25 replies to this topic

[ACJ]

Hi all

Im in the process of building a set of 4 into 1 extractors with Mega Collectors.

To fit a 355 stroker with VN heads, in a LH. Heads have bigger valves, ported and flowed at 525HP. Cam crane solid F288. I�m hoping to make 500 Hp or just over at about 7000 -7200 RPM.

I need some help with the length of the primary pipes and the shape of the collectors.

I think 1 �� primary pipe and the length about 34 or 36 inch would be ok? Is this a good length to give me strong power from 4000 - 4500 and up ?

The shape of the collectors seems to be more important these days than the pipes ? The pictures below is what I had in mind. Is the tuned length to the point that all 4 pipes meet or at the end of the collector ?

I think the outlet of the collector should be 2 �� or 2 �� with a 3� transition up to 2 �� ??

All this meeting a single 3� Systems

I would like to keep all sizes as small as possible for this power outcome.

Any thoughts or criticism much appreciated.

Thanks

[EunUCh]

Exhaust systems are bit of science on their own,some very complicated
shit happens in an exhaust because basically you dealing with gasses
at the speed of sound,and it all changes due to temp.revs.etc.
Tuned lenght is just that,remember the days of AM radio,(turn the
dial to the station and it comes on strong but either side it is weak)
I would suggest make prim.pipes as practical as poss. and use the
merge collector.

[ACJ]

Thanks guys, good information.

This is my understanding in a very simple way

I think the smaller the diameter the better. If it does not restrict the flow at hight RPM. The higher velocity help draw the gas out of other primary pipes.

The lengh of the primary determines the time it takes for the presure waves to go down one primary and back up another one to help scavenge another port ( the longer the pipe the longer time it takes, so it works at a lower RPM and the shorter pipe will get back quicker for higher RPM ) If I get it wrong the extractors will still work but the best gain will not match up with my cam power band as good.

If it is as simple as I think or as complicated as it may be. This just tells me onething. extractors we buy from a shop will only work properly on a motor with the same specifications as the extractors were designed for.

So with as much information as I can get ( I will also Use PipeMax thanks ) I think I have more chance of getting it right or closer than some from a shop. I am thinking of making up small extension ( between the collector and the primary ) just for the dyno and if nesasary I will remake new length primary pipes.

Any more thoughts or criticism much appreciated specialy on the lengh.

Thanks

[EunUCh]

This formula may or may not help for primary pipe lenght
I think its always good to throw around a few ideas before
diving in.
P=(ASD)squared, divided by (1400 x(d squared)
P=primary pipe length in feet
A=exhaust valve opening period in degrees of crank rotation
S=stroke(inches)
D=bore (inches)
d=exhaust valve port diameter(inches)
this formula is supposed to help in determining best wave action in pipe.
The diameter of pipe to use accoding to the source should be slightly larger
than the valve throat diameter as measured below the valve,its all in theory of course but need to start somewhere.

[myss427]

I have built many systems for Toranas, big block 4 into 1's, LS2 into toranas all 4 into 1's and the main problem your going to face is the steering area interfearing with your design. It is going to be almost impossible to maintain an exact copy of side to side designs without altering the steering coloum and crossmemeber for extra room. It can be done if you make extra space like trimming chasis rails, shortening outside of coloum and running Tuff mounts.

[rodomo]

At any rate I wouldn't stress too much about getting them all exactly the same length, if there was no more than 2 or 3 inches variation I don't think you'll notice the difference.

Is that because a pulse is a pulse? Regardless of where it is in the pipe? I've thought that myself. And over an inch or two, all we're counting is friction?

Next question? Does this hold any merit? Given that the firing order on this bank would be 1-5-3-7? Timing position of primary into collector?

Attached Files

•  Collector.jpg   32.16K   0 downloads

[EunUCh]

Sorry all,thanks oldjohnno for picking that up,my mistake
only the "D" on top line is squared
only the "d" on bottom line is squared
I know we have computers do all this stuff for us now,but for anyone interisted
the book is call"scientific design of exhaust and intake systems".interisting read.

[ACJ]

Thanks, more good information

I had a go at this formula with a good outcome of 33.57 incher.

But the cam degrees was advertised (296) not @ 50�(260). Valve throat diameter of 1.4�. As the valves are 1.6� and the inside edge of the seat was 1.45 so I had a guess at 1.4� for the throat diameter.



Yes, I would appreciate if you could run my numbers through PipeMax



Seems to be a lot of variables and critical darter to make these formula work accurately ? I still think if I make a very simple set of extractors with 30 inch primary and 8 x 2 inch long and 8 x 4 inch long extension pipes to slip on the end of the primary befor the collectors when it�s on the dyno may be the best result ?

Some fianger I made.

[warrenm]

I've used the formulas from the book "Scientific design of exhaust and intake systems" then used Pipmax, the pipe lengths were 1/4" different using the same info.
oldjohnno, What can you direct me to some of Gordon Blair's work please,books etc.

Edited by warrenm, 07 July 2011 - 08:50 AM.

[warrenm]

These are the headers that I made using Pipemax, I picked up 3/10 sec on the 1/8th mile going from Genie headers to these.

Attached Files

•  Headers.jpg   545.62K   4 downloads

[ACJ]

Hi Warrenm

Your extractors look good to me. The primary must be about the same lengh and nice flowing bends. The angel that the primary meat together is shalow. All this together I think help, 3/10 off your time card is very good.

Did you sand bend your primary pipe ?

To oldjohnno

Thanks for lots of good information (and eveyone). Do you know the RPM per inch of primary pipe eg If my pipes are out 1000 rev would you cut off 1 inch or 5 inchers ?

All in all I think Mistagear hit the nail on the head �Just thinking aloud, sorry for interrupting your discussion, good memories and fun to tell other people who may realise just how difficult and crazy playing around with cars can become� Love it

Thanks

[warrenm]

I cut & welded mandrel bends. I pulled the last few remaining strands of hair from my head building them.

[ACJ]

Thanks very much for running pipemax.

I have 3 different lenghs from 29 to 33 incher. So if 3 � incher is about a 1000 rpm and I made my starting point 31 inches I should only be about 500 rev out. This would be a very good starting point.

I have a question about the collectors as I will be running a full exhaust and muffler.

If the collector and tapered collector are 3 � inch dia at the out let, Do I put a reverse cone back to 2 � or 3 inch and then continue the exhaust pipe. If not what determines the end lengh of the collectors ?

Thanks

[ACJ]

I would like to thank everyone for all the help and good information.

I started playing around and made some flanges and collectors (just out of old pipe for a test ) so far so good

Mite continue this post in fabrication now thanks all.

[ACJ]

The inside point is the length of the goilet.This is with a convergent angle of 12 degree.But this is just a test pipe wich is smaller in diameter so the larger pipe will be longer still.

Thanks