His 2" headers aren't losing anything.... This has been gone over time and time again. On a cathedral head motor like an ls1/2 even bone stock 1-7/8 have been proven on back to back tests to not lose anything anywhere to 1-3/4 headers.

On an ls3 even going to 2" on a bone stock motor makes more power than 1-7/8 and loses nothing in the midrange. See below

http://www.camaro5.com/forums/showthread.php?t=63640

 

Maybe if you only are concerned with dyno numbers, but when looking at 1/4 mi timeslips for bolton cars, 1.75 tube headers rule.

 

Ummmm maybe because that's been the accepted norm for so many years that it's what most people run? There are far many cars running those than bigger sizes so the chances of seeing them on the fast list is better. 10whp isn't going to show up on a 10s time slip anyway.

If you want to dispute evidence that's fine I guess it just sounds like you have 1-3/4 and are in denial. There is literally nothing you could find in that test thatxwould suggest larger headers would make you slower. The dyno is a tool to show differences between mods which is exactly what that was. And in this case bigger is better

Maybe you could explain how the 2" headers on a back to back test losing nothing in the midrange but making 6 more whp up top would make a car slower?

 

you really might not want to start a dispute with HOXXOH

he is one of the fastest Bolt On guys around with hundreds of documented runs of what works and what does not work

how much documentation do you have on the 2 inch pipes losing nothing in the midrange and where did it come from ?

how many tests , how many cars , what were the conditions ?

These are all questions he can answer ......

just saying .......

Dave

 

I'm not saying he isnt...but my statement still stands. There is literally an A-B test done on header sizes. On my old car I made the switch and picked up hp on the dyno, lost nothing down low just as that test showed.

Now when you go to the track will 7whp show up? Probably not, too many factors, but that doesnt mean it isnt there. Thats the whole point of a dyno is to track changes that a racetrack cant always see. Little things will eventually add up.

 

It's OK Dave. Just let him go. He's a dyno guy, not a racer and believes the chart numbers trump the track numbers.

 

NJDennis (RIP) had back to back dyno charts of 1 3/4" headers on the same dyno same LS2 car against 1 7/8" headers. The 1.75" headers had 5-10 more hp/ tq from idle to about 6K rpm. After 6K rpm the 1 7/8" headers pulled ahead by 2-5 hp or something small like that.

I saved the dyno chart to an earlier computer but don't have it on this one.

I can't speak to the 1 7/8" vs. 2" on LS3/ LS7 engines. I do know this, I have about 525 rwhp and my low-mid power is phenomenal and I don't feel as if I'm giving up anything.

 

Lol it seems you're geting a little bent out of shape here calling me a "dyno guy" whatever that means....I'm all for a good argument so let's see proof of larger headers slowing you down? As I said even though larger ones will make more power you won't notice 7whp consistently atba race track

 

I have no reason to be bent out of shape, since my timeslips speak for themselves. A "dyno guy" tunes his car to achieve high numbers on a dyno vs a "racer" who tunes his car to achieve low ET at the track.

Simply gaining just 1 hp at every 100 rpm increment from 4600 to 6000, even if you lose 1 hp at every 100 rpm increment from 6000 to 6700, still means there is a net 7 hp gain. The initial 14 hp in the grunt range moves the car farther down the track than the 7 hp at the high end. It's the same concept that Suns_PSD mentioned about Dennis' car.

So here's a little comparison for you related to hp. Let us assume a location with 1000' elevation, 57*F, 29.92 BP, and 35% H. The DA is 1177' and the dyno hp is 100% at 400hp. Now if we retain everything except the temp and increase it by 12* to 69*F the DA changes to 1992' and the dyno hp falls to 98.3%, but compensates with a 1.017 correction factor. The real hp dropped by 7, yet the dyno readout still said 400. If you take that car to the track with 1992' DA and run 11.5 @ 120 and drop the temp to 57* to get a 1177' DA, the car will now run 11.38 @ 121.5. So yes, you can notice 7 hp at the track on the timeslip, but probably not on your butt.

As far as consistency is concerned, here's an interesting pair of timeslips. Same track, but 24 hours apart. The DA on 1/1/11 (right side slip) was 1068'. The left side slip DA was 1053'.
https://www.corvetteforum.com/forums...post1576398888

Now about the exhaust pipe sizes. Did you ever wonder why the duct size gets smaller as it gets farther away from the furnace on your home heating system? It's because the air is getting cooler/denser and requires less space to maintain the same velocity. Think of the combustion chamber as the furnace and the pipes as the ducts. As the gasses cool they need less space. The volume being produced is directly related to the displacement and rpm. Compare a 6.2 @ 6600 redline to a 7.0 @ 7100 and there is a 21% difference. Yet the square inch volume difference on a 1.75" primary to a 2" pipe is 33%, which initially makes you think that the 6.2 engine should have 1.875 primaries. However, a couple of factors play into the difference. One is that all of those header sizes use 3" collectors (6.49 sq in area) that are fed by 4 pipes of either 2.07 sq in (8.28 total), 2.40 sq in (9.60 total), or 2.76 sq in (11.04 total). The other is that 1.75 tubes have a higher percentage of surface area for cooling, so reducing the pipe diameter to 2.5" (4.40 sq in) shortly after the collectors will maintain a higher velocity. The alternative would be to wrap the primaries to retain the heat and not reduce the pipe diameter for a longer distance. Because header sizes are restricted by the available diameters and the configuration of the car they need to fit, compromises are necessary. There is only one rpm on any car, no matter how constructed or what size/length the primaries are, that they work at peak efficiency. The trick is to fit that rpm into the curve that best complements the rest of the engine.

 

The dyno is a better tool for comparing mods on the same vehicle (as you pointed out, it accounts for variables). I guess if you logged all of your runs and had the DA computed for every run, you might be able to get similar data, but for most people the dyno will do just fine. Unless you are getting paid to wring every last ounce of performance...

Not sure how you drive with a couple of 55 gallon drums under your car (3' collectors) ��

 

I have a pretty good understanding of fluid mechanics but I appreciate the insight...However like I originally asked, do you have ANY proof that larger headers will lose midrange torque and slow you down? I have asked repeatedly and nothing. My guess is you dont have the evidence. Theory is all well and good but it doesnt always play out in testing.

Yes a dyno is just a tuning tool but its also used to show hp increases from mods. Will you ever notice a difference at the track from 7whp? No, most likely from the reasons mentioned above. So thats why you turn to a dyno like whats been posted which clearly shows an A-B comparison you wont notice at a track. It doesnt meant it doesnt exist though. I would like to know thought how a mod that makes the same midrange power and increases top end power would slow you down? If thats the case maybe no one should do headers to begin with lol

 

Pretty much.... bottom line is that there is no evidence that larger headers slows you down on these cars. The difference they make is too small to notice on a race track due to variables, doesnt change the fact they do actually make more power and do not lose tq

 

fixed it. thanks.

Actually I do log nearly every pass. Then record them with the DA and corrections and any pertinent notes about track conditions, tire pressure, changes done to the car or tune, etc.
It's part of the reason I run as quick as I do and that those "most people" who rely only on the dyno results are slower.

I've gone about as far as I can with combinations of off the shelf exhaust parts, so my next step is custom making replacement pieces. It's just a fun challenge from a scientific perspective, not a job. I get to use my many years of racing and automotive experience mixed in with my engineering background in aerospace manufacturing.

 

Apparently LG has the data. They might know a little bit about racing. They recommend 1 3/4 for LS3. And yes there is a torque loss in the mid range range with larger tubes. If your a 1/4 mile junkie then maybe not much difference but on a rode coarse then most likely.

 

How can you assume that larger headers don't slow you down, when dyno results is the only thing you use for comparison? You don't gain or lose speed when parked on a dyno. You can't duplicate the same conditions of a track. Both the dyno and track data can be corrected to a common scientific standard. The difference is that cars are made to be driven and the track results, aka timeslips, even with other variables, are the standard measure of performance.
When you say "the difference they make is too small", certainly doesn't help your cause. It's been documented that simply cinching the tie-down straps an extra couple of clicks can change dyno results by several hp, so variables on a dyno exist too.

I guess my only evidence of exhaust size has been the changes from stock to large showed improvement and then configurations that were smaller showed more improvement. It's all on timeslips, so apparently that's not what you want to see.

 

I remember seeing one of those Sunday morning hotrod shows do a header comparo using an engine dyno. They wanted to see how much hp would be lost from denting the headers (for fitment issues). They did several pulls, each one with increased damage to the headers. IIRC correctly they actually GAINED hp as they beat them up. Not saying this supports either argument, just goes to show reaults dont always = expectations.

I think Burns Stainless has some pretty good info

http://www.burnsstainless.com/techarticles.aspx

 

Hoxxoh, you have an LS2 correct?

I only recently deleted NJDennis' dyno comparison off my home computer comparing the 1 3/4" vs the 1 7/8" on an LS2. I'm going to state right now that if you run an LS2, with the OEM head design, you 100% need to be in a 1 3/4" header.

However the Camaro forum post makes a darn good argument for 2" headers on LS3/ LS7s.

What I guess I can't speak to, is that a dyno is always 100% throttle correct? Are there gains with smaller diameter headers at other throttle positions that can not be calculated on a dyno?

As far as LGs dyno charts that 'prove' that 1 3/4" headers are better, they have been debunked for the simple reason that in an LG header, their 1 3/4" header has longer primaries and therefore is just a better design than their own 1 7/8" headers.

 

1-7/8 have been proven to be better on a stock ls1 too....


Literally no argument can be made for 1-3/4 headers

https://ls1tech.com/forums/generatio...o-results.html

 

I have a LS3, but this thread and the Camaro thread have been so focused on the primary tube size, that no consideration has been voiced for the rest of the system. If you read the entire Camaro thread, you'd also spotted that the 1 7/8 headers were used in the OP's 560hp supercharger package. To most people that would be confusing, since the 2" tubes produced more power as the only change to a stock engine. However, it reinforces the concerns that the entire exhaust valve to tips need to be matched to the ability of the intake's entrance to intake valve capability.

Making the majority of the components working together is the primary reason both Dennis and myself are at the top of our respective categories. Others near the top that still outpace the average, may only have one mismatched component. I'm aware of the slight differences between myself and the next two. They produced similar raw power, but didn't use it as effectively.

 

External Engine Modifications LS2 (Bolt-Ons)
10.626 @ 126.98 - Dennis50NJ - 05 A4 Z51 - CAI, cb, conv, ewp, pfast, 3.73, hdr, ptb, tune, & more, DR

External Engine Modifications LS3 (Bolt-Ons)
10.802 @ 126.84 - HOXXOH - 08 A6 F55 - CAI, conv, ptb, Z06 Exhaust, tune, & more, DR

Number 1 each category and both with 1.75" primary tube headers.
Go fish!