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Discussion Starter #1
Ok the ugly old conundrum is back. Long primaries vs shorter primaries for low-end vs high end horsepower. As long as I have been modifying cars (9 years and still cant stop), longer primaries have made better lowend power on just about any engine I have played with be it mine or friends (and there were plenty of those) regardless of brand or country of origin. I even read a lengthy tech website where the reason was put down in basic sound physics. Well some years went by and I am in a IS300 and then suddenly i hear the exact opposite???

Hmm well while browsing my usual corvette site, i came up on a guys response that brought back memories.
http://forums.corvetteforum.com/showpost.php?p=1551969196&postcount=4
I will renew my efforts to finding the proof of longer primaries make better low-end power and its actually the 1 5/8 diameter primaries that make the headers on the IS feel like it has lost lowend. I am almost willing to bet that if someone used 1 1/2 primaries, they will have the same top end with much better lowend on the IS (no its not due to backpressure).

The mustang with a much bigger bore and stroke than the IS can make over 350RWHP with the right cam with 1 5/8 headers, why is the IS using the same size primaries for NA especially with such a low rev limit (6500 rpm)?
 

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maybe it's due to the fact that the inline config is diff from the v config???
 

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I have thought of that for a while, but despite diferent configuration of the engines in question, resonance stays the same for a given tube with a fixed diameter and lenght. So the flow and scavanging properties of the header will remain the same regardless of the engine's configuration. But then the question of trick scavenging due to the inline design cannot be ignored either..... hmm time to break out the Physics textbooks again lol
 

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Why don't you whip up a header I will drive over and let you know what I think after it has been on my car........
Not sure I am going to finally put my header on my car in the next few weeks......
 

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I knew you wouldn't let this die bro :) keep on with the great info!
 

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Well after looking into the Team Lexus exhaust system, which includes a stepped header design.
As I actually dont have one at my disposal, I am taking complete guesses here. I suppose the header starts out from a 1.75in or 2.0in then goes to a 2.25 then 2.5 and finally to the 3in exhaust.
Perhaps that design is what makes the header so powerful. Plus its equal length design with long runners.
 

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kponti said:
I have thought of that for a while, but despite diferent configuration of the engines in question, resonance stays the same for a given tube with a fixed diameter and lenght. So the flow and scavanging properties of the header will remain the same regardless of the engine's configuration. But then the question of trick scavenging due to the inline design cannot be ignored either..... hmm time to break out the Physics textbooks again lol
true but the thing is that you are asking about the effects of something on the output of the engine...so you're comparing tubes on one type of engine config vs the same type of tubes on a diff config...it's not a really fair comparison if you ask me...maybe try doing some research on other inline 6 headers...maybe it might shed a little more light on the situation... :)
 

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Discussion Starter #8
HyperMKIV said:
true but the thing is that you are asking about the effects of something on the output of the engine...so you're comparing tubes on one type of engine config vs the same type of tubes on a diff config...it's not a really fair comparison if you ask me...maybe try doing some research on other inline 6 headers...maybe it might shed a little more light on the situation... :)
You are right about the configuration. But one thing you cannot ignore is that when you look at V-8 engine, especially one with a true dual exhaust design, the headers are configured for just an inline 4 cylinder. There usually is a crossover somewhere waay back of the exhaust, but its setup in a inline format. One exception I can think of is the LS1 in the Camaro/Trans Am etc.

Ok after some more reading, if I understand how scavanging is acheived on an engine, it is mostly dependent on the firing order. So if cylinder 1 fires first and you allow say one or two other cylinders to fire next (that also depends on crank stroke), then fire the cylinder next to 1 (2 in this case), the air being forced out of cylinder 2 helps push down the air further down in the header from cyl 1. This creates a slight negetive pressure in the primary for cyl one. Now if cyl one is in still in the exhaust stroke, then more exhaust air will be evacuated out of the cylinder itself helping to create a better removal of exhaust gases from the cylinder. The more you increase the diameter of the primaries, the slower the air travels (though more air can travel in that size primary tube). So goes to say, there will always be a fine line b/n header primary and length for a street driven car of a certain crank stroke. This is especially true of the IS cos well face it, out redline isnt all that high. Of course camshaft profiles, intake tract, cylinder bore sizes all have their say in this as well.

I am willing to bet that most of this is not considered when you look at most aftermarket headers on the market today. Rather (from some very reliable sourses) what is done is to step up to an eighth to a quarter inch more than the diameter of the stock header and call it a day. the rest of the time is used to design a longer primary and make it fit into the stock exhaust. I am also guessing this is how the IS header config probably came up. Headers take a lot to design and if you were to take into consideration all the factors I have considered up here alone, you will be charging $1500-$2000 grand for a header.

But one thing that we dont have which will definately help is equal lengths of the primaries. At least that can help with better scavenging. But yeah its harder to do. One other thing that we do have that I think based on some reading I have done so far is the fact that the current aftermarket headers are designed just like the stock unit. But remember, the stock unit has to serve the purpose of getting rid of the exhaust gases in a somewhat effeicient manner, but mainly to fit within the strut towers during robotic assembly (hence the use of exhaust manifolds in older cars) and to aid in cleaner emissions via recirculation of exhaust gases back into the cylinder during a valve overlap for a more complete burn. Also current aftermarket headers and the stock unit for the IS are actually designed like a inline 3 just like the V-8 is make for the inline 4.

Ok enough for now, gotta do some work here and will get back when I find out some more.

But the moral of the story is there is a lot more money involved in header design and most cars just get upgraded sizes and runner lengths from the aftermarket. If you dont have the know how/funds to really do this, the next best is to try out a few primary diameters with the longest primary you can fit and manufacture cheaply within the towers of said car. You have an aftermarket header that will make power and sell. Manufacturers/tuners are also faced with the problem of pleasing us (which can be a difficult task cos frankly a lot of us dont know a damn thing anbout what goes on under the hood, yet we want to modify our cars lol). So if the stock primaries are 1.5 inches and you come out with aftermarkets that are the same diameter, you may face a long line of critisism from those who may say the $400+ can be spent on something better than on a stock just longer primary header. But maybe that is what really works for the car for the stock given rpm.

PS: forgive my spelling, I am working and typing damn it lol.
 

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Discussion Starter #9
Ok just a quick update from the retail side. i did find a set of headers on Ebay that had the 1.5 inch primaries vs the 1.625 inch that is currently used (Toyomoto, Alpha Werks, Megan etc etc). It still had the 2.25 inch exhaust end and was shaped just like the Toyomoto/Megan setup. I was wondering on whether it was worth doing headers at all at the time so I didnt do it. Now I cant find it so if anyone does find it please let me know.

Thanks
 

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Discussion Starter #10 (Edited)
texis_300 said:
Why don't you whip up a header I will drive over and let you know what I think after it has been on my car........
Not sure I am going to finally put my header on my car in the next few weeks......
If you are looking to purchase a header for your car, PM me and let me know. Will love to help with the install and possibly split the cost of dyno pulls so I can add to my data.

My thoughts are actually to learn enough about this, take a cheap header from ebay that I will hack up into the best specs (according to theory) that I can to fit in the IS, then dyno before and after, with mods being the SRT intake and Dragger exhaust only. The SRT cos well the R-ECU has been shown to have great AF ratio even after header install.
 

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Kponti good job man good stuff in there I completely agree
 

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This is the team lexus system...



So far no one has been able to beat my N/A whp and wtq with this system, which was 228 wtq and 229 whp
 

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Discussion Starter #13
danielm said:
This is the team lexus system...



So far no one has been able to beat my N/A whp and wtq with this system, which was 228 wtq and 229 whp
Man welcome, i am soo happy you posted on this. thanks for the pics and you seem to be confirming my suspisions all along. Equal length do work a lot better!!!

Ok so i got a question for ya, What is the diameter of the primaries?

In your opinion, are the primaries longer than say the Toyomoto/Alphawerks average primaries (since they have different length primaries)?.
 

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+rep kponti for making work more interesting.
 

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joecrappa said:
+rep kponti for making work more interesting.
No kidding!
N/A needs to be pushed and researched and this is a fine example.
I've come over from bseries and kseries honda....Totally different world especially as far as N/A goes. Quite sad, actually. :(
 

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Here is a pic of the 2 next to each other..



I didn't mesure but, the 6 main primaries are about an inch and a half in diameter (they where the exactly the same size as the exhaust openings in head), the 2 collecting pipes i would say 2 or 2 1/2" and the main pipe 3".

From the above pic you can clearly see how the team lexus one gets as close as possible to having = primaries ( all the extra bends), at the same time you can see how un = the primaries are on the toyomoto header (the left is way shorter than the right) and in general I would say the team lexus header primaries are almost twise as long as toyomoto ones.

As you I have always seen longer , =, primaries make the best power always!

One a side note, I think a 6 to 3 to 1 design would make the most power on an inline motor, no one has done it yet, but if I ever get another IS i will make one for sure.
 

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Discussion Starter #17
danielm said:
Here is a pic of the 2 next to each other..



I didn't mesure but, the 6 main primaries are about an inch and a half in diameter (they where the exactly the same size as the exhaust openings in head), the 2 collecting pipes i would say 2 or 2 1/2" and the main pipe 3".

From the above pic you can clearly see how the team lexus one gets as close as possible to having = primaries ( all the extra bends), at the same time you can see how un = the primaries are on the toyomoto header (the left is way shorter than the right) and in general I would say the team lexus header primaries are almost twise as long as toyomoto ones.

As you I have always seen longer , =, primaries make the best power always!

One a side note, I think a 6 to 3 to 1 design would make the most power on an inline motor, no one has done it yet, but if I ever get another IS i will make one for sure.
Once again thanks for the info definatley +rep stuff here.

Guys this is telling me that the team Lexus headers are actually the same or less in diameter than the Toyomoto ones??? hmmm that is VERY interesting!

now on the 6-3-1 design, i am willing to bet that it wont make as much power as the current 6-2-1. Why? cos with the extra primary (three primaries before a secondary), you increase the rate of scavenging based on what I was saying before. With only two primaries per secondary, the firing order is of utmost importance, but even that will not build as much negetive pressure as the current setup. Here is a caveat though; If you are going to spin your engine to say 8000+ rpm, then Danielm, your concept will work. but for such a low rpm engine like the IS, a 6-1 direct will give the best powercurve.
 

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kponti said:
Once again thanks for the info definatley +rep stuff here.

Guys this is telling me that the team Lexus headers are actuall the same or less in diameter than the Toyomoto ones??? hmmm that is VERY interesting!

now on the 6-3-1 design, i am willing to bet that it wont make as much power as the current 6-2-1. Why? cos with the extra primary (three primaries before a secondary), you increase the rate of scavenging based on what I was saying before. With only two primaries per secondary, the firing order is of utmost importance, but even that will not build as much negetive pressure as the current setup. Here is a caveat though; If you are going to spin your engine to say 8000+ rpm, then Danielm, your concept will work. but for such a low rpm engine like the IS, a 6-1 direct will give the best powercurve.
Your right! an 8k rpm IS300 has always been a dream of mine, untill then if I ever do get an IS it will be worth it for sure to make a 6/3/1 header just for testing reasons.... but then again I am sure if that was a better design, team lexus would use it.
 

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Discussion Starter #19
danielm said:
Your right! an 8k rpm IS300 has always been a dream of mine, untill then if I ever do get an IS it will be worth it for sure to make a 6/3/1 header just for testing reasons.... but then again I am sure if that was a better design, team lexus would use it.
Hey D, could you take a peek into your engine bay and tell me what type of config the M has for headers?

Also even though the Team Lexus setup is done for higher RPM, it still isnt really that high (I dont think it is more than 7500rpm-correct me if I am wrong). So a better area under the curve will be more important for them than the ultimate highend power (they dont have the rpm needed for that).

Here is something else, when you go with a 6-3-1 setup, the power gains will best be realised with a much shorter primary length (so more help can be aquired from other cylinders at high rpm to increase scavenging). This is why I have always wondered why people on my.is believe shorty headers produce more low-end. If the roles are reversed like people are saying here, then maybe the diameter for the primaries are just too big!
 
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