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ITBs on an N/A
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Rich H  



Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK

PostPosted: Sat Feb 23, 2008 7:00 am    Post subject: ITBs on an N/A Reply with quote

Hey guys,

An idea (One of many...) kicking around my head, what good would individual throttle bodies have on power? Would it kill off the mid range torque?

I am looking at either Motorbike throttles or carving up a pair of twin choke dellorto's to remove the carb bits and leave the throttles.

Worth the effort? I already have Megasquirt EFI up and running so fuel isn't a problem.

Thanks
Rich
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec
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Raceboy  



Joined: 01 Mar 2004
Posts: 2318
Location: Estonia, Europe

PostPosted: Sat Feb 23, 2008 9:36 am    Post subject: Reply with quote

It will NOT kill your midrange unless you calculate total runner length all rong.

But it will definitely improve your throttle response to level it's hard to believe and overall power output, though you should tune intake to correct (read: reflecting your needs) area of the torque curve.
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S
'91 944 S2, sold
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Rich H  



Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK

PostPosted: Sat Feb 23, 2008 10:11 am    Post subject: Reply with quote

Cheers!

Any top tips on getting the length right?

Its for the street so I'm looking for a god spread of torque, would I be right in thinking longer (to a point!) is better?
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
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Raceboy  



Joined: 01 Mar 2004
Posts: 2318
Location: Estonia, Europe

PostPosted: Sat Feb 23, 2008 5:01 pm    Post subject: Reply with quote

Here's one link to simple intake length calculator: http://www.velocity-of-sound.com/velocity_of_sound/calculator2.htm
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche
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Martijnus  



Joined: 29 Dec 2006
Posts: 2019
Location: Netherlands

PostPosted: Sun Feb 24, 2008 4:16 am    Post subject: Reply with quote

I didn't calculate a thing.... I'll see how it goes
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"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment
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Rich H  



Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK

PostPosted: Sun Feb 24, 2008 5:54 am    Post subject: Reply with quote



Thanks guys!

Rich
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec
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Martijnus  



Joined: 29 Dec 2006
Posts: 2019
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PostPosted: Mon Feb 25, 2008 10:24 am    Post subject: Reply with quote

about that calculator url... what should I use for that induction wave number?

I actually have no idea what the other parameters should be...I've used 5000rpm... anyone got an idea? about the cam duration an stuff?
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"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment
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Rich H  



Joined: 10 Jun 2007
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Location: Preston, Lancs, UK

PostPosted: Mon Feb 25, 2008 10:38 am    Post subject: Reply with quote

Cam duration is 255
Waves: the spiel says NASCAR tuners use wave 3
RPM: I chose 3000 as I want mid range torque but it comes up with huge inlet tracts...

TBH its going to be more about packaging it all under the bonnet/hood than exact tuning...

R
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1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec
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Martijnus  



Joined: 29 Dec 2006
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PostPosted: Mon Feb 25, 2008 11:20 am    Post subject: Reply with quote

wow...with those values my power will emerge around 20k rpm and above

seriously... I need 94cm long runners according to that thing

so I wonder how my 10cm long runners will perform... low end will be dead as hell?

it's strange... You should think that increasing the runner diameter would result in longer runners...but it doesn't... changes almost nothing in the length....

why aren't the engine displacement and bore/stroke needed for the equasion? I'd guess that is essential to calculate these things...
how can you say you're runner length has to be the same for a 8 litre V8 and a lawnmower engine with the same runnerdiameter...
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"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment
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Rich H  



Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK

PostPosted: Mon Feb 25, 2008 6:49 pm    Post subject: Reply with quote

As I understand it its all about setting up standing waves with harmonics and so on. the engine will require air in at one point every 2 revs, what you want is the pressure wave to coincide with this demand. You will still have the quick throttle response but you will not get peak power until higher up the rev range.

I don't really understand the number of the wave though.

The biggest challenge as I say is getting it fitted to the car, that is the main requirement! Remember that the runner length is from the valve to the bell mouth, so I would be surprised its one 10 cm...

R
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec
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Martijnus  



Joined: 29 Dec 2006
Posts: 2019
Location: Netherlands

PostPosted: Mon Feb 25, 2008 9:35 pm    Post subject: Reply with quote

Rich H wrote:
As I understand it its all about setting up standing waves with harmonics and so on. the engine will require air in at one point every 2 revs, what you want is the pressure wave to coincide with this demand. You will still have the quick throttle response but you will not get peak power until higher up the rev range.

I don't really understand the number of the wave though.

The biggest challenge as I say is getting it fitted to the car, that is the main requirement! Remember that the runner length is from the valve to the bell mouth, so I would be surprised its one 10 cm...

R


I'm confused too, because the wave duration is in degrees...and I don't see the link between degrees and waves...

my runners are 7,5 cm long... so it's a little above 10cm I guess with the in-head intake.

My reasoning was that the itb's are mounted on a 1000cc engine which will probably have the same air flow because it runs twice the rpm, so if they're close to the head on the motorcycle engine, my 924 would need the same, perhaps a little bit longer.
Longer runners would be hard to build so it's more a matter of practical aspects than performance issues.

They use velocity stacks between the tb's and filters to get peak power at some rpm, i'm not using any because I'm not using a shared filter...

It's not hard to fit tb's on your 24... I'll get some pics
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"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment
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Martijnus  



Joined: 29 Dec 2006
Posts: 2019
Location: Netherlands

PostPosted: Mon Feb 25, 2008 9:47 pm    Post subject: Reply with quote

I've built a manifold from stainless steel (aluminium is wayyyyy easier to work with...) and spaced the throttlebodies.

That's the reason I've chosen gsxr1000 tb's, because newer ones are paired which means you can't space them seperately.

If you can't do that, your runners should make the transition from tb spacing to 924 intake spacing (probably not the right words, but you'll have to curve the stuff)...



the runners with tb's.



mounted on the head with filters...

The way I've built the manifold is by drawing/measuring the holes accurately and copying this information to solidworks to draw the template digitally. Then I printed it out, compared it with my head by laying it over the intake holes and bolt holes. When I was satisfied I copied the drawing on my stainless steel and tried to be as accurate as possible.

After that I've modified my head to ensure a smooth transition from runner to head.
Any ridge will cause tuning problems. I have to modify one runner because there's a little ridge between tb and runner.

These runners couldn't be longer, because they'd hit the hood (the filters I mean)... any shorter would cause problems too because the thermostat would be in the way, but that can be solved easily. I still decided to build longer runners because this would improve my lower end power.

I had to change the studs of the intake by allen bolts because the runners are quite large in diameter which means I can't use nuts simply because there's no room left to turn them.

The only things I'm worried about is the runner length and diameter... could be they're too short and too large in diameter which would #### my low end power... and I don't want to have a top end engine.

edit:


and a pic of my modified ports.
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment
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Rich H  



Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK

PostPosted: Tue Feb 26, 2008 4:38 am    Post subject: Reply with quote

I think the degrees in the calculator is a mis print, I put in 1, 2 or 3 and it came up with reasonable answers.

I don't know much about intake runner length, but I think you will find you have lost some lmid range just because of the size of the throttles.

As I understand it Low/mid range cylinder filling relies on momentum of the air which requires higher intake velocities which means smaller and longer (To a point) intake runners. You have large short runners which will give high end, so don't be suprised if it needs revving and is a bit peaky. My elise was like that when I first ported it, fixed it a bit with a decent exhaust though.

Do you have a standard exhaust?
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec
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Vince Ponz  



Joined: 03 Nov 2002
Posts: 3581
Location: Florida

PostPosted: Tue Feb 26, 2008 5:01 am    Post subject: Reply with quote

A tuned exhaust would help. I had a Stahl header on and it was great. Now they are too expensive. No other arrangement was as good and I tried them all.
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endwrench  



Joined: 07 Dec 2002
Posts: 1629
Location: Victor, Montana

PostPosted: Tue Feb 26, 2008 5:06 am    Post subject: Reply with quote

Try plugging in the #4 on the wave. This will get you a little shorter and be more realistic. The pressure wave bounces back and forth creating a "ram" effect but the higher numbered waves have less effect than the lower numbers. Like ripples in a pond. It needs to be timed to the intake valve opening wich is why the calculator asks for the cam spec instead of engine size etc...

Best thing to do with any street driven vehical is to go as long as you can. Don't sweat it though, it is not the do all and end all to your power curve.

Matrijnus, you need to include the length up to you air cleaners too, not just the length after the ITB's.

Todd
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'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....
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