Light pressure turbo - Page 2 - LotusTalk - The Lotus Cars Community
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post #21 of 23 (permalink) Old 08-23-2019, 09:22 AM
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Originally Posted by h20ham View Post
That is again very helpful Obeisance
I will have time this winter to modify things, or send electronics out.
Cross boarder shopping is difficult, and there are no tuning places near.
RomRaider is interesting, and maybe the best option. If a simple, low boost option does not come knocking.
Some 70’s and 80’s cars have “Cold Start Injectors”. These can be made to turn on without too much. Don’t know if simply open, and a rising rate fuel pressure regulator would add enough. Speculation anyone?

Are larger injectors considered 550+? I suspect most folk who are adding boost, are going big. Race track stuff.
Low RPM injector flow in a 320-350 injector may not be so poorly metered?

Has anyone added one or two injectors, to add extra fuel at boost?

Thanks LT
Unfortunately, turbocharging this car is not simple even with low boost. Don't confuse the technology of this car with the cars from the 80's and 90's. Simple low boost with those cars were easy. I had a 91' Miata and did exactly what you are wanting to do and it worked fine. Those cars had a return fuel system, a way to change the ignition timing without needing access to the computer, they were low compression and the engine was simple (no VVT or VVTi-L). The Lotus is the exact opposite of simple. I spent all of $1000 on a Greddy turbo kit, it was non-intercooled, used stock(ish) injectors, a high pressure fuel pump and a rising rate regulator (10:1 ratio). I ran 6psi with that kit but with around 100-110 psi of fuel for proper A/F ratio's.

If you run the math, you will need around 100-105psi of fuel pressure to support "low boost" using stock Elise injectors which I guess could be done if you convert to a return system (there is no reason to do this though unless you are looking to make big power). However, you still need a way to control the ignition timing which can only be done electronically through the ECU. Also, keep in mind in the grand scheme of things, injectors are cheap compared to the rest of the components of the turbo system.

Originally Posted by MrWong View Post
Take a look at my full build log for boosting a 2ZZ. I would recommend you don't skimp on the fuel delivery and ignition control. With Forced Induction it doesn't take much have things go horribly wrong, especially with the stock internals and the high compression. I'm not running huge injectors Siemens 630cc at 49psi and they behave at lower rpms fairly well. I have seen a lot of really cheap budget turbo builds and they dont last long. The engines that are built for boost (correct compression\charge cooling) and proper (fuel/ign/wideband) control seem to keep running for years. I always say, Do it right the first time, or you'll be doing it again.
^^^^Do this!

Also, I'm running 1000cc injectors and have no issues at idle or low speed.

Originally Posted by h20ham View Post
Anyone know if stock injectors will support 7-8psi?
Or, is it simply easier to add one or more injectors in the plenum. Running off a second computer, or. Same computer, and a rising rate fuel pressure regulator?
Will a barometric pressure sensor, controlling another (or sixth) injector get close?

I will not be racing, simply climbing hills behind RV’s and Logging trucks. Really dont need a bunch of boost. Don’t care much for the second cam. As low rpm boost is fine, free power.

Innovative wideband installed.
The only place these cars make power is on the second cam, boost or not.
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post #22 of 23 (permalink) Old 08-23-2019, 11:37 AM
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Re: injector sizing: the computer (ECU) 'knows' what size the injectors are. It's actually calculating the cc of fuel required for the next intake stroke on the next cylinder, so it has to know how many milliseconds of injector open time that is, which means it needs the injector flow rate. It also (usually) applies fudge factors for low battery voltage (increases injector opening time) and a factor for how long the injector takes to get to full flow and how long to go from full flow to shut.

If you change the injectors you change all those variables. If you're not finding and inserting the correct replacement values in the ECU, it's going to be calculating wrong outputs. The long term fuel trim table dynamically learned corrections will cope with some of it, but if you go too far out of the design box it decides something is broken and throws an error.

The 'stupid/cheap' way of dealing with this on a MAF car is to sell a MAF and injectors as a set. The MAF lies to the ECU in a way that (mostly) balances out the larger flow of the injectors resulting in the ECU getting close enough to right exhaust oxygen signals from a particular injector input that it believes everything is OK. Usually the calibrations from these hacks are not great, and you tend to leave either a lot of power or a lot of safety on the table. Lying to the ECU is how an entire class of tuner hardware works. It's a hack, and usually quite fussy. Honestly, if California and a few other places weren't so draconian about ECU replacements, we'd see a lot more use of third party ECUs to solve these problems.

Probably worth mentioning that a screw or roots (positive displacement) supercharger is going to behave differently on the engine than a turbo or centrifugal supercharger will. One has a (mostly) linear volume delivery curve, so is very predictable in the mass flow/rpm curve. This is easy to tune for. Centrifugal compressors (like a turbo) have non-linear delivery curves that result in things getting more complicated if you're trying to lie to the computer instead of doing it right. Turbos also have inertia, which can confuse an ECU as well.
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post #23 of 23 (permalink) Old 08-23-2019, 03:01 PM Thread Starter
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Thanks so much everyone
Most likely if I were building an engine, I would use a k20 or 24 or a Duratec 2.3.
I have these sitting around for some reason.
The tuning and costs are the issue.

Keep ya posted. Most likely at this point I will get a ready made kit and build an engine. Wish I had time...
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