Tuned length for 1 3/4 primary long tubes

darnoldrs

Registered User
I have made up some long tube headers for my project. It is a very tight fit but it has come up great.
I have 1 3/4" primarys, into a 2 3/4" colector 3" long then will be into hiflow cats and throu a 2 1/2 inch free flowing full twin exaust.
I have got a cam, push rods and double valve springs from XR7 Dave wich are good for 6000rpm so i would like to tune it for around the 4500-5000 rpm. The heads have been ported to aid with good exaust flow but i am still running standard valves for now.
What I need to know it how long do the primary tubes need to be??????
If any one can help it would be apreciated, Thanks
David, from OZ
 

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Tuned vs. UNtuned Headers

What makes them "tuned" is that all the header tubes are the same length. This is done so that the exhaust pulses don't arrive at the collector at the same time. You can then "tune" the TQ band, by using a longer or shorter large collector extension. Not sure how effective collector extensions are on the street.

68COUGAR
 
I have all the primarys with in 1" of the same lenght.( As close as i could get in the confined space i have) But i need to know how long to make them. I cant change the colectors as they are the only ones i have avalible to me but i can change the primary tube length to work with the colector i have for the RPM i want.
1 5/8 primarys need to be 32" long for memory so my 1 3/4 will need to be slightly shorter than that i think.
Thanks. David
 
I know I read a really great article about this in Hot Rod magazine some years ago. But I don't have it on hand. Maybe you could check their website / email someone to get the back issues. I think it was around 1997 or 1998, but the topic probably comes up every few years.
 
Collectors should be 6 inches...As far as optimal primary lenght I am unsure. Now on a forced induction motor I'm unsure how important a tuned or equal lenght header really is but if doing so..Just make sure they are all the same lenght with as little twists as possable
 
darnoldrs said:
What I need to know it how long do the primary tubes need to be??????
I investigated this a few years ago when inquiring about custom headers and two different companies quoted me 33.4 inches. I do not have any data to substantiate their claims however.

Paul

P.S. Looks like the #5 plug is going to be a nightmare with the tube routing, have you test fitted it and a plug wire to make sure the wire will be safe and the plug can be changed without pulling the header?

Paul
 
My Kooks seem to be about 30" x 1.75". Collector length on the header itself doesn't matter, but the collector length (which includes the pipes prior to any crossover or common chamber, should be 14-18" long IMO. Long collectors typically extend down the tuned rpm range of the headers.
 
The best way to figure out what header/collector length you need is to just run the car and see where the heat discharges from discolorization on the collector. It just depends on how far the flame out is on the exhaust valve.
 
The best way to figure out what header/collector length you need is to just run the car and see where the heat discharges from discolorization on the collector. It just depends on how far the flame out is on the exhaust valve.

From what I have read in the past they generally reccomend 6 inches. I can probably dig up the information..If needed
 
Thanks Guys. I have read all the previous threds on here i could find about long tubes and it would seem that they make very little differeance however If i can make them to the corect length then it is FREE :D Hp.
So i guess i should be looking between 30-33" then. I will have to have a look and see how that will fit into the space i have.
There will be no cross over or common pipe in this system uless i need one. I jave just planned it be a totaly seprate twin system.
All the plug leads fit and can be removed with out removing the headers, (Just). I will be ceramic coating them and I will also have to put a heat cover over No.5 plug lead as there is only about 5mm clearance. I had to modify this primary because it wouldnt fit to start with.:mad:
Any more input is welcome. i do have a rough length to work with now, but i need to get the primary tube right the first time:D Thanks to every one. David
 
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Looks great so far. Saw the 2 door that you were going to put the engine in, what body do you have it in now?

'bird
 
It is still going into the same car. I have another spare shell which i am test fitting it to incase i stuff up.:eek:
Why does it need a cross over pipe?? what is its purpose??
none of our local cars V6 or V8's running twin systems have them, however some have an equliser pipe just after the cats, (about 1") between the 2 pipes.
 
I don't think the crossover really does much if anything on these motors. The V6 does not benefit from negative pressure cancellation that V8's have so there is no sound benefit and probably no power benefit either. The biggest thing is going to be getting the right exhaust note out of it.
 
I have heard the same thing Dave said before. The 3.8L V-6 is an even-fire engine (cylinder banks alternate in the firing order), so the x-pipe doesn't make more power.
 
Thanks for that damon. I will look into it when i get it running if I dont like the sound. I can do that later as i am mainly concerntrating on the headers them selves at the moment. Thanks guys for all your help. Im finishe work for the year so i have a couple of weeks to pour into it. David
 
Another thing.

Without a resonator teh SC exhaust will not sound all that sweet. Magnaflow makes a two in two out resonator...Which coincidently is a preforated xpipe in a muffler casing. I'd reccomend that as I dont think you will be to happy running straight dual exhaust
 
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