Target Air Fuel ration N/A engines.?
08-12-2016 | 07:58 AM
#71
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From: On A Dirt Floor
Another thing to note on AFR adjustment is PVCR's. If off idle to cruise is good AFR but lean WOT or moderate accel, enlarge the PVCR's (Note: At a certain point high flow PV's are required). This will enrich the mix only when the PV's are open rather than across the board. My cruise was mid 12's to 13. WOT was 13.0-13.1. I enlarged both Pri and Sec PVCR's .005. Cruise still same (PV's are shut) and WOT is now 12.6. - 12.8
Off the top of my head, and don't quote me, if you have a PVCR thats larger than .080", you'll need to get High Flow Power valves as the standard ones won't flow enough fuel and thus becomes the restriction, which it isn't meant to be.
08-12-2016 | 08:11 AM
#72
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Sounds right SB. I am at .086. I experimented with standard PV's (Pri and Sec). Gained .3-.4 AFR at WOT (leaned up) vs the high flows that were in it. Went from 6.5's to 4.5's. Got a hell of a lean spot to boot during transition. I definitely needed the high flows and 6.5's to open a bit sooner and overall flow the amount the PVCR's wanted.
Another thing I will note: When adding a good amount of PVCR (Above 90) I recommend staggering the PV's vac rating by 1-2". This smoothes out the transition rather than gaining all the extra fuel at once. In a drag setup who cares... Marine definitely good to have curves rather than cliffs. My 2 pennys
Another thing I will note: When adding a good amount of PVCR (Above 90) I recommend staggering the PV's vac rating by 1-2". This smoothes out the transition rather than gaining all the extra fuel at once. In a drag setup who cares... Marine definitely good to have curves rather than cliffs. My 2 pennys
Last edited by Eliminated572; 08-12-2016 at 08:15 AM.
08-12-2016 | 08:18 AM
#73
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From: yorkville,il
This is the only thing that I could thing of. On the exhaust end of it it's no mystery. A motor with a double swap cam sounds like a lame duck compared to a standard firing order. We've seen 16" of vacuum over 3,000 rpm with some double swap motors. Which can be trouble especially when you have a 6.5 PV. Try to get the boat on plane and she starts snap crackle and popping because the carb will not flow any fuel. Put in a 10.5 PV (which are a pain to get) and she's good to go.
Last edited by mike tkach; 08-12-2016 at 08:27 AM.
08-12-2016 | 08:21 AM
#74
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From: chicago
I stopped using those 2 window std power valves years ago.
Like you guys say, the pcvr restrction has a huge effect on fuel flow to the engine. The misconception that if you block a power valve , you need to add xxx jet sizes, is vague. Without knowing rhe pcvr total area, its just a guess. A .035 pcvr is tiny compared to a .097 restrction!
Like you guys say, the pcvr restrction has a huge effect on fuel flow to the engine. The misconception that if you block a power valve , you need to add xxx jet sizes, is vague. Without knowing rhe pcvr total area, its just a guess. A .035 pcvr is tiny compared to a .097 restrction!
08-12-2016 | 08:23 AM
#75
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From: chicago
In regards to the firing order swap on a big block chevy,
Back when GM was doing development on the big block engine series, i wonder if they just decided 18436572 looked good on paper, or did they maybe do some testing on firing orders? Over the 40 years of development and improvements on the big block chevy, did not one engineer at GM, suggest a different firing order ? Its not like it would have required major retooling or anything.
I have never measured any vacuum readings on a LS firing order big block, but , id like to think if it offered some significant increases in idle quality, vacuum, etc , GM would have taken advantage of it many many years ago.
I know the 8.1 truck engines had LS firing orders, but they were also a symmetrical cylinder head too. Seems like most of the bigtime engine builders ive talked to about the ls firing order on a old school bbc, offers very little advantage if any in "most" applications
Im with mike tkach, as i cant understand why a firing order swap alone, would make an engine pull much more intake manifold vacuum? Its not registering
Back when GM was doing development on the big block engine series, i wonder if they just decided 18436572 looked good on paper, or did they maybe do some testing on firing orders? Over the 40 years of development and improvements on the big block chevy, did not one engineer at GM, suggest a different firing order ? Its not like it would have required major retooling or anything.
I have never measured any vacuum readings on a LS firing order big block, but , id like to think if it offered some significant increases in idle quality, vacuum, etc , GM would have taken advantage of it many many years ago.
I know the 8.1 truck engines had LS firing orders, but they were also a symmetrical cylinder head too. Seems like most of the bigtime engine builders ive talked to about the ls firing order on a old school bbc, offers very little advantage if any in "most" applications
Im with mike tkach, as i cant understand why a firing order swap alone, would make an engine pull much more intake manifold vacuum? Its not registering
08-12-2016 | 08:34 AM
#76
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From: On A Dirt Floor
Sound sells many things. Think Harley Davidson and think "I want a heavy thump at idle." :smile:
I actually have a lot of info on the firing order swaps but I need some time to put it into better english than my attempt about an hr ago that I never posted because of brutal english flow. I'll work on it in a bit.
I actually have a lot of info on the firing order swaps but I need some time to put it into better english than my attempt about an hr ago that I never posted because of brutal english flow. I'll work on it in a bit.
08-12-2016 | 08:44 AM
#77
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From: US of A
I agree the double swap cam does sound different. Can't comment on the vac difference (different engine). Just did this in my 632 in Camaro. Can hear the difference
https://youtu.be/hd9ygKmYZ2c
https://youtu.be/hd9ygKmYZ2c
08-12-2016 | 09:00 AM
#78
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From: chicago
08-12-2016 | 09:13 AM
#79
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From: Western N.Y.
My engines have the c swap 5/3, 4/7 cams. I don't notice a difference in the sound. Maybe others can hear it. This video is the last one
https://youtu.be/cYe5ChvBpwY
https://youtu.be/cYe5ChvBpwY
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Straight bottoms and flat decks
Straight bottoms and flat decks
Last edited by bck; 08-12-2016 at 09:40 AM.
08-12-2016 | 09:18 AM
#80
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From: SF Bay Area
Sounds right SB. I am at .086. I experimented with standard PV's (Pri and Sec). Gained .3-.4 AFR at WOT (leaned up) vs the high flows that were in it. Went from 6.5's to 4.5's. Got a hell of a lean spot to boot during transition. I definitely needed the high flows and 6.5's to open a bit sooner and overall flow the amount the PVCR's wanted.
Another thing I will note: When adding a good amount of PVCR (Above 90) I recommend staggering the PV's vac rating by 1-2". This smoothes out the transition rather than gaining all the extra fuel at once. In a drag setup who cares... Marine definitely good to have curves rather than cliffs. My 2 pennys
Another thing I will note: When adding a good amount of PVCR (Above 90) I recommend staggering the PV's vac rating by 1-2". This smoothes out the transition rather than gaining all the extra fuel at once. In a drag setup who cares... Marine definitely good to have curves rather than cliffs. My 2 pennys
By staggering the PVs are you talking about doing, for example, a 4.5 in the primaries and 6.5 in the secondaries?
