Thumpr

[thejunkman]

I'll do my best to keep this as short as possible, but I tend to get long winded....

I did a quick search here and didn't come up with many results. Is anyone running the "thumpr" cam from comp cams?

I have a stock 390 (supposedly, I have never checked stroke), which is said to be an early 70s truck engine. I can't remember off the top of my head the casting numbers on the heads but I am pretty sure last time I searched them they were nothing special, I know they have pretty small exhaust ports. I have a 4bbl intake and 600cfm holley carb on it, and a pertronix kit. Other than that she's bone stock as far as I can tell.

Tranny is a np435 granny gear 4 spd, so first gear is essentially unusable (especially with the tired syncros). Gears in the rear end are stock I believe, I want to say last time I checked they were like 3.25 or something like that?? (I honestly haven't had time for truckin' in like 2 years so everything is foggy in my mind).

Right now I've got a lifter tick (always have), and can't get the tuning quite right. It runs OK but I think there's more in her still. Thinking I might just throw a cam kit in for now and see what happens. Eventually I want to build a big hammer for the truck but not anytime soon.

From what I can tell the thumpr should give me some "slight" power over stock but with a much better sound. I am guessing my current cam isn't even as good as stock should be so any new cam and lifter set should improve things. I don't expect much from a stock early 70s truck engine anyway. I'm sure it's as low compression as they came. Anyone have any words of wisdom for me?

Here's the kit I'm looking at:

https://www.summitracing.com/parts/cca- ... /make/ford

[tnlprt]

Dont take this the wrong way

Knowing as little about your engine as you do

And then just throwing parts at it is a recipe for disappointment

30 cubic inch difference in an engine changes what cam to use

Compression plays a major part in the selection

Gears also play a part

The lifter tick may be a bent push rod or a collapsed lifter

Timing, Proper carb adjustment,ignition upgrades all go farther than just throwing a cam kit in an unknown combination.

[thejunkman]

Dont take this the wrong way

Knowing as little about your engine as you do

And then just throwing parts at it is a recipe for disappointment

30 cubic inch difference in an engine changes what cam to use

Compression plays a major part in the selection

Gears also play a part

The lifter tick may be a bent push rod or a collapsed lifter

Timing, Proper carb adjustment,ignition upgrades all go farther than just throwing a cam kit in an unknown combination.

1) My original question was if anyone else is running a "thumpr" cam and what they have felt about their results. Obviously the fact that I know to check stroke to determine the difference between a 360 and a 390 before ordering a cam indicates that I would be doing so.

2) Compression ratio can fairly easily be determined by knowing above mentioned information and which heads (combustion chambers) I have, etc. The fact is that I am at work right now, not sitting in front of my truck so I didn't have those numbers readily available.

3) I mentioned gearing because I know they play a part

4) Lifter tick is probably a collapsed lifter. Knowing that I will more than likely need to replace lifters (as is common in FEs as we all know) is what initiated my thoughts on changing the camshaft. It's more of a "might as well" scenario than a "Im'a do big burnouts for $400!"

5) Proper carb adjustment is key for sure. Chasing the needle around on a vaccuum gauge knowing you probably have a collapsed lifter is less than ideal when trying to tune an engine. Ignition upgrade = pertronix. As well as a properly curved advance kit.

I'm not trying to be rude, but it sure sounds like you are assuming that I am trying to buy my way to hot rod heaven with low dollar bolt ons and haven't done any of my due dilligence. I would not purchase a cam without running hard numbers by the manufaturer's techs (after doing my research) as a starting point. But talking to guys on a forum where a majority run similar setups (stock FE truck motors), seems like a good starting point, as well as a way to spark some conversation with like minded car guys.

[Ranchero50]

Indeed, wrong cam choice is one of the more aggravating ways to make an engine run worse. Make it run right, then better.

[thejunkman]

Indeed, wrong cam choice is one of the more aggravating ways to make an engine run worse. Make it run right, then better.

I am personally not a fan of throwing new lifters on a 40 year old flat tappet cam of unknown condition, and new hydraulic lifters are probably what it would take to make it run "right."

My original post may have been misleading and I should have left info out. I am not looking to a cam to "fix" my engine. I'm looking to swap the cam WHILE I'm fixing my engine.

Lets pretend I have a perfectly running bone stock FE. Now does anyone have a review of the cam under those circumstances. I don't expect you to tell me how the cam will perform in my particular motor. I just want to know what kind of reviews you guys would give. Streetability/power improvements/idle/sound/etc.

[tnlprt]

It seems that you have already made up your mind


Good luck with your choices

[DuckRyder]

Well I have not run a Thumpr, but I have run a slightly too big cam for a low compression motor in said low compression motor... It didn't sound good, it did not really run that well either...

But we really don't need to have run that particular cam to predict how it will work if we know the details of the engine with some certainty. I know I would not pick that cam if I knew I had a low compression truck motor.

You should be able to search both the grind number and part number of that cam on the FE forum (perhaps the name as well, but that could get muddy due to the way they are named) and find some folks that have run that cam. You should not have to register to do this.

As you seem to realize first step is refreshing your memory on what you have, a truck 390 and a car 390 could make a world of difference in how your plan works out.

No headers?

[rollercam1]

Agreed with the above posts. Confirm the engine specs, validate the "health" of the engine. Might have more in store to repair when pulling it apart for the cam and lifter swap. Headers will absolutely make a huge contribution to the cam selected. I am a huge fan of custom grinds. They are a little more expensive but well worth the payoff. An off the shelf grind will be designed for a broad spectrum, not an exact scenario. The difference may be substantial. Anyways, good luck!

[colnago]

... a truck 390 and a car 390 could make a world of difference in how your plan works out ...

Not meaning to hijack the thread, but the statement above caught my eye. In 25 words or less, what are the differences between a 390 for a car vs a truck?

Joseph

[DuckRyder]

Where that statement is concerned:

Compression ratio

[Ranchero50]

Lets pretend I have a perfectly running bone stock FE. Now does anyone have a review of the cam under those circumstances. I don't expect you to tell me how the cam will perform in my particular motor. I just want to know what kind of reviews you guys would give. Streetability/power improvements/idle/sound/etc.

Bone stock truck 390 FE, don't cam it until you bump the compression. Bone stock 360 FE, don't cam it period, or 4bbl, or headers.

[rabbithunter2005]

To the response on not camming a 360 that is totally untrue I stuck a rv cam in my 360 and a 4 barrel intake and 600cfm vac secondary crab and it runs way better than b4 and i gained a couple mpg doing it. Its all in knowing what u wanna use it for. I own a thumper cam for a 460 I was building I never tried it yet however u wanna match the components your using together. I believe the thumper cam doesn't make any power till 1800rpm so right there u are sacrificing some low end. Just something to keep in mind. An engine build is a recipe it all needs to work together cam, intake, carb, exhaust, and compression ratio. Hope this helps

[My427stang]

I have used that cam and with compression and a good timing curve runs well in a 390 or 428. With stock compression, even in a 390, it is VERY soft on the bottom end. Sounds wicked, but really lazy until your foot is deep in it.

Stock motor, a 268H Comp is a good upgrade, even for a mild 360, anything more will lose on the bottom

[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.

[My427stang]

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