Closed loop Lean cruise and idle and cruise timing

General Tuning Questions And Discussions
vp304
Posts: 451
Joined: Wed May 19, 2010 2:21 pm

Re: Closed loop Lean cruise and idle and cruise timing

Post by vp304 »

immortality bog stock l67
180 thermostat
ported blower myself
11p so no maf
Shorty extractors into single 2.5 inch system with 1 straight through muffler.
Going to decat it soon as im on stock pulley and reading 11psi at 5500 rpm i think exhaust is holding it back a little.
I know 11 psi sounds crazy high for stock pulley
But the exhaust holding it back would mean higher boost
The ported blower and no maf would probably mean higher boost also as less restriction allowing more air into the engine.
Dyno boost refrence to lim
2 bar map
and after market boost gauge i have in car all show close to 11psi at around 5500 rpm
Last edited by vp304 on Sun May 30, 2021 7:14 pm, edited 1 time in total.
'quipt4it
Posts: 675
Joined: Sun Oct 28, 2012 12:57 pm

Re: Closed loop Lean cruise and idle and cruise timing

Post by 'quipt4it »

Decat is not legal. Risking a big fine.
What about an intercooler?
vp304
Posts: 451
Joined: Wed May 19, 2010 2:21 pm

Re: Closed loop Lean cruise and idle and cruise timing

Post by vp304 »

Out of 3 cars i have this is only one with a cat.
Have a intercooler w2a but need to space k frame to fit it under bonnet as stock boost pulley is massive and will stick out of bonnet by around 20mm or so by rough measurements
'quipt4it
Posts: 675
Joined: Sun Oct 28, 2012 12:57 pm

Re: Closed loop Lean cruise and idle and cruise timing

Post by 'quipt4it »

A low restriction exhaust will also improve your fuel economy.
This sounds like it has taken a turn from 'tow horse' and a 'fuel economy squeeze' to an all out drag car :lol:
vp304
Posts: 451
Joined: Wed May 19, 2010 2:21 pm

Re: Closed loop Lean cruise and idle and cruise timing

Post by vp304 »

lmfaooooooo quipt4it
here is video of boost gauge i should get one of pulley then jump in and take of as people would not believe me 11psi on stock pulley
https://www.youtube.com/watch?v=8OZ7r33
Last edited by vp304 on Sun Jun 13, 2021 12:58 am, edited 1 time in total.
'quipt4it
Posts: 675
Joined: Sun Oct 28, 2012 12:57 pm

Re: Closed loop Lean cruise and idle and cruise timing

Post by 'quipt4it »

Just on that cat issue, apart from the smell, I don't think the cat is the big restriction. The whole exhaust diameter would need enlarging. Gutting the cat will give you a big 'hole' in the bottom end response.
Have a look at this chart for your targets.
https://www.exhaustvideos.com/faq/how-t ... -diameter/
vp304
Posts: 451
Joined: Wed May 19, 2010 2:21 pm

Re: Closed loop Lean cruise and idle and cruise timing

Post by vp304 »

quipt4it the factory vt vx vy l67 cars run a twin cat setup exhaust over the single cat used on vs -vy v6
must be a reason for it. V8 ls1 vt vy also run similar twin cat setup
'quipt4it
Posts: 675
Joined: Sun Oct 28, 2012 12:57 pm

Re: Closed loop Lean cruise and idle and cruise timing

Post by 'quipt4it »

I agree. That's why I said the whole exhaust diameter needs enlarging. :thumbup:
vp304
Posts: 451
Joined: Wed May 19, 2010 2:21 pm

Re: Closed loop Lean cruise and idle and cruise timing

Post by vp304 »

If i step up to a 3inch will be a drag car then hehe
'quipt4it
Posts: 675
Joined: Sun Oct 28, 2012 12:57 pm

Re: Closed loop Lean cruise and idle and cruise timing

Post by 'quipt4it »

That's the problem. A single 2.5" is only slightly better than a dual 1.75".
But a single 3" flows substantially more than a single 2.5".
A dual 2" sits right in the middle, but it would cost a lot more.
Is your cat a 2.5"?
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