Holley tuning help...close but still not dialed.
10-15-2012, 10:39 PM
#11
2nd Gear Member
Join Date: Jun 2012
Location: Littleton, Colorado
Posts: 247
I suspect your secondaries are coming in too soon. I suspect that because of having it go lean and stumble every time you apply power. Putting in bigger jets gave enough gas to counter that, but caused it to run rich. Your power valve may not be putting out enough gas. That can also cause a lean situation.
There is also an accelerator pump to help prevent stumble on acceleration. It is also tunable.
For tuning info see Holley's tuning guide:
A guide to how a Holley Carb works and how to tune it.
http://www.holley.com/data/TechServi...ech%20Info.pdf
According to Holley's A Guide on how to Select the right carburetor, you are running a carb that is about 20% too large. for your 302. Holley example--300ci high performance engine maximum 8000rpm =595cfm carburetor.
http://www.holley.com/data/TechServi...Carburetor.pdf
Because you have a Holley 670, it was shipped with a set up for a larger engine. Clearly, the out-of-the-box tune clearly wasn't perfect. Fortunately, Holleys are highly adjustable so I am sure you can get it to run well.
I am not expert on the causes of the bad behavior during coasting. In my experience, by the time I get the carburetor so it pulls smoothly idle-WOT, those problems mostly go away.
Stay on the timing issue. Until the carb and the spark are both set, you won't get the best performance. The above advisers are far better than I at distributor tuning. I find combined vacuum and mechanical timing give the smoothest acceleration.
Good luck!
There is also an accelerator pump to help prevent stumble on acceleration. It is also tunable.
For tuning info see Holley's tuning guide:
A guide to how a Holley Carb works and how to tune it.
http://www.holley.com/data/TechServi...ech%20Info.pdf
According to Holley's A Guide on how to Select the right carburetor, you are running a carb that is about 20% too large. for your 302. Holley example--300ci high performance engine maximum 8000rpm =595cfm carburetor.
http://www.holley.com/data/TechServi...Carburetor.pdf
Because you have a Holley 670, it was shipped with a set up for a larger engine. Clearly, the out-of-the-box tune clearly wasn't perfect. Fortunately, Holleys are highly adjustable so I am sure you can get it to run well.
I am not expert on the causes of the bad behavior during coasting. In my experience, by the time I get the carburetor so it pulls smoothly idle-WOT, those problems mostly go away.
Stay on the timing issue. Until the carb and the spark are both set, you won't get the best performance. The above advisers are far better than I at distributor tuning. I find combined vacuum and mechanical timing give the smoothest acceleration.
Good luck!
10-16-2012, 12:16 AM
#13
Moderator
Thread Starter
Join Date: Dec 2005
Location: Hills of California
Posts: 5,208
The whole holley avenger cfm thing is odd. It sounds too large but the ventures are actually the same size as a holley 600 a 570 avenger is equal to a 450 holley...although that might not mean it can't flow 670 cfm....
I think I'll have it dyno tuned and do my best to learn what I can from asking questions and watching money well spent I think...
Im still betting my timing has more to do with the issue than any other single factor alone.
I'll let you guys know what I learn.
-Gun
I think I'll have it dyno tuned and do my best to learn what I can from asking questions and watching money well spent I think...
Im still betting my timing has more to do with the issue than any other single factor alone.
I'll let you guys know what I learn.
-Gun
10-16-2012, 10:23 AM
#14
Join Date: Nov 2010
Location: Canada
Posts: 34
While I agree you most likely have a timing issue, what about your valve adjustment to address the popping issue in the exhaust? I assume the heads probably run roller rockers or at the very least adjustable rockers? I had a similar issue with the popping and it turned out I had a couple valves out of adjustment. Just a suggestion. Cheers
10-16-2012, 01:53 PM
#15
1st Gear Member
Join Date: Feb 2008
Posts: 57
Yes that is correct about the timing. (9+19 for 28).
In the past I always ran 12 initial then I changed only the heads and cam (roller cam) and I did put miles on the motor at 12 deg but found two issues.
1) during normal light accel the engine would momentarily lean if power wasn't smoothly and continuously applied. It was this way BEFORE the head changed too and I just tried to roll power on smooth to keep accelerator pump pissing. Reducing the timing to about 10 reduced this issue)
2) AFTER the head swap running 12 deg sometimes made it sound like there was a piece of loose metal in the muffler at idle (Which I thought was actually the case since they got banged around a bit during the swap) when I reduced the timing the sound became a single pop say around 10 deg adv. Reducing the timing further made that go away and produced a clean note like it was before the head swap so I left it there at 9 deg because I have not yet determined if: A) thats a normal sound for that style of combustion chamber and high(ish) lift cam. Or B) could produced damage to something overtime.
The intake runners are 170cc
the motor is 302
Thanks
-Gun
In the past I always ran 12 initial then I changed only the heads and cam (roller cam) and I did put miles on the motor at 12 deg but found two issues.
1) during normal light accel the engine would momentarily lean if power wasn't smoothly and continuously applied. It was this way BEFORE the head changed too and I just tried to roll power on smooth to keep accelerator pump pissing. Reducing the timing to about 10 reduced this issue)
2) AFTER the head swap running 12 deg sometimes made it sound like there was a piece of loose metal in the muffler at idle (Which I thought was actually the case since they got banged around a bit during the swap) when I reduced the timing the sound became a single pop say around 10 deg adv. Reducing the timing further made that go away and produced a clean note like it was before the head swap so I left it there at 9 deg because I have not yet determined if: A) thats a normal sound for that style of combustion chamber and high(ish) lift cam. Or B) could produced damage to something overtime.
The intake runners are 170cc
the motor is 302
Thanks
-Gun
10-16-2012, 05:48 PM
#16
2nd Gear Member
Join Date: Nov 2006
Location:
Posts: 356
Hi,
I'll just add, I too am running TFS heads, a 10.6 CR (static) with a dynamic of 9.8, or so. My initial is 15-16 with 23 mech. built-in for a total of 38-39. The benefit of aluminum heads is the ability to run more advance. I too, ran a similar advance when running my Windsor Jr. iron lungs. However, my dynamic Cr was 9.5, or so. I recognize, any given engine is different and will not benefit from similar tuning points from one owner or another. My suggestion was geared more toward allowing greater flexibility.
I do agree, if it can be determine, it's pre-ignition, something else is going on. Perhaps, as mentioned, the choice in a better dist. curve should be sought.
Happy Trails...
I'll just add, I too am running TFS heads, a 10.6 CR (static) with a dynamic of 9.8, or so. My initial is 15-16 with 23 mech. built-in for a total of 38-39. The benefit of aluminum heads is the ability to run more advance. I too, ran a similar advance when running my Windsor Jr. iron lungs. However, my dynamic Cr was 9.5, or so. I recognize, any given engine is different and will not benefit from similar tuning points from one owner or another. My suggestion was geared more toward allowing greater flexibility.
I do agree, if it can be determine, it's pre-ignition, something else is going on. Perhaps, as mentioned, the choice in a better dist. curve should be sought.
Happy Trails...
10-16-2012, 07:36 PM
#17
Moderator
Thread Starter
Join Date: Dec 2005
Location: Hills of California
Posts: 5,208
So here's what I found out.
Yes as we all thought the initial timing was indeed too low. Im now running 36 deg total I think static is 16.
I did good on the primary main jets with 68s
We switched secondary main jets from 68s to 70
Idle and float level was good.
accel pump was left on position 1 stock cam where I had it.
Switched 2nd spring from stock to yellow.
I had made a mistake with how the breather caps on the valve covers were setup and it was causing crankcase pressure to build this was solved and improved HP.
The exhaust noise was indeed a bad muffler and not popping like I was worried about.
So i was close like I thought the two big issues were incorrect breather setup and total timing about 10 deg retarded.
initially it made 257 hp 275 tq
after dial in it made 282hp 292 tq
Drives real nice now
-Gun
Yes as we all thought the initial timing was indeed too low. Im now running 36 deg total I think static is 16.
I did good on the primary main jets with 68s
We switched secondary main jets from 68s to 70
Idle and float level was good.
accel pump was left on position 1 stock cam where I had it.
Switched 2nd spring from stock to yellow.
I had made a mistake with how the breather caps on the valve covers were setup and it was causing crankcase pressure to build this was solved and improved HP.
The exhaust noise was indeed a bad muffler and not popping like I was worried about.
So i was close like I thought the two big issues were incorrect breather setup and total timing about 10 deg retarded.
initially it made 257 hp 275 tq
after dial in it made 282hp 292 tq
Drives real nice now
-Gun
10-16-2012, 07:41 PM
#18
2nd Gear Member
Join Date: Nov 2006
Location:
Posts: 356
OK good for you! But, know, you should be running a good operative PCV system as it has a secondary purpose, while evacuating/reducing crank case pressures, it reduces the tendency of parasitic oil leaks. ...a nice benefit too!