EFI head on carbed engine
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Freshman User
Joined: Apr 2011
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How do I recurve the distributor? What do I need to buy?
Postmaster
Joined: Mar 2005
Posts: 2,949
Likes: 6
From: Earth
You'll need:
a) a dial-back timing light - the stock timing marks don't let you read what's happening at RPM without one.
b) a set of distributor springs - Moroso sells a kit iirc.
c) patience - you'll be pulling the distributor, making changes, reinstalling, and testing a few times.
You're taking the distributor apart to swap the advance springs and change the rate at which the timing mechanically advances. It's not all that complicated, but does require some trial and error. Search around, there are some good write-ups on how to do it.
Option B is to find a shop that has a distributor testing machine and have them do it for you.
a) a dial-back timing light - the stock timing marks don't let you read what's happening at RPM without one.
b) a set of distributor springs - Moroso sells a kit iirc.
c) patience - you'll be pulling the distributor, making changes, reinstalling, and testing a few times.
You're taking the distributor apart to swap the advance springs and change the rate at which the timing mechanically advances. It's not all that complicated, but does require some trial and error. Search around, there are some good write-ups on how to do it.
Option B is to find a shop that has a distributor testing machine and have them do it for you.
Thread Starter
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Freshman User
Joined: Apr 2011
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Kit? Is there something I can get from auto parts store? Do I ask for a recurve kit?
As it stands right now my engine is stock except I have:
-offy c
-2 to 4 barrel adapter
-autolite 2100 w/ 1.08 venturi and #49 jets
-efi manifolds
-walker y pipe
-2.5 to 2.25 adapter on y pipe
-2.25 exhaust pipe
-don't know what muffler but its 2.25 size
-no emissions equiptment
-DS2 dizzy (from junk yard)
-DS2 coil (from junk yard)
-DS2 ignition module (from junk yard)
-19 in Hg of steadyish vacuum
installed.
Would my next priority be? The dizzy recurve?
Until I do recurve the dizzy, can I just stick allen wrench into vacuum advance on the dizzy, and back out the screw as much as possible?
As it stands right now my engine is stock except I have:
-offy c
-2 to 4 barrel adapter
-autolite 2100 w/ 1.08 venturi and #49 jets
-efi manifolds
-walker y pipe
-2.5 to 2.25 adapter on y pipe
-2.25 exhaust pipe
-don't know what muffler but its 2.25 size
-no emissions equiptment
-DS2 dizzy (from junk yard)
-DS2 coil (from junk yard)
-DS2 ignition module (from junk yard)
-19 in Hg of steadyish vacuum
installed.
Would my next priority be? The dizzy recurve?
Until I do recurve the dizzy, can I just stick allen wrench into vacuum advance on the dizzy, and back out the screw as much as possible?
Postmaster
Joined: Dec 2006
Posts: 3,603
Likes: 10
From: Spokane, WA
"...can I just stick allen wrench into vacuum advance on the dizzy, and back out the screw as much as possible?"
What??? Any and/or all adjustments should be only in small steps with trial runs in between to determine the response.
What??? Any and/or all adjustments should be only in small steps with trial runs in between to determine the response.
Lead Driver
Joined: Dec 2000
Posts: 6,289
Likes: 47
From: South central, Minnesota
I've got to know. Now, I would tell anyone to get their head(s) and block checked for cracks before starting in on any machine work, but every time someone mentions "EFI head" folks start chiming in on how they're more prone to crack that carb heads.
Is this just conventional wisdom or has someone actually compiled data on head cracking in 300s? Where are they more prone to crack? And why? They're made by the same company in the same factory as the carbed heads before them, right? So what is it about EFI heads that makes them more likely to crack? The two extra bolt holes tapped for the exhaust manifolds? My carbed '86 has the EFI manifold bolt pattern for the intake/exhaust manifolds. Should I be worried about cracking?
I'm not saying EFI heads aren't more likely to be cracked, but where does this particular factoid come from?
Is this just conventional wisdom or has someone actually compiled data on head cracking in 300s? Where are they more prone to crack? And why? They're made by the same company in the same factory as the carbed heads before them, right? So what is it about EFI heads that makes them more likely to crack? The two extra bolt holes tapped for the exhaust manifolds? My carbed '86 has the EFI manifold bolt pattern for the intake/exhaust manifolds. Should I be worried about cracking?
I'm not saying EFI heads aren't more likely to be cracked, but where does this particular factoid come from?
I've personally had 3 EFI heads that were cracked. I don't think I've ever had a 240 or carbed 300 head that was cracked. Warped yes, cracked no.
I'm not saying they are more proned to cracking. But it sure seems like there are a lot more cracked EFI heads then carbed heads. I wouldn't worry about the head unless you develop an issue. But definitely have them magnafluxed before you sink a bunch of time or money into one.
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Freshman User
Joined: Apr 2011
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From what I have been reading, lighter spring is put in during recurve. So, using deductive logic, I wanted to know if reducing spring tension as much as possible on un-curved dizzy would net me any gains.
Judging from your response it is ludacris to think that. I don't really know what I'm doing. ( It was just a guess)
Is recurving the dizzy the next step to take? If so, what kit do I need?
Judging from your response it is ludacris to think that. I don't really know what I'm doing. ( It was just a guess)
Is recurving the dizzy the next step to take? If so, what kit do I need?
Senior User
Joined: Mar 2010
Posts: 337
Likes: 0
This is why I liked the DUI dizzy, just plug and play with ya setup on there site and they recurve it to fit your setup and then mark it so if ya upgrade more or even change moters they can recurve again no prob like...... just an option like
and is a 20+ bolt on HP gain
many do recurve there own tho on the cheap with a kit and a bit of time ect.
and is a 20+ bolt on HP gainmany do recurve there own tho on the cheap with a kit and a bit of time ect.
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Postmaster
Joined: Mar 2005
Posts: 2,949
Likes: 6
From: Earth
From what I have been reading, lighter spring is put in during recurve. So, using deductive logic, I wanted to know if reducing spring tension as much as possible on un-curved dizzy would net me any gains.
Judging from your response it is ludacris to think that. I don't really know what I'm doing. ( It was just a guess)
Is recurving the dizzy the next step to take? If so, what kit do I need?
Judging from your response it is ludacris to think that. I don't really know what I'm doing. ( It was just a guess)
Is recurving the dizzy the next step to take? If so, what kit do I need?
You need the right amount of spring tension so distributor doesn't advance at idle but does start advancing as soon as you give it gas.
Get a dial-back timing light and tach. Disconnect the vacuum advance, set your base timing, then watch and record how much it advances in 250 or 500 rpm increments until it stops advancing. Then you change springs to adjust the curve for your engine.
Check this link: Duraspark_distributor_recurve_instructions_index
Lead Driver
Joined: Dec 2000
Posts: 6,289
Likes: 47
From: South central, Minnesota
It's been a few years since I had mine( my memory isn't the greatest ) . But I seem to remember mine were cracked in the valve seat/combustion chamber areas. I also seem to remember the # 5 cylinder was where they were cracked.
) . But I seem to remember mine were cracked in the valve seat/combustion chamber areas. I also seem to remember the # 5 cylinder was where they were cracked.
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