Comp Cams "Thumpr" cam?
Thread Starter
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
Comp Cams "Thumpr" cam?
Anyone tried one of the Comp Cams new "Thumpr" cams? I'm rebuilding my 71' base 350 and thought I might try something different. Plus I like the lumpy idle sound.
Drifting
Joined: Mar 2006
Posts: 1,526
Likes: 2
From: Oak Ridge NC
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Looking at the specs you can do a lot better for performance. But if you want a stockish motor to sound really built and optimum performance and economy isn't an issue go for it.
Melting Slicks
Joined: Mar 2006
Posts: 2,465
Likes: 0
From: Orange Park Fl
Different strokes for different folks: I like to look and sound as stock as possible, and watch their jaw drop when the hammer goes down. If you want to sound fast and be slow, I guess that's cool too , but I just don't get it. God bless, Sensei
, but I just don't get it. God bless, Sensei
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
If you're running OE '71 heads ... suggest at minimum flattop pistons (-5cc) & FelPro p/n 1094 gaskets ... or small-dome Sealed Power p/n H618CP pistons (+3.5cc).
Racer
Joined: Feb 2001
Posts: 405
Likes: 15
From: Minneapolis
Jackson is spot on. If you drop a long duration cam into an otherwise stock motor, you'll take a step backward in the power dept.
For that lumpy idle sound, screw your idle jets out of whack. That'll give you a random miss at idle, while still maintaining your current WOT power.
For that lumpy idle sound, screw your idle jets out of whack. That'll give you a random miss at idle, while still maintaining your current WOT power.
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Instructor
Joined: Jul 2007
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... I'll soon find out ...
My 427/390 is nearing completion of it's 2nd rebuild in 21 years... can't complain about that. Last rebuild was stock. This time we're going for stock appearance but a bit more fun. Nothing radical and don't intend to race it, just wanted to treat it to a few benefits of modern bits.
So, we went with Edelbrock Performer RPM aluminum heads, a 454 crank, and the milder of the 3 Thumpr cams. It will also breath thru Flowmaster mufflers.
Is this the cam that offers the maximum HP or max torque... probably not. But that's not the intent of this build. This is a street car. For that reason I'm OK with running the stock pancake intake and exh manifolds, too. The guy building the engine has been doing BBC's for 3 decades and knows his stuff. He feels this combination will provide me a near stock look (painting the alum heads), great attitude and sound, and more than enough torque to keep me smiling.
Will post in a month or so when I've turned some gasoline into noise.
So, we went with Edelbrock Performer RPM aluminum heads, a 454 crank, and the milder of the 3 Thumpr cams. It will also breath thru Flowmaster mufflers.
Is this the cam that offers the maximum HP or max torque... probably not. But that's not the intent of this build. This is a street car. For that reason I'm OK with running the stock pancake intake and exh manifolds, too. The guy building the engine has been doing BBC's for 3 decades and knows his stuff. He feels this combination will provide me a near stock look (painting the alum heads), great attitude and sound, and more than enough torque to keep me smiling.
Will post in a month or so when I've turned some gasoline into noise.
Le Mans Master
Joined: Apr 2005
Posts: 6,350
Likes: 423
From: Seattle Area WA
As long as you are at 9:1-9.5:1, otherwise IMHO, I think its too big for an approximate 8.2:1 stock rebuilt motor.
The XE250 would provide a better DCR of 7.4 with a 1094 head gasket and better throttle response.
The XE262 only provides you with 7.0.
As Jackson said, use some better pistons and/or heads if you want to use the XE262. Comp says to use at least 9.25 with that cam.
Here is some Comp propaganda:
http://www.compcams.com/Technical/DynoSheets/
The XE250 would provide a better DCR of 7.4 with a 1094 head gasket and better throttle response.
The XE262 only provides you with 7.0.
As Jackson said, use some better pistons and/or heads if you want to use the XE262. Comp says to use at least 9.25 with that cam.
Here is some Comp propaganda:
http://www.compcams.com/Technical/DynoSheets/
Last edited by Scott Marzahl; Mar 6, 2008 at 06:42 PM.
Thread Starter
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
As long as you are at 9:1-9.5:1, otherwise IMHO, I think its too big for an approximate 8.2:1 stock rebuilt motor.
The XE250 would provide a better DCR of 7.4 with a 1094 head gasket and better throttle response.
The XE262 only provides you with 7.0.
As Jackson said, use some better pistons and/or heads if you want to use the XE262. Comp says to use at least 9.25 with that cam.
Here is some Comp propaganda:
http://www.compcams.com/Technical/DynoSheets/
The XE250 would provide a better DCR of 7.4 with a 1094 head gasket and better throttle response.
The XE262 only provides you with 7.0.
As Jackson said, use some better pistons and/or heads if you want to use the XE262. Comp says to use at least 9.25 with that cam.
Here is some Comp propaganda:
http://www.compcams.com/Technical/DynoSheets/
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
-edit- corrected for chamfer & land volume.
Last edited by jackson; Mar 6, 2008 at 09:17 PM.
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
My 427/390 is nearing completion of it's 2nd rebuild in 21 years... can't complain about that. Last rebuild was stock. This time we're going for stock appearance but a bit more fun. Nothing radical and don't intend to race it, just wanted to treat it to a few benefits of modern bits.
So, we went with Edelbrock Performer RPM aluminum heads, a 454 crank, and the milder of the 3 Thumpr cams. It will also breath thru Flowmaster mufflers.
Is this the cam that offers the maximum HP or max torque... probably not. But that's not the intent of this build. This is a street car. For that reason I'm OK with running the stock pancake intake and exh manifolds, too. The guy building the engine has been doing BBC's for 3 decades and knows his stuff. He feels this combination will provide me a near stock look (painting the alum heads), great attitude and sound, and more than enough torque to keep me smiling.
Will post in a month or so when I've turned some gasoline into noise.
So, we went with Edelbrock Performer RPM aluminum heads, a 454 crank, and the milder of the 3 Thumpr cams. It will also breath thru Flowmaster mufflers.
Is this the cam that offers the maximum HP or max torque... probably not. But that's not the intent of this build. This is a street car. For that reason I'm OK with running the stock pancake intake and exh manifolds, too. The guy building the engine has been doing BBC's for 3 decades and knows his stuff. He feels this combination will provide me a near stock look (painting the alum heads), great attitude and sound, and more than enough torque to keep me smiling.
Will post in a month or so when I've turned some gasoline into noise.
A tight LSA gives you more overlap for a given cam size. The good part about overlap is that the exhaust gas
on the way out of the cylinder will actually help to draw intake gasses into the cylinder.
With a poor flowing exhaust you just end up with a lot of exhaust gas dilution still in the cylinder on the compresion stroke.
It may work for you with a smallish cam like that, but its certainly far from optimal.
Instructor
Joined: Jul 2007
Posts: 108
Likes: 0
Thanks again>>>>>>>>>
Thread Starter
Le Mans Master
Joined: Mar 2001
Posts: 6,640
Likes: 287
From: Ann Arbor Michigan
I hope it makes you happy, but in general using a cam with tight LSA and a stock exhaust system is bad news.
A tight LSA gives you more overlap for a given cam size. The good part about overlap is that the exhaust gas
on the way out of the cylinder will actually help to draw intake gasses into the cylinder.
With a poor flowing exhaust you just end up with a lot of exhaust gas dilution still in the cylinder on the compresion stroke.
It may work for you with a smallish cam like that, but its certainly far from optimal.
A tight LSA gives you more overlap for a given cam size. The good part about overlap is that the exhaust gas
on the way out of the cylinder will actually help to draw intake gasses into the cylinder.
With a poor flowing exhaust you just end up with a lot of exhaust gas dilution still in the cylinder on the compresion stroke.
It may work for you with a smallish cam like that, but its certainly far from optimal.
