Tips for a better tune... - Team Camaro Tech
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post #1 of 5 (permalink) Old Mar 22nd, 10, 10:16 PM Thread Starter
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Dave
 
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Location: Vacaville CA
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Tips for a better tune...

After reading the thread about crankcase pressure I started think about a better tune on my ZZ383.

Totally stock ZZ383 long block with the exception of 1.6 rockers
Holley 4150 650cfm vac. secondary carb
Edelbrock RPM Air-Gap vortec manifold

With current tune I have 17 very steady inches of vac. @ 900 rpm idle
carb has stock 6.5 power valve and I'm using the "736" pcv valve. I have the cowl hood air cleaner with the hose going to the rear of the right side valve cover. the PCV valve is in the front of the left valve cover over the baffle with the hose going around to the right side of the carb to the base plate on the carb (Full manifold vac.)

jets are 68 pri. with a 31 squiter.

timing is 31 total all in by 3200 rpm

Do you think I would benefit by changing the power valve and PCV valve to something different?

The motor runs well all year round with the choke disabled. But is lazy some times just off idle. It does run better with more initail advance but that really kills the mileage on the highway.

Any other suggestions?

Dave

Known to run with scissors....
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1969 Camaro Z/28 "clone", GMPP ZZ383, Autogear M22W, Moser 12bolt w/TruTrac 3:73.
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post #2 of 5 (permalink) Old Mar 22nd, 10, 10:46 PM
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Steps
 
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Re: Tips for a better tune...

Quote:
With current tune I have 17 very steady inches of vac. @ 900 rpm idle
Forget that...thats just how it sounds and idles...change that around to do what you want it to...

It is what happens when under load and at cruise doing 140 mph across the Nulabour.
ONLY CHANGE 1 THING AT A TIME
1st get the timing in the ball park put a couple springs in so the advance comes off around the 1100/1200 mark
What is the intail without and with VA connected?
Quote:
timing is 31 total all in by 3200 rpm
if you have a nice stable idle now, dont mess with the intial BUT u do need more total cent advance (no VA connected) in the ball park of 36 degs @ around 3200.
Hopefully you can increase the range of the cent and not just have to rely on upping the intial.

And a VA that works around the 12 to 17"
And with 6 to 10 degs in it.

If you just want to have a quick play....
VA disconected Take the rpms up till the cent is all the way in (3200) the set the timing to 36 deg...re connect the VA and take it for a blat.

My Spelling is not incorrect...it is creative

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post #3 of 5 (permalink) Old Mar 23rd, 10, 11:44 AM
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Al
 
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Re: Tips for a better tune...

Fred - what kind of dist do you have? Do you even have vac advance? The General recommends 32 degrees total with those heads, although I'm not sure a degree or two more would hurt.

My motor is very similar to yours, a bit more cam, and a bit less idle vac. I run mine @ 17 initial. Mechanical adds 15, all in @ 3,000. Vac advance adds 10 degrees fully deployed @ 10 inches of vac. Seems to run well.


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post #4 of 5 (permalink) Old Mar 23rd, 10, 09:51 PM Thread Starter
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Dave
 
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Re: Tips for a better tune...

I'm using the MSD 8360. It has a vac, advance but it is not adjustable. You can play with the mech. adv. quite a bit with springs and bushings. I had the motor setup with 36 total advance with the initial right @ 15 deg. On a 40 mile cruise I burned 8 gallons of gas. I backed off the initial to 12 degrees and almost doubled my mileage on the next trip. I'm just wondering. Since I have such high vac @ idle if a change to the power valve or PCV valve would be beneficial. When I backed off on the initial timing I lost some throttle response just off idle that I would like to get back.

Dave

Known to run with scissors....
__________
1969 Camaro Z/28 "clone", GMPP ZZ383, Autogear M22W, Moser 12bolt w/TruTrac 3:73.
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post #5 of 5 (permalink) Old Mar 23rd, 10, 10:56 PM
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Re: Tips for a better tune...

Quote:
On a 40 mile cruise I burned 8 gallons of gas. I backed off the initial to 12 degrees and almost doubled my mileage on the next trip
That signifies the engine is running rich...leaner mixtures require more advance...hence a VA.

Quote:
Since I have such high vac @ idle if a change to the power valve or PCV valve would be beneficial
17" is not considered high for a stock to slightly mild cam and itial advance over 10 degs.

Quote:
When I backed off on the initial timing I lost some throttle response just off idle that I would like to get back.
That will come back with lighter springs

I would be looking at 66 jets.

My Spelling is not incorrect...it is creative

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