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1 3/8 merged vs non merged
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spyvsspy
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PostPosted: Mon May 23, 2011 2:36 pm    Post subject: 1 3/8 merged vs non merged Reply with quote

Does anybody have any idea or knows of testing that was done between a regular header w/j tubes vs the new 1 3/8 merged headers that cb performance is distributing? Any idea of the difference in torque/hp figures?
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DarthWeber
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PostPosted: Mon May 23, 2011 6:31 pm    Post subject: Reply with quote

I haven't seen any actual numbers but merged headers are usually optimum for mid to higher RPMs'. That's where they can really help in scavenging the exhaust and take advantage of the bigger valves and lots of portwork in racing heads. I kind of wondered why HVW's used the CB header on their mileage motor since it kind of runs out of steam around 5k and high RPM's and fuel mileage don't necessarily go together. I mean CB was "allowing" HVW's to use a lot of their parts and I guess that was the showcase for the debut of that header. I believe, for that application, there would be no difference between merged and standard headers. A merged 1 3/8" would work great on a 1600 screamer with really good heads, big carbs and cam. That's my perception, is it reality?
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PostPosted: Mon May 23, 2011 7:33 pm    Post subject: Reply with quote

I am actually looking for a good exhaust for my 1915 cc engine. I'm running all tin, and heads are stage one drd's. Cam is a 110ish and carbs are dual 36 dells. With megajolt inside. Just want a good exhaust that will fit my engine.
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PostPosted: Mon May 23, 2011 7:42 pm    Post subject: Reply with quote

Did you mean DRD L3 heads (35.5 x 32 P&P)? With your cam, dual 36 Dells and 1915cc, I'd be inclined to run a 1 1/2" exhaust. I think a 1 3/8" header would be a little restrictive at mid to upper RPM's.
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spyvsspy
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PostPosted: Mon May 23, 2011 10:17 pm    Post subject: Reply with quote

Yes i have the drd L3 heads. I was inclined to run a 1 1/2 exhaust but dont know of any that is compatible with the cooling tin setup.
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PostPosted: Mon May 23, 2011 10:19 pm    Post subject: Reply with quote

Do you want to run heater boxes or J tubes?
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PostPosted: Mon May 23, 2011 11:30 pm    Post subject: Reply with quote

I don't need heat since I live in the tropics.
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66brm
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PostPosted: Tue May 24, 2011 12:00 am    Post subject: Reply with quote

spyvsspy wrote:
I don't need heat since I live in the tropics.


Inside a barrel? Rolling Eyes
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PostPosted: Tue May 24, 2011 9:07 am    Post subject: Reply with quote

66brm wrote:
spyvsspy wrote:
I don't need heat since I live in the tropics.


Inside a barrel? Rolling Eyes


Lol...inside the barrel means getting tubed while surfing.
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PostPosted: Tue May 24, 2011 10:11 am    Post subject: Reply with quote

I'm thinking, and I could be wrong, that the merged 1-3/8" would be fine with stock-valved ported and polished heads. I don't think a merged collector alone moves the power band up in the RPM range, it's always been my understanding that primary tube diameter is more influential in that arena. The merged collector is merely much more efficient than the standard "swedged" or "stamped" collector of your run of the mill garden variety heater box headers of the 1-3/8" sizing.

Rule of thumb I've always been advised is 1-3/8" for stock valved heads, 1-1/2" for 40x35.5, 1-5/8" for larger than that...
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PostPosted: Tue May 24, 2011 10:16 am    Post subject: Reply with quote

bugnut68 wrote:
Rule of thumb I've always been advised is 1-3/8" for stock valved heads, 1-1/2" for 40x35.5, 1-5/8" for larger than that...
I always thought the rule of thumb was about how big a stick you're allowed to beat your wife with.....really. No thicker than your thumb. Didn't you see "The Boondock Saints" for cryin out loud? Laughing

No offense meant to any of our female readers, just another poor attempt at humor.

RC
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PostPosted: Tue May 24, 2011 10:17 am    Post subject: Reply with quote

RockCrusher wrote:
bugnut68 wrote:
Rule of thumb I've always been advised is 1-3/8" for stock valved heads, 1-1/2" for 40x35.5, 1-5/8" for larger than that...
I always thought the rule of thumb was about how big a stick you're allowed to beat your wife with.....really. No thicker than your thumb. Didn't you see "The Boondock Saints" for cryin out loud? Laughing

No offense meant to any of our female readers, just another poor attempt at humor.

RC


Sorry, that one's lost on me, didn't see that flick... Embarassed Laughing
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PostPosted: Tue May 24, 2011 10:22 am    Post subject: Reply with quote

bugnut68 wrote:
RockCrusher wrote:
bugnut68 wrote:
Rule of thumb I've always been advised is 1-3/8" for stock valved heads, 1-1/2" for 40x35.5, 1-5/8" for larger than that...
I always thought the rule of thumb was about how big a stick you're allowed to beat your wife with.....really. No thicker than your thumb. Didn't you see "The Boondock Saints" for cryin out loud? Laughing

No offense meant to any of our female readers, just another poor attempt at humor.

RC


Sorry, that one's lost on me, didn't see that flick... Embarassed Laughing
That saying really did come about from the "rule" about how big a stick you can beat your wife with. They just explain it in the flick. Not very PC of course.
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PostPosted: Tue May 24, 2011 10:33 am    Post subject: Reply with quote

bugnut68 wrote:
I'm thinking, and I could be wrong, that the merged 1-3/8" would be fine with stock-valved ported and polished heads....
This is true with smaller engines but you have to take into consideration that it's a 1915cc engine so it will move a considerable amount more air, especially at higher RPM's. Even the stock sized valves can flow a lot of air when the restrictive ports are massaged properly.


bugnut68 wrote:
I don't think a merged collector alone moves the power band up in the RPM range, it's always been my understanding that primary tube diameter is more influential in that arena.

The header, in and of itself, doesn't move the power band. It facilitates flow or scavenging of the combustion chambers by using the vacuum created from exhaust pulses from the other cylinders. The merged collector allows this to happen more efficiently.
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AlteWagen
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PostPosted: Tue May 24, 2011 12:50 pm    Post subject: Reply with quote

Ive always tried to match the the tubing diameter to the valve size.

32 = 1 3/8
35 = 1 1/2
37.5 = 1 5/8

To me equal length primary tubes are more important than collector design but since most headers today are made as one size fits all or just for looks, equal length or "tuned" are difficult to come by off the shelf.

As mentioned earlier primary tube length will determine when a header starts to "work" or when scavenging will begin. Longer primaries are commonly known as torque headers, but in the VW world headers with various tube lengths are non existent.

Im sure Modoc will be here shortly as exhaust is his fetish.
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PostPosted: Tue May 24, 2011 1:36 pm    Post subject: Reply with quote

You do not select header tubing size by exhaust valve size alone. You need to also consider displacement, PRM range, compression ratio, vehicle weight, and carburation.

For the OP's needs, I suggest a 1 1/2" exhaust. I believe Gene Berg sells a 1 1/2" exhaust that works with stock tins and thermostat.
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PostPosted: Tue May 24, 2011 1:51 pm    Post subject: Reply with quote

An unmerged header cannot scavenge at any practical RPM. A merged header will always make more power.

Primary diameter partially determines the max RPM of the powerband but also low end torque. Too small and the engine chokes at high revs. Too large, and the exhaust velocity drops and you lose low end torque.

Primary length determines at what RPMs the peak power gains are from the exhaust scavenging harmonics. Short tubes for high RPM, long tubes for low RPM. The closer the primary lengths are to being equal the higher and narrower the power peak. Primaries that are not equal are not necessarily a bad thing as it spreads out the power over a wider rev range but of course with a lower peak. You don't want one at 3 inches and one a 30, but don't obsess over them being perfectly equal.

There's online calculators that will give you the primary diameter based on your RPM/flow requirements and length based on what RPM you want the power peak.
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PostPosted: Tue May 24, 2011 1:59 pm    Post subject: Reply with quote

I guess maybe I should have prefaced my comments with the RPM range of intended usage... The 1-3/8" exhaust will likely be a better performer for low-RPM/bottom end power and torque, but the 1.5-inch will certainly be better for mid-range and top end over the aforementioned 1-3/8" system, especially with stock size valves and a 110 or similar cam.
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PostPosted: Tue May 24, 2011 2:03 pm    Post subject: Reply with quote

vwracerdave wrote:
You do not select header tubing size by exhaust valve size alone. You need to also consider displacement, PRM range, compression ratio, vehicle weight, and carburation.


Correct, I just forgot to put the disclaimer regarding the ENTIRE combination of parts.
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PostPosted: Tue May 24, 2011 5:13 pm    Post subject: Reply with quote

jhoefer wrote:
An unmerged header cannot scavenge at any practical RPM. A merged header will always make more power.


I think he is talking about a merged style, and a standard style header with J tubes. Say, both are using the same size pipe and have the same muffler, and both meet at a collector. Is there any significant gains with the merged?

merged:
http://www.shopatron.com/products/productdetail/Me...?pp=8&

Standard header with J tubes:
http://www.shopatron.com/products/productdetail/La...?pp=8&
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