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Nova Rally 350 sbc soon to be supercharged.... questions ;-)

Hi All,

I just bought a Wieand 142 Series Supercharger from a friend, brand new.

My '79 2dr. Nova Rally currently runs on a 1991 350 SBC used to be TBI, now eqquiped with 650CFM Holly 4150 Double Pumper, Comp Cams XE268H Exteme Energy hydraulic cam (Valve Lift .477" .480", Duration At 0.006" 268° 280, Duration @ 0.050" 224° 230°), Weiand Power +Plus intake manifold, Headman Headers, MSD Dist. and 6AL ignition. All of that hooked to a modified TH700R4 (2500 Stall Converter) and a 3:42 Diff with Eaton limited slip.

Engine compression ratio is 8.6:1 (by the books).

Now for the questions....


First of all, I've been told that no engine modifications are needed to install that Supercharger on a stock SBC, other then an ignition retard control... is that true?

Is my current cam ok with the suggested application?

As above, a 650CFM carb feeds my fuel lover Nova, should I replace it to a bigger Carb.? can I replace the jets to a bigger ones or something like that?

I currenty have a Holly 110GPH 6-8PSI mechanical fuel pump, will it do?

Any other things that you can think of that I might need or do/shouldn't do?

The result of the info. that you guys can help and give will be longer life for my engine, and more Jap. crappy cars that I'll be able to kick ass lol

Thanks!

Lior.
 

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Re: Nova Rally 350 sbc soon to be supercharged.... questions ;-)

Your cam will work but it is not optimized for a blower application. (blower cams want lots of lift and longer duration on the exhaust side).

Carbs stuck on top of a blower need a special rework to prevent surging at idle (generally deals with a boost reference for the idle and off idle circuit as vacuum signal hunts up and down as the motor surges in response to the cyclic pulsing of the engine), and depending upon amount of boost you are seeking and when, you may run out of carb very quickly.

Even though your static compression is 8.4, and your cam is bleeding off a lot of what little compression you had, your cast pistons will not live long if you run lean (run out of carb), or get into detonation (don't pull out enough ignition timing as cylinder pressure rises due to boost. You will have to watch out for either, but rather than worry about dropping coins on the short block look into heads as your next purchase. A blown engine has to be able to breathe, especially on the exhaust side (you are pushing air into the cylinders with a pump but nothing is there to help get the extra spent gasses out).

The carb sits on top of the blower so the carb itself isn't pressurized as is the case with a blow through set-up. As such your fuel pump would have adequate pressure to fill the fuel bowls even at full boost pressure. Where a mechanical pump falls flat is at high RPM because there isn't enough time to cycle the fuel through the pump. The pump sucks on the down stroke (pressurized by the cam lobe, so the diaphragm will move the amount needed to pump the fuel) the problem is the flapper valves in the pump are restrictive and slow the fuel volume through the pump, and the spring (which is what provides the constant 8 psi pressure) is pushing down still trying to evacuate the pump cavity when the next cycle starts again meeting it on the way down.

To provide adequate fuel for a blown application, you will need to read the recommendations of the vendor as to carb size and fuel supply. I imagine they recommend about another 100-150 cfm in size over normally aspirated and an electric pump with a return line to provide adequate volume with required pressure.


Big Dave
 
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