Vtiger ServiceContracts Webforms，如何使其工作

I need to add a Webform for ServiceContracts, witch is not listed as a standard module for webforms.

I did this: i opened "root\modules\Settings\Webforms\models\Module.php", and added in line 21 Array ServiceContracts, like this:

$webformModules = array('Contacts', 'Accounts', 'Leads', 'Potentials', 'HelpDesk', 'Vendors','ServiceContracts');

It works, i can create webforms for my Service Contracts, but it's very very slow when i add it, and i don't understand why..

Is there something else i should do?

Thanks!!!