Carb/cam question

[great_escape]

I'm thinking about adding a 6-71 blower to my 496, To off set the cost I was hopping I could use the 660 carbs off my tunnel ram. I've added a second metering block to them as well as center hung float bowls. they seem to work real well on the tunnel. My motor is also equiped with a solid roller cam the specs are lift (int .638 ext .622) dur @20 (int 285 ext 295) dur @50 (int 252 ext 262) 108 lobe seperation. Would this cam work for this app. Thanks

[ttmott]

I have dual 660 center squirters on my twin turbo motor in a jet boat. A couple of things (maybe you already know) that are needed to understand about the carbs before such an application.
The 660 Holley was designed before the advent of high stall torque converters and trans. brakes in drag racing consequently they have massive enrichment circuits (acc. pumps and four corner squirters) to allow stabbing the throttle from essentially idle compensating for an instant lean condition when all four are opened. The 660 have an aggressive secondary opening profile also. In a blown application such a massive enrichment is not required. If yours has the 50cc (REO) acc pump then it also has a very large acc pump cam (the brown one). This needs to be changed to either a red or orange cam and set to the #2 hole and the pump lever readjusted per Holley instructions. This will get you to a reasonable 20 to 25 cc shot rather than the 36 cc shot. Remember this is all times two carbs. I removed the four shot squirters and changed them to two shot as there is no need to squirt fuel on closed or nearly closed secondarys in part throttle application.
If the primary metering block has an enrichment valve (power valve) you will need to either remove it and install a plug or reference to down stream of the blower. The easiest way is to remove it and upsize the primary jets 5 sizes.
For the engine cam you specified you will probably need to crack the secondarys one half to one turn on the screw in order to keep out of the primary transition slot with the primary throttle plates. This will allow the idle mixture screws to be effective in idle mixture correction.
On test runs watch carefully the plugs for rich / lean conditions and jet as required. My 468 at 1.4 bar boost has 72 jets on the primarys and 76 jets on the secondarys with metering blocks on the secondarys. This is slightly rich, where I like it; I will sacrifice a little power for a long lasting engine.
Lastly, there is no need to mess with the air bleed jets.
Tom

[great_escape]

Thanks all of that info will help out, I already got rid of the power valves so not to much work to do.