[JSchmitz]

Big cam and insufficient compression ratio was one of my first car lessons. I was 16.

[PAUL K]

Originally Posted by JSchmitz

Big cam and insufficient compression ratio was one of my first car lessons. I was 16.

Yeah that second from the bottom of the page Crane cam didn't work well in my buddies stock 77 Trans Am for us either.

[NeighborsComplaint]

Originally Posted by JSchmitz

Big cam and insufficient compression ratio was one of my first car lessons. I was 16.

My first build (16 y/o) was a 2 bbl, low compression, 390 Ford in a '66 Ford Fairlane. I did a top end only rebuild and got a stock 4V intake and a Holley 735. I had the heads done by Bud Richter's Shop (Remember The Gold-digger Mustang Funny Car?).

I had my head screwed on pretty straight for a 16 y/o and I told Bud I wanted a Ford Police Interceptor cam (forerunner to the 428CJ cam) as my motor was pretty much stock and I had a 3:30 gear.

Bud said these exact words to me: "Son, it ain't even a cam if it hasn't got .500 lift and 300 duration and handed me a Mellings grind he had. It was .512" lift and 300 degrees adv duration. The rest of the specs were Greek to me at the time.

Jeezus, it was horrible. It wouldn't make enough vacuum at idle to keep the power valve closed and would flood and stall constantly driving away from a stop. Absolutely gutless to around 3500rpm and I would shift at 5,000 to keep the crappy cast rods in the block. I replaced it with a 428CJ cam from the Ford dealer and lived happily ever after.

[Tom Vaught]

Unfortunately, That post by Neighbor'sComplaint could be posted by more people than your think. For a street cam, the RA-IV camshaft with the typical 400 cid engine was not a good cam by any means. Pontiac Engineers did some testing on the 455 SD engine with that camshaft (and increased compression ratio) and the engine really liked that camshaft.

The Wolverine 744 camshaft with higher lift was a nice camshaft for the 400 engine.

There was a Wolverine cam that had even more duration vs the RA-IV camshaft at .050 lift and it worked very well in the 455 engine. Steve C and others can post the specs of that cam, I believe.

Tom V.

[JSchmitz]

More's Law: If a little is good, More's better.

[JSchmitz]

Have you ever heard anyone say "This isn't working right. Let's turn it down."? Lol! Hell no! Crank it up!

[Jay S]

Anyone know what compression Pontiac engineers were experimenting with on the SD455 trying to run the 041? I have heard that that wanted the 041, but have never seen efforts to raise the compression to make it work??

Thumper series alway appeared to me to be a parade cam. Not much lift to make serious hp. I seriously consider one for the 427 Chevy W engine with 1.75 rockers. But even with the 1.75s the cam we were looking at barely had .5 lift. On a stock headed lower compression Pontiac, I could see it having its place.

More is better. I here that. Yep, My cam lesson: age 17, 318 Plymouth w/8.5 scr....had a SAE rating of
319/329 232/242 at .050 with a 112 LSA. With TRWs first design efforts bleed down lifter. Lol. Would not idle below 1100rpm. Had to throw water at the back tires and get the rpms up to about 7000 to get any good forward momentum.

[Steve C.]

Not sure how we got from THUMPERS... to Wolverines. But there are some Wolverine cams listed here:

http://www.pontiacpower.org/PontiacCams.htm


.

[Jay S]

So are theses cams folks have said they have tried from the flat tappet thumpr series or the Hyd roller thumpr series? Lift isn’t an issue over on the roller series. The HR version looks like it is capable of pretty good power in the right combo. Maybe not more power, just a different way of making it. It does not look much different than some of the 108 lsa cams we have ran.

[Formulajones]

I've only used the flat tappet series, this was back when they first hit the scene. I don't even recall the roller versions being available until a short time later. At least I don't remember seeing them at that time.

[NeighborsComplaint]

I have no experience with the Comp Thumpr cams but I do like the way they sound. For a street driven car, the idle sound and lowered power band from the tight LC's sounds like fun.

I did run a Comp292 Magnum for a while and thought it was pretty wicked. At that time I had a 3500 stall convertor and it was a pretty impressive drive on the street, not so impressive stopping without any vacuum assist and a rock hard pedal. I made a few "two-foot" emergency stops and decided that was not the cam for me. 244 @.050 flat tappet w. 108 LC's. I see the Thumprs are even tighter 107 LC's so not sure how the vacuum is is with them.

[Steve C.]

On the subject of vaccum assist...

I switched to manual brakes but prior to the change I put a electric vacuum pump behind the fender vent on my TA. It cycled on and off as necessary and it was out of sight. Personally with the unit I had and the full 3-inch exhaust I could not hear it. Now today they make quieter units.


One of many sources:

https://leedbrakes.com/i-23439163-el...it-series.html

You can also use used units off production cars from a junk yard.

.

[Cliff R]

Not mentioned previously but insufficient vacuum for power brakes was one of the biggest complaints we get from folks who went to the Thumper 107LSA cams in their new engine builds. Others noted considerably "reversion", or basically what I call the engine being "choppy" well off idle and often to or past 1500-1800rpms or so.

One guy who called here had one in a 396, stock compression, and 4 speed car and said that it was a serious PITA to get the car moving off idle in certain scenarios without revving the engine up and slipping the clutch a bit. He asked me what cam I'd use and I recommended a Speed Pro grind sold by Northern Auto Parts, Summint and several other vendor:

Part #: CS1139R

RPM Range 2200-5500, Adv Dur 302 intake/304 exhaust, Dur @.050 224 intake/232 exhaust, Valve Lift 527 intake/553 exhaust, Lobe C/L 114.

He questioned the choice and wondered if he was going to loose power, because he actually liked the strong mid-range the Thumper cam provided, which is nothing more than a seat-of-the-pants assessment of cramming all the power into a narrow RPM range.

So he makes the switch, and I get a call shorty afterwards. He was much happier with the Speed Pro cam in every area especially the user friendly part for street driving. He thought the engine "pulled" about the same with either one maybe just a little stronger past 5000rpms with the Speed Pro cam, but it wasn't a place he took the engine often as it's more of a car show/street cruiser full restoration and seldom if ever runs it that hard or raced it........Cliff

[Steve C.]

A Short Time Ago, In A Dyno Facility Not Very Far Away, We Tested Comp Cams' Five Most Popular Small-Block Chevy Cams. Here's How They Stack Up.

The Thumpr series does make pretty impressive power gains.

https://www.hotrod.com/articles/hrdp-0808-comp-cams/


BUT WAIT, wait for it......

Don't believe magazine articles. They are made to sell products, and usually find ways to skew the results. Or they picked the wrong cams to compare !

My response, material offered for general interest only and some conversation

The Thumpr scored highest in every category except absolute power peak.


.

[Formulajones]

The car I linked to earlier that I experimented with thumper cams in was a manual brake car, manual steer etc... a no frills Sprint with a 4 speed. Perfect candidate for stuff like this.

So I really didn't care about vacuum production, matter of fact I don't even remember what it made for vacuum.

However, With a power brake car and a cam like that, it would be pretty safe to assume you're going to need some vacuum assistance for the brake booster. Either an extra storage can, a vacuum pump, or maybe a switch over to hydraboost. That's just how these things go with any camshaft that has a bunch of overlap.