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Old 04-25-2013, 01:07 PM
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454 compression test

Alright guys, I'm continuing my build on my 454. I put new umbrella valve seals in yesterday. Today I put the heads back on the block using felpro 1047 head gaskets and arp . The engine looks stock 781 heads flat pistons w/ the little dich in the center. Tomm im doing a compression test. What compression numbers should I look for?

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Old 04-25-2013, 01:11 PM
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Are the rings seated or is this a new build? The cylinder pressure is dependent on different factors, cam specs, etc. What's the static c.r.?
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Old 04-25-2013, 01:15 PM
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Are the rings seated or is this a new build? The cylinder pressure is dependent on different factors, cam specs, etc. What's the static c.r.?
I bought the engine used. This is not a fresh build. Just a freshing up. I would say aftermarket cam due to dual valve springs.
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Old 04-25-2013, 06:02 PM
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As you don't know the engine specs. All you can do is watch for inconsistant readings cylinder to cylinder.
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Old 04-26-2013, 06:37 AM
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I have two compression gages, both the same make and model. One reads 25 or 30 psi lower than the other. So, don't place too much value on the number, as gages can be wrong.

consist numbers between cylinders is what you are wanting to see.

However, don't except much pressure, especially if you there is a bigger cam than stock in there. The stock compression for a 454 with 781 heads and flattops is around 7.75:1 cr. Then the bigger cam with the later intake valve closing point will reduce cylinder pressure even more.

I would except to see 110 to 125 psi numbers.

This engine will like lots of initial ignition timing. I would use 20 initial, 40 total, and add another 10 degrees from an Adjustable vacuum advance canister (crane: summit racing) connected to a manifold vacuum source. So the timing at idle will be 30 degrees (20 + 10) and total when you rev it up will be 50 (40 + 10).
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Old 04-26-2013, 01:55 PM
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Yesterday I installed new felpro gaskets 1047 w/ new ARP bolts. I found a code on the the piston:
H518CP STD 321-0017-a
it has a small dish in the center and 2 slits opposite each other.
Today I did a cold compression test with no rockers and pushrods
1:119
2:121
3:122
4:109
5:89
6:149
7:79
8:145
These numbers are pitiful!
Now 5 and 7 I'm debating if I should retorque the cylinder heads bolts?
6 and 8 have carbon build up.
I then installed the valve train and found #1 intake lobe rounded out.
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Old 04-27-2013, 01:30 PM
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You need rockers and push rods to do a compression test. The valve need to open to let air into the cylinder. Plus a flat came is a problem. Check the bearings
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Old 04-28-2013, 07:01 AM
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Also, after you put the push rods and rockers back on and adjust them. Redo the compression test and mark the weak cylinders. Pull the head and lap in the valves at those cylinders. Then bolt the head back on and try it again.

But you will need a new cam. Get a summit racing cam. Cost 100.00 and comes with lifters. Get the smallest cam summit has for the BBC. This cam has nice soft ramps which makes for a long life. If you get anything more aggressive the odds of a flat lobe go way up.

And, get the springs tested to see how much seat pressure and how much at 0.500". Measure the installed height before removing a spring. The small summit cam doesn't need much spring. 90 to 100lbs on the seat and 240-270lbs at 0.500" will be enough. The trick is to use the least amount of spring force as possible, this will make for a long cam life.

Also look into the BC Engineering over cam oiling systems for BBC. the kit cost about 60.00.

Last edited by 454C10; 04-28-2013 at 07:16 AM.
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Old 04-29-2013, 03:20 PM
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Originally Posted by 454C10 View Post
Also, after you put the push rods and rockers back on and adjust them. Redo the compression test and mark the weak cylinders. Pull the head and lap in the valves at those cylinders. Then bolt the head back on and try it again.

But you will need a new cam. Get a summit racing cam. Cost 100.00 and comes with lifters. Get the smallest cam summit has for the BBC. This cam has nice soft ramps which makes for a long life. If you get anything more aggressive the odds of a flat lobe go way up.

And, get the springs tested to see how much seat pressure and how much at 0.500". Measure the installed height before removing a spring. The small summit cam doesn't need much spring. 90 to 100lbs on the seat and 240-270lbs at 0.500" will be enough. The trick is to use the least amount of spring force as possible, this will make for a long cam life.

Also look into the BC Engineering over cam oiling systems for BBC. the kit cost about 60.00.
I was going threw the summit catalog looking at cam kits and springs. And came across this:http://www.summitracing.com/parts/cca-k11-205-3
Sounds like a nice kit and eliminates all the guess work. My only concern is do I put shims under the springs?
If you look at my recent pictures by name above, you will see 1 shim on the intake valve guide and a larger shim under the exhaust spring.
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Old 04-29-2013, 03:53 PM
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781 heads typically have rotators under the exhaust springs which are normally replaced with thick spacers when stronger springs are used. The springs have a recommended in stalled height so you can used that when you install them. The 268h is a little to big for 7.7:1cr and requires more stall and a 3.55 gear. I would get the 260h if you want to get a kit. What gear, transmission, and stall are you going to use?
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Old 04-29-2013, 05:39 PM
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Quote:
Originally Posted by 454C10 View Post
781 heads typically have rotators under the exhaust springs which are normally replaced with thick spacers when stronger springs are used. The springs have a recommended in stalled height so you can used that when you install them. The 268h is a little to big for 7.7:1cr and requires more stall and a 3.55 gear. I would get the 260h if you want to get a kit. What gear, transmission, and stall are you going to use?
My current setup is 305, 29-3200 stall, TH400 and 3.73 moser 12 bolt.
I can always change the converter when I do the bb swap.
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Old 04-29-2013, 07:38 PM
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You will be fine with the 268H, as the gears and stall are good. Compression is a bit low but it will work. And work with 87 octane with lots of timing. Stall is a little high as 2000 or 2400 rpm would be enough.

Use 20 degrees of timing at idle, 40 total, plus another 10 from a vacuum advance canister (adjustable, with 10 degrees of timing and plugged into a manifold source. So, it should have 30 degrees at idle (20 + 10) and 50 total (40 + 10) when you rev it up in park.
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Old 05-08-2013, 03:26 PM
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Quote:
Originally Posted by 454C10 View Post
You will be fine with the 268H, as the gears and stall are good. Compression is a bit low but it will work. And work with 87 octane with lots of timing. Stall is a little high as 2000 or 2400 rpm would be enough.

Use 20 degrees of timing at idle, 40 total, plus another 10 from a vacuum advance canister (adjustable, with 10 degrees of timing and plugged into a manifold source. So, it should have 30 degrees at idle (20 + 10) and 50 total (40 + 10) when you rev it up in park.
Well I'm considering buying this cam from summit: http://www.summitracing.com/parts/sum-k03052/overview/
With a edelbrock performer rpm #7164 and q jet 750cfm electric choke.
What valve springs would you
recommend?
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Old 05-09-2013, 05:20 AM
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I would use a 750 vacuum secondary Holley 3310 with the regular rpm intake (not air gap, not spread bore).

get the compcam 911-16 springs.

make sure to measure installed height now. some 781's had less than 1.900 installed height which will make too much seat force.

I try to run the least amount of spring possible. I feel the 911-16 are a little too strong. I try to set the seat pressure at 100lbs and around 275lbs at max lift with a cam that size. You need to have some tools and take some measurements to get it right.
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