I dinked around with in a bit this evening. It'll fit horizontally up on the firewall with no problem. I have an auto though...not sure what a clutch pedal would do. I'll have to get creative with spacers to mount it though. The firewall has all kinds of wonky curves and dips in it. Overall, I'm very glad I bought it. The relays on the panel and the 3rd grade level directions is going to make it easier.