We run into this pretty often where someone will want us to build a blown engine but the cost for the blower and additional carbs isn't in the budget at the time, so they want us to build the engine "set-up" to add the blower later. We try to discourage this for several reasons;
1) Most guys have never been in a car with REAL horsepower. They've been accustomed to being TOLD their buddy's car has 500, 600, (or whetever he was lying that day about how much power his engine has), so when you go for a ride in his car that he claims has 600HP and it really only has more like barely 400HP, you get used to the feeling of what 350 - 400 feels like. An honest to goodness 600 - 700HP is a serious handfull in any given street car. When we build an engine that honestly makes that kind of power, it's a butt puckering experience for most poeple, and in most cases, it's a car that'll easily peel-off a 10 second quarter mile time. Now really, how many of the people have you talked to that claim they have that kind of power but when they get to the track, they run 12's or 13's? It's simple... it's because they just aren't making the kind of power they think they are making.
2) It's not uncommon for us to build an engine destin to have a blower added later (or nitrous), and once the customer gets it he is more than happy with how much power it makes without the blower so they never spend the additional funds to follow through with it. This creates an engine that is looser than we would have built if it were designed without a blower in mind, and a cam profile that isn't ideal for a non-blown application, nor the static compression that we would have chosen for a naturally aspirated set-up or even the different types of head gaskets we would use for a blower application. So in a sense, when we've run into this before, even though the customer may be tickled pink with how strong it runs, it is still an engine that is going to smoke a bit more and use a bit more oil than one that wasn't set-up for a blower, plus it isn't making the power it COULD be making if we had originally set it up to be naturally aspirated.
The opposite is true when someone wants an engine built and then later-on (without us knowing) wants to add a supercharger. You are really limited in what you can do. To get the kind of power and performance that we get from our engines, they are built to run on the edge of what today's fuel can handle. if you go spending $4,000 or so for a nice blower set-up, and more on additional carbs, linkages, fuel lines, etc., you are going to be very limited in how much blower boost you can run, so basically you just spent a bunch of money for something that looks neat. This doesn't take into account the naturally aspirated cam profile which will send a good portion of that boost right out the exhaust which doesn't add to making any more power. This also doesn't get into the types of parts used in the engine, such as pistons, rings, bearings, clearances, etc. There IS a difference between blower pistons and non-blower pistons. Pistons designed for blowers and nitrous have more area above the top ring for added strength. The rings will see more temperature under boost conditions so we choose a different type of material for those too.
Blowers (or nitrious) force the engine to burn more fuel. Burning more fuel creates more heat. Heat expands parts, so if clearances aren't specifically built-in during the engine building process to be compatable with a blower (or for nitrous) and those parts get heated up beyond what they are normally exposed to being naturally aspirated, then clearances disappear and things weld themselves together from friction, rings butt together break bust-off the tops of pistons. Piston skirts friction weld themselves to teh cylinder walls. Bearings fail because they can;t take the loads cause under boost conditions, and all kinds of other bad things can (and will) happen. This is why we laugh at cheap priced engines advertised in magazines that either don't have specific parts that are blower frienldy, or that are basically regular engines with blowers stuck on top of them. You're just asking for a failure if you put some boost to those engines.
The thing to remember is; if you want a blown engine, build it as a blown engine with the blower ON IT, because when you don't, or if you decide to not put the blower on it down the road, the engine won't be built as well, or running as well, as it would have been if we had set it up to be naturally aspirated from the beginning.
