calculating primary lengths for a supercharged engine?

[fasterstill]

Hello,
I'm in the process of designing headers for a Jaguar AJ16 supercharged engine but am unsure of the best way to calculate the diameter of the primarys. Pleanty of information on N/A V8 engines across the net but i've been unable to find anything with regards supercharged engines.
Is anyone here able to assist or point me to a source of information.

Best regards

carl

 

[patprimmer]

The main advantage of tuned length is that it helps scavenge exhaust out of the chamber during valve overlap.

This is not a problem on supercharged engines as the inlet manifold pressure helps purge the chamber. It is so effective that many tuners use a substantially less overlap on their cams by spreading the lobe centres.

As they make more exhaust, big free flow pipes are a benefit.

Regards

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[GregLocock]

My first instinct is to say that the intake runner /diameter/ is not really calculable. You don't want the valve to be too much of a restriction, and you don't want too much air in the intake, but those are both handwavy requiremments.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[fasterstill]

A little more info:
What im trying to do is produce a small batch of headers for myself and a group of friends to replace the frankly appaling cast manifold on the Aj16 4lt engine. Every one of us has cracked manifolds which as im sure you guys know are a real pain to weld. New ones are no better and are just as likley to crack.
As with everything else in life there are going to have to be compromises. Myself and one other have the R version (supercharged) but the rest have N/A 4.0lt versions so the design will have to be a compromise between the two. To be honest it would be impossible not to improve on the origionals but i would like to get the design as optimal as possible.
My background is mainly in computers althought i have owned a CNC shop so i do understand whats involved in this little project. Any information/ sugestions you guys can put my way will be egerly excepted.
Thanks for the replys already recived .

 

[GregLocock]

Can you post the dimensions of the 2 versions?

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

The requirements for the NA engine are quite different than the supercharged application, so one question is now 2 questions. Do you have any more.

Tubular exhausts are somewhat noisier and generally less durable than cast iron.

For the supercharged engine, just keep it easy swept turns and large diameter pipe. Don't worry about length or equal length to much.

For NA, you need to research the situation to determine where you want the power band and how much trouble you are prepared to go to to achieve it. A good racing exhaust can cost thousands of $ and can take 4 or 5 sets and a lot of dyno time to optimise.

You might improve the stock manifold by polishing out stress risers and ceamic coating.

Regards

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[GregLocock]

Sorry I thought you were talking about intakes.

Pat is there really much harm in excessive ID for the NA downpipes?





Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

Compared to stock no, nearly anything can gain a bit with bigger primaries and bigger collector and catalytic converter, but once you start to increase CSA by say much more than 50% over stock, you can hurt bottom end and get real noisy if the tailpipe is also biger.

I am talking generalities as I have no idea of individual cylinder capacity, power, rpm range and stock sizes on this engine.

David Vissard published some formula, also some formula should be found via Google.



Regards

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[fasterstill]

Hi GregLocock
Dimensions are identical for both. Two times 3 into 1 manifolds, parallel to the head, no primaries. ID on these is 45mm.

Regarding “is there really much harm in excessive ID for the NA down pipes?” Of the top of my head I believe lengths of primers being the same an increase of 1/8” ID equals a difference of 5-600rpm to point of max Torque.

Hi Patprimmer
Yes there probably will be more questions was trying not to be too excessive on the first post. My experience is if the post is too long and detailed you get less response initially.
So if I get your jist right your saying design should be more biased to N/A engine as the S/C will help to take care of cylinder evacuation efficiently by itself?
With the N/A engine I worked it out to be 31” primaries at 1 3/4” diameter to bring max torque at Aprox 3000rpm.

 

[patprimmer]

It's hard to imagine something so ugly on a Jag, and it is pretty obvious why they break.

What bore and stroke.

1.75" and 31" sounds about right, with 3 into a 2" intermediate pipe. Make sure the 3 going into the same intermediate are 120 deg apar in firing sequence. I would merge the two intermediates into 1 X 2.5" pipe I would not go much bigger on the NA motor.

I would go 2" on the supercharged motor and whatever length is most convenient, merging 3 into 1 X 2.5" pipe and merge the 2 X 2.5s into a 3" tail pipe.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[fasterstill]

Hi Patprimmer

Manufacturer code: XJR6 AJ16 (4.0}
Year of production:: 1995 - 1997
Fuel: gasoline
Supercharger
Camming: DOHC
Cubic capacity: 3980
No. of cylinders / Arrangement: 6 / In-Line
Valves no.: 24
Compression ration: 8.5 : 1
Performance [kW] / RPM: 240 (326 PS) @ 5000
Torque [Nm] / RPM: 512 @ 3050 (~ 378 ft/lb)
Bore x Stroke [mm]: 91 x 102

 

[patprimmer]

I took a wild guess that being a Jag, it was probably about 4 litres, so I presumed about 327 chevy cylinder size.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Tmoose]

Not much science, compared to an XKE's manifolds.

http://www.huwla.com/images/xke/Exhaust/Manifolds4.JPG

Even Volvo 240s had some independent runners for several inches from the head

 

[fasterstill]

Yep, considering this was the flagship model of its day its pretty sad. They are normaly covered by a nice polised piece of stainless steel but you woulds have thought the extra effort could have been put in.
Looking forward to seeing what sort of increases a proper header setup will bring. Should be noticable considering what its replacing.