Secondaries open all the way now that I bent the pulloff rod longer. I really think timing is set correctly now. Runs the best and set according to power timing instructions. I suppose its possible that float could be adjusted but it was about 1/4 in down as suggested. Fuel pump could also be weak. I'll test drive first to see if my mods have improved detonation. Thanks
Just took the car out and filled w 93 octane. Ur5 plugs installed. Got it up to temp and a few wot. Still a bit of detonation below 3000rpm and not as much power as it should have in my opinion. New AX secondary metering rods were installed over a year ago when carb was modified per Cliff Ruggles instructions.....Maybe its still too lean? Detonation is instantaneous with wot so would it have time to lose fuel pressure and/or fuel supply in bowl that quickly? I know that it would be nice to have an af meter. Maybe a fuel pressure gauge? I'm running stock mechanical pump. I can read the plugs but they probably won't tell the whole story. Frustrated a bit. Thoughts?
Never seen that before. What are you trying to accomplish aside from the rods sitting higher out of the jets?
I’m not convinced of that. Low fuel pressure will only result in the bowl not filling faster than it’s being emptied…..noses over, surges, stalls. Same with fuel filter. Fuel pressure in a carb application only fills the carb, the fuel is drawn into the engine from vacuum. You can run 2lbs fuel pressure fine, as long as you drive easy. Try WOT forget it. Fuel injection is a different story, the injectors rely on a minimum pressure to properly atomize and inject the fuel, the injectors have to PUSH the fuel thru, therefore, adequate pressure is nesessary.
Mark, I should have said at full throttle. On my old Holley's, too high a float level would richen idle and too low would lean out at full throttle. I know Holley's like 5-7 psi fuel pressure. Don't know about Quadrajets.
I've watched this thread off and on but don't remember all the earlier stuff so this is just commenting on your most recent attempt. If detonation is instantaneous, it isn't the secondaries. They are vacuum operated and should provide fuel/air as the engine can draw it in. Is the accelerator pump arm set to the inner hole? That will put more fuel in before the secondaries open up, but I still don't think that's the root cause. If 93 octane doesn't keep it from pinging, you have no choice but to retard it a few degrees until it stops.
QJet fuel pressure: Article Info - Carburetor Parts & Rebuild Kits - Carburetor Parts Superstore! (quadrajetparts.com)
Ap arm set to inner hole yes.... I could probably try stiffer centrifugal advance springs. Idk. Retarding it stops pings but response and performance, especially off the line, suffers. If i add 20% racing gas it solves detonation problem and still keeps the great throttle response.
"You need to verify with a fuel pressure gauge that blocking the return line was beneficial. If the gauge shows an increase in pressure at WOT, you should consider installing a return line restrictor." Never thought of that!
Are you sure the carb linkage is going full throttle and throttle plates are going wide open? I'd still retard cam 4 degrees, and then you will have room to advance ignition timing. I think your compression ratio is too high for that cam.
Yes I am sure secondary plates and flaps open fully. I pinched off return line this afternoon and warmed up the motor to test a 1/4 mile on the hyway. Pinged a bit more at all rpms maybe because racing gas was fully purged and motor was slightly warmer. So 284-88h cam and about 9.5 compression, stage one valves with my 3.08 limited slip and I have to use some racing gas to get to low 15s.
It seems like if I retard the timing my et would be worse than adding racing gas where it is but I'm willing to try it.
I talked a couple days ago to Mike at TA where the cam was purchased and he didn't think the cam should have to be retarded and should be great w 9.5 compression and 94 octane. He suggested my mid 15 sec ets were way too slow for my setup. But I do believe the cam could be advanced 2* installed as is according to my degreeing check. Thanks for your recommendations.
I think Mike is mistaken. 9.5 would work fine. The flat top 3.0 V6 pistons give about 10.25. Plus, you are .o30 over and back in the thread I see pictures of the top of block looking pretty clean/surfaced and the heads look to be surfaced too. I believe you are more like 10.5 and around 8 dynamic and that just doesn't work with iron heads and pump gas.
Playing with the compression calculator. .13 more for .030 over flat top pistons, .24 more for .010 off block or heads. So, .61 more compression. Or double that if .020 off block and heads.
Okay.....Initial is at 11 right now and total at 34. Is there a possibility that retarding ignition and stiffer springs may improve performance?
