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Discussion Starter #1
Just finished up a build for a client. Car is a 6 speed with a KB 2.8, Longtubes, and a PWR 419 CI longblock.

Car is a beast and made nice power @ 13psi and pump gas. Timing is a very safe 14* and 11.2 A/F.

I would love to push it but the client wants pump gas only so we are stopping right here.

Dyno sheet attached.
 

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That's awesome Tim. With a forged motor, why so conservative on the AFR? Although at 750RWHP I guess it doesn't really matter haha.

We were recently discussing AFR and weather changes. A 11.8 AFR in winter is like 11.3 in summer from what I've seen so a 11.2 in winter will be high 10s in summer? Josh also informed the adaptives don't really make that much of a difference and that really two tunes are ideal....one for summer and one for winter.
 

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Discussion Starter #6 (Edited)
That's awesome Tim. With a forged motor, why so conservative on the AFR? Although at 750RWHP I guess it doesn't really matter haha.

We were recently discussing AFR and weather changes. A 11.8 AFR in winter is like 11.3 in summer from what I've seen so a 11.2 in winter will be high 10s in summer? Josh also informed the adaptives don't really make that much of a difference and that really two tunes are ideal....one for summer and one for winter.
I donot agree with anything you just said. A/F is A/F period. If a MAP or MAF based car is tuned properly A/F doesn't change on weather or elevation conditions. If boost increases in the winter time and a MAP or MAF is tuned properly the A/F will stay the same. Same goes for summer time, if the air is less dense and less boost is present the a/f will not change if the MAP is dialed in properly.

I tuned 11.2 on this particular car do to inlet temps he will see racing. Slightly richer A/F holds back a little power but cools the combustion chamber a little more. This guy road races so he will build a lot more heat then a normal car.

I also tune spark based on what the spark plug shows me,not what I think the engine wants.

Hope that helps you a little Speedy, I know you're an info nut!

Tim
 

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I agree Tim AF is AF.
 

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That does help Tim. The tuning side of these cars is VERY interesting to me since it's computer related and that's my background.

It may be because I've not seen the back end CMR software to know how the tables look, but there's one thing about the AFR staying the same that confuses me.

So say you tell the CMD AFR to be 11.8 at 5,000 RPMs and a MAP 12psi of boost and it's winter time.

In summer at that same point at 5,000 RPMs it may only be 11psi of boost but the CMD AFR is still 11.8 which would likely result in 11.3 AFR?

Maybe that's not how it works and since I've not seen the back side I'm just not getting it.

Thanks for helping me understand. Nice call on the AFR for the road course racing.
 

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Discussion Starter #10 (Edited)
That does help Tim. The tuning side of these cars is VERY interesting to me since it's computer related and that's my background.

It may be because I've not seen the back end CMR software to know how the tables look, but there's one thing about the AFR staying the same that confuses me.

So say you tell the CMD AFR to be 11.8 at 5,000 RPMs and a MAP 12psi of boost and it's winter time.

In summer at that same point at 5,000 RPMs it may only be 11psi of boost but the CMD AFR is still 11.8 which would likely result in 11.3 AFR?

Maybe that's not how it works and since I've not seen the back side I'm just not getting it.

Thanks for helping me understand. Nice call on the AFR for the road course racing.
Speedy,
You have other table you tune besides Commanded A/F. You set that as to what you want and dial your VE in to obtain that CAF.

You can scale your VE table to different boost levels and if you take your time when ramping the values up and down while dialing in CAF then a boost increase or decrese will fall into the upper or lower VE cells and A/F should stay pretty damn close if the tuner did his job correctly.

If you rape the VE table then you have no chance of holding CAF on an increase or decrese in boost.

If what you are saying were true than any factory tuned S/C car would blow up in a -DA state. They donot because the factory dials in the MAF or MAP or in some cases both to insure A/F remains the same in any situation.

Make sense?
 

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That does help Tim. The tuning side of these cars is VERY interesting to me since it's computer related and that's my background.

It may be because I've not seen the back end CMR software to know how the tables look, but there's one thing about the AFR staying the same that confuses me.

So say you tell the CMD AFR to be 11.8 at 5,000 RPMs and a MAP 12psi of boost and it's winter time.

In summer at that same point at 5,000 RPMs it may only be 11psi of boost but the CMD AFR is still 11.8 which would likely result in 11.3 AFR?

Maybe that's not how it works and since I've not seen the back side I'm just not getting it.

Thanks for helping me understand. Nice call on the AFR for the road course racing.

MAP: Manifold absolute pressure

Your tuning the car based off of manifold pressure. If that pressure changes, that would be a different cell in the VE tables which would result in a different commanded fuel.

How does a centrifugal car have a consistent air/fuel even though boost is changing as rpm increase?

A turbo car might make 10psi at 4000rpm in one condition and 18psi of boost in another condition based on load, but the air/fuel stays the same.

If you tune a car assuming the car will always be at 10psi and you just copy those cells over to anything above that than the tune will be screwed.

This is how the VE tables are setup in the CMR. Across top is RPM, down the side is P-Ratio. Anything in the blue is vaccum and the pink is boost.

2.0=15psi
1.5=7.5psi
1.25=3.75psi

So basically if you are tuning for 6000rpm and 7.5psi, you can find that cell in the spreadsheet below and adjust it till the optimum air/fuel is reached. In the cells directly above that, you would need more enrichment since its safe to assume that the higher boost level will require more fuel. You have to tune for all the cells and not just the ones you are hitting that day on the dyno.

This is all much more simplified than the actual process, but it gives you an idea. You still have seperate tables for VE and WOT enrichment, but it still gives you an idea of why the A/F shouldnt change with the seasons, afterall, Dodge doesnt provide different tunes in the summer vs the winter in our cars or the SRT4 neon which is turbo-charged.
 

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Oh and awesome job BTW tim. How do you like the 9:1 CR vs the 8.5:1 CR? Was the cam bad to tune? That was our new PW-220P blower cam. Should behave very nice and still make power.

Oh and its actually 423 cubes since we used the K-1 4.08" crank in it instead of the 4.05" Manley crank. Still the same 4.06" bore though.
 

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Manley is actually revising their lower compression piston for us to be 9.5:1 moving forward. The motor in this thread was 9:1 which works nice also. Im running 8.5:1 in my motor, but I hope to throw a ton of boost at it and still be on pump gas.
 

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Thanks Tim, and Andy for the screen shot. That info helps me to understand A LOT more.
 

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Everything I have ever read about FI points towards using lower static CR on a boosted app. What effect do the heads and efficiency of the combustion chamber have on the dynamic CR? Is it because the heads flow easier so they can relieve heat better?
 

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That's good info Tim and Andy. I started a thread about the different combo's that are available. If you find time Andy could you put some info in there for us?
 
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