Lowering boost and re-tuning 2001 Cobra

EDrgr

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All,

I'm changing my pulley from a 3.60 to a 3.80 on a Vortech S-Trimmed Cobra in an attempt to lower boost from 11lbs at 6000 to target around 8-9lbs. This is on a stock Cobra and I believe 11lbs may be too much (GT impeller, non-intercooled, and Anderson Powerpipe). This is a street car which I occasionally take to the track. I don't want to hurt this engine is the bottom line.

I self-tuned it with SCT Advantage and Don Lasota wrote the base tune (and helped along the way). I know it needs a re-tune after I change the pulley. My question is after I change the pulley should I start the re-tune process using the base tune and dialing in the MAF again, essentially starting over, or should I just start where I'm at now and start adjusting it?

The second option is to run it the way it is with the 11lbs of boost and not worry about it as it'll be ok. I'm open to suggestions. Thanks!

Eddie
 
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DSG2003Mach1

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reducing boost should not require a re-tune. The MAF is, in theory, already properly scaled for the tube size, position etc...if the car is otherwise running well, lower the boost and keep going.

even when increasing boost - if the MAF is properly scaled it shouldn't need re-tune. I realize that's painting with a broad brush - when increasing boost you do have to consider headroom on the MAF, injectors, fuel pump and power being made on your fuel type.

HP is more of the concern than boost - 99/01 cobras and 03/04 machs are usually considered to be relatively safe around 450rwhp. Personally I'd probably go bigger blower pulley and then just let it eat all the way to 7k. With a P1 procharger kit a 4" blower pulley me right in the 10# area at 7k, car was slightly detuned (pulled timing) to bring it down into the 470s
 

01yellercobra

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I'd check the A/F and go from there. As DSG mentioned you're probably ok.

If you do need to tweak anything just tweak the tune you have. No need to start over. At most you might have to tweak the top of the transfer.
 

decipha

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As has been said if tuned properly then you shouldn't have to do any tune revisions as your basically just giving her less throttle so to speak.

Power itself isn't usually a killer of the stock 4v n/a weak powdered rods its usually just the moons gravitational pull on the seas. I've seen some engines last forever at 500 and some of them crap out under 400. Its not really power I'd be concerned with its more so just luck of the draw.

If she's been happy then I'd leave her be. If you want to be safer go to the act retard function and yank more timing out as air charge temps come up.

How much total timing are you running up top?

Non-inter cooled you should be running water injection at a minimum.
 

EDrgr

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Thanks Decipha! Timing table attached.
 

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decipha

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a timing table is absolutely useless without factoring in all of the modifiers, the values mean nothing

what is your actual logged spark?
 

EDrgr

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Fair enough. I’ll look and see.

I like the statement “if she’s been happy then I’d leave her be.” I’m starting to second guess myself as the car is running really good.
 

01yellercobra

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Fair enough. I’ll look and see.

I like the statement “if she’s been happy then I’d leave her be.” I’m starting to second guess myself as the car is running really good.
As someone that decided to install headers on a perfectly fine car and then had to chase a couple leaks I vote to leave it alone.
 

04sleeper

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I always tell people of lowering boost to think of it as only going like 1/2 or 3/4 throttle. If you are only getting half the boost, or say 3/4, then do you need a retune to drive it? Of course not. Same thing applies. If the tune was set up correctly, no need to change it.
 

Fopar

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Technically speaking you do need to re-tune, but only the O/L TPS vs. RPM table, and maybe the target A/F table (Base fuel).

Also whoever setup your 'base' tune didn't do a great job, your Load axis should have been re-scaled to probably 1.5ish
 

EDrgr

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Thanks for the reply Fopar. I’m currently away and once I get home I’m going to relook a couple of things.

I could probably tweak quite a few things, but with this being a street car and it seems to run pretty well, I really don’t want go to far into it.

Eddie
 

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