better size header

[HP400RW]

ive been doing a lot of research on what headers to get and i was wondering what size would be better for my fairly stock 5.0 1 5/8 shorties or 1 3/4 shorties???

Thanks

[MiracleMax]

well 1-5/8 are probably the better of the two choices. Although it depends??

Are you talking lightly modified (as in just bolt ons, including no heads?) If yes, I'd say even maybe 1-1/2 would do a good job (or 1-1/2 to 1-5/8 stepped headers)

1-1/2 shorties, with a correctly sized X-pipe (read proper dia to work with exhaust flange on header) would do a good job.

The trick here is to maintain exhaust velocity through out the system, yet elminate back pressure.

Ideally zero back pressure is where you want to be so that there isn't any pressure acting against the piston, sapping HP.

There is no plausible reason for maintaining back pressure in the system since it does nothing except hurt the output of the engine.

[Murdock]

Stay with a 1-1/2" primary with a stock head. Max said the magic word velocity. A step header would be best. Also stay with a 2.5 inch exhaust.

Murdock

[HP400RW]

when would you go with a 3in exhaust?

[squid]

I have a set of JBA 1 1/2 unequal shorties I will be putting on in the next couple of weeks. I cant wait to see how they do. I think alot of people are running too large a diameter header. If you have high flowing heads and .550 lift cam I could certainly understand it, but for a street stang with iron heads and under 325 engine HP it doesnt seem to make that much sense. 1 5/8 would probably give you a minor HP increase above 5000 rpm but may sacrifice just as much in torque. 1 3/4..now your talking about some serious HP to fully utilize this diameter. What do you guys think?

[Murdock]

In a dual exhaust system a 3" exhaust is necessary when you start pushing 400 HP.

squid..your thinking is right on the money. I have 1-3/4" primaries on my 5.0, but I'm pushing 500 HP and alot more torque. The JBA 1-1/2's are a good header. I've seen alot of people have there torque killed by using a 1-5/8" header on an E7TE head. Well...good example...the car in my sig is running E7TE heads unported with the old 1.78/1.45 valves and has a 1-1/2, 1-3/4, 2 to 3" step header....I just won't tell you the length

Murdock

[1BAD89]

While 1 1/2" headers might be good for a bone stock motor, makes sense because the stock ones are 1 1/2. IMO your wasting your money going with 1 1/2. First off, they might free up 1hp over the stock "headers" if thats what you want to call them. And if the only mod your planning on is headers, and thats it, headers aren't worth it. Especially running stock heads. Been there done that. The power is in the aftermarket/ported heads. THEN you'll want headers, longtubes at that. If you were to actually spend your money on headers, I'd go with 1 5/8 longtubes. That will compliment mod's to come, and if your like me, the mod'ing never really stops. You really don't want to buy another set of headers down the road, do you? Buying 1 1/2" headers is a waste, you'll see minimal gains if any, hell you won't see much with any headers and stock heads, etc...

[squid]

Hmmmm....let me respond to your reply 1bad89. Have you ever seen stock headers on a mustang? They may say there 1 1/2" but if you sit a JBA 1 1/2 header next to a stock one even you should be able to see there is no comparison. Tube size shape and bends are nothing alike. Its all about velocity, and efficiency. I am not saying everyone is buying the wrong size header, if I had high flowing heads and big cam in mind and didnt have to smog test I would be right in line with some larger tubes. But for now and up to 350HP I wouldnt give up the torque and useable HP.

[Falcons Talon]

I'd like to ask a question. I still have stock heads (searching for 96-97 explorer heads), and the mods on my car are minimal. K&N box filter, autospecialties underdrive pulleys, 84.5 inch belt, removed smog pump. black magic fan, cats removed.
I am going to put in an explorer upper/lower, 65mm throttle body-67mm spacer, and 1 5/8 bbk longtubes with short h-pipe (2.5 pipe) within the next few weeks.
I know that the heads will bring my car to life, but will the mods I am going to bolt on this month liven up my car a bit? What am I looking at?

[MiracleMax]

this is something you may or may not find useful, but


Primary pipe DIA
(CID / # of Clys) x Peak Torque RPM / 88,200 / Pi x ^2 x 2 + (primary pipe thickness x 2) = desired primary pipe OD

Primary pipe length
http://www.bgsoflex.com/auto.html and this right here predicts a 42.50 inch primary length using an 1-1/2 header (playing around with this also indicates that a header length of 14 inhces and 1.5 dia primaries produce best power at 18,000 rpm )


Typically peak torque occures 1500 rpm below peak power so on a 302 designed to see peak power at 5500 rpm the primary pipe dia should be in the neighborhood of 1.55 inches in OD.

The length is figured using 6000 as the max revs.

Thats a pretty long header though. And on a street car with a full exhaust, your probably wouldn't get the real benefit from this.

Anywhosit all this stuff boils down to pressure wave tuning which is beyond the realm of the average car crafter in terms of tuning.

Although if the cam was right, the intake was set up for best torque, this thing would produce a sharp spike at 4000 rpm.

What most people end up with is an exhuast system that isn't optimized for thier combo and provides little in the way of tuning, especially with shorty headers. This isn't as bad as it seems since peaky engines aren't that good at producing best average power.

Its ineresting to note also, using the bowling grippo page, that a 347 with a max engine speed of 7000 rpm using an 1-3/4 primary, needs a 30 inch long-tube. which it seems hooker designs thier header length at

[1BAD89]

Originally posted by squid
Hmmmm....let me respond to your reply 1bad89. Have you ever seen stock headers on a mustang? They may say there 1 1/2" but if you sit a JBA 1 1/2 header next to a stock one even you should be able to see there is no comparison. Tube size shape and bends are nothing alike. Its all about velocity, and efficiency. I am not saying everyone is buying the wrong size header, if I had high flowing heads and big cam in mind and didnt have to smog test I would be right in line with some larger tubes. But for now and up to 350HP I wouldnt give up the torque and useable HP.

Yes I have seen stock headers on a mustang. FYI: I've been mod'ing stangs for years. At 350hp or around there (which would equate to just about 300rwhp) I think 1 1/2" headers are really going to hinder the cars power when you get up to 260-300+rwhp. They might be good for stock headed cars, that don't plan on heads in the future. Headers aren't really going to help on a stock headed(unported), stock intake car. And they surely aren't going to be a better choice than 1 5/8's on a mod'd car. So why get them?

[budgetmaster]

I made the mistake of adding 1 5/8 equal's to my car recently. I have a very simple combo of stock intake, ported e7's, h-pipe, 3.55's etc. With the stock headers, this car dynoed 238hp with a nice flat torque curve. Ran 13.5-13.7 very consistently at 101 or 102. I promise you that the lrge tube headers make my car slower. No doubt about it. I shift at 5200 and don't need the flow, I suppose. Maybe if I was running 4.10's i wouldnt feel the loss as much. I am changing back to the stock headers this wknd(gasp). Headers should be a mod after heads, intake, h-pipe, gears, then maybe you wont be disappointed.

[gtsr515]

Budgetmaster, those headers MAY have slowed you down, But let me assure you those 3:55's ARE the worst draggin' gear for the 8.8, let me ask you this, If you shift at 5200, what gear are you in at the finish line and whats your rpms at the line?????????


Jay

...........get back quickly if you can, I have a theory here for you but need your COMPLETE package........

[ultraflo]

For a non-power adder, nearly stock combo with unported E7 heads... I'd go with the 1 1/2" equal length shorties.

If you are going to further you modifications down the road, then the 1 5/8" may be a viable alternative with that route in mind.

Keep in mind that the NMRA R/S guys are limited to 1 3/4" unequal length short-tube headers and 2 1/2" exhaust and they run in the low 10's (nitrous cars and blower cars alike, w/ class mandated stock camshaft).

I mananged 10.0's with 1 5/8 - 1 3/4 -3" Bassani longtubes on an EFI 306 w/ a 200hp NX single nozzle kit.... going off that, I'd say the 1 1/2" headers are plenty for a nearly stock 5.0 ....IMHO

[squid]

I hear your reasons 1BAD89 that a 1 5/8 may be better in the long run with alot more mods but, if you will look at the original question for this thread it was which header is best for my nearly stock motor. The answer is 1 1/2" shorties.

[budgetmaster]

Hey GTSR515 what happened? i pm'd you about your theory on headers and never heard anything.