Cam selection input for 396 please - Impala Tech
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post #1 of 11 (permalink) Old 01-28-2011, 09:34 AM Thread Starter
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Cam selection input for 396 please

Guys,
I need some advice on cam choice for my 68 and apologize up front for the length of this. First, some background (pics of the build in my album if it helps). It is a numbers matching 396 car and I decided to complete the restoration and add some performance at the same time. Basically, we took it off the frame and I portioned out the work, and then put it back together. I did the frame and suspension work while my friend, who has a successful shop, did the power train and electrical system. I left the decisions to him regarding what to use and overall, I am happy with it; however, the choice of cam is not to my taste and I would appreciate a recommendation for a more suitable cam.

Unfortunately, by the time it was completed I had to drive it 500 miles to put it in storage because I took a job overseas, where I am now. It is stored with a relative currently, so I have some time to do the research before I have someone do the swap.

Specs:
Original 396/325
The block was decked without removing the numbers and bored .030. It received a stroker kit (4.00) with H-beam rods, Keith Black pistons.
Heads got extensive port matching work and new larger SS valves cut to unshroud. Basic stock aluminum intake and electronic ignition.
Original TH400 was built but remains essentially stock feeling and the torque converter stalls at 2800. Stock posi unit 12 bolt (2.73) was rebuilt.
I am sure some of you are wondering why someone would spend the cash to do this, but keep in mind; I want enhanced performance without making the car look overly modified. I attempted to use the original carb, which I built for the refurbished engine, but was unable to use due to the cam (would not idle. It now has a Holley 750 DP, which is likely still too small but was on hand at the time.

Now, the issue. The cam chosen was the COMP CAMS Mutha Thumpr Roller(yes, the biggest – with 319 degrees exhaust duration and 107 lobe separation. I had never heard of it till I picked then car up and by then, I had no time to change anything out. Although the car drives well, I don’t like the way that the power does not appear till 3K and it does not take advantage of the torque of a long stroke. I am also concerned that it could accelerate valve train wear and I actually plan on driving the car when I get back. Bottom line is I would like a modern roller cam that wakes that big car up. I think torque is better in a big car than horsepower and I really don’t care too much about how it sounds.

The first cams that come to mind for me is the Lunati Voodoo and the COMP 272H, but I have not been a cam scholar for at least 2 decades and will gladly defer to someone who has been dealing with cam selection during that time. What do you think the best cam/TC would be?

Thanks,

Throck

68 Impala Sportsroof w/ numbers matching 396/TH400/12 bolt - 53K miles

Last edited by Throck; 01-28-2011 at 09:45 AM. Reason: Add picture reference
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post #2 of 11 (permalink) Old 01-28-2011, 03:34 PM
BA.
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I see you Throck! It may have been 2+ decades for you but I can see in your post that you still know what's important.

I agree with you that the Mutha Thumpa is too big for what you're trying to do, and also agree that something more like a 270-280 is in order. I'd pay closer attention to the Duration spec at the .050" lift though. it's more telling in where it will build power/torque for you.

That extra stroke you got should put you at around 427 inches, right?
I'm not a big-block expert and I do think you're on track, but I'm going to say something that has 222 - 234 of that net duration @ .050" is your target area.

Have you thought about what RPM limit you expect from the engine & valvetrain?
Any plans on bring the rear gear ratio up a little?

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
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post #3 of 11 (permalink) Old 01-28-2011, 06:00 PM
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I agree with Allan on toning it down. The Lunati VooDoo and the Thumper cam add extra duration on the exhaust side so that their "cam sound" shows up without hurting your engines bottom and midrange power "as much" as a non-split duration cam would. An added plus is the BBC is exhaust inhibited with a relatively small port bent at 90 degrees exiting more down than out. So the added exhaust duration actually helps get the spent gasses out of the motor to make room for a fresh charge.

I would look to mud puller, jet boats and short track roundy round cams as well as the drag race page for a better selection of cams. You still can not beat an RV cam with a lot of lift for the street.

Big Dave

Last edited by Big Dave; 01-28-2011 at 09:56 PM. Reason: Spleling
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post #4 of 11 (permalink) Old 01-28-2011, 09:02 PM
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I have a basic stock standard bore rebuild on my 402 (396 with a little off the sides) and I'm running a 515* lift @ .050 with a 224 duration; that is not the "advertised" dur. Along with a 750 Holley and around 34*-36* timing it's a nice ride with a little hint of the cam talking back at you. Advertised power range is 1600-5800. Big cars need the grunt on the low end to move 3800 + lbs. Keep us posted.
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post #5 of 11 (permalink) Old 01-28-2011, 09:55 PM Thread Starter
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Thanks for all the input. It does confirm my suspicions. Like I said earlier, I have not bought a cam in a long time and now that rollers are added to the selection, its all new again for me. I plan to swap gear and find a set of headers that work later on, but for now the cam is my main concern. I am a sucker for acceleration and this engine has way too much work to lag in that area as badly as it does because of the cam. All the power is too high in the RPM band for me. Any brand recommendations to seek out or suggestions to avoid? Thanks again.

Throck

68 Impala Sportsroof w/ numbers matching 396/TH400/12 bolt - 53K miles
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post #6 of 11 (permalink) Old 01-28-2011, 10:16 PM
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Forgot to mention this is for flat tappet cams, but you probably figured that out .
I like the Comp. cams or Wolverine- I cant remember who makes them - which gave me no issues but I may be a little biased.
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post #7 of 11 (permalink) Old 01-28-2011, 10:52 PM
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CompCams, Crane Cams, Iskiderian Cams, Howard Cams, all grind their own cams from their own Lobe Profile collection (the Lobe Profiles are huge wodden hand carved templates 24 to 32 inches tall and the cam grinding wheel follows a pantograph type device to grind the lobe profile onto the cam core). Crane prior to going belly up last year had a contract with GM (before it went belly up) to sell them all of the cams, springs, retainers and roller rockers that GMPP had branded as Chevy parts. I believe CompCams has moved in on Crane's old turff now. Of course the profiles are only used for custom cams and most are ground on computer controlled machines now to turn out a more consistent product at a lower cost.

I do not know who grinds Lunati's cams or cranks. I have suspected in the past that Lunati, which is part of Colt Industries, bought their products, then relabled them; but I do not know. Colt is wallowing in cash thanks to arm sales to the US government over the past few wars and can afford to manufacture anything they want to make.

I have been very happy with Lunati products and have had good luck with them. Better than I have had with CompCams products of late; which was resting on their laurels a little too long in my opinon with out improving their product's quality. (same thing happened to Crane Cams after Harvey Crane sold off his business, and I soon left them to buy Comp Cams stuff). I have always liked Isky cams, but other companies often offered a similar product for less money (even though they sometimes copied Isky or Harvey Crane to bring a product to market, just as they now seem to be copying some of U. D. Harold's inventive cam designs). That being said CompCams has the largest cam catalog on the planet and will have a grind that you will like lurking some where in their catalog.

They also offer a cam picker software package you can down load for free. It is a disabled version of Desktop Dyno 2000 software that also includes their entire cam library (something they sell for $49 bucks). This software will allow you to play "what if" with your motor and any cam and all of the cams in the CompCams catalog (it is hours of fun). Just do not believe their overly optimistic horsepower calculation unless you can input your heads flow numbers (Super Chevy or Chevy High Performance magazine has a flow bench library listing all of the common factory and aftermarket heads that where tested on a West Tech flow bench by the same technician). The numbers are accurate between iterations (how it affects the engines power between trials) and can be believed as to the difference a cam swap will make and where on the torque curve it happens.

Big Dave
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post #8 of 11 (permalink) Old 01-29-2011, 12:26 AM Thread Starter
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Thanks again for the input. I have been lurking though the internet and (using your recommendations and specs) found that Mr. Harold apparently works at Lunati now and they are the fortunate beneficiary of his skills. http://www.chevelles.com/forums/showthread.php?t=17562
After reading his thread, I looked at Lunati's line up and think that the 60211 http://www.lunatipower.com/Product.aspx?id=2154&gid=289 or 60210 might be what I am looking for. I will cal the tech line on Monday to see what they think.

The engine has about 700 miles since the build. Will it be OK to use the roller lifters that were installed with the current cam?

68 Impala Sportsroof w/ numbers matching 396/TH400/12 bolt - 53K miles
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post #9 of 11 (permalink) Old 01-29-2011, 08:58 AM
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Yes that is one of the plusses of a roller lifter. If you want to change a cam the bump stick is all you buy so long as your springs can maintain control. With a flat tappet cam you have to buy lifters as well with every cam swap. That is a great street cam just be sure to install it straight up as it already has six degrees of advance built into the cam for more bottom end when it was ground. I personally prefer a solid lifter as Isky has solved the reliability issue with a solid roller on the street with it's internal oiling. Prior to Ed Iskiderian's Red Lines you got no oiling at low RPM such as idling, as all tappets flat and roller relly upon splash lubrication for oiling unless there is a hole drilled in the bottom of a flat tappet or an oiling groove cut into the lifter body to divert oil to the roller (and lower oil volume and pressure on most stock blocks) to squirt oil from the side feed. On a priority feed block such as the Generation V and VI big block blocks, and all aftermnarket blocks) where the mains and rods are fed oil first before the remaining oil is diverted to feed the lifter galleries: this is a non-issue.

Big Dave

Last edited by Big Dave; 01-29-2011 at 09:18 AM.
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post #10 of 11 (permalink) Old 01-31-2011, 02:19 AM Thread Starter
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Quote:
Originally Posted by 68imp View Post
I have a basic stock standard bore rebuild on my 402 (396 with a little off the sides) and I'm running a 515* lift @ .050 with a 224 duration; that is not the "advertised" dur. Along with a 750 Holley and around 34*-36* timing it's a nice ride with a little hint of the cam talking back at you. Advertised power range is 1600-5800. Big cars need the grunt on the low end to move 3800 + lbs. Keep us posted.
Thats pretty much what I am looking for. I don't want a race car, but it would be nice to hear that old big chevy talk junk and light 'em up once in a while.

68 Impala Sportsroof w/ numbers matching 396/TH400/12 bolt - 53K miles
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post #11 of 11 (permalink) Old 01-31-2011, 02:33 AM Thread Starter
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Quote:
Originally Posted by BA. View Post
I see you Throck! It may have been 2+ decades for you but I can see in your post that you still know what's important.

I agree with you that the Mutha Thumpa is too big for what you're trying to do, and also agree that something more like a 270-280 is in order. I'd pay closer attention to the Duration spec at the .050" lift though. it's more telling in where it will build power/torque for you.

That extra stroke you got should put you at around 427 inches, right?
I'm not a big-block expert and I do think you're on track, but I'm going to say something that has 222 - 234 of that net duration @ .050" is your target area.

Have you thought about what RPM limit you expect from the engine & valvetrain?
Any plans on bring the rear gear ratio up a little?
Allan,
I (based on you guys' sage input) will go with the Lunati (P/N 60210). Sounds like it has just what I am looking for. The valve train was built very well, and in the limited driving that I have done since completion, it really handles high RPM well, but - I don't see the need for much more than 5500 so I think I am OK in that regard. I don't have the receipts with me so I cannot say exactly whats in the heads from memory, but there is a pretty good picture in my album here if you want to look. With regard to the rear end, I do plan to go with a 3 or 4 series carrier later and maybe ever get a set of headers that work.
Thanks again for all the input.

68 Impala Sportsroof w/ numbers matching 396/TH400/12 bolt - 53K miles
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