needed cam change in a 496 BBC

[Grumpy]

New hydraulic roller cam in 496 BBC
I generally look over the posts on a couple automotive web-sites just to see if there's interesting threads,pictures and questions, and every once in a while I find I read through a question, find its interesting and I think,
"well what would I do?" "WHAT NEEDS TO BE TESTED, OR CHANGED?"
.
.
.
I generally think it through, write down a few notes and only then...
I read through the posted suggestions,in that thread, and its absolutely amazing how many times I have yelled at a computer screen,
"are you FUC#$%^&* out of your ever loving mind!"
yeah! bad or totally ignorant advice is common, on the internet, and yes I do occasionally find very good and well though out answers and think,
HELL YES! THAT WILL MORE THAN LIKELY WORK OUT WELL!
almost every mechanics tool box needs a few basic measuring tools and supplies

https://www.amazon.com/Claytoon-Set...d=1466872286&sr=8-17&keywords=plastilina+clay

http://www.utrechtart.com/Plastalin...currency=USD&gclid=CN3G75zOw80CFQgaaQodKbgFjA
EXAMPLE

I am going to change the cam for this year because of drivability. I have a Big Mutha Thumpr hyd roller cam in there now, and it runs and sounds awesome. Except for it won't run on anything less than 32 degrees of initial timing which is hell on starters and flexplates. AND it won't run power brakes. Even with a vacuum canister. (i have a 6 inch polished booster) You get about 1 pump. This has to be low buck as possible. It gets horrible gas mileage at 7-8 just driving very lightly, with no fun and that is with an overdrive... I am thinking of changing it out to the largest Lunati Voodoo cam they have, which isn't very big... 241/249@ .050" but it has a whole lot more lift that the Thumpr .625 both intake and exh. My heads are stock 781 castings with 2.19/1.88 valves.........I am also thinking of changing the carb and intake. I have a port matched Victor JR and probably going to change to a RPM Air gap intake and for the street, I am thinking of changing to an 800 Edelbrock for now, for driveability and mileage. I typically run a 850 HP Annular Booster Holley, but I also have a stock 750 double pumper I can put on it as well. I don't want to spend more than $1000 this year on everything, as I am converting to LS, but this would at least get me by this year, and I might be able to drive out of town with it more with this setup, than what I have now. I like to drive 300 miles to one show, and hoping will help on some fuel mileage, and guessing it will run better than the Thumpr even. Some vacuum will me stop better as well.

The rest of the combo is a 700R4 trans with 3200 lockup converter, 3.90 gear, and 28 in tall tires. But will be changing to a 3.42 gear in the near future. Was on my list to do this year, but funds are limited.

Any help is appreciated. Thanks!.

A GOOD WELL THOUGH OUT very BRIEF ANSWER

If you want a nice streetable cam I would go with this one. I seen this cam in a 496 and it was very streetable and a animal.

BBC 454 to 470 CID ?Old School? OEM 049/781 heads to a max of 5700 RPM - Clay Smith Cams
http://www.claysmithcams.com/bbc-454-to-470-cid-old-school-oem-049-781-heads-to-a-max-of-5700-rpm/

after reading through the question, I said to myself, thats an all too common, mix of badly matched and probably badly tuned components it seems obvious to me at least that for a street driven car, that not much thought or testing went into the original engine component selection or matching it to the drive train and gearing, I then read the post above , and thought,
HELL YES THATS A GOOD STEP IN THE RIGHT DIRECTION.
theres no question that youll pull a bit higher peak power numbers with a cam like this one below
http://www.claysmithcams.com/bbc-47...th-afr-290-or-305-heads-to-a-max-of-6000-rpm/

but the reduced plenum vacuum for power brakes crappy gas mileage in daily driving, lack of off idle torque and harder starting all make that less than ideal over MOST of the daily driver ,usable power band

yeah something like this makes far more logical sense with that rear gearing ETC.
http://www.claysmithcams.com/bbc-454-to-470-cid-old-school-oem-049-781-heads-to-a-max-of-5700-rpm/

 

[87vette81big]

I read through Grumpy.
I know how you feel.
I put so much time and energy into DC.
I am burnt out and of course banned .
Offical message sent to me is Pontiac and Hellcats did it.

496 is 100 times better than LS & X.
Watch Wiz get stomped eventually and others.
Wont be my doing or yours.

At this time the only way to Lead is to work on & Build your own. My game plan in 2016,

 

[Grumpy]

just a few bits of related info, concerning cam selection if your building a high performance 496 big block chevy engine for street use, with an automatic transmission.
Comp Cam's Mutha Thumpa cams are designed to give the car a rumbling lopey exhaust sound but not much else, they typically get really crappy mileage and lack power, they get the sound by having a much longer exhaust duration, and typically sacrifice a great deal of the engines plenum vacuum that allows power brakes too work.
designing the cam to have longer duration than the engine, needs to effectively enhance the exhaust sound also hurts engine efficiency
heres a link to the BBC MUTHA THUMPR CAMS
notice they generally have 12-17 degrees of exhaust duration

http://www.compperformancegroupstor...reen=CTGY&Store_Code=CC&Category_Code=THMSBC5

lets compare the largest BBC MUTHA THUMPR CAMS timing specs to a similar roller from the same source designed for max performance
having virtually the same intended power range and intake duration,the longer exhaust timing does something to increase the lope but can reduce performance

both roller cams max out at 6100rpm,
both have about 243 duration @ .050 lift,
both have about .550 lift
but the

thumper cam needs 9.5:1 CR , 2800+ stall, intake, gears, and headers,
opens its exhaust valve 2 degrees earlier at 86 degrees Before Bottom Dead Center
and holds it open 17 degrees longer,
until 53 degrees After Top Dead Center,

while the more common, cam timing listed on the standard cam,
NEEDS 10:1 compression, 3000+ stall, intake, headers, gears.
closes the valve at 36 degrees After Top Dead Center
opens its exhaust valve at 84 degrees Before Bottom Dead Center

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=487&sb=2

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=446&sb=2

play with the effective compression and cam timing


http://garage.grumpysperformance.com/index.php?threads/crowers-valve-timing-charts.4299/


\OK, first fact! the piston can,t compress anything until both valves seat

you might want to read thru these link's carefully
http://victorylibrary.com/mopar/cam-tech-c.htm

http://members.uia.net/pkelley2/DynamicCR.html

http://www.wallaceracing.com/dynamic-cr.php

http://www.projectpontiac.com/ppsite15/compression-ratio-calculator

https://www.uempistons.com/index.ph...=comp2&zenid=1e826335bfac0f356463eabed4958558

there are plenty of well tested BBC 454 -496 combos, that have been repeatedly duplicated, simply because they are well known to produce the desired results.

you don,t need to do more than decide the approximate budget limitations ,and your skill level if your doing the work yourself , and do some research into your options, there's books and links listed in this thread that will provide a great many options and buying several would be a very wise investment
you don,t need to do everything yourself , you just need to know what needs to be done, how it should be done, how to verify its being done correctly!

http://garage.grumpysperformance.com/index.php?threads/another-496bbc.5123/

INVESTING THE TIME AND EFFORT IN PURCHASING AND READING A FEW BOOKS WILL BE VERY COST EFFECTIVE
a couple days of reading and asking detailed questions can save you thousands of dollars, and months of work

JUST FOR GRINS I DID A DD-2000 SOFTWARE DYNO comparing the two cams on a very similar 496 BBC engine and the software predicted up to a 60 ft lb and 50 hp lower result with the thumper cam
RELATED
http://www.airflowresearch.com/engine-masters-winter-2014-265cc-bbc.php

 

[Indycars]

If I guy ONLY cared about the sound(loppey idle) which cam would have the
best sound? If it's the 2nd cam, then there is no up side to the Thumper, no
matter your objective.