I have been trying to fix my bogging problem for a while, but it keeps coming back. I am running a 383 with a QJet that I rebuilt. I have adjusted the secondary valve spring a couple of times and lately I have been trying different secondary rods/hangers, but I can't get rid of the bog. Off the line and through second everything is OK the air/fuel gauge says about .70-.75, but as I wind out second gear just before I am going to shift I get a lean bog.

How long does it take to empty the QJet bowl? The float is set between 1/4 and 5/16 or so. I have a holley 110 GPH pump and have it regulated to 6 PSI....Could I be running out of fuel or is it more likely that I have to keep messing with the secondary spring/rods/hanger? I have a high flow needle and seat that I could try.

I guess that I'm thinking that it shouldn't be that hard to get my engine to pull strong through all three gears as it a pretty mild 383 with a GM L82 cam.....I don't know, maybe you guys can get me pointed in the right direction here.

What RPMs is the shift happening and what is the configuration of your motor. Any chance that you're beyond or below the power band of the motor?

-dnult

I never really thought of that....It happens about 5000 RPMs in second. It doesn't happen at the same RPM in first though.

I am going to keep tightening the secondary spring until the bog stops....In theory, there should be a point where the spring is tight enough that the vacuum of the engine can't open it far enough to get too much air.

Try backing your timing down a couple of degrees and see if that helps. Too much total advance can cause the same problem.

Just curious, how does the L82 cam run/sound in a 383?

Originally posted by travis:
Try backing your timing down a couple of degrees and see if that helps. Too much total advance can cause the same problem.

Just curious, how does the L82 cam run/sound in a 383? Exactly what I was thinking. Have seen this with my motor at 36* total timing (it normally likes 33-34 total).

I have it set at 14 degrees of initial timing, so you're right it is getting 36 as the distributor adds in 22 degrees all in by about 2500. I'll take out a couple degrees of inital timing and try again.

I kept tightening the secondary valve spring, but I got to the point where I can't tighten it anymore so it can't be the secondary valve.


How does the L82 cam sound/perform in a 383? I don't have any experience with other cams in a 383, so I can't give you a comparison. The idle is very smooth with enough vacuum(16 inches at idle) for all accesories, it's not lumpy at all. It seems to perform very well though. Here goes my speculation on it's performance.....I think that if I can get rid of the bog my 3800 lb ragtop would be mid 13's/105 with poor reaction time and lots of wheel spin of the line. More speculation....I think that with a coupe that is 500 lbs lighter, slicks, a better driver with a better reaction time that 12's would be possible....maybe even mid 12's??? Again, I'm just speculating and I am a novice when it comes to running the 1320. I'm sure that the other more experienced people here could give a better guestimate on how a 383 would perform with the L82 cam(specs are 224/224 .450/.460 114). I do run aluminum edelbrock RPM heads with 10.65:1 compression which helps too.

Oh, by the way....This past week after tweaking my Qjet I got 21 MPG with my setup! I thought that was pretty good for daily driving with 87 octane fuel(there has been a shortage on good gas here lately)!

If backing down timing doen't work, then I suggest an external fuel pressure gauge viewable from the driver's seat while driving. No pressure, no fuel. Maybe not enough fuel in the tank for a siphon to the pump, pump mounted too high, too low of fuel pressure, try 8 lbs.

The L82 cam probably sounds pretty mild in the 383. It performed well in my '67/350/PG/4.11 = 13.30-13.40's at 2900 lbs. But, it was done at 5200 rpm.

My experience with Q-jets is that they work very well with 3# of fuel pressure, I set mine at 3.5# at the carb and have had no problems. Here's a quote from one of Jim Hand's many q-jet articles:

This system can provide much more fuel than the engine can use, and the engine will run through the 1/4 mile perfectly with only 2 1/2# pressure. Some time ago, I was testing a non Q-Jet carb and had set the pressure at 6# for that carb. At the drag strip several days later, the wagon was off .5 second and 3 MPH. After 3 passes, I remembered the high fuel pressure, and after lowering it to 3#, the wagon picked up the lost performance. You may not see this kind of drastic change because each fuel delivery system is different. However, I strongly recommend you find out by strip testing what the lowest pressure will satisfy your vehicle, and then set the pressure about 1/2 # higher for insurance. You may be pleasantly surprised, not only with your Q-Jet but with other brands of carbs as well.

http://www.geocities.com/MotorCity/Factory/4633/Pictures/quadrajetTech.html

Everett, you kind of blew away my speculation that my engine with the L82 cam could get into the 12's in a coupe!! You have much more experience than me, so I'm sure that your estimation/experience is much more accurate than my speculation!


On my QJet....I have a 110 GPH holley fuel pump. I also have a fuel pressure regulator set at 6 PSI. It seems that if I set the pressure higher than that I have problems overrunning the needle and seat. I may be able to go a little higher, but I have found that 6 PSI is very safe! I also installed a high flow needle and seat, but I didn't notice much change. I also took an extra bowl stuffer that I had and shaved about a 1/4 inch off the bottom to add a little more bowl volume. None of this made any difference though....still had the bog around 5000 in second.

I backed the timing off a couple of degrees, but haven't gone for a WOT blast yet. I was kind of sleepy this morning on the way to work and forgot all about it.

Everett, the fuel pressure thing could be the culprit though....If I did install a fuel pressure gauge that I could read while driving that would surely confirm whether or not that's the problem.

Onovakind, hmmmm another possible fuel pressure issue. I do have it set a 6 PSI...


Thanks guys for all of the input!!!! I'll get this thing to run strong through all three gears one of these days. The only trouble is that I think that I'll be too fast for the track! Last time I was 14.1 with a horrible bog!


Here is what DD2000 had to say about my combo:


http://www.stratagaz.com/383DD2000.bmp

I dropped the timing, but I still had the bog.

I changed the secondary hanger to the highest one I had and changed the secondary rods to the richest ones that I had. I also tightened the secondary valve to 1.5 turns past first contact which is pretty tight. Now with my finger I can only open the secondary valve about half way.

I went on a couple of test runs last night and I got past the bog!! I shifted around 5500 RPM and I was surprised as the car without the bog would really jump forward when the tranny shifted. It's never done that before, it shifted solidly but never jumped...it kind of caught me off gaurd.

My O2 sensor showed that the AFR at WOT was between 14.2:1 and 14.5:1. That seems a little lean to me as I thought that the best AFR for power was about 13:1. As I wound out second gear the AFR got as lean as 16:1, but didn't bog.

I think that the primary jets have to be a little bigger to add more fuel and once I change the jets I think that I will be able to loosen the secondary valve some as I think that the 383 can probably use a little more CFM.


Does 14.2:1 - 14.5:1 at WOT seem a little lean to you guys?

YES! 14-16:1 AF ratio is too lean IMO. I have had best luck with right about 13:1.

An overly rich carb can cause a hesitation too . . .

Thanks Eric!

I will change the primary jets and test it tonight and let you guys know(as I just know you are all on the edge of your seats waiting to see if I can fix my 2-3 bog!).

I tried a couple a bigger jets and found that 76 primary jets will feed the 383 pretty well. I was able to loosen the secondary valve and not have a bog!

The problem is that the car is not really drivable with those jets. At cruise it is running very rich, around 13.5:1. I'm sure that it would foul the plugs in a short time running that rich at cruise and I definitely wouldn't be able to drive it everyday since it would burn too much fuel.

Nobody makes large enough primary metering rods to lean the cruise AFR out enough with jets that big. The biggest primary metering rods are .050 which will give me the right cruise AFR with 72 jets but are too small for WOT.

I seem to have a dilemma. I can't run the big jets to feed the 383 at WOT everyday and I can't run the small jets to have good economy because I bog at WOT.

I wonder if anyone can custom make primary metering rods......

I would go ahead and try running your AF at 13.5:1 cruise --- that's fine IMO. My Demon runs good right about there, no plug fouling. Yes it might use a little more gas, but you might get away with a more timing too. If you have an adjustable vac advance can you might try running about 15* in the can for about 50* total at cruise (not WOT). 34* at WOT will probably work fine too.

Just my opinion.