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Does anyone know or could guess the maximum boost pressure that can be run on an L27 without causing damage?

I'm guessing 11 psi.

I never said anything about SUPER charging.. I am just curious as to the actual number would be.

I was pushing upwards of 13 psi when I was toying with that abomination. Pistons held just fine, as did the rods. It was all the bearings that didn't hold up so well...possibly a different hard/softness in the L27 and the L67.

Safely, maybe 6 psi would be the highest I'd go. Theoretically speaking of course.

phoenix_flame220 wrote:I never said anything about SUPER charging.. I am just curious as to the actual number would be.

Any forced induction would have similar results.

My guess is rod flex caused the demise of the "experiment".

Doesn't matter whether you're supercharging or turbocharging. forced induction is the same. They're all forcing more air in the cylinder. That's going to cause issues, period.

What about the UIM? If you used an L67 block and put the L27 intake on it. What the max boost the L67 block can take? I mean the series 1

Going that route, yes. I would, however, use the 1992 upper as it's all aluminum. The plastic uppers, though they don't fail like the L36, flex noticeably when you goose the throttle. I wouldn't trust them under boost.

Wouldnt using the 92 upper mean ide have to delete my egr? I just bought a brand new UIM so it would be a shame if I couldnt use it. I dont knwo if Ide be able to sell it locally. I would prefer to reuse as many parts from my current engine as possible. Especially the custom stuff I had to make for the top swap.

The rods did deflect and twist with the force being applied to them.. Some of the problems are that the NA piston skirt is not designed for Boosted applications, also the Boosted engines used a floating wrist pin as opposed to the pressed..

If you choose to boost this engine I would keep the boost LOW... and depending on what year the L27 you use was you will either have 8.5 : compression or 9.0 : 1 compression..

Keep in mind that the engine was not designed to be boosted

How low is low? My idea was something around 5 psi max. I am curious if it would be possible to get about 200hp. Or bring it to a stock 92 L67 power. What boost do they run stock? I know dropping in another engine would be cheaper better etc, but not as unique. and doesnt go PSST lol The LN3 had a 1 piece aluminum intake so that should be able to handle more boost correct? It isnt a 'tuned' intake but if the LN3 intake manifold was adapted to an L67 then it should be a good combo. I want to keep the EGR system for fuel economy sake. I have a bunch of other questions but I think I should do more research before asking.

GM *did* make a one-off Bonneville that was turbocharged that used the LN3. Just how much the LN3 was modified (i.e. internals) to accept said turbo nobody really knows.

5-7 psi should be do-able for an L27/LN3, but I wouldn't go past that. Even Chryslers 2.2/2.5 turbo motors churned out about 7 psi max (the PCM did allow slightly more boost for I think 5 seconds max, then backed off).

Now then, as fas as the PCM is concerned, you definately want something that can reference boost (map sensor), but even the OBD2 computers (at least the 1997s) don't reference boost (at least there are no tables for them in HP Tuners software). You could try Megasquirt as I believe they do, and if you are running a plain old 4T60, you won't need any sort of shift control.

I do not have enough back ground knowledge of the 3800 so I will not add to the debate.

A fundamental truth of modding is:

Set your priorities

Performance
Reliability
Cost

Pick two, you can not have all three.

What power gain would say 5 psi give?

My goals are to make a reliable engine with better performance. I dont want to spend huge money, so i will sacrifice maximum performance for cost savings. Reliability is paramount. I was painting my garage for 5 hours so i had time to think about this. This is my rough concept. I am trying to incorporate the parts from my current engine as I have them and some are already modified to fit my car. Ive just recently started reading up on this so please tell me where I am mistaken.

92-95 L67 block (they are the same for all years?)
94 L27 heads (that I already have)
92 L27 aluminum intake manifolds with an egr port tapped into it (will my 94 L27 fuel rail and injectors fit?)
Small turbo of appropriate size. Remote mounted under the trunk to avoid modification of exhaust manifolds, and pipe the intake into the L27 TB ( that I also have) . I am not planning on an intercooler at the moment because of the super long intake as it is.
A boost modulated pressure regulator ( or whatever its called, noob remember) to raise the fuel pressure under boost because the fuel system will probably be maxed out.
Upgraded fuel pump.
Maybe a cam to raise the power band a little?
After all is done a custom chip from Sinister.

The transmission will explode so is it possible to swap in the better parts from a 4T60-HD? changing the final drive ratio might be a good idea too. Its 3.33 which Ive heard it a little low, so maybe 2.97? If Im swapping parts I could choose from a bunch of ratios right? I just had this tranny rebuilt so I will be using it.

What else am I forgetting?

My responses in bold itallics.

phoenix_flame220 wrote: 92-95 L67 block (they are the same for all years?) No. Recent information points to the '95 L67 (Series 1) could actually pass as a "Series 1.5". It uses the S2 crank which is lighter, making it slightly more rev-happy.
94 L27 heads (that I already have)
92 L27 aluminum intake manifolds with an egr port tapped into it (will my 94 L27 fuel rail and injectors fit?)
Small turbo of appropriate size. Remote mounted under the trunk to avoid modification of exhaust manifolds, and pipe the intake into the L27 TB ( that I also have) . I am not planning on an intercooler at the moment because of the super long intake as it is.
A boost modulated pressure regulator ( or whatever its called, noob remember) to raise the fuel pressure under boost because the fuel system will probably be maxed out.
Upgraded fuel pump.
Maybe a cam to raise the power band a little? Good luck. Not much in the way of cams for the S1.
After all is done a custom chip from Sinister. Read my last post on this. A custom chip won't do much good if you can't control the boost to go with it. Your PCM isn't capable of that.
The transmission will explode so is it possible to swap in the better parts from a 4T60-HD? changing the final drive ratio might be a good idea too. Its 3.33 which Ive heard it a little low, so maybe 2.97? If Im swapping parts I could choose from a bunch of ratios right? I just had this tranny rebuilt so I will be using it. I would go 3.06. Remember, turbos don't act the same as superchargers...under most conditions, you're turbo will be in bypass anyway, meaning less power and torque available to move the car around until the turbo spools up. The 3.06 should give you a good compromise.
What else am I forgetting?

With sandrock using an L27( It was pristine BTW ) as a test bed... We learned a lot about what the LN3 and L27 could handle but we also found why doing this was not the greatest of ideas..

We found that the Piston skirts had scratched or scuffed the pistons and cylinder bore, this was due to the piston design as the supercharged motor has a piston skirt thats designed for boost, this helps keep the piston from rocking in the bore..

The LN3 and the L27 through 94 are just about the same engine..

The other of the problems was the torsion of the connecting rod flexing the rod ever so slightly enough to eat the edges of the bearings..

The Pistons did take the abuse and were in good shape, with the exception of the scuffing..

You can do low boost like suggested maybe 5 Psi... you will need a better trans and good tuning to do so and like stated you need a way to control and or dump boost..


If you want reliability this is not the way to go

A shortblock, or maybe even a longblock are so cheap for an L67, it's hard to imagine NOT dropping one in if you're already fabbing up your own turbo solution. If you want to talk about sizes, look at what W body guys have in their kits, or mainly use. I haven't researched enough on what's an appropriate size for the 3800.

I wouldn't rear mount personally, not with how much room is in the engine bay.

As far as tuning, I would look DIVE into megasquirt online, and see if you can handle that. But if you're doing that, you might as well do an S2 because pricing between S1 or 2 can't be too far off.

It sounds like using my current block even at low boost would be a risk I dont think I am willing to take. Ide rather have something that was built to be boosted to begin with. For a series 1 a 95 would be the best option then. I could get a brand new crate series 2 L67 for pretty cheap I think from a guy my dad works with. He asked me to make him an offer but I have no idea what it would be worth. My original idea was to get a little more performance using a lot of what I have now and to stick with series 1 because I could hopefully control it off of my current ECM. Is is possible to strengthen my transmission with HD parts? The wastegate would control the maximum boost and the low exhaust pressure at lower rpm and load should keep the turbo from spooling all the time. Like I said before, I am still learning and am trying to get a feel for what I would be up against. Ive found a lot of stuff on turbo sites. Im going to look at picking up some books as well. Would 3800pro be a helpful place to look? Its all series 2 from what ive seen.

phoenix_flame220 wrote:My original idea was to get a little more performance using a lot of what I have now and to stick with series 1 because I could hopefully control it off of my current ECM.

Here's the problem you are going to have with your current PCM. Aside from the fact it has no way to control boost (and I would not go with mechanical dumping. Chrysler used it on the 2.2 turbo for one year and never went back to it...that should say something), there is no way for the PCM to adjust timing under boost, because the PCM thinks the car is NA. No matter how much the tables are changed, it still can't won't be able to be "bi-polar"...it needs to be able to operate the car BOTH in n/a AND in turbo mode. Chrysler PCMs could do it because they had MAP sensors...it sensed boost, it changed timing and tables. Series 1 GMs didn't use MAPs...instead they were programmed to use mainly the TPS, MAF, and knock sensor to determine the strategies needed, but this method changed with the S2...those actually used MAPs.

You want reliable and cheap...well, here is my suggestion. Go with that Series 2 (or Series 3...I can find those REAL cheap around here) and run low boost with it. Use a 4T60E with the 3.06 ratio or a 4T65e with the 3.05...it won't be HD, but it won't need to be...and here is why. Supercharged cars make most of their torque in the low RPM, which really puts a strain on the transmission...that's the largest reason why they are beefed up. But a turbocharged car won't make any more torque off the line than a normal car due to the turbo needing to spool up, so running a standard 4T60e should be fine. But, I would run an external cooler...the largest you can find.

Notice how I gave two choices for the trans? Thats because I suggest running the OBD2 computer for the greater (and faster) response and control. You will need an L67 bin file to operate it that has been modified to act like an L36 most of the time...Sinister will be most helpful with that tune. But...1996 is the only year you can get the S2 L67 and 4T60E combo, and so far Sinister is the only one that can tune that PCM. 1997 PCMs are identical, but the bin file from a '96 can't be flashed to them. 1998 and up PCMs, no matter what engine, will only operate the 4T65E...unless you do what I did and null half of the trans tables and delete a few codes. But that was experimental...I had decent success with that, but I never fully tested it, so I can't on good word reccommend it.

Total cost going that way should be right even with finding a low mileage S1 L67 (which are harder to come by, and more expensive to rebuild), and going this route ensures you will be able to find junkyard parts easier over time.

I want to add one more thing. Nobody here is telling you not to turbocharge what you have now. But dollar for dollar, and for the sake of reliability, upgrading the powertrain to the newer series would be money better spent.