Louis

iTrader: (7)

No, same primary lengths, I saw the same gains Ed did, 2-4, but loss of 10 at 2500-3k.

Shorter 1 7/8s pick up almost 10 uptop, but again, lost over 12-15 in the midrange. By mid range, Im not talking peak Tq, Im talking 1500-4000.

I have graphs, but Im not at liberty to share at this point. It does follow what you would think it would do, thats for sure.

jmilz28

iTrader: (13)

Tired, blurred vision, saw 06, sorry. I may have even been typing two posts at once and hit the wrong window. And no, not relative - hence the "back on topic" comment. Regardless, it seems to show that if you are going bigger, you may as well buy the big tubes the first time. How different were the tunes (AF and timing) for the two sizes?

I can't help but think the split cams that the L92/LS3/LS7 like so much may affect a test like this. How much different do you think the results would have been on a cathedral port car? Thanks for taking the time and posting the results!

1cdub

iTrader: (5)

I still think its impossible to make blanket statements about the header size.

Initially I had cheapo Edelbrock 1 3/4 stepped to 1 7/8 with 3.5" collectors.

I "thought" my 454 could benefit from a larger "quality" header. I went with AR 1 7/8 stepped to 2" also with 3.5" collectors. The car lost almost 1tenth and over 1/2 mph. Keep in mind this is track testing with a very consistent car that made almost 100 passes this summer. This is no few passes one set, a few the next.. I'm talking "corrected" averages with over 40 of those passes made after the switch. The car has a 5k converter in it so the "loss down low" really isn't a factor either.

edcmat-l1

iTrader: (10)

You def have a bad *** car, no doubt. But I've been around drag racing all my life, and I cannot believe a 454 inch motor would ruin better with 1 3/4 primaries than it did with 1 7/8s. Not to mention the fact that it's hard for me to believe that 1/8th inch of primary diameter would knock almost a tenth off it.

In your case I think the only real way to tell would be to put the others back on and see if it picks back up.

Slowhawk

iTrader: (12)

Cam choice is big with header selection.Bigger tube headers more than likely need less exhaust duration compared to a smaller tube header.Of course this is a blanket statement since each header is different.

JS

iTrader: (4)

I'm not knocking the test or your opinon but we did it back to back same day not months apart and we lost TQ with the bigger header too just like 1cdub did,does that mean it will happen to everyone?

No....


Don does make a good point that cam and or what heads are on the engine come into play too..IMO its not one header fits all,but in our case the 402 we built likes the smaller tubes

edcmat-l1

iTrader: (10)

How bout answering my earlier post. Got a graph? How much did you loose and where? For how long? What was the subject test vehicle?

Not knockin your test or opinion either, but it's funny how many people talk about them loosing torque or power, but little or no real data to back it up.
I've yet to see a significant drop in power using larger tube headers. Even hot rod magazine or one of em anyways, did a test of 1 5/8 vs 1 3/4 vs 1 7/8 and picked up each time they stepped up. Not once did they drop even low end torque.

All I want is to see a graph, from you or anyone else. Engine dyno, chassis dyno, whatever. Same brand, same primary length, only change being tube diameter.

1cdub

iTrader: (5)

Facts are facts, I've got almost 100 slips showing the average diff. between the two with my particular combination.

Keep looking for graph and dyno sheets, I gave you a real world example.

DRIVER456

I went back to 1 3/4 long tubes, From 1 7/8 header's.Lost some torque w/ 1 7/8.My car ran faster w/ 1 3/4 header's.....................Paul

JS

iTrader: (4)

Exactly right 1cdub,we tested at the track too in colder air and the larger tubes didnt pick up tee tee either

Dyno smyno,track testing is best

the_merv

iTrader: (88)

I guess it just depends on your setup, I'm interested to see what they do on my 402 with L92 Heads.

If you do the Math, they have about 12.88% more flow area in the Primaries over a 1 3/4 Header.

1989GTA

"If you do the Math, they have about 12.88% more flow area in the Primaries over a 1 3/4 Header."

Is that good or is that bad?

the_merv

iTrader: (88)

I guess it depends on your setup, I was just telling how much bigger they are over the 1 3/4 Primaries..

DemonInside

iTrader: (54)

from what ive read all over here and learned from useing ls3/l92 heads is they dont flow so well on the exhaust side so a bigger header was always suggested.

thats what ive read on here, so if u had a different type of head i.e like a pair of ls6's on a ls6/2 and did the test it would prolly be different?

or am i mistaken.

just curious

the_merv

iTrader: (88)

The OP tested them on a L92/LS3 Head and got a nice little gain, so that has me interested..especially since I'm a decently Cammed Stroker.

1989GTA

PipeMax recommends an exhaust gas velocity of around 260fps. So something in that speed range would be the target. That would give you the best overall power under the curve. There is quite a bit of latitude. To fast or to small a header and you go into sonic choke. To slow or to big a header the torque starts to drop off and reversion becomes a problem.

LIL SS

iTrader: (9)

Hey Don,

I'm guessing the two 1 3/4 headers were different lengths?
Was one of the 1 3/4 the same length as the 1 7/8?

I've recently been playing around with Performance trends engine analyzer, specifically working with headers, diameter and length. It's quite interesting what it spits out are the optimal headers for different packages.


Here is an over lay of my current headers vas what it feels are optimal headers for the most average TQ and also optimal headers for the most average HP based on my combo ans 2500-7400rpm.

Current headers 1.875 x 32"
Optimal TQ 1.622 x 50"
Optimal HP 1.737 x 37"




Then if you change the RPM band and only the rpm band to 4,900-7,400 which is where my motor runs while racing it give much different numbers. Again an over lay of the optimized HP, Optimized TQ and current.

Current headers 1.875 x 32"
Optimal TQ 2.363 x 37"
Optimal HP 2.438 x 35"




As you can see, there are minor difference between the optimized set ups. For the large RPM band, my current headers are leaving a lot on under the curve power according to the program.

Just some toying I thought was interesting.

jbs02somws6

iTrader: (1)

I just read this thread for the first and I'm wondering how everyone if everyone including me is dense regarding the OP's original post. I think the point being made is that out of four total tested vettes (being identical in config.) two dynoed less than the other two. But in each case of comparing two vettes, the 1 7/8ths headers made up for the weaker stock vettes in the comparison to equal the total gains of the 1 3/4in headers (400 peak rwhp). In other words the 1 7/8ths picked up 35rwhp on the two weaker vettes while the 1 3/4 headers only picked up 25whp making all four cars about equal. I'm just wondering if I read it correctly?