Supercharged Compression Test #'s / Question

[.bg.]

Picked up a '96 4Runner a couple of months ago from it's original owner. It has 140k miles and has been supercharged for the last 80k of them. No fuel mods.

It seems to run fine and I haven't detected any audible pinging in the couple of months I've had it, but I'd still like to get it setup correctly with the URD 7th injector kit and go ahead and go to a 2.1" pulley while I'm at it.

Since the s/c is at 80K miles (1st gen), I'm considering going ahead and having it rebuilt.

Before I dump a ton of money into it I wanted to make sure the motor is in good health- especially since it's been run for a long time without any of the fuel upgrades.

If it's not in good shape, I'll refrain from putting any money into it and just run the motor until it blows. But if all is well, I want to get it set up right for good.

Did a compression test this previous weekend and came up with these #'s:

#1: 200
#2: 195
#3: 175
#4: 195
#5: 195
#6: 195

Obviously an outlier on cylinder 3. Recommended #'s are supposed to be 175 with a maximum cylinder difference of 15, however, all of my cylinders are around ~195 with a single one 20psi less.

I know cylinder 3 would also be where I could expect to see cracked heads if that were the case, but I don't seem to be losing any coolant and I would imagine the psi would be much lower than 175 if there truly were such an issue.

As a test, we dumped a capfull of oil into cylinder 3 and tested again. It came up to 185psi. This also seemed inconclusive to me- came up a bit, but not enough to directly mean much?

My #'s don't seem actually bad to me, but I really wish #3 was 5psi higher or so - would have gone a long way in making me feel more confident about dropping the money in it and meaning the engine really was in great condition to start with.

In any case, what do you guys think? Anything to be concerned about?
Or should I just keep an eye on it and dive into getting the fuel mods done, getting the s/c rebuilt, and upping the boost slightly....

 

[Brilliant]

Run the engine till the it craps out. Once it does, get a rebuilt one.

Seems strange to rebuild an engine to get higher numbers on #3, when it will work as is and it will get you by.

I put my SC on with 180k, didnt even check the numbers because it wouldnt change what I was going to do, run the engine till it craps out and get a replacement.

 

[.bg.]

Run the engine till the it craps out. Once it does, get a rebuilt one.

Seems strange to rebuild an engine to get higher numbers on #3, when it will work as is and it will get you by.

I put my SC on with 180k, didnt even check the numbers because it wouldnt change what I was going to do, run the engine till it craps out and get a replacement.

Wouldn't be rebuilding it in any case. Just wouldn't be dumping the money into getting the s/c rebuilt and doing the fuel upgrades if I didn't feel like the motor had a ton of life left in it.

Again, I didn't think it was horrible, but it was just low enough compared to the others to make me hesitate in doing a bunch of work on it.

 

[Brilliant]

Wouldn't be rebuilding it in any case. Just wouldn't be dumping the money into getting the s/c rebuilt and doing the fuel upgrades if I didn't feel like the motor had a ton of life left in it.

Again, I didn't think it was horrible, but it was just low enough compared to the others to make me hesitate in doing a bunch of work on it.

So you'll rebuild the SC for $500?, spend $1000 on fuel mods yet won't buy a $1500 reman engine to drive your 4runner another 200k. :crazy:

 

[Willhickey]

Wet test means your rings are going bad dont stress it you will do more harm than good . With those miles that motor is fine . Spend the money on the sc . That's 2 car payments

 

[.bg.]

So you'll rebuild the SC for $500?, spend $1000 on fuel mods yet won't buy a $1500 reman engine to drive your 4runner another 200k. :crazy:

I didn't bring up doing a rebuild or buying a remanufactured engine. I'm just trying to gauge if the low compression in #3 is something to be concerned about before I go dumping money into having the s/c rebuilt and potentially upping the boost.
Has anyone else had a single outlier # like this? And if so, how did it turn out?

I know there was a thread on customtacos about having low compression on #3 and #4 and it turned out to be a crack running between them with several others mentioning similar issues.

#4 looked fine on my test, but I was still a bit concerned as my one problem cylinder was indeed #3.

It very well might be bad rings- strange that it's local to that cylinder and in that case I'm up for opinions on whether or not upping the boost with the 2.1" pulley would be an acceptable risk to take or not.

 

[SV_Dude]

Those compression numbers are great! The fact that the #3 cylinder came up to 185 is even better. Just out of curiosity, did you do the compression test on a warm engine or a cold one? If cold, do it again on a warm engine.

As for the S/C rebuild, you can do it yourself for a couple hundred bucks if you're savvy with a wrench.

Do the fuel mods and get the 2.1 pulley. I have the 6 injector kit and a 2.1 pulley and my 4runner is a ton of fun to drive. You won't regret doing those mods! There is a HUGE difference in power between a stock s/c and a s/c running the 2.1 pulley and fuel mods.

DO IT!! :first:

 

[.bg.]

Those compression numbers are great! The fact that the #3 cylinder came up to 185 is even better. Just out of curiosity, did you do the compression test on a warm engine or a cold one? If cold, do it again on a warm engine.

As for the S/C rebuild, you can do it yourself for a couple hundred bucks if you're savvy with a wrench.

Do the fuel mods and get the 2.1 pulley. I have the 6 injector kit and a 2.1 pulley and my 4runner is a ton of fun to drive. You won't regret doing those mods! There is a HUGE difference in power between a stock s/c and a s/c running the 2.1 pulley and fuel mods.

DO IT!! :first:

I did do the test with a warm engine (wide open throttle / all plugs out).

A huge difference in power you say? :becky: Not sure I need any more encouragement...

I'm leaning towards pulling the trigger on it all. Just need to come up with my final shopping list!

Thanks!

 

[SV_Dude]

I have recently been in a 3rd gen with a stock engine, no fuel mods and a 2nd gen s/c. It was fast and definitely had a lot of pep and fun to be in. In a comparison to power, the driver of the 4runner thought that by the time his was at about 60mph, mine was already at 80 or so.


Here's a video of me showing off the get up and go of mine. Note that I was taking it easy on the shifts so I wasn't trying to race it but I was stretching out the legs on the engine a little bit. If I was shifting a little more aggressively it would have been a little bit faster.

 

[snivilous]

I have recently been in a 3rd gen with a stock engine, no fuel mods and a 2nd gen s/c. It was fast and definitely had a lot of pep and fun to be in. In a comparison to power, the driver of the 4runner thought that by the time his was at about 60mph, mine was already at 80 or so.


Here's a video of me showing off the get up and go of mine. Note that I was taking it easy on the shifts so I wasn't trying to race it but I was stretching out the legs on the engine a little bit. If I was shifting a little more aggressively it would have been a little bit faster.

Damn dude! Your 0-60 time is like under 10s, mine is around 15s I think lol

 

[.bg.]

I have recently been in a 3rd gen with a stock engine, no fuel mods and a 2nd gen s/c. It was fast and definitely had a lot of pep and fun to be in. In a comparison to power, the driver of the 4runner thought that by the time his was at about 60mph, mine was already at 80 or so.


Here's a video of me showing off the get up and go of mine. Note that I was taking it easy on the shifts so I wasn't trying to race it but I was stretching out the legs on the engine a little bit. If I was shifting a little more aggressively it would have been a little bit faster.

Wow, your truck really hauls! :wow2:

I realize should have said 2.2" pulley instead of 2.1". It's stock now. If I do the urd 7th injector, I figured it wouldn't be too dangerous to jump down a pulley size. But I'm a slight bit hesitant to do any pulley change now with the rings potentially a bit bad in #3 if that could drastically accelerate the wear on it.

Might just stick with the s/c rebuild and 7th injector at the moment and check my compression #'s again after a few thousand miles like this.

There's no real reason for me to make this into a speed demon. I've had enough truly fast toys over the years... This 4Runner is a lot of fun and I really enjoy having a big goofy 5spd supercharged suv, but I also drive it like an old lady... I've only had one tank come in under 18.5mpg (with a couple at just over 20.5mpg) if that gives any indication. :twitch: But it's awesome knowing that the power is there if needed. Although seeing videos like yours does really start tempting me to head down that "let's just see how fast it can be" road again!

 

[SV_Dude]

But I'm a slight bit hesitant to do any pulley change now with the rings potentially a bit bad in #3 if that could drastically accelerate the wear on it.

Might just stick with the s/c rebuild and 7th injector at the moment and check my compression #'s again after a few thousand miles like this.

175-185psi in a cylinder is hardly a sign of a bad ring(s). If your psi was down near 140 or so then I may be a little hesitant but not at where your engine sits. I wouldn't hesitate to put your engine through the ringers with the numbers you're showing. These 5vz's are known to handle quite a bit of power (upwards of 400HP) for a long reliable life.

There's no real reason for me to make this into a speed demon. I've had enough truly fast toys over the years... This 4Runner is a lot of fun and I really enjoy having a big goofy 5spd supercharged suv, but I also drive it like an old lady... I've only had one tank come in under 18.5mpg (with a couple at just over 20.5mpg) if that gives any indication. :twitch: But it's awesome knowing that the power is there if needed. Although seeing videos like yours does really start tempting me to head down that "let's just see how fast it can be" road again!

I understand not turning your 4runner into a race car... wait a second, no i don't! The fact that your runner is a manual transmission adds to the fun of it and you're not at a lot of risk in upping the boost of the s/c. The only downside to upping your boost and tuning a proper fuel map for it is that your fuel mileage will decrease dramitacally. My gas mileage is between 15-16 mpg, MAYBE 16.5-17mpg if I really drive it nice but it's so hard not to play once in a while.

 

[PitbullRescuer]

I'm with SV_Dude on this one. Your compression numbers are fantastic. Ideally you want no more than a 10% variance from highest to lowest, you have 12.5%. And not to pick on you at all, but I doubt all the cylinders were at a 5 or 0 for the last number so your variance may be even less than that.

When I compression test an engine I always do it warm like you said. But I do it both dry & wet. You have your dry numbers. I'd re-test all of them again wet and see where you end up.

Regardless, all signs point to you having a very well taken care of 5VZ. I'd go to town on the S/C mods if this were my truck. Good luck and keep us posted.

 

[.bg.]

175-185psi in a cylinder is hardly a sign of a bad ring(s). If your psi was down near 140 or so then I may be a little hesitant but not at where your engine sits. I wouldn't hesitate to put your engine through the ringers with the numbers you're showing. These 5vz's are known to handle quite a bit of power (upwards of 400HP) for a long reliable life.

I understand not turning your 4runner into a race car... wait a second, no i don't! The fact that your runner is a manual transmission adds to the fun of it and you're not at a lot of risk in upping the boost of the s/c. The only downside to upping your boost and tuning a proper fuel map for it is that your fuel mileage will decrease dramitacally. My gas mileage is between 15-16 mpg, MAYBE 16.5-17mpg if I really drive it nice but it's so hard not to play once in a while.

Oh, just don't want to end up knee deep in a project vehicle. I know how crazy things can get when the power bug bites!

It already has the centerforce stage 2 clutch and borla exhaust out back. It sounds awesome and is a lot of fun to drive. I hesitate to call anything this big "fast" though!

If I do the 7th injector install and setup up all of my fuel maps, I imagine I would have to re-do all of them again if I changed the pulley size afterwards right? If I want to do the tuning all once then I need to be doing it with my final setup...

That gets me closer to justifying doing the smaller pulley all at the same time as the fuel kit. :eyebrows:

We'll see. I've got a few weeks to decide.

I'm with SV_Dude on this one. Your compression numbers are fantastic. Ideally you want no more than a 10% variance from highest to lowest, you have 12.5%. And not to pick on you at all, but I doubt all the cylinders were at a 5 or 0 for the last number so your variance may be even less than that.

When I compression test an engine I always do it warm like you said. But I do it both dry & wet. You have your dry numbers. I'd re-test all of them again wet and see where you end up.

Regardless, all signs point to you having a very well taken care of 5VZ. I'd go to town on the S/C mods if this were my truck. Good luck and keep us posted.

Yeah, the gauge was pretty difficult to read the specific #'s off of, so we rounded to the nearest 5 and wrote those down.

In any case, thanks for the responses, I'm going to start getting my to do list together for getting all of this work done. Can't wait to see how fun the truck is on the other side!

 

[SV_Dude]

You will most definitely need to tune after you put in a smaller pulley or else you will be running lean.