OK now on to Plan D 1986 Bonneville GS

[Jim_Rockford]

yeah I think 86 and 87 are one year only PCMs figured they were different before looking them up seeing as how My current 86 prom is only a 3 letter code VS 4 digits for the 87 and newer
I read a few thread over on Third gen.org and several folks did the swap and said their stuff ran better, another thing that I need to check on, is I dont think Im feeling the converter lock, I tested the lock up solenoid before I reinstalled it it worked fine, so I suspect this ECM might have a problem. I havent tried to pull codes on it mainly cause I have been busy getting it road worthy. new front brake hoses, New pad, swapped out the airplane gears for normal street car gears, stuff like that, im currently installed a set of factory rally gauges and will have the Tach hooked up tomorrow and I can see if the RPMs are dropping.

[stew86MCSS396]

I think this is the one you want... http://www.montecarloss.com/communit...Number=1027530

[Jim_Rockford]

good thread, I went over today so I could bring the car home from the shop to my house...(Hard to drive 2 vehicles at the same time. ) and grabbed two proms I had and I was correct The one chip is for the 87 L69 ss the other was a old chi from a 90 9C1 police car I owned withe TBI LO5 so thats one isnt going to do me any good..LOL

[Jim_Rockford]

Took the first road trip in it and the result was 21 mpg so Its close and thats with a 3.42 gear stockers where 2.41s.

[Fast355]

Took the first road trip in it and the result was 21 mpg so Its close and thats with a 3.42 gear stockers where 2.41s.

At one point I played with that system in an 88 Cadillac Fleetwood with a vin 9 307. That car had a 180 hp 307, 200-4r and 2.53 gears. 27 mpg but no power on hills. Was gifted a solid main 403 out of a late 70s GMC motorhome that I helped put a 500 cadillac into. Put a set of earlier 70s olds 350 heads on that 403 along with a mondello cam and an edelbrock intake. Car would get 25 mpg and never slowed down. Was able to get it to run well without tuning the ECM although later made some small changes to that 830 ecm.

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.

Still like my old school q-jets. Actually just finished completely rebuilding a virgin 84 305 G20 carb that came off a van nearly 20 years ago in the wrecking yard. Rebrushed the shafts, removed and resized the idle down tubes, resized the idle channel restrictions, resized the idle air bypass ports, resized the idle mixture screw holes, resized the accelerator pump holes, resized both the secondary pull over enrichment ports as well as the pull over well restrictors. Then changed the jets, metering rods and power piston spring. Finally resized the needle seat and created a new seat for it and the accelerator pump check ball. New secondary hanger cam and windup spring also installed. Removed the choke plate, shaft, and linkage but retained the thermostat and fast idle cam. Started chokeless as soon as fuel reached the fuel bowl, settled to a high idle and just ran great.

I clean my carbs in a heated ultrasonic bath. All kinds of dirt, dried gasoline, carbon and crap come out of the carb.

The one I built running on my 11:1 aluminum head, roller cam 383. Actually ran 8 minutes and 36 seconds without a load at 2,000 rpm on 1 quart of fuel.

https://youtu.be/l7XDuEvqFR4

[Fast355]

I built an Edelbrock 1406 as well in the last couple of weeks and jetted it up enough to feed the 383. It ran for 7 minutes and 24 seconds with the last 20 seconds or so on one float bowl and on 4 cylinders. Well dialed in Q-Jet definately has better low-load fuel consumption numbers. The quadrajet had 15% longer run time on the same exact fuel volume and ran on all 8 until it stalled, something the Edelbrock did not do. That being said both carbs have great throttle response and idle manners and are seamless in throttle transitions. A couple of throttle rips on the primaries had it up to 6,000-6,200 nearly instantly.

HEI was setup to give 15° centrifical mechanical advance by playing with the center plate and weights. With medium springs from a mr gasket recurve kit, 363 center plate and 053 weights, timing curve started at 1,500 rpm and reached full advance by 3,600. Initial timing set at 16° BTDC. WOT timing is 31° @ 3,600. Vacuum advance is connected to manifold vacuum, canister starts advancing about 7 in/hg and fully in by 12°. Vacuum advance has a hei weight bushing from the mr gasket curve kit slid over the shaft into the guide channel. Limited it about 2°. Total timing at 3,600 rpm with the vacuum advance connected was 46° btdc. Idles at 650 rpm with a stable 31° of timing and nearly 18 in/hg showing on the gauge. Cam is 218/228 on a 108 LSA and 104 ICL. 0.578 lift with the 1.7 rockers. Rhoads V-Max lifters adjusted cold to the bottom of their travel with a 0.014" feeler gauge between the valve tip and rocker arm. The lifters and rockers are a little noisy but run fantastically. The rhoads lifters really tame the idle and low speed manners of the tight LSA cam.

I did the Q-Jet fuel consumption test with and without 2 chambered 40 series flowmaster knock off "rumble" mufflers. The rumble mufflers added nearly 30 seconds of run time to the q-jet and dropped off about 1 in/hg at 2,000 rpm. RPM stayed the same. I believe the mufflers kept the tri-y headers from over scavenging the chambers, allowing for some internal egr.

[Fast355]

This is the edelbrock running with rumble mufflers.

https://youtu.be/7umnODe8nqQ

To get the edelbrock 1406 as responsive as the Q-Jet had to run the largest primary jet and thinnest metering rod in the tuning set. .101 jet and a .070 x .037 rod with the 8 in/hg step up spring. At 2,000 rpm the quadrajets small primaries and triple boosters already have the main metering flowing well. By comparison the Edelbrock is just starting to drizzle fuel from the boosters. The quadrajet has a very nice fanned out spray of metered atomized fuel flowing and the Edelbrock has big fat droplets of fuel pouring down on the throttle plates.

[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.