6.2 Dyno with Common Bolt-ons

kgkern01 · August 2, 2018

30 minutes ago, 10SierraA.T. said:

Yes overall, you will gain torque through the power band (which is primarily dictated from the cam profile). But in the low RPM range, 1500-2500 RPM you will actually lose torque as there is a loss of back pressure (minor) and minimal vacuum from the next cylinder to draw out the exhaust, which works differently in a manifold. You may gain horsepower in that 1500-2500 range, but you will lose a bit of torque 90% of the time. Usually not much to worry about 5-10lb-ft if that, but it is still a loss. However, you may make an additional 20lb-ft on your peak and mid-range numbers. Not a big deal on your sports car running them on track, but if you tow all the time with your truck, I wouldn't look at headers as a performance mod per say. They wont slow you down either but generally a cast manifold or shorty is a better choice for low rpm performance in the truck world.

I am just speaking to what I know about the LS family, maybe these LT's react differently to a set of tubes.

If I am wrong, please lead me to some information as to why, because I am curious to find out how they did it.

My Gen II LT1 gained throughout the powerband both HP and torque when just a bolt-on car. Yes it shifted the powerband up, but there was still a gain that was had in both hp and tq throughout, no loss from 2000 RPM up. That is also basically a SBC, which is a completely different example though.

According to the OP's dyno charts in this thread, it appears to show the same, his bolt ons netted a gain in hp and tq from around 1700+ (where his graph starts) all the way across. Given the stock manifolds are already basically shorty headers, and as long as you don't go too large with the primaries (losing velocity will cause power loss), and stay no more than 1-3/4" with the LT's, the increased exhaust velocity is what allows still having an increase in both tq and hp down low, not to mention it is more efficient. I haven't seen a dyno yet that someone actually lost torque going to a "properly sized primary" LT header, but I have on large primary LT's. Bigger isn't always better when it comes to exhaust, even though some people (especially some diesel guys lol) tend to think so, haha.

Edited August 2, 2018 by kgkern01

Jon A · August 2, 2018

1 hour ago, 10SierraA.T. said:

But in the low RPM range, 1500-2500 RPM you will actually lose torque as there is a loss of back pressure (minor) and minimal vacuum from the next cylinder to draw out the exhaust, which works differently in a manifold. You may gain horsepower in that 1500-2500 range, but you will lose a bit of torque 90% of the time. Usually not much to worry about 5-10lb-ft if that, but it is still a loss. However, you may make an additional 20lb-ft on your peak and mid-range numbers. Not a big deal on your sports car running them on track, but if you tow all the time with your truck, I wouldn't look at headers as a performance mod per say. They wont slow you down either but generally a cast manifold or shorty is a better choice for low rpm performance in the truck world.

That can be true for shorty-style headers, which primarily reduce back pressure. Long tube headers generally improve cylinder scavenging which helps low end torque. While it's not exactly the same, it's a similar concept to an intake manifold with longer runners being better for low end torque. Of course all designs won't be exactly the same, some will work better than others, but there's generally no downside power-wise to long tube headers vs. stock manifolds. A very worthwhile mod in my opinion.

14 gmcl83 · August 5, 2018

So I have a 5.3 l83 it best for me to buy a l86 intake and tb and swap to make more power and tq? Can. ISO that and be on the stock tune, or would I need a tUne right away ?

Edited August 5, 2018 by 14 gmcl83

Nasty · August 5, 2018

1 hour ago, 14 gmcl83 said:

So I have a 5.3 l83 it best for me to buy a l86 intake and tb and swap to make more power and tq? Can. ISO that and be on the stock tune, or would I need a tUne right away ?

If you floor it , it will throw a code. As the increased amount of air coming in fron what i was told

14 gmcl83 · August 5, 2018

Ok thank you.so what do most people on here use for tuning hand held or dyno tune , my plans headers cold air intake flow master duals swap intake that’s it.

Mileguru · August 6, 2018

6 hours ago, 14 gmcl83 said:

Ok thank you.so what do most people on here use for tuning hand held or dyno tune , my plans headers cold air intake flow master duals swap intake that’s it.

Most of the hard-core guys insist on dyno tunes. The guys that do basic mods like you listed use Black Bear or Lew (Diablew).

BB68 · October 10, 2018

On 3/18/2016 at 5:57 PM, Jon A said:

I intended to do this a long time ago but have just been so busy over the last year and a half I never got around to it. I really want an accurate before/after for the next (and likely last) bolt-on I have planned so it was finally time to see what I've gained so far. New mods since the initial (mechanically stock) dyno:

How did this effect MPGs? I would think with all that low end torque it should actually improve. Im seriously considering an exhaust system on mine now.. even though Im perfectly happy with it. I just have to sell the wife on the "need" for it

M1ck3y · October 10, 2018

2 hours ago, BB68 said:

How did this effect MPGs? I would think with all that low end torque it should actually improve. Im seriously considering an exhaust system on mine now.. even though Im perfectly happy with it. I just have to sell the wife on the "need" for it

You'll get the same or worse mileage, the need to hear that power is too tempting! Good on you if you have a wicked sounding truck, and can drive it like your on your way to church in a corolla.

BB68 · October 11, 2018

16 hours ago, M1ck3y said:

You'll get the same or worse mileage, the need to hear that power is too tempting! Good on you if you have a wicked sounding truck, and can drive it like your on your way to church in a corolla.

I tow 3 to 4 hours depending on the race track, every 1mpg savings buys lunch.

Jon A · October 11, 2018

22 hours ago, BB68 said:

How did this effect MPGs? I would think with all that low end torque it should actually improve. Im seriously considering an exhaust system on mine now.. even though Im perfectly happy with it. I just have to sell the wife on the "need" for it

I didn't notice much difference. While the headers, etc, technically may have helped it's probably a small enough amount it would be difficult to detect. Accurately measuring mileage is tough. I've made identical long trips with identical setups and had mileage vary significantly, due to which way/how hard the wind is blowing, etc.

I also did something that probably hurts mileage a bit--I tuned out the "EGR Effect" to try and minimize reversion and keep the valves clean as possible long-term (won't have any effect on a dyno). A good change from a performance standpoint but might hurt mileage a tad so it's all probably a wash.

BeerPwningTexan · June 25, 2019

I had my 2018 6.2 Sierra 4x4 dyno and tuned by Pat G Tuning this past weekend. Couldn't get much of a base since already had AFE Power CAI and Borla ATAK. Really happy with his tune! 385rwhp/425rwtq

Edited June 25, 2019 by BeerPwningTexan