stock turbo compression

[Guest sabum]

What kind of compression should I get on a stock turbo block with a p90 head? I tested with all the plugs in except the cylinder I tested.

[Guest sabum]

I forgot to mention I have a 2mm head gasket.

[Guest sabum]

Does anybody know?? Im only getting 100 on each cylinder. Im afraid this is bad. I always thought 150-180 was ok. Is a turbo that much lower?

[TimZ]

Originally posted by sabum:

Does anybody know?? Im only getting 100 on each cylinder. Im afraid this is bad. I always thought 150-180 was ok. Is a turbo that much lower?

Why are you running a 2mm head gasket with the stock turbo block and P90? That combo gives a 7.4:1 CR with the stock gasket. By my calcs, the 2mm gasket should yield about a 6.9:1 CR. This might be part of your problem.

[SleeperZ]

On stock L28ET motors, at 5800' elevation, all I ever get is 100-110. This is normal - they have very low static compression. With a 2mm gasket, you will get less.

[awd92gsx]

On a stock pistoned L28ET with a P90, the 2mm head gasket will yield a 7.0:1 compression ratio (according to lengine.exe)

 

That, in my opinion, is way to low. I'm going to shoot for around an 8.5:1 for my turbo engine if possible.

[Guest sabum]

This combo did work. I was running consistant mid 12's @ 110 then something took a turn for the worse. I started running high 14's. Thats when I checked the compression and saw 100 psi. I was worried because I did not remember seeing an L series that low. When I saw they were all @ 100 so I thought I would ask. Thanks! I feel a little better now. I was worried I burnt rings or something worse

[awd92gsx]

Cool...have you checked for boost leaks? Boost leaks can REALLY slow you down.

[Guest sabum]

how would you find something like that?

[Lockjaw]

My compression is 150 psi, but not stock.

 

You can check for boost leaks by removing all the plumbing from the compressor to the throttle body. Check the hoses for holes/cracks. If you have an intercooler, you should fill it up with water and see if it leaks, and then let it dry after pouring the water out.

 

A good sign you have a boost leak is black smoke from the tail pipe when you first hit boost and some stumbling.

 

What kind of turbo are you running?

[awd92gsx]

Actually, the easiest way to find boost leaks is to make a boost leak tester

 

It's actually quite simple. Basically, you go down to home depot and you buy a 2" to 2" coupler (or to whatever size your turbo is, but a 2" rubber coupler fits most turbos, unless they're really big =o) a small PVC 2" 90 degree elbow, and a PVC cap (to cap one end of the elbow)

 

Then, you drill a hole into the cap and insert a male air hose quick disconnect fitting into it and use a nut to secure it from the other side. Seal it with silicone after it's secure.

 

PVC Glue the cap onto one end of the elbow and put the rubber coupler onto the other end. Pull off your AFM to turbo intake pipe and insert the testing tool onto the inlet side of the turbo.

 

Using a REGULATED air supply, pressuring the intake to about 12-18psi and just listen for any leaks that you may hear coming from the intake system.

 

If this sounds confusing I'll try to find a picture of what I'm talking about...

[Guest sabum]

Lock jaw: I am running a stock t3. When I did the compression test I did not have the throttle open. Am I supposed to?

 

Bill: I like your Idea however, I do not have air compressor equipment. I just changed my plugs and sprayed tunerwash on just about all the electronic connections.I also scraped the connections with a dentist explorer. I will be dragging this friday night. I will have to see how it does.

[awd92gsx]

I've heard of people having good luck with using normal bicycle pumps. In this case, though, I'd put an airtight cap on the intercooler piping at the throttle body connection.

[awd92gsx]

btw...yes, you should have the throttle plate open when you do a compression test, but, in all honestly, it will only affect your test marginally.

[SleeperZ]

Originally posted by awd92gsx:

btw...yes, you should have the throttle plate open when you do a compression test, but, in all honestly, it will only affect your test marginally.

I've heard this before, but never done it. How much would you expect it to change your compression measurements? I could test it, of course, but I've no need to pull my plugs at the moment

[awd92gsx]

I've done it both ways at the same time on the same car because a fellow tech started crying about how you have to hold the throttle plate open (in all honesty, I just forgot to hold it open). I didn't see enough of a change to make it worth redoing. Maybe a psi or two.

 

There are too many places for air to be pulled through into the intake manifold for it to be a completely tight seal.

[Lockjaw]

Oh I forgot to ask, you did your compression check with the throttle wide open right? That could have an effect on your reading.

[Lockjaw]

Ok I am confused about that pressure tester deal. You attach it to the inlet on the turbo? IS that right?

 

If so, that would mean your turbo would be spinning without oil. Although the speed may not be very high, I wouldn't do that to my turbo.

 

Now capping the thing and putting it in the turbo compressor outlet line, I can handle. That is really a good idea, and I guess if you capped both ends, and did not put enough pressure in there to trigger the BOV, that would work.

 

You should do your compression test with the throttle open according to most published sources, although I to have not noticed much difference. I think as long as you consistently do the same thing, that is what matters. After all, two different compression testers on different engines will give the same reading.

 

For example, I did a compression test on one of my NA engines along time ago at my buddies shop and it told me something like 90 psi. So I used a different one, and it was up around 160 or so. Same engine same cylinder, different tester.

 

You are mainly using the tester to check for variation between cylinders or dropping pressure as time passes.

 

You are running some good times for a t3 turbo. Mid 12's is stroking. Wonder if anyone has run faster than mid 12's with a t3?

[awd92gsx]

LOL, no, you won't spin the impeller by filling the intake system with compressed air. I've tested dozens of cars personally and find that about 9 out of 10 cars has a leak *Somewhere* in the system. It's a fairly common DSM trick and I've never ever heard of anybody spinning their turbo by applying compressed air via the above method.

 

There just isn't enough velocity through the elbow at the low pressures (no more than 15-18psi max) to spin the turbo at the speeds you're talking about.

 

You can find boost leaks at clamps, injector o-rings, throttle body o-rings, gaskets, etc...You'd be amazed at how much a little boost leak can affect the way a car runs.

 

It probably wouldn't affect a Z as much as a DSM, but a boost leak can affect ANY air flow meter equipped car in one way or another.

[Guest sabum]

I would really like to do this leak test. I am just noe equipped to do it at this time. Im currious as to what I would gain by going to a t3/t4 hybrid?? You guys seem to be up on this. quicker is always better........ I will let you know how I did on friday. I hope it will be fixed. 2 of the plugs seemed a little dark and who knows what cleanning the connections did.