302 cubes for Suburbia

[1project2many]

at 25-30 kpa -2400-2800 it shows a lot different than the rest of the table, could make for knocks in them cells.

It's not so uncommon to see GM throw a bunch of advance at an engine after a certain MAP and RPM. But the telltale is that spark advance begins to drop rapidly as rpm increases. For the L30 GM pulls 4-5 degrees along a given MAP range as RPM increases while the L31 sees only a degree or two at most.

What's even more interesting for comparison is the L99 table. Same bore as L30 but with shorter stroke, longer rod, and reverse flow cooling there's an additional 10 degrees advance at WOT.

The 305 just seems to have issues with advance.

[Fast355]

It's not so uncommon to see GM throw a bunch of advance at an engine after a certain MAP and RPM. But the telltale is that spark advance begins to drop rapidly as rpm increases. For the L30 GM pulls 4-5 degrees along a given MAP range as RPM increases while the L31 sees only a degree or two at most.

What's even more interesting for comparison is the L99 table. Same bore as L30 but with shorter stroke, longer rod, and reverse flow cooling there's an additional 10 degrees advance at WOT.

The 305 just seems to have issues with advance.

Not sure where you are getting all that WRONG SA info on a 305. Keep in mind the L99 was in a car that is lighter and more aerodynamic than the trucks and vans the L30 was put into. The mechanical engine fan alone tends to make the engines more SA sensitive in hot weather as it puts a heavy load on the engine in hot weather. The L99 also has longer rods and a better rod/stroke ratio that makes it less sensitive to detonation under heavy load.

The 305 is not spark advance sensitive, just does not need as much advance as a 350 with its smaller bore the flame front travels more quickly across its smaller area. If anything the 305 is more detonation resistive than the 350. I ran 10.8:1 compression and 230 psi static compression with the old iron 601' casting 305 heads on 93 octane pump gas with a carb and ran 34* total advance doing it.

[1project2many]

Not sure where you are getting all that WRONG SA info on a 305.

The table I've posted is a comparison of stock tables taken directly from GM calibrations. Why do you say it's wrong?

The 305 is not spark advance sensitive, just does not need as much advance as a 350 with its smaller bore the flame front travels more quickly across its smaller area.

Based on experience and backed by what I've seen come out of GM engineering, I disagree fully with your statement. I've been working on 305 equipped vehicles since the '70s. Stock 305's have always had a greater tendency for spark knock. In the '80s, the only GM truck to receive knock control without a fully computerized ignition system was 305 equipped. That wasn't just an experiment to see if it would work. I know what happens when you disable or remove that system. Look through cals matching year for year, 350 to 305, you'll see consistent indications in the form of more aggressive knock retard, less aggressive restore rates, and timing tables that favor less advance on top end. It is not because the 305 needs less advance to create peak pressure at the same time as the 350. Based on the number of degrees difference, the amount of time involved is too great.

Keep in mind the L99 was in a car that is lighter and more aerodynamic than the trucks and vans the L30 was put into. The mechanical engine fan alone tends to make the engines more SA sensitive in hot weather as it puts a heavy load on the engine in hot weather. The L99 also has longer rods and a better rod/stroke ratio that makes it less sensitive to detonation under heavy load.

I am fully aware of the stock configuration of the L99. Which is why I said the stock spark tables make an interesting comparison. And while I agree that a mechanical fan puts more load on an engine, I think it would be naive to say this factor is more important in the L99 timing tables than reverse flow cooling. Cooler heads inhibit combustion rates and the reverse flow engines run substantially cooler heads than standard flow engines.

If anything the 305 is more detonation resistive than the 350. I ran 10.8:1 compression and 230 psi static compression with the old iron 601' casting 305 heads on 93 octane pump gas with a carb and ran 34* total advance doing it.

I have experience tuning. Personally I built and ran a 10.8:1 350 on 87 octane fuel with a manual transmission and a tunnel ram style marine intake on iron heads. That engine was in the 400 horse range. I own a Pontiac Turbo Sunbird 2.0 running 17 psi boost on the stock turbo and fuel system and it hasn't launched the headgasket. That's a tough feat to accomplish with that engine even with upgraded parts. Mine's tuned for 89 octane and I've got a *lot* of time into the cal. I ran a 2.2L engine with 9.4:1 and nearly 8 lbs boost. The engine is stock with the addition of a very small turbo and no intercooling. It was a huge challenge to tune between the wide range of intake temps and the way too large TBI injectors in the PFI intake but the point was to prove it could be done. It made fair power, and the engine didn't blow up as many had predicted. And to make it fun I kept it on 87 octane. I pulled the engine, still running, when I sent the car to the junkyard for rust and saved it for future use. I also have a 302 powered '57 Chevy pickup with Crossfire injection. First installed in '92, I used a 305 ecm from an '83 Firebird. I moved on to a 7747 in '99, and now use a 7427. I have retuned it with each ecm change and have plenty of hours working with the spark tables in that engine as well. For perspective, that engine uses 601 castings and 1.84" valves.

Are you emotionally invested in defending the 305? I'm not discussing (or dissing) it's worth as a potential powerplant. Hog suggested using stock 305 spark tables as a starting point for my 302. I do not believe those tables are the best starting point and I've indicated why.

[1project2many]

Well, the truck made the trip successfully. I'm guessing I was pulling about 4k lbs between the tractor, trailer, and a bunch of "stuff" I pulled out of an old garage. I know that's not a large load but it's probably typical of what I'll be hauling. Overall I'm satisfied that this truck will work out although if I was crossing the Rockies or maybe even towing on the high plains the current combination probably wouldn't make me happy.

There were a couple of larger hills on this trip and at least twice I spent a significant time at WOT on the way home. Dyno software predicted the engine would feel flat around 2500 with the stock intake and boy, does it. At 65 mph I'm right in the middle of that flat spot. The combination of 3.42 gears with the current intake keeps the trans busy which means I've got more work to do nailing the shift tables. I'm going to see if there's a tow/haul or economy switch that will fit right into the dash to make use of dual shift patterns. 3.73 gears would be nice but I'm not likely to go that far. I was towing the entire trip of 335 miles which meant no OD. Empty trailer one way, loaded trailer the other, lots of hills in the middle so I was surprised to see 12 mpg when I calculated the fuel economy. Not that it's engine related, but I'm going to be replacing the gear oil with full synthetic. The diff gets warm when towing and the airflow around the truck carries the smell of hot gear oil right into the passenger area.

So subsequent work will be:
install large trans cooler (didn't have time to install during engine adventures)
service differential with synthetic fluid
Tow / haul button
Adjust shift tables for faster TCC unlock and quicker downshifts, and to hold downshift longer
hot restart parameters still need adjustment
-->Fix A/C!!!<---

[EagleMark]

-->Fix A/C!!!<---

Yup!

[Hog]

Glad you made your trip, I really wish I could take a 302 for a spin just compare the powerband.Thats weird about the 505 being less detonation resistant. All else equal, a smaller bore should exibit more detonation resistance. Every chart I have ever seen says that higher coolant temp, larger bore, lower fuel octane will be less detonation resistant than lower coolant temps, smaller bores and higher octane gasolines. I have no experience of my own that compares the 2 bore sizes. I am interested in doing a short stroke engine, the L99 crank is interesting. Take care.