Exhaust Pressure Testing

[Proshop]

It depends on the situation. I see your car is a Roush blower on E85. Your airflow and knock margin will not change appreciably so I believe you mostly likely wouldn't benefit from a re-tune. If you're using a centrif or na, then airflow will increase so you would need to ensure the fuel system is hanging in there.

If you are knock limited, then you would benefit from additional tuning. I spent some more time tuning my borderline timing tables since getting backpressure down to the target range and I've discovered some pretty significant changes. I'm able to run up to 24 deg timing at 10 psi boost on true 93 octane, which is phenomenal considering I couldn't reach 14 deg before these projects. This improvement is due to both the exhaust work and the XDI pump, plus some more tuning changes I made.

Thanks Mike for the reply. Not exactly what I was expecting to hear but the truth is the truth. I definitely have plenty of fuel, I can not thou speak to knock limited part. I will have to check my last log I sent to my tuner for clarification but I think I’m running 17 or 18 degrees in timing on around 13.8 psi.

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[engineermike]

Proshop, if you’re running 14 psi on e85, I would expect more like 22-23 deg timing.

 

[Proshop]

Proshop, if you’re running 14 psi on e85, I would expect more like 22-23 deg timing.

I will confirm later when I get home. The timing is controlled by my tuner thou correct?

 

[engineermike]

I will confirm later when I get home. The timing is controlled by my tuner thou correct?

Yes, it is. It’s a more complicated calculation than you would think…

 

[Proshop]

Yes, it is. It’s a more complicated calculation than you would think…

I’m sure it’s way way over my head. I will have to reach out to my tuner with some questions.

 

[Proshop]

@engineermike looks like the highest I go during a pull is 21.8 but is only for a nanosecond and then bounces around. At one point it does stay consistent at 21.3 but maybe for half a second and then bouncing around. 13.8 psi is the highest I see during the pull and highest knock retard was at -1.5 and correction 1.5 but almost always at 0.

The picture below is about the middle of the pull when timing was highest.

 

[engineermike]

Yea, your timing isn’t doing what I would expect. Who’s doing your tuning?

 

[Proshop]

Yea, your timing isn’t doing what I would expect. Who’s doing your tuning?

Wengerd and they have had good success with some other Roush’s with the same modifications.

 

[K4fxd]

Mike, is the stainless brothers bullet true 3 inch or does it neck down?

 

[engineermike]

Mike, is the stainless brothers bullet true 3 inch or does it neck down?

I’m not sure about the bullets but the dual 3” in/out is definitely true 3” all the way through.

 

[Proshop]

Yea, your timing isn’t doing what I would expect. Who’s doing your tuning?

So Mike what should timing in general look like? Is it linear as rpm rises or dependent on boost etc etc? I’m a total noob to the inner workings of this stuff but I do love learning new things. To add on to my prior post my boost seems to bounce around just like the timing does.

 

[Brad1810r80]

Here is my cars timing , you wanna look at the spark table , positive kr is means pulling timing negative means it’s adding.

This is e30 fuel.

So Mike what should timing in general look like? Is it linear as rpm rises or dependent on boost etc etc? I’m a total noob to the inner workings of this stuff but I do love learning new things. To add on to my prior post my boost seems to bounce around just like the timing does.

 

[engineermike]

So Mike what should timing in general look like? Is it linear as rpm rises or dependent on boost etc etc? I’m a total noob to the inner workings of this stuff but I do love learning new things. To add on to my prior post my boost seems to bounce around just like the timing does.

Usually when I see a timing curve jump around its due to individual cylinder borderline adjustments. When running e85, I would expect these tables to be zerod out so the timing curve should be smooth and steady. I would also expect higher timing on an e85 car at that boost level.

 

[Proshop]

Thank you @engineermike and @Brad1810r80 for the responses. I will be reaching out to my tuner with questions about this to see their thoughts and see what if anything can be changed.

I honestly kick myself all the time for going the direction I did in SCer choice. I’ve contemplated pulling it off and selling so I can go a different direction. My wife would skin me alive probably if I did so.

 

[TX-Ripper]

every 18+ Roush owner thinks the same, but don’t want to admit it

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