sn60 boost pressure and carb reccomendation

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jackg
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sn60 boost pressure and carb reccomendation

Post by jackg » 25 Feb 2019, 13:40

I am in the process of putting together an R3 (half dished aluminum pistons 60 over along with a R3 plus cam) and am at the stage where I need to source a carb for the R3 box and a pressure balanced regulator. Couple of QUESTIONS: what is the normal boost pressure of an SN60 and would a 750 CFM carb be a good choice? What would the base fuel pressure be typically. Thanks in advance for the help

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PackardV8
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Re: sn60 boost pressure and carb reccomendation

Post by PackardV8 » 25 Feb 2019, 14:44

Unknowable.

Boost pressure is in some respects a measure of work done which actually consumed but did not make horsepower. The more freely an intake system flows, the less boost is backed up in the intake manifold and registering on a gauge.

An SN60 on a stock 289" turning 6,000 might produce 7 PSI, but on an R3 might only produce 5 PSI.

Also, cams with long duration and a lot of overlap (define R3+ ?) will let boost right out the exhaust, producing less gauge pressure.

So, if you can provide head flow and cam duration and we might be able to make more informed suggestions.

jack vines

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Mike Van Veghten
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Re: sn60 boost pressure and carb reccomendation

Post by Mike Van Veghten » 25 Feb 2019, 19:28

Jack wrote -
""Also, cams with long duration and a lot of overlap (define R3+ ?) will let boost right out the exhaust, producing less gauge pressure."

Also should add, long duration and high overlap cams will be low on power compared to an actual "blower" cam.

Jack G - Note, you might want to check your overbore numbers... You mean .060", not 60...correct ? BIG difference.

Mike

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R5 Lark
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Re: sn60 boost pressure and carb reccomendation

Post by R5 Lark » 26 Feb 2019, 10:04

Average normal boost pressures from a stock blower you can expect 5 lbs at 5000. Higher at higher rpms. Some claim 7 etc. 750 would work on a race only motor. 600 cfm would be better for street driving. I use Aeromotive fuel regulators for boost to fuel tracking. Idle pressure is 6 lbs with fuel pressure tracking as the boost goes up. Holley carbs though can take a seat needle pressure of 6 lbs. AFB's take around 5. Hope this helps. You might be ok with a boost reference mechanical fuel pump like the factory used.

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