Thumpr

[bwlyon]

There have been magazines that have tested the Thumpr Cams from Comp, and they do indeed make more power over stock. Since you are running a manual transmission vacuum isn't a huge concern, if you have manual brakes it's even less of a concern. What can give you fits if you try running a mutha thumpr or a big mutha thumper is very low carb signal (i.e. not enough vacuum to draw the appropriate amount of fuel at idle) and a difficult to tune carburetor/engine. If you stick with the smaller thumpr cam you should be ok. Just be prepared to lose some low RPM power, and use nothing bigger than a 650 CFM carb with an otherwise stock FE less than 400 cubic inches, less is more. Stock carbs are less than 500 CFM. Throwing on a 750 CFM carburetor will decrease throttle response, and make the motor even more sluggish in the lower RPMs.
As for the ticking, FE engines are notorious for bending push rods (they are very long and thin). I recently bought a truck, with an FE, that had sat for years, and it ticked like a time bomb. Pulled the valve cover on the offending side and with a gloved hand started grabbing rocker arm with the engine running and found the culprit. I pulled the rocker shaft off and found 3 bent push rods, pulled the other sides valve cover and rocker shaft and found a 2 more bent push rods. The push rod that was ticking was almost bent into an L. When you get them out roll them on a flat surface it will be readily apparent which push rods are bent.

I don't want to sound like a bad guy and I know you are trying to help, but this really is misleading for the OP. As an engine builder, who has used one of these in a 390, the cam is not a good choice without plenty of gear, a very quick timing curve, and a tight quench, and if you do that, there are cams that will make MUCH more power. This cam sounds good at idle, that's all. At higher RPM it does start to pull, but to say it's soft on the bottom is an understatement. Sure the peaks will show more power, but the rest of the curve does not, and usable power wins on the street.

The vacuum issue is not about it drawing fuel at idle, it's about dilution of the chamber due to the excessive overlap from the tight lobe center and way too much exhaust duration. Until it gets to a higher RPM, and only if you have a good fast header with a small primary tube, will it start to clean up the burn. There is some idle issue though, and that's often due to reversion and fuel falling out of suspension

Finally, the bent pushrod deal, FEs don't bend pushrods, but you do see a common issue, any engine that sits likely varnishes, and in some cases, but less likely, rust the valves to the iron guides. When you fire them, the valves stick and it bends pushrods, common in any engine.\

Very smart to stay with a more traditional cam unless you are looking for the radical sound

Here is what they sound like by the way, certainly cool, but better off with a more traditional grind that ounds similar but makes more power

http://vid528.photobucket.com/albums/dd ... kuuhnp.mp4

[DuckRyder]

Is my browser messed up again or is that last post just a quote of the previous?

That does sound good.

Now might be a good time to talk about dynamic compression ratio. There are a number of calculators for this, I believe Patrick Kelly had one of the better ones.

Based on usual history of "Truck has a 390" it will probably be a 360, which means not only does it have 8.2:1 compression but it is down 30 CI on the typical 390 used by cam companies to describe cam characteristics.

If you want it to run good, picking a cam that maintains as much DCR as possible is a good start, lets be realistic, you're not going to reuse this cam when you build the motor, so pick one that works for now...

[My427stang]

You are spot on.

That 279 Thumpr, installed on 102 (as instructed by Comp and if you verified it with a degree wheel) needs 9.56:1 static to get to 7.81 DCR using PKelley's calculator. I'd call that safe on pump gas even in a truck and even with a quick timing curve. You could go higher, but I wouldn't recommend lower

If it's in a 360, the same cam would want 9.6 static to be in roughly the same place. However, IMHO, that's a little too much cam for a 360 in a truck.

Assuming an 8.5:1 compression in a 360, DCR would be 6.90 (very soft down low) and in a 390 at 8.5 would be at 6.98 (better, but still soft)

Also, if already at 102 ICL, it's not like you can advance it much more, because the intake valves will soon hit.

FWIW, that link in the picture is a low compression 390. The customer brought it in because of a mismatched build and they couldn't get it running. I got it running pretty well, but it took a ton of initial timing a very quick timing curve, some carb work, and still was soft on the bottom. However, we later added a TKO500 5 speed so the 3.27 1st gear helped it a bit, but it was still a band aid to avoid building the engine with the compression it should have had in the first place.

FYI we didn't add the 5 speed because of the cam mismatch, we added it because it had a close ratio car 4 speed, which had too tall of a 1st gear and no OD, so the TKO made it able to run in traffic or on the highway very happily. It was a lot of fun when done, but if the compression was right it would have been a monster and ran better everywhere. The game plan (if he hadn't sold it) was to put a 428 crank in it to bring compression up, more displacement, and tighter quench

[Busboy]

Finally, the bent pushrod deal, FEs don't bend pushrods, but you do see a common issue, any engine that sits likely varnishes, and in some cases, but less likely, rust the valves to the iron guides. When you fire them, the valves stick and it bends pushrods, common in any engine.\

I've found numerous bent pushrods on FE's lately and really haven't reached a conclusion as to why. I really can't assume that over-revving was the culprit based on the previous owner so you're explanation is as feasible as any.