23 replies to this topic

[markv]

I saw a post about the Milltek end damper for an NA having a larger bore then the standard downpipe. At the moment I've got a spare downpipe here and I did some measuring. The connection to the exhaust manifold has an inner diameter of 68.5mm. At the other end of the pipe, so just after the main cat it as a diameter of 47.5mm. It looks like it goes down from 68.5 to 47.5mm very soon after the pre cat. I've asked Milltek how big the diameter is of the end damper (and also asked a dealer over here in the netherlands). They say it is 2", so that should be 50.8mm. Guessing that is outer diameter, but it sounds to me like it should fit on the standard downpipe. However, if I understand correctly, when you buy the Milltek downpipe it actually does not increase the diameter of the whole exhaust system. At the best it will go down to 2" after the main cat, but judging from pictures it does so at the start of the pipe, just like the original downpipe. Would guess that with people that go over 200bhp with the NA it might be intresting if the whole exhaust system would be a larger diameter. Anybody got any comments/ideas or more information on this? Thanks!! Mark

[clipping_point]

Found THIS.

Basically, you should calculate the flow at your top rpm, and then select the diameter for the primary tubing. After that you simply multiply that value with 1.75...

Hmm, based on my WeaponR header tubing i should have a 2,5" pipe secondary system

[minime]

the system on mine is 63mm all the way:)

[Thorney]

If there was enough interest I'm happy to sort a cat bypass for the NA if people wanted?

[clipping_point]

Basically, you should calculate the flow at your top rpm, and then select the diameter for the primary tubing. After that you simply multiply that value with 1.75...

However the calculation is not too easy, since it involves pressure drops etc....

[markv]

Basically, you should calculate the flow at your top rpm, and then select the diameter for the primary tubing. After that you simply multiply that value with 1.75... 

However the calculation is not too easy, since it involves pressure drops etc....

Yup, I also found that article a while ago.

What I've also seen is that a lot of the time the bore of the exhaust is upped somewhere around the 200bph mark. People usually seem to go to 2.25" or 2.5" exhaust systems. You see the same with the system on the turbo, that is 2.5" if I am correct. But ofcourse, that is a turbo, so it's a different story.

What might be an interesting combination is the milltek turbo damper on a 2.2 engine with a custom downpipe. So you would only need a bigger bore downpipe and an other main cat, cause the damper for the turbo is 2.5". Would be interesting to see if it makes a difference on a more tuned NA (compressor or maybe the TB's).

Mark

[clipping_point]

Yep, you´ve started me thinking...since I am aiming for 220 HP and use the Milltek combined with my WeaponR mani. I think the downpipe should be 2,5" to match.......

[markv]

What is the diameter of the weapon-R? And are you running with the NA milltek or the turbo one? Mark

[Dibba]

If there was enough interest I'm happy to sort a cat bypass for the NA if people wanted?

Count me in as an interested party please - maximising the flow from manifold to rear Miltek please

[Woden]

I have a bog standard NA and I'm looking for all the standard NA engine specs that I can enter into the exhaust calculators

 

The different calculators ask for different specs with the usual BBDC. ATDC, overlap degrees etc

 

It's a bit like reinventing the wheel but I like the maths, sad, hoping to come up with a decent 4-2-1 system 

[smiley]

With a stock NA you will be spending plenty for a 3 bhp gain when just doing the exhaust. Most horsies can be found on the intake part as that is restricted to create low down torque.

[oakmere]

Calculated for a modified N/A engine by a race team. 490mm long primaries - 44mm, 490mm long secondaries - 55mm, collector 64mm. I think only Vocky has achieved this with his double loop exhaust. I have the tusudo manifold from the states and it works very well using 1+3 & 2+4 config.

[vocky]

this was my attempt at making a decent 4-2-1 looped system, and it works great

 

271 BHP and 213 ft lb of torque - normally aspirated

 

[techieboy]

271 BHP and 213 ft lb of torque - normally aspirated

But very far from a run of the mill 2.2 though.

[vocky]

 

271 BHP and 213 ft lb of torque - normally aspirated

But very far from a run of the mill 2.2 though.

 

 

it's all from the exhaust, honestly  

[Woden]

Brilliant I'll have one of those Vocky, well something made locally as close as possible, maybe it'll give 4 BHP

 

I've read that the 2.4 intake is the way to go, but I've got a lot of homework to do with the remapping and where the sensors go etc

 

I can't find any detailed info on the stock NA specs, anyone know where I can find it, I like playing with calculations

 

Hope to get it on a track next month, can't wait.

[vocky]

it gives about 20 ft lb more torque than a 4-1 good quality aftermarket exhaust system

 

standard NA specs are quite poor, the engine was restricted to get the 145 bhp. Cams are only 244 degree.

 

The z22se also loves 11:1 CR with NA tuning, also do the balancer delete and open up the exhaust ports

 

Z22yh pistons and rods are a straight swap and will give you 11:1 CR or simply skim 1mm off the head

[Woden]

Trying to work out from your photo where the loops go underneath

 

It looks like you've paired 1+4, and 2+3 primaries.  Oakmere above mentions a 1+3 and 2+4 system which seems to tie in with the 1,3,4,2 firing

[vocky]

most manifolds are paired 1+4 and 2+3, it creates the exhaust pulses which keeps the flow moving though the 4-2-1 manifold. 3 pulls 1, 1 pulls 4, 4 pulls 2, 2 pulls 3, etc, etc

 

[Woden]

Nice one thanks Vocky, great system you've got there, is that a Cat2 after the U bend.

 

The pre a post sensors are so close to each other did you have any dramas with that