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| Lost performance after HEI swap https://www.slantsix.org/forum/viewtopic.php?t=63545 |
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| Author: | THOR [ Tue Apr 23, 2019 8:54 pm ] |
| Post subject: | Lost performance after HEI swap |
I'm not sure what the issue is here. Valiant was running great, decided to upgrade ignition system using the part numbers in the how-to. 1973 225, uncut head. NGK ZFR5N plugs at .045. 1973 factory EI distributor. Fires up perfect, revs excellent with fantastic throttle response. Definitely have a loss of performance during acceleration. Timing at 15BTDC, and surprisingly, the damper hasn't slipped. Wondering if the timing curve is the issue, just looking for thoughts. ~THOR~ |
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| Author: | Dart270 [ Wed Apr 24, 2019 4:32 am ] |
| Post subject: | Re: Lost performance after HEI swap |
Need to check timing at higher RPM and w/o vac adv connected. My guess is you have 35-40 deg at full mech advance, which will kill higher RPM power. Lou |
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| Author: | Reed [ Wed Apr 24, 2019 7:14 am ] |
| Post subject: | Re: Lost performance after HEI swap |
Quote: Need to check timing at higher RPM and w/o vac adv connected. My guess is you have 35-40 deg at full mech advance, which will kill higher RPM power.
Agreed. I couldn't tell from your original post if you changed distributors when you did the swap. If so, you could have a fault in the vacuum or mechanical advance systems, or the advance curve could be different. If you are using a stock factory distributor you should open it up, clean it, and regrease everything. Even if it is a NOS unit the factory grease can dry out and cause the advance weights to stick. You can also try swapping the weights, springs, and vacuum advance pod from the old distributor (if you change distributors).
Lou |
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| Author: | Joshie225 [ Wed Apr 24, 2019 8:49 am ] |
| Post subject: | Re: Lost performance after HEI swap |
That 1973 distributor was meant to be initially timed at TDC, or close to it. You have far too much total timing. You will have to weld up the advance slots to limit total timing to about 30-32°. I made this exact mistake with my '66 Dart over 20 years ago. With low dynamic compression it never would ping, but the negative torque from too early ignition killed power. |
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| Author: | THOR [ Wed Apr 24, 2019 10:24 am ] |
| Post subject: | Re: Lost performance after HEI swap |
Quote: Need to check timing at higher RPM and w/o vac adv connected. My guess is you have 35-40 deg at full mech advance, which will kill higher RPM power.
This makes sense. I will state that I have lost power over what seems to be the entire range, so I'll be checking the curve and plotting it later today.Lou Quote: Agreed. I couldn't tell from your original post if you changed distributors when you did the swap. If so, you could have a fault in the vacuum or mechanical advance systems, or the advance curve could be different. If you are using a stock factory distributor you should open it up, clean it, and regrease everything. Even if it is a NOS unit the factory grease can dry out and cause the advance weights to stick. You can also try swapping the weights, springs, and vacuum advance pod from the old distributor (if you change distributors).
That is one thing I failed to mention! I did change from a points distributor that had a Pertronix kit installed to the '73 vintage stock unit. I do know the vacuum advance works, can't recall what the number on the can is off the top of my head. Should be able to verify whether weights are moving well when I slap the timing light on it.Quote: That 1973 distributor was meant to be initially timed at TDC, or close to it. You have far too much total timing. You will have to weld up the advance slots to limit total timing to about 30-32°. I made this exact mistake with my '66 Dart over 20 years ago. With low dynamic compression it never would ping, but the negative torque from too early ignition killed power.
This also makes sense due the what I presume would be a huge difference in the curve. I also have low dynamic compression, and on 87 octane, it won't ping. Funnily enough, it would ping with the old system (Pertronix, ballast and stock coil). Thanks for the input! ~THOR~ |
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