[Alloytec] Designing tuned length alloytec 190 extractors

[OS-Mike]

So iv got a few weeks of holidays coming up and i know ill get board not working on cars all day so im going to make some extractors custom made for my engine to learn something new iv never really looked at the science behind extractors and iv spent 3h a night for the last 3 nights collecting raw data calculating and designing and its making my head hurt so i give up for tonight lol. But i can tell you there is not one set of properly made extractors for an alloytec 190 not even the pacemaker "tuned length" ones they dont even look close and what exactly are they tuned for? i have seen one nice set for a 335hp camaro but the dimensions are to big for alloytec190's ill add a pic at the bottom of post.

Is there any engineers out there (not the welding or fabricating kind) or exhaust gurus that can help with some numbers i think iv got it right but this engine is a nightmare to calculate the ideal length for the pressure wave's due to cam phasing.

Design goals: Its a street car so broad torque curve with peak pressure wave efficiency at 4500rpm-5000rpm in theory about -3 to -5 psi at the exhaust valve.

Extractor design: Mild steel material, laser cut flanges port matched, 3 into 1 primaries, custom made venturi style merge collectors, secondaries meeting at a siamese crossover pipe.

Data: 594cc per cylinder, 94mm bore x 85.6 stroke, Exhaust cam specs that come from a GM workshop manual and i can tell there is an error in these and i cant be bothered degreeing my ex cam. all values at 0.150mm lift: Duration 238, opens -229btdc = 69bbdc, closes 9 atdc, centerline 111, overlap 0, cam lift 42.5mm, valve lift 10.8mm, Ecu controlled phasing upto +50 but my ex cam phase map shows +20 across the rev range at wide open throttle . I would love to know the ex valve size anybody have this also has anybody actually degreed an alloytec i only need ex cam specs the error from the GM manual is the degreeing dosnt match the duration FAIL!

Calculations: Primary pipes 1.5"dia x 40" length for 4500rpm 38" for 5000rpm, Collector 6.17" length 2"dia venturi tapered out to 2.25" exit, secondaries 2.25"dia 37" lenght to crossover.

Thats about where im at so far ill probly put flanges on collectors where they get to 2.5" so i can take out the venturi and experiment with length, venturi size and taper for fine tuning. Also another science experiment i would like to try is using a tuning fork and microphone and watching how sound waves travel through each pipe if i make them right all pipes should be in perfect harmony its just a theory because sound is just a pressure wave if i record it and watch it on a pc it will be like a pressure wave scope well see how this goes im not holding my breath for this to work.

And to make things a little easier i have access to a really nice engineering workshop and dyno. You need a really fancy cutter to make the cuts for the merge collector im not even going to try and bother explaining it ill take some pics when i make them and i priced up materials to make them today worked out about $600nz.

Im open to ideas and suggestions so fire away if you have any advice.

 

[Tree cutter]

You say this is for a street car at 4500 to 5000RPM. Where i come from you will end up in serious trouble with the law if you are revving your engine that high on the streets. You will only be revving to about 2000RPM at 110Kph so i think you would be better off tuning your pipes for a lower rev range where you will use it most. Your setup will probably work for a track car that is running at high revs most of the time but i cant see much benefit using a setup like this on a street car. Most off the shelf designs will be for normall street use at low revs and will be a lot shorter than your design.

 

[Dr HaxZaw]

the whole problem with tuning it the way you want to is that it will work wonderfully well in that specified rev range but terribly elsewhere
as you said the pacemakers arent up to that standard but they are more deigned with exhaust pulse in mind not so much for the frequency harmonics... this means they work well over more of the rev range than those tuned to a much narrower rpm range
to be honest i dont think you'd see any gains over the pacemakers with your custom made set but i would love to see some dyno results proving me wrong

 

[OS-Mike]

You say this is for a street car at 4500 to 5000RPM. Where i come from you will end up in serious trouble with the law if you are revving your engine that high on the streets. You will only be revving to about 2000RPM at 110Kph so i think you would be better off tuning your pipes for a lower rev range where you will use it most. Your setup will probably work for a track car that is running at high revs most of the time but i cant see much benefit using a setup like this on a street car. Most off the shelf designs will be for normall street use at low revs and will be a lot shorter than your design.

The shorter the header primaries the higher the tuned rpm most off the shelf stuff is made to bolt on so compromise is made. And i think 4500 is right for street use ill gain low down torque and make more top end power if my calculations are right.

 

[OS-Mike]

I hope they preform across the whole rev range thats why im making fancy collectors. ^Dr HaxZaw

 

[OS-Mike]

Finally parts turned up to day so had a few beers and had a play with mock up this is not my final design just getting started.

And here is a half finished merge collector i started making last week.

Ill do a proper update if i get time tomorrow explaining design how to work it out etc.

 

[OS-Mike]

Update: Had way to many parties over christmas and new years still haven't got round to welding them up yet iv got most of the pipes cut and the hard parts made just need to pull my exhaust system off and tack them up on the car. Trial fitted PVC mock ups and measured each pipe length and volume and cut up bends etc.

How i got the measurements for these extractors

Length:

Primary Length=850xED/RPM-3 ED=180+degrees before bottom dead center Exhaust valve opens RPM=revs your tuning for

ED. for alloytec was tricky ex valve normally opens 131* (* means degrees) but with VVT at full throttle =20*retarded so 131+20= 29*before bottom dead center. ED=209

RPM. I chose 4500 because the inlet manifold changes to single plenum at 4000rpm and my dyno graph shows torque drops off around 4500-5000 its a good compromise good mid range and shouldn't be restrictive high in the revs.

Here is the equation (850x209)=(177650/4500)=(39.48-3)= 36.5 inches from the exhaust valve to the collector.


Primary diameter:

There is a fancy calculation: cc of 1 cylinder 594cc, divided by (p+3)x2 which is 79 so 594/79=7.52 then x2.1=15.79 so the inside diameter of the primary is 1.57"ID =1 5/8" tube

But generally 1 1/2" OD tube is good for 25-40 hp per cylinder 1 5/8" for 35-50 hp so 1 1/2" is good for 240 hp and 1 5/8" is good for 300 hp and the car already made 211 hp at the wheels.

Primary tubes = 1 5/8"ODx36.5" long


Venturi merge collector:

Normally its just one diameter and that's the area of the 3x1 5/8" primary tubes with a 1.4-1.7 in/out relation so mine starts at just under 1.4 and tapers out to 1.7 with 4 valve heads its all about air speed not how much it flows example Twin 2.5" exhaust systems are too big you'll probably lose power.

Area of 3x1 5/8=3400.62mm squared divided by 1.4= 2429mm2 convert it back to diameter and imperial = 2.18"ID and divided by 1.7 =1.98"ID so im using a 2" out to 2.25" taper.

Im sick of typing now ill explain the rest of the exhaust system next time.


Here is one side iv made a template for test fitted and matched the volume of each pipe there not all 33.5" close to it but they all have 950cc volume.

Tapered 2" out to 2.25" flanges for the collector.

Inside the collector

 

[OS-Mike]

One more

 

[Drawnnite]

liking the effort youve put into this.
awesome job and keep it up.

should be interesting to see how they go.

also loving the PVC pipe test pieces.

 

[WogBoyz]

comming along great mate! deff a good read