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Unread 04-22-2013, 08:14 PM   #1
firemanjim7
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Lost top end speed

Just completed the CRT hei install and instantly noticed no more miss at idle and low end power smooth and increased. Problem is now it will barely hit 70. I increased the timing from 8 to 12 it helped alittle 72 but that's floored flat smooth highway. Before the change out I could cruise at 75 with pedal left. Any thoughts?

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Unread 04-23-2013, 02:10 AM   #2
John Strenk
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I would check the advance curve of the distributor you just installed. Maybe it needs soe tweeking.
Did you change plugs at the same time? What type did you use?
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Unread 04-23-2013, 04:28 AM   #3
86cj74.2L
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Quote:
Originally Posted by firemanjim7
Just completed the CRT hei install and instantly noticed no more miss at idle and low end power smooth and increased. Problem is now it will barely hit 70. I increased the timing from 8 to 12 it helped alittle 72 but that's floored flat smooth highway. Before the change out I could cruise at 75 with pedal left. Any thoughts?

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Do you hear detonation.
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Unread 04-23-2013, 04:50 AM   #4
Matt1981CJ7
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What dizzy was in there before?

Matt
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Unread 04-23-2013, 07:12 AM   #5
firemanjim7
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Quote:
Originally Posted by John Strenk
I would check the advance curve of the distributor you just installed. Maybe it needs soe tweeking.
Did you change plugs at the same time? What type did you use?
Yes changed plugs. Champion copper

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Unread 04-23-2013, 07:14 AM   #6
firemanjim7
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Quote:
Originally Posted by Matt1981CJ7
What dizzy was in there before?

Matt
Just a tad of detonation when I moved it to 12. The previous dizzy was stock.

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Unread 04-23-2013, 07:54 AM   #7
Matt1981CJ7
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I'm with John on this one. Check the total advance curve (centrifugal + initial) of the hei.

If you kept the wiring for the Duraspark, you could also re-install it, then compare the curves. If timing is the issue, the top-end of the curves will likely tell the story.

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Unread 04-23-2013, 08:09 AM   #8
86cj74.2L
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If its a standard HEI curve and not altered for a 258 they have 20 total advance and it comes in quicker then it should
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Unread 04-23-2013, 09:08 AM   #9
swatson454
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What rpm is it knocking at? Can you be pretty descriptive of when it occurs?


Shawn
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Unread 04-23-2013, 09:36 AM   #10
firemanjim7
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Quote:
Originally Posted by swatson454
What rpm is it knocking at? Can you be pretty descriptive of when it occurs?

Shawn
The knock is only under a hard load not any specific rpm. As for the curve set up I'm not sure it was ordered from CRT for the 258. I talked to mechanic and he seems to think I might need a vacuume delay valve thinking it is loosing vacuum too quickly at WOT and loosing advance.

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Unread 04-23-2013, 09:40 AM   #11
82JeepCJ7
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I had the same issue with my HEI. I adjusted the vacuum advance curve (allen wrench goes in where the vacuum line attaches on the advance). Until I adjusted the curve, I could get good idle and regular running, but when advancing hard, it would ping.
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Unread 04-23-2013, 09:46 AM   #12
swatson454
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Quote:
Originally Posted by firemanjim7 View Post
The knock is only under a hard load not any specific rpm. As for the curve set up I'm not sure it was ordered from CRT for the 258. I talked to mechanic and he seems to think I might need a vacuume delay valve thinking it is loosing vacuum too quickly at WOT and loosing advance.

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You really need to remove and plug the vacuum advance and accelerate hard up to redline. This should isolate your problem: either vacuum advance issue (if the knocking goes away) or the centrifugal curve/initial advance setting.

It's a crapshoot without knowing exactly where your problem lies. You might get lucky and make it quit knocking but you won't know if you just slapped a band aid on it; in which case, performance everywhere else could suffer.


Shawn

Edit: if you only got a touch of detonation when you went to 12*, I don't suspect you have a vacuum advance issue. It might be happy just backing off the initial advance 2*.
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Unread 04-23-2013, 09:50 AM   #13
firemanjim7
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Quote:
Originally Posted by 82JeepCJ7
I had the same issue with my HEI. I adjusted the vacuum advance curve (allen wrench goes in where the vacuum line attaches on the advance). Until I adjusted the curve, I could get good idle and regular running, but when advancing hard, it would ping.
Which way did you adjust in or out ? What did your initial timing end up being?

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Unread 04-23-2013, 09:52 AM   #14
firemanjim7
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Quote:
Originally Posted by swatson454

You really need to remove and plug the vacuum advance and accelerate hard up to redline. This should isolate your problem: either vacuum advance issue or the centrifugal curve/initial advance setting.

It's a crapshoot without knowing exactly where your problem lies. You might get lucky and make it quit knocking but you won't know if you just slapped a band aid on it; in which case, performance everywhere else could suffer.

Shawn
I'm pretty sure my knocking is coming from too much initial advance.

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Unread 04-23-2013, 09:56 AM   #15
swatson454
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Sorry dude, I snuck an edit in there
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