Compression Test Results
Thread Starter
Le Mans Master
Joined: Aug 2002
Posts: 8,472
Likes: 38
From: Houston TX
St. Jude Donor '11
Compression Test Results
Recently I did a compression test of my 10.2:1 408 with only a few thousand miles on it if that. It does blow some smoke on decel and has been drinking some oil but I am not sure whether it's from the rings or the turbos which were rebuilt at the same time as I built the motor. I don't have the results in front of me but they were all between 165# and 175# cold and dry which seemed low to me for a 10.2:1 motor but I know cam profile comes into play there and since they were all within 6% I called it good. Now I'm thinking I should have done a wet compression test to see how much they went up but the research I've done on wet to dry increase or the validity of it seems debatable. I guess a leakdown test would be the most accurate but thought I'd get some input.
Racer
Joined: May 2004
Posts: 497
Likes: 3
From: Hafnarfirdi
I think you are ok since all cylinders are within 10 psi
. I have 9:1 and me compression is around 140 psi.
. I have 9:1 and me compression is around 140 psi. Recently I did a compression test of my 10.2:1 408 with only a few thousand miles on it if that. It does blow some smoke on decel and has been drinking some oil but I am not sure whether it's from the rings or the turbos which were rebuilt at the same time as I built the motor. I don't have the results in front of me but they were all between 165# and 175# cold and dry which seemed low to me for a 10.2:1 motor but I know cam profile comes into play there and since they were all within 6% I called it good. Now I'm thinking I should have done a wet compression test to see how much they went up but the research I've done on wet to dry increase or the validity of it seems debatable. I guess a leakdown test would be the most accurate but thought I'd get some input.
Le Mans Master
Joined: Dec 2005
Posts: 6,997
Likes: 1,681
From: Southeast TX
You're OK. You'd have to be damn talented to wear them out that evenly Might also look at valve seals/valve guide wear as a culprit for your decel smoke blowing. Adding a little oil on a compression test "could" eliminate the rings as a trouble spot. I'd bet on the top end or turbos as the source of your oil usage.
Might also look at valve seals/valve guide wear as a culprit for your decel smoke blowing. Adding a little oil on a compression test "could" eliminate the rings as a trouble spot. I'd bet on the top end or turbos as the source of your oil usage.
Le Mans Master
Joined: Oct 2003
Posts: 8,863
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From: PA
St. Jude Donor '08
Bill take off charge pipes and take a look in the compressor cover and see if there is any oil. I have seen turbo cars smoke under decell and compressor cover was covered in oil...
Thread Starter
Le Mans Master
Joined: Aug 2002
Posts: 8,472
Likes: 38
From: Houston TX
St. Jude Donor '11
Well I'm fairly reassured about the rings now. Heads or turbos I can deal with.
Nick I had most of the charge pipes off when I put the motor mounts in about a week ago and they're nine dry. Could be coming out the turbine side which would be hard to detect.
Nick I had most of the charge pipes off when I put the motor mounts in about a week ago and they're nine dry. Could be coming out the turbine side which would be hard to detect.
Racer
Joined: May 2004
Posts: 497
Likes: 3
From: Hafnarfirdi
Bill what about too much pressure in crank case could that be issue under boost? I had issue be for I build breathing system with catch can with 3 tubes in one from each valve cover and one from under manifold if I remember correctly and air filters on the catch can. After this I have no issue with oil.
Thread Starter
Le Mans Master
Joined: Aug 2002
Posts: 8,472
Likes: 38
From: Houston TX
St. Jude Donor '11
Could be. I have the stock nipples on both valve covers running to a vented Jazz catch can and the oil filler cap has an ECS-Like vent on it. I've gotten exactly nothing in the Jazz catch can but there is oil residue around the oil filler vent.
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Safety Car
Joined: Feb 2008
Posts: 3,712
Likes: 3
From: TEXOMA
St. Jude Donor '08-'09
big boi toys
http://www.gzmotorsports.com/LSXVPK.html
those numbers looks fine. those 317's are holding you back! got any local cnc places?
-Carl
http://www.gzmotorsports.com/LSXVPK.html
those numbers looks fine. those 317's are holding you back! got any local cnc places?
-Carl
Thread Starter
Le Mans Master
Joined: Aug 2002
Posts: 8,472
Likes: 38
From: Houston TX
St. Jude Donor '11
7-11 hundred dollar-bucks for a vacuum pump? Pass.
No one local I know of but I'm told I could get a program run on them for ~$700. For that much I'd rather get some patriot stage 3 heads with new springs, valves, etc, do a direct swap and sell mine. There are seveal components "holding me back"; heads, 2.5" downpipes, 58mm turbos. Champion 3" downpipes seem like the best bang for the buck if these results are typical
: http://forums.corvetteforum.com/c5-f...rwhp-dyno.html then some heads would net me an easy 40-50 RW.
But I digress...
No one local I know of but I'm told I could get a program run on them for ~$700. For that much I'd rather get some patriot stage 3 heads with new springs, valves, etc, do a direct swap and sell mine. There are seveal components "holding me back"; heads, 2.5" downpipes, 58mm turbos. Champion 3" downpipes seem like the best bang for the buck if these results are typical
: http://forums.corvetteforum.com/c5-f...rwhp-dyno.html then some heads would net me an easy 40-50 RW.But I digress...
Last edited by 5 Liter Eater; Jun 27, 2012 at 11:43 PM.
Safety Car
Joined: Feb 2008
Posts: 3,712
Likes: 3
From: TEXOMA
St. Jude Donor '08-'09
. There are seveal components "holding me back"; heads, 2.5" downpipes, 58mm turbos. Champion 3" downpipes seem like the best bang for the buck if these results are typical : http://forums.corvetteforum.com/c5-f...rwhp-dyno.html then some heads would net me an easy 40-50 RW.
But I digress...
: http://forums.corvetteforum.com/c5-f...rwhp-dyno.html then some heads would net me an easy 40-50 RW.But I digress...
p.s. what mufflers are you running? I cut open my z06 mufflers and welded the perferated tube closed, my max boost went up 6psi and now it sounds bad ***!
Thread Starter
Le Mans Master
Joined: Aug 2002
Posts: 8,472
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From: Houston TX
St. Jude Donor '11
3" z06 catless center section that goes back down to 2.5" corsa sports. I think the gain you saw removing the mufflers would be similar to me going with 3" dp's.
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Do you have aftermarket or heavily ported heads on the car?
If so it is very common for the intake rocker bolt hole to not be blind, so you have to seal the threads on the rocker bolt or you will have the exact condition your discribing.
Iintake vacuum on decell especially will suck oil into the port threw the threads, I have seen this 100 times on road race cars. The owner thinks the engine is shot and we fix it for minimal $$.
I hope that helps.
If so it is very common for the intake rocker bolt hole to not be blind, so you have to seal the threads on the rocker bolt or you will have the exact condition your discribing.
Iintake vacuum on decell especially will suck oil into the port threw the threads, I have seen this 100 times on road race cars. The owner thinks the engine is shot and we fix it for minimal $$.
I hope that helps.
Melting Slicks
Joined: Jul 2008
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From: Houston Texas
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Bill,
Your compression test numbers don't seem too out of line. I've always put more faith in leakdown numbers when it comes to verifying engine health. I check mine periodically and it's always in the 3% to 5% range.
Your compression test numbers don't seem too out of line. I've always put more faith in leakdown numbers when it comes to verifying engine health. I check mine periodically and it's always in the 3% to 5% range.
Drifting
Joined: Feb 2006
Posts: 1,585
Likes: 15
From: New Hartford IA
How loose did you set up the pistons? Lots of piston rock at BDC (stock iron blocks are the shortest sleeve also) can cause the rings to dance around a little. Not sure how much smoke you are talking though. Do you notice any blowby smell, etc?
Thread Starter
Le Mans Master
Joined: Aug 2002
Posts: 8,472
Likes: 38
From: Houston TX
St. Jude Donor '11
I'm not sure what the piston/bore tolerance is, the ring gaps are .026/.028 if I recall. There is some mist out of the breather at idle (which is what really prompted me to do the compression check) but aside from that it only smokes inbetween shifts and on decel.
Drifting
Joined: Feb 2006
Posts: 1,585
Likes: 15
From: New Hartford IA
Do you run PCV at all (with a check valve for boost of course)? Plugs come out oily at all?
My 383 has a little extra blow by since I built it 5 years ago. Did not stop it from making 500whp NA. It uses some oil when beat, but nothing really when putzing along.
My 383 has a little extra blow by since I built it 5 years ago. Did not stop it from making 500whp NA. It uses some oil when beat, but nothing really when putzing along.
Thread Starter
Le Mans Master
Joined: Aug 2002
Posts: 8,472
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From: Houston TX
St. Jude Donor '11
Yea it's got two campbell hausfeld ~catch cans and a check valve inbetween the lifter valley and TB in addition to the valve cover breathers.
I may have more problems than I thought. It's had a miss after changing the plugs (and installing PFADT motor mounts and some other stuff). Bank 2 is reading lean, pegging the STFTs (LTFTs disabled) and #2 plug is black. I changed the plug, swawpped wires and swapped #2 and #6 coil packs and it stayed with #2. Pulled the valve cover and didn't see any broken spring. I need to turn it over and make sure all the rockers are moving. It "could" also be that the turbo got clocked slightly different on the manifold because the turbo was up against the frame after the PFADT mounts went in for some reason and now the turbo outled is a lot closer to the plug/wire. I put plenty of dielectric grease on the wire but it is possible, maybe, that the current is choosing the path of the turbo outlet, via the fire sleeve. I donno yet and won't be able to look at it until Monday at the earliest.
I may have more problems than I thought. It's had a miss after changing the plugs (and installing PFADT motor mounts and some other stuff). Bank 2 is reading lean, pegging the STFTs (LTFTs disabled) and #2 plug is black. I changed the plug, swawpped wires and swapped #2 and #6 coil packs and it stayed with #2. Pulled the valve cover and didn't see any broken spring. I need to turn it over and make sure all the rockers are moving. It "could" also be that the turbo got clocked slightly different on the manifold because the turbo was up against the frame after the PFADT mounts went in for some reason and now the turbo outled is a lot closer to the plug/wire. I put plenty of dielectric grease on the wire but it is possible, maybe, that the current is choosing the path of the turbo outlet, via the fire sleeve. I donno yet and won't be able to look at it until Monday at the earliest.