Thanks for the answers in my first question. Now, if 1 3/4 headers are better than 1 5/8 for a 5.7L camaro than why is SLP the only company to make that size? Hooker, Edlebrock, or anybody else for that matter doesn't seem to make that size header for our application.
Also, has anyone seen any dyno sheets that prove 1 3/4 is better?

 

Hooker makes 1 3/4 lt headers for our cars. It depends on what mods you have and how much air you are flowing. 1 5/8s might be better on a 305 or stock 350 where as 1 3/4 would be better on a modded 350 where you are flowing more air.

Ben

 

Are the Hookers smog legal?

 

No, and they are long tubes, so they would either need a custom y pipe or you would have to buy mufflex's y pipe which is rather pricy. Since I dont have to worry about emissions though I plan on running the hookers and true duals.

Ben

 

OK i have to disagree with the "you have to have 1 3/4" this really isnt true. if you plan on making over 450 hp then go with the 1 3/4 but for 400 and even 400 plus 1 5/8 are great plus they fit in the engine bay better. i have read enough books by noted engine builders and seen enough dyno proof to believe 1 5/8 is enough for a 350 and then some.

pick up the current chp magazine and they have a 383 pushing over 400 hp with 1 5/8 headers and when they switched to 1 3/4 they picked up a whopping 4 hp, both where hooker long tubes so same manufacturer.

1 3/4 are not a must but buy what you want and feel you need.

 

So will I notice a loss in the lower end if I go with the 1 3/4?

 

Nobody seems to have done a comparison of 1-3/4" primary shorties to 1-5/8" long tubes. The CHP test showed better overall power with the 1-5/8" long tubes, but that tells you nothing about shorties.

SLP tends to know what they're doing, so follow their advice for their headers. If going long tube, 1-5/8" will handle the typical street engine, and provide better driveability. For a race-only car or really, really strong street car, you may want to consider the 1-3/4" long tubes.

 

There is also the fact that there is only 2 brands of long tubes for our cars and depending on what kind of exhaust you are going to be running one may work better than the other. I know that for the hookers you can get a y-pipe from mufflex, and I have heard that the hookers hang lower than the headman so it may cause a problem if you try to use the y pipe with headmans. Also, I have read on the boards that while you may loose some torque with bigger primaries you gain high end. I also read that the long tubes will help keep you from loosing the torque. If these statments are true I would think that if you are going to have a motor that flows pretty decent and want long tubes that the 1 3/4 would not be a bad choice.

Ben

 

Well,
If SLP tends to know what they are doing, I may just have to take their word for it. SLP straight out reccomends 1 5/8 for 305 CID and 1 3/4 for 350 CID (5.7).
I guess I may have to trust this.

 

I will be slapping my 1 3/4 long tubes on my 305 until the ZZ4 comes. I heard the 1 3/4 are good for a slightly modded or more 350. 1 5/8 are for 305s (unless you got some radical 305) and stock 350s. Oh well I got my headers and a full exhaust for $250 so thats why I took them.

 

I was worried about the 1 5/8 or 1 3/4 chioce when I was looking into purchasing my SLP headers. I thought I did my homework and SLP was persistant that 1 3/4s were for 350s and would benefite me so I plunked down the cash and had them install them since I have no driveway here. It took the 3 days to install their headers and to my dismay they DENTED them to make them fit, broke my center bolt wire looms, and broke and replaced my fan switch and had all kinds of custom welding supposedly to make them fit, so much for you get what you pay for. heres the kicker before the headers I went 13.521 after 13.608 and no change in MPH whatsoever. I read some people picked up a few tenths and a MPH or two I got exactly nothing for my $$$ even lost a tad, hopefully you make out better than I did, good luck...

 

Sorry you had such troulble. I have to say though, it doesn't sound right that it took three days to install the headers. It really sounds like someone not qualified to do this did the installation. Maybe that was the problem.

 

First of all when it comes to the flow capabilities of headers, primary size is only part of the equation. But even assuming it was a direct correlation with primary size, 1 5/8" primaries won't start holding you back until you start pushing some serious horsepower (<450), which means they are fine for just about every car on this site. Hell, there's a guy on this board with a hot 383 running in the 11's with hooker 1 5/8" shorties.

 

My main reason for going with the 1 3/4, was to get rid of some of the low end power that the TPI intake provides. But unfortunatly it still has too much power down low. I will go long tube next time.

nick

 

If you want to get rid of some of that low end power...change cams, or change intakes or both.

Altering the exhaust to do that is shooting yourself in the foot...as the only thing a TPI setup has going for it is.......THE LOW END TORQUE...

Long Tube Headers just are not needed until you are making serious power (either above 450 HP or into the 11's, however you want to look at it)

Chevy High Performance did a 406 buildup like 2 years ago with the budget Trick Flow heads and a comp cams extreme energy 274 cam that made 450 HP and 500 Ft/lbs of torque with 1 5/8" shorty headers....and a short length of 2.5" pipe with 2.5" mufflers.

1 3/4" headers just are not needed until over 450 HP...

BTW, did it ever occur to anyone that SLP is in business to make money and not worry about tech requirements? Recommending 1 3/4" headers for a stock 350 is stupid....

Don't get sucked in by the group think on this particular board about the primary size debate...spend the money on better heads before going to long tube headers....and if you have a HOT N/A 305, then 1 5/8" are OK for you, otherwise 1.5" are more what you should use to maximize your engine package...

HTH someone to understand,

 

88TPI,
My 1 3/4 SLP's for my 350 have been on order since last week and that is what SLP recommends. Also, the prices are the same whether you get 1 3/4 or 1 5/8. SLP seems to be a pretty knowledgable out fit and it seems that evey one agrees they make the best headers ( constuction and design, workmanship) not only here on this site but everyone else I talk to. I am really hoping that the 1 3/4 are correct and that I don't regret having not ordered the 1 5/8.

 

Well I did change the cam on my car at the same time, and I will get to the intake next. And I know from a lot of personal experience that the exhaust has a big effect on the powerband.
A less restrictive exhaust has given me a loss of power down low and more of a gain top end then I lost down low. Again this is my experience. If you want me to list 1/4 mile times from my 85 TA with a 305 tpi with different exhaust set-ups I will.

nick

I am going to switch to long tubes eventually, because the SLP shorties go from 1 3/4 primaries to a 2 1/4 intermediate pipe. It is very obvious from looking at the set-up that there is some serious power to be gained from long tubes.

 

Oscar...my recommendation is to simply build up the engine to make the headers work more efficiently...AFR 195 heads, Superram or Miniram, nasty cam, 2800 stall convertor and bulletproof trans, etc...you get my point...On a mostly stock engine though they are still overkill.

89BlueTA, I agree with you. Think outside the box for a second...the SLP headers are OK, so simply ditch the Y-pipe and have one custom made...this is what I did when I bought my headers. I have 1 5/8" Hedman shorty headers with seperate 2.5" pipes that join into a Flowmaster piece with a single 3" outlet and no cat.

The key here is to remember to think of the exhaust system as a "system" not just headers or just a catback.

IMHO, SLP is screwing the customers because of their necked down y-pipe...I don't own a set of these headers and never will until they fix that obvious engineering flaw...yet they don't need to because they continue to sell them as-is.

Sigh

 

I would like to hear them,if you don't mind.. I'm looking into whch headers to buy for my current 305 but I want one that will work on my future 350 also... So this 1 3/4 vs. 1 5/8 debate is important to my making the right choice....

 

Forgot to add...i plan to have my 350 making 425-450 hp or so...

 

i'm running SLP 1 3/4 headers on my 305. i felt no low end torque loss and picked up 3/10's and 3mph at the track.

 

very cool IROC. The more info we get the better. What a debate... My 1 3/4 headers should be in any time now.

 

87 B4Z...I have seen pics from people who bought the 1 3/4" headers from SLP and seen how the Y-pipe necks down to 2.25" just before the cat...That restriction and your experience actually confirms what I am saying about the SLP y-pipe...because technically, those headers should be too big for your 305 and you should suffer a low-end torque loss...if you don't see it, it should tell you something about the restriction.

HTH,

 

88TPI,
I have the dual cats on mine. How does the y pipe affect this?
The two pipes don' t join until after the cats.
thanks.

 

To be honest, I have only seen the single cat setup. I don't think that dual cats are necessary today. They were back then due to the poor design of cats, but a good high-flowing cat (like a Random cat) or a universal 3 or 3.5" cat would suffice as well and would be much simpler. The choice is either two necked down, restrictive cats, or one larger cat. as long as the opening is large enough, then it isn't a restriction.

But I would be suspicious of what/how the y-pipes do join together and make sure it isn't a restriction and that they join cleanly, in a Y-type configuration. A lot of aftermarket Y-pipes will kind of graft one pipe onto the other and this can cause turbulence and become a restriction issue.

HTH,

 

As far as I can tell, the dual cat "extension" pipes for the SLPs don't have a restriction, they're about 2.5" the whole length. They still have the collector restriction that all SLPs have though...

 

88TPI406GTA, here are 2 pics of my SLP 1 3/4 headers and y-pipe

<img src=http://groups.msn.com/_Secure/0MwB0cFURl68nALb6ZfHZ681E7JFfzSzHUc9r5fJlc04Npos!mzywmtMeDqwlbkwGLv3mQyAY1lgX*Kb26nnQGg/Image046.jpg>

<img src=http://groups.msn.com/_Secure/0NAAAAHwR8rgnALb6ZfHZ66E2bqRfO95M5jmhaSdAzfffbsZhVvyh1HfRktLa6AUlWAGTV8E1IuNlZul!!YQS9A/Image0100.jpg>

i dont have the "restriction" you are talking about, its a full 3in.

 

Those definitely don't look like the pics I saw a few years ago. If I remember correctly, there was some smaller diameter piping near the cat hookup.

Also, there was some issues internally on the pipe year the actual y connection. Shine the flashlight up there and look. This was brought up in the same vein as Edelbrock headers and the the beads being on the inside from welding...something else choking flow.

If there design/quality control improved, then so much the better. Please look and let me know. I didn't buy from them at the time because of the restriction/price issues.

Also, what size are the pipes individually before they Y together?

 

i would say there about 2 1/4- 2 1/2

 

That would be important to determine the size...what about the internal restrictions/beads?

 

i didnt see any

 

The other key then is the actual size of the individual pipes before they join. If they are truly 2.5" and merge to a true 3" single pipe, then it isn't so bad. However, if they are 2.25", it is a restriction.

Just my $.02.

 

Actually I dont believe that 2.25 would even really be a restriction, because if you look into some of the debates where people have argued single vs. dual exhaust dual 2.25 has a slightly larger inside area than a single 3 meaning that the 3" portion would be the restriction, and very few people on here consider 3" a restriction or make enough power for it to be.

Ben

 

88TPI406GTA, i see your trying real hard to tell me i have a restriction in my exhaust.

 

FYI, the dual cat SLP 1-3/4" header system has 2.25" pipes going to the cats, the cats themselves exit at 2.5". My Flowmaster Y pipe goes from dual 2.5" to a single 3", and it's an actual Y.

 

Momar, that very well may be, I thought that 2 2.25" pipes flowed a bit less than a single 3" though...I could be wrong.

Synapsis: I have a custom y-pipe to the Flowmaster connection. That is a good setup then.

87B4Z: I am not trying to convince you of anything...If SLP revised their design since a few years ago...Great...but you are the first one to show evidence of it that I have seen on these boards...Congrats on being a pioneer

 

No, the dual 2.25 flow just barely more than a single 3. They are close enough that there shouldnt be a noticable difference between dual 2.25 and 3 unless you have a setup that gets better scavenging one way or another, but since this is in the same system all we would be worried about is the flow so the 2.25s shouldnt be a restriction.

Ben

 

Flow area of 2x2.25" OD vs. single 3" od (assuming 3/32" wall thickness for both):

2.25" - 3/32" for walls = 3.652 square inches. Times 2 = 7.304 square inches.

3.00" - 3/32" for walls = 6.634 square inches.

Difference = 0.670 square inches (2-1/4" duals greater than 3")

If wall thickness is more, 2.25" flow area difference over 3" is slightly less (.6 square inches for 1/8" total wall).

Assuming no boundry area losses (which isn't real-world), the dual 2-1/4" should flow more than a single 3". Depending upon how each is bent (non-mandrel, for instance), the 3" can actually be better.

Not that this has anything to do with the original topic...

 

Shazam...I stand corrected.

I know that all of my pipe is mandrel bent...so I appreciate the calculations again...

Thanks for the info.