Stebro questions...

[RallyBob]

Another point worth mentioning is that the header lengths and diameters would be quite different depending on the application. For a standard engine w/automatic I'd use 1.5" primary diameters that were +/-36" long, with a manual tranny I'd knock about 2" off the primary lengths. If you have other mods such as mild bowl blending and mild cams, then I'd probably go with a stepped header (1.5" into 1.625") that was 31" long to correspond with the higher peak power rpms. I wouldn't step up to 1.625" all the way unless the vehicle had a manual trans and a few more mods...particularly higher compression and hotter cams. The only exception for me would be if you had either a supercharger or nitrous, then the larger 1.625" headers would make sense. Bigger than that, then you'd better have a bunch more cam, compression, and headwork, and be revving it up pretty high!

[oab_au]

Originally Posted by TomsSVX

Sound and performance are always mixed w/ the 3.3

the #1 thing if you want power from the exhaust is the headers a nice 30" equal length header will do more than any cat-back. In this case sound are performance are a compromise.

Tom

Originally Posted by longassname

Would clearance be any harder at 28 or 29 inches?

Have you all tried working the length out?

30" will resonate at 9000 rpm.
28" will resonate at 9642 rpm.

Where do you expect to develop peak torque?
Are you really talking about a svx engine?

Harvey.

[TomsSVX]

Originally Posted by oab_au

Have you all tried working the length out?

30" will resonate at 9000 rpm.
28" will resonate at 9642 rpm.

Where do you expect to develop peak torque?
Are you really talking about a svx engine?

Harvey.

Yes, but remember I am also talking about an SVX and things still need to make their way under the car. That being said, the 30" length is a compromise between the length you may want, and what will fit. Also you might want to add the 6" of collector into that as well. Not everything can be numbers.

Tom

[oab_au]

Originally Posted by TomsSVX

Yes, but remember I am also talking about an SVX and things still need to make their way under the car. That being said, the 30" length is a compromise between the length you may want, and what will fit. Also you might want to add the 6" of collector into that as well. Not everything can be numbers.

Tom

Sure I know there are space problems, but if you can't fit the right tuned length in, why do it its not going to help.

It is better to just use a header with short branches to suit the No. of degrees, that will prevent the exhaust gas pressure from cause interference between cylinders. Then keep the down pipe the same overall length, that suits the rpm that you want the peak torque to occur.

Keeping the header branches short and compact, will help to maintain the sonic wave that the right tuned length will provide.

Harvey.

[longassname]

120*1700fps/7200rpm=28.33"

[oab_au]

Originally Posted by longassname

120*1700fps/7200rpm=28.33"

Why 120*, that would bring the negative wave back at 115*BTDC. far too early. Needs to be around 55*/50* BTDC.

1700 fps is a bit high for our exhaust system, it won't get that hot.

7200 rpm Is this where your engine is going to make peak torque????

180* X 1500 fps / 5000 rpm = 54".

Harvey.

[longassname]

I think maybe you are calculating the end of the collector. I was talking about the begining. 7200 would be peak power; on a race car it's most common to tune to reinforce peak power rather than torque. I come up with 28" to 33" primary lengths with 14.5' to 16.5" collector lengths.

Originally Posted by oab_au

Why 120*, that would bring the negative wave back at 115*BTDC. far too early. Needs to be around 55*/50* BTDC.

1700 fps is a bit high for our exhaust system, it won't get that hot.

7200 rpm Is this where your engine is going to make peak torque????

180* X 1500 fps / 5000 rpm = 54".

Harvey.

[oab_au]

Originally Posted by longassname

I think maybe you are calculating the end of the collector. I was talking about the begining. 7200 would be peak power; on a race car it's most common to tune to reinforce peak power rather than torque. I come up with 28" to 33" primary lengths with 14.5' to 16.5" collector lengths.

Mike I think we are talking about two different types of exhaust headers. Probably an Australian thing.

I took it that Tom was talking about his type of "equal length headers" Three tuned length pipes, into an expansion area.
Bob was on a "branched pipe collector" header, and I see you are on the same as Bob, OK.

I design an exhaust to suit the cams that the engine is going to run. Three tuned length pipes into an expansion area (chamber, large dia collector, etc) is the best, keeps all the energy to goes back to start the inlet wave.

If they can't be fitted, then a short branched header, with the branches just long enough to prevent the exhaust pressure plug from entering the cylinder next to it, that is on overlap.
Then doing the same tuned length measurement from the ex. valve to the expansion point, that brings the negative pressure pulse back to the combustion chamber, for the opening of the inlet valve.
Just a slightly long branches that it is now.The branching needs to be as compact as it can, so as not to lose too much of the sonic wave pressure..

The rpm that the pulse is returned, has to match the rpm that the inlet lobe center is set for. Maximum cylinder filling, gives Maximun torque. The rpm that torque is produced gives the 'peak power', not what is most common.

Harvey.

[RoughSilver92]

http://www.wallaceracing.com/header_length.php

using
4400 for engine speed (peak tq)
202.476 for displacement
55 for exhaust valve opening

Your Primary Tube Length is 55.92
Your Primary Tube Diameter is 1.06 inches
Your Collector Length is 27.96 inches
Your Collector Diameter is 2.02 inches .

I think this calculator is for a v8, though, since 1" primaries seem tiny. I need to find a more comprehensive calculator, or invest in a good book! Based on these lengths, though, where does the rest of the system go??

[RoughSilver92]

http://www.slowgt.com/Calc2.htm#Header

Better calculator using bore and stroke.
Stock engine using peak torque:
1.46" primaries @ 42.4"
2.78" collector @ 21.2"

Stock engine using peak hp:
1.62" primaries @ 34"
3.08" collector @ 17"

Still huge! I think for my simple purposes I'll stick with the stocker! Now I don't even know if porting it is worthwhile, since it's at about 1.5" already.

[oab_au]

Originally Posted by RoughSilver92

http://www.slowgt.com/Calc2.htm#Header

Better calculator using bore and stroke.
Stock engine using peak torque:
1.46" primaries @ 42.4"
2.78" collector @ 21.2"

Stock engine using peak hp:
1.62" primaries @ 34"
3.08" collector @ 17"

Still huge! I think for my simple purposes I'll stick with the stocker! Now I don't even know if porting it is worthwhile, since it's at about 1.5" already.

Some good calculators on that site.
It would be very easy to work it out, IF it was so cut and dried.

I can work out the lengths on a bike engine and it is going to be very close. The system we have to have on a car, is not so easy. There are too many variables, every change in dia will produce a wave change, so the system has many different waves running up and down the pipes.

Then there is the temperature, that the exhaust gas will run at. This changes the speed of sound in the gas, to change the time of the negative pulse return. How many have pulled off the tin covers on the pipes and cats, that maintain the exhaust gas temp.

The system that we have, has been worked out on a computer to bring the negative pressure back to the cylinder at the right time. They then put the whole system on an engine dyno to see what the results are. The system is then trimmed to correct the difference, and get the maximum effect on the inlet opening.

So the length that we measure on the car now, down to the resonator, has been set to incorporate all the variables that the cats, temp, etc produce. While we stay with the same results that they have got, we can't go too far wrong.

Removing the front cats, replacing the resonator with a straight pipe, joining the two header pipes with a Y pipe, will alter the resonate system and down grade the power.

Harvey.

[RoughSilver92]

Wait, when you say "the system we have..." do you mean the stock manifold, or are you saying that you and others are designing a system and dyno testing it?

[oab_au]

Originally Posted by RoughSilver92

Wait, when you say "the system we have..." do you mean the stock manifold, or are you saying that you and others are designing a system and dyno testing it?

Shock, horror, Yes the ones that Subaru designed to get this engine to produce the HP that it does.

They flow the exhaust gas away, with very little restriction, deliver a strong negative wave back to the inlet.

What more could do to improve them for the rpm range, that the cams are going to run at.

If the exhaust cam duration is increased more that about 15*, a new header that has branches slightly longer, would to needed. That doesn't mean 'the longer the better,, as the extra volume of the header will absorb some of the returning negative pulse.



Harvey.

[TomsSVX]

A gain of .5 seconds in ET and a gain in excess of 6mp in trap speed with the only change being in my headers and exhaust system, I would think I was getting an increase?? Who knew I was losing power

tom

[oab_au]

Originally Posted by TomsSVX

A gain of .5 seconds in ET and a gain in excess of 6mp in trap speed with the only change being in my headers and exhaust system, I would think I was getting an increase?? Who knew I was losing power

tom

Not to mention all the other variables that go with 1/4 mile runs.

I guess you mean this version of yours.



A great job of plumbing, but they were too short to resonate at a engine speed that you could get the engine to rev at.
They do a good job of preventing the interference that the cams that you used, would develop.

If the three pipes were at the resonate length, and entered an expansion box, it would be fantastic, but it has to fit under the svx.

If the three pipes were kept short enough to prevent the interference, then run into the standard header pipe, it would fit under the car and it would still be able to use the std cats for emissions.

You would sell a lot more of this set up that you did of the
other.

Harvey.