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Old 25-12-2008   #1
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Effect on exhaust sound from 4-1 header??

Hi guys,

I am waiting for my 4-1 exhaust header to arrive very soon.

The only thing I forgot is that the sound from exhaust will be different when new header will be installed.

I am not making a race car so I am worried if it will be too loud for city environment.

Does anyone have exprience with running X1/9 with 4-1 headers? How is the sound?

P.S: I already have a sport silencer that makes the sound more 'sportive' and it is eventually quite loud.
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Old 29-12-2008   #2
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Re: Effect on exhaust sound from 4-1 header??

Usually it is the silencer that dictates the sound output from the exhaust, or the extent of the baffles or packing inside. You can get additional inserts if you find the system too noisy, usually used to meet track day regulations. You should find that the manifold will give greater performance gains than a change in engine note however I don't have any first hand experience on an X exhaust.
I know a guy that ran a side pipe straight from the manifold, ran it on the road and got pulled by the police straight away and given a heaftey fine and an asbo! As long as you don't do this you should be fine!
Hope this helps.
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Old 30-12-2008   #3
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Re: Effect on exhaust sound from 4-1 header??

A pipe straight from the manifold is a very good idea

Yeah, I think the silencer is the thing to change...

Thanks
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Old 04-01-2009   #4
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Re: Effect on exhaust sound from 4-1 header??

What length primary headers are you running on, 42" I hope? Then the header outlet would be right down at the bottom. You would need to either run the pipe at right angles into the exhaust box or... undergo 3x's 90degree bends to put it in one end. The quietest box is probably the ANSA box with the quad tips... kinda defeats the object of the exercise does'nt it? ... just plumb it straight through!
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Old 05-01-2009   #5
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Re: Effect on exhaust sound from 4-1 header??

Hey All

I Was Wondering If A 4 Branch Manifold To To A Straight Through Cherry Bomb Would Be Any Good.....What Kind Of Torque And BHP I Will Be Gaining? I Know It Won't Be Much...But Just Curious?

Thanks
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Old 06-01-2009   #6
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Re: Effect on exhaust sound from 4-1 header??

Hi Brae,
From past experience...

The best performance I've had from a 1500 X is the CES setup (Now that's with 2x40 DCNF's (130 mains), flowed head, larger valves, HD valve springs, 40/80 cam (FAZA), balanced flywheel... Yes, brakes!) John used to have a 42" primary 4:1 , now you must use a 42" primary (where the branches meet) as that is the optimum resnonance point for all 4 pots.Those of you that have done Mech Eng can explain... That ran into a Peco type box, it still spat flames and noisey enough, so cherry bomb would'nt be far from that! 42" primary would give dramatic BHP increase 12bhp or so, while a 21" (yes, I've tried them all!) Would give you minimal torque increase... hardly worth the $$$. Personally if I'd carried on with the 1500 engine, I'd work on increasing the revs for peakier revs... perhaps going to the over square 1600 block...? Mind you... with a turbo... it doesn't make any difference if it came out of a drain pipe! Huh?!
A little back pressure is not a bad thing.

T :-)
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Old 07-01-2009   #7
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Re: Effect on exhaust sound from 4-1 header??

yeah i was thinking of having a smaller pipe then it is then to get more pressure then fit it to a cherry bomb....i have done abit of research on the back pressure theory and this is what i came up with.....

"An old hot-rodder's tall tale: Engines need some backpressure to work properly and make torque. That is not true. What engines need is low backpressure, but high exhaust stream velocity. A fast-moving but free-flowing gas column in the exhaust helps create a rarefaction or a negative pressure wave behind the exhaust valve as it opens. This vacuum helps scavenge the cylinder of exhaust gas faster and more thoroughly with less pumping losses. An exhaust pipe that is too big in diameter has low backpressure but lower velocity. The low velocity reduces the effectiveness of this scavenging effect, which has the greatest impact on low-end torque. Low backpressure and high exhaust stream velocity can be achieved by running straight-through free-flowing mufflers and small pipe diameters. The only two exceptions to this are turbocharged engines and engines optimized for large amounts of nitrous oxide. Both of these devices vastly increase the exhaust gas volume and simply need larger pipes to get rid of it all"

so if that is right (if it is) then the smaller pipe i have the more pressure thus more torque i will gain....is that correct? lol

don't get me wrong i like doing cars up....but i would prefer to have a fast car then a good looking car if you get me.

i havn't got twin 40's and prob won't as it cost too much lol....i am jsut spending all my money on the body to get it rust free then i will start thinking about the engine (uno turbo, lancia 2.0l etc.) but i lie i am always thinking of wat engine i should put

i had the idea of buying another X1/9 engine and building that one up so i can still drive around and go places E.g work and college.....what would you advise? skimmed head....increased valves sizes? ligher flywheel? uprated camshaft?

but keep the idea's normal as it is only a road not a race car

Thanks A Bunch
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Last edited by Brae91; 07-01-2009 at 14:45.
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Old 07-01-2009   #8
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Re: Effect on exhaust sound from 4-1 header??

hi Brae91,Off topic a bit hows the bodywork going, very long process especially rubbing out filler
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Old 08-01-2009   #9
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Re: Effect on exhaust sound from 4-1 header??

Hey Shaun

it is going good thanks bud...getting close to spraying it now

hows yours going?

(getting back on topic)
Any idea's then?

Cheers
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Old 08-01-2009   #10
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Re: Effect on exhaust sound from 4-1 header??

Lol... Brae,
If you're prepared to stick 4 pipes straight out of your number plate? As I recall, one of the laws of fluid dynamics is that for every time the fluid (or in this case air...) goes round a 90 degree bend, you loose 50% of the velocity... huh?! In order to get that sort of 'venturi' effect... the exhaust pipe has to come straight out! Probably shooting 20ft flames on the downshift!
So if your assumption is correct, it would be pointless to fit larger inlet and exhaust valves, no need to enlarge the cylinder head ports...?
IMHO, as long as the diameter of the pipe is similar or the same as the port size (also... remember to cut out the inlet/ exhaust gasket to the correct hole size to match your larger ports otherwise defeats the idea of the mod!)
Nite, nite.
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Old 09-01-2009   #11
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Re: Effect on exhaust sound from 4-1 header??

Exhaust design and especially manifold design is fairly critical to getting the power out of an engine. There is an optimum bore size for every engine and the critical factor is the cross sectional area, this must remain consistent in order to maintain the gas flow. Bends need to be properly radiused to avoid pinching which makes the loss in velocity worse. Joins in the pipe (collectors in the manifold) are also critical - the area of the individual pipes being joined should be equal to the area of the single outgoing pipe and you should never split the pipe. All of these principles were laid down by a fellow called Carlos Abarth and are adhered to knowingly or otherwise by designers of exhaust systems everywhere.

The optimum size of the individual header pipes is down to the exhaust has flow from the head. Bigger is most definitely not better unless you have as already mentioned a forced induction engine or a nitrous system fitted. Smaller isn't better either, too small restricts the gas flow *but* you do want the pipes as thin as possible. How do you get it right? Without knowing the gas flow characteristics of your engine the simple answer is experimentation, guesswork and intuition.

Increasing valve sizes is likewise guesswork unless you have some proper figures to work from, in general though the exhaust valves are of adequate size but the inlet valves are slightly restrictive so you can gain a bit of torque by fitting larger inlet valves, this in turn means fixing the rest of the induction side as the standard DMTR/DATR carburettor will run out of steam. For small performance changes you need just a rejet but beyond that you are looking at total replacement.

To make things more interesting the changes to the inlet side will also affect the exhaust side. If you were to build the perfect exhaust system without inlet valve modifications and then to change the inlet valves that exhaust system will prove inadequate. The gas volume being pumped will change and the weaknesses in the torque curve will change so you are basically back to square one. The same applies to changing the cam profile or compression ratio.

If you are going down this route all I can suggest is that you decide on a head and cam profile first, get it flow tested so you know what you've got and then worry about the exhaust.
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Old 26-01-2009   #12
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Re: Effect on exhaust sound from 4-1 header??

Hey Theo Chan,

What did you mean by 42" primary headers? Is that the length of the pipes?

Here is the picture of the manifold I've got.
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Old 28-01-2009   #13
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Re: Effect on exhaust sound from 4-1 header??

Hi SpiritX,
That one looks like a 21" header, if you measure it from the exhaust flange to where all 4 pipes meet, it should be about 21 inches. It should bring up the torque of the engine and should be okay and alot quieter that the 42"'s. A nice Ansa 4 pipe tailbox would go great with it!
T :-)
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Old 28-01-2009   #14
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Re: Effect on exhaust sound from 4-1 header??

Yeah, probably 21"...
I remember I've seen a 42", it was a veeery long manifold, where the headers were joining after 90 degree turn.
ut I think I will keep this one. For me its better to have a quiter rather than few bhp more.

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