Camshaft recomendations for SBF

kid vishus · Post by **kid vishus** » Wed May 18, 2005 8:07 am

My current cam was damaged last weekend. One of the links connecting the roller lifters together broke which allowed one lifter to rotate in the bore. That really messed up one lobe on the cam.

I think my current cam was too big anyways. It is 276/286 @ .050, .714/.714 lift on a 106 LSA. I am only shifting at 6500 and that's why I think it's too big.

Motor is a 402" sbf; internally balanced 4" stroke, 6.250 GRP aluminum rods, 15-1 JE pistons, ported and epoxied 4v cleveland heads that flow 360 int/249 exh cfm @ .700 lift, single 950 HP carb, 1 7/8" headers w/ 3 1/2" collectors. Car; '69 mustang fastback, weighs 2800 w/driver, 4.86 gear, 14x32 slicks, ladderbars w/coilovers, 1.82 low powerslide w/5500 convertor. Footbraking the car has gone 6.37 @ 110 mph in the 1/8 with a mediocre 1.43 60' time.

Any recomendations?

67RS502 · Post by **67RS502** » Wed May 18, 2005 12:52 pm

Why are you shifting so low, and does it go faster if you shift higher?

kid vishus · Post by **kid vishus** » Wed May 18, 2005 7:43 pm

A couple of reasons for the low shift points. First, it's a bracket motor. Yes I have tried shifting it at 7000, but it didn't go any faster, and actually lost mph. I figure either my carb is too small, and/or my headers are too small for the extra rpm.

dbusch · Post by **dbusch** » Wed May 18, 2005 10:49 pm

what manifold are you running? hopefully it will flow 340 cfm bolted to your heads and is 3.2-3.5 avg cross section. what is the min. cross section or avg. cross on your heads? yes the headers are too small...2" straight or 2-2 1/8th will allow more rpm. valvetrain could be the cause too. 250 seat/650 open would be plenty of spring, and a 3/8" .080 wall pushrod would work well for .714 lift. the 106 lobe sep is not going to work. too much overlap!! with 15.0 compression you can use 112 or 114 lobe sep no problem. centerline of 110 or 111 is where it needs to be. More cam area via lift would help your cause too, though it may be too maintainence oriented for a bracket car...

kid vishus · Post by **kid vishus** » Thu May 19, 2005 8:35 pm

The intake is an Australian "Vapours" intake that has "Active" cast on one runner. It looks like a Victor Jr knock off. I have no idea what it flows. I don't know what the cross section is. I could measure it, but where does it need measured? The ports are still as wide as a normal 4v head, but the floor has been raised as has the roof.

Unfortunately, with the stock front suspension on my car, the headers I have are as big as I can fit, and even then they don't fit worth a da*n.

Valvetrain should be good for what I am doing. The springs have 250 on the seat, and something like 660 or 670 open (I need to dig the paperwork out to check for sure.) Rockers are Crower stainless, titanium retainers, CV 3/8" diameter .065 wall pushrods, stud girdle, and Ferrea valves.

dbusch · Post by **dbusch** » Fri May 20, 2005 10:58 am

sounds like the manifold is too small: measure the heighth and width at the plenum and also at the gasket flange. make sure you subtract the corner radii. usually they are 1/2" radii, so take h*w*.95 for you area. average the two areas .

avg area*88200/cid of cyl=peak torque rpm. if you come up with 4500 rpm for peak tq that is your problem. peak hp usually comes in about 1500 rpm above peak tq, so that is 6000. 6500 shift is all you could get out of that. to shift at 7000 you need to port the manifold to raise the tq peak up to 5000 or 5250....