I had that Thumpr cam in my 340 and it wasn't too bad performance wise, but it wasn't the best. Sounded great though! It still had some bite to back up that bark. COMP recommends their 995-16 springs (I think...goin' by memory here), which are a double spring. You can run that cam with a beefy single spring but it's not the best idea. When I talked to Comp about using the 901-16 with that cam they said it'd be fine down low but above 5,200 RPM or so, the valves might float. If you don't want to do the machining for double springs, you could probably find a suitable single spring. Also, it doesn't make a lot of vacuum so power brakes are iffy at best. Sounds great but it'd rob performance from your engine. I do NOT recommend this cam for your 318, and I'm speaking from experience here. I won't deny that it sounds wicked though.
Thumpr cam:
I ditched the Thumpr cam in favor of a COMP XE268h, which still sounds pretty good and is better for a street car. This cam uses a 901-16 spring which is a single spring that doesn't need any machine work to fit in the heads. It's a drop in replacement for the stock valve springs. More vacuum, broader powerband, and it's got a choppy but streetable idle. A lot of people have ran this cam in a 318 and it may or may not work well depending on the rest of your combo. There's a LOT to think about when picking out a cam.
XE268h Cam:
When I had a 318, I went with a COMP HE268h cam. It's milder than the XE268h but beefier than the stock cam. Vacuum brakes work well with this cam, and it idles nicely but with enough lumpiness so that people know it's not stock. 901-16 single springs are recommended, no machining required! Unless you are going to do more mods to the 318, you're going to want to keep the cam on the mild side. Wild cam in a stock 318 is the best way to make it gutless and miserable to drive.
318 w/HE268 Cam:
So yeah, if you want it to sound like a muscle car and still perform decently, go with a smaller cam. Something like the HE268 which is similar to a stock 340 cam. If you want a bigger cam, just know that you'll need to do supporting mods to go along with that cam.
Nice info thank you! The XE268h Cam sounds pretty good to me. But I guess the cam wont sound like thta unless I get rid of the stock header first. It sounds like its completely restricted.
