Selecting power valve method Holley 4160
:thumbsup:
You can play with the secondary opening point, but its a bit of a guessing game. I'll come back to this.
The PV number has NOTHING to do with the fuel mixture. That's the opening point (vacuum) for enrichement.
At wide open throttle a 6.5 will be just as open as a 10.5 PV. In other words same fuel mix. The manifoild vacuum is 0 to maybe 3 inHg in a restrictive setup. The fuel mix at wide open throttle is adjusted by changing the power valve channel restriction (PVCR).
For many of us, thats not the way we do it at first. At first we change the primary jets.
IF the best jetting for high speed cruise and top gear wide open throttle is the same, then we're done.
IF the best jetting for high speed cruise and top gear wide open throttle are different, then the jetting for best (leanest) cruise is installed and the PVCR is changed to provide the AFR mixture that provides the best full power.
If the carb was setup correctly by the factory, part throttle mixtures will be fine and all we need to do then is find the vacuum where the PV should enrich the mixture.
Most of this ^^^^ is science and engineering. You can see examples on the datta logs I've posted, and the science is in engineering books like Larew's from which the AFR vs load diagram i(posted in the other thread) were developed.
As far as sequence and procedures, this is my opinion based on my experiences. Others will have different experiences so different opinions.
Playing with secondary opening point.
We can use this a bit to compensate for other things.
I've certainly done it.
The better way is to get primary side to do what it needs to do well. Then get the secondary side tuned to match. Its a bit of an iterative process.
We can isolate the secondaries from a test by delaying their opening or disconnecting them completely.
I find this can be useful. Others don't like to do this because it changes the airflow, especially at wide open throttle. But disconnecting will allow us to get the primary jetting pretty close and if AFR logging is available allow use to get the air bleeds correct for a flat consistant AFR delivery.
An advantage of working on a chassis dyno, with a cooperative operator, is expand the AFR scale to see if the AFR is staying flat.
In this example it was flat at first with the larger jets, but was drifting lean with the smaller jets. The high speed air bleeds are just a bit larger than they should be for those jets. If we only had those two pulls, we would not know if this was both primary and secondary circuits or just one of them.
This getting a bit off the initial focus on the power valve but where I'm going is the secondary opening should not be used for enrichment.
Secondary opening is for more air when the engine can use it. The fuel mix into that addtional air should be the same as the primary circuit's AFR at that same time.
In this post you can see an example of where the primary and secondary circuits are very different. Disconnecting the secondary side allowed me to tune the primaries for WOT. Then with the secondaries connected I knew all the changes had to be made to the secondary side.
So glad mine came with that gage too.
You can play with the secondary opening point, but its a bit of a guessing game. I'll come back to this.
The PV number has NOTHING to do with the fuel mixture. That's the opening point (vacuum) for enrichement.
At wide open throttle a 6.5 will be just as open as a 10.5 PV. In other words same fuel mix. The manifoild vacuum is 0 to maybe 3 inHg in a restrictive setup. The fuel mix at wide open throttle is adjusted by changing the power valve channel restriction (PVCR).
For many of us, thats not the way we do it at first. At first we change the primary jets.
IF the best jetting for high speed cruise and top gear wide open throttle is the same, then we're done.
IF the best jetting for high speed cruise and top gear wide open throttle are different, then the jetting for best (leanest) cruise is installed and the PVCR is changed to provide the AFR mixture that provides the best full power.
If the carb was setup correctly by the factory, part throttle mixtures will be fine and all we need to do then is find the vacuum where the PV should enrich the mixture.
Most of this ^^^^ is science and engineering. You can see examples on the datta logs I've posted, and the science is in engineering books like Larew's from which the AFR vs load diagram i(posted in the other thread) were developed.
As far as sequence and procedures, this is my opinion based on my experiences. Others will have different experiences so different opinions.
Playing with secondary opening point.
We can use this a bit to compensate for other things.
I've certainly done it.
The better way is to get primary side to do what it needs to do well. Then get the secondary side tuned to match. Its a bit of an iterative process.
We can isolate the secondaries from a test by delaying their opening or disconnecting them completely.
I find this can be useful. Others don't like to do this because it changes the airflow, especially at wide open throttle. But disconnecting will allow us to get the primary jetting pretty close and if AFR logging is available allow use to get the air bleeds correct for a flat consistant AFR delivery.
An advantage of working on a chassis dyno, with a cooperative operator, is expand the AFR scale to see if the AFR is staying flat.
In this example it was flat at first with the larger jets, but was drifting lean with the smaller jets. The high speed air bleeds are just a bit larger than they should be for those jets. If we only had those two pulls, we would not know if this was both primary and secondary circuits or just one of them.
This getting a bit off the initial focus on the power valve but where I'm going is the secondary opening should not be used for enrichment.
Secondary opening is for more air when the engine can use it. The fuel mix into that addtional air should be the same as the primary circuit's AFR at that same time.
In this post you can see an example of where the primary and secondary circuits are very different. Disconnecting the secondary side allowed me to tune the primaries for WOT. Then with the secondaries connected I knew all the changes had to be made to the secondary side.
