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Lots of questions...

What's the flow rate on our stock injectors?

At what point do they become insufficient?

What are the dermining factors on injector sizing? (Horsepower, air flow, etc.)

What are the options out there for larger injectors? I know of the RC550s...

Why does Uncle Charlie touch me in my no-no place?
 

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Injectors become maxed out typically when they reach 80ish% duty cycle. That'll leave you with a bit of a comfort zone. Your toonah should know how to log the duty cycles.
 

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Oh, speaking of RC, i had RC Engineering clean/flow analysis my 1 year old Denso injectors. Here's the before/after cleaning report you get when you get their basic cleaning services:
 

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I think your problem is that you're asking your uncle to do your tuning. It's quite obvious he's tuning the wrong 'part'. When you ask your uncle to monkey around, what else did you expect him to do.

Now, if you talk to Charlie the Monkey Tuner, you can discuss w/ him your hp goals and what size injectors you should use to get there.

Also, now that you've outed your uncle, you should also tell him to get some legal advice.
 

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Your toonah should know how to log the duty cycles.
Mmmm... chicken of the sea...
:drool:

What are the dermining factors on injector sizing? (Horsepower, air flow, etc.)
Don't overlook the fuel pump. While I've honestly no idea on the Lotus, it's not entirely uncommon to have to step up to a higher volume fuel pump. If the pump can't keep up, bad things can happen.* Note 25psi_Elise_Killer's sig line, for example. The entire fuel system needs to be taken into consideration.

*Although I seriously doubt it's an issue with the Lotus - just mentioning it so all the bases are covered.
 

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Here's some good info for determining injector sizes. Hope you're algebra is up to par. But prolly better to let your tuner decide what injectors/fuel system upgrades you need since they probably did some experimenting to see what works with respective applications. A higher volume fuel pump may/may not be needed, but its always nice to have one as its considered "cheap insurance".

http://www.rceng.com/technical.aspx
 

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Lots of questions...
1- What's the flow rate on our stock injectors?
2- At what point do they become insufficient?
3- What are the dermining factors on injector sizing? (Horsepower, air flow, etc.)
4- What are the options out there for larger injectors? I know of the RC550s...

5- Why does Uncle Charlie touch me in my no-no place?
I've added numbers for clarity to the quote above, and my answers below.... lots of answers.

1.) Stock injector flows ~300-310cc/min @ 45psi (~29lb/hr). But can flow more at higher pressures - 387cc/min @75psi. This is good for 200-275 hp depending on fuel pressure, BSFC, intake manifold/port pressure (changes with naturally asperated or forced induction engines).

2.) Insufficient? This depends on N/A or F/I use as well as fuel system design and pressure... and a host of other factors.

3.) Factors can include power required, Brake Specific Fuel Consumption (BSFC), fuel pressure, max safe duty cycle, intake pressure (boost), etc.

4.) Larger injectors are readily available up to ~1900cc (180lb/hr) and larger, but these are generally low impedance designs. The stock injectors are high impedance units [generally available up to 72lb/hr (760cc)]. The ECU design will determine which units it will run (with or without resistors).

Going larger on injector than is required can result in low rpm fuel atomization issues - this can be slightly corrected with alterations in the tip of the injector for both pintle or disc designs.

The stock injector is a long, thin "pencil" design. Using some other injector designs (external shape) will require modifications to the intake manifold or head, fuel rail, rail mounts, etc. to fit the injector. But there are "pencil" designs available in high impedance that flow 760cc/min at 43.5 psi (more at higher pressures) and will work with the stock ECU.

For some ECU's, it is also possible to run additional injectors in parallel or staged (comes in at a specific rpm) with the stock injectors giving good low rpm transient response with improved air/fuel density of the additional injectors are located farther upstream in the intake track.

The stock fuel pump is good for just under 300 rwhp at stock voltages, but can be over driven at higher voltages for up to 50% more flow at WOT for intermittent usage. Larger flowing pumps are readily available for return or returnless (like the stock system) fuel systems.

5.) Not going there. :no:



This is just the tip of the iceberg, but I hope it helps.
 

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Interesting. I was looking for info on the stock injectors the other day. Celica GT-S (same engine) uses 290 cc/min injectors, so the Denso injectors that Lotus puts in the Elise (different color, different part number) flow slightly more.
 

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Interesting. I was looking for info on the stock injectors the other day. Celica GT-S (same engine) uses 290 cc/min injectors, so the Denso injectors that Lotus puts in the Elise (different color, different part number) flow slightly more.
Just be wary that differnt manufacturers use different flow rates for some strange reasons depending on how much PSI they test at. Denso sells/markets my injectors at 660cc, but many other companies rebrand these same Denso injectors and sell them 680cc. The flow analysis of my injectors above confirm that they do flow at 680cc at the flow rates RC Engineering uses. Maybe JayDeeEm injectors use a different benchmark for measuring flowrates in injectors compared to European/American counterparts?
 

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Well, if you have the need for bigger injectors, make sure your tuner can scale them properly or the car is gonna run pig rich and you'll get like 5MPG :p
 
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Discussion Starter #15
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Assuming 220 BHP for the stock S

Injectors would need to be between 400 and 436 CC, so the S being 440cc makes sense!
 

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do you know this for sure?

100% sure?

i know someone who will buy a set if someone is absolutely sure. even the dealer don't know for sure.
90% sure. I have heard from charlie, jack and a couple others, IIRC. I mean, if the Cup car has 255 and Gotham is 265, it would be a good bet they have the same injectors. The cup car has 440 last I heard.
 

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I've tuned several cars over 300 HP with the stock fuel pump, both the Elise and Exige S. The limitations in the fuel system (at the power levels commonly achievable) are isolated to the injectors and/or the control of the injectors via the ECU, based on my experience.
 
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