compression ratio l28 to l28et

Hi guys

ive tried searching but i couldnt really find the answer i was looking for. ps. im new to the whole turbo thing.

from what ive read to change an l28 to an l28et requires some parts off the l28et from the US to lower the compression ratio.

is it necessary to do this and what is the reasoning behind it. from my understanding its to get the engine similar to the us counterpart as they were made for boost.

im from the honda crowd and most of the engines have a high comp ratio. 11.0:1. Alot of ppl when they boost there engines they leave the stock comp ratio and add a smaller turbo and run less psi. they argue that its better for response and less lag.

as opposed to lower comp ratio and high psi.

would leaving the comp ratio on an l28 and adding a smaller turbo with less psi be worth the trouble, or would it be better to lower the comp ratio and rud be able to run higher psi.

if its been covered before just flame me

Try searching HybridZ, they have lots of turbo Z's.

What engine block/head combo you have will be the first issue.

If you have dished piston's, your comp will be ok for a turbo at around 8.5:1

Small turbo's in a Honda may be ok, but for a Z? Why bother at all?

If your going to do it, do it right.

hi mate,  and welcome

I am in teh process of the same conversion

by my understanding, high boost, and high compression CAN be done, but requires an epic amount of tuning to get it exactly right.

in an NA car, 11:1 is high, but reasonable, esp in such a tightly strung motor like  a K20 or the like from the spoon makers.  the new BMW turbo motors are on 10.5:1, with something stupid like 20PSI boost, but you can imagine how much

in a turbo car, 8:1, 9:1 maybe is the norm.  reason for this is as you say, it allows the PSI to be higher.

The easiest way to lower compression is to increase the size of the combustion chamber (bit between the top of the piston and the valve seats.)

to do that a metal head gasket does the trick nicely.  what size of head gasket will depend on how far you want to lower compression.

A metal head gasket and some head studs to go with it have other benefits as well.  instead of running at atmospheric pressure, or vacuum (depending on throttle position)  you are running with boost, so above atmo pressure.  putting all of that extra pressure in there can lift the heads. which means the coolant and the oil get an intruduction, and you get to blow a head gasket, which is not the most fun to be had.

My suggestion would be to lower the compression, and run mediocre boost, somewhere between 8 and 13psi.  start with a 1mm head gasket, and if while tuning you still get alot of pinging, work your way thicker from there.

Mechanical sympathy, and giving your engine some comfort space in the boost/pressures/detonation/"tightly wound" department will mean you get more km out of the whole set up.

Small turbo's in a Honda may be ok, but for a Z? Why bother at all?

im just trying to understand this statement. are you saying that if you're going to turbo a z, that you may as well go all out and lower cr to run more psi and get higher power figures?

or no point using a small turbo?

because a member on one of my honda forums has got a b18c is running stock comp ratio of 11:1 with gt30 on 7.5 psi and is making 240fwkw (300ish hp).

so surely on a 2.8l z with a lower comp ratio should be able to reach those figures or is that just a difference between the two engines?

thanks herrods

very informative post. so pretty much the best way to turbo an l28 is to lower the comp ratio but it can be done in a few ways?

do you have a build thread atm herrods? would love to follow your progress and learn more.

Hi Aidannn

The L28ET's in the US use used a head called a P90.  It has larger combustion chambers to lower the compression ratio to around 7.4:1 from memory.  In my opinion this is too low and will result in a lack of response.

For a budget L28ET setup I would simply use a standard n/a 280ZX engine with the compression ratio of 8.3:1.  You could go a thick head gasket to get it a little lower as herrods suggested.  If you get a decent intercooler, good engine management, run it on 98 fuel and run around 10-12psi you should be able to get 150-200rwkw depending on what other bits and peices you use.  This is the basics of the initial setup when I bought my car and it was good for 174rwkw with excellent response and torque.  Make sure you buy a computer that controls fuel and ignition so you can pull back the ignition timing when it comes onto boost to stop detonation without loosing response.

Don't worry about the lower power figure, it will have a truckload more torque than your mates Honda.

I'm now running a modified P90 head and flat top pistons to get around 8.0:1 compression but this is not worth the trouble really.  I now have 265rwkw but the biggest gains have been from the turbo (switched from a t03/04 hybrid to a GT3540R), and fuel (I'm now running Sunoco 260GT0.  This allows me to run 21psi boost.

My build thread can be found here.

http://www.viczcar.com/forum/index.php/topic,2662.0.html

I have no build thread.... cause im lazy

so far I have only gone thru the parts buying, adn the taking off old parts stage.  so not much to say so far.

The point you mentioned about about the smaller turbo on the honda, and understanding our points as needing a large turbo for a z, is half true

Half of a turbo's power comes from the pressure you have it controlled at (by wastegate etc)  the second, and often the more important part, is the volume of air that the turbo is able to flow.

you can have a tiny t25, and push 30 PSI through it into a 3L motor, no worries, (assuming its all built)  but it will run out of breath, because not much air at high pressure is stil well... not much air.

you can have a monster turbo, gt3545 on a 1.8L motor, and run 10PSI, no worries, but your tiny motor cant actually push out enough exhaust gass, to get good pressure in the turbo, and therefore, we get lag.

for good response, and good boost, and ultimately good power, you first have to match the motor and the turbo to the application

a GT28, GT2871, 2876 etcm should get you into party mode with a 3 L, its marginally bigger than a manufacturer would put on the car, and with proper management it will flow air into the engine well, and be good for scando's 200km ish figure.

if you want to get your party on really hard, you go larger, but you need the fuel system, the engine system, and the tuning to match it.

going smaller just gets you super response, followed by a car running out of breath @ 5000rpm.  no benefit.

all things in balance grasshopper..... 

I have run 8psi on a mates factory L28e 280zx, heres the recepie

VL turbo injectors (hose tail) about 265cc each

RB20det turbo,

modified R32 split stainless dump (like 'N*Power' brand on ebay) to 2.75 full system

L-series turbo manifold

XR6 turbo intercooler (cheap on ebays)

hobbs switch and water injection (comes on at 3 psi) brass nozzle and parallel washer pumps

adjust the AFM spring tension (looser)

lock dissy, Premium at all times, and a knock box (detects pinging and flashes big LED say 'slow the F down')

this setup made 130kw all day every day, on the factory ECU and everything.

It is a bit basic, but sure beats the 65kw figure before hand!

An aftermarket ECU will make things ALOT easier, and safer...

Above sounds really good for a budget build.  I would stress to go for aftermarket engine management though.  If your budget is really tight then you should be able to pick something up second hand for $300-$500 as long as your patient enough to sort out the wiring!

As far as turbos go, the one I'm running would be perfect for a road car.  It's a 3540R with a 0.63 exhaust housing.  The small exhaust housing makes it come on very quick for a large turbo.  Unfortunately it also creates a lot of heat so I need to move to the 0.82 housing.  On a street car you won't be on the throttle for the extended periods of time so that heat won't be a problem.

First-gen ('81) L28ET's were N42/N42 combo's. The P90 head with dished pistons didn't come about until sometime in '82.

As many of you would know, my (now retired) N42/N42 with bolt on go-fast bits is around the 140rwkW mark, and will pull the 0-60mph sprint in under 6 seconds. The very same motor, with the very same ECU, auto trans and diff ratio (3.90:1) was 68rwkW when it was a fresh N/A motor.

The big limitation with running a blown L-block is the 'primitive' head design (compared to your Honda example), which results in needing to run a low CR for everything to work nicely. The P90-headed engines were ~7.5:1, the N42's were ~8.3:1. Even my motor with lots of development still needed 98RON+octane booster to be 'happy' all the time.

Ben, can you explain what your setup is/was?

Sure (as I recall!) - currently;

Standard L28E (N42/N42)

turbo head bolts

turbo oil pump

custom dizzy

Haltech E6A ECU

standard manifolds w/SK's J-pipe

VG30ET T3/4 hybrid

2.5" SS split dump, 2.5" SS single-muffler system

2.5" I/C piping, 450x300x76 FMIC

380cc injectors, standard rail

rising-rate FPR

Bosch 910 pump, 3/8 feed line (modified 240z tank - use a 260Z one for larger OEM line sizes)

Bosch BOV (re-circulating)

Earls oil cooler (75C thermostat)

Pipercross inline filter + cold air duct

gear-reduction starter

modified 3N71B gearbox, upgraded trans cooler

Pending;

Prepped F54/P90 (forged pistons, head mods, etc.)

Pallnet rail

MoTec or ViPec ECU (anyone wanna buy a never-used MoTec M48 Clubman?)

L28ET exhaust manifold

ported inlet manifold

XR6 TB

Bigger T3/4 turbo

3-3.5" SS system

modified L28ET dizzy (VG30 opticals)

plus a bunch of non-engine upgrades (driveline/brakes etc.)

It all sounds so simple as a list like this, but there are plenty of $ and hours and effort required to make it 'work'...

I run a n42 combo l26 turbo with standard compression 8:3:1 low boost 7psi all standard nissan efi gear; computer, turbo etc, although it has vl injectors hypertechnic dished pistons , grant rings and bearings. I have run this now for 6 years it goes like a cut cat and I have never had any problem with it, so if you don't go silly with high boost you will have a car that will give ample punch when you need it and will embarass crumbledoor,ford and wrx owner. It will give you a good starting point.

cheers Tony