Cam spec for factory exhaust manifolds

Building a new motor for my Merc, going for the clean factory look.

.030 over dove block
Scat cast 4.3 crank
6.700 hbeams
probe 10.5 dished pistons
blended CJ iron heads ss valves, a351 springs, tfs 1.73 rockers.
factory iron SCJ intake
950 holley
worked duraspark ignition
factory iron exhaust manifolds

question is is a c460 cam decent with this combo or should I get something custom? In curious about the exhaust manifolds and power out put, heat build-up, tuning, etc.

I've never done a performance build using manifolds before and just wondering what's a good cam or cam specs to use???

For an engine with exhaust manifolds or any highly restricted exhaust, the valve action is even more critical to get near correct than a high flowing exhaust.
Exhaust manifolds will supply almost no help for the intake and the biggest hurdle is to "get it all out".
A "controlled" valve opening and more aggressive valve closing with the idea of being sure that velocity past the valve is maintained to insure a consistant low pressure at that point is what you should strive for. How you get there is almost a "hit or miss" proposition unless one is very familiar with that particular lobe profile being used.

rmcomprandy wrote:For an engine with exhaust manifolds or any highly restricted exhaust, the valve action is even more critical to get near correct than a high flowing exhaust.
Exhaust manifolds will supply almost no help for the intake and the biggest hurdle is to "get it all out".
A "controlled" valve opening and more aggressive valve closing with the idea of being sure that velocity past the valve is maintained to insure a consistant low pressure at that point is what you should strive for. How you get there is almost a "hit or miss" proposition unless one is very familiar with that particular lobe profile being used.

Will a camshaft with an extended exhaust duration profile work? With 10.5:1 CR (suggested) and cast iron cylinder heads, assuming pump gas is in order, camshaft selection versus cylinder pressure could be a concern, ya think?

Dave.

i always thought a wider lobe seperation was favorable for restricted exhaust cams that are normanly used for nitrous

It seems to me that the most knowledgable people in the world about making power with ex. manifolds are the F.A.S.T. racers.

Those guys are running 10's thru maifolds....very impressive.

Good luck getting cam info from those guys tho....LOL

jm wrote:i always thought a wider lobe seperation was favorable for restricted exhaust cams that are normanly used for nitrous

YES ... valve overlap, (or lack of it), is a big part of what is needed. Also, an earlier exhaust closing point than is used with a higher flowing exhaust side.

On a regular street engine, this is where a "to big" single or almost single pattern camshaft, installed very advanced usually works well. As the power goes up - it gets much more difficult.

83-88T-Bird Guy wrote:It seems to me that the most knowledgable people in the world about making power with ex. manifolds are the F.A.S.T. racers.

Those guys are running 10's thru maifolds....very impressive.

Good luck getting cam info from those guys tho....LOL

They are very impressive, But pretty much only concerned with WOT Performance and Have some pretty specialized parts and work done to them.

Mine going to be 95% street duty and a few trips to the track to verify how it runs. not looking to get crazy and I'd like something I can put 20k miles on and not worry to much about it. I figure that should get me 5-6 years of fun and hopefully only have to clean stuff.

rmcomprandy wrote:

jm wrote:i always thought a wider lobe seperation was favorable for restricted exhaust cams that are normanly used for nitrous

YES ... valve overlap, (or lack of it), is a big part of what is needed. Also, an earlier exhaust closing point than is used with a higher flowing exhaust side.

On a regular street engine, this is where a "to big" single or almost single pattern camshaft, installed very advanced usually works well. As the power goes up - it gets much more difficult.

Randy,

What kind of power do you think this combo will be capible of??? 500hp? at say 5500-6000???

With closed pipes and that iron manifold it won't be that much; maybe 450 or so.
It should be over 500 lb/ft of torque though.

Here is a previous build:

http://www.460ford.com/forum/showthread.php?t=109863

Hope that helps,

Dave

Dave how many inches was that motor?

That was a 466. While I think those numbers are a little generous, the dyno did show a 120 hp drop from a 1000 cfm carb, Victor, and headers to a 780 carb, stock SCJ intake, and stock exhaust manifolds. You could probably use that same 120 hp drop for any combo that you're planning. A custom cam for the exhaust manifolds would definitely help the engine not to lose so much power.

Hope that helps,

Dave

I know this is way old but did you ever build this thing? I've been contemplating doing almost the exact build.

Thanks.

1EFF100 wrote:I know this is way old but did you ever build this thing? I've been contemplating doing almost the exact build.

Thanks.

Never finished it, have the cam sitting on the shelf if you need one.

You might want to extrude hone the exhaust manifolds and try some 1.8 rockerarms on the exhaust side with the C460 cam, just an idea.

Im not sure about the factory cam specs on a 429 CJ or PI, but the FE 390 GT and 428 CJ both used essentially the same cam, and it had 20 degrees more duration on the exhaust.

I believe they had 3 or 4 different cams and it is very hard to get concrete info on them, I have looked awhile. I don't think the split was near that much and the EX. manifolds where quite a bit larger than regular truck/car deals.

dfree383 wrote:

1EFF100 wrote:I know this is way old but did you ever build this thing? I've been contemplating doing almost the exact build.

Thanks.

Never finished it, have the cam sitting on the shelf if you need one.

Thanks for the offer but I'm not sure what I'm going to do yet.

supervel45 wrote:You might want to extrude hone the exhaust manifolds and try some 1.8 rockerarms on the exhaust side with the C460 cam, just an idea.

Yeah, looking into Extrude Hone was definitely in my plans if I go with the manifolds.  

supervel45 wrote:I believe they had 3 or 4 different cams and it is very hard to get concrete info on them, I have looked awhile. I don't think the split was near that much and the EX. manifolds where quite a bit larger than regular truck/car deals.

I believe the 390GT/CJ428 cam is 208 In 220 Ex duration at 0.050.

On a personal note regarding manifolds vs headers. I had a '68 Cougar GT390 car that I had built a 428 for using the Edelbrock heads, TRW CJ pistons, Performer RPM intake and a solid flat tappet Comp cam in the .580 lift area and 252/260 duration at .050. Hooker Super Comp headers with 2.5 duals out the back. 3000 stall with a C6, 3.89 traction lock in the 9 inch.
That car was an animal. You could leave it in drive, take off from a stop and smoke the tires through every gear until you let off. It had nice part throttle response as well.
I decided one day I wanted to get rid of the headers since this was a street car and go to manifolds. I had  a set of either GT390 or CJ manifolds--I don't remember which now-- but man, those things totally knocked the fire out of that engine. I drove up the street about a half mile, turned around, parked it back in the garage and immediately removed them. The headers went back on.

I think I may have just answered my own question regarding manifolds or headers for the 521. lol.

http://www.hemmings.com/magazine/mus/2011/01/Stopgap--Stang---1971-Ford-Mustang-Mach-1/3694811.html Don't give up just yet. The stock CJ/SCJ's mechanical and hydraulic's I think are in the low 220 range at .050" and right around .500" lift.

http://www.mustangtek.com/Camshaft/camshaft.html Here you go, try not to go blind but it should be in here.

I believe the 390GT/CJ428 cam is 208 In 220 Ex duration at 0.050.

.[/quote]

Close ... as they are 206/221 @.050" and 270/290 @S.A.E. "off the seat" for an early exhaust opening, (at those small @.050" durations they were not worried about saving any extra low RPM torque and opening that exhaust valve under a higher cylinder pressure helped the exhaust gasses get out of a restrictive exhaust system). However, those cams are also ground at 115 lobe separation so, the idle quality does not suffer.

Completely different priorities than a Hot Rodder.

Thanks Randy.

just throwing this out there if you look around at exh manifolds they made a set that fits nicely in a 70-71 torino-cyclone that have the extra ribs cast on the outside to help with the cracking of the early model manifolds I believe these are 74-75 big car manifolds and have the scj type outlet that took the steel doughnut gasket. The benfits to using these there is plenty of meat on them to be ground on and flow pretty dam well for manifolds and your not hacking up your rare manifolds I think the castings started with d4 or d5 and took a 2 1/2 pipe from the factory with a little work they take a 3 inch pipe and nobody is wiser except your local ford nuts. I know this cause I had more time than money in my younger years and couldn't buy headers so made due with what I could find.

db post