Thumpr cams-talk to me

[groucho]

On a basically stock 350 SBC, has anyone used a Thumpr cam? How lumpy IS the idle? And does it not affect low RPM power as claimed? Torque converter change needed? Discuss. THX

[Scott Liggett]

On a basically stock 350 SBC, has anyone used a Thumpr cam? How lumpy IS the idle? And does it not affect low RPM power as claimed? Torque converter change needed? Discuss. THX

Not sure if it kills cylinder pressure, where as the Xtreme Energy cams are designed to build it. I suppose they sound like the old Erson cams, all duration and no lift. Sounded great, had shit for bottom/ mid range torque. But, knowing Comp, they designed a much better cam.

Stall convertor necessity will depend on how far down the page you pick the cam. Anything over 230 duration @ .050 will need a 2000 to 2200 convertor.

[Monk]

Wasn't this cam developed for the crowd who wanted an engine
to sound like it had a lot of balls.......without doing all the internal mods?

I have read some posts on other car forums of guys having to switch out
converters........some saying Comp Cam should have had this noted before install.

[oletrux4evr]

You might talk with Comp Cams........

http://www.compcams.com/tech-help/Support.aspx

[groucho]

Comp Cam's gonna ring their own bell. I want outside intel. Personally, after looking at the numbers on 2 I looked at, I'd advise my customer against it. He says the 350 now has a 327/350HP cam. I told him, leave it. Some "king of the drive in" sounding cam's not gonna be as responsive down low as the cam in it now from the numbers I've seen (one's 235 In/249 Ex @ .050!)

You might talk with Comp Cams........
http://www.compcams.com/tech-help/Support.aspx

[Deaf Bob]

Comp Cam's gonna ring their own bell. I want outside intel. Personally, after looking at the numbers on 2 I looked at, I'd advise my customer against it. He says the 350 now has a 327/350HP cam. I told him, leave it. Some "king of the drive in" sounding cam's not gonna be as responsive down low as the cam in it now from the numbers I've seen (one's 235 In/249 Ex @ .050!)

Close to my 327 cam in my 57.. I'd leave it.. I did.. With 3:31 rear, it really performs.. Even outruns big blocks on occasion, I run a Muncie..

[SuperBuickGuy]

hmmm.... sounds like I'm the only on running their Thumpr cam.

1) stall depends on which cam you buy (there's like 5). I have a 4 speed, so I couldn't care less. That said, the first itineration of this set up was with a turbo 350 and 2400 stall.... it sucked, it was like a light switch, and idling down the freeway, it wouldn't make enough pressure (tc) to keep it in 3rd gear... now my problem is keeping clutches in the car.
2) I have the next-to bottom of the page cam. stock 4 bolt main truck 350 with Vortec heads, air gap intake, CR is 10.5:1 and it sounds excellent
3) It's an 108 centerline cam, you expect cadillac torque? I honestly don't think it gives up that much bottom end, but oh good heavens, when it hits 2800 rpm, hang onto your girdle, it'll pull your panties right off all the way up to redline. It also kills vacuum, I think on its best day it might make 9 inches.
4) Everyone, and I mean everyone, gets that stupid grin on their face when they hear it run.

I like the cam, even with the 3:08 gears in my Corvette (3100 lbs)....

[BigAL]

They tighten up the LSA on those cams to give them a more pronounced lope at idle.

As for killing cylinder pressure, that's not going to happen, it's going to "increase" cylinder pressure and create more midrange torque.

[Deaf Bob]

Nothing against the Thumper.. Just that the cam in it is close to perfect.. Might not like what hapens when the cam changes..
Aaron, you built your Vette as a package.. If you were to just put in another cam that is not dialed into what you got, I'm sure it will be a dog, as you say, 4 speeds don't care as much as autos seem to..
We need to remember the car in question is an auto... Otherwise Groucho'd not be concerned with stall..

[NewEnglandRaceFan]

it's for the guys that want the sound without the power and parts cost.. it's an "all hat no cattle" cam line,, for the most part.. They make power, but leave a ton on the table.. There is a ton of people that don't need a 400hp+ engine, but want the sound of it.. and comp said, sure we'll take your money

[groucho]

So far I've only seen 2 Thumpr cams for the SBC. You have a better combo by far (air gap, 10-5, Vortec heads, air gap) for the cam than my customer

hmmm.... sounds like I'm the only on running their Thumpr cam.

1) stall depends on which cam you buy (there's like 5). I have a 4 speed, so I couldn't care less. That said, the first itineration of this set up was with a turbo 350 and 2400 stall.... it sucked, it was like a light switch, and idling down the freeway, it wouldn't make enough pressure (tc) to keep it in 3rd gear... now my problem is keeping clutches in the car.
2) I have the next-to bottom of the page cam. stock 4 bolt main truck 350 with Vortec heads, air gap intake, CR is 10.5:1 and it sounds excellent
3) It's an 108 centerline cam, you expect cadillac torque? I honestly don't think it gives up that much bottom end, but oh good heavens, when it hits 2800 rpm, hang onto your girdle, it'll pull your panties right off all the way up to redline. It also kills vacuum, I think on its best day it might make 9 inches.
4) Everyone, and I mean everyone, gets that stupid grin on their face when they hear it run.

I like the cam, even with the 3:08 gears in my Corvette (3100 lbs)....

[groucho]

This has been my thoughts since that line was introduced (hopes of something for nothing), way before this customer. I told him if it's just a cam change he wants, expect nothing more than the idle you want and less snap down at the bottom

it's for the guys that want the sound without the power and parts cost.. it's an "all hat no cattle" cam line,, for the most part.. They make power, but leave a ton on the table.. There is a ton of people that don't need a 400hp+ engine, but want the sound of it.. and comp said, sure we'll take your money

[Deaf Bob]

it's for the guys that want the sound without the power and parts cost.. it's an "all hat no cattle" cam line,, for the most part.. They make power, but leave a ton on the table.. There is a ton of people that don't need a 400hp+ engine, but want the sound of it.. and comp said, sure we'll take your money

I know of, personally, 2 thumper cammed cars (not counting SBG's as I never felt it run) one was put together with the right stuff and was a very decent car..Great if you wanna say.. The other was not as well packaged, but it still performed well.. Not great like the first..

[Scott Liggett]

They tighten up the LSA on those cams to give them a more pronounced lope at idle.

As for killing cylinder pressure, that's not going to happen, it's going to "increase" cylinder pressure and create more midrange torque.

Forgive me if I am wrong. But, long duration and closing up the lobe separation increases the time both the intake and exhaust valves are open at the same time. Which would bleed off cylinder pressure in the low rpms. It will also require a richer idle mixture because half of the raw gas will be leaving the exhaust valve before it gets burned. Now, some of the cylinder pressure can be returned by very fast opening and closing ramps on the cam lobe, which on a flat tappet is very limited.

[ImpalaSam]

Isn't the cylinder pressure dictated mostly by the intake closing point? Overlap would be affecting
the intake opening, correct? I see where this would have an effect on the idle but wouldn't it have
less on the cylinder pressure? ( lots of question marks here)