I need help with jetting and PV (509ci, 8-71, dual 800cfm, 825HP)
10-27-2008, 03:26 PM
#31
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10-27-2008, 03:41 PM
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The link between the primary and secondary side of the carburetors. Carburetors on top of a Super Charger should use a 1:1 linkage rather than the progressive. This evens out the air (and fuel) going through the carburetors which allows the engine to run more even from side to side.
Are you checking your A/F on both sides of the engine or just one?
Are you checking your A/F on both sides of the engine or just one?
10-27-2008, 04:15 PM
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The link between the primary and secondary side of the carburetors. Carburetors on top of a Super Charger should use a 1:1 linkage rather than the progressive. This evens out the air (and fuel) going through the carburetors which allows the engine to run more even from side to side.
Are you checking your A/F on both sides of the engine or just one?
Are you checking your A/F on both sides of the engine or just one?
I'm checking the AFR on the even side.
10-27-2008, 04:45 PM
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How do you jet the carbs with 1:1 then?
Is there such a big difference between 1:1 and prog when you have the blower underneath? Should the air and fuel mix pretty well in the blower? I can see that it will be a big difference on a blow through motor though.
Last edited by tomas_wallin; 10-27-2008 at 04:47 PM.
10-27-2008, 04:59 PM
#36
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Yes I can see that. I assume the 1:1 linkage makes the prim and sec open simultanesly instead of the prim open first and then the sec?!
How do you jet the carbs with 1:1 then?
Is there such a big difference between 1:1 and prog when you have the blower underneath? Should the air and fuel mix pretty well in the blower? I can see that it will be a big difference on a blow through motor though.
How do you jet the carbs with 1:1 then?
Is there such a big difference between 1:1 and prog when you have the blower underneath? Should the air and fuel mix pretty well in the blower? I can see that it will be a big difference on a blow through motor though.
Yes there is still a big difference since the SuperCharger moves the air and fuel around the rotors. If you were to look at the O2 per cylinder or cylinder pressure you will see there is a big difference.
If you're running 1:1 linkage you can then boost reference both power valves and run them in both sides and start off with the same jetting in both sides.
10-27-2008, 05:05 PM
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Yes there is still a big difference since the SuperCharger moves the air and fuel around the rotors. If you were to look at the O2 per cylinder or cylinder pressure you will see there is a big difference.
If you're running 1:1 linkage you can then boost reference both power valves and run them in both sides and start off with the same jetting in both sides.
If you're running 1:1 linkage you can then boost reference both power valves and run them in both sides and start off with the same jetting in both sides.
The sec powervalves are plugged, or not even drilled.
10-27-2008, 09:04 PM
#39
I don't know why people run boost referenced power valves on all these applications. I would map your manifold vacuum and vacuum under the carb, A/F ratio and exhaust temps at progressively increasing RPM's. Then compare the data to see when the power valves are actually open! They are probably open from 2000 on up, and this is not necessary. Try to have them open at around 4000 rpm or just above you high cruise rpm. Then redue the mapping exercise, to make sure your not too lean.
Sterling and many others, run the power valves from above the blower (standard location). I have run several twin engine blown boats, without boost referencing, with power valves in the 2.5 to 5.5 range with clean transoms and clean oil without problems. The exhaust temps progressively rise with RPM. 4000 rpm is about 1300 degrees.
If you do dyno at cruise range, you will end up mounting the carbs sideways, which you are doing, and that is good for mid range fuel distribution.
Good Luck, John B
Sterling and many others, run the power valves from above the blower (standard location). I have run several twin engine blown boats, without boost referencing, with power valves in the 2.5 to 5.5 range with clean transoms and clean oil without problems. The exhaust temps progressively rise with RPM. 4000 rpm is about 1300 degrees.
If you do dyno at cruise range, you will end up mounting the carbs sideways, which you are doing, and that is good for mid range fuel distribution.
Good Luck, John B
Last edited by John B; 10-27-2008 at 09:11 PM. Reason: error
10-28-2008, 01:49 AM
#40
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I have just about zero vac/boost at 4000rpms. At 3000 I have 10.6-11:1 and a couple mmHg vacuum.
I have a wicked slip with this labbed 31 bravo, that's why the boost is so late. 30%@4000 and 20%@5100... It looks like it should be pretty good for wot though with the falling slip numbers. I will make a few wot test before I put it away for the winter. So I know wot rpms, speed, AFR etc etc.
I have a wicked slip with this labbed 31 bravo, that's why the boost is so late. 30%@4000 and 20%@5100... It looks like it should be pretty good for wot though with the falling slip numbers. I will make a few wot test before I put it away for the winter. So I know wot rpms, speed, AFR etc etc.
