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Author
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Topic: compression results, question
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JoeT
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Member # 298
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posted
 
 
Just wondering if you guys thought this was ok or weird or anything.
Mainly, I'm wondering if 'possibly' I'm hanging a valve open ever so slightly, or if the reduced compression #'s would be attributed to
1) cam bleeding a little compression +
2) increased combustion chamber of TFS TW heads (61cc + mild smoothing porting that probably added 1cc to each combustion chamber) vs. the iron GT-40 heads on factory 93-95 cobras which are supposedly milled ever so slightly for 58-59cc sized combustion chambers.
well, the #'s
#5 150
#6 150
#7 158
#8 152
#1 165
#2 152
#3 165
#4 152
These are all 'cold' readings.
IIRC , cold readings previous to swap where 160+ on all 8 with former GT-40 iron + stock cobra cam.
Previous 'hot' readings were all over 170.
Just curious/paranoid.
(cam stats, Anderson N-41 222/230 @0.05, 110 LSA installed 105.5 ICL, .512/.512 lift)
I also wedged a big screwdriver in backwards in the throttle body to improve air intake during compression testing. Spun it over 4-8 times until maximum reading was obtained.
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1984 Ford Tempo AOD--- RIP
Posts: 6785 | From: San Jose | Registered: Jun 2001
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JoeT
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Member # 298
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posted
triple post ![[Whoo Whooooo!]](graemlins/woowoo.gif)
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1984 Ford Tempo AOD--- RIP
Posts: 6785 | From: San Jose | Registered: Jun 2001
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Stimson
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Member # 51
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posted
For what its worth... here are the numbers I got from my car 3 weeks ago:
#5- 150 psi
#6 149 psi
#3- 143 psi
#1- 145 psi
#4- 145 psi
#2 144 psi
#8- 145 psi
#7- 149 psi
(listed in the order tested)
Your numbers look okay to me... but I'd test # 1&3 again.
Posts: 2373 | Registered: Jun 2000
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JoeT
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Member # 298
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posted
yeah but I was 160+ cold on all 8 like 2 months ago, I was just wondering if I can attribute the drop to the cam + the drop in compression from the bigger combustion chamber... (which I don't have exact measurements for :/ )
also #1 and #3 are repeatable!
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1984 Ford Tempo AOD--- RIP
Posts: 6785 | From: San Jose | Registered: Jun 2001
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Stimson
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Member # 51
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posted
Do all cylinders "keep" their pressure?
What I mean is.... 5-15 seconds after you stop cranking, does the compression guage needle start to drop quickly or does it stay put at 160?
Posts: 2373 | Registered: Jun 2000
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JoeT
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Member # 298
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posted
The gauge I use stores maximum value :/
'course harbor freight (or is it summit?) has like a $30 leak-down tester. That would settle the 'hanging' exhaust valve question...
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1984 Ford Tempo AOD--- RIP
Posts: 6785 | From: San Jose | Registered: Jun 2001
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Yellow94GT
Mr. 60 FT
Member # 431
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posted
I'm not even going to share the numbers fomr my last compression test, (yes, they are that bad ![[Eek!]](eek.gif) )
Lets just say, be happy with what you have
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AED
1994 GT Bucket that will likely never run
1999 SLOLEEN Twin Turbo Coyote
2008 F250 580 RWHP 1129 RWTQ
Posts: 5990 | From: Cameron Park, Ca | Registered: Sep 2001
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90LX
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Member # 1487
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posted
This is off the topic but shadetree do you still have those GT-40's. If you do, do you want to sell them
Posts: 300 | From: San Jose | Registered: Jul 2002
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JoeT
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Member # 298
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posted
ok this is the third or fourth time I've been asked that question in 2 days.
*attention*
The GT-40 irons on my former combo are going to be stage 0.5 ported (by me) and dropped off for a 3-angle valve job and then they're going to be dropped in a junkyard 302 and dropped in my brother's former 6 banger '65 coupe (aka rustbucket)
*attention*
thanks
(I think that 2700# car will see 12.1s @ 111 w/4.10s and ET Streets, said GT-40 irons,junkyard 302, 650 carb, edelbrock perfomer rpm carb intake, and a gearbanger riding a fox T5)
[ January 29, 2003, 02:39 PM: Message edited by: shade-tree ]
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1984 Ford Tempo AOD--- RIP
Posts: 6785 | From: San Jose | Registered: Jun 2001
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90LX
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Member # 1487
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posted
Sorry for asking!
Posts: 300 | From: San Jose | Registered: Jul 2002
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JoeT
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Member # 298
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posted
no need to be sorry ![[Big Grin]](biggrin.gif) just trying to clear things up!
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1984 Ford Tempo AOD--- RIP
Posts: 6785 | From: San Jose | Registered: Jun 2001
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93PONY
Mr. Valve Events
Member # 60
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posted
Hey Joe, GT40 irons come stock with 65.5cc chambers.
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4266 | From: Fair Oaks, CA | Registered: Nov 2000
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JoeT
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Member # 298
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posted
searched the corral archives, that's the size from the motorsport offerings, OEM 93-95 GT-40 irons were in fact milled...
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1984 Ford Tempo AOD--- RIP
Posts: 6785 | From: San Jose | Registered: Jun 2001
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93PONY
Mr. Valve Events
Member # 60
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posted
Are you telling me I have a 9.6-9.7 to 1 compression motor!?!
I shoulda' cc'd the things while they were off...
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4266 | From: Fair Oaks, CA | Registered: Nov 2000
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TheBrain
I'm the Real
John Force
Member # 35
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posted
Joe,
D.F.W.A.I !!!!
Cold compression readings mean absolutely DICK and are unreliable
For what it's worth, the above initials stand for Don't Fucking Worry About It
Later
Brian
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1989 LX vert 342
11.662 @ 116.65 1.57 60ft. N/A
10.227 @ 134.59 1.41 60ft 200 shot 3600lbs
2003 Ranger 4 door
15.99 @ 87
Posts: 1264 | From: Back in Redding CA | Registered: Jul 2000
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jmcclesk
Moderator
Member # 1355
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posted
what the brain said
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Ford trained ASE master tech.
Posts: 4024 | From: marrysville | Registered: May 2002
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04Z06
AX/OT Moderator
Member # 2309
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posted
Do you still have those GT-40 headds and if so do you want to sell them.. j/k
If the #'s are all close together.. don't worry about it.. Unless they are really low.. They look about right.
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2004 Z06
2003 DSG Mach 1 Wife took it in the Divorce
2001 Cobra (scrap yard, I hope)
2003 Blk Cobra (traded)
Posts: 377 | From: Ca. | Registered: Jan 2003
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Stimson
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Member # 51
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posted
For what its worth... I've done before and after tests with a warm and cold motor. Almost a 10 psi difference across the board.
Posts: 2373 | Registered: Jun 2000
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street_illegal_stang
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Member # 1554
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posted
if it makes you feel any better i got 60 psi with the number 8# cylinder on my stang ![[Roll Eyes]](rolleyes.gif)
try checking it when its warm.. ![[Wink]](wink.gif)
Posts: 1276 | From: Long Beach C.A | Registered: Jul 2002
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93PONY
Mr. Valve Events
Member # 60
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posted
IMO compression tests are not worth the effort. A leak down test is MUCH more informative.
The heads/cam profile play a big factor in your readings. Basically, your heads/cam combo don't flow shit at such a low rpm. (starter cranking speed) Low air velocity through the motor.
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4266 | From: Fair Oaks, CA | Registered: Nov 2000
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Primer GR40
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Member # 476
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posted
quote:
Originally posted by 93PONY:
IMO compression tests are not worth the effort. A leak down test is MUCH more informative.
The heads/cam profile play a big factor in your readings. Basically, your heads/cam combo don't flow shit at such a low rpm. (starter cranking speed) Low air velocity through the motor.
Yeah, that and they are usually depressing
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Superdupercharged Cobra
No Transmatic Notch
Posts: 2108 | Registered: Sep 2001
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JoeT
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Member # 298
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posted
I appreciate all the replies.
However, I stand by a quick compression test to verify a proper valvetrain rocker adjustment relatively quickly. I mean either your valves are hanging open or they're not.
I just fixed my vacuum leak (solid 13" at idle now) and of course it runs beatifully. With a vacuum leak and 5" of idle I needed to do a sanity check on the rocker adjustment stuff.
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1984 Ford Tempo AOD--- RIP
Posts: 6785 | From: San Jose | Registered: Jun 2001
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93PONY
Mr. Valve Events
Member # 60
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posted
You have more trouble in the garage then anybody I know.
I've never had problems with vacuum leaks. Well, not big ones like that! Sure, I work slower then some, but I check/double check everything. The worst I had on my car was a hole in the oil pan & a leaky valvecover seal which were vacuum leaks.....Yes, vacuum leaks on my car! Don't ask, it's an original setup.
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4266 | From: Fair Oaks, CA | Registered: Nov 2000
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JoeT
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Member # 298
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posted
well, nothing in my car is original except for parts of the wiring harness and the alternator so I'm probably not doing too badly.
(I did the rear, suspension, control arms, tranny, clutch, motor swap, multiple head/cam/intake packages, etc.)
anyways, I suck. oh well. Just a hobby...
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1984 Ford Tempo AOD--- RIP
Posts: 6785 | From: San Jose | Registered: Jun 2001
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93PONY
Mr. Valve Events
Member # 60
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posted
Hehehe, I remember meeting you at the track.
Me: "Hey bro, your smog pump is about to fall off. It's hanging the timing pointer."
You: "Huh? (checks) I hope it falls off."
Hahahahah!
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4266 | From: Fair Oaks, CA | Registered: Nov 2000
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