I tested my compression today and its at 160 psi on all 8. I found a ratio psi conversion on wiki and it puts the ratio around 10.88:1. what does this mean in the real world. is it a good place to start in building more power? It runs really strong now, but I'd like to have more. I have problems with cooling, (needs bigger radiator), and it still has small tires on it(205 65 15)no track lock, so it doesn't hook up and take off. What rear gears should I run? 1/4 mile. what trans, it has a 3 speed now. I have wheels for it, after I paint I'll put them on and post new pics.( what you see is how it is) doing alot of prep and body work now.. So send me your ideas and input and trying to learn all I can before I spend anymore money
Is this going to be a daily driver with weekends at the strip or is it a race only car or is it a street car that you will sometimes take to the strip? There is no way to directly convert the numbers from a compression test to your compression ratio in any reliable way. You will have to use a graduated cylinder and pipette to measure the compression ratio directly. My experience tells me that 150 - 160 on a compression test (with a stock cam) is about 8:1 to 8.5:1 compression. If the engine has a real wild cam the pressure you got could mean 12.5:1 compression.
as paul said the cranking compression test has no indictaion as to the static comprssion of the motor. the cam has alot to do with that. as for what trans, and rear gears to use, you need to provide more info as to what your inteded use of your car is. do you just want to drag race it on the 1/4 mile or will it be your daily driver and only goto the track once a year? what mocifications does your motor curently have. what ones will it be geting.
okay, so far it has a small edelbrock cam I think its around a 280. I found some info in the car with the cam specs on it and the timing adjustments for it. 2.79 rear, 8". holley 600 cfm. 4160 I beleave. fact. 3 speed, edelbrock intake, rpm 289. I'm out of town on business at the moment so I'm not sure of all the data. I'd like to be able drive it and take to the track to see how well it does. no serious racing .... yet...
When you do a compression test you are looking to see if all the cylinders are within a certain percentage of each other. In other words, using 10% as a guide, if your highest cylinder is 180 and your lowest is 162 the motor is in pretty good shape (how fast it cranks and how long plays into it as well and always do it with all your spark plugs out). As was said before, depending on the cam (overlap and duration) plays big into what you will see. I once had a 14:1 motor that only had 130psi during a compression test because of the radical solid roller that was in it. I would change the gears to a set of 3.55's, get some sticky tires, maybe some old school slapper bars and have fun! You will probably find that if it's not done already you will want to upgrade your ignition as well. At the very least, remove the old points system and step up to electronics (Pertronix makes a nice setup). If you have the cash or can find a good one at a swap meet, consider an MSD6. Maybe when you get that far and still feel 'the need for speed', you can always buy a cheap nitrous system and electric fuel pump off Craigslist and up the fun quotent!
