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Old 08-01-2003, 05:35 PM   #1
MAD REX
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Default went from vf22 to 18g

So I switched from a VF22 running a max of 20 psi to a 18G running a max of 22.5 psi in 4th gear.


Before the switch I had no knock. Now with the added boost I'm getting some knock and I'm wondering if I should just add fuel and leave the timing map alone?

This turbo can run much more efficient at higher boost levels vs the VF22 so most can run leaner or advance more timing.

But I'm getting knock when I do

*sigh*

I need a wideband
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Old 08-01-2003, 06:52 PM   #2
Concillian
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Default Re: went from vf22 to 18g

Quote:
Originally posted by MAD REX
This turbo can run much more efficient at higher boost levels vs the VF22 so most can run leaner or advance more timing.
I think you mean to say:
This turbo can run much more efficient at the SAME boost levels vs the VF22.

You can run better timing at the same boost or the same timing at a little higher boost. 2.5 psi is not a small change, it's totally concevable you have to lower timing.

Where are you getting knock? Are you running out of fuel at high RPM? What are your IDCs? Do you at least have an EGT?
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Old 08-01-2003, 06:57 PM   #3
MAD REX
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Default Re: Re: went from vf22 to 18g

Quote:
Originally posted by Concillian


I think you mean to say:
This turbo can run much more efficient at the SAME boost levels vs the VF22.

You can run better timing at the same boost or the same timing at a little higher boost. 2.5 psi is not a small change, it's totally concevable you have to lower timing.

Where are you getting knock? Are you running out of fuel at high RPM? What are your IDCs? Do you at least have an EGT?
Yes that is what I meant to say

I'm getting knock in the 'knock prone' areas

How would I know if I'm running out of fuel?

IDC's are never above 80 which is pretty normal up here I think

VDO egt probe has fried, need to get a replacement.
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Old 08-01-2003, 09:21 PM   #4
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In the little time I've spent tuning a FP1805H on STi injectors up here, at 22psi your IDC's are much lower than I'm seeing. I put my money on it that your lean. If your timing map was good to go on your VF22 and your running similar boost levels you should be ok. Make sure you rescale your map for 23psi..
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Old 08-01-2003, 09:57 PM   #5
MAD REX
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Yeah I have already rescaled my utec for the 23.5 psi.

I'm going to just put in .2 of fuel everytime I get knock for now.
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Old 08-01-2003, 10:49 PM   #6
Red Rocket
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Default Re: went from vf22 to 18g

Quote:
Originally posted by MAD REX
This turbo can run much more efficient at higher boost levels vs the VF22 so most can run leaner or advance more timing.
That's what they claim......

How much more boost are you running? What kind of fuel?

Kevin
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Old 08-02-2003, 01:12 AM   #7
JustDSM
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Default Re: Re: went from vf22 to 18g

Quote:
Originally posted by Red Rocket


That's what they claim......

How much more boost are you running? What kind of fuel?

Kevin
The 18g IS more efficient at higher PR's than the VF22.
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Old 08-03-2003, 12:43 AM   #8
MAD REX
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22-23 psi 93.5 octane
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Old 08-04-2003, 07:39 AM   #9
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Instead of adding fuel in those knock prone areas. I'd take a .5 to 1 degree of timing to see what happens. Some places it's better to run less timing to prevent det. Especially in knock prone areas.

Imprezd~
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Old 08-04-2003, 05:18 PM   #10
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Quote:
Originally posted by Imprezd
Instead of adding fuel in those knock prone areas. I'd take a .5 to 1 degree of timing to see what happens. Some places it's better to run less timing to prevent det. Especially in knock prone areas.

Imprezd~
hey imprezd, check your pm's Can you send me the 160 bucks back if your not gonna send the coilovers. Thx
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Old 08-05-2003, 08:06 AM   #11
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dude email me...
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Old 08-05-2003, 08:33 AM   #12
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Quote:
Originally posted by MAD REX
22-23 psi 93.5 octane
If you're going to run 23psi on the street, you really should run more than 93 octane.
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Old 08-05-2003, 08:46 AM   #13
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Assumng your IPW is in its sweet spot range, Id start lwoeign timing first. You won't be giving up much by dropping timing a degree or two
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Old 08-05-2003, 10:36 AM   #14
MAD REX
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Quote:
Originally posted by Austin
If you're going to run 23psi on the street, you really should run more than 93 octane.
I'm in denver so the 23 psi is more like 19.5 psi. So not too stressful on the engine.
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Old 08-05-2003, 10:55 AM   #15
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something must be stressing the engine since you are getting detonation.
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Old 08-05-2003, 02:57 PM   #16
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How about the effect of charge density on dynamic compression ratio and therefore detonation threshold? This may be confounding your expected ability to add spark advance which you expect from lower temperature and lower exhaust manifold pressure/end charge pollution etc.

Some consider that requiring less spark advance is a good thing.

Give the engine the timing it needs and worry about torque not about advance figures.
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Old 08-05-2003, 04:10 PM   #17
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Louis,

Your IDCs are a tad on the low side IMHO. With the 20G pushing 23psig (about 19psia), my IDCs are right around a peak of 90 with the STi injectors. When I moved from the TMIC/VF22 to FMIC/20G, I had to add in up to 4% fuel as well as rescale my timing map.

You will be flowing significantly more air through your motor now (what are your before and after MAF readings?), so expecting to be able to run the same peak timing seems a little unrealistic (in my experience at least).

Also bear in mind that the 18G is well outside of it's sweet spot at 23psig up here (a PR of ~3.2). In his book 'Forced Induction Performance Tuning', Graham Bell notes that when approaching the limits of your available octane, more power is almost always available by backing off on boost and running more aggressive timing, versus the other way 'round.

-Pace
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Old 08-05-2003, 06:03 PM   #18
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Pace, thanks for the great info.

What are your richest fuel points in the 4500 - 5250 rpm area?
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Old 08-05-2003, 08:25 PM   #19
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Pace, how you liking that new combo so far? What FMIC did you end up going with?
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Old 08-06-2003, 12:11 AM   #20
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I went the cheap route..

-Pace
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Old 08-09-2003, 04:49 AM   #21
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Gawd I hate the term 'efficiency'. Its the most abused term out there.

Consider this- does compressor 'efficiency' (i.e., 10 or 20 degrees F outlet temp difference) mean diddy-squat with the avg. oversized IC we use?

On paper, yes. In the real world, no.

50F and up, well.............
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Old 08-09-2003, 02:00 PM   #22
bobsterswrx
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When I went from vf30 to 18G There was little or no change in my fuel map as verified on the A/F on the dyno. I could actally run 1-2 more psi everything else being equal. But I run a minimum of 50/50 race fuel (95 oct) when I run above 17 psi at 1200 ft elevation. I only run 101 race fuel above 20 psi, better safe than sorry. On race fuel at 22 psi my IDC's are 92 with sti injectors.
Bob
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