Just watched a Richard Holdener video where he tested 1 3/4 headers against 1 7/8 headers. The test engine was a bored 5.3 to 5.7 with a big cam. Made a little over 480 horsepower with the big cam and 1 3/4 headers and lost 2 or 3 peak hp with the the 1 7/8 headers while substantially lowering power in the mid rpms and lower. On the upside, it gained a whopping one ft lb peak torque. My guess is you have to have an engine making 600 or more for it to START helping.

I just ordered 1 7/8 headers, but I'm forced induction with a goal of 600 rwhp so I'm guessing it would help my situation.

 

I think in your situation you did the right thing. 600HP will make enough exhaust volume to make them worthwhile.

 

Figures, yet another internet myth perpetuated by forum racers.

 

thanks. also, he was testington an engine dyno vs the chassis dyno I will be testing on so I figure I should have at least 200 horsepower more than the engine he was testing. Still, I bet I could've gone 1 3/4 without killing much horsepower.

 

I love myth busting videos. one of my favorite shows is engine masters. Biggest mistaken belief i had was that dented headers kill power. The guys simulated an hack header install where people bend and dent headers to make headers clear steering columns, etc. It did lower power, but power lost was in the single digits....and some of those headers were hammered pretty flat.

 

I'm sold... going with 1-1/2" headers to gain more power and spark plug changes will be a breeze

In all honesty where the 1-7/8" lose power vs the 1-3/4" is around the 3000 RPM range... most guys here blow right through that area with a proper stall converter and gear. I'll take those 3 HP up top for the $25 higher price between the two sets headers.

 

A couple HP either way will never be felt. The 1 and 3/4 are probably the better choice for a street car and 1 7/8 better for a track car. I bet a merge spike and collector would make more difference than the tube size.

 

I think its more about where the power band ends up that how tall the curve is,,
CFM in related to CFM out, and RPM.

Most of the nascar engines use Tri-Y style stepped headers not long tubes.
At least that's what I saw running around the shops in Charlotte a few years ago.

No 1 size fits all answer..

 

Engine Masters is one of the best hot rodding shows out there, challenging long held beliefs with proven data is so much fun to watch.

 

I did this test on our motor at the track. We have a 427 with AFR 245's, Cid intake and an 1100 dominator carb. We went from 2" Kooks to 1 3/4 Hooker super comp. All I can tell you is we lost 3.5 tenths off our time. And the car felt like it was not happy. Tried 4 different length tuner pipes and tried everything tuning wise on the carb and could not get it back. Car just ran different. The launch felt sluggish and it just didn't RPM as fast. Needless to say the 2" Kooks are back on and we are right back where we were. A 3.5"x 24" tuner with turn out included was our sweet spot. Car is running fantastic now too. We even tried different diameter tuners too. Anything we did to reduce the flow the car didn't like it and slowed down. We did 3 passes on each change to be as accurate as possible.

That is real world testing. Not in a building. When our motor came out in the real world, we had to go up 4 jet sizes to finish the tune. Doing so dropped our time by over 5 tenths from the dyno tune. Timing stayed the same inside or at the track. Our motor made 706hp and 616tq on a motor dyno.

 

Guys you have to understand airflow demand here. On a 350 ci N/A 400ish hp engine, the results here are completely believable. But go bigger power with the same cubic inches, and you’ll need more header. Go bigger cubic inches and you’ll need more header. It’s really very rpm/ and hp dependent. No way…repeat…no way this is a blanket test showing that a 1 3/4” pipe is going to produce more (or similar) power than a 1 7/8” pipe in EVERY situation. I find this test of Richards, just like sooooo many others he does, has way, way, way too many variables to say 100% this is gospel. Data doesn’t lie, but you have to compare specifics to specifics. A 350 cubic inch engine that makes peak power at 6k will make best use of a 1 3/4’’ pipe vs a 350 cubic inch engine that peaks at 7k. And even then…header variables include pipe bend radius, primary lengths, and collector design…inside of each given primary sizing will vastly affect how each particular header works, meaning that two different headers, from two different companies, will work differently. ARH vs Hooker for example, etc, and both being 1 3/4”
Now the next internet myth will be a 1 3/4” header will make more power than a 1 7/8” header because Richard Holdner said so.
Remember the three C’s…
COMBINATION
COMBINATION
COMBINATION

 

yes we understand this. This test is referencing the average ls1 f body guy with a heads and cam 346.

 

Exactly. This was a 480 horsepower engine which is a good 80 horsepower more than what the stock ls1 tended to make. What's even crazier is seeing how it made basically 0 increase going bigger, I'm guessing you have to make a good 150 to 200 horsepower over stock to be a worthwhile upgrade.

 

Your engine is 80 cubic inches over stock with upgraded heads, intake,, and cam. Testing was done on a 5.7 displacement.

 

I think Richard's main point is, for the average guy with a 4.8 thru a 6.2 engine, AKA stock LS engine sizes, a 1-3/4" header will more than likely get the job done.
The 1-7/8" will work fine too, but for most of us running near stock engines, the small gain isn't worth the added expense. The butt dyno won't feel 5 HP.

 

I would say even at 500+ rwhp you're pushing enough exhaust for 1 7/8. Anything below that 1 3/4 should be sufficient. The catch is this, when you're driving around let's say 440 rwhp and you have a 150 n2o hit then you're definitely at 500+ whp. Will you feel the difference since you're driving around 98% of your time at 440 rwhp. The answer is no. Especially if it's only 2-3 hp.

 

I was most interested to see the way the exhaust changes moved the power delivery further down. This had been what I always understood, it was only on here I heard any different.

A lot of heads and cam guys down here used to choose Try Y headers to keep the power down low even though it cost them 2-3 rwhp up top. I used them myself on my other LS1 powered SS for that reason but on my Monaro I use shorty 4-1 due to the cat location on the newer car. I've been told it would not be worth swapping to the longer header on my combo.

 

1 3/4 vs 1 7/8 LS header results - search and reading list.

Depends on who's engine dyno data results we're looking at as well. 98Jason a very reputable member posted this long ago stock-motor-1-3-4-vs-1-7-8-engine dyno results. This stock internals LS1 had a Fast intake BTW. Pretty common with bolt on set ups set.

My opinion 1 3/4 & 1 7/8 are both better on a stock LS1 than factory manifolds. Pick headers based on where the build is going.

I picked 1 7/8 headers with 90mm TPIS LS6 intake upgrade etc on my stock 02 LS1 and gained power (46 whp peak) and area under the curve pretty much every where vs stock. Eventually, plan to do 402 stroker LS2, felt 1 7/8 worked best with my game plan. If the old LS1 gets heads and cam the 1 7/8 will work great as well even at modest ~400 to 450 whp level

 

And holdener just put out an updated video with a 383 @ 600 hp and.....still didn't make a difference. And a slight difference with boost at 800

 

i wonder how much im leaving on the table , procharged making 660 whp 600tq and im running bbk 1 5/8" headers along with their y pipe .