[KEN CROCIE]

Anyone use them? Results?

[PAUL K]

We've used a handful of them with good results. They supply the "Burger King drive through" idle and seemed to make better power than expected. However non of them were put on the dyno or any drag strip comparisons made.

[Steve C.]

"Believe it or not, the Comp Cams thumper grinds run very well, and sound real good too. I have used them many times, and the performance is much better than expected, and they have the DRIVE IN IDLE sound that people want."

JOE SHERMAN RACING ENGINES

Cams are like people's personalities, what works for one won't necessarily work for others. If you do a search here on the Thumper subject you will find a lot of negative opinions and comments, like XE flat tappet cams !


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[77 TRASHCAN]

Yo Cliff!

[Steve C.]

Cliff hates them

"I've had two Chevy customers this year yank Thumper cams out of their 396 and 454 engine builds and throw them down over the hill. ABSOLUTELY hating everything about them at every level, to a point where they couldn't deal with the crappy idle quality, stinky exhaust, and quirky power curve. The one guys wife REFUSED to even ride in the car as it stunk her cloths up too much, and about ran them out of the vehicle at stoplights or backing it out of the garage, etc."
Cliff Ruggles

Note early development came from road race applications that needed a very wide power range to allow them to come out of the corners. Someone liked the associated sound of these road race cams. Fast forward and Bingo... they refined and developed the Thumper series for many Hot Rodders who actually enjoy the sound of a rowdy idle on their street cars.


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[PAUL K]

Lots of parts laying at the bottom of the hill behind Cliff's shop.

[Formulajones]

I've used them, albeit in chevy applications, haven't tried one in a Pontiac.

They have worked surprisingly well for me, but I pay close attention to install position, and the end user needs to have quite a bit of tuning knowledge with the particular carb and distributor they are using. Can't just toss these things in and expect it to run out of the box. I typically have to do some idle circuit modifications at a minimum.

Once dialed in they actually provided very good drivability in the few applications I've tried them in. They won't be big HP makers. They were original designed as Steve mentioned off of the old circle track camshafts that provide power right off idle and mid range to drive those cars off the corners. Personally if choosing this cam I only like them in stick car applications.

Here are a couple of clips of the last one I messed with. This was the middle size thumper. They make a Thumper, Mutha Thumper, and a Big Mutha Thumper. This one is the Mutha Thumper. This is a 406 sbc with dart iron heads, 10:1 compression, RPM air gap intake and 750 holley. Muncie M20 and only ran 3.08 gears with a 25" tire. I drove this car everywhere and despite the pro stock type idle, it behaved very well, I could lug the engine down to 1200 rpm in 4th gear without complaint and cruise around town at 30-35 mph no problem. Was a fun car to drive. The 406 was done making power around 5500 rpm, which was fine, I didn't care to spin it higher anyway. Made gobs of torque right off idle and was a blast on the street.

https://youtu.be/XC5HfqFwac0

https://youtu.be/47HgejCVbFs

[Schurkey]

Originally Posted by Steve C.

" Comp Cams thumper grinds... ...on the Thumper subject

Originally Posted by Steve C.

yank Thumper cams out ... ... they refined and developed the Thumper series

Originally Posted by Formulajones

middle size thumper. They make a Thumper, Mutha Thumper, and a Big Mutha Thumper. This one is the Mutha Thumper.

They are not "Thumpers". "Thumpers" is an actual word.

Comp Cams makes "Thumpr" cams. "Thumpr" is not a word, so it can be trademarked--very much like "Flxible" buses, "Cheez-It" crackers, and a bazillion other products.

http://www.compcams.com/catalogsearch/result/?q=thumpr

[Formulajones]

Who cares

[1965gp]

I put one in my Firehawk and it sounds great- but probably doesn’t compare to a traditional Pontiac

[Steve C.]

OH CRAP, he spelled it wrong here as well ....

Thumper camshaft Pontiac 455 comp cam sound

https://www.youtube.com/watch?v=QSTK4gqMWDY




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[Formulajones]

Well I'll sleep better at night knowing that. Thanks Shurkey

[Steve C.]

https://www.youtube.com/watch?v=C5Bbt9extsg



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[Cliff R]

I get more complaints from folks who installed Thumper and Thump Ya Mutha cams than any other.

It's like most other things with this hobby. Well meaning hobbyists and engine builders trust camshaft companies to make a product that will produce some "attitude" at idle and good street manners and live up to the unrealistic advertisement they put right beside their catalog listings.

"Thumpr Camshafts are the hottest cams to hit the streets in more than a decade. That's because they give you the big cam sound you're looking for, without the drawbacks. Applying a camshaft design originally created for sports car endurance racing, they incorporate early exhaust valve opening, long exhaust duration, and a generous amount of intake and exhaust overlap. Best of all, Thumprs will not negatively impact power output or streetability."

NOTHING about super tight LSA and relatively big .050" numbers are going to make for a good scenario at idle and low RPM's especially if you don't have the static compression ratio based on the CID of the engine to support it. That's just the laws of physics with these things and hasn't changed since I got into this hobby way back in the 1970's.

I've actually set up carburetor and distributors for quite a few folks who went that route. Could put up scores of stories here, but I'll just use one instead because it involves considerable "drama" associated with a cam choice.

So we have an owner of a later model Pontiac 400 powered vehicle. He seldom if ever drives his car in cooler/cold weather. It's basically a "stock" 400 for decades, then at rebuilding time the owner hires a well know engine/speed shop to spruce up his low compression 400. I'm not sure how but they tell him compression is raised to 9.5-10 to 1 for pump gas and it gets a Thumper cam, one of the larger ones but the exact specs escape me. It's around 235 something 247 @ .050" on a 107LSA going by memory.

No one on his end can get this thing to run well so the carb goes off to another well known Q-jet company (doesn't like my turn-around time). It doesn't work for chit so ends up here anyhow. I open it up even more for idle and main fuel, it fairs better but the owner continues to bellyache about the crappy idle quality, stinky exhaust and not user friendly. He's able to drive the car but not enjoying it. Hardly a month goes by I don't get a call about it, and finally talk him into changing the cam, but the speed shop simply chooses a smaller version of (to this day I don't know why they stuck with 107LSA). Things fair better but he still doesn't like it and has a ton of money in it at this point and has not enjoyed the car for several years after all these "upgrades".

So the saga continues and he even gets talked into another carburetor but it still doesn't make the grade. So I finally decide to make one last ditch effort to help and on my nickel build his original distributor as that's the only unknown left in the equation and many of the symptoms being described tell me that the aftermarket "high performance" distributor the speed shop installed just isn't making the grade. To combat the issues I put a pretty "tight" curve in it for more initial timing and getting it all in pretty quickly with none in at idle speed. I shorten up the VA timing as well and have him put it on ported vacuum since the engine still isn't making great vacuum at idle. I had him ditch the second carb and install the distributor with the carb I previously set up for him with the re-worked factory distributor.

So I get the dreaded call a week or so after shipping it to him. I recognize the number and hesitant to pick up the phone........... but to my surprise he's the happiest guy in town, finally able to drive the car w/o stalling at stop lights and idle speed all over the map, and he has his Dairy Queen car cruise chitty idle quality everyone loves. At least we get a happy ending from a 2-3 year cycle of drama just because a well meaning engine builder makes a poor cam choice twice and doesn't have the skill sets to nail the tune down to make the engine happy.

One of the fundamental issues with this story that exists to this day is that I don't think the compression ratio of his engine was anywhere near 9.5 to 10 to one. Just a hunch on my part as it's difficult to get there with 6X heads without a domed piston and we never could nail down the engine builder for the piston specifics other than he claimed higher compression. Anyhow, I have at least half a dozen similar stories from big block Chevy owners who's engine builder went that route, and quite a few more from other brand loyalists, Buick, Olds, etc.

These days I have decided to stay away from carb/distributors for folks who went that direction, and I sleep better at night.........FWIW.......Cliff

[Formulajones]

I think that's the key statement out of your post.

So many builders these days just miss the mark when it comes to compression ratios and using bigger camshafts, and then wonder why the engine runs poorly, doesn't idle and won't make enough vacuum.

[PAUL K]

If a combination is built wrong is it fair to blame one part?

This chit isn't that hard!

Low nine second car with a little nitrous...note how quiet the car is and none of the starting line personal needed oxygen due to the stinky smell idle;

https://youtu.be/3LJ-0iRjMsI

Same car making a ten second naturally aspirated pass...note 800 rpm idle with a nice choppy lope ..cam has a completely undriveable 105 LSA. Still none of the starting crew needs oxygen due to us making multiple passes;

https://youtu.be/kk1-oVZED48

Mid ten second pump gas car with dreaded 108° LSA camshaft... note person holding camara gasping for oxygen and nearly passing out from the stinky idle smell;

https://youtu.be/PhDicneJIXs

The last car ran 10 flat at the Pontiac Nationals in Norwalk this past summer....so I know we can eliminate anything funny going on in Ohio causing these cars not to idle.

I know Steve C has run in the ten's with a pump gas stock block combination using a 108° LSA cam and lived to tell about it. Also another board member has ran mid nines with a pump gas aftermarket block combination that I believe uses a 110 LSA camshaft.

[77 TRASHCAN]

Originally Posted by Formulajones

I think that's the key statement out of your post.

So many builders these days just miss the mark when it comes to compression ratios and using bigger camshafts, and then wonder why the engine runs poorly, doesn't idle and won't make enough vacuum.

I have 2 friends that are NOT strangers to the high performance world, they have owned, tuned, modified engines/cars A LOT.

I tell them about zero decking a high 9:1 engine, and our conversations get a little touchy...They tell me NOT to do that, it's the worst thing you could do...and about LSA numbers.....Apparently in the olden days, the LSA numbers were never considered anything important....they are mostly concerned with the peak lift numbers at the valve...I have to change the subject...

[Cliff R]

"If a combination is built wrong is it fair to blame one part?

This chit isn't that hard!"

No, it's not that hard, but you still have to wonder why some folks do OK with 107LSA and others do not. Knowledge, experience and skill levels vary considerably, just a fact of life with this sort of thing. What some folks get away with others can not. It's been like this for over 4 decades for me, and you'd certainly think with all the great information out there these days that folks wouldn't be having these sort of issues with this stuff....FWIW......Cliff

[pastry_chef]

Originally Posted by PAUL K

If a combination is built wrong is it fair to blame one part?

This chit isn't that hard!

Low nine second car with a little nitrous...note how quiet the car is and none of the starting line personal needed oxygen due to the stinky smell idle;

https://youtu.be/3LJ-0iRjMsI

Same car making a ten second naturally aspirated pass...note 800 rpm idle with a nice choppy lope ..cam has a completely undriveable 105 LSA. Still none of the starting crew needs oxygen due to us making multiple passes;

https://youtu.be/kk1-oVZED48

Mid ten second pump gas car with dreaded 108° LSA camshaft... note person holding camara gasping for oxygen and nearly passing out from the stinky idle smell;

https://youtu.be/PhDicneJIXs

The last car ran 10 flat at the Pontiac Nationals in Norwalk this past summer....so I know we can eliminate anything funny going on in Ohio causing these cars not to idle.

I know Steve C has run in the ten's with a pump gas stock block combination using a 108° LSA cam and lived to tell about it. Also another board member has ran mid nines with a pump gas aftermarket block combination that I believe uses a 110 LSA camshaft.

Awesome post Paul, 1000%

[Steve C.]

I've had three engine combinations with a 108 LSA. Starting years ago by the recommendation of Harold Brookshire at UltraDyne.

Two NMCA national records and winner at the Pontiac Southern Nationals three times... no oxygen masks. But seriously no matter what cam my wife says our garage stinks awhile after I park it


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