It is that time! Tear down starts tomorrow on the 97 Express.

[Road Trip]

I will take a shot down the intake later. Seems to have a fairly nice shape to it as is. I need to measure the runner length as well. I have a large mixture of rocker arms at my disposal. Have considered 1.6s on the intake of the outer cylinders and 1.5s on the center 4 cylinders. To help even out the flow and powerband with the inner/outer runner length differences as well. It will either run better or run worse, should not hurt anything either way.

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Nice. Tall manifold provides deep plenum shape. Air turning into runners not nearly the issue as a shorter/flatter intake.

And no doubt good bang/buck given buying a discontinued item. Juggling inner vs outer rocker arm ratios actually makes
sense. (In a perfect world you would have pyrometers on each exhaust and we could 'see' what the rocker arm differences
are doing.) Looking forward to what you end up with. (!)

 

[L31MaxExpress]

My dog and I took a ride in the 97 this afternoon to escape the heat because the ac in the shop was not keeping up. Pulled it in and cooling it off now to start tearing the front end apart. I have forgotten just how torquey the 383 is but even at 1,500 rpm at light throttle around 50 mph in lockup it was shuddering from the overlap induced misfiring. At one point it was shuddering so badly, pulled down into 3rd to clear it up. She loves riding in that middle row captains chair, elevated so that she can see out of the windows.

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[Sean Buick 76]

Nice. Tall manifold provides deep plenum shape. Air turning into runners not nearly the issue as a shorter/flatter intake.

And no doubt good bang/buck given buying a discontinued item. Juggling inner vs outer rocker arm ratios actually makes
sense. (In a perfect world you would have pyrometers on each exhaust and we could 'see' what the rocker arm differences
are doing.) Looking forward to what you end up with. (!)

Good advice, I’m hooking up exhaust temp probes on my race car to monitor each cylinder instead of relying on the average air fuel ratio. I’m adding a bung to each header exhaust primary and will move my probes around to test and compare them. It would have been expensive to do a 8 probe setup so I bought a 3 probe.

 

[L31MaxExpress]

Update on the a/c work last summer too. Still ice cold. It was over 100F when I took off, sun lower in the sky and it cooled down in a couple of miles, then just started on its way to becoming a refrigerator.

I am also having to back off the shift pressures after the Superior shift kit I put into the transmission. With the 6.0L van 4L80E segment swap I used in the P59 and stock 2005 Express shift pressure the 4L85E dang near knocks your head off shifting. 383 moves the pressures up substabtially compared to the 6.0L due to the predictive torque output used to control the line pressure. Shift pressure were 70-85 where the 383 runs torque wise, 90 is max. At part throttle it was chirping 1-2 and heavier throttle chirped 2-3. I reduced the line pressure up to 300 ft/lbs by 25% and smoothed it out to 520 ft/lbs. Likely going to have to pull another 15% out of it including WOT. The Superior kit hits insanely hard with the feed sizes they suggested and their stiffer pressure regulator spring and larger boost valve. It was nearly bark the tires hard shifting the way it was to start with at heavier throttle pre shift kit. Potentially partially my fault on the shift kit install. I drilled the feed holes for their HD Towing/RV specification given I do tow a heavy trailer and the van itself is heavy. Also made the assumption the looser converter would cushion it somewhat as well. Evidently not because it bangs gears hard.

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[L31MaxExpress]

Filmed one last clip of that beefy idle with the Comp cam. Idling at 750 rpm and about 24* advance with the a/c on which smoothes it out a bit from the increased load. Ran pretty good other than the overlap induced misfiring under load at low rpm as previously stated. I was pushing it around Fort Worth pretty hard and ran it in out in 2nd gear to the WOT upshift once getting on the highway (won't say how fast, but shifted 2-3 @ 5,500 rpm, 4L80E, 3.73 gear and a 29.6" tall tire with 125 rpm converter slip, I let off about 4,500 in 3rd and the log showed about 200 rpm converter slip at that point, I was up there) and the fuel economy math I have setup in HP Tuners showed about 12 mpg. Lots of stop lights, idling at those lights and in traffic as well as a lot of moderate throttle accelerations from a stop. I have a feeling the new cam improves on that a good bit. I think it has developed a vacuum leak as well, suddenly it was showing up to 15% fuel being added at times by the LTFTs although that is kind of weird because the Wideband was showing it to be overfueling nearly 20% when it went into lean cruise with the LTFTs showing +12%. Whatever, it is coming apart anyway and will need some tune revisions anyway. Not a hint of knock retard though on nearly 5 month old 91 pump gas. At 196F coolant temp and 100F IATs, I saw 32.5* timing at 5,500, so much for those that claim you cannot run a full timing curve on an 10.65:1 engine that cranks ~215 psi on pump gas. I keep wanting to say 11:1 but I forget it has thicker Felpro 1003 head gaskets now than when initially built with the GM 0.028 Vortec composite gaskets.

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[CumminsFever]

There's a sound not normally heard from a van! I didn't realise how high your compression was. Very cool!

 

[L31MaxExpress]

There's a sound not normally heard from a van! I didn't realise how high your compression was. Very cool!

I built the engine to take advantage of cheap E85 in my area as well as for the added efficiency and torque of higher compression. Really seems to help light, part throttle power output.

Weird fact here, the Germans played with what they called "over compressed" engines in WWI. Basically they increased the static compression ratio and limited throttle opening often by the pilot until the plane was at higher altitude. The German engines could maintain full power output to a higher altitude by raising the comoression ratio past a point the fuel could support detonation wise at or near sea level and reducing that compression by running part-throttle.

I control detonation via a slight timing retard near peak torque. When VE is highest so is the cylinder pressure and octane requirement. Knowing what I know now, I could probably run a 13-14:1 engine on pump gas with a properly dialed in DBW setup. The DBW would be setup not to allow full throttle until higher rpm where the VE is dropping off naturally. Some OEM manufacturers like Ford are actually doing that now. IIRC the 5.0L Coyote is setup that way, if the knock sensor senses detonation the PCM backs off the throttle and adds more fuel. Nissan's VCT (Variable Compression Turbo) engine runs at like 8:1 compression under full boost but runs at like 16:1 compression at light part-throttle loading.

 

[CumminsFever]

I built the engine to take advantage of cheap E85 in my area as well as for the added efficiency and torque of higher compression. Really seems to help light, part throttle power output.

Weird fact here, the Germans played with what they called "over compressed" engines in WWI. Basically they increased the static compression ratio and limited throttle opening often by the pilot until the plane was at higher altitude. The German engines could maintain full power output to a higher altitude by raising the comoression ratio past a point the fuel could support detonation wise at or near sea level and reducing that compression by running part-throttle.

I control detonation via a slight timing retard near peak torque. When VE is highest so is the cylinder pressure and octane requirement. Knowing what I know now, I could probably run a 13-14:1 engine on pump gas with a properly dialed in DBW setup. The DBW would be setup not to allow full throttle until higher rpm where the VE is dropping off naturally. Some OEM manufacturers like Ford are actually doing that now. IIRC the 5.0L Coyote is setup that way, if the knock sensor senses detonation the PCM backs off the throttle and adds more fuel. Nissan's VCT (Variable Compression Turbo) engine runs at like 8:1 compression under full boost but runs at like 16:1 compression at light part-throttle loading.

Ok, so this is really cool info! It sparks my curiosity, how would the raised compression affect efficiency? Say, if you went for 14:1, then tuned it accordingly, would you get better fuel mileage?
You're the guy to do it if anyone is!

 

[PlayingWithTBI]

Say, if you went for 14:1, then tuned it accordingly, would you get better fuel mileage?

Yeah - then you could run diesel

 

[OutlawDrifter]

Knowing what I know now, I could probably run a 13-14:1 engine on pump gas with a properly dialed in DBW setup.

One of my buddies in high school had a 13:1 460bbf in a '78 F150 that we ran on 85 pump gas(4000'+ altitude) during the week through a thermoquad. On Saturday night we would advance the timing on some AV-gas (100+ octane, depending on the cash on hand), swap in the 4.88 geared 9" center section, some worn out drag radials, and let it eat. That rootbeer brown metallic pickup embarrased a lot of cars.