Another approach to ITBs?

[Guest TeamNissan]

I dont know if you guys caught this yet.

 

http://forums.hybridz.org/showthread.php?t=120562&highlight=itbs+twist

[sweetleaf]

Lol I'm drunk... So if this makes no sence don't blame me.. This is one of the best threads lately... The point about maximum airflow vs. boost is on the money..Also, Staged injectors work great. You can still idle , pass emissions, get better MPG, and have better crusing/response.. The guys that posted that info probably know but a lot of others dont... There is only so low you can go on the min.. pulse width of an injector.. So when you run only one set of huge injectors you can't help being overly rich.. But with a set of staged injectors you can have the best of both worlds... ( : .

[Daeron]

thanks to everyone who helped enlighten me.. the thought of running rich at idle on large injectors hadn't occurred to me.. can you tell I've never been outside of 200 horsepower?

[MONZTER]

We aren’t saying Big injectors wont work unless it idles rich, but you must have a system capable of running the injectors in a sequential order, or some sort or rising rate fuel pressure regulator (not so precise). Seqential means the injector only fires on the intake stroke, basically making the injector off time longer. Most new stand-alone systems can do this with the addition of a cam sensor to let the computer know when the intake event is happening. Most older systems run in non-sequential or batch fire, meaning they inject fuel every revolution. So on the exhaust stroke fuel is sprayed on the back of the intake valve, some say help cooling it and improving the throttle response. My understanding is sequential is good for emissions and gas mileage, and non-sequential is for performance.

Anybody have any opinion on this

[RTz]

Anybody have any opinion on this

 

 

Sure, I've got opinions...

 

The effects of oversized injectors partly hinges on the resolution of the EMS. For example, MS's resolution is .1 ms. If you are running slightly lean at 1.2 ms, the next step is 1.3 ms. If injector dead time is 1ms, you just increased fuel volume by 50% (actual 'on' time went from .2ms to .3ms). If, however, you ran an EMS with resolution of say .003ms, you can now make a 1% adjustment.

 

The general rule of thumb for injector placement is close to the valve for idle quality, fuel economy, response, and emissions, while further from the valve generally promotes more HP. Running a staged system, even if done with equal sized injectors, could give you both worlds.

 

Sequentially fired injectors can deliver slightly more HP for their size due to the fact that there is only one dead time instead of two.

 

I don't agree with generalizing that batch is for performance while sequential is for emissions/economy. Sequential will typically produce more power at low RPM and may have a slight advantage through the midrange. At high RPM, there usually isn't enough time to get all the fuel in before the valve shuts (unless you're running monster injectors), so its tit for tat.

 

Another advantage of sequential that is often overlooked is that it requires that there be a dedicated channel for each injector. This in turn means (if your EMS is capable) you can trim fuel on an individual cylinder basis. No engine process's the same volume of air in every cylinder. This means, with batch fire, some cylinders may run rich, while others run lean.

[z-ya]

Another thing to keep mind is that an injector is an electro-mechanical device. Injectors have a minimum opening time that is determined by the mechanical design. This is limiting factor, not the ECU. If the injector has a minimum opening time of .1ms, then the ECU should be capable of at least one half of that for good fueling resolution. Used injectors can have much different minimum opening times resulting in some that might be lazier than others.

 

So if your engine doesn't require much fuel at idle, getting a smooth idle from big injectors may be difficult.

[Daeron]

Another thing to keep mind is that an injector is an electro-mechanical device. Injectors have a minimum opening time that is determined by the mechanical design. This is limiting factor, not the ECU. If the injector has a minimum opening time of .1ms, then the ECU should be capable of at least one half of that for good fueling resolution. Used injectors can have much different minimum opening times resulting in some that might be lazier than others.

 

So if your engine doesn't require much fuel at idle, getting a smooth idle from big injectors may be difficult.

 

Okay, I understood most of the preceding statements already.. but THIS statement leads me to another question...

 

I have scads of stock 280Z injectors. I was planning on building a cleaning/flow test rack like this one to clean and "flow match" myself a set of 6 good injectors. I was also contemplating selling alot of them to some of my subaru friends, because the 80s subaru turbo engines use the ZX injectors as a larger alternative.

 

I take the above statement to mean that, my home made flow test bench will be nothing like actually having the injectors sent out and cleaned and spec'd professionally, because I have no way of determining the "dead time" on each injector, other than eyeballing it.. am I right? I mean, the test bench obviously serves some good in any case.. but probably not as much as I would like, given this new information that I have picked up now.

 

Am I more or less correct?

 

Sorry for the hijack, it just didnt seem worth it to start another thread, since it would be taking these questions out of the context in which they arose.

[z-ya]

Injector flow benches usually test injectors at 43psig, and 80% duty cycle. This method will not identify a lazy injector. OEM 280ZX and 280ZXT injectors after cleaning usually flow within 1% using this method. BTW, I use Witchhunter Performance for all of my injector cleaning and testing. Gordon does great work.

 

Injector staging is one way to get around idle problems with big injectors. The early Wolf units have a very coarse fueling resolution. On my turbo car I run stock ZXT injectors for a good idle, and then use a couple of staged ZXT injectors that have an opening time of 80% of the primary ones to provide enough fuel under boost. The staged injectors do nothing at idle because the opening time is too short (80% of primary).

 

SDS makes a nice addition injector controller. You can also use a Megasquirt for this purpose.

 

I was thinking of building a flow test bench at some point. Thanks for the link!

[MONZTER]

Sure, I've got opinions...

 

 

Another advantage of sequential that is often overlooked is that it requires that there be a dedicated channel for each injector. This in turn means (if your EMS is capable) you can trim fuel on an individual cylinder basis. No engine process's the same volume of air in every cylinder. This means, with batch fire, some cylinders may run rich, while others run lean.

 

Ah yes I forgot about the ability to tune each cylinder That would be so nice, I guess you would need 6 wideband sensors in each header pipe, and then run it on a Dyno. Have you ever seen or done this on a datsun motor. I wonder if the ITB's discussed in this thread would make the engine much more consistant than a single throttle plenum, to the point where it would not be necassary to do this?

[Daeron]

I was thinking of building a flow test bench at some point. Thanks for the link!

 

 

 

You are more than welcome, thanks for the information. The link really doesnt contain much of a secret formula, but it is nice to see what someone else has already done before you embark upon building somthing like that for yourself. Any reason not to just use a stock fuel rail and pressure regulator with the vacuum port vented to the atmosphere? It would obviously also take a dropping resistor.. something like this could (obviously) be rigged up easily and on the cheap, or could be done with varying degrees of complexity (timers etc.) It is a project I have been thinking about in the background for some time now.

[z-ya]

Yes you can use any rail, and a stock regulator. If I build one, I will use a Megasquirt to fire the injectors. I think I may have a way to measure the minimum injector opening time for a given injector. I'll try it in a few days and post the results.

[Tony D]

what about the coates spherical rotary valve cam shafts/head =)

 

 

Coates was contacted and were uninterested in any development of the L-Engine head, regardless of who was footing the developmental costs!

 

"They stopped returning e-mails" is one way of saying it.

 

I worked with Coates-Valved Powerplants, mostly Cat conversions from Diesel to CNG. So I was very familiar with their operation and what they are capable of when put into service over-the-road. Unfortunately, even when dealing with people who know our company was using their product, they were unwilling to experiment with short-run stuff. I was very disapointed, and so was JeffP.

 

BRAAP has my thoughts dead on---I deal with large industrial centrifugal compressors as a daily bread kind of thing. The BIGGEST thing we do to save a customer money is debottleneck their system so they can get the air to where they need it. Our compressors will work fine at 110psi, but the FLOW MORE at 85psi, and if that is all they really need for their plant tools and instrumentation, pumping it up to 110 wastes horsepower. Same with a Turbo driven off the exhaust...if you pump it up, you loose efficiency.

 

Think about CART engines. They continually drop the boost (last I heard they were down to less than 7#) yet their horsepower stays constant... They don't NEED the boost. The more you depend on building pressure to make horsepower, the laggier the turbo driven car will feel. Taking a drive in JeffP's car will feel like an N/A 240Z on steroids. Boost comes on immediately (about 2psi) and like when a 240 comes on the cam around 3500, Jeff's car makes big power starting around 3200 with a rush to the rev limiter at 73 to 7500rpm. He's afraid of the stroker crank at this point...he'll get over it I suppose. But the camshaft profile is more like an N/A grind and so is the power curve...just waaaay up there.

 

Build for flow through the engine, then size the turbo for the flow you will need.

Braap mentions 20psi and 500HP. This is JeffP's case exactly. He WAS making 415 to the rear wheels at 23psi on his last cam/turbo/head. On the current cam/turbo/head he's making over 585 to the rear wheels on an aborted run to only 6300 at just under 20psi.

 

Flow is good, boost is bad. You just need a shove through the valve, no need to cram it in there. If it goes in and out easily, you will make more power.

 

I just get frustrated when I see someone stating they want to build to a specific boost level, instead of a particular horsepower level, or performance benchmark. So you make 20psi. Like BRAAP said, are you making 400 with that, or 500+? Personally I'd like to be the guy making the 500+. if you prepare the engine for the flow, you operate at parameters that aren't so high.

 

FOR INSTANCE: How much heat does your intercooler need to take out at 30psi to return it to ambient? If you make your engine that will flow, and you only have to boost to 15psi to reach that point, doesn't it follow that you will more realiztically be able to meet ambient conditions in a wider range of conditions only generating half the heat to begin with? No matter what, compressing air to 30psi will raise the temp a defined amount. And compressing it to 15psi will be half that (if your compressor is sized accordingly in each case.) Taking out twice the heat will be more difficult.

 

There's just so much that adds up when you mega-boost an engine. For survivability, the lowest boost you can run to make the horsepoer you need is the ideal scenario. The less boost you need, the less lag you should have, the less threshold you should have, and things should generally be happier all-around.

[1 fast z]

One thing that I will add to Tony's comment is, that Boost means nothing. Its CFM, FLOOOOOOOOOOOOOOW. A Gt35R turbo on 5 lbs of boost can have the equivilent of a T3 at 15 PSI. I HATE it when people relate everything to boost. Its CFM flow, that can be determined by a compressor map. Jeff's motor has a different turbo. SO the cfm he had with his old turbo at 28 PSI is probably about the cfm flow of his new GT35R turbo at 20 PSI.

[Tony D]

Jeff's motor has a different turbo. SO the cfm he had with his old turbo at 28 PSI is probably about the cfm flow of his new GT35R turbo at 20 PSI.

 

Jeff is making well over 100+ more HP at a given rpm point than his previous build. 415 to the wheels at 5500rpm and 23psi boost, versus 585 at an aborted 6300rpm run (power peaks at over 7000 on this build) at less than 20 psi. With a full run, the number was well over 100HP more at 15psi (somewhere around 465hp @7250 with 15psi or something like that). The turbo would not flow any more at that point, he couldn't get 28psi from it. At that point he was still thinking he 'needed' 30 psi to make his desired power. (And remember, this was a car with about a 2500rpm boost threshold, hammer it at any speed above 2500rpm, and the boost was INSTANEOUS to 23psi.)

 

The power point has changed as well, it's not just the turbo. The previous turbo was outflowed... incidentally he had 23psi exhaust backpressure pre-turbine when there was 23psi in the intake plenum with the previous turbo. That is a pretty free-flowing environment as it is.

 

What was changed was the camshaft primarily, along with flow increases on the exhaust ports...then the new turbo was sized based on projected horsepower expected. The build has exceeded expectations.

 

And there is still over 30cfm per intake port restriction that is EASILY removed, making for the possibility of much more power potential. But that, as it is, will probably never be seen on the street.

 

Not one that is paved with black stuff...