2018 Silverado loss of power with exhaust??

[Christian Olguin]

I have a 2018 Silverado e assist l83

mods:

speed engineering headers (castles)

voolant CAI

e85 conversion

stock resonator 

magnaflow muffler

tuned by BBP

 

so I finally took the stock muffler off and added a magnaflow and kept the stock resonator. It sounds great but I feel like I lost a little power since now I have more exhaust flow. My question is do you think if I add a l86 ported intake manifold with a ported l86 throttle body it’ll make up for the loss of power.

 

im thinking that I’m getting more exhaust flow but I’m not pulling in enough air to match it but then again I don’t know. Anyone else have this problem after longtubes and aftermarket muffler??

 

[lucas287]

I've been a David Wizard fan since I was a teenager. More recently, I've seen every episode of Engine Masters on Motortrend. Most of my "experience" is gleaned from others. I have built an engine and worked on/tuned a lot of fast cars/trucks that I've owned over the years. That's the credibility behind my response.

 

To clarify, are you experiencing a loss in part-throttle? Or it feels lazy everywhere? You might just need to rework your MAF/VVE now that there's no restrictions. My following pontification is based on an assumption that you've lost part-throttle, low-mid rpm power/tq.

 

An NA 5.3 will only flow so much air. I, personally, feel that 1.875" primary long tube headers merging into a basic 4-1 3" collector is TOO large for an NA 5.3. The primary length helps make up for the primary diameter but any velocity is lost once it hits those massive collectors. Something more appropriate might be a merge/choke collector similar to what ARH uses along with 1.75" primaries. Personally, I'd love to see 5.3 headers that were even smaller with 2.5" collectors and secondary pipes. 

 

Though my above comments seem tangential, it's important to note that any given engine and exhaust combo must be looked at as one. In your case, I think you perceive a power/tq loss from the Magnaflow muffler because you lost a restriction which was helping velocity, which aids in torque production. Let me be clear, back pressure is not important, but, velocity is very important. 

 

I think an L86 manifold would only exacerbate your perception of lost low-mid range. Increasing plenum volume that much will likely hurt your bottom end. 

 

Lastly, engines are fickle and so are people. Some will completely disagree with everything I've said. I'm not claiming I have all the answers or that I'm right. Just an opinion  

[Christian Olguin]

49 minutes ago, lucas287 said:

I've been a David Wizard fan since I was a teenager. More recently, I've seen every episode of Engine Masters on Motortrend. Most of my "experience" is gleaned from others. I have built an engine and worked on/tuned a lot of fast cars/trucks that I've owned over the years. That's the credibility behind my response.

 

To clarify, are you experiencing a loss in part-throttle? Or it feels lazy everywhere? You might just need to rework your MAF/VVE now that there's no restrictions. My following pontification is based on an assumption that you've lost part-throttle, low-mid rpm power/tq.

 

An NA 5.3 will only flow so much air. I, personally, feel that 1.875" primary long tube headers merging into a basic 4-1 3" collector is TOO large for an NA 5.3. The primary length helps make up for the primary diameter but any velocity is lost once it hits those massive collectors. Something more appropriate might be a merge/choke collector similar to what ARH uses along with 1.75" primaries. Personally, I'd love to see 5.3 headers that were even smaller with 2.5" collectors and secondary pipes. 

 

Though my above comments seem tangential, it's important to note that any given engine and exhaust combo must be looked at as one. In your case, I think you perceive a power/tq loss from the Magnaflow muffler because you lost a restriction which was helping velocity, which aids in torque production. Let me be clear, back pressure is not important, but, velocity is very important. 

 

I think an L86 manifold would only exacerbate your perception of lost low-mid range. Increasing plenum volume that much will likely hurt your bottom end. 

 

Lastly, engines are fickle and so are people. Some will completely disagree with everything I've said. I'm not claiming I have all the answers or that I'm right. Just an opinion  

Honestly everything you’ve pointed out makes perfect sense to me and helps me understand what is going on. With the stock muffler the truck felt very fast and now it feels quick on top end but the mid range is ehhh to me now. Maybe a different muffler would help. That and possibly a retune would help clear this up a little. Worst case scenario I can go boost and just forget all these problems lol

[It's Tim]

39 minutes ago, Christian Olguin said:

the mid range is ehhh to me now. Maybe a different muffler would help.

Camshaft profile is the greatest bottleneck. A lot of peeps add an after market exhaust and never notice that stepping on the gas is now a kin to stepping on a wet sponge. 

[lucas287]

9 minutes ago, It's Tim said:

Camshaft profile is the greatest bottleneck. A lot of peeps add an after market exhaust and never notice that stepping on the gas is now a kin to stepping on a wet sponge. 

Definitely true to an extent. More duration, usually, is just going to decrease dynamic compression ratio which even further softens the low-mid range. This is where the relationship between LSA/ICL/Duration becomes important. Does anyone even know what the specs are for an L83? I've never seen published figures. Can't imagine it's much better than Gen III/IV 5.3's. 

 

56 minutes ago, Christian Olguin said:

mid range is ehhh to me now

I'm trying to see if this is something you can fix via tuning...mid range while wide open? Or as we still talking part throttle? more clarification: on tip-in transition from cruising? or it feels soft from a dig? if you want to make the tip in more snappy and build more torque in the low-mid load ranges you could dabble with the VVT settings. This will increase torque in a noticeable way at the expense of pumping losses (hurts MPG a bit) AND it won't take near as much timing before hitting KR. 

 

1 hour ago, Christian Olguin said:

possibly a retune would help clear this up

did BB tune before or after headers? 

[Christian Olguin]

1 hour ago, lucas287 said:

Definitely true to an extent. More duration, usually, is just going to decrease dynamic compression ratio which even further softens the low-mid range. This is where the relationship between LSA/ICL/Duration becomes important. Does anyone even know what the specs are for an L83? I've never seen published figures. Can't imagine it's much better than Gen III/IV 5.3's. 

 

I'm trying to see if this is something you can fix via tuning...mid range while wide open? Or as we still talking part throttle? more clarification: on tip-in transition from cruising? or it feels soft from a dig? if you want to make the tip in more snappy and build more torque in the low-mid load ranges you could dabble with the VVT settings. This will increase torque in a noticeable way at the expense of pumping losses (hurts MPG a bit) AND it won't take near as much timing before hitting KR. 

 

did BB tune before or after headers? 

Feels like off the hit and once it gets to the top end it feels good. I’d say from a dig or low rpm range is where I feel it’s a little sluggish.

 

I haven’t gotten a retune after the headers. Probably what is causing it to be like this. I know I should have done a retune but I’ve been to busy with stuff. Do you think a retune for headers with the muffler will clear things up? Mind you I do have the 2018 Silverado e assist with the 8 speed auto so I think they do it through efi live instead of hp tuners

Edited April 8, 2021 by Christian Olguin

[lucas287]

4 minutes ago, Christian Olguin said:

Do you think a retune for headers with the muffler will clear things up? 

Maybe?  it's hard to tell. It might make it better, but not entirely negate the problem. 

 

The low rpm-high load on the low octane table has barely any timing advance. If you're looking for a way to pick up throttle response and torque everywhere, it doesn't get any easier than e85 conversion. Do that first, then let BB retune to activate the flex fuel parts of the stock programming. 

 

The gains from ethanol are quite dramatic once tuned. Basically anywhere that knock was limiting before can be added back in - and then some. It's more nuanced than that, but long and the short of it is my L86 has very good throttle response and low speed torque on ethanol. Gas is good and all, but ethanol makes this truck feel a lot different and I'd bet it would help your combination too. 

[Christian Olguin]

Just now, lucas287 said:

Maybe?  it's hard to tell. It might make it better, but not entirely negate the problem. 

 

The low rpm-high load on the low octane table has barely any timing advance. If you're looking for a way to pick up throttle response and torque everywhere, it doesn't get any easier than e85 conversion. Do that first, then let BB retune to activate the flex fuel parts of the stock programming. 

 

The gains from ethanol are quite dramatic once tuned. Basically anywhere that knock was limiting before can be added back in - and then some. It's more nuanced than that, but long and the short of it is my L86 has very good throttle response and low speed torque on ethanol. Gas is good and all, but ethanol makes this truck feel a lot different and I'd bet it would help your combination too. 

I’m tuned on e85 right now. Honestly the power loss isn’t anything crazy at all but my butt dyno notices a little bit of loss so I think lol I agree on the e85 part the gains are nice and I’m on the first revision so hopefully the second revision will open it up

[lucas287]

Just now, Christian Olguin said:

I’m tuned on e85 right now. Honestly the power loss isn’t anything crazy at all but my butt dyno notices a little bit of loss so I think lol I agree on the e85 part the gains are nice and I’m on the first revision so hopefully the second revision will open it up

duh - now I remember reading that. something BB should be able to do is manipulate when all the timing gets added in. I've never had a single tank of e85 than was over than 80% alcohol. (maybe it's my sensor) Basically it blends the gas timing table with the flex fuel modifier based on alcohol composition. on the stock table it requires over 80% ethanol to hit that last modifier zone, I rescaled mine and it helps a lot. Look at the difference...

[Christian Olguin]

4 minutes ago, lucas287 said:

duh - now I remember reading that. something BB should be able to do is manipulate when all the timing gets added in. I've never had a single tank of e85 than was over than 80% alcohol. (maybe it's my sensor) Basically it blends the gas timing table with the flex fuel modifier based on alcohol composition. on the stock table it requires over 80% ethanol to hit that last modifier zone, I rescaled mine and it helps a lot. Look at the difference...

I’ll definitely look into that. The highest I’ve seen is 81% at the station down the street from me but I’ve been curious about throwing c85 in the mix for the fun of it. It wouldn’t be a regular thing but just curiosity I guess. Honestly you’ve been a lot of help with all this. Now tomorrow I need to do some data logging and see what a revision will do on e85 and headers

[rlcole321]

Also, Have you thought about a lower temp. Tstat?, that helps if your just looking for performance.

[JONBLARC7]

I wanted to add to this.  When I first started running E85 after adding my headers.  There was a flat spot in the crusing area when running E85.  The truck would down shift on hills that with 93 it would just hold that gear up the hill.

 

How I fixed it was to add 1 to 1.5 degrees of spark to those area's in the main spark table.  Then E85 table will add or subtrack from that number as they need to.  This little adjustment didn't give me any Knock on 93 but made the dead spot completely go away.  I think dailing in the rest of my tune really helped too, like lucas287 said!!!

[JONBLARC7]

And I have my Flex Fuel Spark Mult just like Lucas287.