Cylinder pressures??? GRADY Hissin?

[WHITE94COBRA]

What are your cylinder pressures? When I got my engine redone my pressures were at 190+ and my car dynoed 330 - 357, it has not felt as strong for the last few months, Ran a comp. test all of my cylinders are at 173+ this is doing a wet and dry test. The car is using NO oil, everything else is the same. Went a step further and took it into my tuner for a few dyno pulls, my numbers came back horrible. I had a few rocker studs break on me, and I replaced all of them with new ARP studs, readjusted my rockers and even put in new pushrods just in case I had bent one. My car idles fine, runs fine, no bent valves, but my numbers came back waaaaayyyyyy lower. I got a print out this time for ya grady. My A/F is good..... I'm at a loss. No vaccuume leaks, no exhaust leaks, timing is set right at 14* car pulls fine, but only to 6k rpm's before dropping, before they started to drop right about 6300 rpm. This is starting to wear thin on my nerves.

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[WHITE94COBRA]

Ohh yeah and now I have a vibration until 2k rpm's, not a bad one but an annoying one; after 2k it's smooth as silk.

 

[Stanger007]

I bet you can get away with at least 4 degrees more spark up top.

 

[HISSIN50]

I know Wes will have some very eloquent thoughts on this too.

My take on compression tests: They're like dyno runs on different sessions (instead of leaving a car strapped and making a change). Lots of variables.

With compression testing, there are enough variables (throttle Wide open, hot hot the engine was, etc etc) that it makes it hard to compare. I personally think 173 is fine. Did wet numbers go up much at all vs dry? There should have been a noticable difference on the gauge.

Can you do a leakdown test? Given your recent work, that's where I'd be (you can make a rig pretty cheap if you want. Tom Moss has an article on the internet about doing it, IIRC. One of several I've seen over the years).

I'll leave the rest up to those smarter than I (Grady, Wes, and others).

Good luck.

 

[svt2785]

If your cam was properly degreed in when you built this motor and you used a new chain it is likely that it has stretched somewhat during break in. I have seen double rollers lose 4 degrees + of cam timing before they take a set position. This would retard your cam making the intake close later. (the piston will be further up the bore, heading for TDC before it closes and you will lose some compression. This could account for some of your power loss.
As mentioned by another responder compression test results can vary anyway. Engine temp. air density, throttle position can impact all impact it. Also if your rocker geometry is correct you shouldn't be breaking studs. (try finding Jim Miller Engineering on the web for the best information on valve train geometry that I have found).

 

[WHITE94COBRA]

I checked the timing, it right on. I always do my comp. checks on a cold engine throttle closed. The rocker studs were a bad batch from AFR, they are the old studs. Thanks for the info, i'll check out that website.

If your cam was properly degreed in when you built this motor and you used a new chain it is likely that it has stretched somewhat during break in. I have seen double rollers lose 4 degrees + of cam timing before they take a set position. This would retard your cam making the intake close later. (the piston will be further up the bore, heading for TDC before it closes and you will lose some compression. This could account for some of your power loss.
As mentioned by another responder compression test results can vary anyway. Engine temp. air density, throttle position can impact all impact it. Also if your rocker geometry is correct you shouldn't be breaking studs. (try finding Jim Miller Engineering on the web for the best information on valve train geometry that I have found).

 

[svt2785]

http://mid-lift.com/TECH/TECH-Definitions.htm

Save you some time! As you click on definitions it will take you to detailed information.

 

[final5-0]

I don't think me posting here will do you much good because my memory is not
all that great when I checked the cranking compression of my old self ported
E7 combo.

I seem to think it was around 155 or 160

I put my sig combo together in late 2002 and never did check the squeeze
in all holes but I seem to remember checking just one hole one day and it
was like in the 180's.

Again ... the memory is quite fuzzy :scratch
so
Don't take this stuff to heart here

Now about that dyno chart

I guess I'm at a loss between what you said and what I see

You say it drops off at 6K
but
I see it starts to drop off at 5K

The fuel ratio looks to be too lean if you ask me

4600 rpm is about the only point things are below 13 to 1
and
From that point on ... it steadily rises to like 13.25 or higher

Grady