This is a two-part question regarding a 1974 360. I've rebuilt a 360 for use in my '74 Ramcharger. The motor was align honed, decked, balanced, bored .030-inch over, the stock crankshaft was offset-ground, and the rods were reconditioned with ARP bolts. I used dished TRW forged low-compression pistons, as this was to be used primarily as a towing motor with some get up and go. Long story short, the truck got totaled and I still have the short block sitting around.
I want to use this motor in my '66 Barracuda bracket car. I know I need to change out the pistons to forged flat-top pistons to boost the compression. I know I will have to re-balance the lower end, but, will the stock crankshaft and rods be up to running 6,500 rpm? I am confident in the crankshaft holding up, but the rods I am not sure of. I know they use stock crankshafts and rods in stock-class cars, and they seem to hold up pretty well. Should I change the rods to Eagle SIR or Scat I beams for reliability? Also, I want to use Magnum heads on this engine. I know I have to use Magnum rocker arms and a Magnum intake. I am going to run a flat tappet hydraulic cam, do I need a set of custom length oil through pushrods.
Jesse, I cannot offer an ironclad guarantee, but if it were my 360 I would have no worry about running those stock rods. The OEM forged rods used in the 340/360 were exceptionally good for a stock rod. If they were properly inspected, resized, and fitted with new ARP bolts, they rarely fail in an application such as you have described. I have built and run many small block engines at higher power output and rpm than you are contemplating using the stock rods without a failure.
As for converting to the Magnum heads, the intake, rockers and pushrods are all you need. If you are going to a stud mounted rocker, I would recommend upgrading the studs to with the 7⁄16-inch root instead of running the conversion studs with the factory 5⁄16-inch threads. Actually, for a moderate hydraulic flat tappet cam, the stock pedestal rockers work very well. One thing to be aware of is that the accessory mounting bolt locations on the Magnum are in a different position and the depth is different than those on the older LA series heads. This will foul the accessory mounting, especially for the alternator and air conditioning pump if so equipped. If you are handy at fabrication, the brackets can be modified to work.
On page 16 of September 2013 issue, you make mention of a custom-ground Comp Cam that is a hydraulic roller for a 360 Magnum crate engine. The specs are 224/230 degrees duration at .050 inch, and .573/.568-inch lift. Could you give me all the specs of this cam and also the part number? The dyno chart shows just the power/torque curve that I am looking for with my own build. This would be perfect.
Mike in Kansas
Mike, Our camshaft is a custom-ground hydraulic roller, from Competition Cams, based on the XFI series of lobes. These are very fast acting lobes, with high lift for a given level of duration. The fast action of these lobes provides for maximum power and torque, with a comparatively favorable idle quality. We went with lobe numbers 3015/3036 on the intake and exhaust, respectively, which spec out to 273/282-degrees advertised duration, 224/230-degrees duration at 0.050-inch, and .573/.568-inch lift with the Magnums 1.6:1 ratio rockers. We specified a lobe separation angle of 110-degrees, and installed the cam at 106-degrees intake centerline.
Although this is a hydraulic with a very high rate of lift, what impressed us most about this grind was the outstanding high rpm stability. We pulled the engine on the dyno to over 6,000 rpm, and the valvetrain did not miss a beat. You can order an identical cam by contacting Competition Cam's cam line at 800/999-0853, and giving the technician your engine application, the lobe numbers listed above, the lobe separation angle (110-degrees in this case) and the amount of advance you want (four-degrees).
Where's My Fuel?
I am having problems with my Charger's Six Pack center carburetor's fuel bowl going empty after the car sits for a while. This requires cranking the engine to fill it before the car will start. The carbs are the 2300 Holley series; outboards are PN 4672; center carb PN 4670. I sent the carbs to Promax to be modified as per your article several years ago. They were told about the problem with the center carburetor, and put their own metering block on it and checked it for any problems. They modified the outer carburetors for mixture control, and installed new lower shafts. They perform very well, without any bog when the outboards kick in.
I have checked all the obvious, no leaking fuel lines or fittings, the fuel pump is ok, and the filter is clear. It will start fine, once the center bowl is filled. Left sitting over two days requires cranking to fill the bowl first. I know an electric fuel pump will solve this problem but would prefer to fix it correctly. I wonder about the bowl vent on the center carb allowing evaporation?
Richard, it sounds like you have done a thorough inspection for leaks and have found nothing leaking. If the bowls are dry when your car has been sitting for a while, and there are no leaks to be found, the most likely problem is simply fuel evaporation. Today's fuel blends are designed for sealed fuel systems that operate at high pressure all the way to the discharge point at the fuel injector. Fuel in a carburetor is just sitting there, vented to the atmosphere and at atmospheric pressure. Put a hot 440 under it when pulling into your garage and the gasoline in the bowls will evaporate in no time. You can't change the formula of fuel being sold, so the best alternative is to add that electric booster pump.