Compression Numbers

[jquest2]

Hey Everyone

Some of you already know that I'm searching for a Typhoon. I have another question here if anyone can help.

I wondering what are good compression numbers for a typhoon w/ 100k miles?

I did a search and the numbers varied from 120 to 150. I know that if the variance of compression numbers across each cyclinder are minimal, the better. But I'm trying to make sure that when I buy a typhoon that the engine is solid and that I'm not getting railroaded because the truck looks immaculate.

Thanks in advance.

 

[SCWolverine]

I had the same search findings some time ago, so I can't help with the "what's good". But FWIW when I bought my SY in April it ranged 148-160, this with 127,xxx.

 

[turbodig]

Re: Compression Numbers

Hey Everyone

Some of you already know that I'm searching for a Typhoon. I have another question here if anyone can help.

I wondering what are good compression numbers for a typhoon w/ 100k miles?

I did a search and the numbers varied from 120 to 150. I know that if the variance of compression numbers across each cyclinder are minimal, the better. But I'm trying to make sure that when I buy a typhoon that the engine is solid and that I'm not getting railroaded because the truck looks immaculate.

Thanks in advance.

(These numbers are for stock piston/ring/chamber setups)

Really good = 130+
Good = 110-120
Ok = ~100
Starts to hurt = 80-90
Bad = < 80

Check all of them, if they're above 100 and all cyls are about the same,
(within 10-15 psi of each other) you should be ok. A single slug 30+
psi lower than the others has a problem.

Coupla tips:

Try running a can of Sea Foam through the intake before you run the
test... it'll clean out any flakes of carbon that might partially hold a valve
open and skew the results.

Make sure you test compression with the throttle open.


Later,

Dig

 

[Anthony]

With a cold engine and throttle open, my 110K mile Ty had right around 105 compression. It had just ran a 13.4 @ 99.5 before I checked the compression.

 

[jquest2]

thanks for the info...i'm trying to get the seller to drop the truck off next week to get it inspected and get a compression test done...once that is done, the dealer should be able to send me the results - if everything is good, then i'll be the newest typhoon owner...oh yeah!!!!

btw, the truck is over 10 hours away, that's why need to have a 3rd party check it out.

 

[93ty475]

i just checked my sy the other day...300 miles on new motor...2.02, ported L35's....412 cam...SRP's from RPM...JE file fit rings, filed .020 IIRC...using an el cheapo compression tester from Harbor Freight, we got 150 +/- ~3, on all 6...didn't hold the throttle open though...

 

[manitoufs]

My last check at 75,000 miles -

155, 155, 155, 155, 145, 155

 

[93ty475]

i'm right in the middle of a vortec head conversion/upgrade....i should have done it to begin with....anyway, i'll post the difference in compression numbers if there is any...the vortec heads were retrofitted with larger (2.02) valves, correct springs, and port matched...i'm wondering what will happen to the 150 psi i was getting.....

 

[odium]

Just clicking it over won't yield the right compression numbers will it? I was just messing around with all the plugs out clicking it over. I should put all plugs in and start the truck except the one cylinder to test, right?

 

[93ty475]

Just clicking it over won't yield the right compression numbers will it? I was just messing around with all the plugs out clicking it over. I should put all plugs in and start the truck except the one cylinder to test, right?

you should do it with all the plugs out and somehow disable your ignition at the coil....you don't want to start the truck...around four or five revolutions per cylinder did the trick for us....the gauge should pump up to a max psi then no more....i thought we didnt hold the throttle open when we did mine, but my more knowledgable friend says he did as he was the person cranking and i was the person under the hood holding the gauge....i wonder what the difference in psi would be? i'll have to try it next time...

 

[odium]

Everything seems fine, but i was just wondering, would you definately notice if you weren't getting good compression? I've never had bad compression in an engine, so I don't know.

 

[SCWolverine]

Oops, tested mine closed. Since then I've read in several places to test with open throttle. One of them stated "to ensure the engine gets adequate air intake"...(wouldn't a shortage of air decrease compression?) Same site also said 10 compression strokes, but mine actually peaked on the 2nd or 3rd. Anyhow, I'll try to check mine again this weekend (open) if anyone is curious (I am), it's only been about 50 miles ago.