need help building a tuned intake for inline six 8

[madaz]

Hi all I’m new to this forum. I think it’s the best forum around I love learning thing like this. So anyway I’m currently designing a tuned intake for a inline 6 the car is a XF Falcon (Australian car) the engine is a 250ci 4.1lt inline 6 OHV (250 crossflow).
I want max torque at around 2000rpm the car is driven daily not a race car
I have searched eng-tips looked at a few articles like tea Integra.
From those calculations I need an 52cm long runner.
The car will be running a 350 Holley.
The runners will be the same size as the ports I don’t know how big that is I’m trying to find out.

My questions are:
Will bends effect the bower band or effectiveness? (They have to be bent to fit under the bonnet).
Do velocity stacks help make more power/torque?
I can make it with some adjustability would this be a good idea?
What shape plenum and how big?
How much does size of the runner effect power band?

If there’s any thing else you would like to know just ask.
Any help at all is appreciated.

 

[thundair]

I wasn't very clear about the air box and was not thinking plenum. If you used the 3 SU's carbs and stuck an air box on the end is what I had in mind. I am always thinking of motorcycle applications my mistake..

At any rate the air is denser in a air box where the air is slowed and that was behind the meaning of a huge air box..

There have been a few post on this forum about mega squirt fuel injection which is a fairly easy conversion and now you can get it combined with ignition control so get your data logger out and have a go at the new stuff

Cheers

I don't know anything but the people that do.

 

[patprimmer]

Alchemi

What temperature would you use for your calculations.

Do you think it will be stable.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Alchemi]

I really cant answer that without assembling the motor and getting it dynoed to get the actual VE,CR,charged air temp etc. I havent finalized my cam yet either - another drama unto itself Different sized turbos generate diferent amounts of temp on different motors and then an intercooler and or Water injection drop those again. Ambient temp will throw it out a bit too - its generally hot where i live, 25c winter upto 40c in summer, no matter how good the intercooler or WI is, they will still only cool to within x temp of ambient. How about a massive thermocouple (peltier) on each runner - LOL

One turbo calc i was looking at came up with 195f if you want a ball park figure, this was straight out of the turbo with an ambient of 70f, but i must stress this will change for every different combo

However, off on another forum/site someone has come up with the briliant idea of using rubber hose (heat and fuel proof of corse) for the runners - this would allow you to start long and work down from there or even add bits on easily (with minor restrictions of corse)and bend it where you like, i was picturing having to go back over the top of the rocker cover, which would be a pain with adjustable rockers and other bits n pieces, but if i can just unbolt the plenum from the fire wall and flip it back over the engine, it would be really cool.

 

[starspangled]

There are ways to have your cake and eat it too. This is a relatively low rpm power curve so you can take advantage of that. Sounds like torque will be your best friend compared to horsepower.

You might consider a cam with the highest available lift yet with short duration/overlap. Use a smallish exhaust diameter. These two are pointed at maximum torque production. I don't deal with engines in this displacement so can't give advice on best exhaust diameter but I'm sure others can.

On some of our truck engines we build for say 5,700-6,000 rpm peak power, then advance the cam 4 degrees to bring the whole power curve down for better bottom end and mid-range. You could do that and get closer to your normal operating range and let the torque carry you into peak power.

Tune your intake length to peak torque, and tune your exhaust length to peak power for extraction and better cylinder filling, with carbies sized as already suggested, and a cam able to cover the whole range by its profile and degrees of advance. In this way you can have all the advantages of your torque curve where and when you need it most often, and still have enough left for the transition into higher rpm peak power.

I'm sure others here can comment on the relative value of this plan and give a go/no go on feasability. I think an intake length of about 27.5" from valve face to FI/carb intake lip, with exhaust length of roughly 46"-50" might do well. An adjustable exhaust tip can be used to dial in tuned length.

Starspangled