Quick motor question

[Kocher93]

I have an 89 350 tbi. When I got my truck both a vin check and the PO said the motor had 194k on it. After what I've done were sitting at 220k. Today I finally checked my compression and I'm at 150 + or - 5 at each cylinder. I'm not to bright on motors, but is this normal for 220k or has something been replaced?

 

[ryoken]

that's fine.. you want them all within 10% of each other...

 

[magik235]

that's fine.. you want them all within 10% of each other...

 

[black dawg]

I would say that is above average for 200k. tested a 150k tbi350 the other day that was 120

 

[chulisohombre]

I would say that is above average for 200k. tested a 150k tbi350 the other day that was 120

Anything above 130 and within 10 petcent on the cylinders is doing awesome almost brand new IMHO. Over 150 pci needs premium fuel or better as well.

 

[4X4HIGH]

I checked compression in my 89 engine at 217K and it was 205 psi across the board. Basically, you dont want a difference of more than 10% between the highest and lowest cylinders.

 

[black dawg]

I checked compression in my 89 engine at 217K and it was 205 psi across the board. Basically, you dont want a difference of more than 10% between the highest and lowest cylinders.

why the heck would it have 200psi?

 

[Hogback Fabrication]

The psi isn't super relevant, it depends on the size of the throttle body/carburetor (big variance), whether the throttle blades are shut or open (HUGE variance) and what altitude you're at and how the weather is (again, another big variance).

That's why you're generally looking for a difference in the numbers. Sure, they'll get a little lower as the engine wears but one that's much lower than the rest means something is wrong on that cylinder.

 

[ryoken]

just for the record... a correct compression test has the throttle blades wide open, many don't know that...

 

[4X4HIGH]

just for the record... a correct compression test has the throttle blades wide open, many don't know that...

Also ALL spark plugs out AND engine at operating temp and i'll bet noone does the latter.

 

[K5_Fla]

So what is the process from start to finish… I have never done and I’m curious what mine is. I guess you need to start with this http://www.summitracing.com/parts/sum-900009?gclid=CKLa66PCwrQCFQUFnQod4EcAaQ

Then get the motor hot… turn off and remove all the plugs. Then start at one at a time… just screw in the tester and bump the starter for a few seconds?

 

[ryoken]

engine at operating temp and i'll bet noone does the latter

if it runs, I do...

I'll bet the farm I do more compression tests a yr than anyone in here, by a long shot... it's almost standard on a boat sale/survey, and I usually do em in pairs.. usually at least 2 to 3 dozen a yr...

 

[4X4HIGH]

if it runs, I do...

I'll bet the farm I do more compression tests a yr than anyone in here, by a long shot... it's almost standard on a boat sale/survey, and I usually do em in pairs.. usually at least 2 to 3 dozen a yr...

Well Paul, besides you and I noone else probably does the test at operating temp.

 

[ryoken]

I'm guessing the new gig has you working on a large variety of equipment these days... probably keeps it interesting...

 

[black dawg]

Well Paul, besides you and I noone else probably does the test at operating temp.

I sometimes do both hot and cold. I am still curious how a stock tbi motor could blow over 200 psi. What heads and pistons?

 

[4X4HIGH]

I'm guessing the new gig has you working on a large variety of equipment these days... probably keeps it interesting...

Actually, i've been working on nothing but electrci scissor lifts. I guess at some point I should broaden my horizons but I just like and understand the scissor lifts pretty damn well that EVERYONE in the shop comes to me when they have an issue with any of them. I just bought a Fluke 375 meter to use for checking the charging systems on them and of course it will get used for other electrical checks as well.

 

[ryoken]

I'm in the market for a new meter.. my $500 snappy one and my power probe both got ruined in the hurricane...

I was actually looking around tonight at Flukes site...

 

[4X4HIGH]

I sometimes do both hot and cold. I am still curious how a stock tbi motor could blow over 200 psi. What heads and pistons?

The engine is completely bone stock. Compression readings are primarily based on cylinder volume and camshaft overlap. The higher the compression ratio is the higher your compression test reading will be and also the less overlap a cam has that affects the reading to the high side versus a cam with lots of overlap which will reduce the reading. The new engine I built (well back in 2008) is exactly at 9.48:1 compression ratio and it too is 200psi compression reading.

 

[4X4HIGH]

I'm in the market for a new meter.. my $500 snappy one and my power probe both got ruined in the hurricane...

I was actually looking around tonight at Flukes site...

What do you require in a meter? The Fluke 375 will do BOTH AC/DC volts up to 600V and also AC/DC amps up to 600amps starting at 1 amp with a 0.1 resolution. The meter will also check HZ, ohms, continuity and is a true RMS meter.

 

[ryoken]

yeah, i looked at the 375.. it's a strong candidate.. it covers what I do nicely... the boats are fairly varied with both AC and DC, gen sets, etc... i mainly use the meter these days for HZ and amps... most of my other continuity and DC stuff gets handled by the power probe 3.. well, when i replace it.. that tool has become an absolute godsend on the boats.... powering components, grd, continuity, etc...