Maybe we've discussed this before but...., what adjustment order is best when dyno tuning? I'll be doing a little chassis dyno on Sunday and want to make it productive as possible. I am running a John Osbourne tuned 800 cfm Q-Jet. Currently set up with 46B rods & .076" jets primary and .052" secondary rods. I have the complete rod/jet kit for tuning. Timing is set at ~35 max. degrees (initial is about 28 or so with no vacuum advance connected). Other details: 462 cu-in 413 cammed SP-1 BBB. Compression is 10.3:1. Little weary about running flat out to 6000 rpm's (typical shift point) in high gear. I do have the thicker rocker shafts... I'm thinking timing is the first adjustment after the initial pulls then maybe secondary rods?
My current set-up on the secondary side of the Q-Jet is: hanger G, actual measurment is .547", secondary rod is .051" small diameter I checked my carb. tuning kit to see what I've got. I have hangers that range from .544" up to .627" (7 lengths) and secondary rods (.030", .033", .034", .040", .041", .042", .043", .056", .061"). Leaning towards leaving the jets as is...don't want to have too many variables.
I don't know if your dyno is like ours in omaha, but when I went the operator made me jet up. He said he doesn't ever want anybody hurting there motor at the dyno going too lean. The first pull I was on the lean side and he had me shut down. I fattened it up and made a second pull. Then we messed with the timing. The third change was switching from a 850 holley to a 750 just to see if it would increase at all. Our dyno guy thinks everybody has too much of a carb on there motors, but like I thought the car lost horsepower. So I stick with the bigger one.
Well Rob, I did make it to the dyno but...the car had to stay on the trailer. On the way, following my friend with trailer and GS, I broke down, we had to load mine on the trailer and he had to drive his car (with had DOT slicks). Today I found the problem after about 2 minutes of searching under the hood. Anybody got a good spare RH (exhaust in this case) stock rocker for my `73 455 motor? o No: Man it really spit through the carb. when I tried to restart it, no place for the exhaust to go when the valve does not open. Easy fix with the right part :TU: .
Hey Craig, I have an extra rocker set I would give to you if you pay for shipping. To bad you had trouble. I know I've had my share of problems like that. But thats what I get for fixing old stuff with used parts all the time. I guess I'm too much of a tight waude?
Thanks for the offer Rob :TU: , but I've already ordered a rocker arm from YearOne. I don't think theyve been selling them long. It only cost me $10.30, and should arrive tomorrow. I should have it fixed Sat. morning. I hope the adjustable pushrod is o.k....
Gee Makes me glad I forked out the coin for the rollers, even though I don't plan on running it too hard. Besides that, the adjustment is a snap. I don't want anything marginal in the engine.
Craig are those the aluminum rockers, i have alway ran stock steel rockers and adjustable pushrods, and never have had a problem problem.
No these are stock '73 rockers. I have broken one stock rocker shaft on the passenger side, typical break at the end bolt (about 1800 miles ago), and now a stock rocker arm on the passenger side. I am turning this thing to almost 6K now, maybe that has something to do with it... I agree about the rollers Dan, but that's a lot of money for new ones. I'd like to run into a set of good used rollers for ~$200. With rollers you don't need adjustable pushrods right o No: .
i run the similar 113A cam and shift at 6000 rpm, and have reved to 6500 a few times, i would think your pushrods are to tight, or valve springs are weak???, there are alot of cars running much bigger cams with the stock rockers and shafts. and no you dont need adjustable pushrods with rollers, rollers are great if you have the $$$ and or you need the strenth, but you should not be having problems with the 413 cam and stock steel rockers,
Well I got my new replacement rocker arm today and decided to dig in. After removing the rocker shaft I found that not only was the #3 exhaust rocker arm broken but I also bent the #3 intake (adjustable) pushrod. Here's the sequence of events that resulted in what you see below. 1. Traveling down the interstate at a constant ~68 mph turning ~3400 rpm's (3.42 gear). 2. For no aparent reason I hear a medium to high frequency ticking start, it's not very loud. 3. Look down at the gauges, oil is fine and temperature is fine. 4. Almost at the same time let off the gas (after ~3 seconds of ticking). 5. Ticking gets almost too quiet to hear at speed. 6. Ease back on the gas and ticking matches rpm's. 7. Let off gas again and start to coast. 8. While slowing down merge to the right lane while flashing friend ahead with headlights. 9. I get stopped and try make a call on the cell phone, I then try to re-start the motor. 10. Does not want to restart, motor turns over slowly. But I can't hear what's going on due to traffic going by (I'm stopped under an overpass). 11. About ten minutes later when friend arrives try to restart motor. 12. Motor does try to start but spits back throught the carb. Does not sound good. We then loaded the car on a trailer and carried it home. The picture shows the result. I'm thinking first the #3 exhaust rocker broke and the valve was not opening but the intake was sucking in air. But after ignition of gas (during restart attempt) the air had no where to go. Is caused the intake pushrod to bend under pressure. Makes sense?... want to get other opinions. In the picture the rocker on the right is the broken #3 exhaust and the pushrod to the left is the #3 intake. I placed the #3 exhaust rocker arm "puzzle" back together for the picture. The #3 spark plug is positioned above and looks more black than #1 or others. I checked the other pushrods and they are fine (drivers side only). Are there other things to check or be concerned about before replacing the #3 intake pushrod and #3 exhaust rocker arm?
if it wasnt the pushrod itself coming loose, then jumping around and then breaking, then all i can think of is maybe you have a bad lifter??? as for the starting, sounds to me like you run headers with the stock starter?? ihad the same problems, then went to a mini starter, it was the best money i spent under the hood.
The #3 intake pushrod was still in the cup of both the rocker and lifter, but the #3 exhaust pushrod of course was no longer sitting where it should be. It did not slide effortlessly out of the head, it was in ~somewhat of a bind (but was not bent). If I'm guessing if the #3 exhaust lifter and cam lobe is o.k. then replacing the exhaust rocker and intake pushrod things will be cool. I need to look again for another adjustable pushrod, I swear I had one
Well, it looks like I'm in the clear. Made two test drives today (after replacing the exhaust rocker, intake pushrod and a few retainers), and everything seems to be back to normal.
New Rockers Those rockers are old and tired. I would recommend the HD stock repacement rockers for the rpm you are turning. If they messed up once, it can happen again. Fatigue and age with your cam is asking for trouble for something you drive on the street alot. They will pay for themselves if they keep you from having to ever get picked up off the side of the road. o No:
Now that we have discussed broken rocker arms, cork-screwed push rods, stock steel vs roller aluminum rockers and other topics, I am still curious: What IS the recommended sequence for making adjustments to tune/time an engine while on a chassis dynameter? Is it the same sequence as when doing a basic tune-up? I don't think I am hi-jacking this thread -- in fact, I think this is where it all started . . . Craig PS -- on my 71 Stage 1, I lost three stock rocker arms in less than a month of a re-build. I guess they weren't designed to withstand the shock being transmitted by a solid lifter cam. I had to pry out one push rod with a 10" vise grips -- the cork screw was three dimensional and quite an impressive site when extracted. (That was in 1979; a set of K-B aluminum rockers/HD shafts with K-B 3/8" adjustable push rod solved all my problems.)
Yes, now that I've had to take the long road, lets get back to dyno tuning. Here is a helpful link I found. http://community-2.webtv.net/MATTGRU/Dynotuningisagreat/index.html My planned tuning was optimize total timing first. I already know my advance is all in by 1600 rpm. I was planning to try settings from 30 to maybe 38 total timing. My plugs are Autolite 25's and they are gapped to 0.054" since I have the 6AL ignition box. Had not planned on changing this. I was planning to see what A/F ratio I had. Notice in the picture there are two bungs on the #1 and #3 primary header pipes, with plugs. This is where I planned to make the connection (A/F, oxygen). Since I'm running a Q-Jet I took several sizes of secondary metering rods and a few hangers. These are the only components I had planned on switching out as needed. I had already checked and made sure that the throttle was wide open when the gas pedel was on the floor. I also checked my rear tire pressure to make sure they were right and equal side to side (30 psi). A lower pressure would create more drag. I had also set my kick-down so that it only kicks down at lower speeds, this way I could get good lower rpm readings while in 3rd gear (1:1). I also checked my fuel pressure at idle, I increased it to 7psi. I also adjusted my oil pressure so I get ~70psi at 6000rpm's. Things to keep an eye on during or before each run: -fuel pressure at upper rpm's -engine temperature -oil pressure -after your first pull you can limit the upper rpm's based on when power falls off. I feel I'm loosing ~some lower rpm power. I'm specifically interested in what could be done to address this. Let's hear from those more knowledgable than me on the subject... Heck, I've never even tuned a car on the dyno before :Comp: .
Fan... That Q-Jet is costing you a few HP. But you got the right idea working on the A/F ratio with the secondary rods. Are you running an clutch fan?? You might be surprised at how much HP a fan sucks. If you are you can see if they have a good blower fan so you can remove the fan off the motor and run without it. Swap to a Black magic or something later. Too bad you don't have an HP Carb or one with adjustable air bleeds so you can adjust the fuel curve. I would set the timing around 34 and concentrate on the carb first. The timing requirements can change if its lean or rich on the carb. Try a 1" spacer on the carb if you don't have one yet. Even if it doesn't fit now, you could work on that later.
