How's the fit on LTx engines?

 

I knew optimizining header primary size could optimize flow. I also knew the configuration of LT Headers -- with equal length tubes -- enhanced the process (via scavenging).

Recently, I received a reply (in another thread) stating that headers weren't as important if a motor was being built for lower rpm performance. The implication was that LT headers don't really do much scavenging until above 5k rpm.

Since a specific rpm was not indicated, I'd like to jump in and ask here.... When do the various type of headers begin to kick-in and help? I remember seeing a unique style recently were two cylinders were joined on each side before hitting the collector. The goal of this config was to get the lowest (rpm) level of improvement.

So, when are headers warranted, and what level of rpm do they help with? (Since the OP has a stock motor under his mini, it seems relevant).

Gregg

 

You really need to start playing on the dyno with different headers to figure this one out. I have the plain jane headman 68440s on my 355 and it dyno'd 354rwhp@6050rpm that's a 1-5/8" header also. 1-3/4" tubes definately have uses on larger and stronger motors than mine and also in 4-2-1 configurations. 4-2-1 headers seem to like being larger than their 4-1 counterparts if you want to keep the top end. The theory is that a 4-2-1 will boost midrange torque, slightly larger tubing will help the top end. It's also a science that needs dyno time to get the tubing length right.

 

gregg, you are approaching this with severe maximum overkill.

you are not setting up for nascar and getting top-flight team of mechanics and engineers, and going for .001 of a second for money, trophies and notoriety.

you are setting this up as a daily driver for the street, and you'll find out what i mean when its all over.

H/C/I/E. do what is proven, its all over the board here, you're simply pushing an envelope that doesn't exist.

 

The scavenging starts with the energy the departing "slug" of exhaust can impart in the next slug. The weight or mass of an exhaust slug won't change much with different size tubes. But the velocity will. mass times velocity equals energy. A given size "slug will travel faster in a smaller tube. Stick your thumb over the end of a garden hose to observe the change in velocity, first hand. The smaller the tube the greater the scavenging... Until the tube isn't big enough to handle the volume of flow.


You can read all sorts of fairy tales on a forum like this. That is one of them. There is a hell of a lot of fiction posted by well meaning but unsophisticated neophytes on here. A lot of the misinformation comes from parroting good info for the wrong circumstance.


Those are called "tri-Y " headers. All else being equal, they do enhance low rpm scavenging better than the "4 into 1" headers.

Headers are warranted whenever and wherever they can free up the exhaust flow. The rpm level they help with depends largely on the individual header involved. For a stock TPI, there is no question that a 1 1/2" to 1 5/8" primary tine size will show the greatest improvement over the wider rpm range. As explained above, smaller tubes will become effective at lower engine speeds. The trade off is running out of capacity to handle the flow and remain effective and not become a bottle neck with higher volumes. For a strictly daily driver, that would rarely if ever get wound up, 1 1/2" primary tubes would start being noticed at the lowest rpms. The beauty of the 1 5/8" tubes is that they start to improve low rpm torque at lower speeds than bigger tube headers, but they have the capacity to handle the volume of exhaust gases from a 350, and especially a TPI when it is fully wound out.

As was stated, above, "I am very happy with my 1 3/4 Hooker's. They seemed to work well with my stock L-98". The larger than necessary headers will work in their intended rpm range. And as much as he liked his Hooker, he'd have been happier with a Hedman. The Hookers worked, but he never knew what it was that he didn't get.

RACE ON!!!

 

If you are planning to go bigger cubic inches in the future then go with 1 3/4.

 

Not necessarily. But it is a consideration. It all depends on how you build the engine and what you use it for. Ask Corkvette and ski-dn-it about the 1 5/8" headers they had on their 434s.

RACE ON!!!

 

"You can read all sorts of fairy tales on a forum like this. That is one of them. There is a hell of a lot of fiction posted by well meaning but unsophisticated neophytes on here. A lot of the misinformation comes from parroting good info for the wrong circumstance."

Man you got that right,and there seems to be more of it lately.

 

Thanks. I had a picture in my mind of scavenging being a process similar to siphoning - where the "mass of the slug" sucks the next slug out after it.

I would have thought this would begin at fairly low rpms (i.e., 2000 rpms or even less). Can you comment on the general rpm range where headers help? Or is there a site/post you can think of?

I've wondered better shorties vs LT's too, but that' largely because I already replaced my front "Y" with a 2.5" tube. I know shorties aren't as good, but are they really worthless when you compare them between stock and LTs?

Thanks for your help!

Gregg

Brad,
Learning about headers is never overkill. You're kinda getting annoying and even beligerent. You've already made your opinion known about what I should do.

 

No thank-you. Maybe them will chime in. I will have 1 3/4 on my 421.

 

No thank-you, for what? "Them" is been chimed in on this subject in the past. If you care to be educated, you would look up where them is posted their experiences. Why do I think you don't?


Of course you will.

RACE ON!!!

 

That is a decent analogy. Since the slug has roughly the same mass at WOT, regardless of rpms, the energy, or the amount of suction of the siphon, is greater when the speed of the slug is increased. Smaller tubes increase the speed of the leading slug which gives it more energy, more suction, to pull on the following slug.


That depends on the size of the slug and the size of the pipe. Smaller tubes provide more suction in the lower rpm ranges. That is why I advocate headers that will increase the engine output in the rpm range the engine will be most used.


Almost worthless. They provide less than half the power or torque increase, usually for the same amount of money, sometimes more. The 1991 and older C4s came with a set of poor man's shorties.

RACE ON!!!

 

I meant to say "they". Sorry about that professor. You think you are more educated then me? Your so tuff!

Of course my 421 will have 1 3/4 Hookers. Why would I cheap out and put 1 5/8 Hedman's on? This is a quality build, using top notch parts.

Do you work for Hedman?

 

Damn, I wish I had done a quality build. Better start looking for some Hookers.

 

 

That's what I'm asking but still don't know how to figure that out....

 

I don't think of if, or how much, you might be educated. I have better things to waste my time on. I also don't think I'm "tuff" (sic).

Of course my 421 will have 1 3/4 Hookers. Why would I cheap out and put 1 5/8 Hedman's on? This is a quality build, using top notch parts.

Do you work for Hedman? [/QUOTE]The price of the proper size headers isn't the issue. You could blow a load of dough on custom or stainless steel headers if you are worried about being accused of cheaping out. If the most expensive headers are the best then you HAVE cheaped out with the Hookers. No I don't work for Hedman, I am commissioned by Helm Inc.

RACE ON!!!

 

You've been asking, and I've been telling. What is it that you "still don't know how to figure that out....."???

RACE ON!!!

 

I'm willing to bet money on that!!!

 

Not to add fuel to the fire, but be sure you check availibility for the Hedmans before you order. I was on a "waiting list" for months, before I finally cancelled and bought the Hookers. The Hookers were a nice header and worked OK on my mild L98 383. Would have liked to try the Elites, tho...