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Discussion Starter · #1 ·
I just about ordered the Kooks 1 7/8" headers for the Magnum today, but I had to question the 1 3/4" primary size and backed down. I am *very* sure that we are about to get a 1 3/4" primary header for the SRT-8s and we should see that info in 2 weeks or less. It is also possible that Kooks may produce a 1 3/4" header(which I would like due to the cats they are using, metallic core, incredibly low restriction).

I know we don't have a lot of hard core engine guys on this forum, but any comments would be appreciated. I believe 1 7/8" primaries will really let the 6.1L live in the upper RPM range, but that isn't where I drive each day. The 1 3/4" should really be a boost to the mid-range torque and I expect that we will see significant torque gains over the baseline below the 5000rpm mark.

I would welcome comments from Kooks as well, especially if they can confirm or deny a 1 3/4" primary header future production for this platform. I know we will see some dyno results from them in the coming future for the 1 7/8" primaries and I wish to remove supercharged/turbocharged/significantly mod'd 6.1Ls from this discussion, as I don't plan on taking ours that route and I don't think the vast majority will either. The 1 7/8" primary is the way to go in that situation.

Todd
 

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Decoded the post and .......

Yes 1 3/4" primaries will boost torque in low rev range, and be better for real world street use over 1 7/8" primaries.

I'd wait it out too.


Zilla


.
 

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To put this in perspective keep in mind many 454 (7.4L) big block chevy's run 1 7/8 primaries for torque building power, upto 5500-6K. All my 350 / 383 cu inch street/strip motors run 1 5/8 primaries. 1 3/4 is generally reserved for 5.7 motors looking to maximize peak horsepower. With that being said, we are talking 6.1 L and extremely well flowing cylinder heads. Hard to make a call from generalizations derived from old school experiences. These are modern motors with heads that rival the flow of 18deg racing heads so I would hold out until you can look at the torque/hp curves of both and decide what you can live with.

Just my .02....

Chris
 

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Todd:

I would NOT wait out the 1 3/4 pieces personally. Here are the results of a 1 7/8" LT from Kook's on a LS1 5.7L GTO. ZERO losses over theh entire RPM band compared to stock. See my write up here: http://www.ls2gto.com/forums/showthread.php?t=28017

I just installed a set of 1 3/4" LT Kook's on a LS2 6.0L GTO this Tuesday and say ZERO loses over the entire RPM band over stock anywhere. I will post the numbers tomorrow.

What I DID notice was that the smaller diameter tube netted 15-17 HP @ 11.5 a/f (after cat) and the larger netted 23-25 HP @ 13.5 a/f (after cat). The 05 GTO stands to gain with a good tune as it is still very rich with the LTs. The combination of the LTs and our cat-back w/o tuning netted a 0.3 leaner A/F over stock. Still in the 11's, far too rich.

Considering the displacement and CR of the SRT8 ... you would be shooting yourself in the foot to loose 5-10 HP for nearly the same cost. Just my opinion.

Richard
 

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Discussion Starter · #5 · (Edited)
Richard,

Good info and it is something that a few of my LS1 buddies experienced as well. There was a few sets of 1 7/8" primary headers built for F-bodies with the LS1 a few years back and those I know who swapped from 1 3/4" to the new saw basically no loss down low, but did make gains up top. Some of the HP/TQ pulls would be a line width below the baseline pull with the 1 3/4" headers, but that was already above the stock pull, so I don't consider it a loss.

I am still thinking and I really want those headers.......

Todd

PS: Richard, it is disappointing to see the LS2 GTO dynoing only few rwhp higher than my stock pull on my 98 WS6 M6 before I started the heavy mod run down....Yikes, where is that power going? No wonder SRT-8s run those things down!!
 

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David Vizard recently had a few words on primary pipe size:

Headers — Primary Pipe Diameters

Big pipes flow more, so is bigger better? Answer: absolutely not. Primary pipes that are too big defeat our quest for the all-important velocity-enhanced scavenging effect. Without knowledge to the contrary, the biggest fear is that the selected tube diameters could be too small, thereby constricting flow and dropping power. Sure, if they are way under what is needed, lack of flow will cause power to suffer. In practice though it is better, especially for a street-driven machine, to have pipes a little too small rather than a little too big. If the pipes are too large a fair chunk of torque can be lost without actually gaining much in the way of top-end power.

At this point determining primary tube diameters is starting to look like a tight wire act only avoidable by trial and error on the dyno. Fortunately, a little insight into what it is we are attempting to achieve brings about some big-time simplification. Our goal is to size the primary pipes to produce optimum output over the rpm range of most interest. The rate exhaust is dispensed with, and consequently, the primary pipe velocity, is strongly influenced by the port's flow capability at the peak valve lift used. From this premise it has been possible to develop a simple correlation between exhaust port-flow bench tests and dyno tests involving pipe diameter changes. This has brought about the curves shown in the graph Fig. 4 which allow primary sizing close enough to almost eliminate the need for trial-and-error dyno testing.


Fig. 4:attached, This chart applies to normally aspirated engines. For street headers, where low-speed torque is of prime importance (especially with a stock converter and high rear end gears), use the lower line to select the appropriate primary size. For hot street machines having reasonably big cams and decent compression, use the middle line to size the primary. For race engines, use the top line.

So anybody remember what CFM the SRT8 exhaust ports flow at peak valve lift.?
 

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Worked out port flow using a little applied math

David Vizard’s Flow bench tests show stock 5.7 hemi Exhaust port flows [email protected] .600 lift. Porting produced [email protected] lift.

DCX published material states SRT 8 stock exhaust port has 13% higher flow over the stock 5.7 port. By extrapolation gives 182 cfm @ .600 lift. non-ported.
Ported SRT8 gives about [email protected] lift

Most will not port their heads, and the SRT Cam has 0.550 exhaust lift , so will actually flow a little less than the above flow bench figures. Say 175cfm non-ported and 210cfm ported. @0.550 lift.

The figures applied to Vizard’s graph - Fig.4 above give optimum primary pipe sizes of 1 5/8" with stock SRT8 ex. port, and slightly over 1 3/4" with ported ex. port.

Most will not port their heads: 1 3/4" primaries will give better real world performance than 1 7/8".

Zilla
 

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Not a big fan of Dave Vizard ... too much theroy and not enough REAL testing ... I have come across too much empirical data on my to suggest his laymans anaylsis leaves to mmany real world variables unchecked and his generalized "facts" in contest.
 

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Header size

As far as the primary sizes for the 6.1 it is going to be 1 7/8 x 3 and for the 5.7 it will be 1 3/4 x 3 if anyone has any ? call me at 631 586 9002 George R :wave:
 

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Discussion Starter · #11 ·
JMatt said:
Perhaps..... :wink1:
I hear you. :wave:

George,

Well, since it is 1 7/8" primaries for the 6.1L, it pretty well simplifies this decision. I really like the cats you are using and the rest of your work is excellent, so they may be going on soon.....Now, can you get the price down any? :wink1:
 

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Discussion Starter · #12 ·
btlfed1500 said:
Not a big fan of Dave Vizard ... too much theroy and not enough REAL testing ... I have come across too much empirical data on my to suggest his laymans anaylsis leaves to mmany real world variables unchecked and his generalized "facts" in contest.
Glad you said it and not me........Anyway, those of us who have been on various GM boards for a while know the story of 1 3/4" versus 1 7/8" very well. Both definately have their place, but the 1 7/8" have done very well lately at not loosing the bottom end as so many talk about and write about. I have dyno data that shows 1 7/8" primaries equaling the 1 3/4" down low and starting to make gains by on them by 3500rpm on a small 5.7L motor. I have also seen 1 3/4" headers give some torque down low that the 1 7/8" can't do, so I guess it depends on the situation a bit(the design of the header).

Todd
 

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WhiteDiamond said:
Glad you said it and not me........Anyway, those of us who have been on various GM boards for a while know the story of 1 3/4" versus 1 7/8" very well. Both definately have their place, but the 1 7/8" have done very well lately at not loosing the bottom end as so many talk about and write about. I have dyno data that shows 1 7/8" primaries equaling the 1 3/4" down low and starting to make gains by on them by 3500rpm on a small 5.7L motor. I have also seen 1 3/4" headers give some torque down low that the 1 7/8" can't do, so I guess it depends on the situation a bit(the design of the header).

Todd
It is all a fucntion of the VERY adaptive fuel managment systems that are used on cars today ... Some of the "old" theries substantiated by early fuel injection and manual carburation just dont hold water now.
 

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WhiteDiamond said:
PS: Richard, it is disappointing to see the LS2 GTO dynoing only few rwhp higher than my stock pull on my 98 WS6 M6 before I started the heavy mod run down....Yikes, where is that power going? No wonder SRT-8s run those things down!!
That chart was of the 1 7/8 LT on a 5.7 LS1 GTO

This chart is the 1 3/4 LT on a 6.0 LS2 GTO. The New 6.0 Goat has about 40+ rwhp over the LS1.


As you can see the cat-back had a much ore appreciable effect on the system showing that their is stiill room for more header.
 

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btlfed1500 said:
Not a big fan of Dave Vizard ... too much theroy and not enough REAL testing ... I have come across too much empirical data on my to suggest his laymans anaylsis leaves to mmany real world variables unchecked and his generalized "facts" in contest.
Actually we'll agree to differ on this one.

Virtually everything he publishes he has, or others have built, or he shows hands on test data for, he just shows the theory so we can understand what's actually going on.

I have built engines that Vizard actually built himself, and raced successfully.

Just my 2cents

Zilla
 

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Of course ... you can choose to do that I wasn't trying to sway your impressions of the guy but I think his application of theory to life is too remedial and doesn't take into consideration enough variables to make the generalizations he does. Good information for the garage mechanic or hobbist street car guy but his fundimental assumptions for what makes power just don't hold in my experience. Most my data is emperical testing.

As I said before ...
"It is all a fucntion of the VERY adaptive fuel managment systems that are used on cars today ... Some of his "old" theories substantiated by early fuel injection and manual carburation just dont hold water now."

Many of my expereinces with engine building come from the GM 97+ engine world but what I have come to learn is that "tradional" thoughts on modifications just dont apply. Such things as reverse split duration were a HUGE "NO NO" but have become quite common place in the big cammed LSx cars. Again Vizard makes too many generalizations ... they are OK at best ... you wont blow up your motor listening to him, but you wont have 100% of the potential power either ... Good basics but far from techinical enough to use as "blueprints" for building performance cars.

As you said he is a publisher ... his concern is selling his info. Most racebred information is not so easily found ... it is what keeps fast cars fast.
 

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Discussion Starter · #17 ·
btlfed1500 said:
That chart was of the 1 7/8 LT on a 5.7 LS1 GTO
Ah, my confusion had me wondering why GM put an LS2 in there if the power was the same....Thanks for the clarification.

Todd
 

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btlfed1500 said:
As I said before ...
"It is all a fucntion of the VERY adaptive fuel managment systems that are used on cars today ... Some of his "old" theories substantiated by early fuel injection and manual carburation just dont hold water now."
Actually the Vizard information I provided is current - May 2005 issue of Popular Hot Rodding Magazine!

I would be interested as to a brief explaination of why due to the theories you are using early and late fuel injected cars with the same HP require different primary pipe sizes.

btlfed1500 said:
As you said he is a publisher ... his concern is selling his info. Most racebred information is not so easily found ... it is what keeps fast cars fast.
Personally

Beg to differ have talked face to face with Vizard and understand how he easily engages people talking at their level to get them to share information.

I would be much more wary of a manufacturer, than a respected engineer/writer who does his due diligence.

Zilla
 

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Discussion Starter · #19 ·
goddardzilla said:
I would be much more wary of a manufacturer, than a respected engineer/writer who does his due diligence.

Zilla
Richard's info comes from his years of playing with GMs, as does mine. I have read and seen the header sizing charts for years and what you have presented is nothing new and has been out there for a long time. What is interesting to note, though, is that the GM LSx series of motors is responding to 1 3/4" primary headers in the 5.7L size and it is making more gains with the 1 7/8" primary headers in *most* cases. There is one 1 3/4" primary headers that does do very well in the low to mid rpm range in the torque department, but it is also a very long primary tube header. Richard also comes to a very logical conclusion, in my opinion, as the modern PCM is very adaptive and has multiple timing and fuel maps for all types of situations. It is no longer a linear response across the RPM range, as a set carb and mechanical advance provide, but a very dynamic situation in which the PCM can optimize each and every RPM point.

Todd
 

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Bigger is not always better.

WhiteDiamond said:
Richard's info comes from his years of playing with GMs, as does mine. I have read and seen the header sizing charts for years and what you have presented is nothing new and has been out there for a long time. What is interesting to note, though, is that the GM LSx series of motors is responding to 1 3/4" primary headers in the 5.7L size and it is making more gains with the 1 7/8" primary headers in *most* cases. There is one 1 3/4" primary headers that does do very well in the low to mid rpm range in the torque department, but it is also a very long primary tube header. Richard also comes to a very logical conclusion, in my opinion, as the modern PCM is very adaptive and has multiple timing and fuel maps for all types of situations. It is no longer a linear response across the RPM range, as a set carb and mechanical advance provide, but a very dynamic situation in which the PCM can optimize each and every RPM point.

Todd
It is admirable that you come to the defense of your friend Richard. However my statement was a defense of Vizard, and his genius than a direct attack any manufacturer especially Richard. I just feel Vizard is the most independant.

But your defense do make me ask these questions: Is Richard directly or indirectly involved in the manufacture and distribution of this header as part of a "system for sale"? Has this thread been started to justify the 1 7/8" primary decision in the forum's eyes? Just questions to clarify the situation for us all when reading the thread.

Also your statement above did not specifically answer this straightforward question I posed to Richard, in response to his statement that late fuel inj cars requiring larger primaries:

"why, due to the theories you are using, do early and late fuel injected cars with the same HP, require different primary pipe sizes"

Because these are not, and should not be race headers, we are talking about the best across the RPM range usability for street, not just WOT max HP.

I notice that other manufacturs are recommending different SRT8 header primary sizes, that are in argeement with Vizard: 1 3/4" for naturally aspirated and 1 7/8" for Supercharged . SEE HERE. If this info by GSM posted needs to , or has been updated to reflect all 1 7/8" primaries, show the forum.

Vizard recommends Kooks as a header manufacturer, so he is not at odds with them, on quality just on primary size.

Another question has come to mind: what are the primary sizes on the factory header? Just out of interest anyone know that?

More discussion please

Zilla
 
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