Compression Test

[LGAFF]

Anyone have normal specs for LT-5 compression or tested their car?

[-=Jeff=-]

Anyone have normal specs for LT-5 compression or tested their car?

You break the black one already?? :sign10:

[LGAFF]

checking condition of the engine.

[-=Jeff=-]

checking condition of the engine.


Ah, is there something that has you questioning it?

[LGAFF]

Engine not at temp, will retest,

210 on left side
240 on right side

went back after testing right side to validate # and restested left and got 210.

[jonszr1]

dont know if altitude plays a part in testing compression. my black car tested at 175 -180 cold my altitude is 4000 ft . did they all test 210 on the left side / did you have the plenum and inj housings off? if not was the throttle held open all the way?i wonder if the cam s on tthat one side are timed different. dont know if that is possible ,just sharing thoughts .hope it helps

[flyin ryan]

Engine not at temp, will retest,

210 on left side
240 on right side

went back after testing right side to validate # and restested left and got 210.pretty high...:icon_scra

[Pete]

Lee,i have done compression test with almost every cam timing i have tried.

It's been a while i can't rememmber.
I have to find the paper work.

If i find the paperwork i can almost tell you where your cams are timed at.

Pete

[Nick]

pretty high...:icon_scra
Interesting comment, Ryan. Mine are as follows (with 70,000 miles on the clock; test done per the '94 service manual):

#1: 220
#2: 220
#3: 215
#4: 210
#5: 215
#6: 210
#7: 215
#8: 215

I'm not so sure the numbers themselves are that important. What is important, at least to my mind, is the consistency between the cylinders. But, Ryan, you would know more than I! :worship:

[Pete]

I also remember 210's - 220.

Pete

[jonszr1]

does altitude make a difference in the readings ????

[Sgreg]

does altitude make a difference in the readings ????

Only if you are smoking a funny weed. :mrgreen:

[flyin ryan]

Interesting comment, Ryan. Mine are as follows (with 70,000 miles on the clock; test done per the '94 service manual):

#1: 220
#2: 220
#3: 215
#4: 210
#5: 215
#6: 210
#7: 215
#8: 215

I'm not so sure the numbers themselves are that important. What is important, at least to my mind, is the consistency between the cylinders. But, Ryan, you would know more than I! :worship:Well...when i build an engine from scratch, i always shoot for between 165-185 pumping comp., if it's a maximum effort combo like Super Stock or Competition Eliminator it will get up to 200ish, but those have around 15:1 static comp. ratio too. it's all about balancing out the comp. ratio & camshaft(s), for me. i'm doing a, call it 'serious', comp. elim. engine right now, 358 cube & will be right on 16.2:1, so guys might think well it's going to have a pump. comp. number that's through the roof but this will also have a cam around .970" lift on the intake & 277º@.050" on the Int. & 295º@.050" duration, lobe seperation is 115.5º also. so what it's going to do is bleed off a bunch off cylinder pressure. now of course what we are talking about here is an engine that's turning over on the starter, what's happening, at 10,200 RPM, on this Comp. engine i'm talking about for instance, is a completly different story for another day. also... if i get close to 200 pumping on a good street deal that's say...1.5 HP per Cube, i'll be looking to put in a slightly, for lack of a long winded explanation, 'larger' camshaft to help bleed off some cylinder pressure. i guess an LT-5 could have that kind of cylinder pressure, it does theoretically have 11:1 Comp. ratio from the factory & the camshaft's are teny-tiny, IMO. if those cylinder pressure numbers are pretty close to what they are supposed to be from the factory, i'd have to say the knock sensor must be working overtime under light 'load', not at 'RPM' but lower RPM grunt situation's. Nick's car with his milage & those numbers must be in range, cylinder pressue is never going to go 'up' once an engine is broken in. Lee's on the other hand, that has some 240 numbers...well that's getting crazy high at that point. i'm assuming all the guys the posted here are cracking/opening the butterflies & have all eight (8) plugs removed when pumping. generally five (5) revolution's is the number, even when NHRA P&G's a competitor for cubic inch, (Pump & Gauge), same thing, five. i always measure one (1) pump, reset, then do five (5). both numbers can mean different things that help me.

[jonszr1]

Only if you are smoking a funny weed. :mrgreen:hehe, guess i better retest without the additives .jk:mrgreen:

[Nick]

i'm assuming all the guys the posted here are cracking/opening the butterflies & have all eight (8) plugs removed when pumping. generally five (5) revolution's is the number.
That's exactly what I'm doing, Ryan, except butterflies wide open. Also, the crank sensor is unplugged during the test.

[LGAFF]

I will retry the test this wekend with a warm engine, etc.

[Pete]

My research has found the 4 valve is more efficient then 2 valve motor.

LT5 makes 1.5-1.6hp per inch (550-575chp 350ci) idles (750) and drives like a stocker on punp gas,very well mannered.

Don't get me wrong i'm not saying the LT5 is a better just pointing out they are 2 different beasts,build for different purposes.

I have a question can we build a 358 that can be street driven i.e. (traffic,grocery store,pump gas) idle ok and make 750chp or 650whp?
How much?
You can PM/email me or post here.

Pete

[flyin ryan]

My research has found the 4 valve is more efficient then 2 valve motor.

Ya that's no secret for sure, but they aren't more efficient than the Comp. Elim. engine i was using as an example, that's why it will make 2.6 HP per Cube. again...not a street deal at all & again, it was just an example, wasn't intending to directly compare the two 'styles' of engines.

[flyin ryan]

I have a question can we build a 358 that can be street driven i.e. (traffic,grocery store,pump gas) idle ok and make 750chp or 650whp?
How much?
You can PM/email me or post here.

PeteDefine your idea of 'idle o.k., LOL. honestly you'd be better of going to something with more cubes for a street deal, IMO. at 358, it would have to see some RPM, then you get into expensive valvetrain pieces. 750 HP is 'A LOT' for a 23º type head deal, i've done it on pump gas, but it's a lot, everything has to really well sorted out. 600 HP is one thing but 750? well that's a completely different animal. don't know if that's what you want to hear or not but i'm not going to B.S. you :neutral:

[diamond zr1]

put it on the juice like Kevin

[Ccmano]

does altitude make a difference in the readings ????

Yes it does! I lived in Denver for 5 years. There is 20% less air to compress at 6000ft where I lived. Power was down by the same amount. Very frustrating. I was getting compression readings in the 170's at the time.
H
:cheers:

[jonszr1]

Yes it does! I lived in Denver for 5 years. There is 20% less air to compress at 6000ft where I lived. Power was down by the same amount. Very frustrating. I was getting compression readings in the 170's at the time.
H
:cheers:thak you for the info i feel better now . i was thinking that at 180 at 4000 ft i might be ready for a rebuild . i was going to have my car tested for substance abuse.jk:mrgreen:

[rkreigh]

air density definitely affects cyl pressure and power no doubt about it

dyno it up there and you'll be disappointed. come down at see level and let the beast BREATHE!

high altitude = LT5 asthma

[jonszr1]

thanx for the info . i do love going to the strip, but the best air density reading i have gotten is 1950 ft . drag times has an air correction calc. in the tools sec.. when i have used it i have found that the corrected time for my blk car has come down to 11.45 @123.56 mph .i dont know hhow accurate it is .i would love to go to the east coast where the air is -1000 ft alot .

[KILLSHOTS]

I know I'm opening a super old thread here, but it's still relevant. I've been considering the 400 mile '90 at a dealer in Anaheim, which has been previously discussed here in another thread. It tested with all 8 cylinders reading between 180 and 185 psi. Although the numbers are consistent, they seem low in comparison to some of the numbers I'm seeing here, and Anaheim is not exactly at high elevation. Should there be any concern? Could the lower compression readings simply be occurring because the engine isn't broken in? Thanks.

[XfireZ51]

I know I'm opening a super old thread here, but it's still relevant. I've been considering the 400 mile '90 at a dealer in Anaheim, which has been previously discussed here in another thread. It tested with all 8 cylinders reading between 180 and 185 psi. Although the numbers are consistent, they seem low in comparison to some of the numbers I'm seeing here, and Anaheim is not exactly at high elevation. Should there be any concern? Could the lower compression readings simply be occurring because the engine isn't broken in? Thanks.


I think the spec for the LT5 is in the 180 range and just as importantly how close the individual cylinder numbers are to one another. Some of the compression number is due to cam timing and how good it is and where its set.

[Ccmano]

I know I'm opening a super old thread here, but it's still relevant. I've been considering the 400 mile '90 at a dealer in Anaheim, which has been previously discussed here in another thread. It tested with all 8 cylinders reading between 180 and 185 psi. Although the numbers are consistent, they seem low in comparison to some of the numbers I'm seeing here, and Anaheim is not exactly at high elevation. Should there be any concern? Could the lower compression readings simply be occurring because the engine isn't broken in? Thanks.

In my opinion an LT5 at basically sea level should at least be at 200psi. I think you hit the nail on the head in that with 400 miles the rings simply haven’t had a chance to seat themselves yet. As long as they are all within 10% of each other I would not be concerned. Seems to me the car had other issues though. Nothing major. The price was pretty good for a 400 mile car. Good luck!
H

[KILLSHOTS]

In my opinion an LT5 at basically sea level should at least be at 200psi. I think you hit the nail on the head in that with 400 miles the rings simply haven’t had a chance to seat themselves yet. As long as they are all within 10% of each other I would not be concerned. Seems to me the car had other issues though. Nothing major. The price was pretty good for a 400 mile car. Good luck!
H


Thanks! It does have other issues but the big one has been fixed and the others are workable due to the price.

[Vette73]

I think the ZR-1,has to be,one car that many people who have owned in the past,did not drive very much...

Many many examples of low mileage cars out there...

Sent from my LG-TP260 using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[Ccmano]

Funny, I just looked in the FSM. Typical factory speak. They claim 150-200 psi with a 15% Cylinder to Cylinder variation tolerance. I suppose that gave them warranty leeway.
H
:cheers:

[Ccmano]

I think the ZR-1,has to be,one car that many people who have owned in the past,did not drive very much...

Many many examples of low mileage cars out there...

Sent from my LG-TP260 using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

Yes, back in the day many thought they would make killing if they kept it with low or no miles for 20 or so years. Lol... so much for that.
H

[KILLSHOTS]

Funny, I just looked in the FSM. Typical factory speak. They claim 150-200 psi with a 15% Cylinder to Cylinder variation tolerance. I suppose that gave them warranty leeway.
H
:cheers:


OK cool, based on that, I guess the peak numbers are OK and variation is less than 3%. Thanks.

[DRM500RUBYZR-1]

OK cool, based on that, I guess the peak numbers are OK and variation is less than 3%. Thanks.



I cannot imagine ANY reason to not buy that car.
I am shocked that it is even still around.
Go ahead with your purchase, but best to wear a mask and carry a gun, because your will surely be stealing it!!!
That will be a well-bought car!
Marty

[LGAFF]

I spoke to Scott skinner once about compression testing. He told me new motors were all over the place 150s and some as high as 300 but stabilized after use


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[KILLSHOTS]

Hey guys, as many of you know, this car would only run for 5 to 10 seconds and it was determined that it was a fuel pump issue, which was fixed. One of my biggest concerns was the extent of the "out of storage" fuel system service that the car received a couple years back. I knew it had new injectors but was concerned there would be a nightmare inside the fuel tank. However, I just received this pic of the sending unit that just came out and the one that replaced it. Since the one that came out looks brand new, I'm feeling better about moving forward now...

[phrogs]

That's quite the spread in the FSM but thats the bible. I'm always more concerned with numbers being pretty consistently even across the board.

There's always room for some difference some cylinders wear faster than others too. Use the 15% difference as the guide and don't focus solely on the numbers as many do.


As for the fuel pump I want to say that means the primary pump was dead. Not rare at all.