OK now on to Plan D 1986 Bonneville GS

[Fast355]

For reference, tried two different HEI weight and spring combinations with the same springs. Ran the same total timing but varied the initial timing to make up for the more limited centrifical mechanical advance. 383 is definately alot more responsive with more initial advance and idled better. At 1,500 rpm the new setup has a little less timing (17 vs 24 previously) but seems smoother at that rpm. With vacuum added it was 33 vs 38° respectively at 1,500. 38° at 1,500 was a bit too much and it had a skip or surge in it. At 2,500 rpm + both setups had the advance pretty close to the same values. At 2,000 rpm total advance with vacuum was about 39° now and 42° before. 38-42° at 2,000 rpm with no load is a pretty good starting place for most SBC engines. Depending on chamber/piston design, cam, compression ratio, air/fuel ratio and whether EGR is being used or not 44-52° total advance at 3,000-3,600 rpm is also in the ball park. I can tell you with a 77 jet, 48m primary rod, apt screw 2.5 turns off the bottom and 46° of timing at 3,600 rpm this 383 is dead smooth and instantly responsive to the lightest throttle movement.

Currently tested combination (used in both videos above)
(363center/053weights)
750 rpm = 0 advance
1,000 rpm = 0 advance
1,500 rpm = 1 advance
2,000 rpm = 8 advance
3,600 rpm = 15 advance
Initial set at 16° BTDC
15° vacuum advance, starts at about 7 in/hg and full in @ 12 in/hg.
Idle timing is a steady 31° with vacuum advance on manifold vacuum.

Previous combination
(369 center/41weights)
750 rpm = 0 advance
1,000 rpm = 2 advance
1,500 rpm = 15 advance
2,000 rpm = 18 advance
3,200 rpm = 23 advance
Initial set at 8° BTDC
15° vacuum advance, starts at about 7 in/hg and full in @ 12 in/hg.
Idle timing was stable at 23° BTDC with vacuum advance on manifold vacuum.

[1project2many]

My old 83 G20 with a mechanical q-jet would often get 20-21 mpg highway. LE9 305 with flat top pistons and 601 heads and factory catless dual exhaust with factory tubular manifolds off a 1-ton 350 van that I had added a dr gas x-pipe into. Van had a 700r4 and 3.08s.

Lotsa flat roads in your area? I have a friend in Nebraska and another on OK that report getting very high mpg results and I believe it's the long, flat stretches. Trying to duplicate that tuning in hilly New England results in lean cruise with frequent jaunts into PE. End result is much smaller gains.

[Fast355]

Lotsa flat roads in your area? I have a friend in Nebraska and another on OK that report getting very high mpg results and I believe it's the long, flat stretches. Trying to duplicate that tuning in hilly New England results in lean cruise with frequent jaunts into PE. End result is much smaller gains.

Actually lots of rolling hills here but lots of open roads to run steady speeds on. That old 305 had enough low end grunt to pull most of the grades at 70-75 mph in overdrive even with the 3.08 gears. Had a few that it would downshift to 3rd on along the way. There were a few longer grades that were maybe 1-2 miles long that the cruise would force a 4-3 then a 3-2 downshift on and into the secondaries to hold 75 mph. Biggest killer of MPG in my area is often the 20-30+ mph winds we get. That being said my old 305 used to pull about 10-12 in/hg vacuum at 1,800 rpm at about 75 mph on fairly flat road. The factory power piston enriched at about 5-6 in/hg. Most of the time at cruising speeds even uphill the metering rods were burried into the jets. The cam I ran for the longest was a crane 274H06 and had the Q-Jet on a 7104 performer rpm. Great combination with the flat top pistons and 53cc 601 heads on a 305. After running the factory tubular manifolds for several years, I put throley tri-ys on that old van. The tri-ys woke it up even more. On level road that old G20 would run ~100 mph on the primaries and not exceed 3,000 rpm. The factory engine made peak torque at like 2,000 rpm. The intake, cam and headers pushed it up to more like 3,000-3,500 but it easily made more torque than the factory cam even down below 2,000 rpm.

This is the article years ago that made me decide to run the performer rpm on that old 305. My stock aluminum manifold started leaking and the coolant ports were heavily corroded. Chose the performer rpm over the performer which ended up with me having to later go to a Weiand 7525 when I failed smog for lack of an EGR valve. One of my customers had a few El Caminos and Monte Carlo SS 305s and suggested the 274H06. Swapped that cam in and it was like having 2 stock 305s under the hood. Little 305 really loved that little 218/218 @ 0.050, .450 lift, 106 LSA cam. Low-end power stayed pretty close to the stock power above the 1,500 rpm stall speed, but pin the throttle down and get it up to the 3,000-5,200 rpm range and it pulled like crazy for what it was. Later I played with the governor in the 700r4 and had the trans shifting 5,800ish in Drive. Old 305 didn't like that too much and after about 50K of being spun to 5,800 several times a day with that cam spun 2 rod bearings.

https://www.hotrod.com/articles/ccrp...-engine-build/

[Jim_Rockford]

Sorry folks, Giot distracted, Finally got the 3.42s installed, and found a nice old System 2000 scanner for 50 bucks and bought the TPS and rich idle stop tools off thextons website directly for 25 bucks compaired to the 100 or so everyone wanted on E bay. Got the TPS dialed in, and the rich stop screw set and got the dwell in the 30 degree range and this thing purrs like a kitten, installed a set of hooker long tubes and a nice mandrel bent 2 1/2 dual exhaust with some thrush turbo mufflers, an X pipe crossover and installed a heated o2 in the drivers collector. car starts with just a bump of the key, decent power for what I figure is a low compression 305 . currently building a 350 for it and I will be using a 94 LT1 f body cam, and a set of ported L98 heads . so it should be a lot more fun to drive.
That being said I also had a 87 corvette Spark control module, I had tried it before getting the carb set before and I seemed to give me a check engine light so I just plugged the stock on back in. The other day I was messing around and figured now I have the check engine light at bay and everything is where it belongs I tried the corvette SCM again and the car now feels a bit peppier and no check engine light but Im not sure f the timing curve in in the module or if the Prom handles that I also noticed Im not getting any spark knock from it now either like I was with the original SCM even though I didnt change the Knock sensor, until i swap in the 350 . Anyone know if the SCM has the curve in it, or does it just take the signal from the KS and send the data to the ECM? Im thinking of trying the olds 87 ECM witheh MCSS chip again , and see if the check engine light returns on that .