jnjdragracing Posted July 20, 2007 Share Posted July 20, 2007 Just out of the blue, you mentioned Vortec heads. I had an engine once with a similar issue, I was floating the valve springs. Are you running a stock cam? If not and if you did not replace valve springs to match the cam, this could be your issue under a load. Just an idea........ Usually if igniton is an issue it will breakdown, pop, skip under a load. The only rev limiting that I have seen would be in a computr controlled ignition system. John Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted July 20, 2007 Share Posted July 20, 2007 You do NOT need a 10ga wire to the "batt" terminal on the HEI. I run a 10ga wire on my alternator. A 16ga wire (in good condition) is plenty for an HEI power wire. I've turned 6500rpm with stock junkyard HEIs without problem.....sure, the voltage may drop off slightly at higher RPM, but not enough to limit your RPMs to 4500. Something else is going on. Have you looked at the plugs yet? Its a little harder with an automatic, but if you have a stick....run it WOT in 3rd until it stops accelerating (4500rpm) and keeping your foot flat on the floor, kill the ignition and stand on the clutch. When the engine stops spinning, you can take your foot of the throttle and hit the brakes. Pull a few plugs. This will tell you what ballpark the mixture was in at 4500 RPM. Whats your static timing? whats your total timing? Where do you have the vacuum advance hooked up...ported or manifold vacuum? How did you verify that the secondaries were operating properly? What cam? Any MSD or other wizbang ignition components? Quote Link to comment Share on other sites More sharing options...
Nealio240z Posted August 3, 2007 Author Share Posted August 3, 2007 I forgot to mention that at an idle or any constant rpm, the timing mark jumps... ( using a timing light ) It advances or retards irratically by about 3 degrees... Does that come into play? Will it affect my proformance??? Quote Link to comment Share on other sites More sharing options...
Teekass Posted August 4, 2007 Share Posted August 4, 2007 I forgot to mention that at an idle or any constant rpm, the timing mark jumps... ( using a timing light ) It advances or retards irratically by about 3 degrees... Does that come into play? Will it affect my proformance??? 3 degrees of timing change shouldn't affect your engine as much as you're describing. How much advace are you running at idle, and total? Have you tried disconnecting the vacuum advance, rechecking the timing, then take it for a run without the vacuum advance hooked up? Maybe the vacuum advance is doing crazy things when you put a load on the engine. Quote Link to comment Share on other sites More sharing options...
Nealio240z Posted August 5, 2007 Author Share Posted August 5, 2007 Im running a mild cam that pulls from 1600rpm to 5400rpm... It was doing this before I cammed it... As far as valve springs goes they are stock, but it will rev to 6000 rpm in neutral with no load. when it hits 4500rpm it falls flat on its face, (like I suddenly picked up 2000 pounds) if I hold the pedal down at this rpm it will slowly creep past that rpm barrier. It doesn't pop or miss at 4500rpm but it stops pulling.. timing is set at about 12 degrees or so. The vacuum advance holds suction but has no adjustment provision. It is hooked to a full vacuum port on the carb... The plugs are burning on one side only, clean on one side and brownish black on the other, (on the porcelain). secondaries are opening fully. You can feel the secondaries engage so i'm fairly positive they are working as intended. Q-Jet carb. Any additional suggestions? Quote Link to comment Share on other sites More sharing options...
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