MiguelsC2

I am not happy with my cam selection.

Here are my motor specs.

327 .30 over
10.5 to 1 TRW flattops
461 heads 2.02-1.60 valves untouched ports
461 intake 600cfm DP
2 1/2 inch cast manifolds exiting through a CCentral N-11 exhaust sytem
M-20 wide ratio 2.56 1st gear transmision
3.36 posi
Pertronix II ignition
Aluminum flywheel

It's a Comp Cams "***** Thumpa" Yes, I combined a lack of camshaft knowledge and a need to do something different.

In previous motors I used factory grinds. So I never got off the beaten path.

Polutes,idles at 900-1000 rpms the rough idle doesn't even come with a performance gain. Quite the opposite. If you look at the specs, you will see why.

http://www.compcams.com/Company/CC/c...?csid=108&sb=0

I could not have made a poorer choice for my combo. I fell prey to marketing hype.
This is not a statement against Comp cams. Just my poor choice.

I have a 30-30 camshaft on the shelf. But I am not ready to install it. When I do that I want to pull the motor. Install windage tray,pocket port the heads and do some port matching. And a few other things.

For now I want to install a cam that can use the valve springs currently installed.

That limits me to the L-79 cam or a similar after market unit. If not the L-79 grind, I will probably go with another Comp cam.

I used their Camquest6 software. On that software the ****** %^&&er showed really poor. I can attest that it is.

The following is what I am now considering. I used Camquest6 as a guide.

http://www.compcams.com/Company/CC/c...?csid=111&sb=0

http://www.compcams.com/Company/CC/c...?csid=110&sb=0

http://www.compcams.com/Company/CC/c...x?csid=79&sb=0

http://www.compcams.com/Company/CC/c...x?csid=87&sb=0

http://www.compcams.com/Company/CC/c...px?csid=2&sb=0


Please don't let this turn into a brand bashing thread.

I am open to all suggestions that keep me from changing springs or exceeding lift clearances.

I am sure others are in the same boat as I.

I am looking for an education from the brain trust here.

MiguelsC2

Hey it doesn't have to be the brain trust. A brain fart will do.

MasterDave

I have had 7 different cams in my 64 sb and while they all thumped and bumped, I was not able to get the engine to run clean until at a higher rpm level and I had to constantly blip the throttle to keep from loading up. I've had 3 comp cams, a 270, 280 and 290 and while they sounded great they did not perform well as I said above. I had two different grinds from Summit also and a couple others that I don't remember right now. All that being said, the cam I have in it right now is absolutely perfect. It is a hydraulic flat tappet, Isky 270/280 Megacam. It idles at 650 rpm with a slightly rough idle, strong enough to let people know what's there. It has never loaded up or fouled a plug in the 3 years it's been in. I can pull away at an idle with no goosing of the gas pedal and it rips to over 6000 rpm with no issues. I do have iron Sportsman II heads on it with 202/190 valves. Lots of rodders have used this cam and are very happy with it.

Scott Marzahl

It will be hard to beat the L-79 ('151') cam with your configuration, gearing, heads, intake and exhaust and it loves 10.5:1 and up compression. It has the 114 LSA so it works with stock exhaust manifolds. If you were running headers maybe I would consider a aftermarket hot rod cam but not in this case.

MiguelsC2

Thats pretty much my line of thinking. I know I need to stay away from dual profile durations using cast iron manifolds.

Doesn't speed pro or federal mogul make a replacement L-79 cam?

StingU2

Call up Ron Iskenderian direct @ Isky cams, and ask him what to use.

jimh_1962

comp cams makes a nestolgia L-79 cam. Summit sells it.

Scott Marzahl

@ 1sttexan Yes, Speed Pro makes a replacement L-79 cam (CS-179R). I just picked a new one from Northern Auto for $79. Your other option would be a Crane Cams blueprint series of the L79 cam.

MiguelsC2

Not a bad idea. Certainly a trusted source. I didn't know the family still ran the biz.

MiguelsC2

After more research,I think the choice is obvious. I am going with the L-79 stick.

There just not many that will do better with my drivetrain combo.

Sealed Power L79 (CS179R) with true GM specs,

Northern Auto has it for $60. $128 with lifters delivered.

I am tired of screwing around. Seems that comp cams screws with the factory specs only hurting perf.

I get tired of reving the motor at the light all the time. Bad form.

tach drive 61

I just used the sealed power 151 grind 327 stock bore and lower compression pistons ,double hump heads , as far as idle goes 800/950 best i can get from my setup ! 340 alum intake and a 3269s carter on top !

MikeM

If you'd be happy with the L 79 cam, you might be happier with the old 097 cam if you want solid lifters and a 1000 more rpm. Uses stock springs and will pull from 1000 rpm up without bucking and jerking and has a nice bumpity bump idle.

I like both those cams.

robert miller

Call comp cams in Memphis TN tell them what you have and what you are looking for. I have almost the same cam as the stock 365 hp but more in lower rpm range and went to hyd roller cam in it. These cars in stock motors not really that bad any more with the 383 are a good 400 small block with a good set of heads on it.

jkuzzy

I have almost the identical setup as you except that I have Edelbrock aluminum heads, roller rockers, long tube headers and I am .060 over.
When I rebuilt my motor, I pulled the cam and got the specs. I believe it was an Isky. I called up Comp Cams and gave them the info and told them that I wanted a little bit more, but not too much. He told me that he had just the ticket. I bought the 12-238-2 cam. It has a 110 LSA, 218/224 duration at .050 and it pulls like a mother. The driveability is very normal and that is exactly what I wanted. I get compliments all of the time.

rayvaflav

Very timely discussion for me as I am planning on building a 327, 9.6:1, 2.02/1.60 462 heads, either 2.5 rams horns of the 2.75 Hooker Super Competition shorty headers through side exhaust, an OEM 490 intake with 3367 Holley. I am planning on using the L79 cam but I keep thinking: I am sure that in the last 45 years there must be some better camshaft technology ... Thoughts ?

Ray

427Hotrod

Overlap is what you have to watch. A dual patten cam isn't all bad...IF it's selected properly and matches the whole combo. There are also some cams that just work great even if they don't *look* right on paper. The old LT-1 cam does well and is as simple as you can get.

The Crower #350 circle track cam does a LOT better on the street than the numbers would lead you to believe. It has a 107 LSA..but it's a solid cam with 238/244@.050"..but look at the advertised numbers...they are only 268/274 and lift is only .497"/.503". We've used it in everything from near stock 327's to 383's and it does great. It has fast acting lobes and a short advertised duration which really helps low speed manners. It has a sweet little lope to it and we routinely use it with 3.36 range gears. It will rev to the moon if you want it to also.

The 400" we built for Devildog here on the Forum is using a solid roller..but you might ck out the article I did on it. I was able to spend a LOT of time with Comps head designer going over all the various scenarios of manfolds and heads and I tried to condense his thoughts into the article. Might help a little.

Starts on page 77.

http://editions.amospublishing.com/K...01&pagenum=&f=


JIM

MiguelsC2

Thanks for taking the time. My current cam is a .490 lift and 287/305 duration.107 LCA and 102 intake centerline. I think it is a real pronlem with my cast exhaust.

The other specs are outside my current knowledge. I couldn't tell you what they mean.

Would the cam you mention cause piston valve clearance issues? And maybe a spring change?

For now I am trying to avoid going any further than R&R the cam and lifters.

Down the road I am going to pull the motor and do other things.

MikeM mentioned the 097 cam. I think I need to explore that. From what I gather the 30-30 and the LT-1 will require spring changes. I would prefer a solid lifter cam.

My current springs are the correct spec for the L-79. I think 375lbs? Thats what the Comp site says.

Below are my current spring specs. What kinda cam can I get away with?

http://www.compperformancegroupstore...gory_Code=HFTT

427Hotrod

The Thumper line of cams aren't all bad...but you just have to use them for what they are intended. They get the sound by having a huge exhaust duration number that opens the exhaust valve earlier as the piston is descending. Since the pressure is higher at the earlier opening point you get a nice *pop* out of the exhaust pipe.

They also have a tighter lobe separation angle...107* in your case that causes the intake to open and close earlier and the exhaust to open and close later as compared to a cam with say a 110* LSA. The tight LSA combined with the big exhaust lobe creates a lot of overlap when both the intake and exhaust valves are open at the same time. That's what gets you in trouble with stock ex. manifolds and low RPM cruising as well as idle. You get tons of dilution of the intake mixture as exhaust will push back into the intake manifold during overlap. Makes a cool *lope* sound...and sometimes helps pump up midrange power.

For example..you might see *nitrous* cams listed. They use huge exhaust durations to allow some of the extra exhaust volume out. They will often make less power without the juice..because of the earlier opening exhaust valve taking TQ away...but they do well at WOT with the N20 on. They also usually use a wider LSA...like maybe a 112-114 or so that reduces the overlap that the big exhaust lobe caused. It's all a juggle game!

Just using the Crower cam as a sample...even if it was a hydraulic cam it would have 19* less intake duration and 31* less exhaust duration with the same 107* LSA. You can see that is HUGE effect on overlap. Now you have to compare solid and hyd cams differently due to the valve lash ramps, so the solid is actually even smaller than these numbers imply as far as street manners are concerned.

I hate to tell folks the cam will clear everything, but if the Thumper wasn't hitting anything..then no way this one would. I always ck anyway, but that Crower clears factory 11.0 pistons in a 327 and flat tops in a 383 with plenty of room. The lift at the valve will be .480" range or so so it should be good with what you have. I know te Crower and the LT-1 are very forgiving on valvesprings, but you need to verify what you have for sure..especially with flat tappets. What springs are actually on it??

JIM

MiguelsC2

Jim, great info. I installed the thumper as a kit. Check the link at the bottom of post 17 the spring specs are listed there.

MikeM

I mentioned the L 79 cam and the 097 cam because I thought you had stock valve springs. The stock Chevy valve springs only have about 80 lbs. seat pressure. They work fine for the L 79, Lt-1, 097 and the 30-30 cam. They WON'T work for some of these aftermarket fast ramp, high lift cams.

Some of these same cams also won't work well with cast iron manifolds as you may have discovered.

But, they also won't wear your cam/lifters out prematurely and the camshafts they support will work with the cast iron manifolds and still give good power. That's what they were designed to do.

I keep hearing about "modern" camshaft designs. I suspect the only thing "modern" aobut them is maybe the specs have changed to compliment much better flowing heads than what was available 50 years ago. If you're still using 60 year old stock heads, I'd think there's little to be gained by going after market camshaft unless you want to spend a lot of money. Worthwhile if you like dyno numbers. Pretty much worthless on the street.

JMO