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Discussion Starter #1 (Edited)
180 in every single cyl. I did a search and saw this thread.

Compression Thread

Noticed that A-train mentioned the 180 is wrong on the AED. ??? Do these numbers sound right. Every plug was out of the heads when I did it. Unplugged injectors. I hope everything sounds good. I have some early Xmas presents coming to my house soon. :D

*BTW- The block only has 29K on it
 

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is the engine stock or is it a build with higher c/r ,
me and A -train looked at this different so we wont agree on the same thing if you ask us but 180 ist bad , i had alot lower numbers then that and i was still running good but now that i did the heads i will check the compression again .


Jurgen
 

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Discussion Starter #5
Stock block w/ PI cams and the AED on top. So yeah, basically stock. :)

What is bad, whats normal?

Just want to make sure everything seems well before the new toys go on. The new block is about a year and a half out I think.

Thanks
 

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Discussion Starter #7
Your so mean. This is a very serious subject. :tongue:

Not like the car will be going anywhere anyway. :rolleyes: The new block will come in time. I just want to blow this one up. :D Haha.
 

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How 'bout a leak down while you're at it?

With an even 180 across the motor...
I suppose it's not really that necessary.
 

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That's good news... Especially with all of the cylinders so even. If one or two cylinders were off significantly and the others were all 180-185 or so, then I'd worry.
 

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The wink was to clue you in on my joking. :D

Besides, if you get a sweet new block and some other awesome toys, who am I to complain? More toys to play with and more company up here in the over 400RWHP club.

You know you want to join it... We even get a mug!
 

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Just my opinions on checking cylinders:

Cranking pressure "numbers" don’t mean a whole lot from a troubleshooting standpoint. The cylinder pressure that is built in the cylinder when you just crank it is based a lot on the cam profile, more so than the static CR of the engine. For example, if you have a very high CR, and a huge cam, your “numbers” might be lower than if you have a low CR and a small, torque type cam without a lot of overlap. What the cranking pressure is important though is the balance between the cylinders and as mentioned, they should be close to each other. If they are all the same, you should be good. But as a side note, excessively high numbers may lead to detonation issues/concerns.

Leak down test numbers are the all-important test for a cylinder. They test how all the sealing parts of the cylinder are working (rings, valves, head gaskets, etc.). From what I’ve gathered/researched, brand new racing engines should be somewhere around 2% to 5 % leak down, a good “used” engine should be somewhere between 5% to 12%, and a high mileage, but still acceptable used engine should be 12% to 20%. Anything exceeding 20% and it’s just worn out. If it’s in the 40% and lower, there’s probably a failure of some type (blown head gasket, burnt valve, holed piston, etc.)

The other thing about the leak down test is that you can find the problem. If it’s a burnt valve, the air will leak into the exhaust or the intake system. If it’s worn pistons/rings, it will leak into the crank. If it's a blown head gasket it will leak into the cooling system or the crankcase.

So my engine troubleshooting tests:
Test 1: Cranking pressure test to check for balance
Test 2: Leak down test to find the status of each cylinder

Just some things I’ve learned over the years of diagnosing engine problems. :thumbsup:
 

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Yes, but our stock cams (PI and NPI) don't have ANY overlap, so that kinda takes that out of the equation.
 

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Wow! You're saying that they have 0 degrees of overlap?!?

I didn't think any modern cam had 0 degrees overlap.

But that would explain the 180 numbers though. :D

Are these OEM specs for the 4.6L correct:

http://www.crower.com/pdf/53-104.pdf

Just wondering. :thumbsup:
 

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The guys at Compcams told me that the stock PI cams have 116 degrees of lobe separation. I don't know how that translates to overlap, but they said there was no overlap.

I suppose that's why they work pretty well in an SC application, no boost lost through the exhaust.

JL has been studying cams for these cars, perhaps he can help.
 

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DD94,

It appears from the spec sheet you posted that the stock cams indeed do not have any overlap. I didn't think modern cams when with the 0 overlap scheme either!

If you check out the valve timings link at the bottom of the chart and match up the durations under 114 cam spacing...you can check it out yourself. I think I'm reading the charts right.
 

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Earlier this morning I couldn't get to that link, but now it's working. :confused:

That is amazing that there's no overlap! :eek:
 

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From JL:
One more time....

Non-PI heads:
.466" intake lift
.466" exhaust lift
184 degrees intake duration @.050"
196 degrees exhaust duration @.050"

PI heads:
.510" intake lift
.530" exhaust lift
184 degrees intake duration @.050"
196 degrees exhaust duration @.050"

JL
The overlap issue is mostly due to emissions concerns - Valve overlap brings in the possibility of passing fresh, unburned A/F mix straight through the chamber and into the exhaust... though very small amounts of overlap don't have much of this problem and will help power a bunch. By small I'm talking under about... 10 degrees or so. Much beyond that and it's overkill, IMO. You'd have to spin the engine so fast the gains wouldnt be worth it, plus the hassles lumpy cams cause (idle, pwr brakes, etc.). I'm not going to get crazy about it, but some of the comp cams specs I've researched come pretty close to optimum... but optimum depends on the target RPM and where you want the power to be.

Don't forget the duration numbers are CRANK degrees and not CAM degrees - if you figure it out, I believe there's actually a dead spot where no valves are open. My guess is that this holds in more exhaust, kind of like a secondary version of the EGR functon.. it helps emissions by having a more complete combustion, though it wastes power.
Feel free to disagree, but that's how I see it. Any other thoughts are welcome.
 

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I agree with you 100%. :)

Especially: “… but optimum depends on the target RPM and where you want the power to be.” That’s the key. Where does the engineer want the power band to be?

I guess it's an issue of emissions vs. performance. We all know that some overlap is beneficial from a performance standpoint. If everything is tuned properly, the scavenging effect of the overlap makes power. However, everything has to be working in unison for it to work correctly. I.e. runner length, exhaust tube length, blah, blah, blah...

But now my problem: JL's numbers differ from the ones on Crower Cams site. Obviously I'm not going to say one is correct and one is incorrect.... Well, yeah, I am going to say that, just not which one is right and which one is wrong. :D

So now I get to pull the OEM manuals out and check them. I know the lift spec is in the cam section, but I'm not sure on the duration specs.

Dang it, why does one discussion always lead to more research!! :thumbsup:
 

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94 Daily Driven 4.6L said:
I agree with you 100%. :)

Especially: “… but optimum depends on the target RPM and where you want the power to be.” That’s the key. Where does the engineer want the power band to be?

But now my problem: JL's numbers differ from the ones on Crower Cams site. Obviously I'm not going to say one is correct and one is incorrect.... Well, yeah, I am going to say that, just not which one is right and which one is wrong. :D

So now I get to pull the OEM manuals out and check them. I know the lift spec is in the cam section, but I'm not sure on the duration specs.

Dang it, why does one discussion always lead to more research!! :thumbsup:
Power band... depends -do you want to get crazy and spin to 6500 rpms, or stay nice and calm in the 5000-5500 range? Sometimes you don't want the HP peak to be at your peak RPMs, depending on how much HP it makes after (shape of the HP curve).

I know whose numbers I'll trust :)

Isn't all this research fun? haha.
 
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