02-16-2009, 04:54:54 AM
I've been messsing with my 406 for a while now, trying to get it fine tuned. Since I built the motor a year ago I've never did a compression test. I went to Autozone and borrowed one of their gauges. I got it home and it was broke. I took it back and just bought one. Its an Actron which is a cheap brand.
I did my compression test and all 8 cylinders were over 200lbs. They were probably around 210lbs. They were also within 5% of each other. I've done this test before on other engines and the highest reading I've ever got was 170-180. I'm wondering if this is correct or the gauge is not reading correctly.
My engine is a 406 with 11-1 CR and it has a Comp Cams XE284 cam. This engine has always been hard to crank over. I put a mini starter on it and when its hot it barely cranks it.
Thanks for your time,
02-16-2009, 06:58:13 AM
Does sound a bit high. I ran a dynamic compression calculation on it and got about 170 PSI as the estimated cranking compression.
Here's the link I used:
02-16-2009, 08:54:58 AM
For sure an XE284 cam? 240/244 @ 0.050", .507"/.510 lift on 110 deg. That's a lot of comp. for that much cam. Pump gas?
02-16-2009, 09:50:22 AM
I was at 200-210 on my 355 with the comp cam 252/260 @ 50, yours sounds about right.
02-16-2009, 11:13:22 AM
Hmmm, lifters bleeding down would make the cam smaller than reality. What are you running for lifters?
02-16-2009, 01:53:58 PM
[QUOTE=Joe Prather]I've been messsing with my 406 for a while now, trying to get it fine tuned. Since I built the motor a year ago I've never did a compression test. I went to Autozone and borrowed one of their gauges. I got it home and it was broke. I took it back and just bought one. Its an Actron which is a cheap brand.
I think I have the same gauge its purple right?
I had almost 11.1 in my 406 cranking psi was 228 on average it ran fine on 93.
but when I put it in my work truck with a flat hood it was not to happy I had to back the timing way down and turn it off in gear it didn't like the extra weight and ingesting hot air.
Is your battey in the trunk ? if so try to use a big starter wire.
Do you have coated headers? if not your stater might be getting to hot.
02-16-2009, 10:52:17 PM
Sounds like you need to work on getting the heat down around the starter area. May have to wrap the header pipes near the starter and like stated above make sure you have big wire battery and starter wires. Also if that does not work you might try an ignition interrupt switch. Install a toggle switch that cuts off the 12 volts to your coil and turn it off when you crank the motor over and once it gets cranking flip the switch.
02-17-2009, 05:03:37 AM
Thanks for the link Damon.
I have been running 93 octane. I do have to retard the timing a little so it won't ping. My battery is under the hood and I have a heat shield around the starter. The lifters are what came with the cam.
I'm not completely sure my compression gauge is correct. Even though its new, it is setting on 15 lbs when its not being used. I may take it back and get another. I may have cranked my engine over about 6 times. I've heard 4 times is good. I wonder if my readings would have been less if I only went 4 times. I guess I should have tried it.
Thanks for all of the help and replies.