RE: PSI for a healthy LT1

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RE: PSI for a healthy LT1

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RE: PSI for a healthy LT1 - 1/15/2008 6:48:50 PM

C3 Starship

Posts: 4749
Joined: 7/25/2006
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Well, it's a good thing it wasn't up to 115, or you'd really be screwed.

With those numbers, and the way she runs, that engine was broke in very well.

Sure, you have some leakage, but you have balance between cyl. I collapsed the rings in the ol' 350 and she smoked like heck, but she still ran very strong. I didn't do a comp check 'cause I already knew that it was time for a rebuild.

( ....that's when the 454 was dropped in the hole....)

_____________________________

1980 L-82 Fastback (forward too)
Mono composite front and rear.
Full adjust ride height and
response.
400+ hp, 454, M-22, 3.07

http://i121.photobucket.com/albums/o225/C3Starship/Patch.jpg

2007 H. D. Sportster, XL 883 EFI

(in reply to 78buckshot)

Post #: 11

RE: PSI for a healthy LT1 - 1/17/2008 4:18:12 PM

CFI/EFI

Posts: 5
Joined: 1/15/2008
Status: offline

quote:

ORIGINAL: C3 Starship

Oh ya,.... if you're goin' to do a comp test, you're wastin' your time if ya don't do both dry and wet. I don't care what your initial readings are, get the whole story. ( especially if your lookin' to buy )

"( especially if your lookin' to buy )" and you don't want to purchase a project, why would you perform the wet test if the dry rest shows a problem?

quote:

ORIGINAL: C3 Starship

It is just possible that your 160 reading is due to oil in the cyl., helpin' out some worn rings. Ya think? Hmmmm,.....could be........

Let me see if I understand what you are saying. On one hand you say, "you're wastin' your time if ya don't do both dry and wet" Then you suggest that a dry test on a worn engine is really a wet test. If that is what you are saying, how do I do the wet test that I would be "wastin' your time if ya don't do both dry and wet"? And what would it rell me?

RACE ON!!!

(in reply to C3 Starship)

Post #: 12

RE: PSI for a healthy LT1 - 1/17/2008 4:34:55 PM

CFI/EFI

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Joined: 1/15/2008
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quote:

ORIGINAL: 78buckshot

A compression test at cranking speed can be misleading, if the cam has allot of overlap which would normally be considered a high horsepower cam then it will show lower than normal compression.

I agree that a wild cam will cause an engine to have less cranking compression than a mild cam, but the amount of overlap has absolutely nothing to do with the amount of cranking compression.

RACE ON!!!

(in reply to 78buckshot)

Post #: 13

RE: PSI for a healthy LT1 - 1/17/2008 5:08:58 PM

C3 Starship

Posts: 4749
Joined: 7/25/2006
Status: offline

quote:

ORIGINAL: C3 Starship

Oh ya,.... if you're goin' to do a comp test, you're wastin' your time if ya don't do both dry and wet. I don't care what your initial readings are, get the whole story. ( especially if your lookin' to buy )

"( especially if your lookin' to buy )" and you don't want to purchase a project, why would you perform the wet test if the dry rest shows a problem?

quote:

ORIGINAL: C3 Starship

It is just possible that your 160 reading is due to oil in the cyl., helpin' out some worn rings. Ya think? Hmmmm,.....could be........

Any and all info is a help. What if you are lookin' to buy a project?
Does it need a head job, or a complete overhaul? Warped valve, weak springs, or busted rings? All knowledge is important to me.

Sounds like you have a real prob with doin' a "wet" test. It's real easy, since you already have the plugs out anyway, just squirt a little oil in the hole, and test again. Unless it's just too much bother.

Is this a test? I'm just makin' a reccomendation as to get full info.
You don't wanna do a wet test? I don't care, but I always do a "dry" and "wet" test. The amount of oil you're burnin', don't bother with any tests at all, just junk the engine and start over. (or don't, it's up to you )

I won't argue about it, 'cause I really don't care if you want to "wet" test or not. Others may learn from what they may find.
I know that I do.

_____________________________

1980 L-82 Fastback (forward too)
Mono composite front and rear.
Full adjust ride height and
response.
400+ hp, 454, M-22, 3.07

http://i121.photobucket.com/albums/o225/C3Starship/Patch.jpg

2007 H. D. Sportster, XL 883 EFI

(in reply to CFI/EFI)

Post #: 14

RE: PSI for a healthy LT1 - 1/18/2008 8:29:06 AM

CFI/EFI

Posts: 5
Joined: 1/15/2008
Status: offline

quote:

ORIGINAL: C3 Starship

Any and all info is a help. What if you are lookin' to buy a project?
Does it need a head job, or a complete overhaul? Warped valve, weak springs, or busted rings? All knowledge is important to me.

Good luck detecting weak springs with a compression test.

The purpose of a compression test is to get an idea of the overall condition of the engine. If all the readings are reasonably high and more importantly, fairly close (at least within 10%) of one another, the engine passes the test. There is nothing more to be learned from the compression gauge. If the results of the compression test show problems, and if you only want a car with a healthy engine, once again, you are done. If the car is no longer in consideration, why go to the effort of diagnosing a car you won't buy? On the other hand, of you are willing to buy a project, then a wet test will help you decipher to what degree the valves, and to what degree the rings, contribute to the problems.

quote:

ORIGINAL: C3 Starship

Sounds like you have a real prob with doin' a "wet" test. It's real easy, since you already have the plugs out anyway, just squirt a little oil in the hole, and test again. Unless it's just too much bother.

I have a problem wasting my time and beating a dead horse. If the car is out of the running, why continue to test it? In that case, YES, it's too much bother.

RACE ON!!!

(in reply to C3 Starship)

Post #: 15

RE: PSI for a healthy LT1 - 1/18/2008 3:50:02 PM

78buckshot

Posts: 653
Joined: 1/28/2007
From: Michigan
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Well then, for the sole purpose of continuing the argument with CFI/EFI, since it appears as that is your focus here, what part of the cam grind is going to influence the pressure if it ain't the overlap? Lift at cranking speed?, duration at cranking speed? If the cam has aggressive overlap, the the compression stroke is going to "scavenge" a good deal of the cylinder volume before the exhaust valve closes, effectively lowering the compression pressure at low RPM.

(in reply to CFI/EFI)

Post #: 16

RE: PSI for a healthy LT1 - 1/18/2008 3:54:03 PM

78buckshot

Posts: 653
Joined: 1/28/2007
From: Michigan
Status: offline

CStewTamu, I apologize for the forum and the good intention of it's members, I hope this little rant hasn't deterred you from participating on the boards.

(in reply to CStewTAMU)

Post #: 17

RE: PSI for a healthy LT1 - 1/18/2008 4:39:01 PM

C3 Starship

Posts: 4749
Joined: 7/25/2006
Status: offline

O.K., CFI/EFI, a comp test will not show weak or broken springs, it won't show a warped valve, it won't show broken rings. all it will show is comp loss, O.K.? BUT, these are some things that could possibly be wrong.

You go ahead and do thiings your way and I'll do them mine. I really don't give a squat. I'm a curious little bugger and want to see what's up with an initial test, whether I'm buyin' or not.

You are just so much smarter than I.

Maybe,...some day,......I'll get it right.

So,.....race on...

CStewTamu, I too, apologise for the rant. This is not common practice here. ( and it stops right now

)

_____________________________

1980 L-82 Fastback (forward too)
Mono composite front and rear.
Full adjust ride height and
response.
400+ hp, 454, M-22, 3.07

http://i121.photobucket.com/albums/o225/C3Starship/Patch.jpg

2007 H. D. Sportster, XL 883 EFI

(in reply to 78buckshot)

Post #: 18