18G efficiency and injector sizing help

[SolidBoostTSi]

does the 18G hit peak efficiency @15 psi? The reason I ask is because I'm planning to raise boost levels to 20psi and I know my 550's are going to over 100% IDC, So my next question is what size injectors would provide a decent safety margin as far as detonation goes. I recently took my car out for a 3rd gear pull and my IDC was at 132% and timing advance was at 34 degrees, with a knock sum of 36 . I was leaning towards RC750cc injectors but would those support 20psi of boost @ 43psi base fuel pressure? My plans are just to run mid 12's on pump 93octane and keep the car as a daily driver. The supporting mods are in my profile. And will a MAFT v2.02 be able to compensate the deadtime accurately?

you're help is greatly appreciated

 

[andymoraitis]

The 18G can easily run past the 20 psi mark and still be efficient. I run a Big 16G at 24 psi on pump gas daily and it pulls like a freight train. How efficient, however, will be based on how well you can cool the intake charge and how well you can calm the knock. I would recommend 650cc injectors or even 720's/750's if you'd like more headroom to grow and up the boost. While the MAF-T will work with the 650's, it's not the optimal tuning solution. I would keep it, but invest in a new Keydiver chip to handle the main fuel control and injector compensation. You can then fine tune with the MAFT to make the small adjustments necessary to make safe power.

I'm concerned by a couple of things. Your knock count is insanely high and I don't see an upgraded intercooler in your mod list. Also, your fuel pressure should be set from 37-39 psi and not 43. I'm wondering if that knock count of 36 isn't being caused by a couple of things:

1. Overrun with the 255 since the B&M does not adjust pressure down.
2. Excessive heat in the intake charge from not having an upgraded I/C
3. Fuel starvation from running at 132% IDC
4. A faulty knock sensor

The first indicator points to rich knock while the next two are symptoms of lean knock. In order to really tell what's going on, I'd like for you to pull a spark plug and post a picture of it so that we can read it for you, unless you can do so yourself. I agree that bigger injectors are necessary and if I were you, I'd either richen up the MAFT (see if the knock goes down or goes away) or dial down the boost. You may also want to pull the knock sensor and see if it needs to be replaced (any goo on it is a dead giveaway that it's fried).

Let us know what you find,

Andy

 

[SolidBoostTSi]

thanks for the reply, as far as upgraded intercoolers go, I am currendly using a 89 conquest TSi intercooler which is roughly twice the size of the stock side mount

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. I IDC with a S16G and 550's were 94% at 18psi of boost. and Base FPR setting at 43psi. I know for certain that I am not having overrun issues but it still could be possile. The knock sensor isn't melted (yet) by the finger test and I'll post a pic of number the plugs later on.

Thanks again in advance!

 

[mavisky]

I run an 18g right now at 20psi through a front mount and 510cc injectors. Next year it will be running in the 24-26 range with the 650's installed. I'll put something up letting people know how it turns out.

 

[1SloColt]

I ran an 18g with denso 660s at 18-20psi for quite a while and they were more than enough for that turbo. Buddy of mine runs RC550s on the same 18g at 22-24psi and doesn't have any problems with really high injector duty cycle. I say get some 660s, and retard your base timing cause 34 degrees total timing is insane, and its causing all your knock. I think 18-20psi on pump with 23 degrees total timing should yield no knock if tuned correctly on that conquest front mount.