SoCal Jet Boats

Tech Talk => Engine Mechanical / Electrical => Topic started by: jet fever on April 08, 2014, 05:25:09 PM

Title: help with 496 cam selection
Post by: jet fever on April 08, 2014, 05:25:09 PM

Opinions on 496 Chevy build.  Mark IV 2 bolt converted into 4 bolt, 10;1 bottom end complete forged crank and pistons. 

Question is opinion on head selection and cam selection.  Thinking AFR Heads around 305cc Roller cam off shelf non custom grind but dont want wrong power curve dont want too big and have no bottom end power.  So question is cam selection choice hopefully from experience. 

Berk 12jg will be rebuilt and matched.

I know alot of veriables but wheres a good place to start. Mid 80's Bahner open bow full stringer

Title: Re: help with 496 cam selection
Post by: jyeager on April 08, 2014, 05:35:46 PM

Quote from: jet fever on April 08, 2014, 05:25:09 PM

Opinions on 496 Chevy build.  Mark IV 2 bolt converted into 4 bolt, 10;1 bottom end complete forged crank and pistons. 

Question is opinion on head selection and cam selection.  Thinking AFR Heads around 305cc Roller cam off shelf non custom grind but dont want wrong power curve dont want too big and have no bottom end power.  So question is cam selection choice hopefully from experience. 

Berk 12jg will be rebuilt and matched.

I know alot of veriables but wheres a good place to start. Mid 80's Bahner open bow full stringer

I would talk with chris straub, he really knows his stuff.

http://www.straubtechnologies.com/custom-cams/ (http://www.straubtechnologies.com/custom-cams/)

Title: Re: help with 496 cam selection
Post by: Jet Boat Maloney on April 08, 2014, 05:40:59 PM

Quote from: jyeager on April 08, 2014, 05:35:46 PM

I would talk with chris straub, he really knows his stuff.

http://www.straubtechnologies.com/custom-cams/ (http://www.straubtechnologies.com/custom-cams/)

X2 on that you really don't want to over cam it @10:1 comp and don't over do it when it comes to heads. Bigger isn't always better. Good luck with the build.


Sent from my iPhone using SoCal Jet Boats

Title: Re: help with 496 cam selection
Post by: jet fever on April 08, 2014, 06:04:06 PM

Yeah sorry meant thinking big afr when thinking about 12:1 but bought 10:1 so just want good flow now.  Want to run on pump gas

Title: Re: help with 496 cam selection
Post by: GT Jets on April 08, 2014, 10:09:09 PM

My favorite big block cam of all times is the XM series roller XM270HR

Hydraulic roller with modest lift, use stock ratio rockers and good springs and it will be bulletproof, if you find you need more, increase the rocker ratio one step.

It will run like a pit bull toward the postman... The best part is, with stock rocker ratios, the valve lift is almost dead on .5", you can rest assured it will not need too much tweaking to get the geometry right. You will need an open plenum intake and a square bore double pumper in the realm of 1,000 cfm to make it work.

I have run this in a light aluminum boat (under 350 pound hull) with a crate 454 and it literally pulled to 5300 RPM with a stainless A without any drama at all. We were running 1.72:1 stamped rockers with the kit springs. (The stamped rockers were a rule thing).

Really can't go wrong.

You could probably push it a little, but unless you bump the compression, doubt the ass-o-nometer will detect a difference.

GT


 http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=448&sb=2 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=448&sb=2)

Title: Re: help with 496 cam selection
Post by: MPKardell on April 09, 2014, 09:41:14 AM

My current set-up: I'm running a Lunatti cam in a 496 BBC with 10.5:1 compression and cheap Chinese heads.  It will spin a 9.25" impeller (in an AT-309 pump) to 4700-4800 rpm (~475-500 hp) with a Quickfuel 850 marine carb, through the logs, 650' elevation.  190-195 psig cranking pressure.  Runs on 91 octane at 32 deg (total) spark advance.  For a mild cam, it also has a nice rumpity-rump idle.

http://www.lunatipower.com/Product.aspx?id=2550&gid=337 (http://www.lunatipower.com/Product.aspx?id=2550&gid=337)

Title: Re: help with 496 cam selection
Post by: jet fever on April 09, 2014, 05:31:54 PM

I'm looking at XM284hr comp cam

Title: Re: help with 496 cam selection
Post by: mash on it on April 10, 2014, 09:14:01 AM

I'm running a Howards' roller-

http://www.summitracing.com/parts/hrs-cl120245-12/overview/make/chevrolet (http://www.summitracing.com/parts/hrs-cl120245-12/overview/make/chevrolet)
(.567"/.578", 225*/231* @ .050", 112* l/s)

Pulls a 'AA' A/T Impeller to 4900-4950 in a 9:1, 454, .030 over,  cast iron crap heads, thru logs and snails, Vic jr. and holley 750.

With a 496, a lil more duration at .050" would help, into the 240* range

Also depends on what exhaust your running, and what impeller.

Flat tappet I ran, too-
http://www.summitracing.com/parts/cca-k11-324-4/overview/make/chevrolet (http://www.summitracing.com/parts/cca-k11-324-4/overview/make/chevrolet)
(.568"/.578", 244*/246* @.050) ran like a scalded ape in a 454, Vic. jr. & headers.


Thats all I got.

Dan'l