Got bored and measure the primaries on my hooker long tubes, and they were anywhere from 20-30 inches, so defintely not equal length I know that equal length is nice but not necessary but how much is it a factor into header desing? Which LT1 or LS1 headers are = length?

So,,, what would be more desirable, longtubes that arent equal length or midlengths that are?

 

There's an interesting chapter on exhaust/header design in the David Vizard book "How to Build Horsepower, Vol. 1". I know most of the experts here ridicule Vizard and his writings, but I think in many areas, he reduces complex issues to a reasonable set of "guidleines" that help understand what is important and what is not, on a practical level. His position on bank separated headers in a V8 engine is that the firing pattern on an individual bank is so irregular, that only dyno testing will give you a combination of tubing diameter and tube lengths that will optimize the performance of the exhaust. And, that in general, unless you are looking for the very last HP on a race engine, testing will show that most engines are relatively insensitive to variations in pipe lengths, reduced cross-section, and variations in pipe diameter.

That would reduce it to faith in whether Hooker spent any time optimizing the individual tube lengths of the 4th Gen LT1 headers, or if they just "made them fit", with little regard to optimization.

Often, I see dyno results that fly in the face of theory. I saw AS&M mid-lengths's produce 50 HP more than Hooker LT's on an 850HP blown LT1, from 5,000rpm on up. On the same engine, with a cam change, upping the HP to the 900+ range, the Hooker LT's predominated and produced more HP. I'm using those same AS&M's right now, but plan to swap to the Hooker LT's over the winter, and will measure the impact of the swap on the dyno to make sure it makes things better.

 

Damn granny, jason aint wokin you hard enough.

 

nahh just the opposite! This is what I do on my little bit of free time Who is this BTW, a friend of Azzlicker? Or Feelerup311?

 

Nope my EFA screen name is also texanmutt. You member the guy with the green TA (IllusionalTA) who had his freind help him w/ the street twin install because jason was busy? Thats me. It was the day you were doin a ring and pinion, jason took calvin to meet the guy who'd restall his TQ converter, Shiznity brought over his heads and cam, calvin's tranny was delivered and Oneblackhorse had her cutout installed.

 

Ohh THAT guy! hows it goin man I thought you were a VA native

 

FWIW.. all the professionals I'm lucky enough to deal with ... all their race engines making LOTS of power.. have = length primaries.. and it's a big deal according to the header guys fabbing them. There are some ppl who dont think so.. but guess who's in the back of the pack . They also giggle at vizard. He'll say, "sometimes this works and sometimes this doesnt" for 100 pages rather than "i dont know, im david vizard, a writer, not an engine builder on the level i purport to be"...

of course if he did that, he'd have a pamphlet and not a book.. and wouldnt sell any =P

 

I had the good fortune of testing 4 different sets of headers on my 1995 Impala SS, starting with SLP 1 3/4" shorties, 1 5/8" Tri-Ys 3/4 length tubes, 1 5/8 longtubes and 1 3/4 longtubes. I had the chance to keep any of the headers I liked the most.

Just as background, my Impala runs 13.0s NA and high 11.7s on the squeeze, and weighs in at 4400lbs.

As expected, I made the least power with the shorty 1 3/4 SLPs.
Now, here comes the interesting part. I made the most average HP with the 3/4 length 1 5/8 Tri-Ys over both longtubes, both NA and on the juice. After measuring the tube lengths, the Tri-Ys had the most difference between the shortest and the longest tubes. All three headers were made by the same manufacturer (Clear Image).

The long tubes beat out the Tri-Ys at very low RPM, and then again over 5700. Another interesting thing was that peak HP with all three was right in the 420 range NA, the only difference being where the peak occured.

Needless to say, I kept the Tri-Ys over the 1 3/4 long tubes.

Just from my personal experience, I have to say that the more unequal length headers performed the best for my combination. Between all the headers, I did over 50 runs. In case anyone is interested, I have all the details in the Tech Section of my website.

 

The funny thing is that Vizzard is very good at putting complex issues into comon language. So called "professionalls" also though some of the stuff Smokey Yunick said was bunk. I learned alot from Vizzard and have seen the work of some "professionals" and they could also learn something from him. He is not the know it all of engines, but neither is anybody else.

The reason he can't come up with a difinate answer is because every engine is different. So sometimes it works and sometimes it doesn't is true. Keeping header lengths with in a few inches (1-2) is important, and in Winston Cup i'm sure they are even better than that.

Understanding what's important and what's not is the first step to making mucho power! I have very rarely found engine builders that can do that, when I do alot of good discussions come about.

BTW Vizzard doesn't need to sell books, he is a very good Aero Engineer, and probably a better race car driver than alot of us.

Bret

 

FWIW.. all the professionals I'm lucky enough to deal with ... all their race engines making LOTS of power.. have = length primaries.. and it's a big deal according to the header guys fabbing them.
...
They also giggle at vizard.

You're talking apples and oranges. Vizard's audience are guys like me who want to know why particular things work and how they work. He's not addressing the racing crowd that must eek the last tenth of performance out of their motors.

It's pretty easy to play Monday morning quarterback and take pot-shots at a book [How to build and modify Chevrolet small block V8 cylinder heads] written 11 years ago (published in 1991) but have any of your giggling buddies written a book targetting the audience that Vizard does? Critics abound, but let them try to take on the same task and see how successful they are.

As far as the original question goes, I read a test report not too long ago where a test motor was run with unequal length and equal length headers. The motor was around 400 horses at the crank, and it turned out that yes, the equal length headers made more peak horses. However, the unequal length headers had a flatter and broader torque curve.

 

Welp, I wont argue with you, but certain things are applicable to more than just "race" stuff.

As far as peaky stuff... well.. the guys I know worry about area under the curve.... and thats what i based my comments on, not peaky power.

*shrug* whaddever, doesnt matter.. not like 99% of us will ever get the opportunity to spend $5500 on headers anyway

 

I think we are all talking about the 92-98 ft lb per Liter naturally aspirated race engines here.

That's 540-580 ft lbs from a 358 small block

Think about ft lbs per liter, that's the real measure of a good engine

Area under the curve is one thing, but if you wanna know something as "what's the peak TQ" because it's never a peak but a big buldge and that peak number is the best single number to look at.


Bret