Scaled tune vs. Custom OS SD tune

[68Camaro]

I have been seeing a lot of Scaled tunes for boosted applications talked about on this forum.

I would like to have opinions + pros and cons as to which method to tune a boosted application (20+psi).

I am planning on doing a 88mm turbo build soon and am at war with myself on which way I want to tune this animal. I have tuned a smaller turbo car and did a 2 bar SD tune which worked out nicely but I keep seeing scaled tunes talked about and I don't know much about them.

[SultanHassanMasTuning]

depending on your PCM, and your hard coded MAF limits

[68Camaro]

Thanks for your response. I was hoping for more responses and a little more discussion/information than what I have received though.

[blownbluez06]

There are other limits that you won't enjoy hitting. Even in SD mode, scaling keeps you from hitting airflow ceilings that will put you in reduced engine power and help keep you able to use the spark tables instead of riding the bottom line on the hit. Scale it too small and you won't use any of the table. Scale it too big and you'll hit the bottom airflow line when you hit boost.

[68Camaro]

Thanks blownbluez06 for the info. I am assuming the scaling in SD mode you are talking about is still with a stock OS? Upgrading to a 3 bar custom OS will get me to 29.4 psi before limiting out I believe. It seems a lot of tuners will scale the stock OS so they can still use a MAF for better drivability (street manners and mileage)? These are really the questions I am hoping for some insight as to why scale the stock OS instead of just upgrading the OS to a custom 3 bar deal.

Looks like you are making lots of power (boost). Is your tune scaled or custom OS?

[Ben Charles]

Driveabiltiy and mileage should be the same for either. I prefer scaled MAF Tunes myself

[68Camaro]

Thanks for weighing in Mr. Charles. can you give any pros vs cons between the two methods? I know its just my OCD kicking in but I like to understand (or try to) all angles to try and make the best decision for the application. Thanks again to anyone willing to help a crazy guy out!

[Ben Charles]

Sure, Scaled MAF you can have whatever G/sec limit you want, so a 50% scaled tune, when the computer read 512 g/sec its really at 1024 which from what I have seen is good for around 1000rwhp ( the new GM computer have a 4000g/sec limit) since the tune is scaled the 1.20 limit that's in your computer (gen 3) again a 50% scaled tune makes this 2.40g/cly in your spark tables, so on a low boost setup using SD it will hit the last cell at 1.20 and just reuse it. That might be find at low boost but pushing a lot of boost I like to have full spark control. Something else is you can look at Tq the computer makes if your making big power, the limit in the ECU is 640 in most OS's, so again a scaled tune you can actually see what your tq prediction is, so a 50% scaled tune and it shows 400ftlbs that's really 800.

What I don't really like about SD is on boost setups the IAT swing is typically ALOT so as the computer sees a high temp it actually leans out the AFR, I have seen a 20 point IAT change AFR up to a point or more. Sure you can mess with the Bias, but to be honest its still a problem (or has been for me anyways) and you can play with the PE IAT multiplier to somewhat counter this, but its a lot more time consuming. To be honest all SD tuning should be done it STEADY STATE, and when you differ from your steady state values you should stop tuning till you get back into steady state, that's really the trick to SD tuning. IF you run the system in CL is helps counter this, but cold starts or warms starts will still be in OL and WOT is always OL.

Ultimately the computer just looks at either the MAF or the IAT/MAP sensor for fueling, its your choice what you want to use. I feel like the internet made SD so popular, maybe not the really good tuners, but then again some of them like SD tunes lol.

[68Camaro]

Thank you Mr. Charles! This is exactly the kind of information I was looking for. I understand a lot better and actually think I am going to do a scaled tune for my combo now. I have ran into the IAT problem myself with one SD tune that I did - there isn't access to whatever fueling table the IAT is controlling that I could find and it really made things difficult.

[blownbluez06]

Thanks blownbluez06 for the info. I am assuming the scaling in SD mode you are talking about is still with a stock OS? Upgrading to a 3 bar custom OS will get me to 29.4 psi before limiting out I believe. It seems a lot of tuners will scale the stock OS so they can still use a MAF for better drivability (street manners and mileage)? These are really the questions I am hoping for some insight as to why scale the stock OS instead of just upgrading the OS to a custom 3 bar deal.

Looks like you are making lots of power (boost). Is your tune scaled or custom OS?

I scale all high boost, high power applications.

I see you're in Arkansas and have something that looks like a ProMod. You know my friend, Doc Baker?

[Ben Charles]

Blown does Doc have a red procharged LT1 Camaro?? If so I seen him wear some people out street racing lol

[68Camaro]

I scale all high boost, high power applications.

I see you're in Arkansas and have something that looks like a ProMod. You know my friend, Doc Baker?

I know of him (Doc Baker). We both race at Centerville Arkansas. I'm not sure what he has running right now but he used to have a blown alcohol Studebaker truck that ran pretty well.

[68Camaro]

I scale all high boost, high power applications.

I see you're in Arkansas and have something that looks like a ProMod. You know my friend, Doc Baker?

Just talked to a mutual friend who says he (Doc Baker) is working on a Demon now that's gonna be pretty nasty.

I have one more question - Do you just use the stock OS or are you guys upgrading the OS and then scaling the new OS?

[Ben Charles]

stock OS, no need to upgrade

[68Camaro]

stock OS, no need to upgrade

cool! Thanks for the information!

by the way - where in Arkansas are you? Do you ever come to the track at Centerville?

[Ben Charles]

Im up in the NE part Jonesboro/Paragould area. No I haven't made it up to the 1000ft track, we are about 1.5 from the Motorsports park in Memphis, that or we do 1/8 stuff local

[LSxpwrdZ]

Depending on the power level I scale all boosted tunes normally, stock OS MAF and 2/3bar OS. Gives resolution to the boost region on timing tables because un-scaled 1.2 g/cyl isn't hard to hit. The determining factory for keeping stock OS and custom OS is whether you want to run MAF or SD. Keep in mind the flow through the MAF as well. On a higher boost setup your not gonna run a stock 75mm or 85mm MAF and stay under the 12,000hz frequency of the table in the editor. This will keep you from accurately metering airflow for fueling. You'll have to run a card MAF in a large housing to keep the reported frequency within the 12khz limit.

[Ben Charles]

Yea what James said, best to step up to a card style MAF with a larger tube.

[Pekka_Perkeles]

Yea what James said, best to step up to a card style MAF with a larger tube.

How stable the card-style MAF is? I mean, is it fine with boosted cars, but not that stable with high-overlap cams?

I don't have any evidende for this, just asking.

[blownbluez06]

Just talked to a mutual friend who says he (Doc Baker) is working on a Demon now that's gonna be pretty nasty.

I have one more question - Do you just use the stock OS or are you guys upgrading the OS and then scaling the new OS?

Custom OS

stock OS, no need to upgrade

Adding the third dimension of boost greatly enhances the ability to properly fuel the vehicle when used properly. If I were on a bologna sandwich budget with filet mignon taste, I might hack up a stock OS, but in no way are the two even comparable. This will, I'm sure lead into a discussion of those who have "gotten away" with hacking the stock OS and while we can get away with it, it's not the best course of action in my opinion.