If anyone out there is familiar with my posts, then they know I believe compression is power, and I STILL believe that. I have received a number of calls this year by enthusiasts wanting to make good power with their low compression 400. As most of us know, after 1970, that's all we had to deal with. If you want to make your natually aspirated, low compression engine run, you are going to have to minimize the losses as best you can. So, short of getting into the shortblock and changing pistons and such, we are going to focus on "bolt-ons". Yes, I know, bolt-ons will only take you so far, but if you select the RIGHT bolt-ons, at least you are headed in the right direction. The low compression combination as seen by Sandoval Performance First things first; We have a four stroke engine: Compression, Power, Intake, and Exhaust. There is not one horsepower produced in the cylinder when the valves are open on the intake or exhaust strokes! High compression engines can use a longer cam to let more air in the cylinder so it will make more horsepower at a higher rpm. We don't have that luxury so we MUST trap as much air and fuel in the cylinder as quickly as possible, ignite it, and harness as much of the precious cylinder pressure possible before we exhaust it. Why is that? In a nutshell, after ignition, the cylinder pressure decay gradient in a low compression engines is not as steep as a high compression engine, therefore, the exhaust valve needs to open LATER. ( I am not a physicist, so I hope I stated that correctly!) The bottom line is this: We need to keep the duration numbers down. PERIOD.
Luckily for us, there are more to cams than duration. LIFT, LOBE SEPARATION ANGLE, LOBE ACCELERATION, and OVERLAP all work together to make (or break) a combination. I suggest we look at lift first. Let's lift the valves as high as we can, that dictates we have the necessary valve springs (pressure), retainers, pushrods, proper geometry, and the most important "item"... CLEARANCE! Not enough valve spring retainer-to-valve stem seal clearance will have your engine smoking in no time! Coil bind will lead to catastrophic failure because the cam lobe is trying to lift the valve higher but the spring won't let it! Something has to give! Piston-to-valve clearance is always important, but with the meager duration numbers, it is unlikely to be a problem--- but when you have the opportunity, CHECK IT! All this talk of short duration, high lift, and high spring pressures lead us to the TYPE of camshaft available to us. It will DEFINITELY BE A ROLLER. Now, just how hardcore you are is proportional to the amount of money in your wallet! We won't need a lifter bore brace or a stud girdle or anything like that. Just good aftermarket components. We will need to ensure good machine work and assembly procedures, as usual, and get the numbers we need! Deck height can be a compression killer--- try to get that piston up as high as possible. Piston rings--- gap them the tightest possible. Ring thickness--- use a piston that utilizes a 1/16,1/16, 3/16 ring pack for less friction. Components that have some bearing on volumetric efficiency; Intake manifold- Use a dual plane intake for a better draw on the carburetor. We like the Performer RPM. Carburetor- keep it sensible. Too large will slow down the velocity throught the venturis and kill throttle response. Cylinder heads- aside from the low compression, let's make sure we have a good valve job and porting. At least open up the bowls. And the CAM--- keep the duration relatively short. If you want a rowdy sounding cam, tighten up the lobe separation angle. That's EXACTLY what we did with our LC-3 "low compression compatible" custom ground camshafts. With advertised duration at 266/276, .050" numbers at 214/224, lift at .580" on a 108 degree LSA, you WILL have cylinder pressure! A guy with a low compresion engine could get away with using our Stage 1 cam as well!
Call or E-mail us for more information on our low compression ratio compatible camshafts @ firstname.lastname@example.org
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