Of course, everyone is going to say "yes" because it's not their time or money going into the project. Why do you want to let the customer screw up the combination by choosing the "name of the week" part? Part of your service is selling your knowledge and expertise. Letting the customer choose a weird combination will certainly help your engine building reputation.

Instead of letting someone choose parts, why not ask the customer a set of more general questions....like what engine type, engine size, engine use, installed car specifics, powerband range, etc. and then you quote him some specifics....that way, you can market "custom crate engines" but not "stupid custom crate engines". You can make an Excel spreadsheet that will allow you to price components, etc. fairly quickly.

Your biggest challenge is how to keep the cashless nimrods from wasting your time asking for a price for something that they could never afford. One way we use is to shoot them a "Budgetary" price that is not exact but close and lets them either faint or proceed. Also, forcing them to physically telephone you keeps them from hiding behind the internet shield.

Feature the "Custom" idea but control the product.

mike in tucson