Any power adder will require a modification of your clearances to compensate for the additional heat. A blower will most likely require a hole in the hood unless it is incredibly small. In a blower, size matters, and bigger is better especially with a Roots type. Roots blowers do not pressurize a manifold the same way a centripetal blower does. So the longer the impellers the more air it will move, with less heating.

A centripetal blower will fit beneath the hood, and like a turbo it takes a few seconds to build boost which allows you to get your RPM's up before it builds full boost. This is a good thing with cheap gas. It will build more boost than a small Roots which means more power. Another advantage is a blow through carb is less likely to do any damage if it back fires.

Blown cams have a longer LSA and more duration on the exhaust side to get the spent gasses out. Choice of heads is not as important as you might think as with a blown system the air is cramped into the cylinder under pressure. The Vortec heads are a good choice for the street and may still work well blown. Your stock bottom end will work it is just a question of how long. When it does fail it will be spectacular because cast parts shatter taking everything out around them.

Big Dave

 

I run a 6-71 roots blower on a 355 LT1 in my 67 Camaro. This engine has been running for 15 years mostly in part to the right build for the blower. If you plan on driving this car you will need to build the bottom end up for the blower and have the rotating assembly balanced. How far you go depends on how much boost you plan on pumping in. I can suggest a great streetable combination if you'd like. For the most part you want to stay around 10 psi boost @ 12:1 MAX compression to be able to run pump gas. And the most important part is the pistons and rings. Go with thick top TRW blower pistons and moly-plasma ceramic rings. These require a special hone but its not expensive. As far as heads, you will want something with hardened valve seats for no-lead gas and a good chamber size based on the boost you want to run. You don't need to polish ports as the mixture is so fat it needs a bumpy surface to keep it atomized. (Polished ports force the mixture to puddle.) You will also have to double your fuel volume by running at least 1/2" line from the tank to the regualtor. You will then need to get some fat spark to light all that mixture. An MSD system is a must. And the advance curve must be set up carefully to avoid detonation. Since blower motors can never lean out you will need a good electric fuel pump capable of at least 140 GPH. As far as carbs go, there is a formula you can do to figure out the best CFM for your engine/purposes. Carb set up is a major part of the equation. See if the firm you buy the blower through will help set you up with carbs. Getting the proper power valves and jetting can be quite a task and there are quite a few other mods required. I went through Gary Dyers and he set up my Holleys based on my purposes and they are perfect. I had to play around with spring rates on the vacuum secondaries but that is easy to do with Holley's spring kits.

There are specific do's and don'ts with building any supercharged engine. There are books on supercharging that are invaluable to anyone building an engine like this. They are packed with advice and information from experienced builders that will help you do it right instead of learning expensive lessons.

-Scott

 

Also like Big Dave said you will need a cam with a grind specifically for a blower motor. Engle used to sell a nice valve train kit for blower motors that I run. I'm sure there are plenty others out there.

-Scott