Does Turbo size matters ?

[de_stanny]

Hi All,

I have been reading quite a lot lately as i am looking in buying an Elan in the near future.

Now i see that there are some people that update there turbo with a bigger one and use bigger injecter and a higher rated MAP sensor to get the higher HP's.
Reading more and more i see that when a big exhaust is fitted and CAT's are removed we need to increase the wastegate size to be able to bypass the exhaust gasses or we are getting boost creep above the boost setponit, so this means when we bypass there is more potential in our litlle turbo's, not ??? if we want to run higher boost by using bigger injecters and 3 Bar MAP sensor and boosting the boost by a MBC what is then the advantage of a bigger turbo compared to the std one , if our small one can run the same boost as the big one up to a certain level, i think i did read one person that ran it at 1,6 bar with a MBC and a FCD "which in fact is the same more or less as running a 3 bar MAP sensor, but you don't need bigger injectors to compensate" ? and the bigger turbo should have more lag ...
One more thing regarding the A/F ratio, it seems that our cars have a verry rich ratio running on boost so why should we change to bigger injecters for a few more PSI ? as long as you check the A/F ratio and its not leaning out... and you don't get any engine knock...

If i completetly mis the ball , i would like to learn , thx

Greetz,

Stanny

[hatters]

If it ain't broke don't fix it ,IMHO the Se turbo is quite fast enough as it is but that's my opinion a lot of guys on here would probably differ?

[de_stanny]

I agree with you , if it aint broken dont fix it , i was just wondering if my thoughts where correct .

[racerstev]

You are correct, you can run well over 1 bar with our setup and be completely safe on the A/F ratio's. At lower rpm
our little turbo will go over 20psi and will hold 1 bar at redline with little problem.

There are a few potential problems though. You will lose most of the built in safety from the stock ECU by running a
FCE. You will be running alot leaner then stock and if pushed to the max you will be running too lean, a wideband
A/F gauge is needed to be sure you stay in the safe zone. The air coming out of the turbo is very hot at these boost levels
so you may want to take a few degrees of timing advance out of it just to be safe.

Without a good boost by gear boost controller the car becomes almost undriveable in 1st and 2nd gear. Lots of
wheelspin and torque steer. But yeah it can be fun for shot periods! LOL

Steve

[tigerdog]

Hi Stanny,
It really depends on how much power you plan to try to produce from your engine. The main reason for going to a larger turbo is to be able to significantly increase power output. The stock turbo has been shown capable of producing well over 200 HP. Those who have gone to larger turbos have even higher goals, 250-300 or more HP. At some point, the small turbo cannot move enough air to feed the engine. Another reason for replacing the turbo is an attempt to reduce lag, maybe by going to a ball-bearing turbo to replace the sleeve-bearing original. Of course, a third reason is that your stock turbo is knackered and has to be replaced anyway.

Boost can be increased in several ways, up to a point, by overriding the ECU's pre-programmed boost control. The simplest and safest way is to use one of Alan's Mountain chips. There's tons of discussion on the board about these. Another is to use a manual boost controller (either the "controlled leak" kind or a separate, programmable controller. These are also discussed on the board. In any case, the overboost fuel cutoff is a safety mechanism designed in the ECU. Once the MAP says boost has gone to 1 Bar, the ECU immediately shuts off fuel.

As you point out, the stock fuel system runs somewhat rich when out of closed-loop mode. I understand this to be a safety precaution to provide a little extra insurance against detonation/knock. Knowing that, it is possible to increase boost safely, to a point, with the stock system. That point is, nominally, 1 Bar boost, because above that point the stock MAP sensor delivers no more useful info to the ECU and the ECU doesn't have calibrations for higher values, anyway. There are two flavors of ECU setups on the Elan, with and without oxygen sensors. Without, the ECU relies on a pre-calibrated table to tell the injectors how long to stay open at a given RPM and MAP reading (and maybe throttle position). Any change to MAP sensor or injectors will result in an uncompensated change to the air/fuel ratio. With oxygen sensor, the same is true under acceleration, however, idle and light-load conditions allow the engine to enter closed-loop mode. In this mode, the output of the oxygen sensor is used to adjust the fuel injectors to maintain and "ideal" ratio, improving economy and reducing emissions.

To boost beyond 1 Bar, the fuel system must be altered in one or more ways:

Exhaust: restrictions in the stock system will ultimately limit output; the precat and the flattening restriction in the pipe over the prongeron are the two biggest restrictions, followed by the main cat and silencer. Some folks knock the catalyst out of the precat container, others replace with a custom downpipe. Some remove the main cat. Some go to a larger exhaust diameter. In addition to greater flow, reduced restriction has the advantage of allowing the turbo to spool faster.

Injectors: 330cc/min at stock pressure can't flow enough fuel for boost above 1 bar at full throttle. You must either increase fuel pressure or increase injector size.

MAP Sensor: only delivers information up to 1 Bar boost. At that point, it reaches max output voltage and further increases in pressure deliver cannot be sensed. A 3 Bar sensor changes the relationship between pressure and output voltage. While not exact, think of it as indicating only 2/3 the voltage of the stock system at a given boost. This has the advantage of effectively eliminating the fuel cut defender; by the time the boost reaches the fuel cut voltage, your head gasket will already have blown. It also has the disadvantage of causing the ECU to reduce fuel flow to about 2/3s of what is should be if you keep the stock injectors.

ECU / fuel metering: since the stock ECU uses fixed value tables under most performance conditions, you either have to trick it to give the behavior you want, or simply replace it. On the board, some have replaced with Haltechs, others use (or plan to use) Megasquirt. If you keep the stock ECU, you can get good results if you balance the changes to the MAP with changes to the injectors.

The most common changes begin with improved exhaust and intake airflow, followed by either a) Mountain chip or b) manual boost controller. For >1 Bar operation, the most common change is to use a 3 Bar MAP sensor and balance it with 550cc injectors. The MAP sensor tells the computer there's less boost than there really is, so the computer pulses the injectors to a lower flow rate... but the bigger injectors deliver more fuel per pulse so it (mostly) balances out. In closed-loop mode it balances very nicely; open-loop it's a bit rich. The major drawback to this combination is, the built-in overboost control is bypassed. Finally, a larger turbo can keep the higher boost pressure at high RPM, making ultimately more power.

This is a high-level overview at best, but it gives you a summary of the various approaches available to us.

Happy Elaning!
Doug

[de_stanny]

Hi Doug,

thx for the fantastic reply, its confirms everything wath i have read here on the board,

I am not sure at what pressure our std turbo cant deliver enough air anymore to go to higher boost levels ... Does somebody have a compressor map for the stock turbo ?

As it seems there is more potential in it then the limit of 1 bar , when the exhaust is improved, we even have to increase the wastegate size or it goes into boostcreep.
Anybody experiance with that ?

thx ,

de_stanny

[HJ2]

The compressor can do more than 1 bar, but the injectors cannot keep up and are the limiting factor. So, change injectors, but then the ECU is in error as the new injectors deliver more fuel than it expects. So use another MAP etc etc..... project creep!

I would rather spend money on exhaust, downpipe, porting the wastegate Sports cat or no cat, and an everest chip or switcher. (don't forget to upgrade the brakes for petes sake!)

The money you save on injectors and getting the setup right, I would rather spend on advanced driving lessons, for example on a track with a good drivingschool and some 1 on 1 driving education.

You will see that the car (and you!) have a lot more potential than you will ever gain with a car capable of boosting over 1 bar.
My 2 cents anyway, and it's a lot of fun as well


viewtopic.php?f=31&t=8837
and of course:
viewtopic.php?f=79&t=16507&p=220707

Edit: I must read better myself as i am repeating Doug now! ... sorry!

[de_stanny]

thx for the info guy's,

Today the shipping company is picking up my car so a few more day's until the fun can start .

i was planning to take up the brakes, exhaust and pre cat first then see if i need to push the boost higher

Now i know exactly what route to go , thx everybody.

greetz De_stanny

[Karl Martin]

220 BHP easily and reliably possible by modifying the existing turbo and without the need to go above I bar :-

viewtopic.php?f=31&t=17429 (and I am still working on this....unfortunately redundancy has got in the way....more time but no money! )

Bigger turbos give more lag and move the power further up the rev range, giving you less time to use that power before you need to change up. Anything over 250ish BHP has also been reported to be more or less unusable, due to inducing excessive wheel spin and understeer.