the knock appears.
What on earth possessed you to push the engine to it's current state is beyond me.... it's like trying to make a square wheel roll down a hill as fast as possible without shattering into a million pieces.
That's a great analogy. Ned's car seems to serve as an example for so many people, yet it's built with early to mid 1980's thinking. Computer tuning has been around for 20 years, but the C20GET guys don't seem to utilize it. I figure if I can get one or two people at least thinking about what's possible with good tuning, someone may take an LT3 even farther than Ned's. I know at least one guy is well on the way. If nothing else the fuel mileage and reliability can be increased greatly without losing performance. For me it's a matter of pushing my understanding and abilities.
And since the original poster is from NH, I figured I'd say "hi" if the opportunity shows up.
I'm going to calculate mass airflow numbers with a bunch of variables and see where I end up on the T25 maps..... more out of curiosity than anything else.
Well, you'll probably determine that the engine is running in a near vacuum at a temperature near the melting point of titanium.
I have not blown any rods, broken any cam followers, blown any head gaskets, or done any other damage to the engine.
You can get it off eBay for about $100 or so.
