Will the Elites fit the "L98" angled AFR heads without a problem?

 

I'm not aware of any headers that won't. If a header is listed to fit an L98 engine, it ought to accommodate the spark plugs.

RACE ON!!!

 

What size is appropriate for which rpm range? Where the range picks up (at a minimum). I've seen formulas on intake runner size/length... never for exhaust.

Is there any correlation between intake and exhaust sizing? For TPI intakes, tubes run range from 1.5" to 1.7" (1.75" for the First). I've heard effective measurements for stock exhaust tubes of 1.25". Intake valves are 1.94 and 1.5". If the ratio of intake/exhaust valve were used, we'd only need 1.3" tubes for the larger 1.7" intakes. Except for the lack of same-length runners (e.g., LTs), stock exhaust sounds large enough for stock intakes.

And, for LT upgrades, it seems like 1 5/8" is plenty large -- if not so large as to help high rpms more than mid/low. (I can see where you say 1 3/4" is just huge.) Makes me wonder if even smaller tubes would be more helpful on a non-modified street car.

gp

 

I can't give you starting and ending points for all the different tube sizes. First, it isn't like a light switch. If a certain tube size works from 3000 rpm for instance to 6000 rpms, that doesn't mean that it isn't helping at 2900 rpms. There ARE formulas available and it can become extremely involved. You may want to take some courses on fluid dynamics. I can speak from personal experience that a streetable 350 will not exceed the capacity of 1 5/8" headers. Not only will the 1 5/8" headers not choke the flow at higher rpms, compared to the 1 3/4" headers, they will start working at lower rpms and provide a broader range of improvement. The gain with the smaller tubes will be that they start working sooner.

RACE ON!!!

 

and the LTs will always work better than the shorties simply because of the scavenger effect....all the way through the RPM range....remember, an engine is nothing more than a vacumn machine!
In and out...to a degree.

 

this is my point with you, gregg. you're worrying way too much about your buildup. this is the only car you'll be modding, right? there are no secrets with a 350cid SBC, none. you've got it all in archives, right here on the forum, ad nauseum, cough-cough. there should be no confusion. but yet you remain bewildered. you're on everyday, yet the questions you ask are like you never had a license to drive.

if money is important to you, then i firmly suggest forgetting all about it and leave it stock. this is gonna kill you, and trust me you'll be getting into ancillary expenses as well, to the tune of $1,000-1,500, mark my words.

or just rip the damn truck engine out and put a 502 in there, that'll fix your problems, lol

 

My question about sizing was generalized -- for all the readers of this thread. Obviously, it could apply to my case.

It is not "over-analyzing" to want to want which header helps in what way. I even wondered if 1.5" long tubes existed for 350s. And, if they might serve as a better low end "boost" than 1 5/8". Do 1 1/2" headers even exist? I didn't need EXACT formulas for every length/size. I just wanted a rough idea. I'm guessing an "I don't know" might be in order???

When you say 1 5/8" is generally better than 1 3/4", I get that. Do smaller ones exist? Do 1 5/8" help only at higher ranges?

Again, someone said "tuned" headers might not even be warranted for a car built for street rpms (i.e., 2k-5k). Prove him wrong.

Telling me to take a course is too extreme -- especially when people are saying "do what's proven". What's proven?

In my mind, you need to know where/how 1 5/8" headers will help before you recommend anything. If I'm wrong, say why. If you do know, please be more specific. Isn't that a reasonable request?

If you read my thoughts on intake vs exhaust valve sizing, it should be apparent that these are reasonable questions.

gp

Edit:
If you say stock headers are 1.5" so why would anyone consider that, I'd come back with reports that they are functionally closer to 1.25" and they have air tubes to cause turbulence.

 

I don't know anything about what headers to use. However, I do know that you can only choose from what is offered, or make your own (and do lots of experimenting, as said earlier). So if you are buying something, it's academic what the difference between 1 5/8" vs 1 9/16" would be, or something like that. You can only pick from what's made, and it sounds like 1 3/4 and 1 5/8 are the main choices.

As I like to joke, you seem like a good candidate for a ZR-1. Everything usually has only one choice, so there is no paralysis by analysis. You want an intake, there's only stock. Heads? Hope you like stock. Headers? Only one maker. Even if you go used, most all are 2" and the same shape/layout.

 

agreed

disagree

If size was "academic", discussion about using a smaller header wouldn't have entered this thread. I just took that discussion one step further. And, it was a friggin small step. jeeeeeeezzzzzz

 

Smaller in the context of two readily available sizes. Which is not what you are talking about.

But hey, I don't care either way. Shine on dude.

 

gregg, just read post #44 and do it. you are making rocket science out of a mole hill. this is a daily driver street machine -- "just about", "kinda almost" and "close enough" are perfectly acceptable tolerance metrics and all you need to be concerned about.

pick up the phone, order a set of 1 5/8", and be done.

 

2 sizes? Did you forget you posted 1 9/16" in addition to the 1 5/8 & 1 3/4" mentioned so far? (When I talked to one shop about shorties, they said 1.5 was an option).

Brad,
Just say you don't know the answer. Or say 1 5/8" & 1 3/4" are the only sizes that will fit our cars.

 

1 1/2" Long tube headers were/are avaliable for some SBC economy applications, but I don't know about C-4s. This was around the time of the 70s gas crunch. They would; as some have said, pull well from down low. At some point of RPM,(not that high) they'd reach their max flow capacity, and then the power would level off. This will happen with 1 5/8 or 1 3/4 too, but they move the HP curve higher and up the RPM scale. At what RPM... it depends on many variables...engine size, heads, cam, etc.

 

Not because I thought 1 9/16" was a legitimate size, though. Rather that the difference is academic if no one makes a 1 9/16" header for your car. Anyway, I don't really care that much. I was just trying to explain the point others made about it being trivial analysis. If you don't think it is, keep on posting your way to the bottom of it all.

 

I'm glad you got around to posting that. I was afraid I was going to have to. Some people just don't GET it.

RACE ON!!!

 

The "generalized" questions have all received general answers.


Rough ideas have been given. Asked and answered. If you didn't get it the first few times, start re-reading.


See above about re-reading. 1 5/8" do NOT help only at higher ranges?


Prove someone else wrong, based on what? You prove him right, if you think he is.


Again, time to do some re-reading. I've told you what my experiences are, what has been proven to me. If that doesn't satisfy you, study the subject, take some course, build some engines and try a variety of headers, so you don't have to be dissatisfied with what others have learned by doing. You are the one with all the specific questions that you can't seem to get answers that satisfy you.


I know. I have explained. What isn't reasonable is the relentless inquires to answered questions. If you don't like my answers, feel free to disregard them. If you don't understand my answers, re-read them.


[QUOTE=GREGGPENN]If you read my thoughts on intake vs exhaust valve sizing, it should be apparent that these are reasonable questions.[/QUOUE]Totally a non sequitur.


*I* didn't say "stock headers are 1.5"". Come back with whatever floats your boat. There is no such thing as "stock headers" on a C4. The C4 uses exhaust manifolds.

For those who understand, no explanation is necessary. For those who do not understand, no explanation is possible. QED

RACE ON!!!

 

It feels like this is turning into who can argue better. Too much effort is going into semantics. I don't feel like asking about general rpm range of performance for the various sizes of C4 350 headers is that complex. (I understand it could get complex, but I didn't want that level of detail).

I've looked around forum history and the web. Lots of threads/website/posts on intake runner sizing -- and predicting performance. Couldn't find much on header sizing.



gp

 

gregg, my man. you've got 2 basic choices - 1 3/4 and 1 5/8. don't bother with a custom set, it'll cost you a fortune, and they're best for race cars.

these 2 popular sizes have been around since you were born.

get 1 5/8, pick up the phone, end it. no need for questions, it's inconsequential, no need to postulate, pontificate, or defecate. you've got a basic chevy with a small truck engine, get the 1 5/8.

 

Simple enough. Thanks Brad/CFI-EFI.

(Maybe I should have asked how many options/sizes/brands there were. If only 4-5, maybe that would have been easier).

 

It never was an argument. Your questions were answered multiple times, but you kept repeating them. If you don't get it, re-read where it has been explained. If you STILL don't understand it for some reason and the answers don't satisfy you, then it is YOU that needs to go to school and become the expert. For the the C4, there are two sizes of primary tubes commonly available, not 4-5. Someone as thorough in their research and fact hungry should already be aware of that.

RACE ON!!!