Repair-It

Here's the latest update. The big milestones this weekend were the fuel pressure raised to support future growth (and vacuum/boost referenced), plus actual TCC functionality.

http://www.thirdgen.org/techboard/diy-p ... -2.html#76

An update from this morning.

http://www.thirdgen.org/techboard/diy-p ... -2.html#77

Turbo selection fun.

http://www.squirrelpf.com/turbocalc/

Here are the assumptions. Walking through the numbers...

300hp is the round number target for this endeavor, at this time. We figure around 200hp now. Conveniently, the calculator figures 8 psi boost to get there.

Engine size is a 292 bored 0.030" over, so 296 cid. Notice it doesn't need number of cylinders. Displacement * volumetric efficiency = airflow. It's that easy.

11.5 is a nice, realistic AFR for forced induction on E10 gas.

BSFC of 0.55 is a swag based on the internets.

I/C loss is 0 psi; I don't expect we'll need an I/C for the 300hp goal. Maybe later, or sooner if IAT's are hotter than expected. On that note, Paul needs to order said IAT (and the GM 2-bar MAP sensor).

Figuring 14.55 psi barometric, which is a couple hundred feet above sea level. The barometric pressure is the basis for which to calculate pressure ratio, so this matters a LOT. 300hp implies an absolute airflow requirement. But boost is relative to atmospheric. Therefore, knowing barometric pressure tells you where the pressure ratio will need to fall to get the airflow requirements.

The RPM stuff is just sort of swagged.

5000 rpm is a good redline. The fuel cut is technically 5200 but 5000 will be the highest normal operating RPM. Understand that this 4.125" stroke engine (!) started life putting out 115hp @ 3400rpm and 215 lb-ft @ 1600rpm so this is an accomplishment (wiki tells me the 292 was used in 80s UPS trucks). This will require a governor spring change as it shifts lower than that currently.

So I figured peak power at 4800 but actually this engine could easily make peak power at like 4200 and hold it to 5000 rpm. Maybe I'll run those numbers next.

Max boost at 3500? No idea. Maybe.

Min boost at 1500. The calculator calls this 1 psi, so things are just starting to happen, then all in by 3500.

The volumetric efficiency is taken directly from the 100kPa column of the actual VE tables for this engine, which I trust, because they've been corrected using WB feedback. And actually the calculator seems to agree with my ~200hp N/A assessment if you study the numbers. I would love a calculator with more VE data points, though.

I also swagged the intake temps. I raised them from the defaults due to no intercooler. Air temp translates to air density and you'll need more pressure to flow a given air mass at a higher temperature since the air is less dense. I really believe that below some level, running no I/C makes sense. Likewise, above a certain boost level, an I/C is the way to go. I don't know where that line is, and I figure we're approaching it, but hopefully not over it.

So with all that, this one looks like a good choice. It is a Garrett/Honeywell T04B 62-1. Not really stressing it with around 70k wheel RPM at these boost/flow levels.

If I raise HP to 350 but keep everything else the same, it looks like this: Still below 84k RPM and nicely in the efficiency zone. It wants 11.7 psi to get here, and I think we'd need an intercooler at this point.

So adding an I/C loss of 2 psi (which the turbo has to make up with an additional 2 psi of output), and bringing down intake temps, I arrive at the following map, staying at 350hp: Compressor RPM is still reasonable and the map looks healthy.

Going to 400hp, we now need a full 16 psi of turbo (would be 14 psi at the manifold, minus TB losses, which are probably significant at this power level). This will need a bigger TB much over 350hp I think. Maybe a ported small block TBI. Or even the big block TBI. Or an extra-large ported big block TBI. Which is why I think 300hp with no intercooler is a very reasonable place to start without getting into all that extra cost stuff. That next 100 hp is costly. To say nothing of the transmission's ability to handle it, either.

Posted this 2 years ago. Now the turbo is installed and I roughed in the tune pretty good this weekend.

kevm14 wrote: 11.5 is a nice, realistic AFR for forced induction on E10 gas.

I'd say we have AFRs in the mid 10s to mid 11s. Should be pretty safe. I did have to add a ton of MAP AE (pump shot). I booted it on an entrance ramp and it went totally lean and lost all power, then came back. Somehow this was effected by the turbo? Anyway, I added a bunch of high deltaMAP AE and it seems much happier.

Had to pull a TON of spark advance to get it to stop pinging. It's down around 20° under full boost. The knock sensor does seem to respond, because it does pull timing after knock events. The pinging was audible but I got that settled down. This will be a 93-only truck now. It may be that my existing spark map was way too aggressive, and while the engine tolerated it naturally aspirated, with the turbo, it doesn't. I need to look more into this.

Under warmer temps, I will need to tweak the CTS/IAT spark stuff. Basically there are two tables: a CTS/IAT table by temperature that says how much spark to add or subtract depending on the CTS/IAT blend, and the other table says how much CTS or IAT bias you want across the range of air mass flow (grams/sec, calculated). Generally the engine needs more spark advance at lower coolant/intake air temps, and less spark advance at higher coolant/intake air temps. I set it up to use a little less CTS bias at high airflows (or maybe I just thought about it - need to confirm). If the spark is still too much as the weather warms, I can use that table to pull more spark with hotter IATs. These tables can be tricky to get set right, and they are even more critical with a non-intercooled turbo, imo.

kevm14 wrote:I don't expect we'll need an I/C for the 300hp goal. Maybe later, or sooner if IAT's are hotter than expected.

Intake air temp report: under full ~5 psi boost (actually seems to average more like 5.5 psi), intake temps peaked at +75°F over ambient and then equalized. They cool off very quickly after lifting off which is helped by the very effective cold air intake on the truck. Picks up from behind the grill and then barely 12" right into the turbo.

I feel these temps are very modest and reasonable and it may not be worth the hassle of plumbing in an intercooler. If we go higher, yeah, I think it would be good to add one. But it's all on waste gate right now - no boost controller.

The waste gate is also functioning perfectly.

kevm14 wrote:This will require a governor spring change as it shifts lower than that currently.

WOT 1-2 shift is like 4500, but the WOT 2-3 is like 4000. Too low. Held it to 5,000 manually to get some data and torque does seem to fall off up there but it does keep pulling, as it should.

kevm14 wrote:Max boost at 3500? No idea. Maybe.

Easily! Max boost at 2,500 rpm and probably lower than that except the torque converter won't let us get there.

kevm14 wrote:Min boost at 1500. The calculator calls this 1 psi, so things are just starting to happen, then all in by 3500.

I would have to lock the converter in 2nd gear or something and see what it'll do. It can probably get to "1 psi" at 1,500. Maybe lower.

The engine sounds agricultural as it always does. Sort of a quieter cross of a Cummins (the long stroke inline 6 noise) plus a little bit of Ford 7.3 PSD.

It is very torquey and the stock G20 torque converter actually works very well with this combo. It'll flash to 2,500 rpm and kind of just sit there at medium throttle, as it goes through the gears under some boost. The 3.73 gear isn't as "too short" as I thought it would be - 3.42 might be ideal, but probably not worth the effort at this point.

It feels like a jet taking off if you roll to WOT from a dig and run through 1st into 2nd. If you punch it hard, it'll spin through 1st, get into 2nd and actually keep spinning for a few seconds. Strong.

I bet this is somewhere on the order of 250, 260 hp as it stands, total swag. Probably could cut a mid to high 14 second 1/4 mile if I had to guess.

I think it would be great to tow with. Probably does the closest impression in terms of power and torque to the still-born Duramax 4500 (with scaled back HP and torque since this C10 is pretty light compared to a modern 1/2 ton). Except the trans needs more shift kit. Mushy part throttle shifts on partial boost. The WOT 1-2 is alright and the manual WOT 2-3 is alright. But where it shifts automatically, it is not good.

Other notes:
Fuel pressure is tracking perfectly. It's vacuum and boost referenced. The EBL knows about the vacuum reference, which is part of the calibration. In boost, the regulator adds 1 psi of fuel to 1 psi of boost, so the EBL assumes a constant fuel supply. The extra fuel pressure compensates for the extra boost pressure on the injectors. The pressure is ~26 psi at atmospheric, and then tracks right up to 31 psi under full boost (+5 psi), exactly as it should. Fuel system seemed fine, able to handle the pressure and flow. I had to pull fuel out here and there.

Take a second to remark about that - this is an injection system with electronic spark control which this 83 never saw. Not only that, but we are using a heavily modified TBI computer, and a TBI system that was never meant for forced induction, with fuel pressure up to over 30 psi. The stock system is 9-13 psi! And these are the stock injectors from the G20 van.

So basically, it drives very nice and I'd say the turbo enhanced the drivability. You can feel the turbo working even when it's not in boost. I did have to bring down the TPS % threshold for PE mode (enrichment), because it was looking like it would enter boost in closed loop! Not good. I had to reduce it to a little over 30% at lower rpms, and maybe 35% at higher rpms. This means it will hit enrichment with less throttle, which will impact fuel economy. Remember, the turbo cannot add efficiency to an existing engine - it is just a means to force extra air in, which requires extra fuel. Even if it added that air with 100% efficiency*, it wouldn't add fuel economy (unless you did so without adding fuel, and ran lean - which is why turbo diesels DO get better fuel economy - but with gasoline, you ADD fuel). In the real world, the MPG of this truck will probably go down a bit. It doesn't matter though, because it's fun.

*As it stands, I figure the turbo causes three main points of inefficiency, or conversion losses:
1) Conversion of exhaust gas flow to impeller rotation (less than 100% efficient)
2) Compression of intake charge (less than 100% efficient - someone could probably calculate how inefficient this is from my air intake temp number - some portion is part of physics due to compressing the air)
3) Added exhaust back pressure - you are force feeding an engine that is having a harder time pushing out the exhaust - does that sound like it increases efficiency? It doesn't. The gas doesn't magically all funnel into the turbo - it has to be pumped. As for how much of a restriction it is at part throttle, maybe not bad. But it is also pushing air against a partially closed throttle (not efficient), and that requires some added backpressure to spin the turbine (not efficient).

Oh I almost forgot - no blow off valve! Zero weird sounds or anything that seems unhappy, even letting completely off at full boost.

That truck is quite cool, and I would love to have something like that someday. Just a cool concept, and a great looking truck to go with it. The lawnmower in the back was just perfect.

As for the fuel efficiency comments, I agree that a turbo doesn't improve fuel efficiency. However, I do believe that a turbo can enable a car to incorporate fuel saving features like a smaller engine and/or wider gearing but still be tolerable to drive when on-boost.

In other words, I'm sure you wouldn't see better fuel efficiency in that truck by adding a turbo. But you might if you gave it the 2.93's or 2.56's that might make it very annoying to drive N/A. With the turbo, it would still be driveable with those gears. But not as much fun.

I know that that is not a given either, since you might be flooring a 2.56 car all the time to get up hills.

Fast_Ed wrote:In other words, I'm sure you wouldn't see better fuel efficiency in that truck by adding a turbo. But you might if you gave it the 2.93's or 2.56's that might make it very annoying to drive N/A. With the turbo, it would still be driveable with those gears. But not as much fun.

I know that that is not a given either, since you might be flooring a 2.56 car all the time to get up hills.

Yup, I agree with all that. My only statement is, adding a turbo, and changing nothing else, pretty much can't increase fuel economy on a spark ignition gasoline engine. But being able to use a smaller engine, taller gears, etc, that's a different thing entirely.

And on the 2.56 comment, I especially agree - this thing has to hit PE mode with as little as 30% throttle now. So you can cruise on the highway in closed loop, which is good, with the 3.73s. But with way taller gears, I dunno. It isn't that aerodynamic after all.

How did it sound pulling away? I goosed it a bit in 1st when I was a couple houses down.

Some pics.

He wasted no time. New 2.5" intake piping. Still needs to re-weld the intake hat.

Another drivability comment: this engine isn't really snappy. It drives well but because the intake manifold has no real plenum, it just isn't going to snap like a V8 with a big intake manifold. Which is fine. But it adds to the turbo diesel ambiance.

But the way it launches sort of reminds me of modern turbo automatic cars. It isn't violent but it leaves efficiently and then boost happens almost immediately. It surges nicely to the shift point and you're already in 2nd gear before you know it. Very satisfying.

It sounded good and I heard you hit it a bit down the street. Unfortunately, the mic on my camera didn't quite pick it up.

I could hear a bit of turbo, but I bet it sounds awesome all spooled up on a WOT pass.

Maybe I'll get to see that sometime.