Flattop L28ET?

[Z Dude]

I am going to build a turbo l28 for my 280z which has an n42 motor with dished pistons. I already have a p90a head that i am going to rebuild and put on my block which should make around the stock turbo 7.4:1 compression. My question is if i where to use some n/a flattop pistons to raise compression to around 8.5:1 and low boost would it still be reliable? I wasn't sure if their was a reason that i never see people do this to turbo l28's.

[ozconnection]

I am going to build a turbo l28 for my 280z which has an n42 motor with dished pistons. I already have a p90a head that i am going to rebuild and put on my block which should make around the stock turbo 7.4:1 compression. My question is if i where to use some n/a flattop pistons to raise compression to around 8.5:1 and low boost would it still be reliable? I wasn't sure if their was a reason that i never see people do this to turbo l28's.

 

I did what you want to do. N42 block with a P90 head but I run with VG30DETT JE forgies with custom rods. My R/S ratio is now 1.72 so it revs like an L24. Compression is around 8.3. Pefect for off boost response and still low enough to run decent boost for power. "A" grind stock cam and 1mm oversize valves on both intake and exhaust.

 

I'm running it in ATM, sounds unreal with a 3 inch single pipe and headers, I will do the turbo switchover after a couple of thousand kms.

 

Good luck.....my combo runs beautifully.

 

[Nizm0Zed]

My setup is pretty similar, however the only running my engine has done so far is several minutes of very rough tune in the ECU.

My combo is a N42 head on a L28 block, flat top pistons and a Nismo MLS .06mm head gasket, Haltech EFI and a Garret GT3271 turbo, wastegate minimum pressure at 10psi (will be left there)

the Ozdat engine design utility indicates that my comp ratio will be 10.4:1

Yes, seems high, but with careful fuel and ignition control it should be fine, and very responsive off boost.

I know that it used to be the case that you had to run a low comp ratio for a turbo motor, but there are plenty of modern high comp motors that have been boosted quite reliably, PROVIDED the mapping is done well.

look at some of the Honda motors and turbo kits as an example.

 

As a sensible step back looking at the whole picture though, i understand that many modern high comp motors are 4 or more valves per cylinder and the fuel maps are a lot tighter, but there is no reason why the L series cant accomplish the same.

After all, its Fuel, Air and Spark.

 

http://www.ozdat.com/ozdatonline/enginedesign/

Chuck in your specs and see how it looks.

(bookmark the site, its awesome!)

[s30red240z]

I was thinking about Z22S pistons, F54 87mm bored, L28 crank, L24 rods and P79 head.

 

The C/R is around 7.7, R/S 1.68 and 2.818 liters.

[Zmanco]

When I went turbo I already had a shaved P90 from my NA car so started with that on a stock L28ET block with dished pistons. CR was 8.4 IIRC. As I went beyond 1.5 bar (~7 psi boost at sea level) I found I was retarding the timing more than others with the stock non-shaved P90 which of course hurts max power. I had a stock uncut P90 so I tried that dropping CR to ~7.5. Initially it felt like I had lost top end power, but after retuning to use the extra advance possible with the lower CR, I suspect I have at least as much, if not more, top end power. This setup definitely detonates less, especially on hot days, at the track, etc.

 

The issue is balancing the tradeoff of CR against the ability to run more advance. The general consensus is that you'll make more max power with a lower CR if that allows you to run full advance.

 

There is a small but important difference for what you're proposing: in my situation I am using dished pistons which I would expect don't quench as well as flat tops would. So you may find that you don't have to back off the timing as much as I did.

 

In the end, the difference for me between the two setups was pretty small, and even the low rpm response of the engine isn't much different. There's no doubt that all else equal, a larger CR is desirable. In the real world with tradeoffs, I think perhaps people put too much emphasis on bigger CRs instead of focusing on the entire engine. I suspect you can take either path and will land up with similar results in the end if you take the time to properly tune.

[ozconnection]

My setup is pretty similar, however the only running my engine has done so far is several minutes of very rough tune in the ECU.

My combo is a N42 head on a L28 block, flat top pistons and a Nismo MLS .06mm head gasket, Haltech EFI and a Garret GT3271 turbo, wastegate minimum pressure at 10psi (will be left there)

the Ozdat engine design utility indicates that my comp ratio will be 10.4:1

Yes, seems high, but with careful fuel and ignition control it should be fine, and very responsive off boost.

I know that it used to be the case that you had to run a low comp ratio for a turbo motor, but there are plenty of modern high comp motors that have been boosted quite reliably, PROVIDED the mapping is done well.

look at some of the Honda motors and turbo kits as an example.

 

As a sensible step back looking at the whole picture though, i understand that many modern high comp motors are 4 or more valves per cylinder and the fuel maps are a lot tighter, but there is no reason why the L series cant accomplish the same.

After all, its Fuel, Air and Spark.

 

http://www.ozdat.com/ozdatonline/enginedesign/

Chuck in your specs and see how it looks.

(bookmark the site, its awesome!)

 

.....and design.

 

I remember Saab used to run with a similar concept as you.

 

They were only low boost engines at around 5 psi IIRC.

 

I'm curious about your head and how much work has been done to the chambers. The N42 head is rather prone to detonation when more is asked of it than was originally intended. It's not very modern in its chamber design and there are some coolant issues to compound the situation. Some guys on here have done wonderful things to try and overcome the barriers, it is HybridZ after all, but I hope you have someone who can tune your management, with such a fine line between success and, well, you know what I mean. Failure is the wrong word. I/we don't wish you to fail, at all. I would be the first guy to wish you luck with this or any project but like the other boys who have chipped in so far, you may have some trouble tuning the beast.

 

'ave a go' and let us know how you get on mate.

 

Cheers.

[madkaw]

I have been contemplating a high compression turbo build myself with my p-30, but I would seriously consider switching to e-85 if I did this. It's plentiful here in Indiana and less chance of tearing up the motor

[Z Dude]

If i stuck with the dished pistons keeping the c/r at 7.4:1, could i get away with running 10 pounds of boost without an intercooler?

[Zmanco]

Wasn't the stock factory 280zxt limited to 7 psi boost, albeit with the P90 head? It did not use an intercooler. I'm sure you can make it work at 10 psi, the question is how much timing you will need to pull in order to avoid detonation, which will reduce power. I know others have experience with this approach so maybe they can chime in here.

 

BTW, what engine management system are you running? A programmable one would allow you reduce timing only at higher boost levels. I don't think you have that option with the factory ECU. But could you add the factory knock sensor and rely on it to pull timing only when it detonates? Again, I never ran that so perhaps others can chime in.

[Z Dude]

I am planning on running the z31 turbo ecu and the knock sensor, which according to what i have read is tunable

[SleeperZ]

I am planning on running the z31 turbo ecu and the knock sensor, which according to what i have read is tunable

You may get different results, but I was using the factory Z31 ECU and knock sensor, and the L28 detonation sensor did not work with the ECU. Maybe the Z31 sensor is different and will work on an L28, or maybe the Z31 ECU can be retuned to accurately recognize knock on the L28.

 

I am somewhat skilled with electronics and plan to use the L28 sensor and integrate knock detection on the MegaSquirt. But that's a little ways off, well into 2012.

[s30red240z]

somebody has any experience with turboxs knock lite?

[2eighTZ4me]

"I am somewhat skilled with electronics and plan to use the L28 sensor and integrate knock detection on the MegaSquirt."

 

I spoke with Jerry (owner) at DIY AutoTune and he stated flatly that B&G's existing knock sensing circuit is a piece of trash and doesn't detect very well (if any) at all. They (DIY) are working currently on improving this circuit/sensor setup, but it is still in a beta phase. Based on my discussions with him, I decided to not even bother hooking it up (even though they wired my MS for it) - as Jerry tuned the car personally, and assured me I wouldn't have issues with detonation.

 

Wait about 6 months and then start looking back into that option. They may well have figured it all out by then and have a bona fide golden solution by that time.

[Zmanco]

Knocksense

 

Has some issues with false detects, but it's inexpensive insurance. I had what I thought was a conservative tune done by ear, but the first run with it installed showed me otherwise. A simple test of pulling timing across the board 5 deg under boost eliminated most of the detonation events, suggesting that they were indeed real.

 

Even if you don't tie it in to the ECU, the bright red LED will warn you that you may have a timing issue. Tie it in with datalogging, and you can see if perhaps the mixture is spiking lean, or if it's near the torque peak and needs some timing pulled.

[letitsnow]

I've found 'det cans' to be pretty informative. You can hear even light detonation very well, it sounds like rice bouncing around in a pie tin. It's a very distinct sound, but I can imagine that it would be difficult to program something to pick it out.

 

There is NO way you can hear this detonation over engine and road noise with bare ears unless it bad enough to be breaking things NOW.

[rossman]

I am going to build a turbo l28 for my 280z which has an n42 motor with dished pistons. I already have a p90a head that i am going to rebuild and put on my block which should make around the stock turbo 7.4:1 compression. My question is if i where to use some n/a flattop pistons to raise compression to around 8.5:1 and low boost would it still be reliable? I wasn't sure if their was a reason that i never see people do this to turbo l28's.

8.5:1 static compression is what Dave recommended for my steet engine...BUT he spec'd out a cam with considerably later intake valve closing time than the stock turbo cam. You have to consider dynamic compression (intake valve closing relative to piston BDC). I bet you would get good results with 8.5:1 with a stock N/A "A" cam.

[duragg]

I've got the Knocksense on my 10.3:1 F54/N42 engine with Triples and TwicePipes.

Brand new engine. Stripped interior is noisy so aint no hearing rattle.

And some of the Twice-Pipe harmonics also trigger the light in a very defined & consistent RPM.

Wideband for mixture monitoring.

 

The knocksense LED is ON continuously past a certain RPM even with no throttle.

It false alarms regularly past 4000 rpm even running 100LL fuel and minimal timing.

 

I have worked the adjustments over and over but after speaking with "Boris" we determined the solid-lifter engine to just be too noisy.

Next test was an adjustable resistor to detune the signal or something like that.

 

I finally decided it might be more fun to blow the engine than fret over a bit of klacckery.

Leaned for best power, put the ZAP back in the timing, learned to ignore the LED for now.

 

I think with Boris' help it could be tuned to work better.

[Gollum]

You know, one of these days I'm going to do some documented, scientific testing to put some myths to bed. And here's what I'd like to do.

 

1. Prep two as identical as possible F54 shortblocks, one with flat tops and one with dish pistons.

2. Prep a P90 to as OEM specs as possible.

3. Dyno the head on each shortblock with race gas to find ideal timing requirements.

3. Dyno with pump gas to find true detonation limitations.

 

I have yet to see a SINGLE blown turbo motor using the NA flat top short block that actually failed due to the higher compression. Usually these failures are from people trying to just slap a P90 and turbo or just a turbo on the NA engine without resolving the engine management issues, and it it DOES knock it's because they're running the NA ECU which won't retard timing under boost.

 

I even have a stock '81 280ZX waiting for an engine rebuild, and I have a spare P90 sitting on my shelf... Maybe one of these days I'll get around to it. I still firmly believe that all the hype about "not being able to run as much timing" is widely misunderstood. More timing isn't always better. Ideal timing is ALWAYS better. Know where the power for YOUR setup is, and strive to get there. KNOW the fuel you use, and what it's burn characteristics is. It's well documented that there's more power in timing than in compression, but many people fail to understand that not all setups will make peak power at the same timing specs. I don't know how many ways I can say this, but a smaller chamber space doesn't need as much time to burn completely, thus requires less timing for ideal power. Just because you raise compression with flat tops and can't run as much timing doesn't MEAN you've LOST POWER!!!

 

I'm not saying run as much compression as you want. I'm just saying I don't think we have enough concrete information (from what I've seen) to make blanket statements about what's "best".

[HowlerMonkey]

Replacing the stock pistons with forged flat tops would be the ideal setup as the factory cast flat tops will easily lose parts of thier skirts on relatively mild detonation events.

[madkaw]

I started a thread on this about a manual type sensor based on the human ear used with one of the cheap hearing appliances. Everywhere I read that most detectors are junk and give false indications.

Scientific testing is what we need!

My l24 sounds like it is detonating but it is really the exhaust. No way to be sure until I had to remove the head as saw no evidence. I am running 38 total with pretty high compression- which if you listen around here- that can't be done( could be cam timing allows this advance). Each engine is different

So true evidence and scientific testing is the only way to know